Thermohydrodynamic Research Articles

Parametric Design Optimization of Convergent Textured Thrust Bearing in THD Behaviour

Textured thrust bearing is a technological means capable of providing higher performance compared to untextured bearing. This paper presents a parametric design optimization with thermohydrodynamic (THD) behaviour of textured thrust bearing in a range of convergence ratios. The bearing consists of eight pads (stator), film fluid and a collar (rotor). The main objective of this optimization is to provide higher load capacity, to relatively minimize the maximum temperature of the pad and the friction torque. To this aim, we perform a 3D computational fluid dynamics model for convergent thrust bearing with individual angular sector shaped texturing with a flat bottom profile pad, by using ANSYS. CFX, and considered a thermal effect.

A Mixed Zero-Equation and One-Equation Turbulence Model in Fluid-Film Thrust Bearings

Abstract A thrust bearing is a rotary bearing that facilitates rotational movement between components and is specifically engineered to provide support for a load that is parallel to the axis of rotation. The generation of the inter-surface film pressure is attributed to the relative motion (rotation) of the surfaces, which results in the lubricant being drawn into the converging wedge formed between them. The interface between the unmovable and moving parts is demarcated by a slender layer of lubricating fluid, including but not limited to oil, water, air, or other process fluid. The conventional zero-equation model can be enhanced to achieve higher precision in forecasting and reduce dependence on empirical data, owing to its inherent limitations. A novel turbulence model that combines zero-equation and one-equation approaches has been developed and implemented in the recently introduced modeling tool package for thrust bearings. In the Prandtl one-equation turbulence model, the length scale is a necessary but undetermined term. A novel mixed model has been implemented utilizing the Prandtl one-equation along with a novel-length scale. The tool package is a Thermo-Hydrodynamic (THD) code that involves iterative computations between the Reynolds’ equation, turbulence equation, energy equation within the film, and conduction equation in pad and runner. The new model yields an eddy viscosity that exhibits a substantial level of proximity to both eddy viscosity transport (EVT) and direct numerical simulation (DNS), and exhibits significant enhancements in comparison to the traditional Ng–Pan zero-equation turbulence model.

Artificial neural network for tilting pad journal bearing characterization

Tilting pad journal bearings (TPJBs) are modeled with Reynold-based models or computational fluid dynamics (CFD) approach. In both cases, the estimation of the dynamic coefficients of the oil-film forces and the static characteristic, can be computationally expensive and time consuming. Artificial Intelligence (AI) is assuming a key role in engineering but is rarely applied in fluid film bearing analysis. A properly trained Deep Learning (DL) model can perform very fast predictions of TPJB behavior with accuracy comparable to more time-consuming models. In this case, the main drawback is the time required to build the training dataset. In this work, an Artificial Neural Network (ANN) is trained to predict the dynamic stiffness and damping coefficients along with the main static quantities of TPJBs, such as minimum oil-film thickness and inlet flowrate. At first, a design of experiment is performed to build an appropriate training dataset. Secondly, a Reynolds-based thermo-hydrodynamic (THD) model is used to populate the training dataset and an appropriate test dataset. Then, a feed-forward ANN is trained with Levenberg–Marquardt backpropagation and its architecture is optimized to increase accuracy. Finally, the accuracy of the ANN is tested using the test dataset and experimental data. The time and computational effort required by the ANN regression are much less than those required by the THD model. Therefore, the trained ANN is an effective and efficient tool for the characterization of TPJBs.

Dynamic Behavior of a Tilting-Pad Thrust Bearing Operating Under a Hybrid Lubrication Regime

Abstract The present contribution aims to evaluate the effects of the oil pressure injection on the dynamic behavior of a hybrid-lubricated tilting-pad thrust bearing. First, a thermohydrodynamic model is applied to determine the equilibrium position as dictated by pressure and temperature distributions resulting from both hydrodynamic and hybrid lubrication regimes. Subsequently, the perturbation and frequency reduction methods are applied to determine the stiffness and damping coefficients of the bearing for various operational conditions. The results show that the dynamic force coefficients are strongly dependent on the operational conditions of the bearing, such as static load and rotating speed, as well as the perturbation frequency, for both lubrication regimes. The quantification of the injection pressure influence on the force coefficients of hybrid-lubricated thrust bearings is the main original contribution of this work.

A Mixed Lubrication Deterministic Model of an Elastic Support Water-Lubricated Tilting Pad Thrust Bearing

In order to study the effect of surface roughness on lubrication performance of an elastic support water-lubricated tilting pad thrust bearing, a mixed lubrication (ML) deterministic model is hereby presented based on a unified Reynolds equation model. This very model incorporates the elastic–plastic deformation of asperities and polymer matrix of the thrust pad, as well as the elastic deformation of the rubber support. The randomly distributed surface roughness of the thrust pad is generated by a mathematical model and shares the same distribution characteristics as the measured surface roughness. The Greenwood and Williamson asperity contact model and thin plate deformation model are combined to solve the asperities contact stress and deformation. Meanwhile, the bearing ML performance is compared with the results calculated by a thermohydrodynamic (THD) lubrication model and a thermo-elasto-hydrodynamic (TEHD) lubrication model, while the film thickness is also compared with measurements. The results show that the water film thickness calculated by the ML model is smaller than that by the THD model and the TEHD model, but the water film temperature is higher. The roughness has a great influence on the contact area ratio and the lubrication state, but little effect on the average film thickness. A higher roughness indicates a higher rotational speed required for the bearing to achieve full hydrodynamic lubrication. The film thickness calculated by the mixed lubrication model is closer to the measured results. Overall, it is proved that the mixed lubrication model can more accurately predict the lubrication performance of bearings. Compared to the thin plate deformation model, the elastic deformation simulation based on the half-infinite space model severely overestimates the elastic deformation of the pad surface, making it unsuitable for calculating the elastic deformation of the polymer matrix of the thrust pad under contact force or water film pressure. This ML deterministic model provides an effective means for high-precision prediction of the lubrication performance of the elastic supported water-lubricated thrust bearings coupled with multi-layer soft materials.

Study of Dynamic Characteristics of Water-Lubricated Journal Bearings Using Thermohydrodynamic Cavitating Lubrication Model

Cavitation is prone to occur in high-speed water-lubricated journal bearings. However, the effect of cavitation on the dynamic characteristics of high-speed water-lubricated journal bearings has not been studied thoroughly. This study focuses on this topic. A thermohydrodynamic (THD) cavitating lubrication model was established for the high-speed water-lubricated journal bearings, including the generalized Reynolds equation, the energy equation, and the force balance equation for bubbles. An equilibrium distribution was introduced to describe the cavitation effect, and parameters were obtained by fitting the measured volume distribution of bubbles. The dynamic characteristics of the water-lubricated journal bearings were calculated, considering the influence of thermal and cavitation effects. An experimental setup was developed to validate the proposed model. The simulated results show that two secondary temperature peaks appear in the divergence zone of the bearing due to the cavitation effect. The cavitation effect should be considered when establishing the model for high-speed water-lubricated journal bearings, especially if it is under a large eccentricity ratio.

A new modified boundary slip model for thrust bearing performance under fluid–thermal–structure interaction regime

PurposeThis study aims to investigate the thermohydrodynamic (THD) and thermoelastohydrodynamic (TEHD) performance of an air-lubricated thrust bearing under different slip conditions, especially the slip length effect.Design/methodology/approachIn this study, a new modified boundary slip model was established to investigate thrust bearing performance. The THD and TEHD bearing characteristic distribution was analyzed with fluid–thermal–structure interaction approach. The effect of the slip length on the bearing performance was studied using various bearing structure parameters.FindingsThe increased slip length changed the classical feature distribution of the film pressure and temperature. The sacrifice of the bearing load capacity effectively compensated for the aerodynamic thermal effect and friction torque under the slip condition. The TEHD model has a lower film pressure and load capacity than the THD model. However, it also has lower film temperature, lower friction torque and smaller Knudsen number (Kn).Originality/valueThe bearing THD and TEHD performances of the modified boundary slip model were compared with those of a traditional no-slip bearing. The results help to guide the selection of the bearing surface materials and processing technology of rotor and foil, so as to fully control the degree of slip and make use of it.

Modeling of thermohydrodynamic processes in Lake Chany

The paper presents the results of the computer simulation of the thermohydrodynamic (THD) processes in a shallow water body based on the open software package Delft3D. The object of modeling is closed Lake Chany - the largest natural water body in Western Siberia. To construct a computer THD-model of Lake Chany digital elevation model of its basin was refined and a database containing meteorological information from coastal area stations and hydrological data of the lake and its tributaries was prepared. Simulation calculations of THD processes for open-water period in 2018 are performed. The analysis of the results showed that the constructed 2DH computer model of Lake Chany allows to reproduce the observed features of its thermal regime for the ice-free period.

On the thermohydrodynamic performance of aerated lubricants in steadily- and dynamically-loaded journal bearings

The effect of aerated oil, containing air bubbles, on the steadily and dynamically loaded journal bearing is investigated. The study is based on the thermohydrodynamic (THD) lubrication theory, which fully couples the Reynolds equation with the energy for the oil and heat conduction equations for solids through the oil viscosity. The oil’s effective viscosity is influenced by the presence of bubbles via the surface tension and/or the volume fraction. The Reynolds equation is solved using the mass conservation algorithm and the two-dimensional equations for the temperature fields both in oil and solids are solved simultaneously to save computational time. The bubble radius, density, and viscosity are directly influenced by the pressure and temperature fields, requiring updating their values at each pressure and temperature. The simulations show that with a realistic viscosity model, the effect of the air bubbles in the lubricating oil on the pressure and temperature fields is small at normal operating speeds, while the density and the effective viscosity are reduced noticeably due to bubbles.

Geometric and Thermo Hydrodynamic Investigation of a 3d Converging-Diverging Channel by Taguchi and Anfis Methods

Geometric and Thermo Hydrodynamic Investigation of a 3d Converging-Diverging Channel by Taguchi and Anfis Methods

CFD ANALYSIS OF THERMOHYDRODYNAMIC BEHAVIOR OF NANOLUBRICATED JOURNAL BEARINGS CONSIDERING CAVITATION EFFECT

The present work displays an extensive numerical analysis for the thermo-hydrodynamic (THD) behavior in finite length journal bearings lubricated with different types of nano-lubricants considering cavitation effect. The effects of nanoparticle concentrations, cavitation and temperature rise on the performance parameters of such bearings have been explored. The bearing is simulated using Computational Fluid Dynamic (CFD) approach. The effect of using different types of nano-lubricants with different volume fractions of TiO2 and Al2O3 nanoparticles dispersed in Veedol Avalon ISO Viscosity grade 46 oil has been demonstrated. Modified Krieger-Dougherty equation has been implemented with the thermal viscosity model to to evaluate the oil effective viscosity. The obtained results show that concerning the TiO2 nanoparticles results in a higher oil film pressure and load carrying capacity in comparison with Al2O3. The bearing equilibrium position was obtained by using Response Surface analysis (RSA) with optimal space-filling design technique. The numerical model was validated by comparing the results obtained in the present work with that obtained by Feron et al. The results were found to be in a good confirmation. The attained results show that the maximum pressure grows by 21% when the bearing is lubricated with nano-lubricant.

Operating Behavior of Sliding Planet Gear Bearings for Wind Turbine Gearbox Applications—Part I: Basic Relations

The application of sliding planet gear bearings in wind turbine gearboxes has become more common in recent years. Assuming practically applied helix angles, the gear mesh of the planet stage causes high force and moment loads for these bearings involving high local loads at the bearing edges. Specific operating behavior and suitable design measures to cope with these challenging conditions are studied in detail based on a thermo-hydrodynamic (THD) bearing model. Radial clearance and axial crowning are identified as important design parameters to reduce maximum pressures occurring at the bearing edges. Furthermore, results indicate that a distinct analysis of the gear mesh load distribution is required to characterize bearing operating behavior at part-load. Here, operating conditions as critical as the ones reached at nominal load might occur. Wear phenomena can improve the shape of the gap in the circumferential as well as in axial direction incorporating a significant reduction of local maximum pressures. The complexity of the combination of these aspects and the additionally expected impact of structure deformation gives an insight into the challenges in the design processes of sliding planet gear bearings for wind turbine gearbox applications.

Prediction on Flow and Thermal Characteristics of Ultrathin Lubricant Film of Hydrodynamic Journal Bearing.

This paper focuses on the flow and thermal characteristics of the lubricant film in the micro clearance of a hydrodynamic journal bearing (HJB) at high rotating speed. A thermohydrodynamic (THD) method consists of the Reynolds equation coupled with energy and viscosity-temperature equation with considering the cavitation is put forward. The 3D surface diagrams of the lubricant film thickness, pressure, temperature, liquid mass fraction, flow rate and heat dissipation distributions under different geometric, operating, slip and no-slip boundary conditions are systemically exhibited and analyzed. The results show that with the rise of eccentricity or length diameter ratio, the maximum peaks of pressure, temperature and heat dissipation are rapidly increased, the cavitation is aggravated, and the flow rate is accelerated in different extent. As the bearing speed accelerating, the maximum peak of temperature is strongly increased, whereas, the distinction between peaks of flow rate and heat dissipation is magnified and reduced, respectively. It provides a fruitful inside view of the inner flow and thermal characterizations of HJB for further understanding its flow-thermal interaction mechanisms and offers theoretical support for improving its working performance.

A three-dimensional thermohydrodynamic model for Krasnoyarsk Reservoir

The paper presents a 3D model for a deep flowing water body based on the open software package Delft3D to describe and predict thermohydrodynamic (THD) processes in existing and projected reservoirs of Siberia. As an example, a 3D model for non-stationary THD processes of the Krasnoyarsk Reservoir was built and tested. For its construction, we developed a Digital Relief Model (DRM) for the Krasnoyarsk Reservoir basin, generated a finite-difference grid, identified the empirical constants and formulated the initial and boundary conditions. Numerical simulation of current velocity and water temperature of the reservoir for spring/summer of the scenario year was performed.

Numerical Study of a Journal Bearing with Scratches: Validation with Literature and Comparison with Experimental Data

The lifespan of journal bearings is directly related to the operating conditions they have to face and reducing their maintenance intervals allows one to have a clear idea about their performance when issues occur. The presence of scratches on one of its surfaces degrades the performance of a journal bearing. These effects have already been assessed in experiments; however, numerical studies on this subject are still scarce. This work develops a numerical thermohydrodynamic (THD) program using the finite volume method to simulate the effects of scratches on the performance of journal bearings. To test the validity of the program, the numerical results are compared with the scientific literature and with experimental measurements conducted using the Pprime Institute journal bearing test rig. Some minor discrepancies are observed, but the overall results are in good agreement.

Kriging Approach Dedicated to Represent Hydrodynamic Bearings

Abstract The mathematical modeling of journal bearings has advanced significantly since the Reynolds equation was first proposed. Advances in the processing capacity of computers and numerical techniques led to multiphysical models that are able to describe the behavior of hydrodynamic bearings. However, many researchers prefer to apply simple models of these components in rotor-bearing analyses due to the computational effort that complex models require. Surrogate modeling techniques are statistical procedures that can be applied to represent complex models. In this work, Kriging models are formulated to substitute the thermohydrodynamic (THD) models of three different bearings found in a Francis hydropower unit, namely, a cylindrical journal (CJ) bearing, a tilting-pad journal (TPJ) bearing, and a tilting-pad thrust (TPT) bearing. The results determined by using the proposed approach reveal that Kriging models can be satisfactorily used as surrogate THD models of hydrodynamic bearings.

Influence of Injection Pressure on the Thermohydrodynamic Behavior of Tilting Pad Journal Bearings—Model and Experiment

In rotating machines, tilting pad journal bearings (TPJBs) are widely used because of their enhanced design stability in comparison with alternative bearing configurations. In the present research, a thermohydrodynamic (THD) lubrication model for a tilting pad bearing with injection is developed. Within the THD lubrication model, the lubricant is also fed into each pad through a central injection orifice. The effects on the lubricant oil film pressures and temperatures and subsequent influences on the system dynamic behavior were investigated. Another important factor considered within the THD model is associated with the flexibility of the pivot of each pad and its impact on the behavior of the bearing when subjected to direct lubricant injection. The numerical model results are compared with the measurements of the rotor equilibrium position within the bearing and the pad temperatures obtained from the test rig designed specifically for the TPJB geometry with and without central pad injection. Pad temperatures are measured before the injection orifice position and after it. Agreement between experimental and model-predicted results provides confidence in the model’s ability to evaluate the dynamic behavior of the bearing and its effect on the complete system through the stiffness and damping coefficients.

Investigation of the Tribological Performance of Heterogeneous Slip/No-Slip Journal Bearing Considering Thermo-Hydrodynamic Effects

The slip boundary has an important influence on hydrodynamic journal bearing. However, less attention has been paid to the positive effect of slip on thermal behaviour. In this study, a computational fluid dynamics (CFD) analysis investigating the thermo-hydrodynamic (THD) characteristics of heterogeneous slip/no-slip bearings running under steady, incompressible, and turbulent conditions is presented. A comprehensive analysis is made to investigate the THD behaviours of heterogeneous slip/no-slip bearings in terms of lubricant pressure, temperature distribution, volume fraction of vapor, and load-carrying capacity when they are running under different shaft rotational speeds. The multiphase cavitation model is adopted to represent the real operational condition of the journal bearing. Numerical results show that the load-carrying capacity of the heterogeneous slip/no-slip bearing can be significantly increased by up to 100% depending on the rotational speed. It is also observed that there is an optimal journal rotational speed for maximizing the load-carrying capacity. An insightful new finding is revealed in a numerical framework, wherein it is found that by introducing the heterogeneous slip/no-slip pattern, the maximum temperature can be reduced by up to 25% in comparison with a conventional bearing.

Squeeze Film Damper Suppression of Thermal Bow-Morton Effect Instability

Abstract The Morton effect (ME) is a synchronous vibration problem in turbomachinery caused by the nonuniform viscous heating around the journal circumference, and its resultant thermal bow (TB) and ensuing synchronous vibration. This paper treats the unconventional application of the SFD for the mitigation of ME-induced vibration. Installing a properly designed squeeze film damper (SFD) may change the rotor's critical speed location, damping, and deflection shape, and thereby suppress the vibration caused by the ME. The effectiveness of the SFD on suppressing the ME is tested via linear and nonlinear simulation studies employing a three-dimensional (3D) thermohydrodynamic (THD) tilting pad journal bearing (TJPB), and a flexible, Euler beam rotor model. The example rotor model is for a compressor that experimentally exhibited an unacceptable vibration level along with significant journal differential heating near 8000 rpm. The SFD model includes fluid inertia and is installed on the nondrive end bearing location where the asymmetric viscous heating of the journal is highest. The influence of SFD cage stiffness is evaluated.

Thermohydrodynamic Characteristics and Stability Analysis for a Journal Hybrid Floating Ring Bearing Within Laminar and Turbulent Mixed Flow Regime

Abstract There exist laminar and turbulent flow in the inner and outer fluid film of the hybrid floating ring bearing at high speed. The finite element method (FEM) and finite difference method (FDM) are used to solve the thermohydrodynamic (THD) lubrication model within the laminar and turbulent mixed flow regime which governs the pressure, temperature, viscosity, and Reynolds number of the two-layer fluid films together for a type of the journal hybrid floating ring bearing with deep/shallow pockets. The static and dynamic characteristics are analyzed including the load capacity, the friction moment, the volume flowrate, the stiffness, and damping coefficients with consideration of the mixed flow and thermal effect based on the floating ring balance. The unitized kinematic model of the shaft and floating ring is proposed to deduce the instability criteria and calculate the threshold rotational speed of a rigid Jeffcott rotor system supported on two hybrid floating ring bearings by the Routh–Hurwitz method. The results present that there are non-uniform pressure and temperature profile within the fluid film field, and the laminar flow and turbulent flow appear at certain positions of film through theory and experiment, separately. The mixed flow effect promotes the bearing load capacity and the friction moment at high speed and eccentricity, and the system threshold speed drops within the mixed flow regime. Therefore, the thermal effect and mixed flow existing in the fluid film should be considered into the lubrication analysis for the floating ring bearing.