Energy transfer characteristics of sunroof wind buffeting noise via dynamic mode decomposition

Abstract

To further investigate the reason contributing to the abrupt increase in pressure fluctuations on the sunroof and the characteristics of energy transfer between velocity and pressure, dynamic mode decomposition (DMD) is performed to investigate the dynamic characteristics of related coherent structures on the sunroof. First, a large eddy simulation is applied to a sports utility vehicle with a fully open sunroof, and the simulation results are verified via wind tunnel tests. Subsequently, the steady-state and transient characteristics of the flow field are investigated. The significant pressure fluctuation in the passenger compartment is discovered to be related to the pressure core at the trailing edge; however, the significant amount of energy exhibited by the pressure core at the trailing edge remains unclear. In addition, important information that explains the significant pressure fluctuations is obfuscated by the relatively random fluctuations in the turbulence. Thus, DMD is performed to extract the main coherent structures, including the fluctuating pressure and velocity. Finally, the relationships among the fluctuating pressure, fluctuating velocity, and their energy properties are investigated simultaneously. The results show that DMD is excellent for extracting the dominant coherent structures. A comparison between the model results for the fluctuating pressure and velocity at f = 15.0 Hz shows that the fluctuating pressure in the passenger compartment is primarily related to the positive and negative fluctuating pressure cores near the trailing edge. The significant pressure fluctuations between the center and trailing edge of the sunroof are caused by the vortices expanding and pushing against each other. In addition, the self-sustained oscillation in the sunroof is caused by the vortex extruded from the trailing edge, which causes the new vortex at the leading edge to collapse rapidly.