Aeroacoustic analysis of an NACA 0015 airfoil with Gurney flap based on time-resolved PIV measurements

The present study investigates the feasibility of high-lift devices noise prediction based on measurements of time-resolved particle image velocimetry (TR-PIV). The model under investigation is an NACA0015 airfoil with Gurney flap with the height of 6% chord length. The velocity fields around and downstream the Gurney flap are measured by PIV and used to compute the corresponding pressure fields by solving the Poisson equation for incompressible flows. The reconstructed pressure fluctuations on the airfoil surface constitute the source term of the distributed formulation of the Curle's aeroacoustic analogy. The PIV-based noise predictions are assessed via microphone measurements. Since the Gurney flap height under investigation is much smaller than the emitted acoustic wavelength, the noise source can be considered compact and an alternative implementation of the Curle's analogy based on the unsteady aerodynamic loads can be followed. The results of the two formulations are compared with the simultaneous microphone measurements in terms of power spectra. Both formulations of the Curle's analogy yield noise level of good agreement with the simultaneous microphone measurements for the evaluation of the tonal component. All the calculated far-field noise power spectra reproduce the peak at Kármán vortex shedding frequency, which agrees well with the microphone measurements.