Modeling and analysis of dynamic characteristics of turbopumps with annular seals

Аuthors

Davydov A. V.^1*, Degtiarev S. A.^2**, Ivanov A. V.³, Leontiev M. K.^1***

1. Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia
2. Scientific and technical centre of rotor dynamic Alfa-Tranzit Co., Ltd, 1, Leningradskaya street, Khimky, Moscow region, 141400, Russia
3. Voronezh State Technical University, VSTU, 14, Moskovsky prospect, Voronezh, 394026, Russia

*e-mail: davidovarc@gmail.com
**e-mail: degs@alfatran.com
***e-mail: lemk@alfatran.com

Abstract

Annular seals in turbopumps influence their rotor dynamics significantly. They cause rotor autorotation and may result in the stability loss. The results of modeling for the rotor with hydrodynamic seal in the Dynamics R4 program system environment and their analysis are presented in this paper.
Rotor of the hydrogen turbopump on two supports was the subject of our study. Double deep-annular bearings were used in the supports. Circular vane-type dry-friction damper supports were placed between the case and the bearing outer rings. Tightness of the air-gas turbine and impellers may be provided by annular seals of different types including those with floating rings. Finite elements being the parts of the program library, such as the rod beam elements, inertia elements, elastic and rigid links, etc., were used for the rotor modeling. Every rotor component was simulated separately and was included into the complete rotor model as a separate subsystem. Links simulating junctions and fits in the rotor and its supporting units were specified between the subsystems. The bearings were loaded by axial forces.
The analysis was carried out in linearized and nonlinear statement. Linearized statement may be used only for typical annular seals or if friction forces stop a seal ring. Stiffness coefficients K_xx, K _xy and damping ones C _xx, C _xy were calculated using the procedure developed by Childs for an annular seal. Such coefficients are the functions of seal geometry, rotor speed, liquid properties, and differential pressure. They are defined for the central shaft position in clearance and are used for the analysis in the linearized statement. In nonlinear analysis it is supposed that the ring has inertia, and it is affected by hydrodynamic and friction forces. With such statement, solution is found by direct integration of the rotor system motion equation with the determination of a seal reaction on the rotor and the ring at every integration step. To define the seal reaction, the algorithm, that allows determination of the annular seal hydrodynamic force with consideration of the rotor motion and tracing such force influence on the rotor and ring dynamics, was developed. It is shown that sometimes hydrodynamic force appearing in seals may exceed the rings friction, and they start moving, changing the rotor dynamic characteristics.

Keywords:

rotor dynamics, nonlinear models, floating rings, Dynamics R4

References

1. Ivanov A.V. Turbonasosnye agregaty kislorodno-vodorodnyh zhidkostnykh raketnykh dvigatelei (Turbopumps for oxygen-hydrogen liquid-propellant rocket), Voronezh, Voronezhskij gosudarstvennyj technicheskij universitet, 2011, 283 p.
2. Ivanov A.V.Vestnik Saratovskogo gosudarstvennogo tekhnicheskogo universiteta , 2012, no. 3 (34), ch. 1, pp.303-308.
3. Nikiforov A.N. Snizhenie urovnya vibracij bystrovrash’ajush’ihsya rotorov za schet ih gidrodinamicheskogo vzaimodejstviya s uplotnitel’nymi kol’cami (Decrease in vibration level of high-speed rotors due to their hydrodynamic interaction with sealing rings), PhD thesis, Moscow, IMASH RAN, 2008, 172 p.
4. Childs D.W. Turbomachinery rotordynamics: phenomena, modeling and analysis, New York, John Willey & Sons Inc.,1993, 476 p.

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