The prediction and measurement of incompressible flow in a labyrinth seal

Abstract

A computational/experimental study was conducted on the incompressible flow in a labyrinth seal at a variety of leakage rates and seal rotation rates. The predictions were obtained using a finite difference code that utilized QUICK differencing to minimize the effects of false diffusion. Measured inlet boundary conditions for the axial and swirl velocity components as well as turbulence kinetic energy were employed. Considering the complexity of the flowfield, this yielded fair agreement between velocity predictions and the hot film measurements. The resulting computer code may be used to simulate, and in turn, improve labyrinth seal designs. The effects of leakage rate and seal rotation rate on the overall pressure drop are presented in terms of a loss coefficient. It was determined that when the rotation rate is increased beyond a certain point compared to the leakage rate, a second recirculation zone (SRZ) forms inside the seal cavity. This dramatically alters the flowfield in the seal and results in a substantial increase in the pressure drop across the seal. A flow map is presented indicating the approximate rotation rate required to produce this phenomenon at a given leakage rate. Unfortunately for most practical applications, the SRZ will not form until a prohibitively large shaft speed is reached. Also included in this study are the predicted distributions of the important flowfield quantities and the effects that leakage and rotation rate have on them. Both predicted and measured profiles are presented for the axial and swirl velocity components and turbulent kinetic energy.