Mitigation of laminar separation flutter using active oscillation of local surface

Abstract

This work explores the mitigation effect of laminar separation flutter (LSF) using active oscillation of a local surface at Re = 77 000. Aerodynamic forces and flow field of a National Advisory Committee for Aeronautics (NACA) 0012 airfoil are obtained by numerical simulations using the γ−Reθ transition model. The local oscillation is considered as a harmonic motion of a single mode varying both in temporal and spatial domains. The control effects of oscillation positions, amplitudes, and frequencies on the pitch instability are investigated. The work done by aerodynamic moment per motion cycle when the airfoil undergoes prescribed harmonic pitch motion is defined to evaluate the control performance. The mitigation effect of LSF is demonstrated by a fluid–structure interaction (FSI) method. The results show that the oscillation region should be placed on 0.2c for small oscillation amplitude while the optimal oscillation position is 0.6c for large oscillation amplitude. The flow control mechanism is analyzed in terms of the flow structure. A series of vortices are formed and moved downstream under the effect of active oscillation of the local surface. These vortices suppress the formation of a large-scale laminar separation phenomenon, which improves the pitch stability. The frequency lock-in phenomenon occurs in a certain oscillation frequency range, and it can improve the control performance on the pitch instability. The results of FSI show that the active oscillation of the local surface can completely eliminate the LSF.