Sigh, I wasted my youth! I have to rely on the imperfect google translations, or the work of some bored author. :biggrin:
I've been working with "The Handbook of Hydraulic Resistance", by Idlechick and "Fan Engineering". In an effort to normalize air flow, in 2 Id diameters past a non uniform disruption, I need average flow and temp for a control feedback loop. Turns out stainless sifting mesh can be used at a minimul pressure drop irregardless of Reynolds number. For the flow parameters, A large wire diameter causes complete turbulance and provides perfectly normalized temp readings within 10 wire diameters. I luv it when one thing can be used to solve 3 or more needs.
The ole high wing vs low wing discussion has reared its ugly head. It depends on how intricate the rear design is. A completely flat bottom with no other devices yields no down force, just food for thought.
Taken by itself, an air dam has limitations and a maximum gain is always the compromise. Same for high speed vortex tunnels leading to the rear diffuser. I understand Ferrari has gone in circles on how to control downforce so that straight line speed is not lost. Hence their moveable devices at the front that control the high speed air running down the tunnels.
The diffuser is filling the low pressure drag zone in the void at the rear of the car. Instead of focusing on downforce, look at it from the perspective of pressure. More drag is being shed with a diffuser equalizing the rear low pressure zone than the diffuser is generating. The diffuser is still generating drag, yet equalizing the pressure void at the rear of the car offsets the drag that was generated from the slipstream going turbulent. It's a net gain, but not free. The definition of a diffuser is a device that slows flow and raises pressure. It just so happens a diffuser mounted under the back of a vehicle traps enough high speed flow to generate rear downforce while it partially equalizes the trailing rear low pressure zone resulting from the turbulence being generated and negates some of that turbulence. One thing and 2 positive outcomes, nice.
3-5 degrees ensures that attached flow is not lost and limits the overall diffuser flow. Only flowing enough air to partially fill the vehicles rear turbulent low pressure zone. Upwards of 15 degrees can be safely used while maintaining attached flow in the diffuser. I think the reason that they only used 3 to 5 was because they couldn't get more front downforce cleanly. Any more and Honda would have lost the balance, front and rear, they were aiming for.
Also, the rear underbody layout of the NSX limits the run of the diffuser. Following Greenberet's aero experiments, I can appreciate the head scratching you've had to do. :smile:
