Investigation of shaft labyrinth seal leakage flow in a cryogenic liquid turbine expander with thermal-fluid-solid coupling approach

The study is focused on the shaft labyrinth seal leakage flow in a cryogenic liquid turbine expander. Significant work is performed by previous investigators on the labyrinth seals for conventional turbomachines, but the critical operational conditions (of temperature below -170 °C and pressure up to 60–80 atms) for cryogenic liquid turbine expander have made its seal leakage flow a thermal-fluid-solid coupled problem and calls for an in-depth study. The CFD and FEA models of cryogenic liquid turbine expander leakage flow are proposed based on two-way thermal-fluid-solid coupling, they are verified with experimental and theoretical data, and then used to investigate the labyrinth seal structural deformation of cryogenic liquid turbine expander with different tooth shapes under all realistic centrifugal, pressure and thermal loads, and the solid-coupled seal leakage flows are predicted. The followings are demonstrated:(1) labyrinth seal experiences shrinkage deformation, the clearance is of convergent profile along the leakage direction, and the minimum tip clearance is about 16 % larger than the design; (2) the flow velocity of the jet core with structural deformation is significantly higher than that of without, and the leakage flow rate considering structural deformation is about 27 % higher than that without; (3) the impact of structural deformation on leakage amplifies with rising pressure ratio for labyrinth seals under variable pressure condition; (4) the parametric study reveals that the improvement of leakage performance can profit from small clearance, large tooth height, large inclination angle and small tooth thickness, meanwhile, the interaction effect of those parameters cannot be ignored.