Flow and acoustic characterization of turbulence grids at wind tunnel nozzle exit

Abstract

This study investigates the flow and acoustic characteristics of turbulence grids mounted at a wind tunnel nozzle exit, which is crucial for generating essential turbulence in the research of turbulence interaction noise. Diverse grid parameters, including bar diameter, mesh size, solidity, and geometry, were manipulated to measure flow (turbulence intensity, integral length scale, isotropy) and acoustic (grid self-noise, turbulence–airfoil interaction noise) properties. The study reveals that the grids produced turbulence intensity exceeding 3%, showcasing nearly isotropic flow downstream from the grids. Additionally, noise levels were affected by grid parameters, with smaller bar diameters and lower solidities resulting in reduced noise. Notably, bi-planar grids displayed lower noise levels and the absence of tonal peaks compared to single-planar grids. The signal-to-noise ratio of the turbulence interaction noise was also higher for the bi-planar grids. The introduction of acoustic material on the downstream surface of grid bars demonstrated promise in mitigating grid self-noise while preserving turbulence isotropy. These findings provide valuable insights for optimizing grid configurations in turbulence interaction noise research.