SECONDARY FLOW STRUCTURES AND LOSSES IN A RADIAL TURBINE NOZZLE

An analysis of secondary flow structures and losses in a variable-vane radial turbine geometry is provided based on CFD. A complete turbine stage of a commercial vehicle turbocharger is modeled, including the entire 360 degrees rotor and stator, in order to account for the circumferential non-uniformity of the flow. The full-stage model consists of approximately 12,500,000 nodes. The stator domain accounts for the endwall clearance on the hub side of the nozzle vanes. As an additional feature typical for variable turbine geometries, cylindrical shaft seals at the stator vane axis at hub and shroud as well as four circumferentially equidistant spacers are modeled. These geometrical details allow a more realistic simulation of the stator domain. In an analysis using fields of helicity and Q-Criterion, the present features are found to induce additional secondary vortices in the stator, in addition to the inflow and horse shoe vortices found by previous investigators. A detailed analysis of the secondary flow structures in this realistic stator shows that the spacers contribute 33% to the overall stator losses.