Effect of inclined transverse jets on trailing-edge noise generation

Abstract

In this work, the effect of multiple transverse jets on the turbulent boundary layer developing over a flat plate is experimentally investigated for aeroacoustic purposes. A single line of jet nozzles with different spanwise spacings is located parallel to the trailing-edge of the plate, at approximately 30 jet diameters upstream of the trailing-edge. The axes of the jet nozzles have an inclination of 15 • with respect to the streamwise direction. Two values of the jet velocity ratio (r = u jet /u ∞) are considered, r = 1 and r = 2. The simultaneous measurement of streamwise velocity and surface pressure fluctuations is performed with hot-wire anemometry and flush-mounted microphones, respectively. The mean velocity profiles show that the low inclination angle of the multiple jets prevents the formation of adverse pressure gradients, and therefore, the multiple jets injection does not lead to flow separation, at least at the range of downstream locations under investigation. From the velocity measurements, the jets merge downstream of the jet nozzles and form a layer of jet fluid characterized by a low energy content. The estimates of the far-field noise show that jets injection at a velocity ratio of r = 1 leads to noise attenuation over the whole range of frequencies under analysis. At a velocity ratio of r = 2, jets injection enables to gain a larger noise reduction than at r = 1 at low frequencies, but the estimated far-field noise is expected to increase at high frequencies.

Aeroacoustic Performance of High-lift Airfoil with Slat Cove Fillers

“…The transducer sensitivity obtained from the calibration varied between 20.2 mV/Pa and 23.5 mV/Pa. The unsteady surface pressure measurements using FG transducers were carried out for 16 seconds using a sampling frequency of f = 2 16 Hz.…”

“…The microphone has a flat frequency response at frequencies from 10 Hz to 10 kHz, with a dynamic range of 142 dB. The far-field noise spectra were computed for 16 seconds using a sampling frequency of f = 2 16 Hz. The acoustic data were recorded at a wide range of flow velocities of up to 40 m/s.…”

“…Even though the aircraft engine noise has been brought down substantially by the use of high bypass engines the airframe noise remains a major contributor to aircraft noise. In order to reduce these prominent noise sources several passive and active flow control methods have been investigated in the past it includes morphing structures [1][2][3][4][5][6][7], porous materials [8][9][10][11], surface treatments [12], serrations [13][14][15] and transverse jets [16]. The high-lift devices namely the slats and flaps are one of the major contributors to airframe noise.…”

Uniform flow injection into a turbulent boundary layer for trailing edge noise reduction

“…While passive noise reduction methods have received a significant attention from the research community, active methods are in their early stages of development. Most commonly, previous works focused on the use of flow suction from 4, 38-40 , or flow injection into the boundary layer 41,42 . The main drawback of flow suction is that it requires a significant amount of air to be removed from the boundary layer, namely, it was found that removing approximately 60% of the boundary layer thickness provides the best aeroacoustic performance 40,43 .…”

Numerical Investigation of High-lift Airfoil Fitted with Slat Cove Filler

“…Introduction T HE introduction of high bypass-ratio turbofans engines into civil aircraft have drastically reduced engine noise over the last several decades, making the airframe noise the same magnitude as that of the engine noise, especially during the landing phase. In order to reduce these prominent airframe noise sources several fundamental passive and active flow control methods have been investigated over the recent years, such as, morphing structures [1][2][3][4][5][6][7], porous materials [8][9][10][11], surface treatments [12], serrations [13][14][15] and transverse jets [16]. One of the prominent sources of airframe noises are the high-lift devices namely the slats and flaps.…”