Purpose: The purpose of this paper is to study the working characteristics of hydro-viscous clutch at high rotational speeds and obtain the trend of flow field variation of oil film. Design/methodology/approach: The FLUENT simulation model of the oil film between the friction disks is built. The effect of variation of working parameters such as input rotational speed, oil flow rate and film thickness on two-phase flow regime and transmission torque is studied by using the volume of fluid model. Findings: The results show that the higher the rotational speed, the severer the cavitation is. In addition, the two-phase flow region makes the coverage of oil film over the friction pairs’ surface reduce, which results in a decrease in transmission torque for the hydro-viscous clutch. Originality/value: These simulation results are of interest for the study of hydro-viscous drive and its applications. This study can also provide a theoretical basis for power transmission mechanism of oil film by considering the existence of a two-phase flow regime consisting of oil and air.

In electro-hydraulic servo systems (EHSS), high nonlinearity and time-varying features limit the hydraulic actuator performance. In feedback-based systems, linearization reduces nonlinearities. Their cancellation may produce instability when modeling uncertainty exists. This work uses a robust nonlinear controller based on Lyapunov theory to control the nonlinear position of the electro-hydraulic servo system (EHSS). The dynamics of the system were modeled as extensively as possible, and then a simplified mathematical model based on the EHSS dynamics was created for the controller design. Integral backstepping was used to design the nonlinear robust controller utilizing the Lyapunov theory of nonlinear systems. Lyapunov functions theoretically ensured closed-loop stability. Comparative simulation analysis and experimental investigation in real-time with the proportional integral derivative (PID) controller optimized offline for position tracking control were carried out. Besides tracking performance and steady-state error, the mean square error (MSE), the root mean square error (RMSE), the maximum absolute value of tracking errors ( M e ) , and the standard deviation of tracking errors (σ) was utilized to evaluate the controllers’ performance. The simulation analysis and experimental verification were accomplished under various sinusoidal trajectories using different testing conditions (amplitudes, frequencies, and external disturbance), in all testing conditions the effectiveness of the robust nonlinear integral backstepping controller was demonstrated.

The present work numerically investigates the flow behavior of Newtonian fluid between rotating disk systems. Rotating disk flow is an embranchment of fundamental flow research, which forms the theoretical basis for the flow media in many disk-type hydraulic machinery, and has been widely applied in energy, aerospace, vehicles, medical, and chemical areas. The Reynolds equation model of the rotating disk flow is established based on a series of assumptions, and considers the characteristics of hexahedral surface textures on the friction disk, and the control equation is dimensionless. The velocity, pressure, and pressure coefficient in oil film are solved by finite difference algorithm, and the shear cavitation incipient position is predicted. Graphical visualization and numerical data about cavitation characteristics are also presented. Furthermore, the cavitation process is researched in CFX and the experiment, eventually verifying the correctness of the numerical analysis. The pressure perturbation caused by texture boundaries and the low pressure at the vortex center induce the initial generation of cavitation, and cavitation effect can obviously enhance lubricating performance. The cavitation region extends from micro-dimples towards non-textured region when texture rate increases. This study can guide design of surface structures such as mechanical seals, wet clutches, and disk turbines.

Cavitation is a destructive hydraulic phenomenon; it causes damage to small hydraulic machinery and large water-conservancy projects, and cavitation and cavitation corrosion problems are long-standing problems for hydraulic machinery experts. Micro-textures are often machined onto the end face near the indirect contact point to increase the oil film bearing capacity and reduce the transfer torque in hydraulic machinery, but the pressure disturbance caused by the texture dimple and boundary can induce cavitation. To delay or eliminate cavitation on the textured surface of equipment such as mechanical seals and dynamic bearings, the cavitation effect of a cylindrical texture on a rotating frictional pair was investigated from theoretical, imitational, and experimental perspectives. Low pressure is extremely important for inducing cavitation; once cavitation conditions are met, a full bubble can be formed in about 0.015 s. Cavitation mainly occurs at the outer radius of the rotating end face, i.e., in the high-speed region. There is a mutual mass transfer between gas and liquid phases when cavitation occurs, but the generation of cavitation bubbles is faster than its collapse, thus causing an increasing cavitation region.

A non-direct contact rotary interface uses a viscous fluid as the lubricant working medium. Because the oil film friction coefficient formed is extremely small, so it has great application potential in sealing, fluid transmission, thermosolutal convection, and bionics. Research on mechanical seals, wet clutches, and dynamic load bearing have proven that micro-textures can effectively improve friction and lubrication performance. However, when the fluid flows through the texture boundary, pressure disturbances can induce hydrodynamic cavitation. A pair of rotating disks are selected as our research objects. From the simulation and experiment research, we found that cavitation volume does not always increase with an increase in the texture rate, and cavitation always occurs preferentially at the outer diameter, so it is necessary to avoid machining the texture structure at the outer diameter of the mechanical seal end. Once the conditions for cavitation are met, a complete cavity is formed in approximately 0.015 s. The study also verifies that the cavitation gas originates from the phase change of the oil.