Experimental study of pressure drop in traditional and modified labyrinth seals of Francis turbine

Labyrinth seals are primary non-contact seals used to minimise leakage losses between high and low-pressure regions in Francis turbines. This paper describes the development of an experimental setup (consisting of piping method and pressure sensors) for measuring the pressure drop across simple or traditional straight-through (Seal1) and modified labyrinth seals (Seal2). The study aims to verify the Computational Fluid Dynamics (CFD) approach for predicting the pressure drop in labyrinth seals with experimental measurements. The experimental study utilises pressure sensors to investigate pressure data for flow rates of 0.2, 0.3, 0.4, and 0.5 L/s, with a speed range from 0 to 600 rpm. The data are recorded using the LabVIEW program. The study revealed a gradual increase in pressure drop for the lower rotational speed of (0–200) rpm, and then a steeper rise in pressure drop for higher rotational speed above 300 rpm in both Seal1 and Seal2, indicating increased turbulence, vortex formation and energy dissipation within the seal. Similarly, higher flow rates result in significantly larger pressure losses, indicating a strong dependence on flow rate. Moreover, the pressure drop provided by the modified seal is comparatively lower than that of a straight-through unilateral seal due to the difference in cavity shape and clearance gap between the seals. The comparison of CFD predictions and experimental data, collected using both pipe-based and sensor-based measurement approaches for both seal configurations (Seal1 and Seal2), revealed good agreement across all operating conditions, with an uncertainty of 0 to 8%.