Numerical study on the optimal design of straight-through labyrinth seals for minimum leakage loss of Francis turbine

Abstract Labyrinth seals are important non-contact seals in Francis turbine. They help to reduce leakage flow from high to low-pressure regions. Therefore, this study focuses on the design of labyrinth seals providing more difference in pressure and minimum leakage flow. The 3-dimensional numerical models were built in one of the CAD software. The meshing and the simulation of the different designs of unilateral and bilateral labyrinth seals were done in ANSYS Workbench. ANSYS CFX has been used as a flow solver for steady-state flow analysis with water as a working fluid. The geometries of seals were modified by varying cavity numbers, cavity length, cavity depth, clearance gap and shape of the cavity. The numerical results showed less leakage loss when the cavity number increased for different seal designs. Also, the results verified that leakage losses increase when the depth of the cavity increases and leakage losses decrease when the length of the cavity increases. Similarly, the leakage losses decrease as seal clearance spaces decrease. However, seals with modified cavity shapes with higher cavity numbers had similar pressure differences and leakage losses compared to the original cavity shape of straight-through seals.