A Qualitative Study of Gas Bearings Operating at High Subsonic and Supersonic Tangential Speeds

Abstract

The work presented here is a preliminary study of the Mach number effect based on the usual lubrication assumptions except, for the retention of convective terms in the equations of motion. The essential step in this analysis is to adopt the momentum integral method, i.e., to assume a velocity profile satisfying the prescribed boundary conditions. The first attempt is to assume a second-order polynomial for the velocity profile. Although this may not be able to give a sufficient detail of the velocity field. Nevertheless, the results should, hopefully, give us some more insight into this problem. Analytical results based on perturbation theory are presented for journal, slider, and step bearings. Numerical results for a plane slider are also presented here. All results indicate that when a dimensionless mean speed parameter, namely, the modified Mach number, approaches to unity the pressrue field converges very quickly to the limiting solution ph = constant even at moderate values of the compressibility number. In addition, both small perturbation analysis and numerical results reveal that under some circumstances, e.g., in a plane slider, the pressure boundary condition at the trailing edge should be modified in order to obtain a physically meaningful solution.

Theoretical and Experimental Aspects Regarding Non-Isothermal and Inhomogenous Air Jets

“…Henri Coandă received the patent for the fluid jet propulsion device, and also for the invention of "method and device for the deviation of a fluid into another fluid", this last discovery based on the physical phenomenon "the deviation of a plane jet that penetrates into another fluid, in the vicinity of a convex wall", later called the "Coandă effect." (Constantinescu, 2013).…”

“…The jets projected at a certain angle on a solid surface have industrial applications related to, for example, the heating or cooling of contact surfaces. Countless experiments have been carried out on heat transfer for air jets created at the exit of linear nozzles, but also for air jets created at the exit of radial nozzles with a reattached jet (Constantinescu, 2013).…”