Experimental And Numerical Simulation Of Boundary Layer Transition Of Curved Surfaces

This paper is based on the experimental research project of high lift plane cascade in a low pressure turbine,aims to understand the flow state and mechanism of viscous fluid.A low-speed back flow wind tunnel was designed and built for this experiment and other mechanism experiment of fluid mechanics.On the basis of the experimental platform,the experiments of the boundary layer transition of a flat plate and an airfoil were carried out.The boundary layer transition experiment of the flat plate is to measure the velocity distribution in the different flow direction by using the boundary layer hot wire probe in the zero-pressure gradient.The initial transition point of the plate is determined by comparing the measured velocity profile with the laminar Blasius standard solution and turbulent 1/7 law profile.Then,introduce periodic air flow disturbance at the front edge of the plate and repeat the measurement,the results show that different frequencies of disturbance will advance the position of transition in different degree with the same velocity;at the same frequency,the larger velocity of disturbance,the more forward position of transition.The NACA0012 airfoil boundary layer transition experiment is same as the flat plate experiment.The velocity profile can be used to calculate the thickness of the boundary layer displacement and the loss of momentum,resulting in the shape factor.From laminar flow to turbulent flow,the loss of momentum increases,and there will be a significant decline of the shape factor.Then repeat the measurement under the different attack angle conditions and calculate the shape factor,the results show that with the increase of the attack angle,the initial transition point of the airfoil is more and more forward.Numerical simulation of different experimental conditions of NACA0012 airfoil was performed by using CFX.During the transition from laminar flow to turbulent flow,there will be a sudden increase in parameters such as turbulence kinetic energy and turbulence intermittency.The results show that the position of the initial transition point calculated by CFX under different experimental conditions is basically consistent with the experimental results.