Stephen L. Edney
Dresser-Rand Company, 37 Coats St., Wellsville, NY.
stephen_l_edney@dresser-rand.com
Gregory B. Heitland
Dresser-Rand Company, 37 Coats St., Wellsville, N.Y.
greg_b_heitland@dresser-rand.com
Scan M. DeCamillo
Kingsbury, Inc., 10385 Drummond Road, Philadelphia, PA 19154
Abstract
Testing and analysis of a profiled leading edge groove tilting pad
journal bearing developed for light load operation is described.
This bearing was designed for a generic, small, high speed
steam turbine operating at projected loads of less than 25 psi
(172.4 kPa) and journal surface speeds to 400 ftIs (122 m/s). On
the second turbine application, a rotor instability was
experienced with the oil flowrate reduced to optimize bearing
steady state performance. This instability was eliminated by
machining a taper on the exit side of the feed groove on each
pad. At the reduced flowrate, the profiled groove bearing greatly
improved the operating characteristics of the rotor system by
reducing vibration amplitudes and stabilizing operation at speed.
This paper is divided into two sections. The first section compares
the rotordynamics analysis with test data that shows
improved ,unbalance response and operating stability with the
profiled groove bearing. The second section provides original
insight of the effect of the profiled geometry on the bearing flow
field using computational fluid dynamics models.
Introduction
As machine speeds have increased to pursue improved performance
in turbomachinery, so have the challenges in rotor and
bearing design. Higher operating speeds direct the development
of smaller machines that introduce constraints to the rotor
design. Accordingly, the applicable limits of conventional flooded
bearings can be stretched, especially when operation extends
into the turbulent flow regime. Bearing losses increase
exponentially with turbulent flow which can negatively impact a
machine's overall efficiency. Likewise, high bearing
temperatures can approach the limits of the babbitt.
This is a particular concern to OEMs and users of
turbomachinery since the safety margin against failure may be
reduced.
Presented herein is a case history of a leading edge groove
tilting pad journal bearing used in a generic, small, high speed
steam turbine. Directed lubrication leading edge groove
bearings were used to address temperature concerns at the high
journal surface speeds (approaching 400 ftIs (122 m/s».
Specifically discussed is a pad modification to eliminate a
bearing induced instability in an application with significantly
reduced oil flowrate.
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