Numerical Simulation Of Dynamic Stall Of Cessna 172 Airfoil

Dynamic stall may occur at any speed,attitude and power of the aircraft.Stall will lead to abnormal operation of the aircraft and seriously affect flight safety.Regardless of the cause of stall,reducing the angle of attack is the only way to solve the problem of stall.Therefore,starting from the change of aircraft angle of attack,the evolution process of aircraft dynamic stall under different degrees of attack is studied,and the parameters in the process of stall are analyzed.This paper aims at the R-type of Cessna 172 aircraft,which is a primary education training model in our university.The comutational fluid dynamics method is used to simulate the dynamic stall process of NACA2412 airfoil and three-dimensional wing.Firstly the NACA2412 airfoil is numerically calculated by the dynamic grid technology.Then the results are compared with the experimental results to verify the feasibility of the calculation method.Finally the results of two-dimensional airfoil calculation are analyzed.The numerical calculation method,model and results of two-dimensional airfoil are applied to three-dimensional wing calculation,and the numerical results of three-dimensional wing dynamic stall are analyzed.Through calculation and analysis,the following conclusions can be drawn:1.SST ?-? Turbulence model is more friendly to the flow field with high reverse pressure gradient and vortex,and dynamic grid technology can simulate the whole dynamic stall process better.2.From the numerical calculation of the three-dimensional wing,it can be seen that the negative vortex generated and separated from the leading edge is the main reason for the influence of dynamic stall.When the negative vortex is separated from the leading edge and connected with the trailing edge,a positive vortex will be generated at the trailing edge,and then there will be a positive and negative vortex alternation on the wing surface.To some extent,the formation of the positive vortex will cause the air flow on the lower surface of the wing to surge up,and lead the air flow to the upper surface or the trailing edge of the positive vortex until all the vortex are completely separated.3.At Mach 0.13 and Reynolds number 2.2×10~6,the critical angle of attack of the two-dimensional airfoil dynamic stall is 18.9 degree and the peak value of lift coefficient is 2.54.The critical angle of attack of the three-dimensional wing dynamic stall has different values at different sections,and the variation range is between 12.9degree and 16.7 degree.The critical angle of attack of the whole dynamic stall is 16.3degree from the monitoring lift coefficient,and the peak value of lift coefficient is2.09.4.In the process of dynamic stall,the angle of attack of laminar flow converted to turbulent flow in the upward condition is greater than that in the downward condition.