Numerical Simulation Of Unsteady Boundary Layer In Turbomachinery

In turbomachinery, the flow is very complex. It is obvious that only using traditional steady turbulent simulation to numerical simulate the boundary layer in turbomachinery can not meet the requirements of engineering.First, the unsteady CFD solver used for the simulations is based on the Reynolds averaged Navier-Stokes equations. The original SA turbulence model production term has been reformulated and introduces its transport equation for transition prediction. Finite volume method is used to integrate equation in space, convective fluxes are evaluated using Roe's flux difference splitting to form a third-order MUSCL scheme, while diffusive fluxes are evaluated using central difference scheme, and introduce the low speed preconditioning method. The author developed a CFD solver for turbomachinery complex unsteady flow simulation.Second, the steady transition boundary layer on a flat plate, the unsteady boundary layer with separation bubble on a flat plat, and the separation flow in a cascade have been numerically simulated. The results of comparing the experiments show that, this method has a good prediction performance not only for bypass transition, but also for steady/unsteady separation boundary layer transition. So, it provides a simple and effective method for numerical investigation of turbomachinery complex flow.The last, analyzing the phenomenon of separation boundary layer shows that the size of separation bubble in cascade has great influence on turbomachinery performance. When the bubble is short, it impels the laminar rapid transition to turbulence. As the turbulent boundary layer has great kinetic energy, separate is difficult. It is beneficial to turbomachinery performance. While the long bubble in cascade may change the passage area lead to turbomachinery work under off-design condition and increase flow losses.