Wind Tunnel Analysis of an Automotive Wheel and Comparison with Numerical Simulations

The main purpose of this thesis is to find a relation between the results obtained with numerical simulations and the results coming from the experiments in the case of an automotive wheel. Before this study, it was investigated the phenomenon of the vortex shedding of a 2D cylinder. It was proven that the shedding frequency has a linear relation with the free stream velocity and this relation depends on the Strouhal number. The last stage of this acquistion campaign was to compare the calibration of the hot-wire anemometer with the Pitot probe and the calibration exploiting the vortex shedding frequency, obtaining very similar results. The second step of this study was focused on the wake of three different type of wheels (sharp shoulders, 45 degrees shoulders and rounded shoulders) discovering that the sharp one generates a much larger wake than the other two. Also the Cd was evaluated, through the Trefftz plane method, obtaining a value of 0.98 for the rounded shoulders and 1.3 for 45-degrees one. The wake develpoment was very similar between the 45 degrees shoulders and rounded one. It was also studied the effect of some angles (camber and toe) on the rounded shoulders wheel, the camber (with an angle of -3.5°) produces an asymmetry of the wake, while the toe angle (with an angle of -0.5°) does not affect too much the results. The comparison with the CFD was made with the wheel without any angles of toe and camber[1]. Similar results were obtained in the wake shape and in the evaluation of the Strohual number. In particular the wake shape (visualized through the velocity contours) was compared with the solution of the RANS equations with Spalart-Allmaras turbulence model. Furthermore, the spectral analysis was compared with the Detatched-Eddy-Simulation. Both the S-A and the spectral analysis show a good match between numerical results and experimental ones.