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温度敏感凝胶推进剂中气泡运动特性研究

BUBBLE DYNAMICS IN TEMPERATURE SENSITIVE NON-NEWTONIAN GEL PROPELLANT

  • 摘要: 凝胶推进剂是一种具有剪切变稀特性的非牛顿流体, 其流变性质还会受到温度的影响. 在凝胶推进剂制造和装填过程中, 极易出现气体混入的情况, 这会直接影响发动机的工作性能. 为了探究气泡在凝胶推进剂中的运动特性, 文章采用流体体积法(VOF)模拟研究了静止凝胶中单气泡在浮力作用下的上升过程, 其中凝胶的黏性以改进的Carreau-Yasuda模型描述, 通过连续表面力(CSF)模型计算凝胶的表面张力. 通过改变凝胶中温度、流变指数、特征时间和表面张力等参数, 观察非牛顿流体中黏度和剪切速率的变化, 进而得到其对气泡的纵横比、重心位置和速度的影响. 并探讨了不同温度下, 流变指数与特征时间两种参数对气泡运动的影响. 研究结果表明, 凝胶的高黏性会阻碍气泡的运动并限制气泡的形变, 导致气泡的形变不显著; 温度的升高会降低凝胶的黏度, 从而显著影响气泡的运动轨迹和形态, 使得气泡上升速度增加并增加其变形; 流变指数和特征时间会通过改变液体性质进而对气泡的速度和纵横比产生影响; 此外, 表面张力的变化会对气泡底部的变形产生较大影响.

     

    Abstract: Gel propellants, which are classified as non-Newtonian fluids exhibiting shear-thinning effects, have rheological properties that are influenced by temperature. During the manufacturing and filling process of gel propellants, it is quite common for gas to be inadvertently mixed in, which can have a detrimental impact on engine performance. In order to comprehensively investigate and analyze the intricate dynamics of bubble motions within gel propellants, this paper adopts the volume of fluid (VOF) method to simulate the rising process of a single bubbled driven by buoyancy in static gel propellants, in which the extended Carreau-Yasuda model coupled with temperature is used for the viscosity of the gel propellants, and the surface tension of the gel is calculated using the continuum surface force (CSF) model. By changing the parameters such as temperature, rheological index, characteristic time, and surface tension in the gel, we observed the variation of viscosity and shear rate in the non-Newtonian fluid. Subsequently, we studied their effects on the aspect ratio, centroid position, and velocity of the bubbles. The study also examined the influence of two parameters, namely rheological index and characteristic time, on the motion of bubbles at various temperatures. The results show that the high viscosity of gel propellants will hinder the movement of the bubbles and limit its deformation, so the deformation of the bubble is not significant; the increase in temperature will reduce the viscosity of gel propellants, which will significantly affect the trajectory and shape of the bubble increasing the rising speed of the bubble and intensifying the deformation; the rheological index and characteristic time will affect the velocity and aspect ratio of the bubble by changing the liquid properties; moreover, it is found that the alteration of surface tension will exert a greater impact on the deformation occurring at the bottom part of the bubble.

     

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