Side Exhausts and aerodynamics with pics
01-06-2010, 06:32 PM
#46
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From this link
http://atlasf1.autosport.com/2000/feb16/gray.html
Mark you will see when you read this that one, there is a flat floor and two, your view as to the most efficient way to run the aero is 20+ years out of date, that is you do not want to block off the air, you want it to do work for you. Key sections in bold.
Taking the Lid Off F1
Formula One Technical Analysis
by Will Gray, England
Atlas F1 presents a series of articles by certified engineer Will Gray, that investigates in greater depth all the technical areas involved in design, development, and construction of a Formula One car.
7c. Underfloor aerodynamics
Why is an F1 car shaped the way it is? It's not because the Technical Director likes the curves (although to some extent it can be!), it's because that is the shape that, with the resources the team has to explore the area, is the most efficient at getting through the air obstacle. Rules and regulations help to clone the cars, with 'no-go boxes' stipulated all around the car - rules declaring where bodywork can and can't exist, but ingenious designers can always spot loopholes in these!
The flow of air underneath the car is one of the most important areas of the aerodynamic design. Air travels under the nose and the underside of the front chassis to the chin, which splits the air between that which travels through the sidepods for cooling, and that which goes under the car's floor. At the end of the floor, the air meets the diffuser, which returns it to the outer airstream. This route will now be described in more detail.
The Nose and Chin:
In 1990, Tyrrell, often the innovators in F1 design, came up with a revolutionary high nose - contrary to the low nose trends of the time. The 019 slipped into the F1 field with some interest, but at the time it wasn't clear that the design would change the look of the F1 car for at least the next ten years.
The raised nose - which when it first came out looked like a handlebar mustache - allows the air to flow, undisturbed, to an air splitter (the chin) positioned under the cockpit, at the start of the floor. Before, the front chassis and nose ran flat to the floor, with the aim of obtaining downforce from this area. Instead, Tyrrell saw that by moving these obstacles out of the way, better airflow to the floor created more downforce. The nose was raised, the front wing suspended on pylons, and the front of the chassis was smoothly curved from the high nose down to the chin at floor level. The chin, shown in the diagram, is a semi-circular scolloped face, with a flat, horizontal surface sticking out underneath it. The face guides the undisturbed air around and under the sidepods, and the flat surface prevents the air from being encouraged to go anywhere else. The current school of designers are always looking for more air under the floor, as it is here that the greatest and most efficient downforce can be produced - the nose is now something they want to get out of the way.
Front Chassis:
In 1999, every car in the field has some kind of raised nose, but these have been honed from the Tyrrell Original, to provide very different interpretations of the same thing. It is interesting to see that the McLaren (the most victorious car of recent times), has a relatively low nose. This confirms the view of many designers that the raised nose is not so important, and that what is, is the raised front chassis - the area behind the nose, but in front of the driver, and the entrance to the chin. By curving the chassis up from behind the nose, then back down to the chin in a slight banana shape, the designer can get clean air to the floor without having too high a nose. However, the Jury is still out on this issue!
Floor:
This flat section, close to the ground, is where most downforce is obtained. However, it is not, in itself, a magic surface. It works in the manner of a duct, and requires good inflow and outflow - obtained through good chin and diffuser design. In a duct, there exists a mouth (entrance), a throat (main body of the duct), and a diffuser (exit). The air accelerates in through the mouth, continues to speed up in the throat, and is decelerated to return to the speed of the free-stream flow in the diffuser. On an F1 car, the lower leading edge of the sidepod (coming off the edge of the chin) acts as the mouth, and the flat bottom is the throat. As explained previously, high speed air has low pressure, so the air under the car works to suck the car down. The size of the floor, however, is limited to a maximum width in the rules, but teams tend to vary its length.
The closer the floor is to the track, the more downforce it will produce due to ground effect, so to reduce the downforce created by the floor, the rulemakers stipulate that it is raised from the track. This is enforced by a plank of wood (yes, wood!), positioned underneath the car at cockpit width, running from the chin to the rear.
The Nose and Chin:
The better the diffuser works, the more efficient downforce you have - it is an important area of the 'duct' system. Forming an upsweep from the floor to just under the rear wing, the diffuser decelerates the air towards its original speed. Its design includes vertical fences, some of which are curved, some stepped, and some angled, but all are developed through constant tweaking and evolution in the wind tunnel. The basic job of these fences is to keep apart the many different types of flow found at the rear end of an F1 car - areas of low pressure air due to the rear wheels, and the rear wing, and the air coming under the floor. All these different air flows have different energy levels and different speeds, and their separation makes them easier to deal with.
The main aim in diffuser design is to take it to its limit, and not beyond. If the slope of the diffuser is too steep, we will have flow separation (the flow will no longer follow the surface), causing extra drag. This may not occur in all areas, however. In the outer edges of the diffuser, the air, which has traveled under the car along the outer part of the floor, will have mixed with, and been slowed by, air from outside the floor. Towards the centre, however, the air flows faster, as no extra air has reached that area. For this reason, the diffuser consists of varying slopes, depending on the curve the air can follow before separation.
With rear wing elements helping suck the air from under the car, and the close-packed nature of the car in this area, it tends to be knowledge-inspired trial and error development which changes the shapes of the diffuser - to get a good one takes a lot of time and effort...and a touch of luck!
Greg
http://atlasf1.autosport.com/2000/feb16/gray.html
Mark you will see when you read this that one, there is a flat floor and two, your view as to the most efficient way to run the aero is 20+ years out of date, that is you do not want to block off the air, you want it to do work for you. Key sections in bold.
Taking the Lid Off F1
Formula One Technical Analysis
by Will Gray, England
Atlas F1 presents a series of articles by certified engineer Will Gray, that investigates in greater depth all the technical areas involved in design, development, and construction of a Formula One car.
7c. Underfloor aerodynamics
Why is an F1 car shaped the way it is? It's not because the Technical Director likes the curves (although to some extent it can be!), it's because that is the shape that, with the resources the team has to explore the area, is the most efficient at getting through the air obstacle. Rules and regulations help to clone the cars, with 'no-go boxes' stipulated all around the car - rules declaring where bodywork can and can't exist, but ingenious designers can always spot loopholes in these!
The flow of air underneath the car is one of the most important areas of the aerodynamic design. Air travels under the nose and the underside of the front chassis to the chin, which splits the air between that which travels through the sidepods for cooling, and that which goes under the car's floor. At the end of the floor, the air meets the diffuser, which returns it to the outer airstream. This route will now be described in more detail.
The Nose and Chin:
In 1990, Tyrrell, often the innovators in F1 design, came up with a revolutionary high nose - contrary to the low nose trends of the time. The 019 slipped into the F1 field with some interest, but at the time it wasn't clear that the design would change the look of the F1 car for at least the next ten years.
The raised nose - which when it first came out looked like a handlebar mustache - allows the air to flow, undisturbed, to an air splitter (the chin) positioned under the cockpit, at the start of the floor. Before, the front chassis and nose ran flat to the floor, with the aim of obtaining downforce from this area. Instead, Tyrrell saw that by moving these obstacles out of the way, better airflow to the floor created more downforce. The nose was raised, the front wing suspended on pylons, and the front of the chassis was smoothly curved from the high nose down to the chin at floor level. The chin, shown in the diagram, is a semi-circular scolloped face, with a flat, horizontal surface sticking out underneath it. The face guides the undisturbed air around and under the sidepods, and the flat surface prevents the air from being encouraged to go anywhere else. The current school of designers are always looking for more air under the floor, as it is here that the greatest and most efficient downforce can be produced - the nose is now something they want to get out of the way.
Front Chassis:
In 1999, every car in the field has some kind of raised nose, but these have been honed from the Tyrrell Original, to provide very different interpretations of the same thing. It is interesting to see that the McLaren (the most victorious car of recent times), has a relatively low nose. This confirms the view of many designers that the raised nose is not so important, and that what is, is the raised front chassis - the area behind the nose, but in front of the driver, and the entrance to the chin. By curving the chassis up from behind the nose, then back down to the chin in a slight banana shape, the designer can get clean air to the floor without having too high a nose. However, the Jury is still out on this issue!
Floor:
This flat section, close to the ground, is where most downforce is obtained. However, it is not, in itself, a magic surface. It works in the manner of a duct, and requires good inflow and outflow - obtained through good chin and diffuser design. In a duct, there exists a mouth (entrance), a throat (main body of the duct), and a diffuser (exit). The air accelerates in through the mouth, continues to speed up in the throat, and is decelerated to return to the speed of the free-stream flow in the diffuser. On an F1 car, the lower leading edge of the sidepod (coming off the edge of the chin) acts as the mouth, and the flat bottom is the throat. As explained previously, high speed air has low pressure, so the air under the car works to suck the car down. The size of the floor, however, is limited to a maximum width in the rules, but teams tend to vary its length.
The closer the floor is to the track, the more downforce it will produce due to ground effect, so to reduce the downforce created by the floor, the rulemakers stipulate that it is raised from the track. This is enforced by a plank of wood (yes, wood!), positioned underneath the car at cockpit width, running from the chin to the rear.
The Nose and Chin:
The better the diffuser works, the more efficient downforce you have - it is an important area of the 'duct' system. Forming an upsweep from the floor to just under the rear wing, the diffuser decelerates the air towards its original speed. Its design includes vertical fences, some of which are curved, some stepped, and some angled, but all are developed through constant tweaking and evolution in the wind tunnel. The basic job of these fences is to keep apart the many different types of flow found at the rear end of an F1 car - areas of low pressure air due to the rear wheels, and the rear wing, and the air coming under the floor. All these different air flows have different energy levels and different speeds, and their separation makes them easier to deal with.
The main aim in diffuser design is to take it to its limit, and not beyond. If the slope of the diffuser is too steep, we will have flow separation (the flow will no longer follow the surface), causing extra drag. This may not occur in all areas, however. In the outer edges of the diffuser, the air, which has traveled under the car along the outer part of the floor, will have mixed with, and been slowed by, air from outside the floor. Towards the centre, however, the air flows faster, as no extra air has reached that area. For this reason, the diffuser consists of varying slopes, depending on the curve the air can follow before separation.
With rear wing elements helping suck the air from under the car, and the close-packed nature of the car in this area, it tends to be knowledge-inspired trial and error development which changes the shapes of the diffuser - to get a good one takes a lot of time and effort...and a touch of luck!
Greg
01-06-2010, 08:05 PM
#47
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Floor:
This flat section, close to the ground, is where most downforce is obtained. However, it is not, in itself, a magic surface. It works in the manner of a duct, and requires good inflow and outflow - obtained through good chin and diffuser design. In a duct, there exists a mouth (entrance), a throat (main body of the duct), and a diffuser (exit). The air accelerates in through the mouth, continues to speed up in the throat, and is decelerated to return to the speed of the free-stream flow in the diffuser. On an F1 car, the lower leading edge of the sidepod (coming off the edge of the chin) acts as the mouth, and the flat bottom is the throat. As explained previously, high speed air has low pressure, so the air under the car works to suck the car down. The size of the floor, however, is limited to a maximum width in the rules, but teams tend to vary its length.
The closer the floor is to the track, the more downforce it will produce due to ground effect, so to reduce the downforce created by the floor, the rulemakers stipulate that it is raised from the track. This is enforced by a plank of wood (yes, wood!), positioned underneath the car at cockpit width, running from the chin to the rear.
Greg
This is exactly what I have said.... The floor by itself is useless without the entry, throat and diffuser to regulate the airflow through the underside of the car..
The flat floor by itself can do nothing to speed up or slow down the air.. The downforce is caused by the pressure differential due to the speed of the air through the tunnel created by the combination of the opening, throat, and diffuser... (hence up side down wing creating negative lift aka downforce) It is done through the tunnel instead of a wing on the nose or tail...
Bernoulli, old Italian guy long dead, but not forgotten..
Mc Laren did the same with the F1... The GTR's have a wing, but the standard car without the wing produces more downforce with the fully functioning vents that the GTR...
Cheers,
01-06-2010, 08:09 PM
#48
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I never said block it off, i said vent what you need for on coming air and vent it to the hood, or through a series of venturis and diffusers. Yes, the F1 cars have flat bottoms and dont allow venturs on the bottom, but thats not to say they dont use them on the sides and other areas.
http://www.f1technical.net/articles/4577
If you dont have a way to vent and venturi the air on the bottom , the flat bottom will be the most efficient way to reduce drag. sure the article goes into how it increases downforce, but with sports cars, thats miminal compared to the other factors. When they talk about grabbing as much air as possible, they are doing something with it. (like venting it as I have to the hood /bonnet) this takes the air that normally would go under the car and relieves pressure on the top air that is at a naturally , lower pressure due to its increased speed over the car. This is incredibly hard to discuss over the list, as there are so many factors and things left out. Like talking about "getting more air under the car" . Is this good? that depends. what are you doing with the air under the car. if you are using for venting, through venturies and diffusers, yes. if not, no.
take a look at that link. It visually shows what the air is doing around the major components of an F1 car. much more complex than a sports car.
The 599 has a low front air dam/splitter. it reduces the air under the car, and what does get through is routed underneath to the rear, with side skirts to protects its relatively lower pressure than the sides, but still near ambient, and route that air to the rear diffuser where it slows and meets nicely, the air coming off the body and wing for more downforce and better efficiencies.
http://www.f1technical.net/articles/4577
If you dont have a way to vent and venturi the air on the bottom , the flat bottom will be the most efficient way to reduce drag. sure the article goes into how it increases downforce, but with sports cars, thats miminal compared to the other factors. When they talk about grabbing as much air as possible, they are doing something with it. (like venting it as I have to the hood /bonnet) this takes the air that normally would go under the car and relieves pressure on the top air that is at a naturally , lower pressure due to its increased speed over the car. This is incredibly hard to discuss over the list, as there are so many factors and things left out. Like talking about "getting more air under the car" . Is this good? that depends. what are you doing with the air under the car. if you are using for venting, through venturies and diffusers, yes. if not, no.
take a look at that link. It visually shows what the air is doing around the major components of an F1 car. much more complex than a sports car.
The 599 has a low front air dam/splitter. it reduces the air under the car, and what does get through is routed underneath to the rear, with side skirts to protects its relatively lower pressure than the sides, but still near ambient, and route that air to the rear diffuser where it slows and meets nicely, the air coming off the body and wing for more downforce and better efficiencies.
01-06-2010, 08:12 PM
#49
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Exactly!!
in fact, do you remember the flying auberlin in ALMS? flat bottom car, but yet it flew (i.e. took off like an airplane) back then, there was not enough hood and fender venting to increase downforce regardless if you were following anyone. flat bottom alone does nothing.
in fact, do you remember the flying auberlin in ALMS? flat bottom car, but yet it flew (i.e. took off like an airplane) back then, there was not enough hood and fender venting to increase downforce regardless if you were following anyone. flat bottom alone does nothing.
Greg,
This is exactly what I have said.... The floor by itself is useless without the entry, throat and diffuser to regulate the airflow through the underside of the car..
The flat floor by itself can do nothing to speed up or slow down the air.. The downforce is caused by the pressure differential due to the speed of the air through the tunnel created by the combination of the opening, throat, and diffuser... (hence up side down wing creating negative lift aka downforce) It is done through the tunnel instead of a wing on the nose or tail...
Bernoulli, old Italian guy long dead, but not forgotten..
Mc Laren did the same with the F1... The GTR's have a wing, but the standard car without the wing produces more downforce with the fully functioning vents that the GTR...
Cheers,
This is exactly what I have said.... The floor by itself is useless without the entry, throat and diffuser to regulate the airflow through the underside of the car..
The flat floor by itself can do nothing to speed up or slow down the air.. The downforce is caused by the pressure differential due to the speed of the air through the tunnel created by the combination of the opening, throat, and diffuser... (hence up side down wing creating negative lift aka downforce) It is done through the tunnel instead of a wing on the nose or tail...
Bernoulli, old Italian guy long dead, but not forgotten..
Mc Laren did the same with the F1... The GTR's have a wing, but the standard car without the wing produces more downforce with the fully functioning vents that the GTR...
Cheers,
01-06-2010, 08:38 PM
#50
Rennlist Member
We have to watch what we are trying to do vs other totally unrelated platforms.
now, getting back to the 928, we need to do more of the things I was attempting to do as well as paying attention to the underbody smoothness, to increase downforce and reduce drag. (for high speed tracks)
I have already done a lot of measurements of pressure, vacuum, actual force and have followed known aerodynamic designs and theories. So, lets talk about the trade offs. Lets talk about underbody panels and their expected effects, air dams, splitter shapes and functions, fender vents, wings and side skirts, etc.
now, getting back to the 928, we need to do more of the things I was attempting to do as well as paying attention to the underbody smoothness, to increase downforce and reduce drag. (for high speed tracks)
I have already done a lot of measurements of pressure, vacuum, actual force and have followed known aerodynamic designs and theories. So, lets talk about the trade offs. Lets talk about underbody panels and their expected effects, air dams, splitter shapes and functions, fender vents, wings and side skirts, etc.
01-07-2010, 04:23 AM
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In reference to your last quote Richard, where you say the floor is useless and that the entry throat diffuser etc, I have no real argument with that, well the flat floor will be of some use and it does speed up the air and will not slow it down, however this is what I have been saying all along. I have said get as much air under the car as you can. I also have never proposed shaping the 928's underside like a inverted wing, it is just not possible, that is why I didn't even want to discuss it. I don't want to give anybody the impression that there is a tunnel or tunnels in a F1 car, I think it may be more accurate to describe to the area from the car's flat floor to the road or track as the appeture or maybe something else, it doesn't have any sides so it is not a tunnel.
I bought F1 into the discussion because the underneath of those cars since 1983 has used the same principle as the 599 GTB and XX and obviously there was a big step forward with the Tyrrell in 1990 and anybody who saw that car race on the street circuits against Senna would have been impressed, it appeared very nimble. I think it was driven by Alessi at one stage.
So my position has been guide the air away from the tyres in particular the front tyres and under the car, I avoided using the technical terms that you have used so as to include as many listers as possible and yes it is the Bernoulli principle, I was going to bring in the analogy of a carburettor with my bonnet vents but thought better of it.
Have a look at the technical analysis by Gordon Murray of the front of 599. I think the S4 front end is quite similar to the 599 in aero principles, like the way the bottom black aero pieces pushes the air away from the tyres and to the brakes and is curved to let more air under the car. I am only talking about the front fascia area not further back.
Greg
By Blau928
I bought F1 into the discussion because the underneath of those cars since 1983 has used the same principle as the 599 GTB and XX and obviously there was a big step forward with the Tyrrell in 1990 and anybody who saw that car race on the street circuits against Senna would have been impressed, it appeared very nimble. I think it was driven by Alessi at one stage.
So my position has been guide the air away from the tyres in particular the front tyres and under the car, I avoided using the technical terms that you have used so as to include as many listers as possible and yes it is the Bernoulli principle, I was going to bring in the analogy of a carburettor with my bonnet vents but thought better of it.
Have a look at the technical analysis by Gordon Murray of the front of 599. I think the S4 front end is quite similar to the 599 in aero principles, like the way the bottom black aero pieces pushes the air away from the tyres and to the brakes and is curved to let more air under the car. I am only talking about the front fascia area not further back.
Greg
By Blau928
Greg,
This is exactly what I have said.... The floor by itself is useless without the entry, throat and diffuser to regulate the airflow through the underside of the car..
The flat floor by itself can do nothing to speed up or slow down the air.. The downforce is caused by the pressure differential due to the speed of the air through the tunnel created by the combination of the opening, throat, and diffuser... (hence up side down wing creating negative lift aka downforce) It is done through the tunnel instead of a wing on the nose or tail...
Bernoulli, old Italian guy long dead, but not forgotten..
This is exactly what I have said.... The floor by itself is useless without the entry, throat and diffuser to regulate the airflow through the underside of the car..
The flat floor by itself can do nothing to speed up or slow down the air.. The downforce is caused by the pressure differential due to the speed of the air through the tunnel created by the combination of the opening, throat, and diffuser... (hence up side down wing creating negative lift aka downforce) It is done through the tunnel instead of a wing on the nose or tail...
Bernoulli, old Italian guy long dead, but not forgotten..
Greg and Mark,
It is actually somewhat simple why the current shift to run air under the car. The amount of air is controlled based on venturi opening etc. to increase velocity and create a low pressure zone under the car.
However, the main thing is the shape of the venturis, and the underside, which CFD modeling can address prior to build. If you look closely, the venturis under the car are shaped as upside down wings, which create {negative lift} aka downforce...
The controlled airflow under the car is used to create downforce where in prior situations and design, the airflow was routed around, and over the car....
You are both correct, it is the interpretation of the designer's intent, and use of the vehicle.... Some places allow much faster continuous driving and higher top speed than others.. In other areas, more downforce at slower terminal velocity is more important..
Pick your use, and design for it, including compromises...!
It is actually somewhat simple why the current shift to run air under the car. The amount of air is controlled based on venturi opening etc. to increase velocity and create a low pressure zone under the car.
However, the main thing is the shape of the venturis, and the underside, which CFD modeling can address prior to build. If you look closely, the venturis under the car are shaped as upside down wings, which create {negative lift} aka downforce...
The controlled airflow under the car is used to create downforce where in prior situations and design, the airflow was routed around, and over the car....
You are both correct, it is the interpretation of the designer's intent, and use of the vehicle.... Some places allow much faster continuous driving and higher top speed than others.. In other areas, more downforce at slower terminal velocity is more important..
Pick your use, and design for it, including compromises...!
Last edited by slate blue; 01-07-2010 at 07:58 AM.
01-07-2010, 05:18 AM
#52
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By Mark kibort
Agreed, I know you have done considerable work, however as I have said before on this forum i rarely take positions unless I am sure of my statements, and a fair bit of time with back and forth over a basic statement of fact.
By Mark Kibort
Mark I did have a quick look at that link, those are not actual F1 cars, that paper was part of a study commissioned by the FIA Overtaking Group. It looked at ways to reduce the effect of the front car effecting the following car. I actually have the technical drawings 100 plus F1 cars and the technical analysis that goes with it. I also if I can find it can supply the percentage of downforce the underside of the car supplies.
You would be surprised how advanced these cars are and how clever the engineers are, a very simple thing that got banned and was my personal favourite is Renault's mass damper, if you ever wondered why the Renault's front end was glued to the track, the mass damper was the reason, it was used in the their Championship winning years. If you want something to screw with your mind look up inerter dampers. I can't work it out but apparently they are not that complicated.
By Mark Kibort
Mark I can't agree with this statement about the 599, please see the attached article, it is not an air dam, it does have a small splitter which I am trying to copy. The small splitter not the look. You will see Gordon Murray has a different view to yours in regard to the air going underneath the car. He is also critical of the floor on the 599 GTB which is why mine if I do this will be better, that is smoother. The downforce produced by the street 599 and the 599XX is considerable. as we know the car doesn't have big wings and splitters, I am sure the 599 which ever version, has low drag despite big downforce, that is efficiency born out of a very intensive and expensive Formula One program. Those big wings and splitters seen on some race cars will work quite well at low speeds, not disputing any of that but in regards to this thread they don't fit with what I am doing or what would even be possible in a sympathetic way.
By Mark Kibort
To sum up this is a discussion group and yes please all put your views but to move forward and try and get something we all want or at least are interested in. It is important to be able to sort the wheat from the chaff and these days the way to do it is to run as much air under the car as possible as long as it has an underbody suited to it. This is the point where the discussion started on page 2. I would like to move it on. If nobody on the board knows, so be it, I am not sure of certain aspects, hence my questions. I still suspect the reason that they run the engine cooling air over the bonnet is to raise the pressure by feeding the low pressure zone. Any opinions?
Greg
We have to watch what we are trying to do vs other totally unrelated platforms.
now, getting back to the 928, we need to do more of the things I was attempting to do as well as paying attention to the underbody smoothness, to increase downforce and reduce drag. (for high speed tracks)
I have already done a lot of measurements of pressure, vacuum, actual force and have followed known aerodynamic designs and theories. So, lets talk about the trade offs. Lets talk about underbody panels and their expected effects, air dams, splitter shapes and functions, fender vents, wings and side skirts, etc.
now, getting back to the 928, we need to do more of the things I was attempting to do as well as paying attention to the underbody smoothness, to increase downforce and reduce drag. (for high speed tracks)
I have already done a lot of measurements of pressure, vacuum, actual force and have followed known aerodynamic designs and theories. So, lets talk about the trade offs. Lets talk about underbody panels and their expected effects, air dams, splitter shapes and functions, fender vents, wings and side skirts, etc.
By Mark Kibort
I never said block it off, i said vent what you need for on coming air and vent it to the hood, or through a series of venturis and diffusers. Yes, the F1 cars have flat bottoms and dont allow venturs on the bottom, but thats not to say they dont use them on the sides and other areas.
http://www.f1technical.net/articles/4577
If you dont have a way to vent and venturi the air on the bottom , the flat bottom will be the most efficient way to reduce drag. sure the article goes into how it increases downforce, but with sports cars, thats miminal compared to the other factors. When they talk about grabbing as much air as possible, they are doing something with it. (like venting it as I have to the hood /bonnet) this takes the air that normally would go under the car and relieves pressure on the top air that is at a naturally , lower pressure due to its increased speed over the car. This is incredibly hard to discuss over the list, as there are so many factors and things left out. Like talking about "getting more air under the car" . Is this good? that depends. what are you doing with the air under the car. if you are using for venting, through venturies and diffusers, yes. if not, no.
take a look at that link. It visually shows what the air is doing around the major components of an F1 car. much more complex than a sports car.
http://www.f1technical.net/articles/4577
If you dont have a way to vent and venturi the air on the bottom , the flat bottom will be the most efficient way to reduce drag. sure the article goes into how it increases downforce, but with sports cars, thats miminal compared to the other factors. When they talk about grabbing as much air as possible, they are doing something with it. (like venting it as I have to the hood /bonnet) this takes the air that normally would go under the car and relieves pressure on the top air that is at a naturally , lower pressure due to its increased speed over the car. This is incredibly hard to discuss over the list, as there are so many factors and things left out. Like talking about "getting more air under the car" . Is this good? that depends. what are you doing with the air under the car. if you are using for venting, through venturies and diffusers, yes. if not, no.
take a look at that link. It visually shows what the air is doing around the major components of an F1 car. much more complex than a sports car.
You would be surprised how advanced these cars are and how clever the engineers are, a very simple thing that got banned and was my personal favourite is Renault's mass damper, if you ever wondered why the Renault's front end was glued to the track, the mass damper was the reason, it was used in the their Championship winning years. If you want something to screw with your mind look up inerter dampers. I can't work it out but apparently they are not that complicated.
By Mark Kibort
The 599 has a low front air dam/splitter. it reduces the air under the car, and what does get through is routed underneath to the rear, with side skirts to protects its relatively lower pressure than the sides, but still near ambient, and route that air to the rear diffuser where it slows and meets nicely, the air coming off the body and wing for more downforce and better efficiencies.
By Mark Kibort
Now, why do you think the designers run as much air as they can? the splitter and inlet, with hood vents suggest the opposite. see the pics Ive posted, as those all show the theme of not having much air under the car for better downforce. its all about the ratio of the air that goes under the car vs over the car. think of the concept of the hood vents, and you will break the code. you have as much or more air going over the car based on the nose position. yet, with hood vents, the air traveling under the car normally, would now be routed over the hood, feeding the low pressure zone to reduce the low pressure zone at the hood. the more air molecules going over the ar, the lower the pressure differential vs under the car and that is the goal.
again, think of the car as a wing, actually right side up. air under the car is ambient pressure. this is easy to measure, even at 120mph. over the car the pressure drops dramatically with speed. also easy to measure. you can do things locally with venturis and diffusers, but you are just moving around air flow speeds and pressure. robbing Peter to pay Paul, so to speak. Ill have to dig up this discussion we had on the racing board about this. they show how the venturis and diffusers are used under the car. (F1 included). with F1, you have venturi tunnels that increase the speed of the air, reduce the pressure and create massive downforce. the diffusers at the rear would then be a efficient way to have the air exiting the undercar area, with the least amount of drag. I dont think we are talking venturi tunnels here.
again, think of the car as a wing, actually right side up. air under the car is ambient pressure. this is easy to measure, even at 120mph. over the car the pressure drops dramatically with speed. also easy to measure. you can do things locally with venturis and diffusers, but you are just moving around air flow speeds and pressure. robbing Peter to pay Paul, so to speak. Ill have to dig up this discussion we had on the racing board about this. they show how the venturis and diffusers are used under the car. (F1 included). with F1, you have venturi tunnels that increase the speed of the air, reduce the pressure and create massive downforce. the diffusers at the rear would then be a efficient way to have the air exiting the undercar area, with the least amount of drag. I dont think we are talking venturi tunnels here.
Greg
Last edited by slate blue; 01-07-2010 at 07:35 AM. Reason: Extra material
01-07-2010, 09:12 AM
#53
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Hi Greg,
Just thought I'll throw this in.
http://motoring-projects.blogspot.co...nt%20splitters
Cheers,
Pierre.
Just thought I'll throw this in.
http://motoring-projects.blogspot.co...nt%20splitters
Cheers,
Pierre.
01-07-2010, 04:10 PM
#54
Rennlist Member
Ive seen that graphic before as well. however, it is not entirely accurate. the high pressure at the splitter, nose are is correct. (verified by sensor measurements) so is the reduced pressure going over the hood, just passed the nose. however, under the car the pressure and velocity is still the same as the on coming air. The confustion comes when anyone intuitively thinks about what is going on and slightly abuses Bernoulli's principal. what I mean by that is, just because you have this real small area under the splitter, compared to the oncoming air, it doesnt meant that the air is accelerated. in fact, simple pressure measurements along the under side of the car shows the air under the car is still at ambient, under the splitter, below the engine, and below the passenger compartement, even with a splittler a few inches off the ground. the reason, is that the high pressure area (volume) has increased at the splitter and nose area of the car. It now wants to find a differential pressure. through the radiator or around to the sides. what ever is lower, thats where the air will go. over and in front of the splitter is NOT the way the air will go, and this is very easy to prove with tufts as I have done and video taped as well. so, no additional air is forced over and around the splitter, so no increased volume of air to accelerat and lower the under-car pressure adding downforce.
The downforce comes from two areas. actual pressure on the splitter (i saw near .2psi over the entire 300sq" of its surface, vs the ambient pressure air under it. so, there is 60lbs of force. but the main "downforce" comes from what if that air was allowed to travel under the car. Its speed would increase, but the mass flow would as well. the downforce is the difference of the pressure on top of the car vs under the car. what we are really trying to do is spoil the liftiing forces that the air moving over the car cause. the air from the splitter normally allowed to go under the car, is now routed to the sides of the car and to the hood vents.
This is where the gains of using a splitter are found.
a flat bottom alone creates no downforce.
The best graph or visual Ive seen is that one that looks like its hand drawn. Ill see If can dig it up.
mk
The downforce comes from two areas. actual pressure on the splitter (i saw near .2psi over the entire 300sq" of its surface, vs the ambient pressure air under it. so, there is 60lbs of force. but the main "downforce" comes from what if that air was allowed to travel under the car. Its speed would increase, but the mass flow would as well. the downforce is the difference of the pressure on top of the car vs under the car. what we are really trying to do is spoil the liftiing forces that the air moving over the car cause. the air from the splitter normally allowed to go under the car, is now routed to the sides of the car and to the hood vents.
This is where the gains of using a splitter are found.
a flat bottom alone creates no downforce.
The best graph or visual Ive seen is that one that looks like its hand drawn. Ill see If can dig it up.
mk
Hi Greg,
Just thought I'll throw this in.
http://motoring-projects.blogspot.co...nt%20splitters
Cheers,
Pierre.
Just thought I'll throw this in.
http://motoring-projects.blogspot.co...nt%20splitters
Cheers,
Pierre.
01-07-2010, 04:13 PM
#55
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Hi Greg,
I understand what you are tryingto say. However, I do think you are missing the point I am trying to make. The flat floor by itself does not do much, and the more air under the car if not controlled, as based on the amount of downforce intended to be created can cause more harm than help.
Here's why.
The flat floor is by itself not going to create, nor cause a change in the differential pressure of the airflow under the car. The inclusion of a venturi inlet, and throat is what creates the differential pressure by increasing the airflow from the mouth, or opening, through the throat area, and into the center or body of the area (in this case the floor), and out the diffuser at the rear.
The inverted wing is simply a reference of the leading edge and a trailing edge of an airfoil shape, where by the leading edge is the venturi opening, and throat which, the floor forms as the central portion, and the rear diffuser forms the trailing edge of the wing.
The flat floor in this case is not actually an optimum shape for the center of the venturi tube created, but serves a similar effect based on the principle and physical boundaries of the vehicle.
The change in acceleration of the air occurs at the opening based on the opening shape and outlet.
If you look at the F1 cars, you will be able to see the nose, winglets, and other aids the assist in shaping the airflow around, over, and under the car. The rulebook decides what is allowed in F1. However, if designers were allowed total freedom, the shapes of the vehicles would be a bit different. In any event, the front and rear wings and winglets produce so much downforce, that the car could surely run inverted if neccessary..
Ok, back to the 928... It's a sports car with limited physical parameters.. Surely sealing off the underside and making it flat with controlled airflow around tires will improve aerodynamics... Question is cost, and benefit... How much are you going to spend to gain what, depending on where you drive the car....? Would sealing off the bottom and making it flat help..? In my opinion, yes, but that is based on observation, I have not put the car in a wind tunnel, nor taken a scale model for CFD analysis..
Ideally, one would not want to make the underside completely flat either.. Recent CFD studies in aerodynamics has shown that there should be minor bumps (think of small bubble wrap) on the flat surface. This will serve to increase the laminar boundary layer formation and stability, and increase speed of the airflow underneath the vehicle creating downforce, and also stabilizing the airflow under the vehicle...
Incidentally, this new research was learned from Whales.. The bumps on the leading edge of their pectoral fins have them, and they create more lift at the leading edge than a similarly shaped fin with a smooth leading edge..
Hope that helps..! Always interested in learning some more, and also sharing what I have learned.. Keep up the modding of the 928, it's such a wonderful car..
Incidentally, I started my SC setup to get to the F550/575 performance window, as after driving one, I thought the 928 was the only other GT car I drove at the time that inspired as much confidence at speed, and was easy to drive..
I would like a new 599, but don't want to part with the $$$$.. Incidentally, the 550/575's have now become "affordable," considering how much they were new.... I think I surely have to will wait a few years until the 599's become "affordable" before selling a leg to get one.. like this, of course, as it has to be blue......
I understand what you are tryingto say. However, I do think you are missing the point I am trying to make. The flat floor by itself does not do much, and the more air under the car if not controlled, as based on the amount of downforce intended to be created can cause more harm than help.
Here's why.
The flat floor is by itself not going to create, nor cause a change in the differential pressure of the airflow under the car. The inclusion of a venturi inlet, and throat is what creates the differential pressure by increasing the airflow from the mouth, or opening, through the throat area, and into the center or body of the area (in this case the floor), and out the diffuser at the rear.
The inverted wing is simply a reference of the leading edge and a trailing edge of an airfoil shape, where by the leading edge is the venturi opening, and throat which, the floor forms as the central portion, and the rear diffuser forms the trailing edge of the wing.
The flat floor in this case is not actually an optimum shape for the center of the venturi tube created, but serves a similar effect based on the principle and physical boundaries of the vehicle.
The change in acceleration of the air occurs at the opening based on the opening shape and outlet.
If you look at the F1 cars, you will be able to see the nose, winglets, and other aids the assist in shaping the airflow around, over, and under the car. The rulebook decides what is allowed in F1. However, if designers were allowed total freedom, the shapes of the vehicles would be a bit different. In any event, the front and rear wings and winglets produce so much downforce, that the car could surely run inverted if neccessary..
Ok, back to the 928... It's a sports car with limited physical parameters.. Surely sealing off the underside and making it flat with controlled airflow around tires will improve aerodynamics... Question is cost, and benefit... How much are you going to spend to gain what, depending on where you drive the car....? Would sealing off the bottom and making it flat help..? In my opinion, yes, but that is based on observation, I have not put the car in a wind tunnel, nor taken a scale model for CFD analysis..
Ideally, one would not want to make the underside completely flat either.. Recent CFD studies in aerodynamics has shown that there should be minor bumps (think of small bubble wrap) on the flat surface. This will serve to increase the laminar boundary layer formation and stability, and increase speed of the airflow underneath the vehicle creating downforce, and also stabilizing the airflow under the vehicle...
Incidentally, this new research was learned from Whales.. The bumps on the leading edge of their pectoral fins have them, and they create more lift at the leading edge than a similarly shaped fin with a smooth leading edge..
Hope that helps..! Always interested in learning some more, and also sharing what I have learned.. Keep up the modding of the 928, it's such a wonderful car..
Incidentally, I started my SC setup to get to the F550/575 performance window, as after driving one, I thought the 928 was the only other GT car I drove at the time that inspired as much confidence at speed, and was easy to drive..
I would like a new 599, but don't want to part with the $$$$.. Incidentally, the 550/575's have now become "affordable," considering how much they were new.... I think I surely have to will wait a few years until the 599's become "affordable" before selling a leg to get one.. like this, of course, as it has to be blue......
01-07-2010, 04:23 PM
#56
Rennlist Member
I see that drawing and Gordons comments, if they are indeed his.BUT, I cant see enough of the raised center section that is said to "encourage air to enter the floor are for increased ground effects". if that raised area feeds the radiator, vented to venturi channes, etc, then it would make a lot of sense. If not, then it wouldnt. I suspect it was a nessary evil to give ground clearnance but still keeping the side splitter area low, preserving the routing of air to the sides, as the frontal air flow has a huge path to the radiators and up an over the car via the hood vents.
If what I think you are saying is true, then our nose , routing air under the car, after the radiator, and under the front lip of the lower air dam, would create more downforce and lower pressure, when in fact it does not. thats why the use of conventional splitters are so important to the 928 downforce effects.
Im not just speaking from the hip, I giving you years of testing and actual pressure values from all aound the air dam and splitters Ive used.
so far, i have not seen one bit of pressure change under the car at speeds up to 120mph anywhere from the bottom of the splitter to the rear of the car with and without a 8" splitter, only a few " off the ground. But, ive seen significant changes in and around the splitter, as welll as over the top of the hood. Fortunately, we have the 928 aero charts to work from as starting points, which most cars do not have published.
Mk
If what I think you are saying is true, then our nose , routing air under the car, after the radiator, and under the front lip of the lower air dam, would create more downforce and lower pressure, when in fact it does not. thats why the use of conventional splitters are so important to the 928 downforce effects.
Im not just speaking from the hip, I giving you years of testing and actual pressure values from all aound the air dam and splitters Ive used.
so far, i have not seen one bit of pressure change under the car at speeds up to 120mph anywhere from the bottom of the splitter to the rear of the car with and without a 8" splitter, only a few " off the ground. But, ive seen significant changes in and around the splitter, as welll as over the top of the hood. Fortunately, we have the 928 aero charts to work from as starting points, which most cars do not have published.
Mk
Mark I can't agree with this statement about the 599, please see the attached article, it is not an air dam, it does have a small splitter which I am trying to copy. The small splitter not the look. You will see Gordon Murray has a different view to yours in regard to the air going underneath the car. He is also critical of the floor on the 599 GTB which is why mine if I do this will be better, that is smoother. The downforce produced by the street 599 and the 599XX is considerable. as we know the car doesn't have big wings and splitters, I am sure the 599 which ever version, has low drag despite big downforce, that is efficiency born out of a very intensive and expensive Formula One program. Those big wings and splitters seen on some race cars will work quite well at low speeds, not disputing any of that but in regards to this thread they don't fit with what I am doing or what would even be possible in a sympathetic way.
>>>>>>>
To sum up this is a discussion group and yes please all put your views but to move forward and try and get something we all want or at least are interested in. It is important to be able to sort the wheat from the chaff and these days the way to do it is to run as much air under the car as possible as long as it has an underbody suited to it. This is the point where the discussion started on page 2. I would like to move it on. If nobody on the board knows, so be it, I am not sure of certain aspects, hence my questions. I still suspect the reason that they run the engine cooling air over the bonnet is to raise the pressure by feeding the low pressure zone. Any opinions?
Greg
>>>>>>>
To sum up this is a discussion group and yes please all put your views but to move forward and try and get something we all want or at least are interested in. It is important to be able to sort the wheat from the chaff and these days the way to do it is to run as much air under the car as possible as long as it has an underbody suited to it. This is the point where the discussion started on page 2. I would like to move it on. If nobody on the board knows, so be it, I am not sure of certain aspects, hence my questions. I still suspect the reason that they run the engine cooling air over the bonnet is to raise the pressure by feeding the low pressure zone. Any opinions?
Greg
01-07-2010, 04:47 PM
#57
Rennlist Member
I found what I was looking for.
http://www.superhachi.com/theory/downforce/
Very simplistic, but it gets the points accross.
Here is one of the drawings on from the article.
http://www.superhachi.com/theory/downforce/
Very simplistic, but it gets the points accross.
Here is one of the drawings on from the article.
01-07-2010, 08:07 PM
#58
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Thread Starter
By Blau928
Richard accepted, I thought you were trying to imply, with the language used that there was still some form of inverted wing, to some it may have been confusing. I agree that the inverted wing would be the best but we can never achieve that so I want to leave that alone. I also think that we are on the same page when we/I say that it, a car needs an aero package to work properly, single pieces may not work effectively as in a package environment.
I also agree with the remainder of what you say too. I would just say for some extra comment, that the venturi inlet in the case of the 599 is the raised centre section that Gordon Murray mentions and that the reason Gordon is critical of the less than perfect floor is because the floor is not so smooth and as such the air will not travel as fast as it can. The result being that downforce is reduced from optimum. The 599 also has a substantial rake angle which I mentioned on page 2 all of which assists, even F1 car have rake angles.
Cheers
Greg
Hi Greg,
I understand what you are tryingto say. However, I do think you are missing the point I am trying to make. The flat floor by itself does not do much, and the more air under the car if not controlled, as based on the amount of downforce intended to be created can cause more harm than help.
Here's why.
The flat floor is by itself not going to create, nor cause a change in the differential pressure of the airflow under the car. The inclusion of a venturi inlet, and throat is what creates the differential pressure by increasing the airflow from the mouth, or opening, through the throat area, and into the center or body of the area (in this case the floor), and out the diffuser at the rear.
The inverted wing is simply a reference of the leading edge and a trailing edge of an airfoil shape, where by the leading edge is the venturi opening, and throat which, the floor forms as the central portion, and the rear diffuser forms the trailing edge of the wing.
The flat floor in this case is not actually an optimum shape for the center of the venturi tube created, but serves a similar effect based on the principle and physical boundaries of the vehicle.
The change in acceleration of the air occurs at the opening based on the opening shape and outlet.
If you look at the F1 cars, you will be able to see the nose, winglets, and other aids the assist in shaping the airflow around, over, and under the car. The rulebook decides what is allowed in F1. However, if designers were allowed total freedom, the shapes of the vehicles would be a bit different. In any event, the front and rear wings and winglets produce so much downforce, that the car could surely run inverted if neccessary..
I understand what you are tryingto say. However, I do think you are missing the point I am trying to make. The flat floor by itself does not do much, and the more air under the car if not controlled, as based on the amount of downforce intended to be created can cause more harm than help.
Here's why.
The flat floor is by itself not going to create, nor cause a change in the differential pressure of the airflow under the car. The inclusion of a venturi inlet, and throat is what creates the differential pressure by increasing the airflow from the mouth, or opening, through the throat area, and into the center or body of the area (in this case the floor), and out the diffuser at the rear.
The inverted wing is simply a reference of the leading edge and a trailing edge of an airfoil shape, where by the leading edge is the venturi opening, and throat which, the floor forms as the central portion, and the rear diffuser forms the trailing edge of the wing.
The flat floor in this case is not actually an optimum shape for the center of the venturi tube created, but serves a similar effect based on the principle and physical boundaries of the vehicle.
The change in acceleration of the air occurs at the opening based on the opening shape and outlet.
If you look at the F1 cars, you will be able to see the nose, winglets, and other aids the assist in shaping the airflow around, over, and under the car. The rulebook decides what is allowed in F1. However, if designers were allowed total freedom, the shapes of the vehicles would be a bit different. In any event, the front and rear wings and winglets produce so much downforce, that the car could surely run inverted if neccessary..
I also agree with the remainder of what you say too. I would just say for some extra comment, that the venturi inlet in the case of the 599 is the raised centre section that Gordon Murray mentions and that the reason Gordon is critical of the less than perfect floor is because the floor is not so smooth and as such the air will not travel as fast as it can. The result being that downforce is reduced from optimum. The 599 also has a substantial rake angle which I mentioned on page 2 all of which assists, even F1 car have rake angles.
Cheers
Greg
01-07-2010, 08:13 PM
#59
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By Pierre Martins
Thanks for posting Pierre, I read your article, I concur 100%, in regard to the use of splitters, I don't want anybody to think I have anything against splitters, I don't it is just the streets around here have something against splitters. 
So I needed to find a way that we could all live together.
Is that a special paint treatment you have on the 928 in the top pic or was it just the way the pic was taken? Lots of work in making moulds etc. I think carbon prices have come down a lot since you wrote that article, they were going crazy before the GFC.
Greg
Hi Greg,
Just thought I'll throw this in.
http://motoring-projects.blogspot.co...nt%20splitters
Cheers,
Pierre.
Just thought I'll throw this in.
http://motoring-projects.blogspot.co...nt%20splitters
Cheers,
Pierre.
So I needed to find a way that we could all live together. Is that a special paint treatment you have on the 928 in the top pic or was it just the way the pic was taken? Lots of work in making moulds etc. I think carbon prices have come down a lot since you wrote that article, they were going crazy before the GFC.
Greg
01-07-2010, 09:30 PM
#60
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Mark here's a pic of the 599XX and you will see the deliberate attempt to send the air under the car just like the roadcars aperture in the front bumper. The car does have a small splitter too but no air dam. As mentioned before none of the engine bay air makes it under the car, it exits over the bonnet. So only fast moving air makes it under the car, not turbulent slow moving air.
You can read about it here,
http://www.carvehicle.net/ferrari-59...s-and-reviews/
Here's an interesting part, same of the FFX, air is sucked from under the car and exhausted through the tailights.
In regards to the link you posted, I did read it, the extra source quoted, author Simon McBeath published a book in 1998 called Competition Car Downforce which I have, the material posted is not incorrect but you cannot take it as complete. In fact I can't see anything to the contrary except that it is not dealing with exactly what we are talking about, it is also trying to load every single aero device onto one car and trying to be concise, which is difficult.
Please read carefully.
Simon McBeath also published another book in 2006 called Competition Car Aerodynamics, it is considerably updated and contains lots of CFD info. There is so much info in that book I haven't had time to take it in. However given there seems to be doubters out there about the flat floor benefits, there is a study that I can point to that shows extra downforce just with a flattish floor.
The study was conducted on a Nascar, it was a CFD study and it really does prove my point about increased flow under the car that have correct aerodynamics parts, e.g venturi entrance, flat floor and diffuser side skirts etc. However in this case. A standard Nascar was mapped, and then the floor closed in, that is a partial flat floor was added with no other changes. So what they did was close off the clutter under the car not add a perfect flat floor
The change in downforce was 6.5% in favour of the closed in floor. Why, I hear you ask. Well I am sure you will find it interesting to find that nearly 3/4 of the gains came from encouraging mass airflow beneath the car. Which of course reduced mass airflow over the car. The change in drag was small at 1%.
The study concluded that if a proper flat floor was added the gains in dowforce would be further enhanced and drag would drop again. They also said benefits can be had with the change of the rake angle with the flat floor but that is starting to get obvious.
Greg.
You can read about it here,
http://www.carvehicle.net/ferrari-59...s-and-reviews/
Here's an interesting part, same of the FFX, air is sucked from under the car and exhausted through the tailights.
In regards to the link you posted, I did read it, the extra source quoted, author Simon McBeath published a book in 1998 called Competition Car Downforce which I have, the material posted is not incorrect but you cannot take it as complete. In fact I can't see anything to the contrary except that it is not dealing with exactly what we are talking about, it is also trying to load every single aero device onto one car and trying to be concise, which is difficult.
Please read carefully.
Simon McBeath also published another book in 2006 called Competition Car Aerodynamics, it is considerably updated and contains lots of CFD info. There is so much info in that book I haven't had time to take it in. However given there seems to be doubters out there about the flat floor benefits, there is a study that I can point to that shows extra downforce just with a flattish floor.
The study was conducted on a Nascar, it was a CFD study and it really does prove my point about increased flow under the car that have correct aerodynamics parts, e.g venturi entrance, flat floor and diffuser side skirts etc. However in this case. A standard Nascar was mapped, and then the floor closed in, that is a partial flat floor was added with no other changes. So what they did was close off the clutter under the car not add a perfect flat floor
The change in downforce was 6.5% in favour of the closed in floor. Why, I hear you ask. Well I am sure you will find it interesting to find that nearly 3/4 of the gains came from encouraging mass airflow beneath the car. Which of course reduced mass airflow over the car. The change in drag was small at 1%.
The study concluded that if a proper flat floor was added the gains in dowforce would be further enhanced and drag would drop again. They also said benefits can be had with the change of the rake angle with the flat floor but that is starting to get obvious.
Greg.