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Don't be fooled into thinking that the air around your car is going to be going a certain way at a certain speed. From 10mph - 300 mph, it will look essentially the same. It is a common misconception that speed changes the pattern of how the air flows, but it doesn't.
It seems the Viscosity and Incomingvelocity both change the Re number being used in this simulator, so viscosity and velocity both are changing the "air".
It is only my studied opinion of this that makes me say 120/45 looks best to me. I have thought about this a lot, it is a very educated guess based on having played with the old program for at least 100 simulations using several templates.
I can tell you that using 250/100 looks to me like a vehicle going through 20 weight oil at 90 mph, or a one the size of a blimp going through air at 20mph. you wouldn't get 90% of the air from the top hitting the tailgate like that. You would want to tune it so you get the bottom 20% of the flow hitting the top of the gate, and no closer than the 18" to it.
I'll work up some "Good/Bad" examples later today and post them.
One thing I'm not happy with, it seems no matter what the setting, it does not yield a wake behind the vehicle which matches real world. The wake area creeated is too low to the ground and too dense. So all this could be a discussion in futility in that this is NOT a wind tunnel simulator, it is really just a toy to make images of flow around stuff.
Did I mention that you need to have a decent amount of space above the model too?? I think your probe is too close to the top and it is creating a venturi type effect.
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