Numerical study of shock buffet on three-dimensional wings

Abstract

The paper presents a computational study of the transonic shock-buffet flow instability phenomenon on threedimensional wings. Reynolds-Averaged Navier-Stokes simulations were conducted on three wing configurations, all based on the RA16SC1 airfoil, at shock-buffet flow conditions. Numerical validation is presented for theOAT15Aand RA16SC1 swept wings based on wind-tunnel experiments. The simulated configurations include infinite-straight, infinite-swept, and finite-swept three-dimensional wing models of several sweep angles and span lengths. Based on the results, the effects of three-dimensional flow, wing sweep, and span length on the shock-buffet characteristics are identified. For small wing-sweep angles, the fundamental shock-buffet instability mechanism remains similar to the two-dimensional mechanism, which is characterized mainly by chordwise shock oscillations. For moderate sweep angles, a phenomenon of lateral pressure disturbance propagation is observed. This phenomenon is essentially different from the two-dimensional shock-buffet mechanism yet results in oscillations of the sectional aerodynamic coefficients. The paper presents and discusses both phenomena, and it suggests a connection between them. For highwing sweep angles, the wing is stalled and shock buffet is eliminated. For low-Aspect-ratio wings, the flow is dominated by tip vortices, and shock buffet is eliminated. For high-Aspect-ratio wings, wingtip effects are minor and limited to the tip region. For intermediate-Aspect-ratio cases, tip vortices and shock-buffet interaction results in irregular shock oscillations.