Numerical Simulation of the Flow in a Large-Scale Thrust Bearing

PurposeHydrostatic thrust bearing is a key component of the vertical CNC machining equipment, and often results in friction failure under the working condition of high speed and heavy load. The lubricating oil film becomes thin or breaks because of high speed and heavy load and it affects the high precision and stable operation of the vertical CNC machining equipment; hence, it is an effective way of avoiding friction failure for achieving the oil film shape predictionDesign/methodology/approachFor the hydrostatic thrust bearing with double rectangular cavities, researchers solve the deformation of the friction pairs in hydrostatic bearing by using the computation of hydrodynamics, elasticity theory, finite element method and fluid-thermal-mechanical coupled method. The deformation includes heat deformation and elasticity deformation, the shape of gap oil film is got according to the deformation of the friction pairs in hydrostatic bearing, and gets the shape of gap oil film, and determines the influencing factors and laws of the oil film shape, and achieves the prediction of oil film shape, and ascertains the mechanism of friction failure. An experimental verification is carried out.FindingsResults show that the deformation of the rotational workbench is upturned along its radial direction under the working condition of high speed and heavy load. However, the deformation of the base is downturned along its radial direction and the deformation law of the gap oil film along the radius direction is estimated; the outer diameter is close but the inner diameter is divergent wedge.Originality/valueThe conclusion can provide a theoretical basis for the oil film control of hydrostatic thrust bearing and improve the stability of vertical CNC machining equipment.

PurposeThis paper aims to present a numerical model to investigate the mixed lubrication performances of journal-thrust coupled bearings (or coupled bearings).Design/methodology/approachThe coupled hydrodynamic effect (or coupled effect) between the journal and the thrust bearing is considered by ensuring the continuity of the hydrodynamic pressure and the flow field at the common boundary. The mixed lubrication performances of the coupled bearing are comparatively studied for the cases of considering and not considering coupled effect.FindingsThe simulated results show that the hydrodynamic pressure distributions for both the journal and thrust bearing are modified due to the coupled effect. The decreased load capacity of the journal bearing and the increased load capacity of the thrust bearing can be observed when the coupled effect is considered. And the coupled effect can facilitate in reducing the asperity contact load for both the journal and thrust bearing. Additionally, the interaction between the mixed lubrication behaviors, especially for the friction coefficient, of the journal and the thrust bearing is significant in the elastohydrodynamic lubrication regime, while it becomes weak in the mixed lubrication regime.Originality/valueThe developed model can reveal the mutual effects of the mixed lubrication behavior between the journal and the thrust bearing.

Fluid film thrust bearings are commonly used in industry, providing durable and reliable operation at high values of load carrying capacity, accompanied by low friction losses. A major advantage of hydrodynamic fluid film bearings, over other types of bearings, is their enhanced dynamic behaviour, especially under transient or impact loads. Currently, a systematic approach to identify the dynamic coefficients of thrust bearing geometrical configurations utilising high complexity CFD simulation data has not yet been established. It is therefore imperative to develop a method, capable of evaluating the dynamic characteristics of complex bearing designs and allow the evaluation of bearing response under transient loads. In the present work, a computational approach is proposed to estimate the stiffness and damping coefficients of fluid-film thrust bearings. A CFD-based ThermoHydroDynamic (THD) numerical model of the bearing is developed and utilised for performing an initial steady-state simulation at given rotational speed and thrust load, as well as subsequent transient simulations at increasing or decreasing thrust loads. The former simulation is used to calculate the stiffness coefficient of the bearing at the specified conditions, while the latter are appropriately post-processed to estimate the damping coefficient of the bearing at different values of rotor acceleration. The procedure is repeated at different operating conditions, yielding a map of the dynamic coefficients of the bearing. Finally, a single degree of freedom model is generated, which utilises the calculated values of dynamic coefficients to evaluate transient bearing performance under any given thrust load history. The proposed methodology is applied to compare the dynamic response characteristics of a conventional sector-pad tapered-land thrust bearing and a textured tapered-land thrust bearing of the same principal dimensions.

A thermoelastohydrodynamic (TEHD) coupling model is developed to study the static performance of a heavy-duty tilting pad thrust bearing (TPTB) under the effect of axis misalignment. To ensure the validity in calculating thermoelastic deformation, the calculation accuracy of the mechanical and thermal deformations used in the TEHD model is verified by the finite element method (FEM). The influence of the TEHD model on the flow state prediction is determined using different axial loads, and the numerical analysis of turbulence model and centrifugal inertia term on the bearing pad temperature is conducted at various operating rotation speeds. Compared with the aligned bearing performance, the characteristic distribution of each bearing pad under different misaligned angles is obtained. The effect of misalignment will cause local overheating of the thrust-bearing pads, especially for the heavy-duty TPTD. The results of this study can help to improve the prediction accuracy of heavy-duty TPTB characteristics and avoid harmful misalignment effects. Therefore, it is necessary to consider the effects of misalignment, turbulence, and thermoelastic deformation in the design and analysis of thrust bearings.

A hydrogen-electric car is a fuel-cell vehicle that reacts hydrogen fuel with oxygen in the air to generate electricity to drive the traction motor. An air compressor is a device that compresses air and supplies it to the fuel cell stack. These generally use two types of airfoil bearings: The first is journal bearing, the second a thrust bearing. In this paper, axial thrust bearings are analyzed using 2-Way fluid-structure interactions (FSI). To determine the validity of the 2-Way FSI analysis, a solid thrust bearing was fabricated and the torque was measured. For 60 kr/min 70 kr/min and 80 kr/min rotations, loads were applied at 10 N, 15 N, and 20 N and the resulting torque was measured. For the 2-Way FSI analysis, a 1/6 split model was selected, the turbulence model was Menter’s Shear Stress Trasport (SST), and 10 meshes were made in the air gap using a system coupling condition moving the solid and fluid parts simultaneously. The 2-Way FSI analysis result showed the error within 7.3 %, proving its validity.

Textured surfaces are the subject of a great deal of research work in tribology, which mainly involves numerical studies of lubricated contacts. A variety of shapes and arrangements of textures can be found, these being as numerous as the different authors. Depending on the configuration, it has been shown that the presence of the texture can provide better lubrication efficiency through both a reduction of friction and an increase in load-carrying capacity. However, improving bearing performance implies a specific geometrical configuration for given operating conditions. The improvement in lubricated contact performance by texturing the active surface has been demonstrated using experimental studies concerning, for example, pin-on-disk, mechanical seal, camshaft, journal bearing, thrust bearing, and piston ring set-ups. The objective of the present experimental analysis is to provide, using local measurements, a better understanding of the influence of surface texturing on the steady-state behavior of thrust bearings. To achieve this goal, the experimental device is equipped with 80 sensors such as thermocouples and pressure transducers which allowed a proper assessment of the phenomenology at the film/pad interface. The tests are conducted on five hydrodynamic thrust bearings, among which four are textured. Results show that, for the studied configurations, the textured thrust bearings can help to reduce friction up to 30% at low loads while for heavy loads, their performance is equivalent or even lower than that of an untextured planar bearing.

Up to now, there is no developed ‘universal’ turbulence model in CFD simulation, so employing an appropriate turbulence model is crucial for accurately predicting the hydrodynamics of a ship, especially for submarines. This study focuses on investigating the impact of turbulence models on the predicted results in frictional and pressure resistance components and flow features around the submarine at different ship velocities by the CFD method. Four various turbulence models consisting of the Reynolds Stress Model, realizable k-ε two-layer, standard k-ω, and SST k-ω turbulence models are investigated in this study. The obtained numerical results demonstrate variations in resistance and the flow patterns around the submarine due to the effect of turbulence model. Based on the obtained results, the paper points out that, the choice of turbulence model significantly affects the frictional resistance of the submarine and the SST K-ω turbulence model provided the highest level of accuracy in comparison with experimental data. The model employed in this research is the DARPA SUBOFF submarine model

Flow field characteristics of Falcon separator are studied by CFD simulation based on Euler-Euler model as multiphase flow model and Reynolds stress model as turbulence model, including particle movement state in delamination area and separation area, three phase (Tangential, radial and axial directions) velocity distribution and turbulence field distribution. Simulation results show that particle movement trajectory is a three-dimensional helical structure with circular motion in groove, which can be regarded as “a circular harmonic motion of a roller coaster”; velocity distribution in the delamination area is almost same as other centrifugal separators but it is quite different in the groove; with feeding of recoil water, the turbulence intensity in the separation area is increased obviously, but it has a lower influence on the disturbance at upper layer of convective membrane, which enhanced the separation effect.

Effect of herringbone groove structure parameters on the static performance of gas foil herringbone groove thrust bearings

This work compares CFD results with experimental results of the flow in two different kinds of water turbine runners. The runners studied are the GAMM Francis runner and the Hölleforsen Kaplan runner. The GAMM Francis runner was used as a test case in the 1989 GAMM Workshop on 3D Computation of Incompressible Internal Flows where the geometry and detailed best efficiency measurements were made available. In addition to the best efficiency measurements, four off‐design operating condition measurements are used for the comparisons in this work. The Hölleforsen Kaplan runner was used at the 1999 Turbine 99 and 2001 Turbine 99—II workshops on draft tube flow, where detailed measurements made after the runner were used as inlet boundary conditions for the draft tube computations. The measurements are used here to validate computations of the flow in the runner.The computations are made in a single runner blade passage where the inlet boundary conditions are obtained from an extrapolation of detailed measurements (GAMM) or from separate guide vane computations (Hölleforsen). The steady flow in a rotating co‐ordinate system is computed. The effects of turbulence are modelled by a low‐Reynolds number k‐ω turbulence model, which removes some of the assumptions of the commonly used wall function approach and brings the computations one step further.The computational results are compared to the measurements with respect to detailed velocity and pressure distributions at several measurement sections and several operating conditions. The computational results are also compared to coarse grid wall function computations by the TASCflow CFD code, which uses a similar methodology as the CALC‐PMB CFD code used in the present work. The comparisons show where the computational method is sufficient and where it is not sufficient.The behaviour of the computational method is similar for both kinds of water turbines, which shows that experience of computations in water turbines will ultimately give quantitatively correct results. Copyright © 2003 John Wiley & Sons, Ltd.

Aiming at the problem that the traditional water-lubricated bearing cannot carry the heavy load and adapt to the constantly changing operating conditions for the high-power Rim Driven Thruster (RDT), the principle structure of the Magnetic Water-double-suspension Elastic-support Thrust Bearing (MWETB) is designed and the optimal structure parameters of the bearing are selected using simulation. To demonstrate the reliability of the MWETB under the RDTs’ actual working conditions, performance tests, which include the magnetic flux density, magnetic force, and lubrication performance, are carried out. The simulation and experimental results indicate that the optimal offset ratios are in two intervals, and the magnetic alignment and sheath materials have a great effect on the load reduction. The load-carrying force has obvious zoning characteristics with the change in bearing clearance. Besides, compared with the water-lubricated thrust bearings, the MWETB has advantages in terms of minimum film thickness and friction coefficient.

It is important to suppress cavitation phenomenon for lower vibration and noise, which can be realized by structure optimization to reduce cavitation bubbles of flow field. Nonetheless, performance factors in hydrodynamic retarder are usually conflicted when conducting a structure design, it is hard to simultaneously restrain cavitation and improve the retarding performance. In our study, a combination of comprehensive CFD simulation and multi-objective optimization is developed to improve the retarding torque ([Formula: see text]), lessen the volume of Retarder ([Formula: see text]) and reduce the volume of bubbles ([Formula: see text]) in the internal flow field. First, the elaborate CFD simulation calculation, included a refined hexahedral mesh and the stress-blended eddy simulation (SBES), is proposed to investigate the unsteady flow field considering the cavitation, and its accuracy is validated by experimental data. Then, the RSM (Respond Surface Method) approximation model is constructed by combination of DOE (Design of Method) and CFD methods. The NSGA-II (Non-Dominated Sorting Genetic Algorithm) is selected as multi-objective optimization algorithm, and the weight and scale factor of each sub objective are specified. The optimization results, verified by theoretical calculation, show that [Formula: see text] is increased by 22%–24%, [Formula: see text] is reduced by 32%–45% and [Formula: see text] is reduced by 1%. Furthermore, the comparison of the vortex distributions before and after optimization demonstrates that the optimization improves the flow field impact and pressure loss in the retarder and reduces the number of bubbles resulting in the increasing vortex. Additionally, parameters’ effect on the cavitation and the braking performance are analyzed to efficiently achieve the best comprehensive performance of the retarder design. The newly-developed optimization method, which can understand the optimization principle and guide a balance between the cavitation and the retarding performance improvement, will reduce huge trial cost and time cost in the manufacture.

In this article, an aerostatic thrust bearing with annular elastic uniform pressure plate structure was designed. In order to obtain a relationship between bearing capacity and stiffness of aerostatic thrust bearing designed in this article, first, the stress field mechanics model of the gas thrust bearing was established in the static. Second, deformation control equations of the elastic uniform pressure plate and gas lubrication Reynolds equation were established according to the flow continuity principle. Here, finite element mesh of gas flow field was woven using the technology of grid overlapping and grid stitching. Then, gas–solid coupling control equations were solved using the numerical method. Gas film pressure distribution and gas static bearing capacity of thrust bearing were analyzed. Function relationship between bearing capacity and the stiffness and the thickness of gas film was obtained. Finally, the results of theory analysis and experiment were compared. The results of the comparison can be listed as, under the effect of gas pressure, orifice area and the equilibrium pressure groove depth are changed due to elastic deformation of the elastic uniform pressure plate. The static stiffness of aerostatic thrust bearing with elastic equilibrium pressure groove increased by 30% than the static stiffness of aerostatic thrust bearing with rigid equilibrium pressure groove. The maximum carrying capacity occurred in the gas film thickness of 3.5 µm. The maximum static stiffness appeared in the gas film thickness of 5.5 µm. It can be seen from the comparison results of experiments and theoretical analysis that data results of gas film thickness and the bearing capacity are the same. The feasibility of the theoretical analysis method is validated.

The geometry of the 2-lobe rotors of a roots blower is proposed by the combination of three arcs and is parameterized by two independent variables. By considering a standard combination of these variables, attempts are made to grasp the unsteady interior flow phenomena and thermal interaction in the blower as well as to comprehend the effect of main influencing factors on the performance of the blower using a transient finite volume-based dynamic-mesh-rearrangement method. A grid-independent test is conducted, and the adopted methodology is validated. At first, an endeavor is made to realize the transient internal flow field and heat interaction within the roots blower. Then, individual efforts are made to apprehend the effect of rotor speed, discharge pressure, and clearance size (provided in between the rotors or in between the rotors and casing) on the said transient flow dynamics and heat interaction. Time variation of the discharge velocity, mass flowrate, and discharge temperature are found to be fluctuating in nature. Pressure, velocity, and temperature distributions in the blower, as well as the leakages, backflow, vortices in the blower, etc., at different moments, are found to be strongly dependent on the rotor speed, discharge pressure, clearance size between the rotors or between the rotor and housing. The nature and amplitude of the time variation of exhaust velocity, discharge mass flowrate, outlet-temperature, and the blower performance are also found to be very much sensitive to the chosen rotor speed, discharge pressure, and clearance size.

A typical submersible well pump was investigated in this article. The whole flow field of submersible well pump was numerically simulated by computational fluid dynamics software. The influence of clearance of wear-rings on the external characteristic and internal flow field was analyzed through comparing the calculation results with experimental results. The result of the numerical simulation shows that changing clearance of front wear-ring has a greater impact on pump performances than changing clearance of back wear-ring, and the head and efficiency of pump decrease with the increase in the size of clearance. Especially when the size of clearance is larger than 0.5 mm, decreasing becomes more obvious. When the front and back wear-ring size of the clearance comes to 1.0 mm, the efficiency decreases from the highest point of 75.31% to 65.44% at rated flow, and the head of pump decreases about 3.5 m. When the size of clearance is 0.2 mm, reverse-flow will appear in the front shroud cavity of the impeller, and leakage from back wear-ring through the balance hole into the impeller, which has a little influence on the flow field of the impeller inlet.