热力学敏感流体空化流动三维数值模拟研究

发布时间：2018-05-28 15:23

本文选题：热力学敏感流体 + 空化流动　；参考：《哈尔滨工业大学》2016年博士论文

【摘要】：近年来,随着载人航天和深空探测的需要,对液体运载火箭的推力提出了越来越高的要求。用作推进剂的低温流体在流经推进系统时容易发生空化,使得内部流场变得不稳定而引起强烈的机械振动,从而降低了液体火箭发动机的可靠性和推力性能。用作进剂的液氢和液氧等热力学敏感流体介质在空化过程表现出明显的热力学效应,使得空化流动变得更加复杂。因此,掌握预测热力学敏感流体空化流动特性的数值计算方法以及获得热力学效应对空化流动影响机理具有重要理论意义和应用价值。本文采用数值计算与试验数据相结合的方法,开展了热力学敏感流体定常和非定常空化流动三维数值模拟研究,主要研究内容和成果如下:基于均质平衡流模型,建立了计算热力学敏感流体空化流动问题的基本数学模型和数值方法。通过CEL(CFX Expression Language)语言对CFX软件进行二次开发,将液氢、液氮以及氟化酮流体介质的物理属性随温度变化的关系函数引入到求解软件中,在能量方程中通过添加能量源项的方法考虑了汽化潜热的影响。同时将空化模型和湍流模型添加到CFX求解器中,并与基本控制方程耦合,形成了计算空化流动问题的基本数值方法。基于热力学敏感流体定常空化流动特点,评价了修正经验常数和引入热力学效应的空化模型对热力学敏感流体空化流动的适用性,建立了计算热力学敏感流体定常空化流动的三维数值模拟方法。针对三种常用的空化模型,修正蒸发常数和凝结常数后的Zwart空化模型和Merkle空化模型在预测空化流场温度和压力方面优于Kunz模型,但是数值计算结果与试验数据仍有一定的差异。基于汽液两相间的热扩散方程和能量方程给出了考虑热力学效应的修正Zwart空化模型,改进后的Zwart空化模型实现了对热力学敏感流体定常空化流场的准确预测。基于本文建立的计算定常空化流动数值方法,开展了不同热力学敏感流体定常空化流动特性研究,掌握了空化热力学效应影响机理。通过对液氢、液氮绕圆头水翼和尖顶拱模型开展的三维定常空化流动计算分析,获得了空化流场温度、压强、混合区液/汽体积分数、两相间质量转化率以及典型热力学参数变化特性,给出了流体介质物理属性对空化流场特性影响规律,揭示了空化热力学效应影响机理。基于空化湍流流场流动特点,对PANS湍流模型中控制参数进行了敏感性分析,建立了计算热力学敏感流体非定常空化流动的三维数值模拟方法。通过减小PANS湍流模型中的控制参数,实现从雷诺时均化RANS方法到直接数值模拟DNS方法的过渡,改善了对空化流场湍流粘度和小尺度旋涡的描述。通过与试验数据对比,验证了改变控制参数的PANS湍流模型对热力学敏感流体非定常空化流动空泡演变过程和流动细节预测的有效性。基于本文建立的计算非定常空化流动数值方法,开展了氟化酮、液氢以及液氮三种介质绕带攻角水翼非定常空化流动研究,掌握了空化流场非定常空泡演变机理。通过分析空化流场旋涡结构、涡量传输、流体动力、速度矢量以及温度梯度变化等特性,揭示了热力学效应下空化流场空泡生成-发展-脱落-溃灭复杂的演变过程机理。
[Abstract]:In recent years, with the need of manned spaceflight and deep space exploration, the thrust of the liquid launch vehicle is becoming more and more demanding. The low temperature fluid used as the propellant is easy to cavitation in the propulsion system, which makes the internal flow field unstable and causes strong mechanical vibration, thus reducing the reliability of the liquid rocket engine. The thermodynamic effect of the liquid hydrogen and liquid oxygen, which is used as the liquid hydrogen and liquid oxygen, shows obvious thermodynamic effects in the cavitation process, which makes the cavitation flow more complicated. Therefore, the numerical calculation method for predicting the characteristics of the cavitation flow in the thermodynamic sensitive fluid and the mechanism of the effect of the thermodynamic effect on the cavitation flow have been obtained. The main research contents and results are as follows: Based on the homogeneous equilibrium flow model, the problem of calculating the thermodynamically sensitive fluid cavitation flow problem is established. The basic mathematical model and numerical method are developed for two times through the CEL (CFX Expression Language) language. The relation function of the physical properties of liquid hydrogen, liquid nitrogen and fluoridated fluid medium with the temperature change is introduced into the solution software. The influence of the latent heat of vaporization is considered by adding energy source term in the energy equation. At the same time, the cavitation model and turbulence model are added to the CFX solver and coupled with the basic control equations. The basic numerical method for calculating the cavitation flow problem is formed. Based on the characteristics of the constant cavitation flow of the thermodynamic sensitive fluid, the cavitation flow model of the modified empirical constant and the thermodynamic effect is evaluated for the thermodynamically sensitive fluid flow. For three commonly used cavitation models, the Zwart cavitation model and the Merkle cavitation model are superior to the Kunz model in predicting the temperature and pressure of the cavitation flow field. The experimental data still have a certain difference. Based on the heat diffusion equation and the energy equation between the two phases of the vapor and liquid, the modified Zwart cavitation model considering the thermodynamic effect is given. The improved Zwart cavitation model realizes the accurate prediction of the steady cavitation flow field of the thermodynamically sensitive fluid. The characteristics of constant cavitation flow of different thermodynamically sensitive fluids have been studied, and the effect mechanism of the cavitation thermodynamic effect is mastered. The temperature, pressure, liquid / vapor volume fraction of the mixing zone and the mass conversion rate between the two phases are obtained by the calculation and analysis of the three-dimensional steady cavitation flow of liquid hydrogen, liquid nitrogen around the round head hydrofoil and the spires arch model. The influence of the physical properties of the fluid medium on the characteristics of the cavitation flow field is given and the influence mechanism of the cavitation thermodynamic effect is revealed. Based on the flow characteristics of the cavitation turbulent flow field, the sensitivity of the control parameters in the PANS turbulence model is analyzed and the unsteady cavitation flow is built to calculate the thermodynamically sensitive fluid. By reducing the control parameters in the PANS turbulence model, the transition from the Reynolds averaged RANS method to the direct numerical simulation DNS method is realized. The description of the turbulence viscosity and the small scale vortex in the cavitation flow field is improved. By comparing with the experimental data, the PANS turbulence model that changes the control parameters is verified by the thermodynamic model. The evolution process of the unsteady cavitation flow and the effectiveness of the flow detail prediction are studied. Based on the numerical method of unsteady cavitation flow, the unsteady cavitation flow of the hydrofoil, liquid hydrogen and liquid nitrogen with three kinds of medium angle attack angle hydrofoil is studied. The mechanism of the unsteady cavitation evolution of the cavitation flow field is grasped. The characteristics of vortex structure, vorticity transmission, fluid dynamics, velocity vector and temperature gradient change in cavitation flow field are analyzed, and the mechanism of the complex evolution process of cavitation flow formation, development, exfoliation and collapse under the thermodynamic effect is revealed.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O35

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