JFO Boundary Conditions Research Articles

Effect of lubricant inertia on textured journal bearing implementing mass conserving (JFO) boundary conditions

Purpose Cavitation plays a significant role in the performance of textured journal bearings. Furthermore, because of the usage of low-viscosity lubricants and the high working speed of machines, it is pertinent to consider the lubricant inertia while analyzing the operating characteristics of bearings. This paper aims to investigate the influence of lubricant inertia in the case of a spherically textured journal bearing, considering both protrusion and dimple texturing and implementing the mass-conserving (JFO) boundary conditions. Design/methodology/approach A novel modified Reynolds equation has been developed to accommodate the effects of lubricant inertia and cavitation. The cavitation is treated by using mass-conserving (Jakobsson−Floberg−Olsson [JFO]) boundary conditions. The governing equation is solved by the Gauss−Seidel method with successive over-relaxation. To enhance computational efficiency and expedite the convergence process, the progressive mesh densification (PMD) method has been integrated into the solution process. Findings The current study indicates that the JFO boundary conditions result in higher load-carrying capacity and lesser friction variables for heavily loaded bearings, whereas the flow coefficient is reduced due to the application of JFO boundary conditions. The lubricant inertia effect enhances the flow coefficients for lightly loaded and protrusion-textured bearings. Originality/value It is crucial to understand the combined effects of lubricant inertia and cavitation for the effective design of textured journal bearings. The findings from this work will help in designing textured journal bearings more effectively and accurately, particularly when low-viscosity oil is used. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2024-0276/

A model of contact deep groove seals based on partition model and JFO boundary condition

Unlike nuclear main pump seals, deep groove seals in aero-engines operate on a contact basis. However, the precise working mechanism and accurate quantitative methods for assessing their sealing performance remain elusive. This paper introduces a fluid-solid-thermal coupling model for contact deep groove seals, utilizing a partition model and considering JFO boundary condition, mixed lubrication, and detailed heat calculations. The model significantly enhances accuracy compared to original approaches. It comprehensively accounts for contact effects, thermal deformations, convergence wedges, radial waviness, hydrodynamic pressures, groove drainage, and convection, revealing characteristics of contact deep groove seals such as high stiffness, effective heat dissipation, wear resistance, and prolonged service life. The proposed model and working mechanism provide theoretical guidance for designing diverse deep groove seal structures.

Influence of mass conservation cavitation boundary on transient performance of water-lubricated bearings

Given the current research gap regarding cavitation phenomena and startup conditions in water-lubricated bearings (WLBs), this study offers an innovative approach by integrating the mass conservation boundary condition proposed by Jakobsson, Floberg, and Olsson (known as the JFO boundary condition) with a transient mixed lubrication model of WLBs. It also considers the impact of elastic deformation and surface roughness peaks, thus establishing a transient startup model of WLBs that incorporates the cavitation effect. Furthermore, the dynamic behaviors of this boundary condition are contrasted with the commonly used Reynolds boundary condition during the startup process of the bearings, as well as under eccentric and step load impacts. The findings demonstrate that the JFO boundary condition, accounting for cavitation effects, significantly influences the transient performance of WLBs. The presence of a cavitation region diminishes the damping of the bearing system following step load impacts, leading to increased overshoot and adjustment time while weakening the system's self-adjusting ability against step loads. This study offers valuable insights for theoretical analysis of ship propulsion systems operating under complex conditions.

An arbitrary Lagrangian–Eulerian formulation for the Reynolds equation considering the JFO boundary condition

AbstractIn the realm of lubrication theory, the hydrodynamics of the fluid lubricant are commonly elucidated through the Reynolds equation. Its establishment stems from using the Eulerian description method, restricting the fluid domain to a fixed spatial configuration. However, certain scenarios necessitate coupling the Reynolds equation with solid deformation, wherein the fluid boundary undergoes alterations concurrent with the displacement or deformation of the solid. In such cases, the employment of a movable fluid domain becomes imperative. To address this requirement, this contribution introduces the arbitrary Lagrangian–Eulerian method, which effectively transforms the reference system of the Reynolds equation into a fluid domain amenable to arbitrary movement. Subsequently, the weak formulation associated with the movable fluid domain is derived and synergistically combined with a preexisting cavitation formulation. This integration facilitates an efficient solution of the Reynolds equation utilizing the finite element method while duly accounting for the mass‐conserving cavitation effects. Ultimately, a transient hydrodynamic lubrication example is presented to demonstrate the feasibility of the newly developed formulations.

Performance of rough surface hydrodynamic circular and multi-lobe journal bearings in turbulent regimes

This article deals with the steady and dynamic performance analysis of rough surface circular and multi-lobe journal bearings operating with non-Newtonian lubricant in turbulent regimes. The numerical solution of Reynold's equation was obtained using the finite element method. To account for surface roughness, the Patir and Cheng model was used, and fluid turbulent behavior was modeled using the turbulent theory as proposed by Ng and Pan. The non-Newtonian behavior of the lubricant is presented by the Rabinowitsch fluid model, and JFO boundary conditions are used to solve Reynold's equation, considering gaseous cavitation. The bearing with micro-roughness has been considered in numerical analysis and transverse roughness has been reported to improve bearing performance indices. Among the different bearing design configurations, the two-lobe bearing configuration provides significantly improves the minimum film thickness, hydrodynamic pressure, and dynamic parameters. The presence of turbulent flow and transverse surface roughness produces a synergistic effect that enhances the minimum film thickness, stiffness, and damping parameters of journal bearings. This study provides a detailed comparison between various bearing designs and recommends the use of two-lobe bearings for high-speed applications.

Influence of spherical protruded and dimple texture on the journal bearing performance: A comparative theoretical analysis implementing JFO boundary conditions

PurposeThe purpose of this paper is to compare the spherical protruded and dimple textured journal bearings performance characteristics with the untextured bearing.Design/methodology/approachThe governing Reynolds equation considering the mass conserving (JFO) boundary conditions is solved using the computationally efficient progressive mesh densification (PMD) method. The central difference scheme is used for the discretization of the governing Reynolds equation. The numerical code developed is validated with the experimental results available in the literature.FindingsFrom this numerical study, it has been observed that the protruded textured journal bearing gives better performance compared to the dimple textured and untextured journal bearing for friction variable, whereas dimple textured journal bearing provides better performance compared to the protruded textured and untextured journal bearing for load carrying capacity and flow coefficient. For better performance, dimple and protruded textured bearings must be textured in second-half textured region configuration.Practical implicationsThe results shown here would be quite useful for the researchers generally and the bearing designers particularly.Originality/valueThe load carrying capacity should be maximum whereas, the friction coefficient should be minimum and also the adequate flow of lubricant is necessary to maintain hydrodynamic lubrication and to remove the heat generated within the bearing due to friction, which impacts the bearing performance and life. Thus, this study would be significant in effective bearing design aspect.

Effect of slip position on the hydrodynamic performance of liquid film seal

Purpose The purpose of this paper is to investigate the effect of slip position on the performance of liquid film seal. Design/methodology/approach A mathematical model of liquid film seal with slip/no-slip surface was established based on the Navier slip model and JFO boundary condition. Liquid film governing equation was discretized by the finite difference method and solved by the SOR relaxation iterative algorithm and the effects of slip position on sealing performance are discussed. Findings The results indicate that boundary slip plays an important role in the overall performance of a seal and a reasonable arrangement of slip position can improve the steady-state performance of liquid film seal. Originality/value Based on the mathematical model, the optimal parameters for liquid film seal with boundary slip at groove are obtained. The results presented in this study are expected to provide a theoretical basis to improve the design method of liquid film seal. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2020-0082/

Texture shape effects on hydrodynamic journal bearing performances using mass-conserving numerical approach

ABSTRACTIt is a known fact that incorporating textures in the contact surfaces can significantly enhance bearing performances. The purpose of this paper is to outline the effects of texture bottom profiles and contour geometries on the performances of hydrodynamic textured journal bearings. The analysis was conducted using computational approach to test eight texture shapes: rectangular, cylindrical, spherical, triangular (TR, T1, T2, T3) and chevron. The steady-state Reynolds equation for modelling the hydrodynamic behaviour of thin viscous film was solved using finite difference technique and mass conservation algorithm (JFO boundary conditions), taking into account the presence of textures on both full film and cavitation regions. The comparison with the benchmark data shows good consistency and an enhancement in bearing performances (load carrying capacity and friction). The results clearly show that the mechanisms of wedge effect and micro-step bearing for the full/partial texturing feature are the main crucial parameters, where the convergent wedge effect present in T2 triangular texture shape can significantly enhance the load-carrying capacity, while the divergent wedge action causes a net load loss. Considering the right arrangement of textures on the contact surface, their surface contours can have a significant impact on the performance of hydrodynamic journal bearings at high eccentricity ratios.

Influence of micro-grooves on the lubrication performance of a misaligned bearing

Surface texturing for improving the lubrication performance of journal bearings has been widely investigated in the last two decades. In practical applications, the misalignment of a journal bearing occurs due to the asymmetric bearing load, elastic deflection, manufacturing tolerances, and installation errors. However, there has been little discussion on the influence of grooves on the lubrication performance of misaligned bearings. In the present work, numerical predictions of lubrication performances are presented to test the influence of the grooves. Based on the JFO boundary condition, a mass conservation algorithm is implemented to automatically determine the position of oil film rupture and reformation. The load-carrying capacity, friction force, friction coefficient, and bearing moment are computed numerically. The influence of angular position of the groove is first conducted in a misaligned bearing. Subsequently, the groove depth and width are investigated with different values of [Formula: see text] and [Formula: see text] ratios, respectively.

Performance of hydrodynamic journal bearing under the combined influence of textured surface and journal misalignment: A numerical survey

A wisely chosen geometry of micro textures with the favorable relative motion of lubricated surfaces in contacts can enhance tribological characteristics. In this paper, a computational investigation related to the combined influence of bearing surface texturing and journal misalignment on the performances of hydrodynamic journal bearings is reported. To this end, a numerical analysis is performed to test three texture shapes: square “SQ”, cylindrical “CY”, and triangular “TR”, and shaft misalignment variation in angle and degree. The Reynolds equation of a thin viscous film is solved using a finite differences scheme and a mass conservation algorithm (JFO boundary conditions), taking into account the presence of textures on both full film and cavitation regions. Preliminary results are compared with benchmark data and are consistent with a positive enhancement in misaligned bearing performances (load carrying capacity and friction). The results suggest that the micro-step bearing mechanism is a key parameter, where the micro-pressure recovery action present in dimples located at the second angular part of the bearing (from 180° to 360°) can compensate for the loss on performances caused by shaft misalignment, while the micro-pressure drop effect at the full film region causes poor performances. Considering the right arrangement of textures on the contact surface, their contours geometries can have a significant impact on the performance of misaligned journal bearings, particularly at high eccentricity ratios, high misalignment degrees and when the misalignment angle α approaches to 0° or 180°.

Influence of Spiral Angle on the Performance of Spiral Oil Wedge Sleeve Bearing

Spiral angel is an important structure parameter of spiral oil wedge sleeve bearing, which produces greater impact on bearing performance. Based on JFO boundary condition, the generalized Reynolds equations considering four slip conditions are established. Using the concept of partial derivatives, stiffness and damping coefficients of sleeve bearing are calculated. The results show that carrying capacity and friction drag of oil film decrease, temperature rise decreases first and then increases, and end leakage rate, stiffness, and damping coefficients generally increase first and then decrease with the increase of spiral angle. The carrying capacity, friction drag, temperature rise, stiffness, and damping coefficients are smaller and the end leakage rate is higher considering wall slip and JFO condition compared with reckoning with no slip and Reynolds boundary condition.

Influences of journal with 3D form errors on dynamic coefficients of hydrodynamic bearings yielded to JFO boundary conditions

The dynamic characteristics of the journal with form error are analyzed, including normalized stiffness and damping coefficients. A new expression for journal surface with form error is presented, which is capable of formulating any types of form errors on the journal, and the dimensionless Reynolds equation is renewed and solved suffering from the Jakobsson, Floberg, and Olsson boundary conditions. The results show that form errors do have a significant influence on the dynamic performance of journal bearings and that the uncertainty attribute of form error could result in variations of dynamic properties so significantly that the system might operate in an entirely different way. Therefore, it is necessary to take more operating information into account, such as the elaborate state of the journal surface, in order to predict the bearing performance more accurately.

Research on two methods for improving the axial static and dynamic characteristics of hydrostatic lead screws

This paper researches two methods for improving the axial static and dynamic characteristics of hydrostatic lead screws, i.e. (a) using membrane restrictor instead of capillary restrictor and (b) utilizing the intentional periodic pitch errors in the nut to generate hydrodynamic effect of the lubricating film. The Reynolds’ equation, which is applicable to the lubricating film in hydrostatic lead screws, is deduced based on the equivalent plane of the flank surface of threads. The perturbation technique and the finite difference method are used to obtain the static and dynamic characteristics. The JFO boundary condition is used for capturing the cavitation. The results show that the axial static and dynamic characteristics can gain a marked improvement by combining the two methods.

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

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

그루브 위치가 리니어 압축기용 피스톤과 실린더의 윤활특성에 미치는 영향

LG Electronics Inc.(Received December 10, 2015; Revised January 10, 2016; Accepted January 10, 2016)Abstract − In this paper hydrodynamic lubrication analysis is carried out to investigate the effects of groovelocation on the lubrication performance of a piston and cylinder system in a linear compressor. The rectangleshaped grooves having a constant groove depth and width are applied on the lubrication area of the piston. TheUniversal Reynolds equation is used to calculate the oil film pressure, and the Elrod algorithm with the finitedifferent method is used to solve the governing equation. The JFO boundary condition is applied to predict cav-itation regions. Transient analysis for different locations of the grooves on the piston is carried out using the typ-ical operating condition of the linear compressor in order to estimate the variations of frictional power losses andminimum film thicknesses. When the grooves are applied on the lubrication area, both the frictional power lossand the minimum film thickness decrease. The frictional power loss can be reduced effectively, while main-taining a minimum film thickness to enable the piston operation without direct contact with the cylinder surface,by means of choosing a proper location of the grooves. The optimum location of the grooves to improve a lubri-cation performance depends on the operation condition or the system requirements specification.Keywords − linear compressor(리니어 압축기), hydrodynamic lubrication(유체 윤활), piston(피스톤), cylinderliner(실린더 라이너), groove(그루브), groove location(그루브 위치)

A comparative study of full and partial textured hybrid orifice compensated circular thrust pad bearing system

This work concern with the performance of hybrid circular thrust pad bearing having partial and full textured surface, operating with power law lubricant has been studied. The governing Reynolds equation is non-linear with pressure. Finite element method with JFO boundary conditions has been implemented to obtain fluid film pressure on the bearing surface and cavitation zone. The numerically simulated results reveal that, among the different non-Newtonian lubricants, the dilatant one provides the minimum value of frictional power loss. Results show that surface texture and the behavior of lubricant significantly changes the frictional power loss and other performance parameters. It is expected that the result obtained will be very much quite useful for bearing designer and academic community.

Analysis of a Hydrodynamic Spiral Grooved Upstream Pumping Face Seal Considering Cavitation

A numerical analysis of an oil-lubricated spiral grooved upstream pumping face seal, accounting for the occurrence of cavitation, have been performed in this paper. The “equivalent flow model”, which is a theoretical scheme for taking the JFO boundary condition into hydrodynamic lubrication theory, was applied to the analyses by a finite difference treatment of the Reynolds equation that dealt with the geometry of logarithmic spiral groove. The calculated results were compared respectively based on Reynolds model and JFO model. The load capacity, cavitation ratio, frictional torque and leakage rate were also theoretically calculated. The difference between the theoretical results based on two boundary conditions for cavitation occurrence is considerable. The JFO boundary condition should be used in theoretical studies on sealing characteristics rather than Reynolds equation, especially in the conditions of less groove depth and high rotary speed.

Thermal analysis of microtextured journal bearing using non-Newtonian rheology of lubricant and JFO boundary conditions

This paper presents investigations related to the combined influences of viscous heat dissipation and non-Newtonian rheology of lubricant on the performance parameters of micro-textured journal bearing. The model proposed herein is solved using finite difference technique by incorporating mass conservation algorithm (JFO boundary conditions) and oil mixing temperature concepts. Some results have been also presented with Reynolds boundary conditions (RBC) for comparison point of view. Based on the present numerical investigations, it is found that JFO boundary conditions yield realistic results in comparison to RBC. Moreover, JFO boundary condition provides numerical stability in getting the converged results with micro-textured surfaces of journal bearing. Reductions in average temperature of the lubricant have been noticed in presence of surface texturing in comparison to smooth surface of the bearing.

A uniform cross-speed model of end-face seal ring with spiral grooves for wet clutch

A uniform cross-speed model of end-face seal ring with spiral grooves for wet clutch is developed in this paper. The uniform model considers the asperity contact, hydrodynamic effect of spiral groove and cavitation effect. The asperity contact of rough surfaces is modeled by means of fractal theory, the mixed lubricating model taking into account the centrifugal effect is given based on average flow model and the cavitation model is built by using the JFO boundary condition. The influences of speed and closing pressure are studied by simulating. And test results show good agreement with simulation.

A Finite Element Cavitation Algorithm Using Free Mesh for Mechanical Face Seal

A finite element cavitation algorithm to Reynolds equation is presented for the calculation of the flow field in the film between the faces of the mechanical seal. As using free mesh, the algorithm is particularly useful for the computational domain which shape is complex. The JFO boundary condition which satisfies mass conservation is implemented by introducing Kumar and Booker’s algorithm. A non-traditional finite element method is derived to avoid the process of the functional analysis and can obtain the flow rate on boundaries conveniently. The results show that the algorithm is reliable, effective and correspond to the literature results. Moreover, the algorithm can be also used for the sliding bearings lubrication problem which shows the well adaptability.