The Flutter Analysis Of An Airfoil Based On CFD

As Fluent can be used to compute fluid problem and its UDF fuction can be used to sovle structure models and transfer datas, it can analyse aeroelastical problems by fluid-structure coupling numerical method. This method has an important significance for engineering applications and provides effective instrument for analyzing nonlinear aeroelastical problems of complex structure in time domain.To analyse the aeroelasticity problems correctly, the oscillating airfoil's unsteady characteristics is analysed first by CFD,including linear forces in small angle of attack and unsteady forces in dynamic stall. And some compare is made between CFD results and experiment results. At small angle of attack it is easy to get good results, and at big angle of attack the trends of the two results are the same, but there is some difference between numerical values. The cause of the difference is analysed followed. And then the influence of the average angle, oscillating amplitude and converting frequency on unsteady characteristics is analysed.Structural dynamic equations of 2d airfoil and 3d wing are derived, and then flutter performance is numerically simulated with fluid-structure coupling method. Linear flutter is analysed for 2d airfoil first, and the results are consistent to the results from NASTRAN with linear aerodynamics theory. Then stall flutter is analysed. While freestream velocity is small, the aeroelastic response converges. With the increase of freestream velocity, limit cycles appear, and the amplitudes increase. But when freestream velocity gets to some value, the aeroelastic response diverges. For 3d wing only linear flutter is analysed, and velocity of flutter what we get is consistent to the results from NASTRAN. This method can also be used for complex problems such as big angle of attack aerodynamics and stall.The aeroelastic response of 2d airfoil which has freeplay nonlinearity is also analyzed in this paper. And the fluence of freestream velocity, initial pitching angle, freeplay clearances, freeplay position and friction in the freeplay on aeroelastic response is analyzed. They have a great influence on aeroelastic response. When they get to some values, limit cycles appear. And the amplitudes increase with freestream velocity, reeplay clearances and freeplay position, while decrease with friction and keep constant as initial pitching angle changes.