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This paper studies the effect of the dimple cross-sectional profile on the behavior of gas parallel slider bearings using the numerical method. The numerical method is performed in MATLAB software. The influence of geometrical parameters of dimples on the dimensionless average pressure is studied for different dimple cross-sectional profiles. The geometrical parameters of dimples include dimple depth, dimple area density, transversal textured ratio, and longitudinal textured ratio. It is found that the hydrodynamic lubrication of dimple-textured gas parallel slider bearings is controlled by the dimple depth, dimple area density, transversal textured ratio, longitudinal textured ratio, and dimple cross-sectional profile. Furthermore, the impact of sliding speed on the hydrodynamic lubrication is studied for different dimple cross-sectional profiles. The results indicate that the optimum sliding speed for maximizing the hydrodynamic pressure is controlled by the dimple cross-sectional profile. [ABSTRACT FROM AUTHOR]

Minimizing the entropy generation rate is one of the key performance indicators for enhancing the thermal design of heat exchangers. This paper introduces a comprehensive numerical entropy generation analysis of turbulent water flow inside—newly proposed—conical tubes with dimples subjected to a constant heat flux. The effect of different tube diameter ratios (DR = 1, 1.5, 2, 3, and 5) and flow modes (convergent and divergent tube configurations) on the thermal, viscous, and total entropy generation rates is investigated within Reynolds number (Re) range of 3 × 103–40 × 103 using ANSYS-Fluent package. Realizable k-ε (RKE) turbulence model is adopted in this study. A well-validated 3D model was adopted to estimate the dimensionless indices: Bejan number (Be), enhanced entropy generation ratio (Ns,en), and the irreversibility distribution ratio ( ϕ s ) to characterize the entropy generation performance and to compare conical dimpled tubes to smooth ones. The results showed that total entropy production rate values for dimpled tube geometries are lower than those for the corresponding smooth ones, especially for convergent dimpled tubes. Convergent dimpled tubes with DR in the range of 1.5–3 achieved the lowest total entropy production values over the whole Re range, with an average value of 0.20 W K−1, as compared to an average value of 0.34 W K−1 for the smooth configurations. The average Ns,en values for dimpled convergent tubes with DR = 1.5–3 are 0.46 and 0.80 at Re = 3000 and 40,000, with reductions of 50.54% and 3.61% at both Re values, respectively. The study also showed that the entropy generation analysis could provide an effective tool to highlight the optimal design of tube heat exchangers based on the minimum entropy generation and the enhanced entropy generation ratio. [ABSTRACT FROM AUTHOR]

Minimizing the carbon footprint of the aviation industry is of critical importance for the forthcoming years, allowing the mitigation of climate change through fossil fuel economy. Significant progress toward this goal can be achieved through the aerodynamic optimization of wing surfaces. In a previous study, a custom-designed wing equipped with an Eppler 420 airfoil, including an appendant custom-designed blended winglet, was developed and studied in flight conditions. The present paper researches potential improvements to the aerodynamic behavior of this wing by attempting to regenerate the boundary layer. The main goal was to achieve passive control of the boundary layer, which would be approached by means of two different configurations. In the first case, dimples were added at the points where the separation of the boundary layer was expected, for the majority of the wing surface; in the second case, bumps of the same diameter were added at the same points. Both wings were studied in two different Reynolds (Re) numbers and five angles of attack (AoA). The computational fluid dynamics (CFD) simulations were implemented using a pressure-based solver, the spatial discretization was conducted with a second-order upwind scheme, and the k-omega SST (k-ω SST) turbulence model was applied by utilizing the pseudo-transient method. The experimental procedure was conducted in an open-type subsonic flow wind tunnel, for Reynolds 86,000, with 3D-printed models of the wings having undergone suitable surface treatment. The numerical and experimental results converged, showing a degradation in the wing's aerodynamic performance when bumps were implemented, as well as a slight improvement for the configuration with dimples. [ABSTRACT FROM AUTHOR]

Dimples are small concavities imprinted on a flat surface, known to affect heat transfer and also flow separation and aerodynamic drag on bluff bodies when acting as a standard roughness. Recently, dimples have been proposed as a roughness pattern that is capable of reducing the turbulent drag of a flat plate by providing a reduction of skin friction that compensates the dimple-induced pressure drag and leads to a global benefit. The question whether dimples do actually work to reduce friction drag is still unsettled. In this paper, we provide a comprehensive review of the available information, touching upon the many parameters that characterize the problem. A number of reasons that contribute to explaining the contrasting literature information are discussed. We also provide guidelines for future studies by highlighting key methodological steps required for a meaningful comparison between a flat and dimpled surface in view of drag reduction. [ABSTRACT FROM AUTHOR]

Surface texturing has emerged in the last decade as a viable option of surface engineering, resulting in significant improvement in tribological properties like wear resistance, coefficient of friction, load carrying capacity, etc. of mechanical components. In this paper, the effect of surface texturing on tribological properties of Polyamide (PA66) composite materials is studied considering elliptical texture pattern with varying orientations so as to observe the comparative friction and wear behavior of Polyamide (PA66) composites with and without surface texturing on mating surface at dry and wet lubrication using a pin-on-disc tribometer. The results show that the coefficient of friction varies considerably with surface texture patterns; some texture patterns show a higher load carrying capacity and due to that negative coefficient of friction is observed. Scanning Electron Micrographs (SEM) show that wear of some textured surfaces is reduced compared with the non-textured surface at both the lubricating conditions. [ABSTRACT FROM AUTHOR]

The golf ball is a very interesting aerodynamic device. As a sphere, the coefficient of drag should be about 0.48. However, because of the surface of the golf ball, the drag coefficient can be much lower, up to 12%. This paper explores the multitude of ways, designs and concepts that create such a lower drag coefficient, through computational fluid dynamics analysis, and using those findings how to use them when designing new parts to increase the efficiency and reliability of the device that uses said parts while increasing the quality of life of the user of the devices. [ABSTRACT FROM AUTHOR]

In this paper the influence of oil pockets location on extraction of surface topography features was taken into account. Plateau-honed cylinder liners with additionally added dimples were taken in consideration. The effect of dimples location on the application of various procedures (cylinder fitting procedure, polynomial approximation) for areal form removal was taken into account. It was noticed that application of 3rd (or greater) degree of the polynomials can caused false estimation of reference plane; extraction of surface topography features by polynomial approximation cannot provide good results when the distance between dimples is too small. For two-process surfaces (plateau-honed cylindrical elements containing wide and deep valleys) the digital filtering was proposed. Application of robust techniques (robust Gaussian regression filter) allowed for areal form removal improvement. However, some of the wide dimples were distorted when the dimple-to-edge distance was too small (smaller than filter bandwidth value). [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study to evaluate the possibility of using SLM additive technology to produce structures with specific surface morphological features. Qualitative and quantitative tests were conducted on samples fabricated by 3D printing from titanium (Ti6Al4V)-powder-based material and analysed in direct relation to the possibility of their use in medicine for the construction of femoral stem and models with a specific degree of porosity predicted by process-control in the self-decision-making 3D printing machine. This paper presents the results of the study, limitations of the method, recommendations that should be used in the design of finished products, and design proposals to support the fabrication process of 3D printers. Furthermore, the study contains an evaluation of how the printing direction affects the formation of certain structures on the printed surface. The research can be used in the development of 3D printing standardization, particularly in the consideration of process control and surface control. [ABSTRACT FROM AUTHOR]

Numerous works have been carried out in the design and analysis of Heat Sink, however hardly any work have been reported with studies on dimples and protrusions being added to the heat sink geometries. This paper aims to find the worthiness for addition of dimples and protrusions to the common plate fin heat sink geometries for heat transfer enhancement. Analysis was carried out in forced convention environment for 9 different velocities computationally for 12 heat sink geometries at constant heat flux boundary condition applied to base of heat sink. Decrease in base temperature and thermal resistance of heat sink was considered as the performance factors. Further these computational results were validated experimentally. The results obtained from computational analysis were in good agreement with experimental results. The research outcome show that addition of dimples has proved its worthiness at slightly higher velocity regime with thermal performance being increased for a dimpled heat sink as compared to non-dimpled heat sink. Therefore, currently developed dimpled heat sinks can be a potential model that can be used in forced convection environment for better thermal performance and economy. [ABSTRACT FROM AUTHOR]

In various industrial applications, the high performance of heat exchanger demand is increasing. Subsequently, the energy resources depletion, for instance, in power plant, airconditioning system and food processing systems. The important field for saving energy was through improving thermal performance, which can provide high performance heat exchanger. Present enhancing approaches can be classified by three changed types, which are passive technique, active technique and compound technique. Dimple, twisted tape and corrugated pipe are the passive heat improvement technique which includes more surface extensions. Hence, this research work concentrates on verifying the computational calculations of flow in the heat exchanger pipe with different surface extensions in the pipe. It is carried out for turbulent flow with a range of Reynolds number from 1000 to 15000 using CFD methods. The numerical outcomes illustrate that change twisted tape configurations have more effect on flow and heat performance. Experimental and numerical results agreement can confirm the simulation technique reliability, which adopts in this investigation. The deviation errors are observed by less than 6% compared with the normal pipe. Pressure drop increases due to the rise of twisted tape dimensions (width and thickness), leading to more mixing of fluid, secondary flow, and swirl flow inside the pipe. As the tape geometrical parameters increase, the f value also increases due to more variance in velocities flow between liquid layers, which are adjacent to tape surfaces a pipe wall, and pipe core flow layers, become higher. Correspondingly, compared to the normal pipe, twisted configurations can rise f about 5.4 to 33.5%. The better thermal evaluation factor is at a twisted tape of 1x1 mm at Re number of about 1000. The range value of the thermal evaluation factor is more than 1.67. [ABSTRACT FROM AUTHOR]

• Dimpled airfoils, arranged in-line, exhibit a reduction in noise across a wide range of frequencies. • The noise reduction in in-line configurations demonstrates an upward trend, correlating with higher jet velocities and resulting in reductions of approximately 3.5–5.5 dB compared to the baseline. • In the case of the dimpled airfoil, there is a discernible decrease in coherence within the flow field compared to the baseline. This paper presents systematic and comprehensive experimental investigations into the use of circular dimples to reduce broadband noise on airfoils. The dimples are introduced on the suction surface of symmetric NACA airfoils with different thickness ratios for the control of broadband noise over a wide range of frequencies. The effects of dimple arrangements (inline and staggered) and their locations (1/3rd and 1/5th of the chord from the leading edge) on the noise characteristics are studied in detail to determine the best dimple arrangement, location, and airfoil geometry for low noise. Results indicate that the inline arrangement of dimples positioned at 1/3rd of the chord from the leading edge provides significant noise reductions of about 6–8 dB, particularly from mid to high frequencies. When the dimples are shifted to 1/5th of the chord from the leading edge, the degree of noise reduction decreases, which indicates that the noise reduction performance of airfoils decreases when the dimples are introduced near the leading edge. Further, it reveals that the inline arrangement of dimples on thicker airfoils provides superior noise reductions (6–8 dB) as compared to thinner airfoils (4–6 dB). Flow visualization reveals that the flow field is inconsistent throughout the span of the dimpled surface due to the evolution of small vortices from the dimple corner. It enhances mixing and accelerates flow structures passing over the dimpled surface, which is indicated by the presence of a high degree of spanwise decoherence/phase lag in the hotwire measurements. The presence of higher spanwise decoherence/phase lag due to the presence of the inconsistent flow field leads to significant reductions of far-field noise in dimpled airfoils. Further, the inline arrangement of dimples exhibits much higher levels of noise reduction as compared to staggered ones, due to the presence of a greater degree of spanwise decoherence/phase lag resulting from the substantial disruption of the flow field in the spanwise direction. [ABSTRACT FROM AUTHOR]

The effect of cold working on hydrogen embrittlement of Monel-400 alloy has been investigated in this report. Monel-400 alloy having 50 and 60% cold working has been selected for this study. A part of these cold-worked materials is annealed. A series of slow strain rate tensile tests of the cold-worked as well as annealed materials are carried out in two different environmental conditions—air and with hydrogen charging in 3.5% NaCl solution. Alloy with 60% cold working exhibits the highest reduction in ductility with hydrogen charging. The reduction in ductility is lower for the annealed materials compared to that of cold-worked materials when tested with hydrogen charging. The results lead to infer that (i) the alloy becomes more detrimental to hydrogen embrittlement with the increase in percentage cold working, which reduces ductility significantly with increasing strength under hydrogen charging, (ii) annealing of cold-worked materials decreases their susceptibility to hydrogen embrittlement, and (iii) hydrogen damage promotes brittle fracture for the cold-worked materials. [ABSTRACT FROM AUTHOR]

Studies on the effect of surface texture on cylinder liner wear is of great importance in many research areas due to the fact that a major part of the mechanical power losses in an engine are caused by friction in the piston-cylinder liner system. Interest from both manufacturers and customers in optimizing this mechanical system seems to be similar. The surface roughness of cylinder liners plays an important role in the control of tribological properties. Cylinder liner surface topography, which affects running-in duration, oil consumption, exhaust gas emissions and engine performance as well, was taken into detailed consideration in this paper. They were measured with a stylus (Talyscan 150) or non-contact—optical (Talysurf CCI Lite white light interferometer) equipment. Precise machining process and accurate measurement equipment may not provide relevant information about surface texture properties when the procedure of processing of received (raw) measured data is not selected appropriately. This work aims to compare various type of procedures for detection and reduction of some-frequency surface topography measurement errors (noise) and consider its influence on the results of wear analysis. It was found that assessments of some extracted areas (profiles) may be much more useful than the characterization of the whole of measured details when noise was defined. Moreover, applications of a commonly-used algorithm, available in the commercial software of the measuring equipment, for measurement errors suppression may be potentially decisive in the definition of measurement noise but, simultaneously, scrupulous attention should be paid if they are implemented adequately. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study to evaluate the possibility of using SLM additive technology to produce structures with specific surface morphological features. Qualitative and quantitative tests were conducted on samples fabricated by 3D printing from titanium (Ti6Al4V)-powder-based material and analysed in direct relation to the possibility of their use in medicine for the construction of femoral stem and models with a specific degree of porosity predicted by process-control in the self-decision-making 3D printing machine. This paper presents the results of the study, limitations of the method, recommendations that should be used in the design of finished products, and design proposals to support the fabrication process of 3D printers. Furthermore, the study contains an evaluation of how the printing direction affects the formation of certain structures on the printed surface. The research can be used in the development of 3D printing standardization, particularly in the consideration of process control and surface control.

Highlights • Heat transfer and pressure loss in swirl cooling tubes with dimples were numerically obtained. • Total heat transfer performance of the swirl tubes with dimples can be increased. • Pressure loss of the swirl tubes with dimples can be decreased. • Dimple depths have appreciable influences on the heat transfer and pressure loss. • Detailed interactions of the swirling flow with dimples at the wall were provided. Abstract This paper presents a numerical study of heat transfer and pressure loss characteristics in a swirl cooling tube with five tangential inlet jets and with dimples on the tube inner surface. The swirl tube has a length of 20 times the tube diameter, and the Reynolds number based on the tube diameter ranges from 10,000 to 40,000. Polyhedral meshes as well as the SST k - ω turbulence model were chosen for the numerical calculations. A swirl cooling system with a smooth tube was investigated as baseline, and comparatively with dimples on the tube inner surface. The results showed different swirling flow and heat transfer patterns in the swirl tubes. Dimples on the tube inner surface can reduce the wetted-area averaged heat transfer coefficient on the tube inner surface. However, the total heat transferred in the dimpled swirl cooling tubes can be increased by up to 7.2% due to the increased heat transfer area and the interactions between the swirling flow and the dimpled wall. On the other hand, the pressure loss in the dimpled tube can be appreciably reduced by up to 17.6% compared with that of the smooth swirl tube. Detailed flow interactions between the jets, the tube wall and the dimples are illustrated to explain the heat transfer change and pressure loss reduction mechanisms. [ABSTRACT FROM AUTHOR]

Passive heat exchangers (HXs) form an inseparable part of the manufacturing industry as they provide high-efficiency cooling at minimal overhead costs. Along with the aspects of high thermal cooling, it is essential to monitor pressure loss while using plate-fin HXs because pressure loss can introduce additional power costs to a system. In this paper, an experimental study was conducted to look at the effects of dimples on the pressure drop characteristics of single plate-fin heat exchangers. To enable this, different configurations of National Advisory Committee for Aeronautics (NACA) fins with smooth surfaces and 2 mm-diameter dimples, 4 mm-diameter dimples and 6 mm-diameter dimples were designed and 3D printed using fused deposition modelling (FDM) of ABS plastic. The depth to diameter ratio for these dimples was kept constant at 0.3 with varied diameters and depths. These were then tested using a subsonic wind tunnel comprised of inlet and outlet pressure taps as well as a hot wire velocimeter. Measurements were taken for pressure differences as well as average velocity. These were then used to calculate friction factor values and to compare the smooth fin to the dimpled fins in relation to their relative pressure drop performance. It was observed that for lower velocities the 4 mm dimples provided minimum pressure drop, with a difference of 58% when compared to smooth fins. At higher velocities, 6 mm dimples increased the pressure drop by approximately 34% when compared to smooth fins. It can also be concluded from the observed data in this study that shallower dimples produce lower pressure drops compared to deeper dimples when the depth to diameter ratio is kept constant. Accordingly, deeper dimples are more effective in providing drag reduction at lower velocities, whereas shallower dimples are more effective for drag reduction at higher velocities. [ABSTRACT FROM AUTHOR]

An experimental study of heat transfer and hydraulic losses in a channel with one wall being a surface with trench dimple was carried out. The working surface had four rows of dimples located alternately at angles of 45° and −45° to the channel axis. In the laminar regime, the transfer of heat and the losses of pressure turned out to be close to the parameters of a smooth channel. In the turbulent regime, a 1.5-fold enhancement of heat transfer with respect to the transfer of heat in a smooth channel was obtained. The dependence of the increase in pressure losses on the Reynolds number qualitatively agreeing with the dependence for the channels with sandy roughness is obtained. [ABSTRACT FROM AUTHOR]

This paper described unique hysteresis phenomena that appear in the hydrodynamic lubrication properties of dimpled thrust bearings. A seal-type thrust bearing specimen was textured with dimples. The load-carrying capacity and frictional torque were measured with a constant film thickness and compared to those of a dimple-free specimen. For examining the size of cavitation bubbles that occurred in various conditions, the lubricating area was observed during experiments. The used dimpled specimen produced the load-carrying capacity, and it exhibited an interesting hysteresis phenomenon, the difference in the values in the increasing and decreasing processes of rotational speed. The visualization test results revealed that the size of cavitation bubbles occurring within the dimples strongly affected this phenomenon. In addition, the dimpled specimen was able to reduce the frictional torque compared to the dimple-free specimen. However, the frictional torque did not show the hysteresis loop similar to that shown in the load-carrying capacity. [ABSTRACT FROM AUTHOR]

In this paper, the influence of occurrence of surface texture features on the values of surface topography parameters calculated after the application of various data processing techniques was presented. Different types of surface topographies were considered, as follows: cylinder liners, some with additionally burnished dimples, turned, ground, milled, laser-textured, composite, ceramic, or isotropic in general. The effects of feature size on the areal form removal, noise suppressions, or end-effect reducing in surface texture measurements were studied. The variations of the ISO 25178 standard surface topography parameters were taken into consideration in detail. It was assumed that some of the feature sizes, distributions, and densities have a substantial impact on the values of surface topography parameters calculated after applications of regular (commonly used) algorithms and procedures, defined as basic operations, provided for raw surface texture data obtained directly from the measurement process. In the end, some of the practical applications for receiving the relevant values of surface topography parameters were proposed. [ABSTRACT FROM AUTHOR]

The flow characteristics and loss behavior over an array of parallel recessed dimples on a high turning linear compressor cascade have been investigated using the Reynolds-averaged Navier–Stokes approach. Steady simulations have been carried out at three dimple locations of 10–32%, 38–60%, 60–82% chord length of suction surface with the inlet Mach number of 0.7. Flow conditions were compared in exit loss coefficient, static pressure rise, streamline patterns, vortex structures, boundary layer parameters, and blade surface pressure between the smooth and the modified cascades. The results indicate that the dimples prior to the separation line report an overall enhancement in the aerodynamic performance in comparison to that of a smooth blade. Symmetric spanwise vortex, which energizes the boundary layer, can roll up inside the dimples. Therefore, the boundary layer with the higher momentum can bear the adverse pressure gradient, which will suppress the flow separation and associated losses. Three dimpled configurations can all eliminate the separation bubble on the suction side, but the dimples located at 60–82% chord length take the negative effect on the aerodynamic performance due to the more chaos condition in the corner separation region. The comparison results also indicate that the optimum location of dimples may exist in front of the separation bubble. Loss reduction of 18.8% and 10.8% can be achieved under the 10–32%c and 38–60%c dimple configurations, respectively. [ABSTRACT FROM AUTHOR]

The paper is addressed to the application of Eulerian–Lagrangian Large Eddy Simulations (LES) for the investigation of the interaction between turbulent flow structures, heat transfer and particulate fouling in aqueous suspension on structured surfaces, which is an important research field in context of particle-laden two-phase flows. An efficient Lagrangian-Particle-Tracking algorithm is used to predict the trajectory of each suspended foulant particle (dispersed phase), suitable for dilute and dense dispersed two-phase flows by taking the fluid-particle (two-way coupling) as well as inter-particle interactions (four-way coupling) into account. The complex turbulent carrier flow (continuous phase) is calculated by eddy-resolving LES. Calculations have been performed for fully developed turbulent channel flows at moderate Reynolds numbers in combination with a sharp-edged spherical dimple considering a dimple depth/diameter ratio of t / D = 0.26 and a rectangular cavity with an equal cavity depth/side length ratio for comparative purposes. In order to get a detailed insight into fundamental fouling processes and to verify the numerical results high-precision experimental investigations of particulate fouling of different dimpled surfaces have been carried out. The fouling investigations are conducted using a relatively low mass loading of up to 0.2% and particle diameters of 3 µm and 20 µm for the simulations, whereas a particle diameter of 3 µm is used for the experiments. The simulated fouling layer distribution for the spherical dimple within a smooth, narrow channel is compared with these experimental measurements and exhibits a satisfying agreement. Additionally, the arising local flow structures and thermo-hydraulic performances of the selected surfaces are numerically investigated in absence and presence of particulate fouling. [ABSTRACT FROM AUTHOR]

Studies of surface topography including processes of measurement and data analysis have an influence on the description of machined parts with their tribological performance. Usually, surface roughness is analysed when a scale-limited (S-L) surface, excluding short (S-) and length (L-) components from the raw measured data, is defined. Errors in the precise definition of the S-L surface can cause the false estimation of detail properties, especially its tribological performance. Errors can arise when the surface contains some burnished details such as oil pockets, dimples, scratches, or, generally, deep or wide features. The validation of proposed methods for S-L surface definition can also affect the accuracy of the ISO 25178 surface topography parameter calculation. It was found that the application of commonly used procedures, available in commercial software (e.g., least-square fitted cylinder element or polynomial planes, regular or robust Gaussian regression, spline, median or fast Fourier transform filters) can be suitable for precise S-L surface definition. However, some additional analyses, based on power spectral densities, autocorrelation function, texture direction graphs, or spectral characterisation, are strongly required. The effect of the definition of the S-L surface on the values of the ISO 25178 parameters was also comprehensively studied. Some proposals of guidance on how to define an appropriate S-L surface with, respectively, an objective evaluation of surface roughness parameters, were also presented. [ABSTRACT FROM AUTHOR]

This paper presents the effect of laser texturing on the tribological properties of PEEK surfaces under a ball-on-flat contact configuration. Thus, surfaces with circular dimples of various diameters and depth were created. Tests were conducted with a normal load of 5 N and a sliding velocity of 0.01 m s −1 , using bovine calf serum at 37.5 °C as a lubricant. The tribological conditions including the sliding frequency and the lubricant viscosity indicate that tests were performed under boundary lubrication regime. Results showed that discs with higher dimple depth exhibited higher friction coefficient and caused more abrasive wear on the ball specimen. Nevertheless, tribosystems (ball and disc) with dimpled disc surfaces showed a higher wear resistance. In the frame of our experiments, wear rates obtained for tribosystems including dimpled surfaces were 10 times lower than tribosystems including limited patterned or untextured surfaces. Applications such as design of spinal implants may be concerned by such a surface treatment to increase wear resistance of components. [ABSTRACT FROM AUTHOR]

• The leaf springs and dimples transfer forces and acceleration in the nuclear fuel assembly. • A presented material model considers leaf springs and dimples' inelastic deformation and the deterioration of stiffness under cyclic loading. • The use of this model and the effect of the inelastic deformation in the leaf springs is demonstrated. This paper presents a newly developed plastic model to represent the nonlinear inelastic behavior of some fuel assembly components, such as leaf springs and dimples, as translational springs. Nuclear fuel rods are bundled into fuel assemblies constrained by spacer grids located at discrete locations, which transfer load or acceleration to the fuel rods through the leaf springs and dimples. In the current state of practice, leaf springs and dimples are modeled as linear, or nonlinear elastic, translational springs, without considering plastic deformations. It is essential to consider the plasticity and deterioration of the spacer grid assembly to better predict the response of the spent nuclear fuel (SNF) rods subjected to the dynamic loads that may take place during storage and transportation. The presented model considers the kinematic strain hardening algorithm to account for the plastic deformation of the spring in compression only, and incorporates some of the peak-oriented hysteretic model rules to account for stiffness deterioration in the plastic region. The material model is written in the C++ language in the open-source finite element (FE) software MASTODON. The material model is validated by applying simple loading protocols to the two-noded spring. The use of the material model in the fuel assembly is demonstrated by using a small segment of the SNF rods. This new model captures the intermediate reversals when the fuel rod is subjected to vibrations. Numerical examples show that the model can accurately predict the plastic deformations of the leaf spring and dimples. The introduction of nonlinear inelastic capabilities in the FuelCompressionSpring resulted in higher deformations of the leaf spring and longer time periods of the displacement response. The developed hysteretic models can efficiently reproduce the elastic and plastic response of leaf springs and dimples, and can be used in large fuel assembly models. [ABSTRACT FROM AUTHOR]

• TU Delft drag-reduction concept by dimples under turbulent boundary layer is tested. • New experiment and Direct Numerical Simulation predict drag increase of at least 1%. • Design variations, tested by DNS, failed to resolve the issue. • Doubly-periodic boundary conditions with source term facilitated DNS. A very convincing experimental paper from TU Delft, of 2016, motivated this joint study. They directly measured a reduction in drag of up to 3% for the developed turbulent boundary layer flowing over an array of shallow dimples, of diameter comparable with the boundary-layer thickness. The Reynolds numbers were not high, but nor marginal either. Our experimental set-up has been well validated by previous riblets studies. The simulation approach contains more new features, which are described, and passed the essential tests. It is a Direct Numerical Simulation, at the correct Reynolds number. The key finding is that both of our approaches predict a drag increase of at least 1%, with an uncertainty of the order of 1%. Not having identified any flaw in the 2016 work even through discussions with the authors, we are currently unable to explain the contradiction. We do note however that these initial results had a Reynolds-number dependence which we consider puzzling, and also that a 2018 paper from TU Delft by almost the same set of authors presents some less favourable findings. [ABSTRACT FROM AUTHOR]

Plate heat exchangers including offset-strip fins or dimple-type turbulators have a wide application in the automotive field as oil coolers for internal combustion engines and transmissions. Their optimization is a complex task since it requires targeting different objectives: High compactness, low pressure drop and high heat-transfer efficiency. In this context, the availability of accurate Computational Fluid Dynamics (CFD) simulation models plays an important role during the design phase. In this work, the development of a computational framework for the CFD simulation of compact oil-to-liquid heat exchangers, including offset-strip fins and dimples, is presented. The paper addresses the modeling problem at different scales, ranging from the characteristic size of the turbulator geometry (typically µm–mm) to the full scale of the overall device (typically cm–dm). The simulation framework is based on multi-scale concept, which applies: (a) Detailed simulations for the characterization of the micro-scale properties of the turbulator, (b) an upscaling approach to derive suitable macro-scale models for the turbulators and (c) full-scale simulations of the entire cooler, including the porous models derived for the smaller scales. The model is validated comparing with experimental data under different operating conditions. Then, it is adopted to investigate the details of the fluid dynamics and heat-transfer process, providing guidelines for the optimization of the device. [ABSTRACT FROM AUTHOR]

A complex study of the properties and characteristics of discrete structure surfaces with mechanically formed dimples has been carried out. It is shown that the combination of scientific research on friction and wear processes in different scientific and engineering areas, such as mathematical statistics, mechanics of contact, physics of surfaces and magnetism and hydrodynamics, provides a deeper explanation of the processes that take place on discrete surfaces of contact elements. [ABSTRACT FROM PUBLISHER]

The impacts of conflicting aerodynamic forces and side drifting forces are the primary unstable elements in automobiles. The action of an unstable environment in automobile vehicles increases the chance of an accident occurring. As a result, much study is required to determine how opposing aerodynamic forces and side drifting force affects function, as well as how to deal with them for safe and smooth navigation. In this work, an intercity bus is chosen as a main object, and computational fluid dynamics (CFD) analysis is used to estimate aerodynamic forces on the bus in all major directions. Experimentation is also carried out for validation reasons. CFD findings for a scaled base model and a dimple-loaded model based on experimental results from a subsonic wind tunnel are demonstrated to be correct. The drag forces generated by CFD simulations on test models are carefully compared to the experimental drag findings of same-dimensioned models. The error percentages between the results of these two methods are acquired and the percentages are determined to be within an acceptable range of significant limitations. Following these validations, CATIA is used to create a total of nine distinct models, the first of which is a standard intercity bus, whereas the other eight models are fitted with drag reduction techniques such as dimples, riblets, and fins on the surface of their upper cumulus side. A sophisticated computational tool, ANSYS Fluent 17.2, is used to estimate the comparative assessments of the predictions of aerodynamic force fluctuations on bus models. Finally, dimples on the top and side surfaces of the bus model (DESIGN–I) are proposed as a more efficient model than other models because dimples are a vital component that may lower pressure drag on the bus by 18% in the main flow direction and up to 43% in the sideslip direction. Furthermore, by minimizing the different aerodynamic force sources without impacting the preparatory needs, the proposed model may provide comfortable travel. The real-time bus is created, and the finalized drag reduction is applied to the optimized places over the whole bus model. In addition, five distinct size-based bus models are developed and studied in terms of aerodynamic forces, necessary energy to resist aerodynamic drag, required forward force for successful movement, instantaneous demand for particular power, and fuel consumption rate. Finally, the formation of aeroacoustic noise owing to turbulence is estimated using sophisticated computer simulation. Last, for real-time applications, multi-parametric studies based on appropriate intercity buses are established. [ABSTRACT FROM AUTHOR]

Minimizing the carbon footprint of the aviation industry is of critical importance for the forthcoming years, allowing the mitigation of climate change through fossil fuel economy. Significant progress toward this goal can be achieved through the aerodynamic optimization of wing surfaces. In a previous study, a custom-designed wing equipped with an Eppler 420 airfoil, including an appendant custom-designed blended winglet, was developed and studied in flight conditions. The present paper researches potential improvements to the aerodynamic behavior of this wing by attempting to regenerate the boundary layer. The main goal was to achieve passive control of the boundary layer, which would be approached by means of two different configurations. In the first case, dimples were added at the points where the separation of the boundary layer was expected, for the majority of the wing surface; in the second case, bumps of the same diameter were added at the same points. Both wings were studied in two different Reynolds (Re) numbers and five angles of attack (AoA). The computational fluid dynamics (CFD) simulations were implemented using a pressure-based solver, the spatial discretization was conducted with a second-order upwind scheme, and the k-omega SST (k-ω SST) turbulence model was applied by utilizing the pseudo-transient method. The experimental procedure was conducted in an open-type subsonic flow wind tunnel, for Reynolds 86,000, with 3D-printed models of the wings having undergone suitable surface treatment. The numerical and experimental results converged, showing a degradation in the wing’s aerodynamic performance when bumps were implemented, as well as a slight improvement for the configuration with dimples.

The solar water heating system efficiently converts available solar energy into useful thermal energy. The collector is the predominant unit of the solar water heating system. Using a heat transfer enhancer in the tube is pondered as one of the effective methods to improve the thermal efficiency of the system. Dimples are used as heat transfer enhancer and created using a punching machine. The primary objective of the research is to endow a numerical investigation on the influence of dimples and its various parameters on the thermal efficiency and friction factor of the solar collector. Simulation is performed by varying pitch-to-dimple diameter ratio (P/Dd), number of dimples and mass flow rate. For the result to be independent of mesh, the optimum number of control volumes is identified as 2.2 million. Numerical modeling is done in such a way that the experimental and CFD results are in good agreement with each other and the error percentage is below 10%. Dimples on the tube disturb the fluid flow and reduce the hydraulic diameter, thus enhancing the heat transfer rate and efficiency of the collector. A maximum of 2.5 times increment in the Nusselt number was observed for the dimpled tube with P/Dd ratio 3 and six dimples between two pitches than plain tube at a mass flow rate of 2.5 kg min−1. The friction factor due to the presence of dimples increased by 11.1% compared to that of the normal tube. The relative better enhancement in thermal efficiency with less friction factor makes dimples a superior heat transfer enhancer. [ABSTRACT FROM AUTHOR]

Dimples are small concavities imprinted on a flat surface, known to affect heat transfer and also flow separation and aerodynamic drag on bluff bodies when acting as a standard roughness. Recently, dimples have been proposed as a roughness pattern that is capable of reducing the turbulent drag of a flat plate by providing a reduction of skin friction that compensates the dimple-induced pressure drag and leads to a global benefit. The question whether dimples do actually work to reduce friction drag is still unsettled. In this paper, we provide a comprehensive review of the available information, touching upon the many parameters that characterize the problem. A number of reasons that contribute to explaining the contrasting literature information are discussed. We also provide guidelines for future studies by highlighting key methodological steps required for a meaningful comparison between a flat and dimpled surface in view of drag reduction.

This paper deals with the study of dimple type RF MEMS capacitive shunt switch using different meandering techniques for high isolation and low actuation voltage. The novelty of the proposed RF MEMS switch is it incorporates the meanders and dimples, which help to reduce the actuation voltage. The proposed switch structure is optimized, designed, and simulated with FEM analysis such as electromechanical and electromagnetic by using COMSOL and HFSS tools respectively. The best performance of the switch is observed by varying different parameters such as beam material, beam thickness, dielectric thickness, and airgap. The proposed switch with different meandering techniques attains the pull-in voltage in the range of 10.3-46 V, particularly the three uniform meander technique has low actuation voltage of 10.3 V. The RF performance of the device is particularly tuned in the range of 26.5-40 GHz frequency range and it is analyzed for all types of meanders. Among them, the non-uniform single meander has attained the best isolation of -54.13 dB at 40 GHz in the off state. The insertion and return losses of the device are -0.514 dB and -17.35 dB over 1-40 GHz frequency in on state.

In this paper the influence of oil pockets location on extraction of surface topography features was taken into account. Plateau-honed cylinder liners with additionally added dimples were taken in consideration. The effect of dimples location on application of various procedures (cylinder fitting procedure, polynomial approximation) for areal form removal was taken into account. It was noticed that application of 3rd (or greater) degree of the polynomials can caused false estimation of reference plane; extraction of surface topography features by polynomial approximation cannot provide good results when the dis-tance between dimples is too small. For two-process surfaces (plateau-honed cylindrical elements containing wide and deep valleys) the digital filtering was proposed. Application of robust techniques (robust Gaussian regression filter) allowed for areal form removal improvement. However some of the wide dimples were distorted when the dimple-to-edge distance was too small (smaller than filter bandwidth value).

Passive heat exchangers (HXs) form an inseparable part of the manufacturing industry as they provide high-efficiency cooling at minimal overhead costs. Along with the aspects of high thermal cooling, it is essential to monitor pressure loss while using plate-fin HXs because pressure loss can introduce additional power costs to a system. In this paper, an experimental study was conducted to look at the effects of dimples on the pressure drop characteristics of single plate-fin heat exchangers. To enable this, different configurations of National Advisory Committee for Aeronautics (NACA) fins with smooth surfaces and 2 mm-diameter dimples, 4 mm-diameter dimples and 6 mm-diameter dimples were designed and 3D printed using fused deposition modelling (FDM) of ABS plastic. The depth to diameter ratio for these dimples was kept constant at 0.3 with varied diameters and depths. These were then tested using a subsonic wind tunnel comprised of inlet and outlet pressure taps as well as a hot wire velocimeter. Measurements were taken for pressure differences as well as average velocity. These were then used to calculate friction factor values and to compare the smooth fin to the dimpled fins in relation to their relative pressure drop performance. It was observed that for lower velocities the 4 mm dimples provided minimum pressure drop, with a difference of 58% when compared to smooth fins. At higher velocities, 6 mm dimples increased the pressure drop by approximately 34% when compared to smooth fins. It can also be concluded from the observed data in this study that shallower dimples produce lower pressure drops compared to deeper dimples when the depth to diameter ratio is kept constant. Accordingly, deeper dimples are more effective in providing drag reduction at lower velocities, whereas shallower dimples are more effective for drag reduction at higher velocities.

Spherical dimples in cylindrical tubes enhance heat transfer and lead to a more uniform radial temperature profile. To combine these positive properties with a low pressure drop, a single dimple was optimized through a genetic algorithm. Multiple design parameters such as width, height, and curvature of the dimple were investigated. Heart‐shaped dimples outperformed spherical dimples. Three‐dimensional reactive simulations of a Millisecond propane steam cracking reactor showed that both the spherically dimpled and the heart‐shaped dimpled coil positively affect the light olefin selectivity, mainly through an increase in propylene selectivity. The optimized dimples could reduce the high pressure drop penalty by 21%. Run length simulations proved that the optimized dimple shape results in an additional run length extension of 18%. Next to this, the fuel rate consumption can be decreased by 6% compared to a bare coil, which could theoretically result in 4% less CO2 emissions. [ABSTRACT FROM AUTHOR]

Through fabricating the micro-textures to improve surface property, the surface texturing technology has become a widely used way to prepare the functionalized surface. This study proposed a surface texturing method of one-dimensional ultrasonic vibration–assisted turning to generate micro-textured end face. The generation principle for the micro-textured end face was presented through the description of cutting conditions, the theoretical analysis of textured features, and the simulation prediction of surface topography. The polycrystalline diamond cutting tools with different clearance angles (7° and 20°) and nose radiuses (400 μm, 200 μm, and 100 μm) were used in the experimental tests to investigate the influence of tool geometry on the micro-dimple features. The results show that the micro-dimples with different sizes and shapes can be successfully fabricated on the end face of Copper 1100. Same as the theoretical analysis and simulation prediction, through changing the cross-sectional profile of dimple along cutting direction, the clearance angle and the radius of observed point were verified to play a key role in the shape of micro-dimple. The oval-like dimples and the scale-like dimples can be respectively manufactured under the different intersection states between the flank face and the cutting trace. It was also confirmed that by choosing proper nose radius and the corresponding feed rate, the textured surface covered by micro-dimples of different widths can be generated. This texturing method used for fabricating the micro-textured end face was verified to be feasible and efficient, which laid a foundation for further research on the application of the textured surface. [ABSTRACT FROM AUTHOR]

This paper described unique hysteresis phenomena that appear in the hydrodynamic lubrication properties of dimpled thrust bearings. A seal-type thrust bearing specimen was textured with dimples. The load-carrying capacity and frictional torque were measured with a constant film thickness and compared to those of a dimple-free specimen. For examining the size of cavitation bubbles that occurred in various conditions, the lubricating area was observed during experiments. The used dimpled specimen produced the load-carrying capacity, and it exhibited an interesting hysteresis phenomenon, the difference in the values in the increasing and decreasing processes of rotational speed. The visualization test results revealed that the size of cavitation bubbles occurring within the dimples strongly affected this phenomenon. In addition, the dimpled specimen was able to reduce the frictional torque compared to the dimple-free specimen. However, the frictional torque did not show the hysteresis loop similar to that shown in the load-carrying capacity.

golf ball is a very interesting aerodynamic device. As a sphere, the coefficient of drag should be about 0.48. However, because of the surface of the golf ball, the drag coefficient can be much lower, up to 12%. This paper explores the multitude of ways, designs and concepts that create such a lower drag coefficient, through computational fluid dynamics analysis, and using those findings how to use them when designing new parts to increase the efficiency and reliability of the device that uses said parts while increasing the quality of life of the user of the devices.

A strip steel pad with a polyurethane board pad is suggested to improve the quality of multi-point die forming. In this work, the formability of four different forming processes, namely without a cushion, using a polyurethane pad, using a strip steel pad, and using a strip steel pad with a polyurethane board, was compared via numerical simulations and experiments. The results show that using a strip steel pad with a polyurethane board in multi-point die forming can effectively improve the stress and strain of the blank and suppress the defects of dimpling, straight edge, and wrinkling. This work demonstrates that the use of the strip steel pad with a polyurethane board in the multi-point forming process can improve the sheet forming conditions and quality. [ABSTRACT FROM AUTHOR]

Plate heat exchangers including offset-strip fins or dimple-type turbulators have a wide application in the automotive field as oil coolers for internal combustion engines and transmissions. Their optimization is a complex task since it requires targeting different objectives: High compactness, low pressure drop and high heat-transfer efficiency. In this context, the availability of accurate Computational Fluid Dynamics (CFD) simulation models plays an important role during the design phase. In this work, the development of a computational framework for the CFD simulation of compact oil-to-liquid heat exchangers, including offset-strip fins and dimples, is presented. The paper addresses the modeling problem at different scales, ranging from the characteristic size of the turbulator geometry (typically µm−mm) to the full scale of the overall device (typically cm−dm). The simulation framework is based on multi-scale concept, which applies: (a) Detailed simulations for the characterization of the micro-scale properties of the turbulator, (b) an upscaling approach to derive suitable macro-scale models for the turbulators and (c) full-scale simulations of the entire cooler, including the porous models derived for the smaller scales. The model is validated comparing with experimental data under different operating conditions. Then, it is adopted to investigate the details of the fluid dynamics and heat-transfer process, providing guidelines for the optimization of the device.

In this paper, a modified U-shaped micro-actuator with a compliant mechanism is proposed. It was analyzed with a uniform and modified thin arm, as well as a similar variation in the corresponding flexure, in order to observe the impact of the compliant lumped mechanism. The use of these compliant mechanisms implies an increment in the deformation and a reduction in the equivalent stress of 25% and 52.25%, respectively. This characterization was developed using the Finite Element Method (FEM) in ANSYS Workbench. The design, analysis and simulation were developed with Polysilicon. In this study, the following performance parameters were also analyzed: force and temperature distribution. This device is supplied with voltage from 0 V up to 3 V, at room temperature. The modified U-shaped actuator was applied in both arms of a microgripper, and to evaluate its electrothermal performance, a static structural analysis has been carried out in Ansys Workbench. The microgripper has an increment in deformation of 22.33%, an equivalent stress reduction of 50%, and a decrease in operation frequency of 10.8%. The force between its jaws is of 367 µN. This low level of force could be useful when sensitive particles are manipulated.

Laser surface texturing (LST) followed by an ultrasonic nanocrystalline surface modification (UNSM) process was applied to graphite cast iron to improve the friction and wear behavior. The surface hardness of the UNSM-treated and UNSM + LST-treated specimens was increased significantly compared to the polished and LST-treated specimens. The friction and wear behavior of the specimens was assessed using a ball-on-disk friction tester at an applied load of 10 N and a speed of 5 cm/s in both dry and lubrication conditions. The friction coefficient of the UNSM-, LST-, and UNSM + LST-treated specimens reduced in both dry and lubrication conditions compared to the polished specimen by 64, 30, and 64% and 63, 67, and 75%, respectively. In lubrication condition, the friction coefficient of the UNSM- and LST-treated specimens was further reduced by about 30 and 25% by UNSM + LST processes. In dry condition, the UNSM + LST-treated specimen exhibited a reduction in the friction coefficient of 46% compared to the LST-treated specimen, whereas no reduction in friction coefficient was found compared to the UNSM-treated specimen. The wear resistance of the UNSM-, LST-, and the UNSM + LST-treated specimens was enhanced by 22, 11, and 37% in the dry condition, respectively, whereas minuscule wear was observed in the lubrication condition that was difficult to quantify in our experiment. UNSM and LST processes were effectively combined to improve the friction and wear behavior of graphite cast iron. [ABSTRACT FROM PUBLISHER]