THERMOELASTIC DISTORSION AND ITS CONTROL IN THIN FILM HYDRODYNAMIC LUBRICATION THRUST BEARINGS

Presented byFarooq Ahmad Najar

Under track Fluid Film Bearings2015 STLE Annual Meeting & Exhibition,17-21 May 2015

Venue: Trinity 1, Omni Hotel Dallas, Texas USA

Time: 2030 hours

Dated: 21 May 2015

Session Chair: Michael Fillon

THERMOELASTIC DISTORSION AND ITS CONTROL IN THIN FILM HYDRODYNAMIC LUBRICATION THRUST BEARINGS

By Farooq Ahmad Najar

Research Scholar Under the Supervision of

Prof. G A Harmain

Department of Mechanical Engineering National Institute of Technology

Srinagar-190006, (J&K), India

Contents Outline

Objectives of present work

Motivation

Methodology

Numerical work & Solutions

Reynolds Equation

Energy Equation

Heat Conduction Equation

Biharmonic equation

Results and Discussions

Conclusion

Overview Conventional cooling of thrust bearings

Thermo elastic deformation

Piezoelastic deformation

Material Failure of pads due to overheating.

Innovative method of cooling pads.

Increased Efficiency and availability of serviceability

Thrust bearing pads and their characteristic dimensions.

Deformations and damage of Thrust Segments

Less due to Pressure & More due to Temperature

Handmade Pad Set Model for Thrust Bearing Presenting the new Cooling arrangement

Problem Description The present problem addresses the control of thermal

effects on a sector shaped pad extensively used in thrust bearings which supports the heavy axial loads.

Large hydro-generator thrust bearings are susceptible to thermo-elastic deformation when oil film thickness is subjected to high pressure and temperature which can even lead to the bearing failure.

The present study is an effort towards reducing the oil film temperature by incorporating a suitable cooling arrangement in the proximity of heat source.

The cooling circuit, in this study, essentially follows a path of hot spots observed by solving energy equation and generalized conduction equation.

The numerical scheme followed during investigation is finite difference method (FDM).

 

Objectives

To compute the pressure distribution in the oil film between pad surface and runner by solving generalized Reynolds’s Equation after introducing a cooling circuit.

To compute the temperature distribution in the oil film by solving Energy Equation with and without viscosity variation in conventional pad and non conventional one.

To compute the heat transfer between pad and water circuit by solving 3D heat conduction equation.

To study the pressure induced deformation and temperature induced deformation of pad by solving 4th order bi-harmonic equation.

Motivation Control of thermal effects. Temperature-viscosity variations lead to hot-spots ----

thin Babbitt lining gets damaged to a great extent. The conventional cooling --outside of thrust bearing

pads. An alternative way of cooling --Close proximity of

cooling arrangement to the actual location of heat production.

Governing Equations Generalized Reynolds Equation

Equation of Film Geometry

Energy Equation

Three Dimensional Heat Conduction Equation

4th Order Bi-harmonic Equation.

Reynolds Equation

where h is the film thickness, µ is the viscosity of oil and ω is the angular speed of the runner.

Equation of Film Geometry

where h is the film thickness, h0 is the minimum film thickness, hs is the taper, θ and θt are the general angular extent and total angular extent of the pad respectively.

Energy Equation

where, ρ is the density of oil and cv is the specific heat of the oil

Three dimensional heat conduction equation

Kr, Kθ and Kz represent thermal conductivity of the pad in radial, circumferential and (thickness) directions respectively, and r,θ and z are the cylindrical coordinates.

Biharmonic Equation

Where Load = Hydrodynamic Pressure or Thermal stress

The numerical strategy followed for pressure distribution

Continued

Continued

Pressure Generation

Different possible cooling arrangements in a thrust pad

Flow chart for computation

Continued

Temperature Profile

Maximum nodal Temperature (oC) Values along with the depth of Pad.

Pad DepthIn terms of Z’s

Flow Velocity(V=0.5m/s) Flow Velocity(V=1.0m/s) Flow Velocity(V=1.5m/s) Flow Velocity(V=2.0m/s)

Z=2 57.30 56.14 55.11 54.18

Z=3 52.05 50.48 49.05 47.70

Z=4 49.85 48.11 46.50 44.77

Z=5 48.93 47.11 45.43 43.09

THANK YOU