Numerical Approach to Determine Wind Tunnel Blockage Correction for the External Aerodynamics of a Vehicle 2007-01-3462
To experimentally determine the Coefficient of Drag (CD) for a vehicle, the vehicle has to be placed inside a wind tunnel. To accurately determine the CD, the size of the wind tunnel should be large enough to capture the wake region and the turbulence regions around the vehicle. Placing a vehicle in a wind tunnel also applies an unnatural boundary around the vehicle. Determining the exact size of the wind tunnel for a particular type of a vehicle running at a particular speed or changing the size of the wind tunnel experimentally is not practical.
However, we do not have such limitations on geometry or wind tunnel size while using the commercially available Computational Fluid Dynamics (CFD) code Fluent . However, using large wind tunnels in numerical studies increases the computation time exponentially.
This paper presents a way to determine the wind tunnel blockage corrections that needs to be applied to find out the final CD using a smaller wind tunnel. This is achieved by repeating the simulations by increasing the size of the wind tunnel until the error in the CD value between the two consecutive iterations is negligible. Once this correction factor is obtained, it can be used to find out the accurate CD with smaller wind tunnels for the same category of vehicles.
This paper also discusses the limitations and advantages of using small and big wind tunnels. CD prediction with and without the heat exchanger module and its impact on the final CD is also discussed.