Wind Tunnel Ground Plane Boundary Layer

[JamesEtch]

Hello there. I'm using a small open jet wind tunnel in order to test 1/10 scale models of a solar powered car. I have been investigating the performance of the cars at yaw angles and have obtained some pretty strange results. One of my theorys is that the cause could be the ground plane boundary layer thickness burying the effects at yaw. We are using an elevated ground plane, however, I have measure the b.l. 99% thickness at around 23mm, integrating up to give displacement thickness around 1.5-2mm. I was wondering if anyone knew of any tried and tested rules of thumb for model ground clearance vs b.l. thickness for wind tunnel testing? ie I've seen that displacement thickness should be < 1/5 ground clearance. Any help is much appreciated, cheers James Etchells

 

[WhiteRabbit]

It is possible to diffuse the lower wall to allow the boundary layer none cross sectional area change in the test section.

A very difficult method of boundary layer control would be to have a treadmill spinning at the same free stream velocity to simulate the ground. A car will not have a boundary layer formation on the lower wall as with a wind tunnel.