An experimental study of aerodynamic noise from large obstructions in turbulent boundary layer flows

Abstract

This paper reports an experimental study on the aerodynamic noise generated by a two-dimensional large obstacle in a turbulent boundary layer. Square and triangular obstacles with varying heights of h/δ=0.48,0.8,1.2,1.6, and 2 (where δ is the boundary layer thickness measured without the obstacle present) are tested at various flow speeds ranging from 20 to 50 m/s. The Reynolds number based on step height and free stream velocity ranged between 7500 and 79 000. A linear microphone array is arranged aside to measure the sound radiation in the spanwise direction. It is suggested that both square and triangular obstructions can lead to a broadband source with a dipole-type directivity. A consistent increase in the noise strength is observed with obstacle height and flow speed. The underlying noise source is revealed by comparing the acoustic spectra of different obstacle geometries. The low-frequency noise is contributed by the turbulence modification due to the flow impingement onto the obstacle, while the high-frequency sound is mainly caused by the diffraction of hydrodynamic pressure by the sharp leading edge.

Measuring acoustic velocity map in turbulent flow using sub-Nyquist-rate PIV system

“…Measuring the acoustic velocity field inside a duct in the presence of turbulent flow is crucial for several applications such as aerodynamic noise generation by obstacles (Zhou et al, 2020;Sundeep et al, 2022), and liner or wall acoustic impedances (Alomar and Aurégan, 2017;Léon et al, 2019). Although microphones are commonly used for acoustic measurements in these environments, the use of pressure probes for inflow measurements faces challenges.…”