Gas Turbines: Structures and Dynamics

On the Effect of Thermal Energy Transport to the Performance of (Semi) Floating Ring Bearing Systems for Automotive Turbochargers

[+] Author and Article Information
Luis San Andrés

Fellow ASME, Turbomachinery Laboratory,  Texas A&M University, College Station, TX 77843lsanandres@tamu.edu

Vince Barbarie, Avijit Bhattacharya

 Honeywell Turbo Technologies, 2525 W. 190th Street, Torrance, CA 90504

Kostandin Gjika

 Honeywell Turbo Technologies, Zone Industrielle Inova 3000, 2 Rue de l’Avenir, 88155 Thaon-les-Vosges, France

The discussion focuses on a bearing system supplied at its middle plane. Commercial configurations have a variety of feed ports, including a supply at one end of the bearing.

A pin or a button prevents the rotation of the ring which can precess or whirl within the outer film region.

In practice, the inner film axial length differs from the outer film length.

Analysis and practice demonstrates that oil lubricated TC bearings operate under laminar flow conditions with Reynolds numbers Re*=(ρΩR/μ)c/R<1. Hence, both fluid inertia and turbulent flow effects are negligible.

The THD model implements a number of generic wall heat convection transfer models, including those for fixed or developing wall temperatures and heat flows.

The large variability in clearance dimensions for similar size bearings in commercial TCs is a result of low cost mass production.

A simpler (S)FRB configuration without adequate flow ports would lead to higher inner film temperatures, at times higher than the shaft temperature, even reaching the lubricant flash temperature. Clearly, such operating condition could cause the failure of the bearing system supporting the TC.

J. Eng. Gas Turbines Power 134(10), 102507 (Aug 22, 2012) (10 pages) doi:10.1115/1.4007059 History: Received June 20, 2012; Revised June 20, 2012; Published August 22, 2012; Online August 22, 2012

Bearing systems in engine-oil lubricated turbochargers (TCs) must operate reliably over a wide range of shaft speeds and withstand severe axial and radial thermal gradients. An engineered thermal management of the energy flows into and out of the bearing system is paramount in order to ensure the component’s mechanical integrity and the robustness of the bearing system. The bearings, radial and thrust type, act both as a load bearing and low friction support with the lubricant carrying away a large fraction of the thermal energy generated by rotational drag and the heat flow disposed from a hot shaft. The paper introduces a thermohydrodynamic analysis for the prediction of the pressure and temperature fields in a (semi) floating ring bearing (S)FRB system. The analysis simultaneously solves the Reynolds equation with variable oil viscosity and the thermal energy transport equation in the inner and outer films of the bearing system. Flow conditions in both films are coupled to the temperature distribution and heat flow through the (semi) floating ring. Other constraints include calculating the fluid films’ forces reacting to the externally applied load and to determine the operating journal and ring eccentricities. The predictions of performance for a unique realistic (S)FRB configuration at typical TC operating conditions reveal a distinct knowledge: (a) the heat flow from the shaft into the inner film is overwhelming, in particular, at the inlet lubricant plane where the temperature difference with the cold oil is largest; (b) the inner film temperature quickly increases as soon as the (cold) lubricant enters the film and is due to the large amount of energy generated by shear drag and the heat transfer from the shaft; (c) a floating ring develops a significant radial temperature gradient; (d) at all shaft speeds, low and high, the thermal energy carried away by the lubricant streams is no less than 70% of the total energy input; the rest is conducted through the TC casing. To warrant this thermal energy distribution, enough lubricant flow must be supplied to the bearing system. The efficient computational model offers a distinct advantage over existing lumped parameters thermal models and there is no penalty in the execution time.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Engine-oil lubricated turbocharger and the (semi) floating ring bearing system. Lubricant flow paths are shown into the bearings on the turbine and compressor sides.

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Figure 2

Schematic view of the (semi) floating ring bearing system for the turbocharger: geometry and coordinate systems

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Figure 3

Kinematics of journal and ring centers and notation for eccentricities

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Figure 4

Schematic axial view of the inner and outer films and nomenclature

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Figure 5

Schematic view of heat flows in the floating ring bearing system

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Figure 6

Pressure and temperature fields in the inner film of the (S)FRB. The shaft speed is at 240 krpm.

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Figure 7

Maximum (exit) and average temperatures for inner and outer films versus the shaft speed. The temperature of the mixed outlet stream is also shown.

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Figure 8

ID, OD, and mean radius temperatures in the floating ring versus the shaft speed

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Figure 9

Lubricant viscosity at the average temperature of the inner and outer films; dimensionless with respect to viscosity at the supply temperature (5.85 cP)

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Figure 10

Lubricant flow rates through the inner and outer film regions; dimensionless with respect to total flow rate at top speed

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Figure 11

Heat flows and drag power loss versus shaft speed in the (S)FRB; dimensionless with respect to energy input at the highest shaft speed

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Figure 12

Schematic representation of energy flows in the (S)FRB at two shaft speeds: 45 krpm and 240 krpm. The width of the boxes denotes the intensity of the energy flows.

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Figure 13

Dimensionless inner film radial clearance and static eccentricity versus shaft speed




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