Numerical simulation of turbulent cascade flows involving high turning angles

Numerical simulations of three dimensional turbulent incompressible flows through linear cascades of turbine rotor blades with high turning angles have been performed using a generalized k-epsilon model which is a high Reynolds number form and derived by RNG (renormalized group) method to account for the variation of the rate of strain. The convective terms are approximated by using a second order upwind scheme to suppress numerical diffusion. Boundary-fitted coordinates are adopted to represent the complex cascade geometry accurately. For the case without tip clearance, secondary flows and flow losses are shown to be in good agreement with previous experimental results. For the case with tip clearance, the effects of the passage vortex and tip clearance flow on the total pressure loss as well as their interactions are discussed. The flow within the tip clearance has been analyzed to illustrate the existences of the tip clearance vortex and vena contracta.