Research On Measurement Method Of Residual Propellant Based On Helmholtz Resonance

On-orbit propellant volumetric measurement is important for spacecraft life prediction and long-term on-orbit operations,but it is not easy to measure the volume of propellant because of the microgravity and cryogenic environment.While traditional methods have various disadvantages on on-orbit volumetric measurement,the cavity-resonance measurement may be a possible alternative.This paper investigates the basic principle of cavity resonance measurement method and gives mathematical models based on the one-dimensional acoustic plane wave approximation to analyze specific parameters which are important in on-oribit conditions.The present model is verified by numerical simulations and ground experiments.First,the one-dimensional resonance model based on the plane acoustic wave hypothesis is established.The actual tank structure is simplified,and the whole process of the sound wave propagation is divided into combinations of different models,including variable cross-section disturbance propagation,reflection of plane wave,and half-space circular sound source vibration,then the dynamical matrix of resonance model is built.The theoretical model is verified by the literature,meanwhile the incompressible propellant assumption is acceptable,which provide support for subsequent research.Secondly,parameters analysis is implemented by numerical simulations based on COMSOL,including the hemispherical structure of the tank,steady/unsteady non-flat continuous propellant-gas interface,and droplet in the tank.Results show that structures of a hemispherical tank can influence the resonant frequency,the present model can optimizationally compensate such effect.The continuous non-flat propellant-gas interface changes the resonant frequency.A flatter interface leads to smaller influence.On the other hand,the unsteady low-frequency low-amplitude wave-like movement of the propellant-gas interface imposes negligible effect on the resonant frequency of the tank.Finally,effects of the droplet in cavity with small size and location far from the inlet of the tank is limited,but will be serious when the droplet is in the neck.Finally,ground experiment is designed for the verification of theoretical and simulation results.The resonance is aroused by the flow-excited acoustic-vortex interaction,meanwhile a virtual instrument software based on Lab VIEW is developed.Due to the ground conditions,only several schemes of different parameters are designed,including the cylindrical and non-cylindrical tanks with identical volume,axial position and volume of droplets in the cavity,and sloshing liquid.Results of theory and simulation are verified by experiments,which proves the effectiveness of the one-dimensional model in predicting the resonance frequency of the tank.