The effect of angle of attack on turbulence interaction noise with a porous leading edge

Abstract

The paper is concerned with the effect of angle of attack on the interaction noise between a turbulent flow and a NACA 0012 airfoil. This experimental study considers an airfoil with a porous leading edge up to 10% of the chord and compares the noise levels to a solid airfoil leading edge at a Reynolds number of 𝑅𝑒 = 2.5 × 10 5 . Turbulence is generated by the means of a passive grid and the direct noise measurements are performed using a microphone array. The airfoil is instrumented for both steady and unsteady wall pressure measurements. The 𝐶 𝑝 distribution over the surface of the airfoil is considered up to large geometric angles of attack for both the solid and porous leading edge cases. From far-field noise measurement, it is found that radiated sound is reduced at small geometric angles of attack at low frequencies for the porous airfoil. At higher angles of attack the 𝐶 𝑝 distribution of the porous leading edge case appears to be similar with that of a stalled airfoil, suggesting porous leading edges at higher angles of attack stall earlier than a solid airfoil.

The role of porous structure on airfoil turbulence interaction noise reduction

“…The pressure coefficient results for this configuration are omitted as they are previously reported. 23,24,43 The surface pressure taps were connected in a remote sensing configuration using Panasonic WM-61A microphones, which have a reliable frequency range between 10 < f < 6000 Hz. 47,48 The Panasonic WM-61A microphones measure the pressure fluctuations at the pressure tap via a brass tube which is connected to the microphone in a custom-made holder that is acoustically terminated.…”

“…The chordwise size of the porous leading edge on the airfoil was selected through the previous study which demonstrated that 10% of the chord was the optimum length of chord that maximized noise reduction, while minimizing the amount of chord that would be occupied by the porous structure. 24 Three leading edges of different porous structures were selected to study the effect of the bulk porous structure on the reduction of airfoil turbulence interaction noise. The three selected structures were of the triply periodic minimal surface (TPMS) family, namely, Schwarz-P, diamond, and gyroid (Fig.…”

“…9,10 Reduction of aerodynamically generated noise is proven to be effective through the means of passive flow control, be that through the use of serrations [11][12][13][14][15][16][17] or porous materials. [18][19][20][21][22][23][24] Serrations have been the subject of many studies for the reduction of turbulence interaction noise due to their ease of implementation; 16,[25][26][27][28] however, they require a fundamental change to the design of the airfoil geometry at the leading edge. The use of a porous treatment for the reduction of turbulence interaction noise results in the preservation of existing airfoil geometry with a change of the main material's porosity.…”

Numerical Simulation of Grid-Generated Turbulence Interaction with a NACA0012 Airfoil

“…Turbulence interaction is among some of the most important noise generation mechanisms due to its relevance and diversity of engineering applications and it arises from the turbulence distortion and scattering as it impinges on the solid body [4] . There have been numerous experimental studies on turbulence-interaction noise of airfoils and bluff bodies [5][6][7][8][9][10][11][12] and their noise mitigation strategies [13][14][15][16][17][18]. To this day, the experimental production of turbulence upstream of a solid body is being achieved with grids installed within the wind-tunnel nozzle contractions [19,20] and have been extensively used to produce turbulent inflows since the work of Simmons and Salter [21], producing a large number of aerodynamic and aeroacoustic measurements [22][23][24][25][26].…”