Acoustic radiation of subsonic jets in the vicinity of an inclined flat plate

Abstract

Acoustic measurements of turbulent jets in the vicinity of a flat plate, mimicking a neighbouring wing, were compared to results from two wavepacket-based source models previously studied in the literature: the Tailored Green's Function method, which considers the radiation of the turbulent structure in the vicinity of a semi-infinite flat plate, and the Boundary Element Method, which can represent the full geometry of the plate used in the experiments. Particular interest is given to analysing how the angle of attack of the plate (α) affects the sound radiated by an installed jet with trailing edge 6 diameters away from the nozzle and 1 diameter away from the centerline for 0° ≤ α ≤ 45°. The results herein confirm the behaviour identified by the models: the scattered acoustic field follows the rotation of the plate, shifting a silence region with negligible scattered sound, and creating regions with lower noise levels in positions that correspond to the ground for an aircraft with engines under its wings. This is further explored by means of a Mach number analysis for M = 0.5, 0.7, and 0.9, showing that this trend is present whenever trailing-edge scattering of jet disturbances is dominant in the acoustic field.

Acoustic radiation of a simplified jet-flap-thrust gate configuration: numerical and experimental investigation

“…The next step is to analyze the case of a flat plate with a nonzero folding angle at the trailing edge. We expect to observe a phenomenon similar to the one described in previous works [14], where a rotation of the scattered directivity pattern was seen. Since the plate scattering has a dipolar shape for low frequencies, with silence zones aligned with the leading and trailing edge directions, we expect a rotation of the scattered directivity in an angle between 0 • (angle of the leading edge) and the folding angle (for this case, 30 • ).…”

“…Based on these facts, it seems reasonable to expect a change in the directivity when the same geometry is positioned with other angles. For a large flat plate, this was confirmed experimentally, numerically and by using an analytical Green's function approximation for the case of a semi-infinite flat plate [14]. In the case of folded plates, similar trends are expected, since the new noise sources are located at the nearest trailing edges.…”

“…The parameter k h is calculated by k h = ω/U c , where the convective velocity is U c = 0.9U and U is the jet exit velocity and k h L is chosen as 5 [14].…”

“…On the other hand, during the lading procedure, a high deflection angle is required. Besides that, we want to analyze how a 30 • folding angle changes the directivity pattern of the scattered pressure to the far field, since it is already known that inclining the whole plate will change this pattern with a rotation in the same direction [14].…”

On the application of acoustic liners for the reduction of jet-flap installation noise

“…Ref. [31]. The wavepacket center is located around 6D, which was defined base on a calibration procedure with a baseline installed case.…”