Search results

This paper aims to combine the grooves with an annular air thrust bearing with multi-hole restrictors and discusses the influence of the groove parameters on the bearing performance.

Four models of aerostatic bearings with grooves of different geometries are established. The pressure distribution, load-carrying capacity (LCC), stiffness and flow characteristics of the flow field in the bearing clearances are obtained by computational fluid dynamics simulation.

The numerical and simulation results show that air bearing with grooved restrictors can slow down the pressure drop at the air inlet and increase the LCC and stiffness of the bearing. The gas flow in the aerostatic bearing is also studied, and the air vortex in the recess is analyzed.

This research optimizes the structure of the annular air thrust bearing, analyzes the gas vortex in the recess, improves the LCC and stiffness of the bearing and provides a reference for the bearing in the selection of groove parameters.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2023-0006/

The present paper aims to analyse the synergistic effect of pocket orientation and piezo-viscous-polar (PVP) lubrication on the performance of multi-recessed hybrid journal bearing (MHJB) system.

To simulate the behaviour of PVP lubricant in clearance space of the MHJB system, the modified form of Reynolds equation is numerically solved by using finite element method. Galerkin’s method is used to obtain the weak form of the governing equation. The system equation is solved by Gauss–Seidal iterative method to compute the unknown values of nodal oil film pressure. Subsequently, performance characteristics of bearing system are computed.

The simulated results reveal that the location of pressurised lubricant inlets significantly affects the oil film pressure distribution and may cause a significant effect on the characteristics of bearing system. Further, the use of PVP lubricant may significantly enhances the performance of the bearing system, namely.

The present work examines the influence of pocket orientation with respect to loading direction on the characteristics of PVP fluid lubricated MHJB system and provides vital information regarding the design of journal bearing system.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2023-0241/

This study aims to understand how the texture shape, number of textures and addition of nanoparticle additives in lubricants impact the dynamic characteristics of journal bearing by comparing six different texture shapes like triangle, chevron, arc, circle, rectangle and elliptical applied in pressure-increasing region under various geometrical and operating conditions.

The finite element method approach has been employed to solve governing Reynold’s equation, assuming iso-viscous Newtonian fluid, for computation of performance parameters like stiffness and damping coefficient, threshold speed, etc. By using a regression model, the impact of adding nanoparticles Al₂O₃ and CuO to the base lubricant on viscosity variation is calculated for selected temperature ranges and weight fractions of nanoparticles.

The arc-shaped texture with an area density of 28.27%, eccentricity ratio of 0.2 and texture depth of 0.6 exhibited 35.22% higher direct stiffness and 41.4% higher damping coefficient compared to the lowest value in the circle-shaped texture. Increasing the number of arc-shaped textures on the bearing surface with low area density led to declining stiffness and damping parameters. However, with nanoparticle additives, the arc-shaped texture further showed 10.75% and 8.11% improvement in stiffness and 9.99% and 4.87% enhancement in damping coefficient for Al₂O₃ and CuO, respectively, at 90 °C temperature and 0.5% weight fraction.

By understanding the influence of texture shapes on the dynamic characteristics, engineers can design bearings that exhibit improved stability and enhance overall performance.

The floating ring generates elastic deformation as the film pressure for high-speed floating ring bearings (FRBs). The purpose of this study is to investigate the influence of ring elastic deformation on the performance of a hydrodynamic/hydrostatic FRB, including floating ring equilibrium and minimum film thickness.

The finite element method and finite difference method are used to solve thermohydrodynamic (THD) lubrication models, including the Reynolds equation, energy equation and temperature–viscosity equation. The deformation matrix method is applied to solve the elastic deformation equation, and then the deformation distribution, floating ring equilibrium and minimum film thickness are investigated. The maximum pressure is compared with the published article to verify the mathematical models.

The deformation value increases with the growth of shaft speed; owing to elastic deformation on the film reaction force and friction moment, the ring achieves equilibrium at a new position, and the inner eccentricity increases while the ring-shaft speed ratio declines. The minimum film thickness declines with the growth of inlet temperature, and the outer film tends to rupture considering elastic deformation at a higher temperature.

The floating ring elastic deformation is coupled with the THD lubrication equations to study ring deformation on the hydrodynamic/hydrostatic FRB lubrication mechanism. The elastic deformation of floating ring should be considered to improve analysis accuracy for FRBs.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2023-0139/

The mixing of fuel and air plays a pivotal role in enhancing combustion in supersonic regime. Proper mixing stabilizes the flame and prevents blow-off. Blow-off is due to the shorter residence time of fuel and air in the combustor, as the flow is in supersonic regime. The flame is initiated in the local subsonic region created using a flameholder within the supersonic combustor. This study aims to design an effective flameholder which increases the residence time of fuel in the combustor allowing proper combustion preventing blow-off and other instabilities.

The geometry of the strut-based flameholder is altered in the present study to induce a streamwise motion of the fluid downstream of the strut. The streamwise motion of the fluid is initiated by the ramps and grooves of the strut geometry. The numerical simulations were carried out using ANSYS Fluent and are validated against the available experimental and numerical results of cold flow with hydrogen injection using plain strut as the flameholder. In the present study, numerical investigations are performed to analyse the effect on hydrogen injection in strut-based flameholders with ramps and converging grooves using Reynolds-averaged Navier–Stokes equation coupled with Menter’s shear stress transport k-ω turbulence model. The analysis is done to determine the effect of geometrical parameters and flow parameter on the flow structures near the base of the strut where thorough mixing takes place. The geometrical parameters under consideration include the ramp length, groove convergence angle, depth of the groove, groove compression angle and the Mach number. Two different strut configurations, namely, symmetric and asymmetric struts were also studied.

Higher turbulence and complex flow structures are visible in asymmetric strut configuration which develops better mixing of hydrogen and air compared to symmetric strut configuration. The variation in the geometric parameters develop changes in the fluid motion downstream of the strut. The fluid passing through the converging grooves gets decelerated thereby reducing the Mach number by 20% near the base of the strut compared to the straight grooved strut. The shorter ramps are found to be more effective, as the pressure variation in lateral direction is carried along the strut walls downstream of the strut increasing the streamwise motion of the fluid. The decrease in the depth of the groove increases the recirculation zone downstream of the strut. Moreover, the increase in the groove compression angle also increases the turbulence near the base of the strut where the fuel is injected. Variation in the injection port location increases the mixing performance of the combustor by 25%. The turbulence of the fuel jet stream is considerably changed by the increase in the injection velocity. However, the change in the flow field properties within the flow domain is marginal. The increase in fuel mass flow rate brings about considerable change in the flow field inducing stronger shock structures.

The present study identifies the optimum geometry of the strut-based flameholder with ramps and converging grooves. The reaction flow modelling may be performed on the strut geometry incorporating the design features obtained in the present study.

Micro-texture is processed on the surface to reduce the friction of the contact surface, and its application is more and more extensive. The purpose of this paper is to create a texture function model to study the influence of surface parameters on the accuracy of the simulated surface so that it can more accurately reflect the characteristics of the real micro-textured surface.

The microstructure function model of rough surfaces is established based on fractal geometry and polar coordinate theory. The offset angle θ is introduced into the fractal geometry function to make the surface asperity normal perpendicular to the tangent of the surface. The 2D and 3D contour surfaces of the surface groove texture are analyzed by MATLAB simulation. The effects of fractal parameters (D and G) and texture parameter h on the curvature of the surface micro-texture model were studied.

This paper more accurately characterizes the textured 3D curved surface, especially the surface curvature. The scale coefficient G significantly affects curvature, and the influence of fractal dimension D and texture parameters on curvature can be ignored.

The micro-texture model of the rough surface was successfully established, and the range of fractal parameters was determined. It provides a new method for the study of surface micro-texture tribology.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2023-0298/

This study aims to research the influence mechanism of microtextured geometric parameters of dry gas seal end face on the tribological behavior under dry frictional conditions.

The microtexture was processed using laser processing, while the diamond-like carbon (DLC) film was applied through magnetron sputtering; the experimental platform of friction vibration was established, the frictional and vibrational properties of different geometric parameters were tested; the data signals of vibrational acceleration and frictional torque were collected and processed using data acquisition instrument. The entropy characteristic parameters of 3D vibrational acceleration were extracted based on wavelet packet decomposition method. The end-face topography was measured with ST400 three-dimensional noncontact surface topography instrument.

The geometry of pits plays a key role in influencing friction performance; the permutation entropy and fuzzy entropy of the vibration acceleration signal changed with variations in microtextured parameters. A textured surface with appropriately size parameters can trap debris, enhance the dynamic pressure effect, reduce impact between the friction interfaces and improve the frictional vibrational performance. In this research, microtextured surface with Φ150 µm-10% and Φ200 µm-5% can effectively reduce friction and vibration between the end faces of a dry gas seal.

DLC film improves the hardness of seal ring end face, and microtexture improves the dynamic effect; the tribological behavior monitoring can be realized by analyzing the characteristics of vibration acceleration sensitive parameter with friction state. The findings will provide a basis for further research in the field of tribology and the microtexture optimization of dry gas seal ring end face.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2023-0389/

Polymer laser powder bed fusion (PBF-LB/P) is an additive manufacturing technology that is sustainable due to the possibility of recycling the powder multiple times and allowing the fabrication of gears without the aid of support structures and subsequent assembly. However, there are constraints in the process that negatively affect its adoption compared to other additive technologies such as material extrusion to produce gears. This study aims to demonstrate that it is possible to overcome the problems due to the physics of the process to produce accurate mechanism.

Technological aspects such as orientation, wheel-shaft thicknesses and degree of powder recycling were examined. Furthermore, the evolving tooth profile was considered as a design parameter to provide a manufacturability map of gear-based mechanisms.

Results show that there are some differences in the functioning of the gear depending on the type of powder used, 100% virgin or 50% virgin and 50% recycled for five cycles. The application of a groove on a gear produced with 100% virgin powder allows the mechanism to be easily unlocked regardless of the orientation and wheel-shaft thicknesses. The application of a specific evolutionary profile independent of the diameter of the reference circle on vertically oriented gears guarantees rotation continuity while preserving the functionality of the assembled mechanism.

In the literature, there are various studies on material aging and reuse in the PBF-LB/P process, mainly focused on the powder deterioration mechanism, powder fluidity, microstructure and mechanical properties of the parts and process parameters. This study, instead, was focused on the functioning of gears, which represent one of the applications in which this technology can have great success, by analyzing the two main effects that can compromise it: recycled powder and vertical orientation during construction.

The author proposed a friction plunge micro-welding (FPMW) method and applied it to column grid array packaging to realize the connection of copper columns without precision molds assisted positioning. The purpose of this paper is to study the flow behavior of the solder undergoing frictional thermo-mechanical action during the FPMW and to determine the source of the solders in the micro-zones with different microstructure characteristics near the solder/Cu column friction interface.

Three kinds of Sn58Bi/SAC305 and SAC305/Pb90Sn composite solder samples were designed to study the flow behavior of the solder during FPMW using Bi and Pb as tracer elements.

The results show that most of the solders in the position occupied by the copper column was softened and plasticized during the welding process and was extruded to side of the copper column, flowing axially, circumferentially and radially along a trajectory similar to a conical spiral line. Under the drive of the tangential friction force and the radial hold-tight force, the extruded out visco-plastic solders fully mixed with the visco-plastic solders on the sides of the copper column, and bonded with the solders that deformed plastically on the periphery, so that a stir zone and a dynamic recrystallization zone finally evolved. The outside plastically deformed solders evolved into a thermo-mechanical affected zone.

The flow behavior of the solder during the FPMW was determined, as well as the source of the solders in micro-zones with different microstructure characteristics.

The purpose of this paper is to use a wear test to determine the effect of sand on the wear rates of materials typically used in aerospace applications. Once a repeatable wear test has been established, it can be used to test any combination of materials or coatings. The effectiveness of several different test methods will also be evaluated, including the sample height, surface roughness and mass difference. In addition, the current work will observe the differences between applying sand before the samples are brought into contact or after. The wear rates obtained from these tests could also be used to predict the wear of other components in similar abrasive particulate environments.

A modified block-on-flat wear test of anodized aluminum on hard coat anodized aluminum was used to study this. The experiments were performed with and without sand to study the effects of the sand. Two methods of adding sand were also evaluated. Weighing and profilometry were used to study the differences between the tests.

Wear rates have been calculated based on both the change in the masses of the samples and the change in the height between the upper and lower samples over the course of each test. The wear rates from the change in the masses are repeatable with and without sand, but the results for the change in height show no repeatability without sand. In addition, only in the presence of sand do the trends for the two methods agree. The wear rate was found to be non-linear as a function of load and therefore not in agreement with Archard’s Wear Law. The wear rate also increased significantly when sand was present in the contact for the duration of the test. The sand appears to change the wear mechanism from an adhesive to an abrasive mechanism. Black wear particles formed both when there was sand and when there was not sand. The source of these particles has been investigated but not determined.

This work has not been previously published and is the original work of the authors.