齿轮泵多连通容积内空化演变过程及其影响研究

发布时间：2018-01-20 16:03

本文关键词： 齿轮泵空化空化演变流体动力学空化产热　出处：《北京理工大学》2015年博士论文　论文类型：学位论文

【摘要】：外啮合齿轮泵因结构简单、工作可靠被广泛应用于液压传动系统。随着工业应用和环境保护要求的提高，，齿轮泵正朝着低噪声、低流量脉动以及高压高速化的方向发展。通常条件下由于回路的背压有限，入口压力较低，齿轮泵容易发生空化，析出的气体对齿轮泵的工作特性产生不利影响。因此，空化问题是齿轮泵研究中的一个重要方向。本文针对当前油液空化模型与齿轮泵流体动力学仿真模型的不足，围绕着外啮合齿轮泵内的空化演变过程和空化对齿轮泵工作特性的影响两条主线展开了系统的研究，运用理论建模、CFD仿真和试验分析相结合的研究手段，构建了基于集中参数法的齿轮泵多连通容积空化演变模型，揭示了齿轮泵内的空化演变规律，为进一步提高齿轮泵设计方法和探究空化与其它物理现象的耦合规律提供了有力工具，具有重要的理论和工程应用价值。通过考虑油液中空气析出与消解过程的时变性，建立了密闭容积内油气两相的动态空化模型，推导了油液属性（如密度和有效体积弹性模量）与含气率之间的本构关系，继而通过试验验证了该模型的有效性，并解释了密闭容积压缩膨胀过程中油液密度的“迟滞”现象。研究表明，油液密度主要受质量含气率影响而油液有效体积弹性模量主要受体积含气率影响；油液膨胀过程中空气的析出速率要大于压缩过程中空气的消解速率。将密闭容积内油气两相动态空化模型推广至连通容积，综合考虑容积内空气的析出和消解、相邻连通容积之间的质量交换以及容积自身体积的变化，推导了含气率微分方程。应用该方程建立了泵入口节流段的集中参数模型，研究了泵入口两相临界流效应，进而获得了喉口直径、油箱压力以及空气析出系数等对临界压力和泵极限供油转速的影响规律。结果表明，临界状态下节流段喉口区油液的流速等于声速；减小空气析出速率对改善齿轮泵空化性能有重要作用。将外啮合齿轮泵等效为多个连通的控制容积，建立了基于集中参数法的齿轮泵多连通容积空化演变模型，分析了气体在不同齿腔内的析出、流动、分布以及消解等演变过程，研究了齿腔内油液压力和含气率的变化特性，揭示了空化对齿轮泵内建压过程、容积效率以及压力流量脉动等特性的影响机理。研究表明，齿轮泵空化时内部泄漏增加，容积效率降低，出口压力脉动变大。最后，研究了空化对齿轮泵开式回路温升特性的影响。分析了回路中元件对外界的散热率，结合气体在齿轮泵流场中的演变行为，提出了空化产热的计算方法。利用液压系统的热力学方程，建立了齿轮泵开式回路的热力学模型，分析了空化时齿轮泵回路的油温变化过程，并通过了试验验证。研究表明，空化产热来源于齿轮泵建压过程中对气体的压缩做功，空化使回路中油液温度上升变快。
[Abstract]:External gear pump has the advantages of simple structure, reliable work is widely used in hydraulic transmission system. With the increase of industrial application and environmental protection requirements, the gear pump is moving towards low noise, low flow pulsation and high speed development direction. Under normal conditions due to the limited pressure loop, entrance pressure is low, easy to gear pump the occurrence of cavitation, adversely affect the working characteristics of precipitation of gas on the gear pump. Therefore, cavitation is an important direction in the study of gear pump. This paper aiming at the deficiency of fluid cavitation model and fluid dynamics simulation model of gear pump, gear pump around the cavitation effect on the characteristic of gear pump the evolution of the two main lines and cavitation are systematically studied, using the theory of modeling, simulation and experimental research method of CFD analysis, constructed the lumped parameter method based on gear The evolving model of pump multi connected volumetric cavitation reveals the evolution law of cavitation in gear pump. It provides a powerful tool for further improving the design method of gear pump and exploring the coupling rule between cavitation and other physical phenomena, which has important theoretical and engineering application value.
By considering the time variability of precipitation and air oil in the digestion process, establishes the dynamic model of gas oil two-phase cavitation within the confined volume, derived oil properties (such as density and effective bulk modulus) and the constitutive relation between the gas holdup, and the validity of the model is verified by experiment, and explain the closed volume compression expansion process of oil density lag. The study shows that the oil density is mainly affected by the quality of gas and effective fluid bulk modulus is mainly affected by the impact of the gas volume rate; oil expansion process air precipitation rate is greater than the compressed air in the process of digestion rate.
The sealed volume of gas oil two-phase dynamic cavitation model is extended to the communication volume, considering the volume of air in the precipitation and digestion, change of mass exchange between adjacent connected volume and volume of their size, derived gas rate differential equation. The lumped parameter model of the pump entrance throttling section has been established using the equation of pump the entrance of two-phase critical flow effect, and then get the influence of throat diameter, tank pressure and air separation coefficient on the critical pressure and pump speed limit control. The results show that the critical state of the throttle section throat oil liquid velocity equal to the velocity; reduce the air release rate has an important role to improve the cavitation performance of gear pump.
The external gear pump is equivalent to multiple connected control volume, a gear pump lumped parameter method based on multi connected volume cavitation evolution model, analyzed the precipitation of gas in different material flow distribution and elimination process, change of oil hydraulic force teeth and gas content. Reveals the cavitation on the gear pump internal pressure process, the influence mechanism of volumetric efficiency and pressure pulsation characteristics. The results show that the gear pump cavitation when the internal leakage increases, the volume efficiency, outlet pressure fluctuation becomes larger.
Finally, study the influence of cavitation rise characteristics of gear pump open loop temperature. Analysis of the circuit components on the outside of the heat dissipation rate, combined with the gas evolution behavior of the gear pump in the flow field, puts forward the calculation method of cavitation heat production. Using the thermodynamic equation of the hydraulic system, a thermodynamic model of a gear pump open loop. Analysis of cavitation temperature of gear pump loop process, and has been verified by experiments. The results show that the compression work of gas from the gear pump cavitation heat pressing process, the temperature of the oil liquid cavitation loop rise faster.

【学位授予单位】：北京理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TH137.51

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