Gas Foil Bearings for Micro-Turbomachinery

MAJOR APPLICATION: Oil-Free Turbomachinery, Micro-Turbines, etc

Sponsors: National Science Foundation (03-06), USAF Wright-Patterson (04-05), Turbomachinery Research Consortium (04-08), Capstone Turbine Corp. (07), NASA Glenn RC (07-09)

Objectives:

To quantify the physical parameters of bump foil gas bearings for micro turbine applications

To measure the rotordynamic response of a rotor supported on gas foil bearings and to identify the bearings force coefficients

To develop computational models, benchmarked to test data, to predict the forced performance of gas foil bearings

Status: Identification of foil bearing structural stiffness and dry-friction (damping) parameter for increasing loads and frequencies and shaft temperatures completed. Available operating test rig with hollow rotor supported on gas foil bearings, top speed 50 krpm. The computational analysis developed shows excellent correlation with published load capacity data. The test rig will provide much needed information on dynamic force coefficients.

Current work: Rotordynamic Performance of Foil Gas Bearings: Tests and Analysis

Research program, analytical and experimental, to advance the technology (design and operation) of gas foil bearings for oil-free turbomachinery. The major tasks are:

· Comprehensive modeling of gas foil bearing performance (static and dynamic) operating at high speeds with minute film gaps. The model includes thermo-elastic deformations of the foil and elastic members (bump strips), including hysteretic effects due to dry friction from coatings and local contact zones.

· Exhaustive (independent) experimentation of foil bearings in a test rig for accurate determination of rotor lift and touch down speeds, load capacity and drag power losses, and identification of rotordynamic force coefficients.

The construction of a rotordynamic test rig for foil gas bearings was completed in early 2004. A DC motor, with maximum speed of 50 krpm, drives a 2.2 lb hollow rotor supported on two foil gas bearings. Presently, experiments to identify the rotor-bearing modal stiffness and damping parameters are close to completion. The test rig incorporates an electromagnet to apply non-contacting loads on the rotor. The proposed tasks are:

a) To develop reliable methods for identification of stiffness and equivalent (viscous) damping force coefficients in foil gas bearings.

b) To conduct rotor imbalance response tests to extract the equivalent stiffness and (viscous) damping coefficients of the test gas foil bearings.

c) To correlate the experimentally identified FB force coefficients to predictions derived from a parallel computational analysis effort.

Turbomachinery users and manufacturers will benefit from a planned research effort to characterize foil bearings thus increasing their confidence on the deployment of foil gas bearings in commercial products.

To learn more, order/read our PUBLICATIONS

TEST RIG FACILITIES

(Left) Generation II Gas foil bearings (Right) set up for shaker excitations

Rotordynamics test rig (Max. speed: 50 krpm)

STRUCTURAL STIFFNESS for TEST FOIL BEARING

COMPUTATIONAL MODEL PREDICTIONS ANCHORED TO TEST DATA

Minimum film thickness and journal attitude angle (Test data from literature)

Torque and load capacity (Test data from literature)

Rotor synchronous response and phase angle, measurements vs. predictions

Non-synchronous force coefficients (Test data from literature)

ROTORDYNAMIC PERFORMANCE WITH SIDE PRESSURIZATION

FORCED NONLINEAR ROTOR RESPONSES

2003: Rotordynamic Performance of Foil Gas Bearings: Tests and Analysis

TEST RIG FACILITY

(left) rotordynamics test rig (right) set up for shaker excitations

Measured STRUCTURAL STIFFNESS for TEST FOIL BEARING

VIRTUAL TOUR – download Video clip of test rig (11 MByte)

COMPUTATIONAL MODEL

Comparisons of journal attitude angle and minimum film thickness vs. load (Test data from literature)

To learn more, order/read our PUBLICATIONS