Quote:
Originally Posted by Sven7
My friend and I got into a discussion at the EcoMarathon about low speed aerodynamics. We know that the airflow changes at lower speeds, but we don't really know how.
Most of the prototype cars there are more or less teardrop shaped tadpole trikes, like what you would design for a highway-speed car. He thinks that you could basically build a delta trike with a conical body that was chopped off at the back. Is this the ideal design? What is the ideal aero shape for low speed vehicles?
There doesn't seem to be much info out there about this stuff. Hopefully someone will have an idea!
Thanks in advance!  |
For the lowest drag,you need a supercritical Reynolds number.
If the body is too short to achieve this,you'd have to introduce artificial roughness to trigger the transition to a turbulent boundary layer.
Otherwise,the flow would separate before it ever got to the point of maximum cross-section.
Trip wires,sand,VGs,and dimples could be used for the trigger.After that,then it's either a wing-based body,or pumpkin seed for the lowest drag.Whatever the driver could tolerate.
Cones have full-frontal area-wakes.There's no pressure recovery possible with them.They have double the drag of a reversed-cone with convex hemispherical nose.This data dates to as early as 1898 with Alexander Gustav Eiffel's research at his famous tower in Paris.They violate the entire premise of streamlining.You want full boat-tailing if you can do it.Reduce or eliminate the wake.
Here you see the effect of low Reynolds number and enormous wake
