Numerical investigations of a low-pressure turbine purge flow control concept for reducing aerodynamic losses

Interaction between purge flows and main flow path is known to impact negatively the aerodynamic performance of the gas turbines. This paper focuses on the leakage flow through hub cavity re-entering into the main flow path upstream of the second rotor blade row of a two-stage low-pressure turbine (LPT). The stator well considered in this paper consists of second stator vane upstream and downstream cavities connected with a labyrinth seal mounted on an annular seal carrier. A device to reduce the mixing and subsequent row losses is numerically evaluated by assessing its impact on the turbine efficiency, as well as on the radial distribution of relevant characteristic quantities (circumferential velocity, flow angle, turbulent kinetic energy…). The feature is located underneath the nozzle guide vane endwall and a significant part of the leakage flow is passing through it, before mixing with the other part of the leakage flow and re-entering into the main flow. This paper presents numerical results of unsteady 3D simulations of a two-stage axial turbine with the turning device located upstream of the second rotor blade row. Results of three configurations are compared: the two-stage axial turbine including its inner cavity without, and then with the device and finally, the former associated to a modified nozzle guide vane platform. An increase of the turbine efficiency of 0.114% can be noticed in the best case. The turning feature reduces mixing losses between the two leakage flows before entering into the main flow path and then improve the efficiency of the subsequent row.