Influence of geometrical and operational parameters on the leakage flow of a radial labyrinth seal for application in inward flow radial supercritical CO2 turbine

Inward flow radial ( IFR) turbines are preferred for small-scale power generation due to their compact and efficient design. The parasitic loss due to leakage of working fluid and disk friction at the back face of the turbine is a concern issue at smaller power scales. In the presented work, a radial labyrinth seal at the backface of the inflow radial turbine is used and analyzed to control the leakage rate. CFD studies are carried out to understand the influence of the geometric and operating parameters of the radial labyrinth seal on the leakage rate through the seal. CFD predictions reveal that for a particular pressure ratio of 1.26, the variation in axial clearance (c/s) varied from 0.025 to 0.0625, results in a similar to 57.2 % increase in the leakage rate. However, the variation in height (h/s) from 0.25 to 0.75 results in a marginal 4.24 % leakage reduction. It is also observed that there exists an optimum number of teeth for a given effective seal length to improve seal performance. Furthermore, the increase in rotational speed from 10,000 rpm to 1,00,000 rpm results in a similar to 67.16 % reduction in leakage rate with the temperature rise of s-CO2 through the seal by similar to 62 degrees C for the case with clearance (c/s) 0.05. The ratio Taylor to Reynolds number (Ta/Re) is found to be an essential parameter in deciding the evolution of tangential velocity. A critical value of 0.15 for the ratio is identified, beyond which the tangential velocity evolution is seen to be profound.