Unsteady Flow Simulation in an Axial Flow Turbine Using a Parallel Implicit Navier-Stokes Method

The unsteady flow in an axial flow turbine stage with a second stator blade row is investigated by means of a Navier-Stokes code especially developed for turbomachinery applications. Due to the low aspect ratio of the blades of the test machine a highly three-dimensional flow dominated by secondary flow structures is observed. Simulations that include all blade rows are carried out. The present investigation focuses on the stator/rotor/stator interaction effects. Secondary flow structures and their origins are identified and tracked on their way through the passage. The time-dependent secondary velocity vectors and total pressure distributions as well as flow angles and Mach number distributions as perturbation from the time-mean flow field are shown in cross-flow sections and azimuthal cuts throughout the turbine. Simulations and measurements show a good overall agreement in the time-dependent flow behaviour as well as in the secondary flow structures.