A method for identifying aerodynamic sound sources in near-wall turbulent flow and its application for automobiles

Abstract

Addressing the challenges in accurately identifying sound sources within near-wall turbulent flows, this study represents sound quadrupole sources as a composite of numerous small-scale spherical sources. Through a detailed derivation that links the radiated sound pressure to the fluctuating pressure on the sphere’s boundary, we establish a relationship between the sphere’s resultant sound radiation and the fluctuating components of the Lighthill stress tensor. This method was validated using a subsonic jet noise case characterized by prominent sound quadrupole source features. By applying this method alongside the dipole identification method proposed by our team, we successfully identified both aerodynamic sound dipole and quadrupole sources on a specific SUV. This approach revealed the characteristics of sound dipole sources on the vehicle’s surface and sound quadrupole sources within the near-wall flow field, providing a new perspective on the precise location and magnitude of the sound sources. The study shows that the sound power of the main dipole sources, such as those near the front wheel, A-pillar-rearview mirror-front side window, can reach approximately 120 dB, significantly greater than the maximum sound power of the main quadrupole sources, which are primarily found in the wake region of the rearview mirror, adjacent to the chassis flow field, and in the vehicle’s rear wake area, peaking at around 51.5 dB. Moreover, the study clearly demonstrates that the sound power emanating from flow separation points significantly surpasses that from secondary attachment and boundary layer flows. This pivotal distinction underscores the significant influence of flow separation in shaping sound dipole sources, with dipoles originating at separation points and terminating where the separation vortices completely detach.