Numerical Aeroacoustic Analysis of a Linear Compressor Cascade with Tip Gap

Abstract

A wall-resolved compressible large-eddy simulation is performed on a linear compressor cascade with tip gap to investigate the tip-leakage noise sources. The cascade is composed of eight 4%-thick modified circular-arc blades with a 254 mm chord and a 235 mm spacing. The chord-based Reynolds number is , and the Mach number is 0.07. The gap considered in this study is 4.0 mm (1.6% chord). An aerodynamic analysis of the tip-leakage flow coupled with a Ffowcs-Williams and Hawkings analogy to compute the noise in the far field allows identifying the main tip-noise mechanisms. The acoustic contribution of the tip-leakage flow is highlighted by comparison with the trailing-edge noise contribution obtained with a 25 mm slice configuration at midspan without tip gap. This small-span configuration is also simulated using large-eddy simulation and allows computing the blade trailing-edge noise. A dynamic mode decomposition performed on the full configuration close to the tip highlights the main noise source, located around 75% chord with a propagation frequency between 5 and 6 kHz. The acoustic waves propagate mostly downstream of the cascade and on the pressure side. This study provides the first high-fidelity wall-resolved compressible simulation of a linear compressor cascade comprising a comprehensive investigation of the tip-leakage noise sources, which is a necessary first step toward fan tip-noise prediction.