Research On The Mechanism Of Fluid Power Transmission By Shear Stress In Hydroviscous Drive

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.