Computed effect of rub-groove size on stepped labyrinth seal performance

A numerical study was undertaken to explore the effects of the size of wear -in rub grooves that are typically cut into the abradable land of stepped l abyrinth seals. The elliptic form of the 2-D axisymmetric Navier-Stokes equ ations for compressible turbulent flow were solved. The relationships among the friction coefficient, the leakage Reynolds number, the groove depth an d width and the pre-rub radial clearance are examined. It was found that the standard k-, turbulence model and wall functions are effective for computing the friction coefficient and leak-age for labyrinth seals with honeycomb land surfaces, both with and without the presence of rub grooves. The so-called rub grooves are the result of labyrinth teeth cu tting wear grooves into the abradable surface of the land (stationary, hous ing of the seal). Furthermore, it was found that the case of a small pre-ru b tooth radial clearance, a wide rub groove and an intermediate step height is the most sensitive to the presence of a rub groove, with a leak-age inc rease over the no-groove case of about 100 percent and 194 percent for the shallow and deep grooves, respectively. It was also found for example, that the leakage varied with pre-rub clearance and groove width, in order from lowest to highest leakage, as: (a) small clearance and narrow groove, (b) s mall clearance and wide groove, (c) large clearance and narrow groove and ( d) large clearance and wide groove.