Abstract
Although a two-stage brush seal (TSBS) plays an important role in gas turbine machinery, few studies have investigated the complex flow and tip frictional force distributions of the TSBS. This article contributes to the ongoing investigation of the TSBS by proposing a 3D slice model employing computational fluid dynamics to analyze the flow and tip frictional force characteristics of a contacting TSBS using the torque balance principle and linear superposition methods. Our calculations reveal that as the inter-stage imbalance of the pressure decreases, so do the aerodynamic and tip frictional forces between the upstream and downstream bristle packs. In addition, the effects of the number of bristle axial rows and protection clearance height on the inter-stage imbalance are analyzed. The results indicate that the TSBS exhibited significantly less leakage and lower aerodynamic and tip frictional forces than a single-stage brush seal. However, the inter-stage pressure differential results in an inter-stage imbalance in the aerodynamic and tip frictional forces that can be aggravated under high pressure conditions. This study determined that reasonable adjustments can be made to the number of bristle axial rows and protection clearance heights of the upstream and downstream stages to alleviate this inter-stage imbalance. The findings of this study contribute to the design and implementation of more efficient TSBSs.Although a two-stage brush seal (TSBS) plays an important role in gas turbine machinery, few studies have investigated the complex flow and tip frictional force distributions of the TSBS. This article contributes to the ongoing investigation of the TSBS by proposing a 3D slice model employing computational fluid dynamics to analyze the flow and tip frictional force characteristics of a contacting TSBS using the torque balance principle and linear superposition methods. Our calculations reveal that as the inter-stage imbalance of the pressure decreases, so do the aerodynamic and tip frictional forces between the upstream and downstream bristle packs. In addition, the effects of the number of bristle axial rows and protection clearance height on the inter-stage imbalance are analyzed. The results indicate that the TSBS exhibited significantly less leakage and lower aerodynamic and tip frictional forces than a single-stage brush seal. However, the inter-stage pressure differential results in an inter-stage i...
Highlights
Due to its excellent leakage characteristics and good flexibility, the brush seal is increasingly being used in gas turbine machinery instead of the labyrinth seal.1 The brush seal comprises a large number of fine bristles situated at an angle to the shaft closely clamped between and welded together with a front plate and a backing plate
This study details the calculation of the flow properties of a two-stage brush seal (TSBS) based on a 3D slice computational fluid dynamics (CFD) model
The tip frictional forces on the TSBS bristles due to aerodynamic forces were calculated by applying the torque balance principal and linear superposition methods
Summary
Due to its excellent leakage characteristics and good flexibility, the brush seal is increasingly being used in gas turbine machinery instead of the labyrinth seal. The brush seal comprises a large number of fine bristles situated at an angle to the shaft closely clamped between and welded together with a front plate and a backing plate. Experiments performed by Hendricks et al. indicate that for an MSBS, the upstream bristle pack receives 40% of the total pressure differential compared to 60% for the downstream bristle pack This uneven pressure distribution brings about inter-stage imbalances; the more pressure that is applied to the downstream bristle pack, the greater the tip forces and wear between the shaft and the bristles. Huang et al. established a 3D slice model with 22 axial rows of bristles based on a test brush seal; the calculated leakages, tip forces, and torques were compared with the experimental data. The study presented in this paper, based on a theoretical method, analyzed the flow and tip frictional force distributions in a two-stage brush seal (TSBS) revealing the inter-stage imbalance of pressure drops as well as the aerodynamic and tip frictional forces.
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