The Wind Tunnel Test And Numerical Simulation Of Flow Around The Airfoil And Its Application

The problem of flow around a structure body has always been one of the focuses of fluid mechanics research which involves flow separation,boundary layer transition,generation,evolution of vortices,and their interactions.For a streamlined airfoil and non-streamlined bluff body structure,the vortex shedding will generate a cyclical fluctuating pressure in the flow direction and lateral direction at the structure surface.When the pulsation frequency is close to the natural frequency of the structure,vortex-induced vibration will occur,and in extreme cases it will cause catastrophic accidents.For the problem of flow around a structure body,if only from the experiment or numerical simulation means,will limit the researchers to a comprehensive understanding of the flow field information,combining these two methods can better get the flow field information.For this reason,this paper mainly combines the PIV test and CFD software to analyze the flow field structure in the flow.In terms of experiments,this paper is mainly based on the wind tunnel test platform of the Ministry of Education Key Laboratory of Fluid and Power Machinery of Xihua University.By using PIV flow field testing technology to study the flow field changes under different working conditions,and the instantaneous and average flow field are obtained.The POD technique was used to perform the reduced-order decomposition of the flow field to obtain the low-order modes of the flow field.In the numerical simulation,the ?-Re_? turbulence model and the k-? SST turbulence model were used to simulate the flow around the square and the airfoil.The influence of the grid and the time step on the calculation was compared.The comparison of numerical simulations and experimental data help to get more comprehensive analysis of the flow field information,and the following conclusions are obtained:The PIV test results based on the wind tunnel platform have a good accuracy,which are in good agreement with the LDV test results,besides,the PIV test can accurately observe the flow field change process.Compared with the k-? SST turbulence model,the ?-Re_? model is an excellent turbulence model,which can accurately calculate the St number and C_D around the square.The calculation results can accurately show the turbulent kinetic energy of the wake and the transition point of the airfoil upper surface,which agrees well with the experimental results.And the frequency,size,and position of the vortex shedding of flow around the square can be accurately obtained by the ?-Re_? turbulence model.Proper orthogonal decomposition(POD)can be used to decompose the flow field to get the low-order modes of the flow field.The 6th order POD mode of the flow around square accounts for 78.7% of the total energy.The first six modes can accurately capture the characteristics of the unsteady flow field under the large Reyn-olds number.At wind speeds of 10m/s(Re = 1.02×10~5),there is a reattachment phenome on the suction side of the NACA 64418 airfoil at an angle of attack of 16° to 23°.When ? is greater than 23°,reattachment will not occur.The critical velocity of reattachment phenome increases with angle of attack.The NACA 64418 airfoil has a large stall angle of attack,and there is almost no separation at angles of attack between 0° and 9°.When ? is approximately 10°,some vortices begin to separate.As the angle of attack continues to increase,vortex shedding exhibits a strong periodicity.In the application of vertical axis wind turbine,according to the pressure coefficient distribution of the blade,it can be obtained that the axis wind turbine formed by straight blade has better aerodynamic characteristics than the axis wind turbine formed by curved blade in overall aerodynamic performance.The vertical axis wind turbine blade composed of NACA 64418 airfoil does not have large vortex shedding on the surface of the blade between-34.17° and 45.72°.The laminar flow separation bubble appears on the blade surface at the angle of attack between 45.72° and 85.83°.Laminar flow separation bubbles increase the complexity of the vertical axis wind turbine flow field,which results in a decrease in vertical axis wind turbine performance.