Study on the Leakage Flow Field in the Shaft Brush Seal of Steam Turbines

Abstract

The leakage flow behavior through a three stages shaft brush seal in steam turbines was numerically investigated using the Reynolds-Averaged Navier-Stokes (RANS) solution and the porous medium model based on the commercial CFD software FLUENT. At first, the permeability coefficients of the bristle pack were determined according to the published experimental data. Then, the leakage flow rate and flow characteristics of a typical shaft three stages brush seal used in steam turbines were studied at seven pressure ratios and five sizes of the sealing clearances using the calibrated permeability coefficients. In addition, the leakage flow field of the stepped labyrinth seal with the same axial distance at the same flow condition was also conducted. The numerical results show that the leakage flow rate of the three stages shaft brush seal with five sizes of sealing clearance is smaller than that of the labyrinth seal at the same pressure ratio. Moreover, the pressure ratio can affect the leakage flow rate while its influence on the leakage flow pattern can be neglected. The leakage flow rate increases linearly with the increase of the pressure ratio at the fixed sealing clearance for the three stages shaft brush seal. The leakage flow rate of the three stages shaft brush seal decreases with the decrease of sealing clearance at the fixed pressure ratio.