Identification of Buffet Onset by means of Global Stability Analysis

Abstract

The transonic buffet phenomenon can limit the flight envelope of commercial aircraft for certain cruise conditions in terms of angle of attack for a given Mach number and Reynolds number. It consists of the oscillation of the shock on the suction side of the wing, coupled with variations in size of the flow separation. These oscillations change the pressure distribution around the wing, inducing lift and drag variations. Usually, the structural motion of the wing is completely neglected [1]. In this sense, the buffet phenomenon is purely a fluid instability problem [2]. Numerically, unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations are used to determine at which parameter combination (usually Mach number, angle of attack, Reynolds number) the onset of buffet phenomenon appears. Alternatively to the computationally expensive URANS simulations, steady RANS computations combined with Global Stability Analysis (GSA) are able to link the appearance of an unstable global mode with the transonic buffet onset [2].