No 1 (2021) Technical mechanics
Technical mechanics, 2021, 1, 29 - 36
Mathematical simulation of hard excitation of cavitation self-oscillations in a liquid-propellant rocket engine feed system
Dolgopolov S. I.
Dolgopolov S. I.
Institute of Technical Mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine
Hard self-oscillation excitation differs from soft excitation in that self-oscillations are set up only if
the initial departure of an oscillating system from equilibrium is strong enough. Experimental studies of
cavitation oscillations in hydraulic systems with cavitating pumps of liquid-propellant rocket engines
((LPREs) include works that describe hard excitation of cavitation oscillations. By mow, hard excitation
regimes have not been explained theoretically, to let alone their mathematical simulation.
This paper presents a mathematical model of hard excitation of cavitation oscillations in a LPRE feed
system, which comprises a mathematical model of cavitation self-oscillations in a LPRE feed system that
accounts for pump choking and an external disturbance model. A mechanism of hard excitation of cavitation
oscillations in a LPRE feed system is proposed. It is well known that hard excitation of cavitation
self-oscillations may take place in cases where the pump feed system is near the boundary of the
cavitation self-oscillation region. In this case, the self-oscillation amplitudes are small, and they
are limited only by one nonlinearity (cavity volume vs. pump inlet pressure and flow relationship).
Under excitation of sufficient intensity, the pump inlet pressure and flow find themselves in the choking
characteristic; this may be responsible for choking and developed cavitation self-oscillations, which
remain of interrupted type and do not go into the initial small-amplitude oscillations even after
excitation removal. A mathematical simulation of hard excitation of cavitation self-oscillations was
conducted to determine the parameters of cavitation self-oscillations in a bench feed system of a test
pump. The simulation results show that without an external disturbance the pump system exhibits
small-amplitude self-oscillations. On an external disturbance, developed (interrupted) cavitation
oscillations are set up in the system, which is in agreement with experimental data. The proposed
mathematical model of hard excitation of cavitation self-oscillations in a LPRE feed system allows
one to simulate a case observed in an experiment in which it was possible to eliminate cavitation
self-oscillations by an external disturbance.
liquid-propellant rocket engine, inducer-equipped centrifugal pump, cavitation, cavitation self-oscillations, hydrodynamic model, choking, hard excitation
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