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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 labyrinth seals. The elliptic form of the 2-D axisymmetric Navier-Stokes equations for compressible turbulent flow were solved. The relationships among the friction coefficient, the leakage Reynolds number, the groove depth and 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 leakage 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 cutting wear grooves into the abradable surface of the land (stationary housing of the seal). Furthermore, it was found that the case of a small pre-rub tooth radial clearance, a wide rub groove and on intermediate step height is the most sensitive to the presence of a rub groove, with a leakage increase 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 tile leakage varied with pre-rub clearance and groove width, in order from lowest to highest leakage, as: (a)small clearance and narrow groove, (b)small clearance and wide groove, (c)large clearance and narrow groove and (d)large clearance and wide groove.