Generalization of Experimental Elasticity of Cavitation Bubbles in LRE Pumps that Differ Significantly in Size and Performance
Keywords:liquid rocket engine, POGO-oscillations, cavitating pump, frequency of oscillations of cavitation bubbles, experimental and computational method, elasticity, volume and resistance of cavitation bubbles, and number of initial cavitation.
Introduction. Consideration of cavitation phenomena in liquid rocket engine (LRE) pumps is necessary for determining the frequency characteristics of the engine, when calculating transient processes in propulsion systems during engine start-up and stop, and, especially, for addressing the problem of ensuring the stability of longitudinal oscillations of liquid rockets (POGO-oscillations).
Problem Statement. Currently, the theoretical determination of the characteristics of cavitation flows in LRE pumps has not been widespread because of extremely low accuracy. The disadvantage of the existing experimental and calculated dependences of elasticity, volume, and resistance of cavitation bubbles on the mode parameters is the limited range of cavitation numbers for which these dependences are reliable.
Purpose. The purpose of this research is to determine the elasticity, volume, and resistance of cavitation bubbles in LRE pumps in the whole range of existence of cavitation bubbles, based on the results of dynamic tests of 26 pumps that differ significantly in purpose, size, and performance.
Materials and Methods. The information and analytical method, the methods of the theory of oscillations, the impedance method, and the method of least squares have been used.
Results. It has been shown that the experimental values of the elasticity of cavitation bubbles for different pumps generally agree satisfactorily with each other. The dependence of the relative elasticity of cavitation bubbles on the number of cavitation and the flow coefficient has been approximated with the use of the formula that allows describing the cavitation phenomena in pumps in the entire range of existence of cavitation bubbles. Three types of deviations of experimental frequencies of oscillations from the natural frequencies of oscillations of fluid in a hydraulic system with a cavitating pump have been described. The first and second types of deviations are caused by the interaction of the fluid and the structure of the feed pipeline, while the third one is associated
with developed self-oscillations of cavitation bubbles.
Conclusions. Semi-empirical dependences of elasticity, volume, and resistance of cavitation bubbles in LRE pumps on the mode parameters in the entire range of existence of cavitation bubbles have been built.
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