Gas-dynamic reasons for vibrations origination in turbopump units

Aeronautical and Space-Rocket Engineering

To the 100th anniversary of B.V. Ovsyannikov


DOI: 10.34759/vst-2021-3-54-62

Аuthors

Kochetkov Y. M.1*, Burova A. Y.2**

1. Keldysh Research Centre, 8, Onezhskaya str., Moscow, 125438, Russia
2. Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: swgeorgy@gmail.com
**e-mail: frambe@mail.ru

Abstract

Powerful energy-propulsion units differ from the others by the elements, subassemblies and structures associated with powerful turbo-machines and gas generators as a part of them. The high rpm of the turbines shafts rigidly affects the structure, which may lead to its destruction. High-frequency vibrations, which occurrence is possible in the turbopump units of liquid propellant rocket engines, are of especial danger.

The purpose of the study consists in the following:

– the problem setting of high-frequency instability prediction in powerful energy propulsion units on the example of the turbopump unit of a liquid propellant rocket engine, determining instability parameters in this subassembly and required ratio of the turbulent gas field parameters;

– formalization of vibrations automatic monitoring condition by the digital methods of multi-step discreet Fourier transform without performing hardware-consuming multiplication operators.

The presence of constant free volume is necessary for setting constant stable turbulence mode for the high frequency stability ensuring. This fact actualizes the study of the additional possibility of setting constant stable turbulence mode with the gas or liquid flow velocity increase. Namely turbulence is in charge of high-frequency instability, and, hence, vibrations occurrence. Turbulent flow originates practically always in turbopump units.

The occurring high-frequency instability of the process, accompanied by the oscillation of the working fluid particles inside the turbopump unit, impacts the walls of the apparatus that restrains the working volume. The walls of this apparatus begin reacting to the force impacts of the gas and naturally impede it, generating vibrations of the structure. The effect on the system occurs as the impact of a compelled force in the form of a harmonic component coming from the gas. The equation of the oscillating link for the structure will look like a second-order differential equation with respect to the walls displacements.

The study employed the principles of vibrations diagnostics of liquid propellant rocket engines on the example of a turbopump unit by digital methods of a multi-stage discrete Fourier transform.

An increase in the vibration level of liquid propellant rocket engines may lead to the increased thermal loads with subsequent possible burnouts of the walls of the turbopump assembly units. This requires quality improving of the vibrations diagnostics of liquid propellant rocket engines and increasing the information content of methods employed for the level control of these vibrations.

Vibration diagnostics may and should be ensured with the software and hardware for digital signal processing from signaling sensors using digital filtering and discrete Fourier transform of such signals. The term «unerroric» (from the Latin «errare») in relation to such digital signals deductive processing defines an active process of the errors level reducing in digital signal processing when setting various values of integer difference coefficients of digital difference filters applied for multi-stage discrete Fourier transform. Such unerroric reduces the error of automatic vibration control.

Gradual tightening of the requirements for the liquid rocket propellant engines reliability contributes to the problem actualization of such engines vibrations diagnosing under conditions of their mass production.

Keywords:

turbopump unit, high-frequency instability, vibration diagnostics, difference filtering, turbulent flow, digital signal

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