Effect of a ring type barrier and rotational speed on leakage flow of gas turbine brush seal

Abstract

This paper investigates the effect of inserting a ring type barrier on leakage flow of brush seals with different bristles clearances (the distance between bristle pack tip and rotor surface). The ring is placed on both upstream and downstream sides of the bristles. An axisymmetric CFD model is employed to calculate radial pressure distribution along backing plate, axial pressure variation on rotor surface, and leakage mass flow rate of the brush seal. Reynolds-Averaged-Navier-Stokes (RANS) together with non-Darcian porous medium approach is performed to solve the flow field. The accuracy and reliability of the model are evaluated through comparison of the numerical results and experimental data. The results show that inserting the ring is not effective for the brush seal with zero clearance, neither at upstream nor at downstream. In other cases, the downstream ring is considerably more effective than the upstream one, when the ring is tangent to the back of bristles. The greater the distance between the bristles and the ring, the less reduction in leakage flow. Also, the best performance is obtained for the ring height equal to clearance size. Moreover, the effect of rotor rotation on leakage flow is investigated. The results show a negligible decrease in brush seal leakage flow with increasing the rotational speed.