Vortex Generators on Undertray?

[260DET]

After doing a bit more research and brain exercise, my conclusion is that vortex generators could be beneficial on an undertray to counter any airflow disattachment or to direct airflow, although strakes or ducting would be more effective for the latter purpose. As the new undertray is basically flat and level it's unlikely that there will be any airflow disattachment so it's been decided not to use them. While the core of a vortex is low pressure I think any low pressure effect from that source would be very small and could be countered by increased drag and consequential slowing of the undercar airflow.

 

For an amateur with no testing facility I think it's best to use those aero devices and techniques which are predictable in use.

[ovenfood]

I also doubt there would also be an advantage if you put vortex generators on an undertray. We use vortex generators on planes to create lamina flow over the flight controls because if the air does not flow over them its the planes equivalent of driving on ice

[JMortensen]

I don't think you use vortex generators to create laminar flow. You use them to create the opposite, a vortex. The idea is that when you have flow separation, it's better to keep the flow energized (as in a vortex), so that it can still do something when it hits the control surfaces. I think there might be a case for vortex generators on the underside for the same reason that AirTabs work. They will keep the flow headed in the right direction even if it isn't attached and laminar, but Richard has it right, if the surface is flat and smooth, there isn't going to be a huge boundary layer, so the vg's just aren't needed.