Slat Noise from an MD30P30N Airfoil at Extreme Angles of Attack

Abstract

This study investigates the slat noise of a two-dimensional scaled, unswept, and untapered MD30P30N high-lift model. The experimental data refer to aeroacoustic and aerodynamic measurements in a closed-section wind tunnel for a wide range of angles of attack (from −6 deg up to the stall; approximately at 18 deg) and Mach numbers between 0.07 and 0.1. Three slat configurations (the original MD30P30N, another with a higher slat deflection, and one with smaller slat gap and overlap) are studied experimentally. The signal processing applied to the acoustic data involves conventional beamforming enhanced by two deconvolution algorithms, namely, DAMAS and CLEAN-SC. An original variation of the beamforming cluster approach that is based on the coherence level among microphone pairs is introduced, and it improves the results obtained by DAMAS. Below −2 deg and above 12 deg angles of attack, the slat noise is very small and mostly below the wind-tunnel background noise for all configurations. Between −2 and 12 deg angles of attack, the slat noise spectra are substantially affected by the slat configuration, although it always contains a dominant low-frequency content, a midfrequency broadband noise, and a single high-frequency broad peak. Within this range, the lower angles of attack display the strongest low-frequency narrowband peaks. In fact, at lower angles of attack, the low-frequency narrowband peaks scale with a Mach power above 10.

Dynamics of the large-scale structures and associated noise emission in airfoil slats

“…For cases olBα4 and olCα4, the agreement is within 5 dB Hz −1 . The reduction of the low-frequency slat noise with increasing angle of attack captured by the present simulations agrees with previous results in the literature (Dobrzynski & Pott-Pollenske 2001;Kolb et al 2007;Imamura et al 2009;Amaral et al 2017). Low-frequency sound amplitude, especially for the narrowband peaks, is reduced as the overlap is increased, to the point that the peaks are not observed for the largest overlap simulated, olCα4.…”

“…2009; Amaral et al. 2017). Low-frequency sound amplitude, especially for the narrowband peaks, is reduced as the overlap is increased, to the point that the peaks are not observed for the largest overlap simulated, .…”

“…2014; Pagani, Souza & Medeiros 2016; Amaral et al. 2017). The consistent observation in this regard is that the noise at this range decreases significantly and the frequencies of the narrowband peaks decrease slightly as the angle of attack increases.…”

“…The effect of the airfoil's angle of attack on the low-mid-frequency slat noise has been thoroughly investigated (Kolb et al 2007;Imamura et al 2009;Murayama et al 2014;Pagani, Souza & Medeiros 2016;Amaral et al 2017). The consistent observation in this regard is that the noise at this range decreases significantly and the frequencies of the narrowband peaks decrease slightly as the angle of attack increases.…”

SPOD analysis of noise-generating Rossiter modes in a slat with and without a bulb seal

“…Pagani, Souza & Medeiros (2017) and Amaral et al. (2018) studied the effect of gap, overlap and slat deflection on the noise. They found that the narrowband peaks are relevant in the angle-of-attack range roughly between 0 and 12.…”