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published_or_final_version / Electrical Engineering / Master / Master of Philosophy

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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.

Cyanobacteria are prokaryotes that can grow photoautotrophically using oxygenic photosynthesis. Some filamentous cyanobacteria in media with insufficient fixed nitrogen develop a regular pattern of heterocyst cells that fix nitrogen for the remaining vegetative cells. We have built an integrated computational model of fixed nitrogen transport and cell growth for filamentous cyanobacteria. With our model, two qualitatively different experimentally observed nitrogen distributions between a pair of heterocysts are reconciled. By adding dynamic heterocyst placement into our model, we can optimize heterocyst frequency with respect to growth. Further introduction of modest leakage leads to distinct growth rates between different heterocyst placement strategies. A local placement strategy yields maximal growth and steady state heterocyst spacings similar to those observed experimentally. Adding more realistic fixed nitrogen storage based heterocyst commitment together with lateral inhibition to the model allows us to address initial heterocyst commitment and qualitatively reproduces many aspects of heterocyst differentiation. We also investigate patterns of starving cells and correlations of fixed nitrogen in filaments without heterocysts. We find percolation transitions in both spatial one dimensional patterns and space-time two dimensional patterns.

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