Analytical Approach for Investigating Bristle/Backplate Hysteresis Phenomenon in Brush Seals

Abstract

Brush seals are an important innovation, increasing the efficiency of turbomachinery for both land-based and aeronautical applications. However, a performance drawback termed brush seal hysteresis has been reported that can promote seal leakage, thereby undermining the effectiveness of the brush seal system. It is generally recognized that hysteretic behavior may be attributed to complex frictional forces that are generated within the brush seal during service, and that appropriate steps must be undertaken to understand, quantify, and minimize this source of inefficiency in brush seal performance. This paper focuses on investigating hysteresis phenomenon that can be traced to a mechanical interaction between the bristle and back plate of the brush seal. To this end, a mechanics-based model is developed that can forecast both bristle deformation and friction forces that arise between the lateral surface of the bristle and the edge of the back plate. The model uses general bending theory to examine three-dimensional deformation of the fiber that is caused by transient, flow-induced axial loads within the jet engine. Correctness of solutions obtained from the model is validated by a direct comparison with known results that have been published in the literature. On the basis of the mechanics model, a friction force path-based approach is proposed for quantifying brush seal hysteresis, and results are presented indicating that the model can successfully forecast a stick-slip phenomenon that naturally arises due to the axial flow of gases through the annular interspace between the rotor and brush seal back plate.