Cd for a car(2D model),help me!
 

Hi every body.
I'm working on a project deals with calculating drag coefficient of a car(a 2d model from cross section),
i dont know that where is my mistake that my answer is about 10-20 times smaller than absolute value and is about .015!
first:for calculating CD,should i select all of the car body az an unique body?
second:what should be my boundry condition?
please help me,i'm so confused!
thanks