The Study Of Transition On Controlled Diffution Airfoil Using Large Simulation

As one of the core components of a heavy gas turbine,the compressor plays a great role of the aerodynamic performance.Controlled diffusion airfoil(CDA),which has attracted much attention in the research of compressors,has the characteristics of wide range of attack angle,high load and difficult separation of boundary layer.The shape of the airfoil is designed to accelerate the gas to a maximum Mach number in order to provide a favorable pressure gradient near the leading edge of the suction,which ensures that the laminar boundary layer does not separate,and then reduces the gas flow velocity and begin to transition.Therefore,predicting the position of the transition plays a vital role in the design of the controlled diffusion airfoil.In this thesis,large eddy simulation will be used to study the problem of transition for controlled diffusion airfoil.Concerning the effects of different Reynolds numbers,different angles of attack,and different incoming turbulence intensity on the transition position,three Reynolds numbers(10~5,3×10~5 and 6×10~5),four angles of attack(3°,0°,-3° and -6°) and three incoming turbulence intensity(1%,2%and 3%)are selected as working condition samples to investigate transition through observing the contours of time-averaged velocity,a series contours of instantaneous turbulent kinetic energy,pressure distribution and skin friction distribution along the airfoil surface.The results show that,for the suction section,the larger the Reynolds number is,the closer the transition point is to the leading edge;when the angle of attack is negative,the more it deviates from the axial position,the farther the transition point is away from the leading edge;at the positive angle of attack,a laminar separation bubble appears at the leading edge of the airfoil.The flow subsequently undergoes a relaminarization and transition again.For the pressure section,due to the angle of attack is closer to the design point,the boundary layer always maintains laminar without separation and transition.