AN EFFECTIVE METHOD TO SEPARATE THE FORWARD AND BACKWARD NATURAL FREQUENCIES IN TURBOMACHINERY VIBRATION TEST MEASUREMENTS
Abstract
As speed and power density increase, validation of analytical prediction with actual test data plays an important role to ensure avoidance of critical speeds in high-speed turbomachinery and a reliable design. For a typical centrifugal compressor, the location of its second critical speed usually limits the maximum speed it can operate. Due to the gyroscopic effect, the difference between some forward and backward natural frequencies increases with the rotating speed. To identify the two different natural frequencies experimentally, common engineering practice requires excitations with forward and backward rotating excitations, separately. This paper includes two case studies to benchmark the method. The first case study is a comparison between theoretical predictions. The second case study presents a comparison between predicted and measured results from a 21,700 HP (16 MW) full-load, full-pressure test. This test was conducted using a magnetitic bearing exciter applied to a 6 stage back-to-back centrifugal compressor designed for natural gas processing. The example provided will show identification and extraction of the natural frequencies below MCOS, excited sub-synchronously and above MCOS, excited super-synchronously. Additionally, based on the Bently Nevada full spectrum plot theory, the paper presents an effective approach to identifying the forward and backward natural frequencies from a single planar excitation, reducing 50% of the test time and cost. The theory and characteristic equation will be shown along with the comparisons with both simulated and test results which serve to validate the accuracy of this method.
Description
LectureCollections
Citation
Wu, Tingcheng; Maier, Martin D. (2021). AN EFFECTIVE METHOD TO SEPARATE THE FORWARD AND BACKWARD NATURAL FREQUENCIES IN TURBOMACHINERY VIBRATION TEST MEASUREMENTS. Turbomachinery Laboratory, Texas A&M Engineering Experiment Station; Texas A & M University. Libraries; Texas A & M University. Libraries. Available electronically from https : / /hdl .handle .net /1969 .1 /196721.