A Semi-analytic and Experimental Study of Porous Leading Edges

Abstract

This paper presents a semi-analytical investigation into the aeroacoustic properties of aerofoils with porous leading edges, complemented by an experimental study of flat rigid plates with a perforated leading section. Interest in partially porous aerofoils arises from their potential to reduce noise emission from wind turbines and commercial aeroplanes whilst maintaining aerodynamic performance. Developing theoretical models will be helpful for understanding the dominant physical mechanisms and thereby designing optimal implementations. We consider a simple theoretical model that captures acoustic scattering from a finite plate with a porous leading edge. This yields a matrix Wiener-Hopf problem which is solved by an iterative approach that facilitates reliable and rapidly computable solutions. This allows a quantification of acoustic reductions that may be anticipated, and a comparison between studying a porous leading edge on a finite and semi-infinite plate. Experimental results are presented for a flat rigid plate with a perforated leading edge section that demonstrate some qualitative agreement with the theoretical model.

On the noise reduction mechanisms of porous aerofoil leading edges

“…al. [12], whereby a complex impedance parameter would result in an additional phase term which would also allow for a shift in peak frequencies. However, this effect is a comparatively minor effect and for simplicity we consider η=1.…”

“…This paper deals with an alternative approach for reducing broadband interaction noise that involves introducing porosity at the leading edge. This control principle has previously been investigated experimentally [3,[8][9][10][11] and theoretically [12], where significant reductions in broadband interaction noise of up to 10dB were reported at some frequencies.…”

“…al. [12] have predicted analytically the noise radiation from a flat plate comprising a number of circular holes interacting with a harmonic vortical gust. The Wiener-Hopf method was used to provide the solution and a homogenised impedance-type boundary condition was applied in which the mass flow rate through the holes was related to the jump in velocity potential across the holes via an impedance term related to the Rayleigh conductivity.…”

“…Predictions were compared against the measured noise reduction spectra from a flat plate comprising of a number of regularly spaced circular holes distributed between the leading edge and some downstream location. In [12] the noise reduction spectra were predicted to peak at the non-dimensional frequencies of f l/U =0.5 and 1.5, where l is the length of the porous section.…”

Experimental and Analytical Investigation of the Distortion of Turbulence Interacting with a Porous Airfoil

“…Another possible explanation for the lower performance of the porous treatment is represented by the center-plane. Indeed, the acoustic waves generated on the airfoil surface can potentially penetrate the porous medium and interact with the solid walls of this component, similarly to the effect of the material junctions in the case of a porous leading-edge insert [48]. Further parametric studies will be performed in the near future to analyze the influence of the center-plane on the noise reduction.…”