Quote:
Originally Posted by JulianEdgar
You seem to be implying that the pressures on the trailing edge of the roof will match the pressures found in the wake. That is not the case on modern cars; it may be the case on older cars with premature flow separation.
Current cars:
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1) ' The pressure on the rear face of the body, in the separation region, is found to be approximately uniform and equal to the pressure just outside the boundary layer at separation.' P. W. Bearman, Dept. of Aeronautics, Imperial College, London, England, Re: ' Review- Bluff Body Flows Applicable to Vehicle Aerodynamics, Journal of Fluid Engineering, Sept. 1980, Volume 102, page- 265.
2) This pressure induces lift over the horizontal component of the panel. This low pressure contaminates the wake, affecting overall base pressure.
3) Porsche's truncation of the roofline IS the premature separation, on a modern car.
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4) ' The angle ( Greek symbol Theta ) between the shear layer at separation and the free stream direction is an important factor in determining base pressure.' Bearman.
Porsche's premature separation gives up this additional advantage of vectored flow into the wake, which would have occurred had the roof not been ' complexified.'