Intermittency analysis of high-lift airfoil with slat cove fillers

Abstract

Experimental measurements were carried out to assess the aeroacoustic characteristics of 30P30N airfoil fitted with two different types of slat cove fillers at the aeroacoustic facility at the University of Bristol. The results are presented for the angle of attack α = 18 • at a free-stream velocity of U ∞ = 30 m/s which corresponds to a chord-based Reynolds number of Re c = 7 × 10 • . Simultaneous measurements of the unsteady surface pressure were made at several locations in the vicinity of slat cove and at the far-field location to gain a deeper understanding of the slat noise generation mechanism. The results are analyzed using a higher-order statistical approach to determine the nature of the broadband hump seen at low-frequency for the 30P30N high-lift airfoil observed in recent studies and also to further understand the tone generation mechanism within the slat cavity. A series of cross-correlation and coherence of the unsteady pressure measurements are carried out to identify and isolate the low-frequency hump. Wavelet analysis is performed to investigate the nature of the slat-wing resonant intermittent events in both time and frequency domains. The far-field noise measurement results showed that significant noise reduction can be achieved by the use of slat cove fillers. A series of far-field and near-field correlation are also presented to show the propagated noise from the slat.

Flow characteristics of slat cove fillers

“…The results here show that the use of H-SCF and SCF does not necessarily affect the flow at the slat wake and the boundary layer over the main-element. The slightly increased mean velocity components observed at the slat near-wake region for the H-SCF and SCF configurations also corresponds to the improved aerodynamic performance for the H-SCF and SCF configurations seen in the author's previous studies [28][29][30][31]. It is noteworthy that the H-SCF influence on the slat wake showed a tendency to increase as the angle of attack is decreased, whereas the H-SCF configuration showed a minor impact for the reported angles of attack.…”

“…The tests were performed for three configurations, namely Baseline, Half-slat cove filler (H-SCF) and slat cove filler (SCF), as shown in Table ??. The 30P30N three-element high-lift airfoil has a retracted chord of c = 0.35 m, slat chord c s = 0.15c and a span of l = 0.53 m. The other geometrical properties are the generic parameters used for a 30P30N high-lift airfoil [28][29][30][31]. The cartesian coordinate system (x, y, z) starts from the leading edge point of the retracted 30P30N airfoil as shown in Table ??.…”

“…If the SCF profile is larger than the slat shear layer profile then the flow at the slat gap gets restricted, which consequently affects the suction peak and aerodynamic performance of the main-element. Nevertheless, an SCF profile that eliminates the large recirculation region within the slat cove, while maintaining the aerodynamic performance at the same time is highly favorable as they are viable sources of noise reduction, as shown by Imamura et al [25,26], Tao [27] and also by the authors in [28][29][30][31].…”

“…Several passive and active flow control methods have been investigated in the past to attenuate airframe noise, the methods include morphing structures [1][2][3][4][28][29][30][31], porous materials [5][6][7], surface treatments [8] and serrations [9].…”

“…More recently, the authors [28][29][30][31] have performed detailed aerodynamic and aeroacoustic study for 30P30N airfoil fitter with Half-slat cove fillers (H-SCF) and SCF. The study showed that the H-SCF and SCF configurations can maintain the same aerodynamic behavior as that of the baseline while portraying substantial levels of noise reduction of up to 5 dB.…”