Three dimensional unsteady flow field around a simplified fastback car in process of accelerating was simulated numerically with computational fluid dynamics(CFD)method.The aerodynamic drags were calculated at different speeds and different accelerations.The calculated results show that the aerodynamic drag at a certain speed and acceleration are closely related to the current speed and acceleration.Through twice linear fittings

the computational formula of aerodynamic drags was obtained.This formula could work out immediately the aerodynamic drag of the aerodynamic characteristics of a car in accelerating process at a certain speed and acceleration value.