Stephen L. Edney
Dresser-Rand Company, 37 Coats St., Wellsville, NY.
Gregory B. Heitland Dresser-Rand Company, 37 Coats St., Wellsville, N.Y.
Scan M. DeCamillo Kingsbury, Inc., 10385 Drummond Road, Philadelphia, PA 19154
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.
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.
Read full PDF