Investigation And Application Of Free Surface Flow In Curved Channels Under Microgravity

Liquid propellant management technology is one of the key technologies of spacecraft propulsion systems,including the storage,control and transportation technologies of propellant.The unique microgravity environment of space makes surface tension the dominant force in controlling liquid behavior.Due to the surface tension,the flow characteristics are different from the ground.Understanding the flow characteristics of liquid under microgravity is the premise and basis for ensuring the normal operation of the spacecraft propulsion system.Due to the difficulty in obtaining microgravity experimental conditions,the research on liquid flow characteristics under microgravity is still not enough.In this paper,the key mechanism problems in the propellant management process of the surface tension tank are studied:the gas-liquid free surface modeling under microgravity,differential pressure driven-flow along curved channels and curved interior corner flow.On the basis of theoretical research,the design of the surface tension tank is investigated,and a refillable surface tension tank for microsatellites is designed.The main work of the thesis is summarized as follows:?1?Research on gas-liquid free surface approximation modeling under microgravity.Based on the gas-liquid free surface modeling problem under microgravity,this paper proposes a approximation modeling method to replace the gas-liquid free surface governing equation due to the traditional numerical method have some drawbacks,such as the initial value selection,poor convergence and low efficiency.In order to further reduce the calculation amount and improve the calculation efficiency,a double-layer radial basis approximation model is proposed by improving the radial basis approximation model.By layering the variables,large-scale matrix operations in the approximation modeling process are effectively avoided and rounding errors are reduced.The double-layer radial basis approximation model,the radial basis approximation model and the shooting method are compared.The calculation efficiency,success rate and accuracy of the three methods for solving the gas-liquid free surface are tested.Compared with the shooting method,the radial basis approximation model improves the computational efficiency by 73.89%and the success rate to 100%.The computational efficiency of the double-layer radial basis approximation modeling method is further improved by 97.95%compared with the radial basis approximation modeling method,and the root mean square error is only 1/40 of the latter.?2?Research on the differential pressure driven-flow along the curved channel under microgravity.Taken the process of propellant drainage as the background,the differential pressure driven-flow along the curved channel under microgravity is studied theoretically and numerically.Based on the momentum equation,continuous equation and Young-Laplace equation,a one-dimensional theoretical model of the differential pressure driven-flow of the curved channel is established.The effect of the centrifugal force caused by the curve motion on the free surface and pressure loss is fully considered in this model.In order to verify the theoretical model,a series of three-dimensional CFD numerical simulations are performed.It can be seen that the one-dimensional theoretical model solutions have good consistency with the three-dimensional CFD simulation results,and the average relative error and root mean square error between them are only 1.51%and 0.0237.?3?Research on the curved interior corner flow under microgravity.Based on the process of propellant wetting and rewetting in the surface tension tank,the curved interior corner flow under microgravity is studied theoretically and experimentally.By simplifying the curved interior corner flow to the straight interior corner flow with the centrifugal force,and considering the centrifugal force effects on the free surface and the flow resistance function,the governing equation of the curved interior corner flow is established.In order to verify the correctness of the curved interior corner flow theory model,a series of microgravity experiments are carried out with the help of the microgravity drop tower located in the Institute of Mechanics,Institute of Science and Technology,Beijing.The drop tower experimental results are compared with the theoretical results.It is found that there is a good consistency between them.Both theoretical and experimental results show that as the channel curvature increases,the velocity of the liquid increases.?4?Research on the surface tension tank design based on the theory of free surface flow along curved channels.Based on the research on the free surface flow mechanism along the curved channel,the design of the surface tension tank is investigated.Considering the factors of the service life,satellite weight,propellant type,flow rate,maneuver acceleration,ignition,centroid control,vibration environment,which directly affect the performance of the tank,eight design principles to be followed in the design process of surface tension tank are put forward.Three common vane structures—inner vanes,outer vanes,and inner/outer combined vanes—are discussed in detail.The advantages,disadvantages,and applicability of the three vane structures are analyzed.Based on the free surface flow theory of curved channels,the analysis models of three kinds of vane structures are established.Considering the gas-liquid distribution,venting,drainage,acceleration disturbance,a refillable surface tension tank for microsatellites is designed and the design details are revealed.?5?Numerical and experimental research on the flow characteristics of propellant.Considering the economic,time and labor costs,a performance test experiment matrix is designed for the microsatellite refillable surface tension tank designed in Chapter 5 to test the surface tension tank performance under various normal conditions and abnormal conditions.With the help of microgravity drop tower and CFD simulation,the wetting,rewetting,filling and drainage efficiency of the surface tension tank and the performance when subjected to acceleration are tested.The test results show that the filling rate and drainage rate of the surface tension tank meet the design requirements,and the surface tension tank can still work normally under the acceleration environment of 10^-3g.It shows that the combination of theoretical analysis,numerical simulation and microgravity experiment used in the thesis is feasible in the preliminary design process of the surface tension tank.In summary,the thesis conducts in-depth research on the free surface flow along curved channels under microgravity through theoretical analysis,microgravity experiment and numerical simulation,and further enriches the microgravity fluid mechanics system.The application of free surface flow theory in the optimization design of surface tension tank is discussed to provide theoretical support for surface tension tank design,which has great theoretical significance and engineering value for improving the design level of surface tension tank.