Computational study of the flow in an axial turbine with emphasis on the interaction of labyrinth seal leakage flow and main flow

This paper presents a numerical study of the flow in a 1.5 stage low-speed axial turbine with a straight labyrinth seal on the rotor blade and focuses on the interaction of the leakage flow with the main flow. The influence of the leakage flow on the flow field of the turbine is examined using the Navier-Stokes code ITSM3D. The impact of the re-entering leakage flow on the main flow in dependency of the leakage mass flow rate is studied at two different clearance heights of the labyrinth in the simulations. As demonstrated in this paper, leakage flow not only introduces mixing losses but can also dominate the secondary flow and induce severe losses. In agreement with the experimental data the computational results show that even at realistic clearance heights the leakage flow gives rise to negative incidence over a considerable part of the downstream stator which causes the flow to separate.