|
I've been looking further in my references for the relationship between surface body pressures near the back of the car and base (ie wake) pressures.
As I said above, most publications appear to draw no direct connection between the two. However, Aero of Road Vehicles 2nd ed (ie Aerohead's favourite) does say something about this.
By tapering the body moderately the flow is subject to a pressure increase which ensures that the pressure at the rear of the vehicle, the 'base pressure' is comparatively high, which itself then reduces overall drag. (P19)
In the 5th edition the same section re-states this, although in a slightly different form. But everywhere else in this book, base pressure is treated largely through wakeflow patterns (vortices, etc).
I have written to some professional car aerodynamicists I know, asking this:
I have a question. It's one of those deceptively simple ones that may be unanswerable!
Assuming attached flow to the rear of the car, what is the relationship between surface pressure measurement on the car's rearmost panels (eg roof and side) and base pressure?
None of my references really cover this. Some talk about pressure recovery (eg through boat-tailing) and then imply this has implications for increasing base pressure, but never spell out the connection. In my own measurements, on some cars (eg squarebacks), upper body pressures just ahead of separation are similar to base pressures, but on other cars (fastbacks) they aren't.
I always thought average base pressure was more likely to be influenced by wake flow patterns - so do increased body pressures ahead of separation result in weaker vortices in the wake... and that's the connection?
I don't ask them many questions, so hopefully they'll take the time to answer.
|