Effect of Rub-Groove Wall Angle on the Leakage of Abradable Stepped Labyrinth Seals

Abstract

Rub grooves are generally formed in gas-turbine labyrinth seals of the abradable type during various transients. The rub-groove shape, often the slope angle of the groove downstream wall, varies and largely depends on the rotordynamics and the thermal expansion rates of the rotor and the stator. The effect of rub-groove shape on stepped labyrinth seal leakage was studied by varying the slope angle of the groove downstream wall, using various tooth axial positions and various prerub radial clearances. The investigation was done for compressible flow, with air as the working fluid. A finite volume method was used to solve the two-dimensional axisymmetric, Reynolds-averaged Navier-Stokes equation system. The high-Reynolds-number k-ϵ turbulence model was used along with wall functions. It was found that the wall angle of rub groove has a significant effect on the leakage as well as on the flow pattern. For the cases considered here, when the seal operates with the tooth positioned axially within the rub-groove axial width, the leakage decreases with an increase of the rub-groove downstream wall slope angle. However, for operation when the tooth lies axially just downstream of the groove, the leakage is slightly increased with an increase of the rub-groove wall angle. For cases with a certain tooth axial position and prerub radial clearance, a small change of groove sloping wall angle results in a large change in flow pattern. Presented at the AIAA/SAE/ASME/ASEE Joint Propulsion Conference in Ft. Lauderdale, Florida July 12-14, 2004 Final manuscript approved March 16, 2005 Review led by Jim Netzel