Experimental and Numerical Study of the Aero-Acoustics of Flow over Structured Sheet Metals

This paper investigates experimentally and numerically the aero-acoustic noise generated by airflow around sheet metals with periodic hills of three different geometries named KMT, PWO and WAB used in automotive industry. Each sheet was tested experimentally in a wind tunnel at airflow of free-stream-velocity of 18 m/s and Reynold’s number based on the respective sheet thickness in the range of 1800–4200. The experiment was based on measuring the aero-dynamic sound generated by each sheet using a microphone. Moreover, it was based on measuring the velocity fluctuation after the sheets trailing edge by a Hot Wire Anemometer (HWA). Finally, an acoustic camera was used to locate the locations of sound sources in the flow. On the other hand, the numerical analysis used turbulence model as Large Eddy Simulation with Kinetic Energy Transport as a sub-grid model. Ffowcs-Williams & Hawkings model was used to predict the acoustic sources. Agreements were found between the trend of acoustic noise produced from experiment and numerical simulation over some ranges of frequency. The experiment has showed that the three sheets had comparable sound pressure level over the whole spectrum while the numerical results have showed that KMT sheet has achieved significant loudness at frequencies under 400 Hz while the WAB sheet has achieved significant quietness at frequencies below 400 Hz. The velocity contours obtained from the simulation showed that flow is laminar over some length before it changes to turbulent at a transition point. This behavior agrees with other data presented for long sheets subjected to flow of similar values of Reynolds Number.