Insights into airfoil response to sinusoidal gusty inflow by oscillating vanes
Zhenlong Wu, Galih Bangga, Thorsten Lutz, Gerrit Kampers, Michael Hölling
Abstract
Gust response is one of the classic topics in aerodynamics. Two different transfer functions, Sears and Atassi, have been used to model the unsteady lift responses of an airfoil experiencing a sinusoidal gust over the past few decades. However, a significant discrepancy against measured data has consistently been observed. Although the discrepancy at high frequencies was solved by a correct normalization of the lift response of an airfoil [Wei et al., “Insights into the periodic gust response of airfoils,” J. Fluid Mech. 876, 237 (2019)], totally opposite trends emerged between the experimental data and both functions at low frequencies. To clarify the observed discrepancy, both wind-tunnel experiments and numerical simulations are performed in this study to characterize the Sears and Atassi inflow conditions generated by oscillating grid vanes. A scaling law is established for fast determination of the oscillation parameters of the vanes required to generate a specific gust angle. The gust-angle phase shift between the empty-tunnel and test airfoil cases is quantified. A universal transfer function normalization method is proposed for arbitrary sinusoidal gusts and arbitrary airfoil shapes. The discrepancy between the measured and theoretical lift responses at low gust frequencies is found to be related to the dynamic effect of the highly turbulent wakes of the oscillating vanes as well as the large installation angle of the test airfoil.