Flow Resistance Coefficients of Porous Brush Seal As a Function of Pressure Load

Abstract

Developments in brush seal analyses tools have been covering advanced flow and structural analyses since brush seals are applied at elevated pressure loads, temperatures, surface speeds, and transients. Brush seals have dynamic flow and structural behaviors that need to be investigated in detail in order to estimate final leakage output and service life. Bristles move, bend and form a grift matrix depending on pressure load. The level of pressure load determines the tightness of the bristle pack, and thus, the leakage. In the CFD analyses of this work, the bristle pack is treated as a porous medium. Based on brush seal test data, the flow resistance coefficients (FRC) for the porous bristle pack are calibrated as a function of pressure load. A circular seal is tested in a static test rig under various pressure loads at room temperature. The FRC calibration is based on test leakage and literature based axial pressure distribution on the rotor surface and radial pressure distribution over the backing plate. The anisotropic FRC are treated as spatial dependent in axi-symmetrical coordinates. The fence height region and the upper region of bristle pack have different FRC since the upper region is supported by backing plate while bristles are free to move and bend at the fence height region. The FRC are found to be almost linearly dependent on the pressure load for investigated conditions. The blow-down is also calculated by incorporating test leakage and calibrated FRC.

Using a three-dimensional tube bundle model to investigate the leakage flow characteristics of the rotating brush seal

“…Due to its low consumption of the computational source and good accuracy of the calculation, the porous medium models are widely used to numerically obtained the leakage flow characteristics of traditional brush seals. 18 Qiu 19 presented a detailed investigation into the flow behavior of the multi-stage brush seal. The aerodynamic force acting on the bristle pack was also analyzed.…”