A Fluid Dynamic Study of Gas Bearing for High Speed Mini-Scale Turbo Machinery

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Research was carried out from the points of view of three terms, which were a flow analysis of gas bearing by way of numerical approach, low speed experimental investigation of scale up model. and heat transfer investigation of air for mini-scale passage.The numerical investigation was executed for a spindle of 31.8mm diameter,45mm length and radial clearance of 20μ for rotational speed of 10,000,50,000 and 100,000 rpm. Numerical result showed a conventional relationship between non-dimensional load coefficient and bearing number, which represented load capability and rotational speed respectively. Air flowed in and out through the shaft end clearance due to the pressure distribution inside the bearing and was found to contribute to the cooling of the bearing.A specification of test stand for low speed model test was based on the numerical result. The spindle was designed as 144mm diameter, 100mm length and 0.12mm radial clearance and was driven by an electric motor with static type pr … More essurized bearing. The peripheral velocity of the spindle was 7.5m/s for maximum rotational speed of 1,000 rpm in the experiment. Three high frequency pressure transducer were installed in three axial points of the spindle and the pressure distribution in the peripheral direction of the bearing was measured by phase locked sampling system to decide a bearing number and non-dimensional load coefficient. The non-dimensional load coefficient decreased due to the leakage of air according to the pressure distribution. A seal of leakage air was considered to be important for practical application.A steep peripheral pressure gradient was created due to the strong shear in the journal bearing. The pressure gradient gave significant effect on the heat transfer characteristics. At the inlet portion of the mini-scale channel of about 1 mm diameter, it was found that heat transfer was greatly enhanced. The heat transfer performance was equivalent to the impingement heat transfer, which was well known to have a high heat transfer performance. Less