lnfluence of Geometrical Parameters on the Sealing behavior of Band side Stepped Labyrinth seals of Francis turbine

The sealing behaviour of labyrinth seals plays a crucial role in minimizing leakage losses by preventing unwanted flow between high-pressure and low-pressure regions and hence, enhancing the efficiency of Francis turbines. Stepped labyrinth seals are mostly common in high-head Francis turbines. Leakage loss and, consequently, the sealing behavior of stepped seals are significantly influenced by geometrical parameters such as cavity numbers, length, depth, distance between the cavities and shape of the cavity. Most of the studies regarding the design of stepped labyrinth seals deal with the steam turbines. Therefore, in the case of Francis turbines, it is now necessary to get deep insights into the impacts of various geometrical factors on the stepped seals. The three-dimensional band side stepped labyrinth seals consisting of different cavity or step dimensions, clearance gap and distance between the cavities for the numerical study were built in CAD software. The meshing and the simulations were carried out in the Ansys workbench. The leakage losses for every numerical model were investigated in the study. The numerical results showed that 0.1 mm clearance gaps, 5 cavity numbers, 4.5 mm cavity depth and optimal 4 mm cavity length have a significant reduction in the leakage losses for the band side stepped labyrinth seals. Similarly, the results also conveyed that, there is a minimal control of leakages with the increase in distance between the cavities in comparison to the cavity length. This research work provides valuable insights for designing stepped labyrinth seals to enhance the operational efficiency and reliability of Francis turbines.