Quote:
Originally Posted by examorph
Hello, I am back, this project has not been started yet and I have been very busy lately so have had no time to do much extra work on it but now I finally have a bit more time to spend thinking about how I should design the car.
I have modelled the car and have ran some wind tunnel tests on it and got some results but dont really know how to read them....the wind tunnel test results show me the drag coeficient (what I wanted) but this is on a graph over time, as time pass's the drag coeficient changes, the velocity of the air going over the vehicle also changes, this is strange because I set the value for the air speed and it should be constant, so I dont understand why the drag coeficient and air speeds are changing, any ideas?
The graph I see is the exact same graph as the one shown at the bottom of this picture:
http://gfxspeak.com/wp-content/uploa...6541711650.jpg
and here is the 2d slice air flow image I see constantly changing with time:
http://gfxspeak.com/wp-content/uploa...6541170698.jpg
Please note, these images were from google and are not of the car I have designed, I will get some images of that soon. |
For vehicles the size of an automobile,their length as associated with velocity renders a transition to turbulent boundary layer at around 20-mph (32 km/h).The air around a road vehicle is considered turbulent itself and Reynolds number acts accordingly.
For this reason,coefficients of aerodynamic drag are constant above 20 mph and do not vary.So I'm as confused as you are about some of the results you are getting.
CFD modelling for 3-Dimensional flow requires the complete Navier-Stokes solution which may not be included in your software package.Not long ago,it would require supercomputers to solve these 3-D 'problems.'