On the use of leading-edge serrations for noise control in a tandem airfoil configuration

Abstract

Passive noise control for a tandem NACA 65-710 airfoil configuration is experimentally investigated by applying leading-edge serrations on the rear airfoil. With a sliding side-plate mechanism that allows the rear airfoil to move in the vertical direction relative to the front airfoil, the position of maximum turbulence interaction noise is first identified from the far-field noise measurements. Subsequently, detailed static surface pressure distribution and unsteady surface pressure fluctuations are acquired to shed more light on the physical phenomenon and underlying noise-reduction mechanism of the leading-edge serrations. The far-field noise measurements confirm that a notable turbulence interaction noise reduction can be achieved from 600 Hz < f < 3000 Hz, agreeing well with the previous literature on the effectiveness of the leading-edge serrations. The near-field hydrodynamic analyses obtained using remote-sensing techniques of the fluctuating pressure fields over the airfoil show that a significant reduction in the surface pressure fluctuation levels up to 20 dB/Hz can be observed at the serrated-tip plane of the rear serrated airfoil close to the leading-edge regions, over the range of frequencies investigated. Although reduction can also be observed on the serrated-root plane, the magnitude is much less significant. The present results suggest that the modification of the unsteady loading on the rear airfoil by the leading-edge serrations plays a crucial role in the reduction of turbulence interaction noise in the tandem airfoil configuration, which may find practical application for noise reduction in aerodynamic systems involving rows of airfoils, such as contra-rotating open rotors and outlet guide vanes.

Wake-aerofoil interaction noise control with trailing-edge serrations

“…Similar remote sensing technique and the calibration procedures have been used to study the aerofoil trailing-edge noise in static and dynamic conditions [37,38]. The synchronous measurements were acquired with National Instruments PXIe-4499 data acquisition modules at a sampling rate of 2 16 Hz for 16 seconds and subsequently subjected to Welch function for post-processing to yield the power spectral density (PSD) and sound pressure level (SPL) of the nearfield pressure fluctuations and far-field noise, respectively. With a window size of 2 13 and 50% window overlap, the frequency resolution, i.e.…”

“…They concluded that altering the relative position of the two aerofoils in tandem led directly to the changes in which the rear aerofoil interacted with the front aerofoil wake and hence, the aerodynamic noise generated during the dynamic interaction. Later, a number of studies have focused on several aspects of the wake-aerofoil interaction phenomenon, such as its aerodynamic performance at low to moderate Reynolds numbers [4,5,6], the interaction noise characteristics and effects of aerofoil geometries [7,8,9,10,11,12] and the reduction of interaction noise using passive control methods [13,14,15,16,17], just to name a few.…”

Airfoil Trailing-Edge Noise Reduction by Application of Finlets

“…the dynamic pressure information is carried to the microphone via plastic tubing. A detailed description of the applied remote sensing method is given by Vemuri et al [31] for a similar configuration. The direct and remote sensing transducers are arranged along the center line of the chord.…”

Aeroacoustic characteristics of slat finlets

“…High-lift components, such as slats consisting of broadband and narrowband features in particular, contribute greatly to the airframe noise. Several passive and active flow control methods, such as morphing structures, [1][2][3][4][5][6][7][8] porous materials, [9][10][11][12][13] surface treatments, 14 serrations, [15][16][17][18][19] and transverse jets, 20,21 are being investigated to minimize the overall airframe noise. Despite this, the noise related to the conventional slat and wing configurations remains unresolved.…”