Session: 20-01 Compressor and Gas Turbine Development and Testing

Paper Number: 125936

125936 - Natural Gas Overhung Pipeline Compressor Rotordynamic Design, Test Validation, and Consideration of Morton Effect 

This study examines a new natural gas pipeline compressor design and its potential for “Morton effect” instability. The compressor is designed to utilize a rotor with one or two stages arranged in an overhung configuration.  An overhung rotor design allows for increased compressor efficiency by lowering the inlet losses in the compressor, eliminating a balance piston, and minimizing leakage by having only one dry gas seal. Comprehensive rotor-dynamic analysis was performed on the rotor-bearing system accompanied by an iterative design optimization. The rotor dynamic unbalance and stability characteristics were good for both designs having either one or two overhung impellers. Another important aspect “Morton effect” for overhung rotor was also carefully examined because the new rotor design has large overhung weight, long overhung length and high bearing surface speed making it subject to a high Morton effect risk. Bearing optimization, for example, using offset pivot tilting pad bearing and adjusting bearing clearance was tried to minimize the Morton effect risk through the Morton effect analysis. Eventually a test rotor was built to experimentally validate the rotor-dynamic performance of the worst case rotor design, which had two overhung impellers. Varying amounts of unbalance were applied and the rotor was operated up through its trip speed.  It was validated that the new rotor design is rotor-dynamically sound and there is no Morton effect within the operating speed range of the rotor.

An attempt was then made to induce Morton Effect by altering the rotor from the intended design to one where Morton Effect would be more likely.  Larger amounts of unbalance were applied.  Some additional amplitude and phase change was observed; however, this did not become the classic Morton Effect instability.

Presenting Author: Brian Pettinato Elliott Group

Presenting Author Biography: Brian Pettinato is Manager of Aero and Structural Dynamics at Elliott Group in Jeannette, Pennsylvania. He has been with Elliott Group since 1995. His primary area of expertise is machinery dynamics. Prior to joining Elliott Group, he worked as a project engineer for CentriMarc. Mr. Pettinato received his B.S. (1989) and M.S. (1992) Mechanical Engineering degrees from the University of Virginia. He has coauthored over thirty technical papers and holds four U.S. patents. Mr. Pettinato is a fellow member of ASME, a member of STLE, and a registered Professional Engineer in the State of Pennsylvania. He serves on the Turbomachinery Advisory Committee of Texas A&M and on the API 684 rotordynamics task force.

Authors:

Wei Li Elliott Group
Christopher Braman Elliott Group
Hiroki Hatori Elliott Group
Manish Thorat Elliott Group
Brian Pettinato Elliott Group