Pair Of Cylinders Research Articles

A Study of Fit and Friction Force as a Function of the Printing Process for FFF 3D-Printed Piston–Cylinder Assembly

Current 3D printing processes for polymer material extrusion are limited in their accuracy in terms of dimension, form, and position. For precise results, post-processing is recommended, like with assembled parts such as pistons and cylinders wherein axial mobility is desired with low friction force and limited radial play. When no post-processing step of the printed parts is accomplished, the fit and the friction force behavior are strongly dependent on the process performances. This paper presents a study on parameters of significance and their effects on sliding and running fits as well as their friction forces for fused filament fabrication of such assemblies. A series of experiments were performed with multiple factors and levels, including the position or layout of printed objects, their layer thickness, the material used, the use of aligned or random seam, and the printer type. Piston–cylinder pairs were printed, measured, assembled, and tested using a tensile test frame. A mathematical model was developed to describe the oscillating friction force behavior observed. This study presents the feasibility and limitations of producing piston–cylinder assemblies with reduced play and friction when using appropriate conditions. It also provides recommendations to obtain and better control a desired running and sliding fit.

On the dynamics of transporting rolling cylinders

AbstractA common, yet hazardous, method of transporting cylindrical tanks used to carry compressed gas involves rolling both tanks at opposite angles of inclination to the vertical. By propelling one of the tanks while maintaining point contact between the tanks, both tanks can be moved such that their centers of mass move in a straight line. The purpose of this paper is to explore this locomotion mechanism. First, the problem of supporting an inclined cylinder in point contact with a rough surface is examined. The analysis shows that dependent on the geometry of the cylinder and the coefficient of static friction, a wide range of angles of inclination are feasible. The presence of non-integrable constraints on the motion of the rolling cylinder is explored using the concept of a holonomy. The problem of transporting two cylinders using the aforementioned mechanism is then analyzed with the help of Frobenius’ integrability criterion for constraints and numerical simulations. The results show the mechanical advantage of transporting a pair of cylinders, the range of possible angles of inclination, and the forces needed to sustain the motion.

Investigation of dynamics of a droplet impacting a pair of circular cylinders

Investigation of dynamics of a droplet impacting a pair of circular cylinders

Experimental investigation of the Eckert-Weise effect (aerodynamic cooling) of pair side-by-side circular cylinders in a compressible cross-flow

The rear surface of a thermally insulated circular cylinder placed in a subsonic high-velocity cross-flow is significantly cooled, this phenomenon is known as aerodynamic cooling or the Eckert–Weise effect. This effect is associated with the redistribution of the stagnation temperature (energy separation) in the unsteady vortex wake. Experiments show that the effect is maximal at Mach numbers of the free-stream flow of 0.5–0.7, resulting in negative values of the temperature recovery factor (the temperature of the cylinder rear surface becomes lower than the static temperature of the free-stream flow). In this case, the cooling of the rear surface can reach tens of degrees. This effect can be utilized as the basis for a novel energy separation device, as it enables heat transfer between flows with the same stagnation temperatures. As shown in a numerical study (Aleksyuk, 2021), the effect is highly sensitive to the flow interference behind side-by-side cylinders, this is especially important for its practical application. In this study, the aerodynamic cooling of a pair identical circular cylinders in side-by-side arrangement, is experimentally investigated within the Mach and Reynolds number ranges of M = 0.34–0.58 and ReD = 1.6∙105–3.1∙105. The cylinder spacing considered in this study (P/D = 1.1; 1.5; 2.0; 3.0; and 4.0, where P is the center-to-center cylinder spacing and D is the diameter) covered the key regimes of vortex interference, that is, single, bistable, and coupled vortex streets. Also, investigations were conducted for a single circular cylinder with the same diameter within the Mach and Reynolds number ranges of M = 0.34–0.68 and ReD = 1.6∙105–3.4∙105. The channel blockage ratio was found to be 8% for a single cylinder and 16% for a pair of cylinders. Consequently, this study focuses on confined flow or flow past a confined cylinder with a uniform profile of oncoming flow velocity. It is shown that the Eckert-Weise effect for the pair of cylinders can either increase or decrease depending on the interference regimes and is sensitive to the blockage ratio value.

Stability Analysis of the Secondary Motion of a Textured Piston

Piston–cylinder pairs are very common in industrial mechanisms. While a piston is primarily designed for axial reciprocating motion, the occurrence of secondary motions—lateral and rotational—due to the small clearance between the piston and the cylinder may lead to frictional contact, energy loss, wear and an increase in unwanted leakage. This study focuses on mitigating the secondary motion of a ringless piston. The influence of a Rayleigh step bearing and partial surface texturing with numerous micro-dimples on the dynamic stability of the secondary motion is studied. A linear model was used to obtain the trajectory of the secondary motion and Floquet theory was applied to analyze the stability and draw stability maps. The influence of various texturing and step parameters, including the dimple area density and aspect ratio for partial texturing, as well as the length and depth of treatment for both partial texturing and step profiles, on the stability of the secondary motion was examined. The normalization method is presented, enabling the expansion of the results for various operating conditions and geometries. Conclusions and guidelines regarding the optimal parameters, in terms of a wider stability range and higher decay rate, are formulated.

Flow around a pair of 2D cylinders using a hybrid Eulerian-Lagrangian solver

The field of external aerodynamics encompasses various engineering disciplines with a significant impact on wind energy technology. Aerodynamic investigations provide insights not only into the characteristics of individual blades or standalone wind turbines but also into entire wind farms. As advancements in wind turbine design continue, understanding the interactions between turbines in close proximity becomes crucial, presenting a multi-body problem. Researchers require efficient and accurate tools to comprehensively study such dynamics. This paper presents a hybrid Eulerian-Lagrangian solver designed to leverage the strengths of Eulerian solvers in resolving boundary layers and Lagrangian solvers in convecting wakes downstream without introducing significant numerical diffusion. The solver adeptly handles multi-body simulations, allowing the construction of independent Eulerian meshes that communicate seamlessly through Lagrangian particles. In this way, the computational study of multibody problems does not require very large and dense meshes. Validation in single-body cases has already been conducted, with this paper demonstrating the solver’s application to a pair of cylinders in different configurations. A comparative performance analysis is carried out against pure Eulerian solvers. The results highlight that the hybrid solver efficiently reproduces the accuracy of the Eulerian solver, demonstrating its effectiveness in handling complex aerodynamic simulations.

The onset of instability and bifurcations in the transitional wake of two tandem square cylinders

Unsteady three-dimensional simulations are performed to elucidate the hidden transitional flow dynamics and Hopf bifurcations along the topological corelines of the created von Kármán streets behind a pair of square cylinders positioned in tandem. Our simulations provide significant new insight into the three-dimensional wake evolution and governing flow physics. We explain how pressure, velocity, and vorticity fluctuation along the Kármán vortex corelines in the increasingly unstable wake amplify, facilitating the growth of various modal instability patterns. The existing knowledge of wake transition through the intertwining of modes A, B, and C instabilities and associated linear stability analysis helped to gain some insight into the overall wake feature. The current study explains how exactly the transitional disturbances physically spread behind a pair of inline and tandem cylinders through the self-excited spanwise-periodic oscillation of the wake and created a sequence of variable length scaled Hopf bifurcations and their swapping for varied gaps between the cylinders and Reynolds number. The growth of a slow mode of the spectral frequency at the bifurcation points seemed crucial in initiating the near-transitional flow irregularity.

Complete mode conversion of elastic waves by utilizing hexapole resonances in a double-scatterers structure

In recent years, the emergence of elastic metamaterial has provided new methods to manipulate the polarization of elastic waves, achieving elastic mode conversions. This paper theoretically investigates a complete mode conversion effect, where longitudinal waves are completely converted into transverse waves after being reflected by one layer of metamaterial slab. The slab structure contains a pair of cylinders, and the conversion is attributed to the out-of-phase coupled hexapole resonances of the two cylinders. Unlike the monopole, dipole, and quadrupole resonances, the hexapole resonances induce trivially, nearly constantly, effective parameters. The proposed design does not follow the recent popular “reversely designing parameters” method. The conversion based on the hexapole resonances is relatively broadband and wide-angle, which is beneficial for practical applications such as sound absorption.

The CUFF, Clenching Upper-Limb Force Feedback Wearable Device: Design, Characterization and Validation.

This paper outlines the design, characterization, and validation of a novel wearable haptic device capable of delivering skin stretch, force feedback, or a combination of both, to the user's arm. In this study, we conducted physical and perceptual characterization with eleven able-bodied participants, and two separate experiments involving discrimination and manipulation tasks, encompassing a total of 32 participants. In both experiments, we used the CUFF device in conjunction with the Pisa/IIT SoftHand. The first experiment was a discrimination task in which participants were required to differentiate between pairs of cylinders based on their dimensions and perceived softness. The second experiment called for participants to control the robotic hand in order to grasp objects. Following the experiments, participants provided a subjective evaluation of the device. The results from the experiments and the participants' feedback underscored the effectiveness of the proposed device. Thanks to its versatility and structural design, the device shows promise as a viable solution for a variety of applications, including teleoperation, guidance, rehabilitation tasks, and prosthetic applications.

Hydraulic cylinder rod part surface quality improvement on the local thermal effect basis

In modern mechanical engineering, one of the urgent tasks is to improve the quality of manufacturing of surfaces of contact pairs of hydraulic cylinders. This task is connected, first of all, with the grinding operation, which leads to the formation of burns, microcracks, and scarring. The presence of defects on the surface leads to the formation of a poor-quality protective chrome layer. Destruction of the protective layer during operation breaks the sealing ability of the sealing rings. For this reason, abrasive microparticles enter the contact zone, forming adhesive wear on the surfaces. To increase the performance characteristics of hydraulic cylinders, it is necessary to comply with the quality requirements in the technological process. So, for the part “rod” surface roughness should be Ra = 0.63 μm. It is possible to achieve a given surface quality by replacing the grinding operation with mechanical processing with local thermal influence.

Flow and heat transfer analysis over a pair of heated bluff bodies in a channel: Characteristics of non-linear rheological models

In this computational study, the tribological characteristics of the flow of a visco-plastic fluid around a pair of cylinders in a channel are thoroughly analyzed. To numerically solve the governing equations, this investigation makes use of the Galerkin's Finite Element Method (FEM) in conjunction with Newton's and PARDISO solvers. The stable finite element pair (P2/P1) has been selected for the space discretization purpose. The impacts of several physically important parameters on the flow characteristics are investigated in depth, including the spacing ratio (GP), the power law index (n), the Bingham number (Bn), and the Reynolds number (Re). When using different gap spacing ratios (GP), the drag coefficient (CD) and lift coefficient CL were found to be strongly dependent on GP. The pressure, velocity, and viscosity profiles are plotted for varying n and Bn. In addition, the velocity behavior is observed along y-direction in a channel through line graphs. Code validation is done as special case when Bn=0andn=1. It has been observed that the gap between the obstacles can influence the overall flow pattern and subsequently the drag and lift forces.

Experiments on flow-induced vibration of four flexible cylinders with large aspect ratio in a square configuration

A system consisting of four cylinders positioned in the quadrilateral arrangement represents the prevalent and fundamental constituent within pipe bundles and tube banks in numerous engineering scenarios. This research presents a laboratorial study on flow-induced vibration (FIV) exhibited by four flexible cylinders positioned within a square geometric arrangement. The uniform flows were produced by a carriage on the top of a towing tank. Considering flow velocities and structural parameters, Reynolds number could reach 16000. The spacing between the cylindrical centres was selected as 6.0 D (D denotes the outer diameter of cylinders), and two typical incidence angles 0° and 45° were examined. For each flexible cylinder model, strain gages at seven distinct measuring positions were utilized to collect the oscillation data in cross-flow (CF) and in-line (IL) directions. Principal vibration modes, response frequencies, response amplitudes and motion trajectories were presented to understand the FIV features. For incidence angles 0°, considering the four flexible cylinders as two sets of tandem cylinders arranged in parallel is not appropriate due to the proximate effect. The behaviours of the two upstream cylinders resembles those of the pair of cylinders positioned in a side-by-side configuration, whereas behaviours for the downstream cylinders are influenced by wake interference generated from leading cylinders. IL response frequencies decrease to the values close to the CF response frequencies, resulting in the elliptical-shaped motion trajectories with large IL displacements. For incidence angles 45°, the upstream cylinder displays characteristics akin to those of a solitary cylinder experiencing vortex-induced vibration (VIV). Reactions for the central pair of cylinders result from the amalgamation of VIV and wake-induced flutter. While, reactions observed for downstream cylinder are characterized by low frequencies, significant IL displacements and more chaotic trajectories.

Mixed Convective Flow Past Reverse Doublet like Rotating Side by Side Cylinders

The flow unsteadiness and the consequent evolution of the vortex shedding for flows around bluff objects are significantly important in fluid dynamics. Rotating the bluff objects may help in controlling such flow instabilities. Depending on the rotational speed, the unsteady flow may be transfigured into a steady pattern. On the other hand, multiple objects placed transverse to the incoming flow have destabilizing wake interactions. The instability even gets amplified with the introduction of thermal buoyancy. Under such conditions, the rotation plays an important role in stabilizing the wake dynamics. In view of the above, the present study aims to numerically investigate the wake and the thermal characteristics around a pair of circular cylinders arranged in side-by-side fashion in an unconfined medium. The top and the bottom cylinders are rotated in the counterclockwise and the clockwise directions, respectively, replicating a reverse doublet like configuration. The Reynolds and the Prandtl numbers are fixed at 100 and 0.71, respectively. The effect of the rotation on the flow instability is studied for Richardson number 0 to 1. The computations are performed using a finite volume method for the dimensionless cylinder spacings 0.7, 1.5, 3.0, and 5.0. The unsteady and the steady attributes are examined using the vorticity, isotherm-streamline contours, and lift signals. Finally, a regime diagram is constructed to exhibit the critical rotational speeds at which the flow becomes steady for various cylinder spacings.

Flow regime identification and flow instability analysis of oscillatory flows over twin circular cylinders

Oscillatory flows past two identical circular cylinders are investigated by two-dimensional direct numerical simulations in the parameter space of gap ratio (0.5 ≤ G ≤ 4.0), angle of flow incidence (0° ≤ α ≤ 90°) and Keulegan–Carpenter number (4 ≤ KC ≤ 12) with a constant Reynolds number Re = 150, where G = L/D, KC = UmT/D and Re = UmD/υ with D being the dimeter of the identical cylinders, L the shortest surface-to-surface distance between the two cylinders, Um and T being the velocity amplitude and period of the sinusoidal oscillatory flow, respectively, and α is defined as the angle between the flow direction to the line connecting the centers of the two cylinders. Comparing with the tandem or side-by-side arrangements of twin circular cylinders in oscillatory flows, the staggered twin cylinders (0° < α < 90°) involve more diverse flow regimes, including the periodic, quasi-periodic and chaotic flow states, due to the inherent asymmetric flow interference around the cylinder pair. In addition to introducing four flow regimes for the tandem and side-by-side arrangements, this study newly identifies 11 flow regimes for the staggered twin cylinders. The newly reported flow regimes in this work are collaboratively identified through the flow visualizations, steady streaming, frequency spectra of fluid forces and Lissajous phase diagrams, as well as the temporal-spatial symmetry features of the wake flows. Connecting with the previous work by Zhao and Cheng [“Two-dimensional numerical study of vortex shedding regimes of oscillatory flow past two circular cylinders in side-by-side and tandem arrangements at low Reynolds numbers,” J. Fluid Mech. 751, 1–37 (2014)], this study presents overall regime maps in the KC-α plane for varied gap ratios. It is found that the flow regimes previously and presently identified for the tandem and side-by-side arrangements may also appear for the staggered twin cylinders. The present numerical results suggest the sensitive dependence of the flow regimes on the parameters of KC, α, and G. It is also found that a specific flow regime with narrow parameter bands may appear within another flow regime, forming the abnormal regime hole in the regime map. To understand the profound influence of the control parameters on the flow regime transition, and the relevant temporal-spatial symmetry breaking, the linear Floquet stability analysis is conducted in this work. It was confirmed that the variation of the KC number may result in the Ky symmetry breaking over several periodic flow regimes, while the change of the angle of flow incidence may account for the H2 symmetry covering various periodic and quasi-periodic flow regimes. The stability analysis also explains the temporal flow transition and the abnormal occurrence of the regime holes within either quasi-periodic or chaotic flow regimes.

Hydrodynamic interaction between two polygonal cylinders in uniform potential flow

The analytical solution for uniform potential flow around two similar or dissimilar polygonal cylinders is obtained by using complex potential function for a doublet trapped in an annulus. The annulus of two circles is mapped conformally to the pair of polygonal cylinders by unique combination of bilinear and hypotrochoidal transformation and mathematical formulas to get velocity, pressure and hydrodynamic force distribution around two polygonal cylinders are presented. The effects of center distance between the cylinders, shape, orientation and corner radii of cylinders, and flow angle on the hydrodynamic interaction between the cylinders are also investigated and presented. The comparison of some of the numerical results obtained using present method is done with the results obtained from commercial CFD software package and results from literature.

Flow-induced vibration of tandem flexible cylinders with a larger-diameter upstream cylinder

A systematic experimental study is conducted for the flow-induced vibration (FIV) of tandem flexible cylinder pairs with diameter ratios (D,u/D,d) ranging from 1 to 2. The diameter of the downstream cylinder (DC), D,d, is fixed at 16 mm, while that of the upstream cylinder (UC), D,u, evenly varies from 16 mm to 32 mm. Cylinders with a total length of 2.7 m and an immersion depth of 1.2 m are allowed to freely oscillate in the cross-flow and in-line directions. Results are examined for Re = 1600–11,200 (based on D,d) and a fixed streamwise separation between the cylinder centers T =6D,d. It is shown that the FIV of the DC (DC-FIV) is strongly sensitive to D,u/D,d, and that increasing D,u/D,d significantly weakens the high-mode and high-frequency response of the DC. A deeper analysis of the dual-cylinder interaction reveals the perturbation mechanism of the UC on the DC-FIV, i.e., the UC forces the DC to oscillate following its dominant frequency and dominant mode through “vibration control”. A map containing eight response patterns is further provided in the D,u/D,d–Vr plane. The Strouhal number rule between DC-FIV and its reduced velocity, which is broken by the UC, is reconstructed with a variation factor.

Investigation of the Effects of 0W20 and 10W40 Lubricating Oils on Cylinder Liner Wear

Proper lubrication regime in engines significantly impacts engine performance, fuel efficiency, durability, and environment. Lubrication regimes reduce friction between engine components, control wear, and ensure long-lasting parts. This study conducted experiments on a wear-testing device to determine the amount of wear between the piston ring and cylinder pair. The experimental work was performed at different loads and speeds. The tribological properties of 0W20 and 10W40 lubricating oils were examined in the study. As a result of the experimental work, when using 10W40 lubricating oil in the wear testing device, lower cylinder wear was observed compared to using 0W20 lubricating oil. The study found that the amount of wear increases as the load on the cylinder sample increases. The maximum cylinder wear was obtained under an 80N load. The minimum cylinder wear was determined under a 40N load. SEM images of the cylinder samples were also examined to determine the damage after wear.

Numerical investigation of free convection around a pair of vertically-aligned isothermally-heated vertical hollow cylinders

Efforts are made to delineate the free convection analysis numerically from a pair of vertically attached vertical hollow isothermally heated cylinders with negligible wall thickness immersed in the air within the laminar flow regimes. Thermofluidic behavior around the cylinders is characterized in detail by employing the influence of several relevant dimensionless parameters such as, Rayleigh number (103 ≤ ≤ 107), spacing-to-length ratio and upper to lower cylinder diameter ratio Importantly, heat transfer and fluid flow patterns around the upper cylinder due to the presence of a lower cylinder are thoroughly elucidated, which is not fully understood in the existing literature. It is seen that the enhancement of heat transfer rate from the inner surface is greatly influenced at for lower value of and A linear growth and non-linear reduction patterns against are observed for Nusselt numbers for inner and outer walls, respectively, for fixed value of and Lastly, a suitable correlation has been proposed for net average Nusselt number as a function of relevant input dimensionless parameters. The correlation shows an excellent agreement with the computed data points within ±6%. This correlation is also expected to be helpful for the relevant engineering calculations and provide values for various academic and industrial purposes.

Particle dispersion over side-by-side square cylinders: Proximity interference effects

This paper investigates the dispersion of tiny inertial particles in the two-dimensional laminar wake from a pair of square cylinders placed side-by-side to each other. The flow Reynolds number (defined based on the cylinder size h and uniform inflow velocity Uc) in our study is fixed at 75. The wake pattern resulting from the interaction between vortices shed from individual cylinders depends on the cross-stream spacing between the cylinders, i.e. spacing ratio s/h. We examine the effect of varying the cross-stream spacing between the cylinders on the body impaction and dispersion of particles in the wake flow over a range of their responses. Three different spacing ratios, s/h = 0.3, 2, and 4 are considered. We find that the impaction efficiency of Stokes number St = 0.1 particles is not sensitive to the spacing ratio. However, the impaction efficiency of St = 1 and 10 particles is dependent on the spacing ratio and increases with the latter. We illustrate how the distribution and clustering of representative inertial particles (i.e., with Stokes number unity) evolve over a vortex shedding cycle uniquely due to the wake flow in each spacing ratio configuration and explain the physical mechanism of particle clustering using backward tracking. The non-uniform clustering of particles with different responses to the wake flow in each spacing ratio configuration is analyzed using the Voronoï diagrams. The spacing ratio effects on the dispersion of particles are quantified in terms of mean statistical quantities such as mean local concentration, clustering intensity, and velocity statistics. The local concentration of St = 1 and 10 particles at streamwise positions away from cylinders is significantly influenced by the wake flow behavior governed by the choice of the spacing ratio. Further, the combined effect of gravity and hydrodynamic drag forces on the impaction and clustering behavior of particles is reported, where the Froude number Fr=0.32. In all the cases, particles exhibit ballistic behavior, showing a significantly reduced tendency to form clusters and a drastic increase in the impaction efficiency.

An investigation into the micro-geometric tapered-shape surface design of the piston bore of a piston–cylinder interface in an axial piston motor

Abstract. In pursuit of design solutions that reduce energy loss and improve wear resistance for the piston–cylinder interface in an axial piston motor, a fluid-structure interaction numerical model and a new test rig of the friction force of the piston–cylinder pair are developed to achieve the analysis and design of the micro-geometric tapered-shape surface of a piston bore. The piston bore with the tapered-shape surface axial distribution length ratio of 49.44 % of the overall length is found to be the relatively optimized one. Furthermore, how the shaft speed, load pressure, and swash plate angle influence the performance of the two-type interface is analyzed. Numerical analysis results show that, compared with the traditional cylindrical piston bore design, the piston–cylinder interface with the optimized tapered-shape piston bore in the axial piston motor can achieve a significant reduction in leakage flow and friction force, and the experimental results are consistent with the simulation results.