Accurate numerical simulation of compressible transitional flows in turbomachinery

An accurate and efficient methodology is provided for computing turbulent and transitional flows by solving the compressible Reynolds-averaged Navier-Stokes equations with an explicit algebraic stress model and k-omega turbulence closure. The space discretization is based on a finite volume method with Roe's approximate Riemann solver and formally second-order-accurate MUSCL extrapolation. Second-order accuracy in time is achieved using a dual time-stepping technique combined with an explicit Runge-Kutta scheme and multigrid acceleration to converge the false transient at each physical time level. The turbulence model has been validated computing the vortex shedding behind a two-dimensional turbine cascade. Furthermore, the transition model of Mayle for separated flow has been combined with such a turbulence model; this methodology has been validated computing the flow through the T106 low-pressure turbine cascade with separated-flow transition at the suction-side boundary layer. Finally, the three-dimensional flow through the T106 linear cascade has been computed providing the analysis of the loss-coefficient distribution downstream of the cascade and the description of the interaction between the secondary flow pattern and the suction-side separation bubble.