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Investigations of Rubbing Phenomenon During Coast-Up Operation of a Cryogenic Engine Turbopump

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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.

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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

HPFTP:

High-pressure fuel turbopump

HHS:

Hilbert–Huang spectrum

c g :

= g/Xcr, clearance ratio

Cr, C :

Effective damping matrices: rotor, combined system

d s :

Ratio of chosen stator beam diameter to reference stator beam diameter

f :

Global force vector of body forces and surface traction

g :

Gap or clearance between contacting bodies

\(g_{\text{N}} ,\,\,{\mathbf{g}}_{\text{N}}\) :

Normal gap function and the array of all the normal gap functions

\(\dot{g}_{\text{T}} \text{,}\,\,{\dot{\mathbf{g}}}_{\text{T}}\) :

Time derivative of tangential gap function and the array of all the \(\dot{g}_{\text{T}}\)

GN, GT :

Global contact matrix for normal and tangential direction

G NT :

= GN + µGT, global normal-tangential contact matrix

Kr, K :

Stiffness matrices: rotor, combined system

Mr, M :

Mass matrices: rotor, combined system

q :

Number of active nodal contact pair

r d :

Radius of the disc

u * :

Displacement update without contact

u c :

Corrective displacement vector

u, u̇, ü :

Displacement, velocity, and acceleration vectors for the system

X 0 :

Vector defining the initial gap between contacting nodal pairs

X cr :

Peak-response amplitude at critical speed

\(\lambda_{\text{N}} ,\,\,\lambda_{\text{T}}\) :

Normal and tangential contact force

\({\varvec{\uplambda}}_{\text{N}} ,\,\,{\varvec{\uplambda}}_{\text{T}}\) :

Normal and tangential contact force vectors

µ :

Friction coefficient

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Acknowledgements

This research is supported by Aeronautics Research and Development Board, Defence Research and Development Organization, Government of India (Project ref. no. DARO/08/1041661/M/I). The authors gratefully acknowledge the financial support.

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Authors and Affiliations

  1. Department of Mechanical Engineering, Indian Institute of Technology Delhi, New Delhi, 110016, India

    Md. Asjad Mokhtar, Ashish K. Darpe & K. Gupta

  2. Darbhanga College of Engineering, Darbhanga, Bihar, 846005, India

    Md. Asjad Mokhtar

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  1. Md. Asjad Mokhtar
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  3. K. Gupta
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Correspondence to Md. Asjad Mokhtar.

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Mokhtar, M.A., Darpe, A.K. & Gupta, K. Investigations of Rubbing Phenomenon During Coast-Up Operation of a Cryogenic Engine Turbopump. J. Vib. Eng. Technol. 8, 737–749 (2020). https://doi.org/10.1007/s42417-019-00181-6

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  • DOI: https://doi.org/10.1007/s42417-019-00181-6

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