EXPERIMENTAL CHARACTERIZATION OF A TWO STAGE BRUSH SEALS: LEAKAGE AND TORQUE MEASUREMENTS

Two-stage brush seals were experimentally investigated in the present work. The test rig was originally developed to operate with pressurized hot water but was recently adapted also for pressurized air. The brush seals were designed to seal high pressure differences. The bristles are made of Haynes 25 and the rotor is coated with a layer of chromium carbide. Brush seals had identical back and front plates inner diameters, a small fence height and a bristle pack/rotor interference (negative clearance). They were tested for both water and air. The inlet mass flowrates were measured for centered operating conditions while the supply pressure was modified for constant discharge pressure. Water tests were performed for various rotation speeds. The resistive torque, the water temperatures and pressures along the housing were measured. Results are discussed in order to highlight the impact of rotor speed, supply pressure and wear on brush seals performance. In the second part of this work, the results obtained for air are compared to data from the literature, using the equivalent effective clearance. Then, another approach is used for estimating the leakage rate of brush seals by considering the brush as a porous medium. The identified values of the permeability in the Darcy law for air and water are very close. The calibration of the porous medium is then independent of the incompressible or compressible character of the fluid because the velocities through the bristle pack are very small. Moreover, the identified permeability is in agreement with theoretical values. Thus, an accurate estimation of the leakage flow rate of brush seals of similar design can be easily made.