Comprehensive modeling of gas foil bearings (GFBs) anchored to reliable test data
will enable the widespread usage of GFBs into novel turbomachinery applications,
such as light weight business aircraft engines, hybrid fuel cell-turbine power systems,
and micro-engines recharging battery packs for clean hybrid electric vehicles.
Pressurized air is often needed to cool GFBs and to carry away heat conducted from a
hot turbine in oil-free micro turbomachinery. Side end pressurization, however,
demonstrates a profound effect on the rotordynamic performance of GFBs. This
dissertation presents the first study that devotes considerable attention to the effect of
side end pressurization on delaying the onset rotor speed of subsynchronous motions.
GFB performance depends largely on the support elastic structure, i.e. a smooth
foil on top of bump strips. The top foil on bump strips layers is modeled as a two
dimensional (2D), finite element (FE) shell supported on axially distributed linear
springs. The structural model is coupled to a unique model of the gas film governed by
modified Reynolds equation with the evolution of gas flow circumferential velocity, a
function of the side end pressure. Predicted direct stiffness and damping increase as the
pressure raises, while the difference in cross-coupled stiffnesses, directly related to
rotor-bearing system stability, decreases. Prediction also shows that side end
pressurization delays the threshold speed of instability.
Dynamic response measurements are conducted on a rigid rotor supported on
GFBs. Rotor speed-up tests first demonstrate the beneficial effect of side end
pressurization on delaying the onset speed of rotor subsynchronous motions. The test data are in agreement with predictions of threshold speed of instability and whirl
frequency ratio, thus validating the model of GFBs with side end pressurization. Rotor
speed coastdown tests at a low pressure of 0.35 bar evidence nearly uniform
normalized rotor motion amplitudes and phase angles with small and moderately large
imbalance masses, thus implying a linear rotor response behavior.
A finite element rotordynamic model integrates the linearized GFB force
coefficients to predict the synchronous responses of the test rotor. A comparison of
predictions to test data demonstrates an excellent agreement and successfully validates
the rotordynamic model.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2088 |
| Date | 15 May 2009 |
| Creators | Kim, Tae Ho |
| Contributors | San Andr? Luis |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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