Should I Port/Polish My 951 Head?
01-31-2005, 07:30 PM
#91
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It's more like, "laminar flow can only exist below a certain RE or corresponding speed".
Above that, the air is ripped to pieces and the individual molecules do not adhere to each other. This leads to that the air in the center of a pipe is not slowed down by the wall friction so it is good.
Above that, the air is ripped to pieces and the individual molecules do not adhere to each other. This leads to that the air in the center of a pipe is not slowed down by the wall friction so it is good.
"When Reynolds number exceeds appr 2300 the flow in a pipe can transform to an unordered movement, turbulence, there the mixing of flow elements is great. (It should be noted that by keeping the flow free from disturbances it's possible for the flow to remain laminar up to Re appr 50000. Under Re appr 2000 it is never possible to create turbulence regardless of how large disturbances that exists in the flow.) The transfer of flow elements in radial direction causes a transport of movement quantity (probable a bad translation, my note) which according to the law of movement quantities causes a force. This resistance to the flow is significantly larger than the resistance to laminar flow."
What I remember from school was the experiments was that when you increased the speed of the flow, you would have laminar flow for a while and the something random disturbed the flow and it would break down in to turbulence and would never stabilize again.
Tomas
01-31-2005, 08:01 PM
#92
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What is an aerodynamic body? Bodies can be designed for different aerodynamic purposes like minimum drag or maximum up/down force. For minimum drag you would like to have turbulence behind the body or otherwise you would need an extremely long body. For maximum up/down force from a wing you want the flow to follow the wing and you want to use the combined forces of all the air molecules. Therefore you need the media to be able to transfer the forces i.e laminar flow.
In some cases you can design so that you get turbulence at a set speed and therefore limit downforce and drag but this is tricky since you are dependant on air density wind conditions etc.
Wing shapes or drop shapes like a 911 body have high lifting forces and high drag. Box shapes with slant nose and cut off rear have low drag, contrary to popular belief.
In some cases you can design so that you get turbulence at a set speed and therefore limit downforce and drag but this is tricky since you are dependant on air density wind conditions etc.
Wing shapes or drop shapes like a 911 body have high lifting forces and high drag. Box shapes with slant nose and cut off rear have low drag, contrary to popular belief.
Therefore you get the least evil thing, acceptable drag and minimized lifting forces, if you cut of the tail abruptly.
At subsonic speed drop shaped bodys have the lowest drag but due to packaging reasons and the need to maximize downforce they are not practical. For a track car downforce is much more important than top speed and drag. A formula one car has a Cd of above 1.
This thread definitely took a turn for the better. I'm both learning a lot, and am also completely lost about some of it. But, one question, How do aerodynamic bodies related to ports? Other than the obvious, that air flows over/around/near both, aren't they very different concepts? Aerodynamic bodies are only affected, in our context, by air flow when in motion themselves. Yet, in our application we are talking about air being pushed/pulled in the application of a head port. Shouldn't some of the key aerodynamic concepts of each application be very different from one another? Also, there's the concept of temperature, that must have a very significant effect on the density of the air. It takes a pretty fantastic wing to fly at 100,000 ft, because of the lack of molecular density of the air. So doesn't the density have a huge effect on the different propertis of the aero bodies described, and the aerodynamic effects within a head. After all, the air in a head works a lot more like a tornado, the it does like an airplane. Anyway, those were some thoughts/ slash questions that I was having. TIA for more info. E
Yes, the air density will effect the flow properties, density is part of most equations in fluid mechnics.
Don't we have someone on the list that works as an aerodynamics engineer for the McLaren or Williams F1 teams, even one from Ferrari would be acceptable
??Tomas
01-31-2005, 08:37 PM
#93
Drifting
Sorry to rewind back to the angry portion of this thread - but I'm interested in the specifics of wet testing. Is the method m42racer referred too simply involve pumping water through the head, or is it primarily air with a mist of water. Its seems that using a mist of water with a dye would give you your visual, but the vapor would follow the characteristics of the gas (air) flowing through the head. Just curious - fun thread btw.
02-01-2005, 02:09 PM
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For minimum drag turbulence behind the car is not a good idea. It creates a low pressure zone behind the car
Otherwise I stand corrected by the Teacher ;-)
02-01-2005, 03:00 PM
#95
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I think that there has to be a low pressure zone behind a cut off tail.
I don't know if this theory of why holds up...
The air that travels the top and the bottom of the car has a certain horizontal speed (relative to the car), when it passes the the tail it still wants to continue in its original direction. Some of it though has to change direction and turn in in the empty space behind the car to fill it out. If it weren't to do that we definately would have a very low pressure (vacuum) zone behind the car. Still to convince the ait to make this turn there has to to be a driving force, that has to be because the pressure is lower behind the car. If the air behind the car formed a completely static cone, then I would agree that it would give lower resistance. But now we have great turbulence in this area and the energy must come from increased drag.
The 911 tail is not a good design with the roof sloping downward. It will absolutely give lift if it's not cured with a ducktail. My guess is that it will have lower drag without the ducktail. A better design would be to have the bottom of the car turning up and the roof continuing straight back. Sort of like venturi tunnel cars. Unfortunately the engine is in the way and the car may not look that good either.
But the main reason for the 930 wing is not aerodynamic, it has to be that it makes the car look like it has 200 hp more....
I don't know if this theory of why holds up...
The air that travels the top and the bottom of the car has a certain horizontal speed (relative to the car), when it passes the the tail it still wants to continue in its original direction. Some of it though has to change direction and turn in in the empty space behind the car to fill it out. If it weren't to do that we definately would have a very low pressure (vacuum) zone behind the car. Still to convince the ait to make this turn there has to to be a driving force, that has to be because the pressure is lower behind the car. If the air behind the car formed a completely static cone, then I would agree that it would give lower resistance. But now we have great turbulence in this area and the energy must come from increased drag.
The 911 tail is not a good design with the roof sloping downward. It will absolutely give lift if it's not cured with a ducktail. My guess is that it will have lower drag without the ducktail. A better design would be to have the bottom of the car turning up and the roof continuing straight back. Sort of like venturi tunnel cars. Unfortunately the engine is in the way and the car may not look that good either.
But the main reason for the 930 wing is not aerodynamic, it has to be that it makes the car look like it has 200 hp more....
02-01-2005, 03:42 PM
#96
Nordschleife Master
Originally Posted by Tomas L
But the main reason for the 930 wing is not aerodynamic, it has to be that it makes the car look like it has 200 hp more....
02-01-2005, 05:17 PM
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Originally Posted by Duke
The main reason is the intercooler.
Yes, the 930 has the intercooler in the wing but Porsche put a very similar wing on the 911 carrera which has no IC so I suppose there must be some other reason also. Don't tell me they did it for styling reasons...
