Here you go Robbie,
A simple 2 min example of using fluids to simulate a wind tunnel, like I said it probably isnt very accurate, but if your just giving a demo of it then its probably effective enough.
I made the "car" then put it inside a fluid container, made a cube scaled it to fit a wall and then made it emit the fluid, added an air field to push the fluid to the car and then set the car to collide with the fluid.
With some tweeking of colours of the fluid and maybe a nice bit of mel to cange the colour with the velocity of the fluid you could get some really good results for a display.
You can see on the first pic that the fluid is less dense to the rear of the car, and less dense on the sides in the second pic showing that it's moving round the object.
You could use particles too if youve got complete rarther than unlimited, also with particles you could assign arrows as sprites so they move and change direction etc with the movement
Hope its what your after, and if not it might give you some ideas
"No pressure, no diamonds" Thomas Carlyle