Polished ports VS rough 'dimpled' ports
03-13-2003, 10:04 AM
#16
Track Day
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Danno:
<strong>The idea behind a slightly rough surface and dimples are not the same. They may be similar in final results (best air-flow velocity and fuel mixing).
The rough surfaces are best in the intake ports. This removes the shear friction on the layers of air close to the contact surface. This friction is caused by the zero-flow layer directly in contact with the surface. Then as you move away from the surface, the velocity increases, but due to contact with the underlying layer, there's some friction and velocity differences. The speed function vs. distance away from the wall is a parabolic funciton with zero at the surface.
The rough surface is kinda like a whole bunch of Gurney flaps which causes a vortex on the surface. This vortex acts like a bunch of ball-bearings allowing the air layer just above it to flow at full speed.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Correctemundo!
This is exactly what I would write, but end it up and emphasize that it is a laminar flow in the intake with a turbulent boundary layer.
BRG
Dr.CFD a.k.a. D. Bengtsson
<img border="0" alt="[bigbye]" title="" src="graemlins/xyxwave.gif" />
<strong>The idea behind a slightly rough surface and dimples are not the same. They may be similar in final results (best air-flow velocity and fuel mixing).
The rough surfaces are best in the intake ports. This removes the shear friction on the layers of air close to the contact surface. This friction is caused by the zero-flow layer directly in contact with the surface. Then as you move away from the surface, the velocity increases, but due to contact with the underlying layer, there's some friction and velocity differences. The speed function vs. distance away from the wall is a parabolic funciton with zero at the surface.
The rough surface is kinda like a whole bunch of Gurney flaps which causes a vortex on the surface. This vortex acts like a bunch of ball-bearings allowing the air layer just above it to flow at full speed.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Correctemundo!
This is exactly what I would write, but end it up and emphasize that it is a laminar flow in the intake with a turbulent boundary layer.
BRG
Dr.CFD a.k.a. D. Bengtsson
<img border="0" alt="[bigbye]" title="" src="graemlins/xyxwave.gif" />
