Mitigation of transonic shock buffet on a supercritical airfoil through wavy leading edges

Abstract

Mitigation of shock buffet phenomenon over a supercritical aerofoil by means of wavy leading edges (WLEs) is analysed with implicit large eddy simulations (ILES). A Dassault Aviation's V2C aerofoil is simulated in a transonic flow with Re ∞ = 5.0 × 10 5 and M ∞ = 0.7 at α = 7.0 o . This aerofoil profile is designed for transonic flows, delaying the onset of wave drag and decreasing the skin friction drag. The results of this upstream flow condition on a straight aerofoil is a large oscillation of lift and drag coefficients. In the first part, timeaveraged aerodynamic characteristics over a straight leading edge (SLE) aerofoil and three modified aerofoils with different wavy amplitudes are compared. The results show that overall WLE aerofoils are more efficient than SLE ones and the aerofoil with the lowest amplitude (h = 0.0075) is the most efficient, increasing lift coefficient and decreasing drag coefficient. The flow unsteadiness has a key role for aerofoils in transonic flows at moderate and high angles of attack. Hence, the second part of the paper is a detailed unsteady analysis of flow phenomena. The starting point is an investigation of unsteady aerodynamic performance. It is observed that WLE aerofoils are capable of significantly decreasing low-frequency oscillations' amplitude, identified with shock buffet. The best performance is obtained with h = 0.0125 where a high-frequency oscillation becomes the dominant unsteady phenomenon. High-frequency oscillations are identified through the application of a frequency filtering method to the flow field. It is proved that the oscillation on the SLE aerofoil is related to vortex shedding, while the one on WLE aerofoils is related to laminar separation bubble (LSB) breathing. Overall, the unsteady analysis shows a connection between shock buffet and LSB breathing phenomena on wavy aerofoils and identifies the WLE amplitude as a key parameter to control this relation and mitigate the shock buffet.

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