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Session: Shocks
Session starts: Tuesday 18 June, 11:00
Presentation starts: 11:30
Room: Room 1.3

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Magan Singh (Indian Institute of Science)
Kartik Venkatraman (Indian Institute of Science)

Abstract:
Transonic buffet, or shock oscillations, over stationary wing sections and finite span wings, is well investigated for more than two decades. There is a reasonable understanding of the mechanisms that cause shock buffet. The present work is concerned with the nature of shock oscillations in an oscillating finite span wing. Raveh (2008), besides introducing the term ‘buffet’, showed that in a transonic flow over an airfoil pitching about a mean angle of attack, the large shock oscillations interact nonlinearly with the flow-field generated due to pitching. At small amplitudes of pitching, the lift coefficient frequency response shows two distinct frequencies---the buffet frequency and the pitching frequency. However, at higher amplitudes of oscillation, the participation of the buffet frequency decreases, till at a particular amplitude of pitching, the buffet frequency vanishes, and the frequency response is entirely dominated by the pitching frequency. This is known as frequency lock-in. The amplitude at which lock-in occurs depends on the ratio of the buffet frequency and airfoil pitching frequency. In this paper, the nature of shock oscillations over the Benchmark Supercritical Wing (BSCW)--- a finite span wing with an aspect ratio 2 and a supercritical wing section---pitching about an axis, is studied at a Mach number of 0.8, Reynolds number of 4 x 106, and an angle of attack of 5o. This test case is the validation case for the 3rd Aeroelasticity Prediction Workshop (AePW-3) High Angle Working Group (Chwalowski, et al., 2024). The buffet characteristics of this test case are interesting in that there is no dominant buffet frequency. A broad band of frequencies are present in the low frequency region, and multiple peaks at higher frequencies. Therefore, the focus of the study is to investigate the influence of wing oscillations on buffet, and the frequency response of the flow field. URANS simulations with a variant of Spalart-Allmaras turbulence closure model, known as the Edwards-Chandra modification, is used for the analysis. Time domain and frequency domain results are presented at different amplitudes of oscillation of the pitching wing. The wing pitching frequency is set at 10 Hz. References 1. Raveh, D.E. 2008. A Numerical Study of an Oscillating Airfoil in Transonic Flows With Large Shock Wave Oscillations. AIAA 2008-1756. https://doi.org/10.2514/6.2008-1756. 2. Chwalowski, P., McHugh, G. R., Massey, S. J., Poplingher, L., Raveh, D. E., Jirasek, A., Singh, M., Venkatraman, K., . . . Slotnick, J. (2024). Shock-buffet prediction report in support of the high angle working group at the third aeroelastic prediction workshop. In AIAA Dynamics Specialist Meeting-Aeroelastic Prediction Workshop Summary Results, AIAA SciTech Forum, January 8-12, 2024; Orlando, Florida, USA.