Browsing by Subject "Seal"
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Item A linear fluid inertia model for improved prediction of force coefficients in grooved squeeze film dampers and grooved oil seal rings(2009-05-15) Delgado-Marquez, AdolfoIn Squeeze Film Dampers, (SFD), grooves (deep or shallow) are used to feed oil into the damper and prevent oil starvation within the fluid film lands. In oil seals with film land of clearance c, short shallow grooves (depth ? 15c, length ? 30c) are machined to reduce the cross-coupled stiffness coefficients, and thus improve the seal stability characteristics. Moreover, test stands for these devices can also incorporate grooves or recesses as part of oil feeding/ discharge arrangements. A common assumption is that these grooves do not influence the test system forced response. However, unexpected large added mass coefficients are reported in these configurations and not adequately predicted. In the case of grooved oil seals, experimental results also show that circumferential grooves do aid to reduce cross-coupled force coefficients but to a lesser extent than predictions otherwise indicate. A linear fluid inertia model for analysis of multiple-groove SFD or oil seal configurations is advanced. A perturbation analysis for small motion about a journal centered and off-centered position yields zeroth and first order flow equations defined at each individual flow region (land and grooves) of constant clearance ( c ).The analysis considers both the circumferential and axial dynamic pressure variations across the groove and land regions. At the groove regions, an effective groove depth ( d? ) and effective clearance (c d c ? ? = + ) are defined based on qualitative observations of the laminar flow pattern through annular cavities. This depth differs from the actual physical groove depth. The boundary conditions at the inlet and exit plane are a function of the geometric configuration. Integration of the resulting dynamic pressure fields on the journal surface yields the force coefficients (stiffness, damping, and inertia). Comparisons between predicted and experimental force coefficients for a grooved oil seal and a SFD show excellent correlation over a narrow range of effective groove depths. The results confirm that large added mass coefficients are associated to the feed/discharge grooves in the scrutinized test configurations. Furthermore, predictions, benchmarking experimental data, corroborate that short inner land grooves in an oil seal do not isolate the pressure field of the adjacent film lands, and hence contribute greatly to the force response of the seal.Item Analytical and experimental evaluation of the leakage and stiffness characteristics of high pressure pocket damper seals(Texas A&M University, 2004-09-30) Gamal Eldin, Ahmed MohamedThis thesis presents numerical predictions for the leakage and direct stiffness coefficients of pocket damper seals. Modifications made to earlier flow-prediction models are discussed. Leakage and static pressure measurements on straight-through and diverging configurations of eight-bladed and twelve-bladed seals were used for code validation and for calculation of seal discharge coefficients. Higher than expected leakage rates were measured in the case of the twelve-bladed seal, while the leakage rates for the eight-bladed seals were predicted reasonably accurately. Results are presented for shake tests conducted on the seals at pressures of up to 1000 Psi (6.90 MPa). Test variables included pressure drop across the seals and rotor speed. The experimentally obtained stiffness coefficients are compared to results of a rotordynamic damper seal code, which uses the corrected mass flow-rate calculation method. Results show that the code under-predicts the magnitude of the seal's stiffness for most test cases. However, general trends in the frequency dependency of the direct stiffness are more accurately predicted. The expectation of high values of negative stiffness in diverging seals is confirmed by the results, but the frequency at which the sign of the stiffness becomes positive is considerably lower than is predicted. In addition to presenting high-pressure test data, this thesis also attempts to provide some insight into how seal parameters can be modified to obtain desired changes in seal stiffness.Item A fundamental approximation in MATLAB of the efficiency of an automotive differential in transmitting rotational kinetic energy(2012-05) Vaughn, James Roy; Matthews, Ronald D.; Bryant, Michael D.The VCOST budgeting tool uses a drive cycle simulator to improve fuel economy predictions for vehicle fleets. This drive cycle simulator needs to predict the efficiency of various components of the vehicle's powertrain including any differentials. Existing differential efficiency models either lack accuracy over the operating conditions considered or require too great an investment. A fundamental model for differential efficiency is a cost-effective solution for predicting the odd behaviors unique to a differential. The differential efficiency model itself combines the torque balance equation and the Navier-Stokes equations with models for gear pair, bearing, and seal efficiencies under a set of appropriate assumptions. Comparison of the model with existing data has shown that observable trends in differential efficiency are reproducible in some cases to within 10% of the accepted efficiency value over a range of torques and speeds that represents the operating conditions of the differential. Though the model is generally an improvement over existing curve fits, the potential exists for further improvement to the accuracy of the model. When the model performs correctly, it represents an immense savings over collecting data with comparable accuracy.Item Measurements versus predictions for rotordynamic coefficients and leakage rates for a novel hole-pattern gas seal(Texas A&M University, 2007-04-25) Seifert, Brent AlanResults are presented for measured and predicted rotordynamic coefficients and leakage for hole-pattern seals with a hole depth that varies axially along the seal. Testing was done to discover how pressure ratio, inlet preswirl, and rotor speed affect the seals?????? rotordynamic characteristics and leakage. The results were compared to a constant hole depth hole-pattern seal. Experimental results show that the seals?????? rotordynamic characteristics are not strongly influenced by pressure ratio. There were three preswirl conditions tested, each separated by a 6.9 bar (100 psi) difference in inlet pressure. Therefore, normalized preswirl results were compared. The normalized results indicate that introducing inlet fluid preswirl affects the crosscoupled stiffness and effective damping coefficients. Inlet preswirl increases the magnitude of cross-coupled stiffness. Effective damping decreases with inlet preswirl, as well as the effective damping cross-over frequency increasing. These results indicate that swirl brakes would be of great value. Rotor speed had a significant effect on the cross-coupled coefficients; both increased with speed. Experimental results were compared to results for a constant hole depth holepattern seal. The variable hole-depth seal has higher direct damping. The crosscoupled stiffness and cross-coupled damping coefficients were very similar. The direct stiffness was always lower at lower frequencies and higher at higher frequencies for the variable hole depth hole-pattern seal. This was also the case for effective stiffness. The effective damping of the variable hole-depth seal was not only larger than for the constant hole depth seal, it also had a drastically lower cross-over frequency. The difference in cross-over frequency was 40 percent on average. Experimental results for rotordynamic characteristics and leakage were compared to theoretical predictions by ISOTSEAL 2, a modified version of ISOTSEAL. Both cross-coupled stiffness and damping are reasonably predicted. Direct damping is always under-predicted. ISOTSEAL 2 does a poor job of predicting direct stiffness. Direct stiffness is over-predicted at lower frequencies and under-predicted at higher frequencies. This is also the case for effective stiffness. ISOTSEAL 2 under-predicts the direct damping, but does an excellent job of predicting the direct damping crossover frequency. Seal leakage is well predicted by ISOTSEAL 2.