Aerodynamic coastdown analysis of a passenger car for various configurations

Experimental coastdown analysis were performed on a full scale passenger car model FIAT Linea to obtain the drag coefficients for three different test configurations as engine-cooling airflow closed with smooth underbody, enginecooling airflow closed with detailed underbody, and engine-cooling airflow open with detailed underbody. The comparison of the drag coefficients for all three coastdown configurations were in good agreement with the CFD results and FIAT wind tunnel results. The coastdown tests predicted the model drag coefficients 5.3 % to 7.8 % less than FIAT wind tunnel drag coefficients for three test configurations. The contribution of the engine-cooling airflow and the detailed underbody configuration on the total drag coefficient were measured as 9.6 % ~ 10.4 % and 14.6 % ~ 16.7 %, respectively in the coastdown, FIAT wind tunnel tests and CFD analysis. In the CFD analysis,steady RANS equations were solved by STAR-CCM+ code. The turbulence model was selected as realizable k-ε two layer model. Model surface pressure contours were compared for all three test.