An interdisciplinary systems analysis is presented for high-speed gas turbine engine mainshaft roller bearings which will enable the designer to meet the demands for ever higher rotative speeds and operating temperatures. The latest elastohydrodynamic experimental traction data are included. Analytical results cite a need for better definition of the rolling friction portion of the total traction. A fluid mechanics model for the detailed analysis of fluid drags is developed based upon a turbulent vortex-dominated flow and includes the effect of lubricant flow through the bearing. A complete thermal analysis including dynamic and thermal effects upon bearing dimensions and resulting clearances is also included. Heat transfer coefficients are given in detail. Shaft power loss and cage slip predictions as a function of load, speed, and lubricant supply correlate well with available experimental data.
Experimental data are presented for local heat transfer rates near the entrance to a flat duct in which there is an abrupt symmetrical enlargement in flow cross section. Two enlargement area ratios are considered, and Reynolds numbers, based on duct hydraulic diameter, varied from 70,000 to 205,000. It is found that such a flow is characterized by a long stall on one side and a short stall on the other. Maximum heat transfer occurs in both cases at the point of reattachment, followed by a decay toward the values for fully developed duct flow. Empirical equations are given for the Nusselt number at the reattachment point, correlated as functions of duct Reynolds number and enlargement ratio.
A general analytical technique is presented for the evaluation of rolling element bearings when their structural support significantly influences the equilibrium solution. A cylindrical roller bearing supported by an elastic outer housing with two stiff leg supports is analyzed to illustrate the application of this computer oriented method. Experimental determination of the roller load distribution by “footprint” measurement techniques shows excellent agreement with the analytical predictions. The method of solution is outlined with sufficient detail to enable the cooperation of structural and bearing analysis in the solution of a class of problems requiring both disciplines.
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