Numerical simulation of tip leakage flows in axial flow turbines, with emphasis on flow physics: Part II - Effect of outer casing relative motion

A pressure-correction based 30 Navier-Stokes CFD code was used to simulate the effects of turbine parameters on the tip leakage flow and vortex in a l inear turbine cascade to understand the detailed flow physics. A baseline c ase simulation of a cascade was first conducted in order to validate the nu merical procedure with experimental measurements. The effects of realistic tip clearance spacing, inlet conditions, and relative endwall motion were t hen sequentically simulated, while maintaining previously modified paramete rs. With each additional simulation, a derailed comparison of rite leakage flow's direction, pressure gradient, and mass flow, as well as the leakage vortex and its roll-ltp, size, losses, location, and interaction with other flow features, was conducted. Part II of this two-part paper ser ies focus es on the effect of relative motion of the outer casing on the leakage flow and vortex development. Casing relative motion results in less mass flow t hrough tile gap and a smaller leakage vortex. The structure of the aerother mal losses in the passage change dramatically when the outer casing motion was incorporated, but the total losses in the passage remained very similar . Additional secondary flows that are seen near the casing are also discuss ed.