Effects of tip clearance, number of teeth, and tooth front angle on the sealing performance of straight and stepped labyrinth seals

In the gas turbine, gaps inevitably exist between the stationary and rotating parts. To improve the performance of gas turbines, tip leakage flow through the gaps must be minimized. The labyrinth seal increases the flow resistance by placing a number of teeth to minimize leakage flow. The labyrinth seal is still adopted in many fields because of its relatively high thermal resistance, simple structure, and wide pressure range. In this paper, the effects of geometric parameters (straight and stepped with solid land, tip clearance, number of teeth, and tooth front angle) on leakage flow were experimentally studied and the seal performance was described using the flow function. Also, flow visualization within the labyrinth seal was conducted using the Schlieren method. The dimensionless tip clearance (C/a) was adjusted from 0.8 to 3.3 (where a is tooth tip width) and the pressure ratio was adjusted from 1.1 to 3.0. The tooth front angle of the stepped seal was 90° and 60°. Results show that the flow function increased as the pressure ratio increased, however it tended to remain constant if the pressure ratio was higher than 2.0. At the same test condition, the flow function of the stepped labyrinth seal was smaller than that of the straight seal for all tested pressure ratios. Also, the seal performance was better for larger number of teeth, smaller tip clearance, and smaller tooth front angle cases. Based on the measured results, a new correlation for the labyrinth seals was suggested.