Analysis of Hybrid Brush Seal Rotordynamic Coefficients According to Position of Brush and Clearance Using 3D CFD

Abstract

The hybrid brush seal in which brush seal replaces one or two labyrinth teeth is preferred in turbomachinary to improve the efficiency and rotordynamic stability. Precise prediction method of leakage and rotordynamic coefficients is required in designing an effective hybrid brush seal. In this paper, the 3D CFD analysis method for rotordynamic coefficients is developed based on the seal dynamic analysis method using the relative coordinate system. The complex shape of the brush seal made of bristle wire pack is assumed to be a porous medium in this model. To evaluate the effect of the position of brush and clearance of brush seal on the rotordynamic coefficients, SSB and BSS type of hybrid brush seal are analyzed using FLUENT with cold clearance = 0 and 0.31mm. The rotordynamic coefficients(K, k, and C) obtained by the prposed analysis method are comparble to that of Pugachev's experimental results. The SSB seal shows better stability than the BSS seal when compaing the whirling frequency ratio as a result of brush position and clearance effect. Both SSB and BSS seal shows 30% reduction of leakage and better stability at cold clearance = 0 than at 0.31 mm. These results indicate that the position of the brush seal should be located at the end of hybrid brush seal, while maintaining the contact between the brush seal and rotor.