Radius Clearance Research Articles

Analysis of turbulent cavitation effects on water-lubricated bearing in single screw compressors

PurposeTo guide the stable radius clearance choice of water-lubricated bearings for single screw compressors, this paper aims to analyze the effects of turbulence and cavitation on bearing performance under two conditions of specified external load and radius clearance.Design/methodology/approachA modified Reynolds equation considering turbulence and cavitation is adopted, based on the Jakobsson–Floberg–Olsson boundary condition, Ng–Pan model and turbulent factors. The equation is solved using the finite difference method and successive over-relaxation method to investigate the bearing performance.FindingsThe turbulent effect can increase the hydrodynamic pressure and cavitation. In addition, the turbulent effect can lead to an increase in the equilibrium radius clearance. The turbulent region exhibits a higher load capacity and cavitation rate. However, the increased cavitation negatively impacts the frictional coefficient and end flow rate. The impact of turbulence increases as the radius clearance decreases. As the rotating speed increases, the turbulence effect has a greater impact on the bearing characteristics.Originality/valueThe research can provide theoretical support for the design of water-lubricated journal bearings used in high-speed water-lubricated single screw compressors.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2024-0029/

Experimental and Analytical Investigation of Performance of Liquid Metal Herringbone Grooved Bearings with Cylindricity Errors

Liquid metal herringbone grooved bearings (LM-HGBs) are customarily used in high-performance x-ray tubes to support the high-speed rotating anode and facilitate heat transfer from the anode to the coolant. This article investigates the impact of cylindricity errors on LM-HGBs performance through simulations and experiments. The analysis considers both the Reynolds equation modified by turbulence and the film equation incorporating cylindricity errors to construct the prediction model of LM-HGBs. An experiment rig was constructed to measure the friction torque of LM-HGBs. The predictions were validated by comparing to experimental results. The pressure distribution was predicted under different cylindricity errors. The test and experimental results demonstrate that cylindricity error impacts the uniformity of groove depth and has a significant effect on the friction torque of the bearings. Theoretical results reveal that concavity and convexity errors alter the pressure distribution and have opposing effects on bearing static and dynamic parameters. Decreasing the ratio of error amplitude to groove depth and the ratio of error amplitude to radius clearance can reduce the effect of cylindricity errors.

Dynamic Characteristics Study of Elastic Ring Squeeze Film Damper with Rigid–Elastic–Oil Coupled Model

Due to the coupling of the damper journal with the elastic ring and oil film, the elastic ring squeeze film damper (ERSFD) shows better dynamic performance in comparison with the traditional squeeze film damper (SFD). Therefore, a novel rigid–elastic–oil coupled mathematical model was established. The elastic ring deformation, as the key point, is solved according to the planar bending theory. Then, based on the pressure governing equation of the oil film, using the central finite difference method, the oil film pressure was addressed. Meanwhile, the Simpson method was implemented to calculate the dynamic characteristic coefficients (equivalent stiffness and damping Ce) of ERSFD (DCCEs). Also, we analyzed the influence of journal eccentricity, oil film radius clearance, flexibility coefficient and damping hole diameter on the DCCEs, and the results were compared and verified with the existing literature. The sensitivity of each parameter to the DCCEs was analyzed by using the linear regression method. According to the results, the flexibility coefficient has the greatest effect on the DCCEs, followed by the oil film radius clearance. The eccentricity of the journal and damping hole diameter have the least impact. This work will provide a theoretical basis for reflecting on the bearing dynamic characteristics more truly and accurately.

Theoretical and experimental study on the stability of water lubricated high speed journal bearing with lobe pockets

The stability problem prevents the application of water lubricated journal bearing in high speeds conditions. To improve the bearing performance, the lobe pocket with Archimedes helix profile is designed in the water lubricated hydrostatic and hydrodynamic hybrid journal bearing. Bearing stiffness coefficients, damping coefficients and threshold speed are investigated with considering turbulence. Effects of radius clearance, pocket parameters, water supply pressure, restriction parameter and external load are analyzed. The results indicate that decreasing radius clearance and increasing pocket depth both improve the bearing stability, while there are optimal values for pocket widths. The water supply pressure and orifice diameter increase the threshold speed at low speeds. The results obtained provide useful information for designing high stability journal bearings.

Numerical and experimental investigation on the performances of a liquid metal bearing with spiral groove structures

Liquid metal is a perfect lubricant due to its low melting point, good fluidity at room temperature, higher thermal conductivity and high temperature stability. In this work, the novel hydrodynamic liquid metal bearing with spiral grooves is studied. Influences of the eccentricity, the bearing radius clearance, and the groove structural parameters on the pressure distributions and the load carrying capacity of journal liquid metal bearing are deeply numerically investigated. Meanwhile, the bearing clearance and the structure parameter of herringbone grooves on pressure distribution and load carrying capacity of thrust liquid metal bearing are also numerically conducted and experimentally validated. Numerical studies are conducted based on the finite element method. Results show that the pressure distribution and the load carrying capacity of journal liquid metal bearing are significantly affected by the eccentricity, the bearing clearance and the groove structural parameters. Specifically, for journal bearing, the load carrying capacity increases with the growth of the eccentricity and the groove spacing, while it decreases with the increase of radius clearance, the groove depth and the groove ridge ratio. Besides, it turns out that when the spiral angle is larger than 37.5 degree, the increase of the groove spiral angle results in a decrease of the load carrying capacity, while when the spiral angle is lower than 37.5 degree, the value of load carrying capacities at different spiral angle depends on the specific value of eccentricity. As for thrust bearing, the load carrying capacity increases with the decrease of bearing clearance, and the increase of groove depth. Besides, the groove numbers of 13 and the angle between two vertices of herringbone groove of 13 degree are beneficial for improving the load carrying capacity of thrust liquid metal bearings. Based on the above observations, optimal design parameter sets are selected to obtain much higher load carrying capacities up to four times for both journal and thrust bearings compared with the bearings with original parameters.

Investigation on the lubrication characteristics of low-viscosity lubricated micro-grooved bearings considering turbulence and misalignment

This paper numerically investigates the effect of turbulence and journal misalignment on the lubrication characteristics of micro-grooved bearings with low-viscosity lubricant. The generalized average Reynolds equation satisfying the mass conservation cavitation algorithm is developed by integrating the average flow model proposed by Patir and Cheng, the Ng–Pan turbulent model, and the P-Θ model proposed by Elrod and Adams. With this model, the finite difference method is used in the numerical procedure. Moreover, the mathematical models of micro-grooves with different bottom shapes, that is, rectangle, isosceles triangle, left triangle, and right triangle, are given. The validity of the proposed model is verified by the comparisons with the published literature. Based on numerical simulation, the minimum film thickness, eccentricity ratio, attitude angle, maximum film pressure, friction torque, misalignment moment, film thickness, and pressure distributions under different external loads, rotational speeds, radial clearances, misalignment angles, and micro-groove parameters between models with and without turbulence and misalignment are comparatively analyzed. The numerical results reveal that turbulence may occur under heavy external load, high rotational speed, and large radius clearance. Concurrently, turbulence increases the minimum fluid film thickness and attitude angle, decreases the eccentricity ratio and friction torque, and enhances the bearing capacity. Furthermore, the larger misalignment angle results in the smaller minimum film thickness, eccentricity ratio and attitude angle, and the larger maximum film pressure, misalignment moment, and axial tilt of film pressure. Numerical simulations can provide theoretical guidance for the optimization of the geometrical parameters of micro-grooved bearings.

Coupling analysis of turbulent and mixed lubrication of water-lubricated rubber bearings

Water lubricated rubber bearings (WLRBs) are widely used in steam turbines, submarines and other large equipment. Due to the low viscosity of water, water-lubricated bearings are usually in a turbulent and mixed lubrication state at operation. Therefore, a turbulent mixed lubrication model of WLRBs was established by developing an extended average Reynolds equation and includes turbulent, and its rationality was verified by experiments. The results reveal the effect mechanism of turbulence on mixed lubrication under different load, rotational speed, axial misalignment and radius clearance. The contact pressure of WLRBs presents chaotic distribution after considering turbulence. The results also give an optimal axial misalignment and radius clearance that can maximize the turbulent force. The numerical simulation can provide some guidance for the theoretical analysis of WLRBs.

Thermal Management and Dynamic Performance of a Cooler Design for the Supercritical CO2 Turbine Shaft Cooling

This paper presents the results of a numerical study on a supercritical CO2 (SCO2) turboshaft cooling device by considering heat transfer and hydrodynamics. A micro-cooling device with a radius clearance of 50 micron and a nozzle diameter of 4 mm was designed and used to investigate the heat transfer characteristics of a micro-spacing impinging and gas film dynamics. Sixteen nozzles (N = 16) are equally spaced around the shaft in single or double rows. Investigations include journal speed- and eccentricity-dependent forward and cross-coupled force coefficients, and the effects of nozzle layouts and mass flow rate on the heat transfer efficiency. Analysis of the correlation coefficient shows that the gas density in the radial clearance is the dominant factor affecting the convective heat transfer performance, while the fluid velocity is a secondary factor. And the cooling efficiency (mass flow utilization rate) at low cooling pressure (ps < 0.7 MPa) is significantly greater than that at high cooling pressure (ps > 0.7 MP). In addition, considering the structure alone, a dual-row cooler exhibits a higher average Nusselt number, also registers a higher mass flow rate at the same pressure. Once the shaft is heated only one end, the difference in effectiveness between single- and dual-row cooling is not significant, so coolers with a single-row configuration should be preferred. Then, experimental values for the temperature of the heated rotor are provided under specific cooling airflow conditions. Dynamic analysis results show that the force coefficient of the single-row configuration is more dependent on the journal rotation speed and eccentricity ratio, and exhibits a negative direct stiffness coefficient at higher inlet pressure and journal rotation speed. Moreover, cross-coupled terms (stiffness coefficient) generally have a more explicit variation tendency than direct terms, and are more sensitive to changes in shaft speed and eccentricity. Small clearance cooling is a relatively complex technology aimed to improve heat dissipation efficiency in gas cooling devices while minimizing the effect of hydrodynamic pressure. Comparing the gas force coefficients of different journal speeds reveals a drastic increase in the effect of hydrodynamic pressure when the journal is eccentric. The cooler may be considered for operation with compliant support (such as bump foil) to generate additional damping and appropriately compensate for the eccentricity of the rotor.

Study on failure mechanism and sealing performance optimization of compression packer

In order to accurately describe the mechanical behavior of rubber materials, and the uniaxial tensile and uniaxial compression experiments of three common rubber materials of packer are carried out combined with the function requirements of the rubber cylinder of packer. In addition, the sealing performance of the compression packer is studied in the setting stage by using the finite element software based on the investigation and analysis of the hyper elastic mechanical properties and constitutive models of rubber materials in this paper. It is found that contact deformation of the rubber cylinder begins to accelerate as the time increases through the analysis. When the packer completes sealing process, the upper rubber cylinder mainly plays a sealing role, and excessive stress will cause the shoulder of the upper rubber cylinder to be compressed and fatigue failure. The contact sealing performance of expanded rubber cylinder under different radius clearance and different pressure difference is studied. Under the given wall thickness and radius clearance, the limit pressure load is applied, the rubber cylinder is in a safe working state, and the sealing width is close to the contact length of the rubber cylinder, which ensures good sealing performance. Moreover, the rubber cylinder is in a good elastic deformation range without serious backlog.

Assessing the Potential Replacement of Mineral Oil with Environmentally Acceptable Lubricants in a Stern Tube Bearing: An Experimental Analysis of Bearing Performance

Abstract This study compares the performance of a plain bearing, with a similar structure to a tail shaft stern bearing, lubricated with either mineral oil or an environmentally acceptable lubricant (EAL). The main characteristic of the bearing is its length/diameter ratio of <1. Measurements are carried out with the bearing operating under loads from 0.5 to 1 MPa and seven speeds ranging from 1 to 11 rev/s. The bearing lubricated with either mineral oil with a viscosity grade of 100 or an environmentally acceptable lubricant (EAL) with a viscosity grade of 100 or 150 is investigated according to the ISO standard. Bearing wear is simulated by increasing the clearance circle by 0.1 mm. According to the results obtained, the use of an EAL in place of mineral oil does not cause significant changes in the bearing performance, regardless of the value of the clearance radius. The pressure distribution in the oil film, bearing load carrying capacity, eccentricity and friction coefficient have similar values for the entire load and speed ranges considered, and the discrepancies in the results are within the range of the measurement errors. Only an increase in EAL viscosity causes significant changes in bearing performance and these changes comply with the general theory of lubrication.

Energy Characteristics of Full Tubular Pump Device with Different Backflow Clearances Based on Entropy Production

In this study, the entropy theory was used as the evaluation standard of energy dissipation, and the effect of backflow clearance (the gap between motor rotor and motor shell) on energy characteristics of a full tubular pump was investigated by 3D unsteady flow simulation. The calculated results validated through testing shows that backflow clearance produces additional head loss and the rotation of the motor rotor requires more shaft power. The additional energy losses lead to a significant decline in the efficiency of tubular pump device. Under design conditions, the total dissipation of backflow clearance, rear guide vane, and outlet passage decreases with the increase of clearance radius, but that of the impeller decreases first and then rises with the increase of clearance radius. In addition, the increase of the clearance radius leads to disorderly flow pattern in the impeller. The total dissipation rate on the impeller suction side and near the impeller inlet increases with the increase of backflow clearance radius, but that on the impeller suction side decreases with the increase of backflow clearance radius. The total dissipation rate of the suction side of the guide vane and the wall of the outlet passage decreases with the increase of backflow clearance radius. This work can provide an intuitive analysis of the energy dissipation caused by backflow clearance and reference for engineering applications of full tubular pump.

Numerical investigation on the cooling performance of a novel jet cooler design for a supercritical CO2 turbine rotor shaft cooling

Numerical investigation was carried out to study the heat transfer performance for a high-speed rotating cylindrical surface subjected to single row array round jets impingement, under a very small gap spacing. Various parameters that affect heat transfer, such as the fluid density, flow velocity and Nusselt number distributions of the radius clearance were studied based on varied nozzle to target surface spacing H and mass flow rate. It has been found that the fluid density was a dominant factor and the velocity was the secondary factor for the gas jet heat transfer performances. The overall heat transfer was improved with a reduction in the number of nozzles, for given inlet mass flow rate boundary conditions. The decrease of H/di (di, nozzle diameter) may have positive or negative effects on the heat transfer performance from the impingement surface. Reducing the radius gap H, for a certainty, increases the average density of the fluid in the clearance, which is desirable in applications that enhance heat transfer performance. But when the radius gap (H) is small enough, increasing di may have a negative impact on heat transfer.

The Effect of Root Clearance on Mechanical Energy Dissipation for Axial Flow Pump Device Based on Entropy Production

The axial flow pump is a low head, high discharge pump usually applicable in drainage and irrigation facilities. A certain gap should be reserved between the impeller blade root and the impeller hub to ensure the blade adjustability to broaden the high-efficiency area. The pressure difference between its blade surface induces leakage flow in the root clearance region, which decreases hydraulic performance and operational stability. Therefore, this study was carried out to investigate the effect of root clearance on mechanical energy dissipation using numerical simulation and entropy production methods. The numerical model was validated with an external characteristics test, and unsteady flow simulations were conducted on the axial flow pump under four different root clearance radii. The maximum reductions of 15.5% and 6.8% for head and hydraulic efficiency are obtained for the largest root clearance of 8 mm, respectively. The dissipation based on entropy theory consists of indirect dissipation and neglectable direct dissipation. The leakage flow in the root clearance led to the distortion of the impeller’s flow pattern, and the indirect dissipation rate and overall dissipation of the impeller increased with increasing root clearance radius. The inflow pattern in the diffuser was also distorted by leakage flow. The diffuser’s overall dissipation, indirect dissipation rate on the blade surface, and indirect dissipation rate near inlet increased with increasing root clearance radius. The research could serve as a theoretical reference for the axial flow pump’s root clearance design for performance improvement and operational stability.

A method to calculate the life of sliding bearings based on fatigue and wear failure considering fluid lubrication

In this paper, a sliding bearing is taken as the research object to study the life simulation and calculation under conditions of a certain eccentricity, a radius clearance, inlet and outlet pressures, a radial load, and taking into account fatigue and wear failure modes. For a calculation case when the eccentricity is 0.6, the average radius gap is 0.05 mm, the inlet pressure is 2 MPa, the outlet pressure is 0.1 MPa, and the radial load is 5000 N. The calculated fatigue life is infinite and the wear life is 7.1×104 revolutions. This paper focuses on providing a method for quantitatively estimating the life of sliding bearings.

Research on the seawater-lubricated sliding bearing of a novel buoyancy-regulating seawater pump considering the working depth

ABSTRACT Seawater hydraulic pump is a key component in buoyancy regulation systems. In this paper, a novel full-water-lubricated three-plunger seawater pump was designed in which the plunger suction and drainage are driven by the crankshaft. For this structure, the sliding bearing that supports the crankshaft is a very important factor affecting the pump characteristics. The pressure flow model and the thermal coupling system model of the left/right sliding bearings were established, and the deformation of the left/right sliding bearings in the deep sea environment was analysed by ANSYS Workbench. The change of the fit clearance has a great influence on the work of the hydraulic pump. Different fit clearances at different seawater depths under different radius gaps are obtained. The results show that the fit clearance of the left/right sliding bearings decreases as the depth of the seawater increases. As the depth of the seawater increases, the sliding bearing is gradually changed from the frictional lubrication of the liquid to the boundary friction lubrication. With the increases of the radius gap, the working water depth of the hydraulic pump first increases and then decreases, and the optimal radius clearance and the optimal working depth are obtained.

Transient tribo-dynamic model for journal bearings during start-up considering 3D thermal characteristic

The study presents a transient tribo-dynamic model for journal bearings to reveal the mutual effect between the mixed thermoelastohydrodynamic (mixed-TEHD) performance and the journal dynamic behavior during start-up. In the developed model, the bearing shell, oil film, and journal are considered as a heat conduction coupling system, whose transient 3D thermal characteristic is determined by a general transfer equation. The established model is verified by comparing the numerical predictions, including the transient temperature distribution, maximum temperature, axis orbit and contact time, with the published results. The evolution of the mixed-TEHD performance during start-up is presented. And the impacts of the acceleration time, radius clearance and bearing shell thickness on the transient mixed-TEHD performance are evaluated. The simulation results indicate that the dynamic contact load during start-up may be underestimated when the thermal characteristic is absent. The simulation results also indicate that a maximum temperature can be observed before the hydrodynamic pressure is fully formed. Furthermore, the present study demonstrates that although a short acceleration time can reduce the asperity contact pressure, it leads to a relatively large temperature rise. The present study also demonstrates that a smaller radial clearance and a thinner bearing shell tend to generate a larger maximum temperature and thermal expansion, which leads to the increase in the risk of the thermally induced failure during start-up.

Coupling transient mixed lubrication and wear for journal bearing modeling

Abstract A transient Mixed Lubrication-Wear coupling model (MLW coupling model) is developed to investigate the mixed lubrication and wear performances of journal bearings, and a wear experiment for journal bearing is performed to support the validity of the developed numerical model. In the coupling numerical model, the transient interaction between the behaviour of mixed lubrication and wear is considered by incorporating the wear depth distribution, which is determined by the developed friction fatigue wear model, into the film gap equation. The evolutions of the worn surface profile, wear rate, fluid pressure and asperity contact pressure over operating time are calculated by the developed numerical model. The simulated results demonstrate that the transient wear process affects the distribution trend of lubrication performances significantly, and a worn surface profile may exist that provides an optimal tribology performance of journal bearings. The simulated results also demonstrate that there are two wear stages, identified by initial and steady wear stage, of journal bearings under mixed lubrication condition. Furthermore, the effects of the input parameters, including the radius clearance(C), surface roughness (σ), asperity curvature radius (β) and boundary friction coefficient(μc), on the predicted mixed lubrication and wear performance are evaluated.

Reactive Trajectory Generation for Multiple Vehicles in Unknown Environments With Wind Disturbances

Unmanned aerial vehicle use continues to increase, including operating beyond line of sight in unknown environments where the vehicle must autonomously generate a trajectory to safely navigate. In this article, we develop a trajectory generation algorithm for vehicles with second-order dynamics in unknown environments with bounded wind disturbances in which the vehicle only relies on its on-board distance sensors and communication with other vehicles to navigate. The proposed algorithm generates smooth trajectories and can be used with high-level planners and low-level motion controllers. The algorithm computes a maximum safe cruise velocity for the vehicle in the environment and guarantees that the trajectory does not violate the vehicle's thrust limitation, sensor constraints, or user-defined clearance radius around other vehicles and obstacles. Additionally, the trajectories are guaranteed to reach a stationary goal position in finite time given a finite number of bounded obstacles. Simulation results demonstrate the algorithm properties through two scenarios. First, a quadrotor navigating through a moving obstacle field to a goal position and, second, multiple quadrotors navigating into a building to different goal positions.

Lubrication performance analysis of crankshaft bush in compressor

Abstract The instability of lubricating oil film has a great effect on the wear of friction pairs and carrying capacity of the parts as well as smooth running of the machine. The lubrication system of crankshaft bush plays an important role in the good operation of compressor unit, reduces production cost while improving production efficiency. In this paper, lubrication performance of the crankshaft bush in compressor was investigated. Parameters involved in the lubrication of bush are studied and analyzed systematically during the stable rotation of crankshaft. Effects of lubrication parameters, such as width diameter ratio, crankshaft speed, inlet pressure, attitude angle and the minimum oil film thickness, on the pressure and distribution of lubricant film were discussed. At last, the optimum value and recommended range of some parameters of bush are determined, and the quantization is carried out within a certain range. The results show that two symmetrical distributions of positive and negative high pressure concentrated areas on both sides of bush oil groove can be formed when the crankshaft is stable. The speed and width diameter ratio have a great effect on the maximum pressure value of oil film. The inlet oil pressure and the minimum oil film thickness are the second, and the inlet attitude angle has little effect. With the increase of width diameter ratio, the maximum pressure value of the positive high pressure concentrated area increases, and the negative areas decreases. With the increase of oil inlet pressure, the maximum oil film pressure increases too but the influence is small. With the increasing of minimum oil film thickness, the maximum pressure and carrying capacity of oil film decrease. If the clearance between crankshaft and bush is too small, oil film can't be formed. For the analysis model in this paper, it is recommended that the radius clearance of bush is 0.04 mm. The inlet oil pressure range of lubricating oil is 0.32–0.36 MPa. Those results can be used in the design, testing and evaluation of the crankshaft system in compressor.

Оценки радиуса просвета конечного множества единичного шара в Rn

Оценки радиуса просвета конечного множества единичного шара в Rn