摘要
液体粘性传动是流体传动领域中的一个新兴学科分支,其依靠平行旋转圆盘间隙内流体剪切力来传递转矩动力,改变摩擦副间隙即可实现输出转速的调节,在高电压、大中功率水泵及风机的流量调节系统中具有明显节能和较高性价比优势。在此前研究中,一般都忽略了科氏力影响；关于油槽所引起的动压对传动性能影响的研究内容较少。本文以液粘调速离合器中一对摩擦副间隙内流体流动为研究对象,考虑离心力、科氏力、粘度—温度特性及油槽的影响,对其传动机理开展研究,主要内容如下：
第一章,对液粘传动技术特点及其工程应用背景进行阐述。在分析了国内外相关技术研究现状基础上,提出了本文的主要研究内容。
第二章,对液粘调速离合器传动特性的研究。建立了一对摩擦副间隙内流体流动的简化数学模型(忽略油槽和粘度—温度特性影响),采用迭代法求解,获得了近似解析解。文章分析了科氏力、摩擦副间隙及输入压力等因素对流场速度、流量及输出转矩的影响。最后,推导出传动效率计算公式,研究了最大传动效率与摩擦副间隙的关系,并指出传递效率随着输入压力的增加而降低。
第三章,对摩擦副间隙内流体传热现象开展研究。利用计算流体动力学软件Fluent对摩擦副间隙内流体传热进行研究(考虑粘度—温度特性的影响),发现等温边界条件下的计算结果更接近于实验结果。继而分析了摩擦副间距、输入输出转速、输入流量等因素对流场温度的影响。最后,对摩擦盘表面的局部努赛尔数Nu和平均努赛尔数Nuav进行了研究。
第四章,分析了粘度—温度特性对传动性能的影响。利用Fluent计算出摩擦副间隙内流体压力、温度、剪应力及转矩,并将计算结果同定常粘度条件下的计算值进行比较。研究结果表明,在一定条件下,可忽略粘度—温度特性的影响；考虑粘度—温度特性时的传动效率与定常粘度时的传动效率基本一致。
第五章,对摩擦盘表面油槽的研究。利用Fluent对摩擦盘表面加工有油槽的摩擦副间隙内流场进行研究,得到了流场压力、温度、速度、推力及粘性转矩的数值解。研究结果表明油槽引起的动压会削弱从动摩擦盘上的输出转矩。继而研究了油槽深度、数量、面积比、几何形状及油槽倾斜角对传动性能的影响,并提出了油槽设计参数的建议。
第六章,实验验证研究。搭建了液粘调速离合器功能实验台的软、硬件系统。对一对平行摩擦盘间隙内流体压力、温度及转矩传递特性进行了实验研究。此外,对输入流体温度Ti与输出转速ω2之间的关系也进行了实验研究,发现当外负载、输入转速及摩擦副间隙等参数保持不变时,ω2与Ti之间呈近似线性单调递减函数关系。
第七章,对全文的主要研究工作进行了总结。阐述了主要研究结论和创新点,并对课题的后续研究提出了展望。
Hydroviscous drive (HVD for short) is a new branch of fluid power transmission, in which the power is transmitted from the driving disks to the driven ones through the action of the fluid shear force in the oil friction pairs. The output speed of HVD can be regulated by adjusting the clearance between friction pairs. HVD has been widely used in the flow regulation of heavy fans and purmps in the industrial applications. It has porved to be efficient in energy-saving. In the previous works, few authors consider the effect of Coriolis force on the flow in the gap between disks in hydro-viscous drive. In addition, few researchers consider the effect of dynamic pressure caused by oil grooves on the torque transfer performance and transmission efficiency. The object of this dissertation is to explore the basic operation principle of HVD with consideration of the effects of centrifugal and Coriolis forces, viscosity-temperaute characteristics, and oil grooves. The main contents are as follows:
In chapter 1, the technical characteristics of HVD and its engineering applications are briefly introduced. A review of HVD related technologies is presented. Then the main research contents are put forward.
In chapter 2, the transmission characteristics of HVD are studied. A simplified mathematical model of the flow between a pair of disks in HVD is established without consideration of the effects of viscosity-temperaute characteristics and the grooves. An approximate solution to the model is obtained by means of iteration method. The effects of Coriolis force and the gap on the flow velicities, the rate of flow and viscous torque are analyzed. Then the formular of HVD's transmission efficiency is derived. The relationship between the maximum transmission efficiency and the clearance is studied. It points out that transmission efficiency decreases as input pressure increases.
In chapter 3, the heat transfer in the gap of friction disks in HVD is investigated. The flow considering the effect of viscosity-temperaute characteristics is solved by means of computational fluid dynamics (CFD) code FLUENT. Numerical results are obtained. It is found that the numerical resulet of temperature under isothermal boundary condition is in agreement with experimental data. The effect of the factors such as the gap, input and output speed, input flow rate on the temperature distribution is analyzed. Then the local Nusselt number Nu and the average Nusselt number Nuav are investigated respectively.
In chapter 4, the effect of viscosity-temperaute characteristics on the HVD is investigated. Numerical results of pressure, temperature, viscous stress and torque are obtained by FLUENT. The results show that the effect of viscosity-temperaute characteristics on the flow can be ignored under certain condition. The transmission efficiency considering viscosity-temperaute characteristics is almost identical to that under constant viscosity.
In chapter 5, the effect of the oil grooves on the driven disk surface is discussed. The flow between a grooved and a flat disk is investigated by FLUNET. Numerical results related to the flow such as pressure, temperature, velocities, axial force and viscous moment are obtained. It shows that the viscous torque on the driven disk is severely weakened by the dynamic pressure caused by oil grooves. Then the effects of groove depth, grooves number, ration of the grooved area to total area, groove geometry and angle of inclination on the HVD's performance are discussed. The relevant parameters for the optimization design of groove are proposed.
In chapter 6, experimental studies are carried out. The function test bench of HVD is developed, and the hardware and the software of the test bench are designed. The experimental studies of flow pressure, temperature and torque transfer characteristics are carried out respectively. The relationship between input flow temperature and the output speed is also investigated experimentally. The results show that output speed decreases linearly as input flow temperaute increases when the load, input speed and clearance keep constant.
In chapter 7, the main work of this dissertation is summarized. Conclusions and innovative points are introduced. Finally, the subsequent research on the HVD is prospected.
引文
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