Elasto-Hydrodynamic Model of Hybrid Journal Bearings for Aero-Engine Gear Fuel Pump Applications

Abstract

Gear pumps are largely employed in aero-engine fuel systems to provide the combustor with fuel at adequate pressure and flow rate. The radial load applied on the gears, as a consequence of the pump pressure rise, is entirely supported by the hybrid journal bearings. Lubrication of these is accomplished using low viscosity aviation fuel, which makes the design and analysis of journal bearings particularly challenging. A numerical model has been developed to support the analysis and future design of hybrid journal bearings for fuel pump applications. The primary objective of the tool is to characterise the equilibrium position of the journal during steady-state operation at part and full load, where the resultant elastic displacements are more significantly affecting the pressure distribution of the lubrication film. The developed method effectively combines Elrod's cavitation algorithm with the dimensionless pressure definition known as the Vogelpohl parameter, resulting in a simple and robust methodology to characterise the pressure distribution within the lubricant for different bearing designs and operating conditions. Six different multidimensional root-finding solvers have been implemented and their performance evaluated against robustness, accuracy and computational speed requirements. Newton-Raphson based methods have shown promising trade-offs for the problem at hand. Validation of the tool has been made comparing experimental film thickness measurements, performed on a fuel pump from a modern turbofan engine, with predicted data from the numerical model.

Identifying the influence of design parameters of single-chamber hydrostatic bearing of fuel pump on its main characteristics

“…A scheme of a hydrostatic bearing with one supporting chamber located under the line of action of the external force is proposed. The above analysis of the influence of the design parameters of a single-chamber hydrostatic bearing on its characteristics was not considered in [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The calculation results show the possibility of using a single-chamber hydrostatic bearing in fuel pump supports.…”

“…However, the cited work does not pay attention to the influence of lubricant temperature on the reliability of the hydrodynamic characteristics of plain bearings. Work [4] discusses gear pumps for fuel systems of aircraft engines. The radial load applied to the gears is fully absorbed by the hybrid support bearings.…”

Identifying the influence of design parameters of a hydrostatic bearing in an aircraft fuel pump on its static characteristics

“…However, the work does not pay attention to thermal processes in the bearing, which, due to the characteristics of the lubricant used, can have a significant impact on the characteristics of the bearing. In [2], an elastic-hydrodynamic model of a hybrid sliding bearing for gear fuel pumps of aircraft engines is considered. The radial load applied to the gears due to increased pressure in the pump is fully absorbed by the hybrid plain bearing.…”

A decoupled approach to enhance the Elrod algorithm

“…This leads to a well-regularized algorithm with reduced arithmetic cost. (2) The algorithm is more stable. For all studied cases, including a journal and a thrust bearing, the algorithm converges consistently.…”

“…The Elrod algorithm is a famous cavitation algorithm that can efficiently solve the bearing cavitation problem. [1][2][3][4][5][6][7][8] The algorithm was proposed by Elrod and Adams 9 in 1974 and later improved by Elrod 10 in 1981. Since its inception, the algorithm has attracted wide attention for its mass-conserving approach to the study of bearing cavitation.…”