The present work advances progress on the validation against measurements of
linear and nonlinear rotordynamic models for predicting the dynamic shaft response of
automotive turbochargers (TCs) supported on floating ring bearings. Waterfall spectra of
measured shaft motions at the compressor and turbine ends of a test TC rotor evidences a
complex response, showing synchronous (1X) and multiple subsynchronous frequencies
along the entire operating speed range (maximum shaft speed ~ 65 krpm). Postprocessing
of the raw test data by mathematical software allows filtering the
synchronous and subsynchronous vibration components for later comparisons to
predicted shaft motions. The static performance of the floating ring bearings is analyzed
with in-house software (XLSFRBThermal®), which considers thermal expansion of the
shaft and bearing components as well as static loading on the bearing due to lubricant
feed pressure. In addition, the program calculates rotordynamic force coefficients for the
inner and outer films of the floating ring bearing. The turbocharger Finite Element (FE)
structural model for the linear and nonlinear analyses includes lumped masses for the
compressor and turbine wheels and the thrust collar. The mass imbalance distribution on
the TC rotor is estimated from the test data using a procedure derived from the two-plane
balancing method with influence coefficients. The linear model yields predictions of
rotor synchronous (1X) response to imbalance and damped eigenvalues. The analysis
evidences that the rotor cylindrical-bending mode is unstable at all shaft speeds while the
rotor conical model becomes more unstable as lubricant feed pressure decreases. The
predicted synchronous (1X) motions agree well with the test data, showing a critical
speed at approximately 20 krpm. The linear stability results indicate the existence of three critical speeds occurring at 4, 20 and 50 krpm. The second critical speed
corresponds to the rotor cylindrical-bending mode, showing larger amplitudes of motion
at the compressor nose than at the turbine end. The third critical speed associated to the
rotor first bending modes is well damped. In the nonlinear transient analysis, the
nonlinear equations of motion of the system (rotor-FRB) are integrated, and the bearing
reaction forces are calculated at each time step in a numerical integration procedure. The
model then yields predictions of total motion which is decomposed into synchronous
(1X) and subsynchronous motions, amplitudes and frequencies. The nonlinear analysis
predicts synchronous (1X) amplitudes that correlate well with the test data at high shaft
speeds (> 30 krpm) but underpredicts the imbalance response at low shaft speeds (<30
krpm). The time transient simulations predict multiple frequency subsynchronous
motions for shaft speeds ranging from 10 krpm to 55 krpm, with amplitudes and
frequencies that are in good agreement with the measurements. Finally, the shaft motion
measurements and predictions demonstrate that the turbocharger dynamic response does
not depend greatly on the lubricant feed pressure and inlet temperature for the conditions
tested.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3723 |
| Date | 16 August 2006 |
| Creators | Rivadeneira, Juan Carlos |
| Contributors | San Andres, Luis |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 1749475 bytes, electronic, application/pdf, born digital |
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