Test versus predictions for rotordynamic coefficients and leakage rates of hole-pattern gas seals at two clearances in choked and unchoked conditions

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Title: Test versus predictions for rotordynamic coefficients and leakage rates of hole-pattern gas seals at two clearances in choked and unchoked conditions
Author: Wade, Jonathan Leigh
Abstract: This thesis documents the results of high pressure testing of hole -pattern annular gas seals conducted at the Texas A &M University's Turbomachinery Laboratory . The testing conditions were aimed at determining the test seals sensitivity to pressure ratio , inlet fluid preswirl , rotor speed , and rotor to seal clearance . The rotordynamic coefficients showed only small changes resulting from the different pressure ratios tested . Only the damping terms at the lower frequencies showed some influence . One other notable result from the testing of different pressure ratios is that the seals were tested in a choked flow condition , and there was not a significant change in the seal behavior when the seals transitioned to the choked condition . The inlet fluid preswirl only had a notable effect on the cross -coupled stiffness in the larger clearance tests . These results lead to the conclusion that a swirl brake could have some rotordynamic value , but only if the seals have sufficiently large clearance . Conversely this also means that if hole -pattern seals are being implemented with a small clearance , then a swirl brake would not be an effective way to improve the rotordynamic stability of the system . The only significant effect that the rotor speeds had on the rotordynamic coefficients were that the cross -coupled coefficients increased as the rotor speed increased . This is the expected result because as the rotor speed increases there is a greater shear force on the gas as it passes through the seal resulting in more fluid circumferential velocity , which results in stronger cross -coupled coefficients . The changes in clearance resulted in drastic changes in the magnitude of the coefficients . The smaller clearance yielded much higher coefficients than the larger clearance . All of the rotordynamic coefficients were predicted well by ISOTSEAL . The code was found to do a good job predicting the seal leakage as well . This gives more credence to the coefficients and leakage that ISOTSEAL predicts .
URI: http : / /hdl .handle .net /1969 .1 /424
Date: 2004-09-30

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Test versus predictions for rotordynamic coefficients and leakage rates of hole-pattern gas seals at two clearances in choked and unchoked conditions. Available electronically from http : / /hdl .handle .net /1969 .1 /424 .

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