Oscillation quenching and physical explanation on freeplay-based aeroelastic airfoil in transonic viscous flow

Abstract

Limit Cycle Oscillation (LCO) quenching of a supercritical airfoil (NLR 7301) considering freeplay is investigated in transonic viscous flow. Computational Fluid Dynamics (CFD) based on Navier-Stokes equations is implemented to calculate transonic aerodynamic forces. A loosely coupled scheme with steady CFD and an efficient graphic method are developed to obtain the aerodynamic preload. LCO quenching phenomenon is observed from the nonlinear dynamic aeroelastic response obtained by using time marching approach. As the airspeed increases, LCO appears then quenches, forming the first LCO branch. Following the quenching region, LCO occurs again and sustains until the divergence of the response, forming the second LCO branch. The quenching of LCOs was addressed physically based on the aerodynamic preload and the linear flutter characteristic. An “island” of stable region is observed in the flutter boundary, i.e. the flutter speed versus the mean Angle of Attack (AoA). The LCO quenches when the aerodynamic preload crosses this stable region with the increasing of airspeed. The LCO quenching of this model in transonic flow is essentially induced by destabilizing effect from aerodynamic preload, since the flutter speed is sensitive to AoA due to aerodynamic nonlinearity.