On the effects of fan wake modelling and vane design on cascade noise

Gea-Aguilera, Fernando, Gill, James and Zhang, Xin (2019) On the effects of fan wake modelling and vane design on cascade noise. Journal of Sound and Vibration, 459, [114859]. (doi:10.1016/j.jsv.2019.114859).

Abstract

This paper investigates simplified and representative configurations of fan wake-cascade interaction noise, which is a major source of broadband noise in ultra-high bypass ratio turbofan engines. To this end, two-dimensional computational aeroacoustic simulations are performed by using synthetic turbulence and solving the linearised Euler equations. Several fan wake modelling assumptions are investigated, including isotropic turbulence and cyclostationary variations in both turbulent kinetic energy and turbulence length scale. Results indicate that broadband noise mainly depends on the circumferentially-averaged turbulence spectrum that is perceived by the cascade. Furthermore, the turbulence length scale plays a significant role on cascade noise. Variations in the circumferential distribution of the turbulence length scale modify the slope of the noise spectra, and the maximum noise level can vary significantly. A parameter study on cascade noise has also been performed, including variations in the vane count, aerofoil thickness, camber, mean flow Mach number, stagger angle, and inter-vane spacing. It is shown that noise reduction due to vane thickness at high frequencies can be estimated as a linear function of the frequency, thickness, and mean flow speed in the upstream and downstream directions. A modal spectral decomposition has been performed to study the contribution of cut-on circumferential modes to the sound power level. Variations in vane design parameters lead to significant changes in the cut-on modes and modal spectral distributions. However, their effect on the amplitude of the sound power level spectra is normally below 2 dB, which reinforces the suitability of the flat plate assumption for the prediction of cascade noise at an early design stage.

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