Numerical investigation of flow structures near various nozzle exit geometries of the air bearing

Numerical investigation of flow structures near various nozzle exit geometries of the air bearing
Bearings (machine parts); Computational fluid dynamics; Drills; Pressure distribution; Air bearing; High pressure zones; Maximum pressure; Negative pressures; Nozzle geometries; Numerical investigations; Radial direction; Stagnation points; Nozzles
Issue Date
Transactions of the Korean Society of Mechanical Engineers, B, v.38, no.3, pp.235 - 242
To investigate pressure distributions on the shaft surface of the air bearing, the commercial CFD software was employed to study three different nozzle geometries to improve the nozzle performance: general drill-shaped, matched cube-shaped and trimmed exit nozzles. Under the influence of stagnation point, the maximum pressure was observed at the center of shaft surface for all cases. Owing to the blocking effect of a fine gap between the shaft surface and the nozzle exit, the drill-shaped nozzle has the rapid local pressure increase near the nozzle exit corner, generating the ring vortex in the radial direction within pressure ratio of 6.92, and its pressure becomes negative in a certain range of downstream. In comparison, the contoured nozzle showed a local pressure increase in the measured range of pressure ratios, but a negative pressure appeared within the pressure ratio of about 10. The trimmed nozzle was seemed to extend the high pressure zone near the stagnation point in the radial direction substantially, and no negative pressure was appeared in the whole range. Based on these observations, it is found that trimming nozzle exit becomes more effective for improving the performance than modifying the nozzle inside contour. ? 2014 The Korean Society of Mechanical Engineers.
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