Characteristics of laminar separation flutter of two-dimensional airfoils at low Reynolds numbers

Highly nonlinear and complex viscous effects occur in laminar separation flutter at low Reynolds numbers, so it is very difficult to predict and analyze this phenomenon. However, this phenomenon can affect the flight stability of some flying animals and micro-air vehicles significantly. Therefore, it is essential for us to investigate the mechanisms of triggering and sustaining oscillations, in order to suppress and even avoid this type of flutter during flight. The unsteady Reynolds Averaged Navier-Stokes (RANS) equation and γ-Re_θt transition model are used to simulate the complex viscous flow phenomena, and are coupled with the structure motion equation to establish the time domain aeroelastic analysis method. The solution for the time domain is the fourth order implicit Adams linear multi-step method, which is based on the prediction-correction method. This aeroelastic analysis method is used to simulate the laminar separation flutter responses of the NACA0012 airfoil. The results indicate that this method can simulate laminar separation flutter accurately. The characteristics of laminar separation flutter at different turbulence intensities have been compared and analyzed. It can be found from transient flow results that laminar separation plays a critical role in initiating and sustaining pitching oscillations, and the shedding vortex with high frequencies enhance only nonlinearity of aerodynamics. Turbulence can inhibit Limit Cycle Oscillation (LCO) to some extent. A comparison of the responses of laminar separation flutter of the airfoils of different thicknesses and cambers shows that laminar separation flutter can be suppressed when the thickness of the airfoil decreases or the camber of the airfoil increases properly.