Some questions about making a car racing simulation
 

hello
my team need to design the external shape of student racing car
so first of all, we want to calculate the Cd and Cl of the last year car by Fluent
and then compare it to experinces

i read alot toturials and discussions and yet, of course, i have more questions.
i tried to calculate the Cd in my computre:
enclosre:
5 car length in the front
20 car length in the rar

inflation: only on the car (the car is 5 cm from the road a=- Fluent dosn't like it so much)

max size cells - 8 cm , size rate 1.1
max size cells on the car - 0.2 cm

100 iteration of frist order
and then more 500 in secend order
skewness = 0.2,
aspect ratio = 1.8
500,000 cells
in the important part of the car (70%) Y+ is under 150
and the velocity is 20m/s
the Cd is 0.8

and my team mate tried as well
he got Cd=2.8


the problem is that we don't know how to indicate if the solution quality

can someone note ot refer me to good information source please?
what are the important things we need to know?

we are trying to do simulations for month and each time get we other answers by other toturial or recommended settings



thanks!