Application of the vortex identification algorithms in the study of the shear layer in a 3/4 open jet automotive wind tunnel
By means of particle image velocimetry(PIV) measurements, this paper uses vortex identification algorithms to find and analyze the coherent structures in the shear layer region. The experiment was carried out in a 1:15 scaled 3/4 open jet automotive wind tunnel with a high Reynolds number（about 10^6）. The proper orthogonal decomposition(POD) is used to process the PIV experimental data, for reconstructing the velocity fields. Based on the vortex identification functions, the locations of the center, the rotation direction and the radius of vortex can be computed. Furthermore, this paper uses the statistical method to study the regularities of distribution of these vortexes, in a two-dimensional plane, and identify the vortex pairing process in the shear layer region. This paper also chooses different vortex identification algorithms to find the most accurate and suitable algorithms.
Wheel Aerodynamics is an important part of whole vehicle aerodynamics. The wheels can notably influence the total aerodynamic drag, lift and ventilation drag of vehicles. In order to simulate the real condition of driving cars, the moving floor and wheel rotating condition is of great significance in CFD. However, the rotated wheel condition is difficult to be reproduced exactly, so this is still a critical topic which needs to be worked on. In this paper, a study, which focuses on two types of cars: the generic sedan and the DrivAer, is conducted. Comparing three different wheel rotating simulation methods (Moving wall, MRF and Sliding Mesh) , the effects of these different methods on the numerical simulation of vehicle aerodynamics are considered. Then, the discrepancies of aerodynamic forces between the methods are discussed as well as the flow field, and the simulation results are also compared with the published experiment data for validation.
Abstract Based on a 1:15 scaled 3/4 open jet automotive wind tunnel, this paper studies the effect of vortex generator on the buffeting phenomenon. The mean velocity, static pressure gradient, turbulent intensity as well as frequencies of fluctuant velocities have been explored experimentally with and without vortex generator. It shows that the less protruding vortex generator could control the buffeting phenomenon and improve the flow quality. Furthermore, the unsteady coherent structures in the jet shear layer have been visualized and analyzed by Detached-eddy simulation (DES). The vortex-ring pairing process is identified in the shear layer along with obvious frequency characteristics and velocity fluctuations. The vortex generator can postpone and restrain this vortex-ring pairing process, then reducing the velocity fluctuations.