Chao Wei

Theoretical and Experimental Study of Cavitation Effects on the Dynamic Characteristic of Spiral-Groove Rotary Seals (SGRSs)

A theoretical model is developed to analyze oil-film stiffness and damping coefficients of SGRSs using two different cavitation models, i.e., the Reynolds and JFO boundary conditions. By applying the small perturbation method, the steady and perturbed Reynolds equations could be obtained. The control volume method was used for the spiral grooves, and the upwind scheme was applied to improve the convergence of the solution. The performance of the computation algorithm was studied by analyzing the mesh dependencies and computing power. A new test setup was built to measure oil-film stiffness, to verify the theoretical models, and to study the validity of the Reynolds and JFO boundary conditions. A representative SGRS was analyzed at different operating speeds and inlet pressures to investigate the occurrence of cavitation and the dynamic characteristic. The effect of the spiral-groove parameters on the dynamic characteristics is also discussed.

Analysis and Experimental Study on the Characteristics of Leakage of Rotary Seal Using Sealing Ring

To solve problems of seal failure on composite transmission because of high temperature, an analytical and experimental analysis for the characteristics of leakage is presented. Basic on the principle of hydraulic resistance network, via establishing mathematical model of each section belonged to flow system, a leakage model of flow system is set up. Using the analytical model and the experimental methods, the factors of leakage are discussed. The results indicate that the characteristics of leakage depend on the working conditions, structural parameters of rotary seal and viscosity-temperature characteristics of lubricating medium.

Research on Effects of Groove Shape Optimization on Cavitation and Lubricating Characteristics for Microgroove Rotary Seal

ABSTRACT This article studies the effects of groove shape optimization on cavitation and lubricating characteristics of microgroove rotary seals (MGRS). A lubrication model considering cavitation effects for MGRS is established to obtain the variation in cavitation and lubricating characteristics with operating conditions. Furthermore, an optimization model of groove shape based on the lubrication cavitation model is developed and an optimal groove is obtained by co-designing the parameters of both groove shape structures and molded lines. The effects of optimal grooves and ordinary spiral grooves on cavitation and lubricating characteristics are compared and validation tests are carried out. Theoretical and experimental results indicate that the lubrication cavitation model based on the mass conservation boundary condition for MGRS could accurately predict the cavitation region of ordinary spiral grooves. Optimal grooves improve the pressure distribution of the groove area and restrain the generation of a cavitation region; therefore, the fluid bearing capacity and dynamic stiffness of optimal grooves are much larger than those of ordinary spiral grooves.

Influence of Fluid Slip on Operation Characteristics for High-Speed Spiral Groove Seal Ring

The multi-phase method applied in cavitation region believes gas and oil phase separated and oil slips over gas layer, so slip plays a role for fluid flowing in cavitation region. Spiral groove is widely applied in seal ring for its perfect hydrodynamic effect, but the cavitation is easy to occur in divergence region of groove. Therefore, influences of both cavitation and slip on operation characteristics for spiral groove seal ring at high speed have been discussed in multi-phase method. In order to attain this goal, a new hydrodynamic model based on multi-phase method, apparent local slip theory and JFO cavitation theory is built up. An accurate prediction of lubrication characteristics is represented by comparing with published experimental data. Also, the slip region is observed by a designed test and the observed results are almost the same with simulation, which further confirms the rationality of the new hydrodynamic model based on multi-phase method. The results show the cavitation ratio and area of slip region increase with the rise of speed and spiral angle. However, as to slip level, it rises with speed but decreases with spiral angle. Then, the damping and stiffness obtained from new model are compared with conventional model. Stiffness coefficient in new model is smaller than conventional model, while the damping coefficient is larger.

Study of Separation Characteristics of Micro-groove Rotary Seal Considering Different Cavitation Boundary Conditions

AbstractnMicro-grooves have superior hydrodynamic characteristics; therefore, the operating state of the micro-groove rotary seals (MGRSs) used in wet clutches of vehicles change from mixed lubrication to full-film hydrodynamic lubrication with increased rotating speed. These transition characteristics of the lubrication state of the MGRS are called “separation characteristics.” However, simultaneously the increase in rotating speed also leads to the cavitation effect. In contrast to the convergent wedge-shaped gap, “negative effects” exist in the diverging gap that lead to the reduction in the hydrodynamic pressure on the sealing end face. When the pressure is less than the cavitation pressure, the oil film undergoes cavitation and then ruptures. Thus, a large cavitation region reduces the bearing capacity of the oil film. Cavitation effects significantly influence the separation characteristics of the MGRS. Here we report on a theoretical model that has been developed through coupling asperity contact, fluid lubrication with micro-grooves and axial motion dynamic characteristics of the seal. Separation characteristics of the MGRS under Reynolds and Jakobsson–Floberg–Olsson (JFO) cavitation boundary conditions are systematically investigated in this study. The results show that pressure distribution and fluid bearing force under the Reynolds cavitation boundary condition are larger than those under the JFO condition, while friction torques are almost the same under both conditions. The cavitation region is observed in experiments and found to become larger with increases in speed. The JFO cavitation boundary condition predicts larger separation speed of the MGRS than does the Reynolds cavitation boundary, and the separation speed predicted by the JFO cavitation boundary condition is significantly closer to the experimental result than that predicted by the Reynolds condition. For the best separation characteristics of the MGRS, selected micro-groove parameters are as follows: Ngxa0=xa035–40, βxa0=xa017–23° and hgxa0=xa015–25xa0μm.

Numerical and experimental study on the separation characteristics of microgroove rotary seals

The microgroove rotary seals used in the wet clutches of a vehicle operate in a mixed-lubrication state at low rotational speeds. When the speed increases to a certain value, the full-film hydrodynamic-lubrication state occurs in the sealing end face. The transition characteristics of the microgroove rotary seal in this operating state are called the separation characteristics and the critical speed is called the separation speed. In this paper, the separation characteristics of microgroove rotary seals are studied. First, a theoretical model considering the asperity contacts, the fluid lubrication with microgrooves and the axial motion dynamic characteristics of the seal is established. Then, the variation in the separation characteristics is studied systematically using the microgroove parameters, such as the number Ng of microgrooves, the groove width ratio δθ, the extent δr of the radial seal dam and the spiral angle β. The optimum ranges of the microgroove parameters are determined: Ngu2009=u200940–50, δθu2009=u20090.65–0.75 and δru2009=u20090.7–0.8 for radial grooves and Ngu2009=u200930–40, δθu2009=u20090.5–0.7, δru2009=u20090.7–0.8 and βu2009=u200912–17° for spiral grooves. Finally, the variations in the microgroove parameters of the separation characteristics are verified by several experiments. The experimental results are in good agreement with the simulation results.

CFD investigation on the influence of jet velocity of oil-jet lubricated ball bearing on the characteristics of lubrication flow field

Oil-jet lubrication which is widely applied in aero engine, turbo machinery, high power transmission system is one of the most common form of the high speed bearing lubrication. The complex oil-air two-phase flow will exist in the cavity of the oil-jet lubricated high speed rolling bearing because of the stirring of the rolling elements and the cage. The characteristics of the two-phase flow field have a decisive influence on heat generation and temperature distribution of the bearing, which affect performance and service life of the bearing sighificantly. Jet velocity is an important factor that affects the oil-air two-phase flow field in the bearing cavity. The VOF method for multiphase flow and the RNG k-3 turbulence model were used. The flow field in the bearing cavity at different operating speeds and jet velocities was numerically calculated and analyzed. The effects of the jet velocity and the operating speed on the oil volume fraction in the bearing cavity and the churning torque were investigated.

Fractal Prediction Model of Friction Coefficient in Dry Friction Pair

To research the friction coefficient of rough surface under different contact loads. A mathematical model is proposed between the fractal parameters D and G and the non-dimensional real contact area based on M-B fractal contact model, surface profile curves are scanned by APE500 surface morphology, dimension change index k and size change index s are identified in tests, the model is verified on UMT-3 pin-on-disk wear apparatus. Results showed that the modeling method relying on limiting cases is feasible, this model could improve prediction accuracy of friction coefficient, and the experimental results are consistent with the theoretical prediction.

Analysis Methods of Power Characteristics for Hydraulic Pressing of the Traction Drive Device

Analysis Methods of Power characteristics for hydraulic pressing of the traction drive device are studied. The operating principle of hydraulic pressing of the traction drive device is analyzed, Probe into the rule of variation of the inner and outer Friction Pairs about the traction coefficient and the transmission ratio, A mathematical model of transmission traction characteristics is built up based of the Elasto-hydrodynamic lubrication theory, to explore the power characteristics of the friction pairs under different slip roll ratio and normal loading force, and the transmission of the input power and output power under different total sliding rate and loading force. The results showed that the transmission power of hydraulic pressing of the traction drive device is increasing when the normal loading force is increasing under some sliding Rate, but the transmission power tend to stable when the shearing stress is close to limiting shearing stress；and with the Sliding Rate increasing the transmission power increase under some normal loading force, but the transmission power eventually tend to stable when the Shearing Stress is close to limiting shearing stress.

Research on Dual-Cones CVT Based on EHL

A novel configuration of CVT that contains two cones located in the same shaft face to face is researched about the traction performance under high speed based on the theory of elastohydrodynamic lubrication(EHL). The effects of load, radii of curvature and slip-roll ratio on the traction characteristics and power transmission are analyzed. The results show that with increasing load the traction coefficient enhances close to linearly where the load is not heavy and the minimum film thickness decreases linearly when the inner wheel radii of curvature less than 0.085m. The leftmost position could transmit higher power. The power transmitted improves slightly as slip-roll ratio enhances in an appropriate range.