Unsteady Analysis of Inter-Rows Stator-Rotor Spacing Effects on a Transonic, Low-Aspect Ratio Turbine

Abstract

The aerodynamic performances of an axial turbine are affected by the distance between the stator and the rotor. Previous studies have shown different trends, depending mainly on whether the turbine is subsonic or not. The present paper aims at improving the understanding of the effect of rows spacing on the flow through a transonic turbine. A one-stage, low aspect ratio, high pressure turbine case is investigated using CFD. Steady and unsteady phase-lagged RANS computations are performed on this configuration with different inter-blade rows distances. The results are successfully compared with experimental data from a cold air turbine rig. Entropy production balances are used to emphasize the main loss areas and the loss variations caused by changes in inter-blade rows distance. Two techniques are compared for computing these balances, and one of them appears to perform much better. The flow features causing these losses are then identified. Finally, an optimal inter-rows spacing is found. It is a compromise between the losses created by strong stator-rotor interactions at small inter-rows gaps and the losses generated at the endwalls in the inter-rows space at large distances.

Stator-Rotor Interaction in Axial Turbine: Flow Physics and Design Perspective

“…As the stator shock sweep the rotor leading edge region, unsteadiness in the static pressure is found and for this in the boundary layer evolution; luckily, this happens where the boundary layer momentum deficit is close to be the smallest at the very beginning of the boundary layer evolution. As reported by [1,[36][37][38], the rotor trailing edge region is slightly affected, at least in term of static pressure and for this the boundary layer and the rotor wake are expected to be almost steady. The highest interaction is found in the leading edge/suction side region as clearly reported in Figure 12; the shock sweeping on the rotor leading edge first interact with the suction side of the blade (approx.…”