Fluid-induced forces acting on a rotating impeller are known to cause rotor-dynamicudproblems in turbomachines. The forces generated by leakage flow alongudthe front shroud surface of a centrifugal turbomachine impeller play an importantudrole among these fluid-induced forces. The present research was aimed toudgain a better understanding of these shroud forces. An experimental apparatusudwas designed and constructed to simulate the impeller shroud leakage flow. Hydrodynamicudforces, steady and unsteady pressure distributions on the rotatingudshroud were measured as functions of eccentricity, width of shroud clearance,udface seal clearance and shaft rotating speed. The forces measured from theuddynamometer and manometers agreed well. The hydrodynamic force matricesudwere found skew-symmetric and statically unstable. This is qualitatively similarudto the result of previous hydrodynamic volute force measurements. Nondimensionalizedudnormal and tangential forces decrease slightly as Reynolds number increases.udAs the width of the shroud clearance decreases and/or the eccentricityudincreases, the hydrodynamic forces increase nonlinearly. There was some evidenceudfound that increased front seal clearance could reduce the radial shroududforces and the relative magnitude of the destabilizing tangential force. Subharmonicudpressure fluctuations were also observed which may affect adverselyudthe behavior of the rotor system.
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