Mathematical simulation of dynamic processes in the propellant feed system of launch vehicle space stages in microgravity

Abstract

The steady trend towards the development of space stages capable of putting into orbit several spacecraft with a single launch vehicle (LV) by multiple restarts of the stage sustainer engine in microgravity calls for the solution of a complex of problems aimed at assuring the continuity of the liquid propellant components in the propulsion system feed lines. The aim of this paper is mathematical simulation of dynamic processes in the propellant feed system of LV space stages to assess its operability in microgravity in passive flight segments with an operating attitude control and stabilization system and at sustainer engine starts in periods with minimum tank filling levels. To solve these problems, the authors developed a methodology based on the finite-element method, the volume of fluid method, 3D CAE technologies, and the impedance method. The paper presents mathematical models of dynamic processes in a liquid-propellant LV space stage propulsion feed system that has a capillary propellant management system. The mathematical models of spatial oscillations of a LV space stage with a spacecraft developed with account for the design features of the in-tank devices and propellant feed systems made it possible to determine the mode shapes and the motion parameters of the free surfaces of the propellant components in the tanks (the oxidizer tank and the fuel tank) of the stage and identify flight regimes potentially dangerous in terms of the possibility of the pressurization gas or the substituent gas dissolved in the propellant components penetrating into the engine propellant lines. Quantitative estimates of the propellant management device operability in these regimes were obtained. The mathematical models of hydrodynamic processes in a space stage liquid propellant propulsion system presented in this paper allow one to identify sustainer engine start conditions in which the pressurization gas may penetrate in the engine propellant lines and determine the parameters of dynamic processes in a space stage feed system at sustainer engine starts and cutoffs. The mathematical model of low-frequency hydrodynamic processes in a space stage feed system at sustainer engine starts and cutoffs was tested using the results of experimental studies (on water) of space stage sustainer engine cutoffs, and the calculated oscillation frequencies and amplitudes were shown to be in satisfactory agreement with the experimental ones.