Quote:
Originally Posted by mar5ka
I was just reading road and track classic from 2006 were they take a 1959 4 door chevy and put it in a wind tunnel, they proclaim that the pointed rear fins or gull wings create air seperation and decrease drag for the rear of the car......Is this right? I thought that any sharpe edge on a moving body creates vortex's that increase drag. So then explain to me about the ford bi wing which reduces drag by 5% when the first wing creates air seperation or vortex's?
|
I'm with Frank Lee,more data if the article has it.Vorticity forms as a function of two air masses,either with a differential pressure,or a differential velocity commingling together.It happens a lot at wing tips where pressure differences above and below the wing cause the high to flow into the low,spiraling into a vortex.Its also common around A-pillars,and its famous for pseudo-Kammback,fastback car C-Pillars,where air over the roof moving at a relatively higher velocity,collides with slower-moving air along the sides,spiraling into the vortex.Once the vortex is formed,it robs an enormous amount of engine power to feed this circulation. As to the patented bi-wing rear spoiler,the spoiler forces the air to take a "longer" path over the back-lite and boot of the car.A locked-vortex is created by the spoiler,which robs some engine power,however drag reduction gained by the free-stream flowing over the new "virtual" aft body out weighs the loss for a net gain in efficiency.I think the fins on the Chevy were just for styling.That car did not suffer from cross-wind instability,the reason for which fins are usually employed.