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Conference Papers Year : 2020

Experimental Investigation of the Acoustic Radiation of an Oscillating Airfoil

Abstract

In open rotor applications, such as wind turbines and propellers, the angle of attack of a blade can vary during its rotation, due to an inhomogeneous inflow. This causes a variation of the broadband noise radiated by the blades, which is a possible explanation for the amplitude modulations of wind turbine noise that can be measured <i>in situ</i>. The goal of this experiment is to characterize the broadband airfoil noise in static (fixed angle of attack) and dynamic (oscillating airfoil) configurations. Experiments are conducted in the anechoic wind tunnel of the Ecole Centrale de Lyon, at Reynolds numbers between 2x10<sup>5</sup> and 6x10<sup>5</sup>, in which a symmetrical NACA 0012 airfoil is tested at constant angle of attack, or with a sinusoidal pitching motion. Aerodynamics around the airfoil is characterized with wall pressure measurements (low frequency static probes and high-frequency remote microphone probes) synchronized with far-field acoustic pressure measurements using four microphones. The effects of inflow turbulence and of the Reynolds number on the noise are first investigated in order to identify the different noise sources developing for a static airfoil at low incidence (trailing edge noise and turbulence-impingment noise) and at larger incidence (separation and stall noise). In particular, the turbulent intensity of the incident flow is shown to have a strong effect on the separation and stall phenomena at high angles of attack. It is then shown that these different noise sources can develop for a pitching airfoil; the boundary layers on the airfoil and the noise emitted adapting to the oscillating angle of attack. In particular, the effect of the pitching frequency and of the inflow conditions on the dynamic stall noise are investigated.
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Dates and versions

hal-03233651 , version 1 (26-05-2021)

Identifiers

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David Raus, Benjamin Cotté, Romain Monchaux, Baptiste Lafoux, Emmanuel Jondeau, et al.. Experimental Investigation of the Acoustic Radiation of an Oscillating Airfoil. Forum Acusticum, Dec 2020, Lyon, France. pp.2319-2321, ⟨10.48465/fa.2020.0273⟩. ⟨hal-03233651⟩
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