Fangwei Xie

Drive Characteristics of Viscous Oil Film Considering Temperature Effect

Taking account of temperature and the effect of pressure difference and inertia force on oil film, the analytic solutions for pressure, radial velocity, and transferred torque were derived. The results show that considering the effect of temperature, the pressure reduces at the same radius and inertia force makes the pressure decrease. Compared with the pressure decrease caused by the inertia force, the radial velocity caused by the pressure difference is very small and can even be neglected. As the rotational velocity difference increases, the transferred torque also increases. Meanwhile, the transferred torque reduces when considering the effect of temperature.

Oil film hydrodynamic load capacity of hydro‐viscous drive with variable viscosity

Purpose – The purpose of this paper is to reveal the characteristics of hydrodynamic load capacity and torque transferred by oil film with variable viscosity, and the effect of groove number, width and depth on the hydrodynamic load capacity and torque transfer.Design/methodology/approach – The radial temperature of friction pair and viscosity of YLA‐N32 hydraulic oil were measured through experiments, and a viscosity‐diameter expression was deduced using polynomial fitting method. Analytical expressions for hydrodynamic load capacity and torque of the oil film were deduced based on hydrodynamic lubrication theory.Findings – The investigation shows the hydrodynamic load capacity and transferred torque with variable viscosity are much less than that with constant viscosity. Load capacity increases with the increase of groove depth which is the most significant influence factor, while it has the least influence on torque. Groove width has great influence on load capacity and torque. The load capacity increa...

Thermal Behavior of Multidisk Friction Pairs in Hydroviscous Drive Considering Inertia Item

Considering the influence of the inertia item on temperature distribution of multidisk friction pairs in hydroviscous drive (HVD), transient temperature models are derived with the aim of revealing the effect of engagement pressure, lubricant viscosity, viscosity–temperature correlation, surface roughness and the ratio of inner and outer radius of disks on temperature distribution. The results indicate that unsteady temperature gradient can be avoided by matching the suitable materials for multidisk friction pairs. The average temperature for the case of neglecting the inertia item is lower than that of the case of including the inertia item. It is shown that during the soft-start, the temperature along the radial direction achieves its peak value near the outlet and keeps decreasing along the axial direction; while after the engaging process, the temperature distribution tends to be uniform. It is also shown that the decrease of engagement pressure, surface roughness and the ratio of inner and outer radius of disks can reduce temperature gradient effectively as well as the increase of lubricant viscosity. The average temperature for the case of including the viscosity–temperature correlation is much higher than that for other cases.

Numerical simulation research on effect of oil groove forms on thermal behavior of friction pair in hydro-viscous clutch

Purpose – The purpose of this paper is to study the influence of different cross-sectional shapes (rectangular, trapezoidal, oval and triangular) and layout forms of oil grooves (radial, circumferential, inclined, compound, helical and double-helical), and determine the optimal section shape and layout form of oil grooves on the temperature field. Design/methodology/approach – Heat conduction theory model was established based on startup characteristics and friction heat principle of hydro-viscous clutch (HVC), and then the theoretical expression of angular velocity of the friction pair and control pressure were deduced, and the heat flux and its distribution on friction disk and separator disk were calculated. Finally, the finite element method was used to solve the temperature field of the friction pair. Findings – The studies show that the circumferential oil groove got the highest temperature, and on the surface of all other structures, hot spots appear with different sizes and temperatures, and the m...

Effect of deformed interface on hydro-viscous drive characteristics

In this article, the effect of the deformed interface on the hydro-viscous drive characteristics was investigated through a three-dimensional fluid simulation and experiments. The main parameters such as pressure field, velocity field, and torque transferred by the oil film were simulated in FLUENT software in the light of the principle of the computational fluid dynamics. The results found that the dynamic pressure and velocity of the oil film goes up gradually along the radial direction, and the dynamic pressure at zone with groove is much higher than that without groove due to the hydrodynamic effect. After the interface deforming, the dynamic pressure decreases; while the torque transferred by the oil film increases slightly. Furthermore, a special hydro-viscous drive test-bed was developed to verify the correctness and validity of the theoretical results.

Numerical Evaluation on Heat Transport Characteristics Between Al2O3 and ZnO Materials in Nanoscale Situation

The aim of this article is to provide a systematic method to perform numerical evaluation on the cross-plane thermal conductivity of Al(2)O(3)/ZnO film interface. The Equilibrium Molecular Dynamics (EMD) simulations method is used to investigate the cross-plane thermal conductivity of Al(2)O(3)/ZnO film interface along the direction of Z axis at different equilibrium temperature and film interface thickness. The Buckingham two-body potential function and Green-Kubo linear response theory are used for modeling and calculation. The results show that the size effect is obvious. It implies the film interface thickness is 23.4-52 Å and the equilibrium temperature is 300-600 K. The cross section thermal conductivity of Al(2)O(3)/ZnO film interface increases with the increase of interface thickness, and decreases with the increase in equilibrium temperature.

The effect of N-doping on the electronic structure of graphene nanoribbon

To analyse the effect on electronic structure of nitrogen-doped graphene nanoribbons, the parameters such as the lattice, band structure, density of states of intrinsic graphene nanoribbon, N-doped graphene nanoribbons are calculated by using first-principle method. The results demonstrate that the band gap of graphene nanoribbon mainly comes from the new surface states in the edge. The N-doping in the middle of graphene nanoribbon has less influence on the band gap performance than in the edge region, which indicates the atoms in the edge do great contribution to the band gap properties. The N-doping makes the band gap narrower; the sharp changes of the band gap also show that the N-doping is a promising candidate to make the n-type graphene structures.

Numerical investigation of cavitation effect on two-phase oil film flow between a friction pair in hydro-viscous drive

This paper describes a three-dimensional computational model of oil film between a friction pair to investigate the characteristics of both single-phase and two-phase flow of the oil film in hydro-viscous drive. For the single-phase oil film, the distribution of pressure is very regular from inlet to outlet of the friction pair; its value decreases gradually. On the other hand, the temperature in the middle part of the oil film is considerably lower and the velocity increases at a faster rate near the outlet and has a parabolic profile, which is mainly caused by both the shear stress and extrusion force. By comparison, the physical phenomena at the outlet of the oil film are entirely different for two-phase flow with cavitation. For two-phase simulation of flow with cavitation, we first obtain the volume fraction of air bubbles at rotation speeds of 500, 1000, 2000, 3000, and 4000 revolutions/min. With increase in the rotation speed, the volume fraction of air bubbles increases, and their maximum value becomes even greater than 10%. Furthermore, due to cavitation, the torque transferred by the oil film is no longer linear with the rotation speed; its value decreases gradually. These results are important in the study of hydro-viscous drive and its applications; they shed a new light on the mechanism of power transmission through oil film in the presence of cavitation.

Dynamic transmission of oil film in soft-start process of HVD considering surface roughness

Purpose n n n n nThe purpose of this paper is to study the dynamic transmission of the oil film in soft start process of hydro-viscous drive (HVD) between the friction pairs with consideration of surface roughness, and obtain the distribution law of temperature, velocity, pressure, shear stress and viscous torque of the oil film. n n n n nDesign/methodology/approach n n n n nThe revised soft-start models of HVD were derived and calculated, including average Reynolds equation, asperity contact model, load force model and total torque model. Meanwhile, a 2D model of the oil film between friction pair was built and solved numerically using computational fluid dynamics (CFD) technique in FLUENT. n n n n nFindings n n n n nThe results show that the maximum temperature gradually reduces from the intermediate range (z = 0.5 h) to the inner side of the friction pair along the direction of oil film thickness. As the soft-start process continues, pressure gradient along the direction of the oil film thickness gradually changes to zero. In addition, tangential velocity increases and yet radial velocity decreases with the increase of the radius. n n n n nOriginality/value n n n n nIn this paper, it was found that the viscous torque calculated by the numerical method is smaller than that by the CFD model, but their overall trend is almost the same. This also demonstrates the effectiveness of the numerical simulation.

Effects of structural parameters of oil groove on transmission characteristics of hydro-viscous clutch based on viscosity-temperature property of oil film

Purpose n n n n nThe purpose of this paper is to study the influence of structural parameters of oil groove (such as central angle number, depth and so on) on pressure, flow, load capacity and transmitted torque between friction pairs of hydro-viscous clutch. n n n n nDesign/methodology/approach n n n n nAccording to the working process of friction pairs of hydro-viscous clutch, mathematical models of hydrodynamic load capacity and torque transmitted by the oil film were built based on viscosity-temperature property. Then analytical solutions of pressure, flow, load capacity and transmitted torque were obtained; effects of central angle of oil groove zone and friction contact zone, oil film thickness, number of oil grooves on pressure, flow, load capacity and torque were studied theoretically. n n n n nFindings n n n n nThe research found that the central angle of oil groove zone, number of oil grooves and oil groove depth have similar effects on flow, which means that with the increase of central angle, number or depth of oil grooves, the flow also increases; pressure in friction contact zone and oil groove zone drops along radial direction, whereas its value in oil groove zone is higher. With the increase of the central angle of oil groove zone, pressure in friction contact zone and friction contact zone rises, and the load capacity increases, whereas the transmitted torque drops. Number of oil grooves has little effect on load capacity. When the oil film thickness increases, its flow increases accordingly, whereas the pressure, load capacity and transmitted torque drops. Meanwhile, the transmitted torque decreases with the increase of number of oil grooves, whereas the oil groove depth nearly has no effects on transmitted torque. n n n n nOriginality/value n n n n nIn this paper, mathematical models of hydrodynamic load capacity and torque transmitted by oil film were built based on viscosity-temperature property in the working process of hydro-viscous clutch, and their analytical solutions were obtained; effects of structural parameters of oil groove on transmission characteristics of hydro-viscous clutch based on viscosity-temperature property were revealed. The research results are of great value to the theory development of hydro-viscous drive technology, the design of high-power hydro-viscous clutch and relative control strategy.