Investigations of Rubbing Phenomenon During Coast-Up Operation of a Cryogenic Engine Turbopump
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ORIGINAL PAPER
Investigations of Rubbing Phenomenon During Coast‑Up Operation of a Cryogenic Engine Turbopump Md. Asjad Mokhtar1,2 · Ashish K. Darpe1 · K. Gupta1 Received: 19 June 2019 / Revised: 6 September 2019 / Accepted: 20 September 2019 © Krishtel eMaging Solutions Private Limited 2019
Abstract Background A turbopump is an important and critical component in the liquid rocket engine assembly where a small deviation in the system parameters such as unbalance level, dimensional tolerances, rotor–stator clearance, etc. can have significant influence on its dynamic behavior and may lead to various faults such as rub. Hence, a detailed rotordynamic study is essential for the entire operating speed range. Purpose Most of the earlier studies on rotor-stator rub were carried out for simplified rotor models and its implementation on a rotor assembly such as turbopump will be of immense practical relevance for researchers and engineers. Contact mechanics-based Lagrange multiplier method is used to enforce the contact constraints that incorporate compliant stator model which respond to the axial and lateral forces during contact. Methods A full-scale cryogenic engine turbopump rotor system consisting of turbines, impellers, inducer, bearings and seals is modelled using FE framework to investigate the rotor–stator contact interaction during coast-up. The stator model the a circumferentially positioned beams around rotor disc and investigated using more realistic contact mechanics-based Lagrange multiplier method. Results The eigenvalue analysis on the FE model gives the rotor critical speeds and the corresponding vibration modes. The constraints imposed by the stator beams and tangential friction due to rub cause a continuous phase shift in the rotor vibration during contact. The physical insights into the distinct rotor vibration features in the two lateral directions are discussed in detail. The influence of clearance level on the observed backward whirl nature of the turbine is established through a full-spectrum analysis. Conclusion The tighter clearance between rotor and stator gives rise to dominating presence of backward whirl components that may be detrimental to the fatigue life of the shaft due to stress reversal. Duration of the contact interaction is found to decrease significantly with increase in rotor–stator clearance and decrease in friction coefficient. With tighter clearances, the influence of stator stiffness becomes more significant and the rotor response during contact exhibits nonlinear and complex vibration. Keywords Turbopump · Rub · Contact duration · Four-pin stator · Full spectrum · Lagrange multiplier Abbreviations B1 Bearing no. 1 CFD Computational fluid dynamics CL1 Clearance line for stator beam 1 SSME Space shuttle main engine HPOTP High pressure oxygen turbopump * Md. Asjad Mokhtar [email protected] 1
Department of Mechanical Engineering, Indian Institute of Technology Delhi, New Delhi 110016, India
Darbhanga College of Engineering, Darbhanga, Bihar 846005, I
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