Research on oil-gas and thermal characteristics of high-speed ball bearing after oil cutoff

This study presents a novel roller piston pump, in which a cam guide-roller type rolling support is adopted to replace the sliding pair support of the swash plate-slipper pair to achieve the oil suction and discharge of the piston cavity. In addition, the shaft distribution is used to replace the original valve plate distribution and the driving shaft is used as the distribution shaft to remove the valve plate structure, which greatly simplifies the design of the axial piston pump. Such a configuration largely reduces the number of sliding friction pairs of the pump, and avoids the influence of the sliding friction pair on it under high-speed and variable-speed conditions. Firstly, mathematical models of the mechanical and volumetric efficiencies of the roller pump are deduced respectively through force analysis and the compressibility equation. Based on the numerical simulation of MATLAB and AMESim, the effects of load pressure and rotational speed on mechanical and volumetric efficiencies are studied respectively, and it is verified that the roller pump has no structural flow pulsation. The prototype pump is then designed and built, along with a special test rig. The outlet pressure, outlet flow, and torque of the pump under different load pressures and rotational speeds are measured, and the mechanical and volumetric efficiencies of the prototype pump under various load pressures and rotational speeds are obtained. The experimental results are in good agreement with the simulated analysis. When the load pressure is 8 MPa and the speed is 5000 r/min, the mechanical and the volumetric efficiencies are 85.5% and 96.8%, respectively. When the speed is increased to 10000 r/min, the mechanical and the volumetric efficiencies are 66.7% and 95.6%, respectively. The experimental results show that the proposed roller piston pump has excellent efficiency under wide-speed and high-speed conditions and can be a potential solution as a fuel pump in aerospace fuel systems.

This paper investigates the transient flow behavior and distribution patterns of lubricating oil within high-speed bearings through in-situ visualization. An experimental setup, comprising a transparent bearing and a visualization platform, was developed. Experiments were conducted under varied rotational speeds using two lubricants with different viscosities. A corresponding numerical model was established to simulate the lubrication flow field. The research results indicate that the two lubricants exhibit distinct transient flow characteristics inside the bearing. At lower speeds, spherical oil droplets form on the cage surface, which then deform, elongate, and are ejected. As speed increases, the oil transition to finer filaments or accumulate on the outer ring, depending on the oil viscosity. The Oil Volume Fraction (OVF) on the inner ring, cage, and balls decreases with increasing rotational speed. In contrast, the variation of OVF on the outer ring follows different patterns under ambient and high-temperature conditions, as well as with different lubricants. Overall, the effective oil volume retained inside the bearing cavity is relatively limited, ranging from approximately 0.5 mL to 7.8 mL. The findings of this study provide theoretical guidance for the design of oil-jet lubrication systems in high-speed bearings.

Deep-groove ball bearings for the eAxles of electric vehicles must adapt to higher rotational speed conditions because the speed of eAxle motors have been increasing as the size and weight of the motors decrease. Therefore, understanding the oil-lubricated conditions inside ball bearings at high rotational speeds is essential for optimizing their design for eAxles. To clarify the oil-lubricated conditions inside ball bearings at these high speeds, a new test apparatus was developed. This apparatus is capable of simultaneously measuring the friction torque of deep-groove ball bearings, the oil-film thickness on the rolling balls, and observing the oil distributions inside the bearings at rotational speeds up to 20,000 min-1. The oil-film thickness was measured using three-wavelength optical interferometry, and the oil distribution was observed using fluorescence. It was found that the oil-film thickness became constant at rotational speed conditions exceeding approximately 7,700 min-1. Oil starvations were observed on the raceway around the rolling ball, and these regions increased with increasing rotational speeds. Additionally, in the deep-groove ball bearing with a crown-shaped cage, the oil was mainly supplied to the rolling balls from the inner ring side through the space between the cage claws that held the ball. Moreover, the amount of mixed air tended to increase as the rotational speed increased to approximately 7,700 min-1. Those oil starvations and increasing air in oils were considered to be factors that prevent the increase in oil-film thickness. The findings of the reported study will contribute to the development of multibody dynamic technology for high-speed ball bearings necessary in electric vehicles.

The counter-rotation of dual rotors presents significant advantages in mitigating the gyroscopic effects inherent in aircraft engines. In this paper, a numerical investigation was conducted to analyze the flow and heat transfer characteristics within the double fulcrum bearing chamber using the CLSVOF method. Upon comparing the flow field characteristics within the bearing chamber under differing rotational directions of the high and low-pressure shafts, further investigation explored the impact of rotational speeds and bilateral oil flow rates on the flow and heat transfer characteristics of the bearing chamber. The results indicate that under counter-rotation, significant flow vortices are generated within the double fulcrum bearing chamber, causing opposing directions of wall streamlines, and thereby rendering the complexity of the flow dynamics. With increasing counter-rotating speed or speed ratio, the volume fraction of oil on the wall increases while the oil film thickness decreases. The oil film speed significantly increases. When the bilateral oil supply or oil flow rate ratio is higher, both the volume fraction of oil on the wall and the oil film thickness increase, but the increase in oil film speed is relatively small. Increasing the rotation speed and oil flow rate can enhance the wall heat transfer coefficient.

Rotating electrodes can effectively improve the processing performance of micro-electrical discharge machining (micro-EDM), but there is still a lack of systematic research on the specific effects of electrode rotation and rotational speed changes. In this paper, the effects of electrode rotation and rotational speed on the discharge channel, debris stress, and debris motion in micro-EDM were analyzed theoretically. An AISI304 sheet was used as the workpiece and helical tungsten carbide alloy as the electrode. The through-hole drilling experiments of micro-EDM were carried out at low and high discharge energy and different electrode rotational speeds. In terms of processing efficiency, the effects of electrode rotation and rotational speed on material removal rate (MRR), relative tool wear ratio (RTWR), and short circuit number were analyzed. The results show that MRR increases first and then decreases, RTWR and short circuit number decrease first and then increase. In the aspect of processing precision, the impacts of electrode rotation and rotational speed on taper angle and overcut were analyzed. The results show that the electrode rotational speed has little effect on the change of the taper angle. In addition, when the electrode rotational speed is small, there is no obvious change in overcut. When the speed is too high, the overcut increases obviously and shows a trend of continuous increase. Finally, by comparing the experimental results, the optimal electrode rotational speeds of micro-EDM with two kinds of discharge energy were determined. The final experimental results also verify the correctness of the previous theoretical analysis.

Under-race lubrication can increase the amount of lubricating oil entering a bearing and greatly improve lubrication and cooling effects. The oil-air two-phase flow characteristics inside a ball bearing with under-race lubrication play a key role in lubrication and cooling performance. The motions of ball bearing subassemblies are complicated. Ball spin affects the oil volume fraction. In this paper, the coupled level set volume of fluid (CLSVOF) method is used to track the oil-air two-phase flow inside the ball bearing with under-race lubrication. The influence of various factors on the oil volume fraction inside the ball bearing with under-race lubrication is investigated, particularly rotating speeds, inlet velocity and the size of oil supply apertures under the inner ring. The influence of the ball spinning is analyzed separately. The result demonstrates that, on account of the centrifugal force, lubricating oil is located more on the outer ring raceway at rotational speeds of 5000 r/min, 10,000 r/min, 15,000 r/min and 20,000 r/min. The oil volume fraction inside the bearing gradually increases at an oil inlet velocity of 5 m/s, 10 m/s and 15 m/s. The circumferential distribution of oil is also similar. As the diameter of the oil supply aperture increases from 1.5 mm to 2 mm, the oil volume fraction increases inside the ball bearing. However, the oil volume fraction slightly decreases from 2 mm to 2.5 mm of oil supply aperture diameter. Ball spin does not affect the circumferential distribution trend of the lubricating oil, but slightly reduces the oil volume fraction. Furthermore, ball spin causes the surface fluid to rotate around its rotation axis and increases the speed.

The variable speed pump-turbine is usually used to adjust the rotational speed to improve the efficiency in turbine mode and change the input power in pump mode because its rotational speed can vary within a certain range. In order to explore the evolutions of pressure pulsation and flow patterns caused by changes in the rotational speeds, the steady operating conditions under different rotational speeds in turbine and pump modes were investigated by using three-dimensional numerical simulations. The results show that as the pump-turbine operates with the highest efficiency at the rated rotational speed, the change in the rotational speed leads to the variation in macro-parameters, deterioration of the flow patterns, and increase in pressure pulsations. In addition, under a certain guide vane opening, with the increase in the rotational speed, the torque, power, and discharge increase in the turbine mode, while these parameters decrease in the pump mode. And when the rotational speed is too high or too low, it causes an obvious increase in pressure pulsations.

Dynamics of a powered disk in clay soil

Refill friction stir spot welding (RFSSW) is an effective technique for achieving high-quality joints in metallic materials, with rotational speed being a critical parameter influencing joint quality. Current research on RFSSW has primarily focused on low-melting-point materials such as aluminum alloys, while limited attention has been given to pure copper, a material characterized by its high-melting-point and high-thermal-conductivity. This study aims to investigate the effects of rotational speed on the microstructure and mechanical properties of RFSSW joints in pure copper. To achieve this goal, welding experiments were conducted at five rotational speeds. The welding defects, microstructure, and hook morphology of the welded joints were analyzed, while the variations in axial force and torque during welding were studied. The influence of rotational speed on the microhardness and tensile-shear failure load of the welded joints was explored, and the fracture modes of the welded joints at different rotational speeds were discussed. The results indicated that the primary welding defects were incomplete refill and surface unevenness. Higher rotational speeds resulted in coarser microstructures in the stir zones. As the rotational speed increased, the hook height progressively rose, the peak axial force showed an increasing trend, and the peak torque continuously decreased. The high microhardness points in the welded joints were predominantly located at the top of the sleeve stir zone (S-Zone), while the low microhardness points were observed at the center of the pin stir zone (P-Zone) and in the heat-affected zone (HAZ). The tensile-shear failure load of the welded joints initially increased and then decreased on the whole with the rising rotational speed, peaking at 5229 N at a rotational speed of 1200 rpm. At lower rotational speeds, the fracture type of the welded joints was characterized as plug fracture. Within the rotational speed range of 1200 rpm to 1600 rpm, the fracture type transitioned to upper sheet fracture. The initial fractures under different rotational speeds exhibited ductile fracture. This study contributes to advancing the understanding of RFSSW characteristics in high-melting-point and high-thermal-conductivity materials.

Variable tooth thickness gears have significant effects on the characteristics of the flow field inside the gearbox and the lubrication efficiency under high-speed operating conditions due to their complex parameters, such as tooth profile, cone angle, rotational speed, and oil injection speed. To investigate the impact mechanism of oil injection velocity on the working flow field of high-speed variable tooth thickness gears under varying parameters, this paper establishes an oil injection lubrication model under high rotational speeds of variable tooth thickness gears, based on computational fluid dynamics (CFD) methods and the Volume of Fluid (VOF) model, combined with the dynamic mesh technique. This paper analyzes the lubrication issues at the initial oil injection moment of involute variable tooth thickness gears. By computing the lubricant distribution state at 0.1 s after the oil injection onset based on the stabilized flow field under no-oil-injection condition, discussions are conducted on the single-phase and two-phase flow fields within the gear casing at different cone angles and rotational speeds separately examining the flow states near the oil nozzle and the distribution patterns of lubricant at the meshing portions. The results indicate that, without oil injection, the pressure near the oil nozzle gradually increases with an increase in rotational speed and decreases with an increase in cone angle; at the initial oil injection moment, the lubricant volume fraction at the gear meshing portions gradually increases with an increase in rotational speed and rises with an increase in cone angle.

Rotational atherectomy (RA) is an important technique for the management of severe coronary calcification. However, optimal rotational speed is yet to be defined. A total of 372 coronary heart disease (CHD) patients were retrospectively analyzed between February 2017 and January 2022. The patients were divided into four groups based on the maximum RA speed: group 1 ( 150,000 rpm, 76 cases), group 2 (150,000 rpm, 156 cases), group 3 (160,000 rpm, 90 cases) and group 4 ( 170,000 rpm, 50 cases). The outcomes analyzed were procedural complications, six-months major cardiovascular and cerebrovascular events (MACCE) and chronic heart failure. Patients in group 4 had a higher incidence of slow flow during the RA operation (p = 0.025). There was no significant difference in other complications among the four groups, as well as six-month MACCE. After adjusting for confounding factors, increase in rotational speed led to a higher probability of slow flow (p for non-linearity = 0.131; adjusted model) and MACCE (p for non-linearity = 0.183; adjusted model). Logistic regression analysis showed that rotational speed was a predictor of slow flow during RA operation (OR = 1.25, 95% CI: 1.05~1.49, p = 0.01). Moreover, the analysis demonstrated that individuals with lower rotational speed ( 150,000 rpm) were at 230% higher risk of vasospasm compared with a higher rotational speed (160,000 rpm) (OR = 3.3, 95% CI: 1.08~10.09, p = 0.036). CHD patients treated with a rotational speed of 170,000 rpm had a higher risk of slow flow after RA. Rotational speed is an independent risk factor for slow flow in CHD patients. Moreover, a rotational speed of 150,000 rpm was associated with a higher risk of vasospasm compared with rotational speed of 160,000 rpm. There was no significant difference in six-month outcomes in comparison to elective CHD patients with different rotational speeds, and the probability of MACCE was intensified with increase in rotational speed.

High-speed electric submersible pumps (ESPs) for downhole oil production typically operate with rotational speeds in excess of twice that of conventional pumps. These pumps need gas handlers to ensure satisfactory operation at higher gas volume fractions (GVFs). This study presents an evaluation of the operational capabilities of high-speed gas handling. Knowledge of these capabilities aids production engineers and field operators to make more informed decisions for efficient downhole oil production operations. The evaluation was performed for high-speed gas handling for downhole pumps with 2.17, 3.19, 338, 400 and 538 series housing sizes. These pump size architectures were for typical casing/liner diameters varying from 4.5" to 7.0". In the evaluation, the inlet pressure was fixed, whereas the GVF and rotational speeds were varied. The GVF range was from 0 to 0.75, and the rotational speed varied from 3500 to 12000 revolutions per minute (RPM). The total volume flow rates varied from 4500 barrels of fluid per day (BOFPD) to upward in excess of 10000 BOFPD. The results show that for a given inlet pressure increasing the rotational speed of a gas handling device increases its capability to process and pump the downhole fluids. There is also a tendency for higher gas handling capability when the rotational speed of the device is fixed and the dimensional size of the downhole equipment is varied. The observation will tend to suggest that for a given GVF, the gas handler operating at a higher rotational speed would be more tolerant to gas than the unit operating at a lower rotational speed. There is a tendency for the operational capability of the gas handler to be limited by the rotor dynamics and mechanical component, such as the shaft. This limitation will tend to depend on the size of the gas handling unit. These observations suggest an upper operation limit of the high-speed gas handling system can be attributed to a limitation of some of the specific system components. This study highlights the importance of understanding capabilities of high-speed gas handling systems, which are needed for high gas content wells for downhole oilfield production operations. Knowing the parameters that limit high-speed gas handling is beneficial for deciding which device is most appropriate to use in a particular well. Such knowledge is vital for the operator to make strategic decisions to efficiently produce hydrocarbons using the field asset, and maximize the economic bottomline for the operator.

Particle Trajectory in Turbulent Boundary Layer at High Particle Reynolds Number

Kinetics of formation of polysaccharide-covered micrometric oil droplets under mechanical agitation

Understanding the behavior of plain zinc dialkyldithiophosphate (ZDDP) oil in the presence of iron fluoride (FeF3) catalyst is of paramount practical significance. In this article, the tribological and chemical interactions of ZDDP/FeF3 underlying their improved wear performances were examined. Optimized 0.4 wt% FeF3 catalyst + 0.1% P (0.1% phosphorus concentration) plain ZDDP oil was investigated under the protocol of two different rotational speeds (100 rpm for the first 5,000 revolutions and 700 rpm until failure or 100,000 revolutions, whichever came first) and steady-state speed (700 rpm until failure or 100,000 revolutions). A Plint T53 SLIM modified ball-on-cylinder machine (Phoenix Tribology, Whitway, England) and different contact loads were used for all tests. A design of experiment (DOE) with a two-level factorial design was used to investigate the failure and wear responses with respect to catalyst interactions in plain ZDDP oils. An optimized load of 336 N (2.6 GPa Hertzian contact pressure) was reflected in the high-desirability DOE data when using different rotational speed protocols. The two different rotational speeds indicated better performance than the steady-state speed protocol, especially in the presence of FeF3 catalyst. The tribological properties of each compound under optimized loading conditions were evaluated using a ball-on-cylinder tribometer. Scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and auger electron spectroscopy (AES) were used to examine the wear tracks of FeF3/ZDDP mixtures and to characterize the chemical properties of tribofilms generated under extreme loading and different rotational speeds. The mechanism of tribofilm formation and breakdown was followed carefully by monitoring the friction coefficient over the duration of the test. It was found that the optimized loading sample under the two different rotational speeds performed better and the addition of catalyst increased the friction-reducing capacity of the tested samples. It was also shown that higher contact loads at 2.77 GPa Hertzian contact pressure resulted in premature breakdown of tribofilms, rendering their antiwear resistance under the steady-state rotational speed insignificant. However, the optimized loading sample under steady-state speed performed better than the extreme load (405 N) samples. Chemical analysis showed more phosphorus and more iron oxide (Fe3O4) nanoparticles in the tribofilm of the 0.4 wt% FeF3 + 0.1% P ZDDP sample conducted under 2.6 GPa Hertzian contact pressure and two different rotational speeds. Transmission electron microscopy analysis of the wear debris indicated that a larger fraction of the crystalline particles at higher contact loads of 405 N were Fe2O3. This was true even for different rotational speeds. Fe2O3 is significantly more abrasive and resulted in rapid breakdown of the tribofilms. Auger electron spectroscopy indicated thicker film in the optimized sample. This might be due to the higher phosphorus concentration and the greater reduction in oxygen inside the wear track.