Finite element grid discreteness selecting for rotating parts of inter-rotor bearing of a gas turbine engine considering surface roughness

DOI: 10.34759/vst-2020-1-171-179

Аuthors

Semenova A. S.^*, Kuz’min M. V.^**

Lyulka Experimental Design Bureau, branch of the United Engine Corporation – Ufa Engine Industrial Association, 13, Kasatkina str., Moscow, 129301, Russia

*e-mail: anna.semenova.lulka@gmail.com
**e-mail: maxim.kuzmin@okb.umpo.ru

Abstract

The presented work is devoted to the development of a technique for selecting the finite element grid size of the bearing rotating parts, contacting among themselves, with account for the surface roughness for strength calculation. It is customary in static calculation to thicken finite elements in the area of contact to ensure its accuracy. For the dynamic calculation, where parts are rotating, this technique does not work.

It is well known that reliability of machines and mechanisms operation depends substantially on their bearing blocks operability. This is especially important for aircraft engineering products as bearing blocks for aircraft engines, reducers and other products are one of the most critical components and, as a rule, limiting their resources. The inter-rotor bearing is one of the most problematic parts of the aircraft engine. While revealing signs of defect of the inter-rotor bearing the engine is removed fr om operation since this can lead to rotors jamming and the engine failure. The main cause of the rolling bearings failure under normal conditions is occurrence of contact stresses and, consequently, the rolling surfaces wear-out.

Most of the known analytical calculating methods of the contact compacting stress in bearings are based on the Hertz theory of static contact of two bodies. However, there is a number of simplifications for this theory:

– no friction;

– the contact area is smaller compared to the curvature radius;

– the contacting bodies materials are homogeneous, isotropic and perfectly elastic.

Numerical calculation allows solving contact problems without the Hertz theory simplification:

– friction simulation;

– accounting for nonlinear properties of the material;

– accounting for the contacting surfaces roughness by selecting finite element grid size.

The developed technique allows estimating stresses and deformations of the rotating parts of rolling bearings of any shape.

The purpose of the presented work consists in determining the optimum size of finite elements for dynamic calculation wh ere the contacting parts are rotatting.

Comparative evaluation of stresses and strains in contact of rollers with raceways of the 5AV1002926R4 bearing in 2D statement of the two options was performed:

– the size of a grid was selected with account for the surface roughness of the contacting bodies;

– the grid size was reduce by half compared to the first option.

The grid discreteness evaluation was performed with the LS-DYNA software package.

The developed technique is suitable for all types of planar and solid-state finite elements.

Keywords:

inter-rotor bearing, surface roughness, contact area, contact stresses

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