Aerofoil geometry effects on turbulence interaction noise

Chaitanya, Paruchuri, Gill, James R., Narayanan, Subramanian, Joseph, Phillip, Vanderwel, Christina, Zhang, Xin and Ganapathisubramani, Bharathram (2015) Aerofoil geometry effects on turbulence interaction noise. In 21st AIAA/CEAS Aeroacoustics Conference. American Institute of Aeronautics and Astronautics.. (doi:10.2514/6.2015-2830).

Abstract

A detailed experimental study has been performed to understand the influence of aero-foil geometry on turbulence - aerofoil interaction noise. Systematic noise measurements have been carried out by varying aerofoil thickness and leading edge nose radius separately. Flat plate analytical theory has been shown to be in very close agreement with the measured data. In this paper we investigate the sound power level reduction ΔPWL due to aerofoil geometry compared to a flat plate. The main findings from this study are as follows: Sound power reductions increase with increasing aerofoil thickness t, Sound power reductions are highly sensitive to the aerofoil nose geometry and radius, Sound power reductions for a particular aerofoil geometry are found to follow a Strouhal dependence, Sound power reductions are most sensitive to nose radius effects for thin aerofoils, Sound power reductions are independent of camber and angle of attack. It is demonstrated that the sound power reduction predicted by Gershfeld, ΔPWL=10log10(exp(−πft/U)), where f is frequency and U is mean velocity, represents an upper limit, which is closely followed for small values of ft/U but deviates at higher values. Gershfelds’s model is therefore the upper limiting case for noise reductions due to aerofoil thickness. Particle Image Velocimetry has been used to observe the flow characteristics around the aerofoils, particularly in the vicinity of the stagnation region, whose interaction with the impinging turbulence is believed to be the main noise reduction mechanism compared to a at plate. The paper concludes by comparing the measured radiation spectra with computational aeroacoustic noise predictions, which are shown to be in very close agreement, and by investigating trends of thickness-based noise reduction with increasing Mach number.

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Contributors

Author: Christina Vanderwel

Author: Bharathram Ganapathisubramani

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