Side Of Cylinder Research Articles

Analysis of Residual Stress in the Rotational Autofrettage of Thick-Walled Disks

Autofrettage is a means of generating compressive residual stresses at the inner side of a thick-walled cylinder or hollow disk by causing nonhomogeneous plastic deformation of the material at the inner side. The presence of residual compressive stresses at the inner region of the cylinder/disk enhance the pressure withstanding capacity, fatigue life and the resistance to stress corrosion cracking of the component. Despite the hydraulic and swage autofrettage are the widely practiced processes in industries, there are certain disadvantages associated with these processes. In view of this, in the recent years, researchers have proposed new methods of achieving autofrettage. Rotational autofrettage is such a recently proposed autofrettage method for achieving the beneficial compressive residual stresses in the cylinders. In the present work, the rotational autofrettage is studied for a thick-walled hollow circular disk. A theoretical analysis of the residual stresses produced in the disk after unloading are obtained assuming plane stress condition, Tresca yield criterion and its associated flow rule. The analysis takes into account the effect of strain hardening during plastic deformation. Further, the effect of residual stresses in the typical SS304 and aluminum disk is studied by subjecting them into three different types of loads viz., internal pressure, radial temperature difference, and rotational speed individually. A three-dimensional (3D) finite element method (FEM) validation of the theoretical stresses during rotational autofrettage of a disk is also presented.

A Hollow Cylinder Radial-Seepage Apparatus for Evaluating Permeability of Sheared Compacted Clay

Compacted clay is widely used to control seepage in earth and rock-fill dams in favor of its low permeability. The clay at certain locations of dams often experience large shear strain due to differential settlement, which may lead to changes in seepage resistance. A new apparatus was developed to examine the permeability evolution of compacted clay during shearing. The apparatus tests a hollow cylindrical specimen holding by a set of inner and outer laminar rings. The specimen can thus be compressed in the height direction and sheared in the circumferential direction. The permeability is measured by radial seepage from the inner side to the outer side of the hollow cylinder. A series of tests on heavily compacted specimens of a core-wall clay were conducted to demonstrate the performance of the new apparatus. The permeability of unsheared specimens under different surcharge pressures and hydraulic gradients was investigated firstly, and the observed phenomenon agreed well with those in conventional permeameters. Then the permeability evolution during shearing was investigated under constant surcharge pressures. It was found that the compacted specimens deformed non-uniformly with a well-developed shear band, and the permeability of the shear band determines the overall seepage resistance. The permeability of the shear band increases during shearing under low surcharge pressure, whereas under high surcharge pressure, it varies insignificantly. Such behavior is related to different structural changes of shear bands under low and high surcharge pressures. The preliminary test results highlighted an important fact, that the heavy-compacted clay under low surcharge pressure could generate low seepage resistance shear bands when subjected to a large shear, leading to a high risk of concentrated leakage and erosion. The new apparatus could prove useful for clarifying stress conditions triggering low seepage resistance shear bands in compacted clays.

Viscous-Flow-Based Analysis of Wave Near-Trapped in a Four-Cylinder Structure

The hydrodynamic analysis of multi-floating bodies is important and widely used in marine engineering. In this study, we systematically simulated the wave diffraction problem of a fixed vertical four-cylinder structure in regular waves in the time domain in a viscous numerical wave tank. The hydrodynamic interaction of waves with a bottom-mounted structure consisting of four vertical cylinders arranged at the corners of a square shows a complicated interference phenomenon. In this paper, we illustrate and analyze the run-up around the structure and the corresponding wave forces. To investigate the viscous effect on the near-trapping phenomenon, we pay particular attention to investigating the waves near-trapped inside the four-cylinder structure, and make a comparative study of the viscous- and inviscid-flow solutions with the experimental measurements. The results show that the maximum wave elevation occurs on the inner side of the leeside cylinder, and that the wave elevations on the outer side of the cylinders are lower than those on the inner side. We can conclude that viscosity has an obvious damping effect on wave elevations inside the structure. The cylinders show a tendency to drift apart from each other when the near-trapping phenomenon occurs.

Optimization of thin-walled sealing structure based on mechanical simulation

In the hydraulic and gas pipelines, even thin-walled cylinder device, the built-in elastomeric O-rings are widely used to ensure their sealing. Unfortunately, a case of excessive radial contact pressure will lead to leakage risk. At the same time, the aging of elastomeric O-ring will result in decrease of radial contact pressure, which can also bring about leakage risk. To increase the life of the seal structure, the external shape memory alloy (SMA) sealing ring is subsequently developed for the actual product. However, excessive contact pressure will cause the leakage risk with the lateral deformation at the outside of the sealing interface of the thin-walled cylinder. Based on mechanical simulation, a proposal for the optimization design of seal structure with thin-walled cylinder is given. That is, the radial contact seal on the inner and outer side of the thin-walled cylinder can simultaneously made by SMA. Results gained show that the theoretical value of the resultant force from the SMA at the inside and outside of the sealing interface of the thin-walled cylinder is zero. The bilateral seal structure with SMA ring can avoid the leakage risk caused by the unilateral force and deformation on the thin-walled cylinder, and effectively prolong the service life of the sealing device.

Vibrations of a square cylinder submerged in a wake

A numerical investigation is conducted on the flow around and vibration response of an elastic square cylinder (side width $D$) in the wake of a stationary cylinder at Reynolds numbers of $Re=100$ and 200 based on $D$ and the free-stream velocity. The downstream cylinder, referred to as the wake cylinder, is allowed to vibrate in the transverse direction only. The reduced velocity $U_{r}$ is varied from 1 to 30. Cylinder centre-to-centre spacing ratios of $L^{\ast }(=L/D)=2$ and 6 are considered. Simulations are also conducted for a single isolated cylinder, and the results are compared with those for the wake cylinder. The focus is given to vibration response, frequency response, fluctuating lift force, phase relationship between the lift and displacement, work done and the flow structure modification during the cylinder vibration. The results reveal that the dependence of the Strouhal number $St$ on $U_{r}$ can distinguish different branches more appropriately than that of the vibration amplitude on $U_{r}$. The vibration response of the single cylinder at $Re=100$ is characterized by the initial, lower and desynchronization branches. On the other hand, that at $Re=200$ undergoes initial, lower and galloping branches. The galloping involves the characteristics of both the initial and the lower branches or the initial and the desynchronization branches depending on $U_{r}$. For the wake cylinder, the gap flow has a significant impact on the vibration response, leading to (i) the absence of galloping at either $Re$ and $L^{\ast }$, (ii) the presence of an upper branch at $Re=200$, $L^{\ast }=6$ and (iii) an initial branch of different characteristics at $Re=100$, $L^{\ast }=6$. The different facets are discussed in terms of wake structures, work done and phase lag between lift and displacement.

CFD simulation of nanofluid forced convection inside a three-dimensional annulus by two-phase mixture approach: Heat transfer and entropy generation analyses

The behavior of water–Al2O3 nanofluid inside the three-dimensional horizontal concentric annulus is investigated by the two-phase mixture procedure regarding the first and second laws of thermodynamics. The annulus walls are subjected to constant temperature boundary condition. Heat transfer and entropy generation rates, nanoparticle distribution, skin friction coefficient, and temperature distribution are evaluated at different concentrations and Reynolds numbers. The results show that nanoparticle concentration at the bottom of annulus and the upper side of inner cylinder is greater than other regions. In addition, the heat transfer and thermal entropy generation rates increase with increment of concentration and Reynolds number. Moreover, the lowest and highest thermal entropy generation rates happen in the annulus central part and near the walls, respectively. Bejan number is very close to 1 at all cases under study, which shows the dominance of thermal entropy generation.

Investigation of Flow Rate on Chemical Bath Deposition of Silver Films Inside Hollow Polymer Cylinders

In thin film solar cells made as planar structures, the absorption of solar light and hence, the solar conversion efficiency, is heavily determined by the position and orientation of the sun. One way to overcome this is to use solar cell geometries that could better absorb sunlight from different angles. One potential geometry is a hollow cylinder, which has the ability to better absorb the sun’s rays incident at various angles due to the light trapping nature of the cylindrical geometry. If such solar cells could be fabricated inside polymer tubes with micrometer diameters, many potential applications built around non-woven or woven textiles could be realized. Here we investigate the deposition of homogeneous thin metallic films inside hollow polymer cylinders using the process of chemical bath deposition (CBD). Although films deposited via CBD have been studied extensively, mechanisms to achieve high quality deposition inside hollow cylinders are still not well understood. The objective of this project was to deposit a smooth, homogeneous silver film inside a hollow cylindrical structure using varying flow rates. The early stage film growth for very short deposition times was observed by the localized surface plasmon resonance of the silver nanoclusters via absorption spectra along the length of the tube. For longer deposition times, silver films formed and were analyzed for their morphology, thickness, roughness, and resistance using a combination of optical microscopy, scanning electron microscopy, and two-probe conductivity. The findings from this study showed that deposition under flow with different Reynolds numbers had a strong influence on the morphology and electrical resistance of the deposited films. KEYWORDS: Thin-films; Chemical Bath Deposition; Nanoparticles; Solar Cells; Silver

Experimental investigation on the efficiency of circular cylinder-based wind energy harvester with different rod-shaped attachments

The performance of a circular cylinder-based piezoelectric wind energy harvester with two small-size rod-shaped attachments on the main circular cylinder was experimentally investigated. The rod had three different cross-sectional shapes: circular, triangular, and square. The two rods were attached on two sides of the main circular cylinder at a series of circumferential locations. They were parallel to the cylinder axis and symmetrical to the stagnation line. It was found that attaching these three rod types at the circumferential locations of 45° and 60°, harvested power continuously beyond the critical wind speed. It was, therefore, dramatically superior over both the plain circular cylinder and the cases with other attachment locations. Additionally, the output voltage for a circumferential location of 60° was greater than that 45° one over the whole working wind speed range. Furthermore, attaching the triangular rods on the main circular cylinder showed a better performance than the other two rod types. The force measurement results indicated that the circular cylinder with triangular rods at the circumferential location of 60° had larger transverse force coefficients than the other two rod type cases, verifying the findings in the energy harvesting tests. Therefore, it is recommended to attach two triangular rods at the circumferential location of 60° on the main circular cylinder in order to enhance the performance of a circular cylinder-based wind energy harvester.

DNS of Taylor–Couette flow between counter-rotating cylinders at small radius ratio

A counter-rotating Taylor-Couette flow with relatively small radius ratios of $\eta$ = 0.2--0.5 was investigated over a wide range of the Reynolds number, from laminar to turbulent regime, by means of three-dimensional direct numerical simulations. We investigated the $\eta$ dependence of the flow structure and determined a critical value between $\eta$ = 0.2 and 0.3, below which, the stable outer cylinder side exhibited a modal structure that was different from the Taylor-vortex flow on the inner side. At $\eta \geq$ 0.3, the Taylor-vortex on the unstable inner side dominated the entire flow field between the cylinders, whose footprints were observed in the vicinity of the outer cylinder wall. However, for $\eta$ = 0.2, the influence from the inner side was limited up to the centre of the cylinder gap. Moreover, on the stable outer cylinder side, there appeared a modal structure that was axially homogeneous, azimuthally periodic, and similar to the Tollmien-Schlichting (TS) instability wave. As the Reynolds number increased with a fixed $\eta$ = 0.2, the modal structure changed its azimuthal wavenumber and thickened radially in the wall unit. Although the Reynolds shear stress on the outer side remained approximately zero, the intensity of the velocity fluctuations was comparable to the Taylor-vortex flows in the central part.

Large eddy simulation of flow over inclined wavy cylinders

The wavy cylinders have been proven effective in suppressing the Kármán vortex shedding and mitigating the aerodynamic forces. As yet their performance in the inclined incoming flow has not been well understood. In the current work, large eddy simulations are carried out to unveil the aerodynamics of the flow around inclined wavy cylinders at the Reynolds number of 5000. Three inclination angles, 0°, 30° and 45°, together with 2 × 2 combinations of shape parameters, namely λ∕Dm=2 and 6, a∕Dm=0.1 and 0.15, have been taken into consideration. Firstly, the aerodynamic force coefficients in terms of both the span-wise averaged and sectional values are discussed at length. It is revealed that the growing inclination angle invites not only a surge in their span-wise averaged values, but also an enlargement in the sectional difference of the force coefficients. The span-wise correlation of the lift force is found to be enhanced for the wavy cylinders with the increase of inclination angle, while the opposite is true for the normal cylinders. By examining the mean wake properties, it is disclosed that the increase in the span-wise averaged drag force coefficients is closely related to the shrinkage in the vortex formation length and the regression of the base pressure, whereas the sectional distribution of the drag coefficients is largely affected by the stagnation pressure. The mean wall shear stress fields are exploited to shed light on the flow topology of the cylinder surfaces. It is discovered that the wavy cylinders, especially the short-wavelength one, exhibit significant span-wise variation in the separation structure in the inclined flow. Besides, the chaotic surface flow in the rear side of the non-inclined cylinders could be regulated to maintain symmetry by the secondary axial flow in the near wake of the inclined cylinders. The instantaneous three-dimensional vortical structures are visualized by the Q isosurfaces at last to collaborate the previous discussions. A preliminary mechanism for the cessation of flow control efficacy for the wavy cylinders in inclined flow is also presented.

Edge curvature effects of a square cylinder on self-sustained oscillations

A square cylinder at zero angle of attack is known to exhibit a self-sustained response beyond the lock-in region. This self-sustained response is characterized by a frequency that is lower than the vortex shedding frequency and with large amplitudes. However, this self-sustained oscillation is not present for circular cylinders. Prior literature indicates that shape changes through altering the corner sharpness can help to reduce these self sustaining oscillations. In this work, shape changes are realized through altering the curvature of the edge(side) of the square cylinder. For different edge curvature and rounded corner combinations, characterization of these self-sustained oscillations is studied. Detailed flow analysis is performed to study the effect of straight edge, curved edge, sharp corner and rounded corner on the pressure distribution. A proper combination of edge curvature and corner sharpness proves to be beneficial in reducing self-sustaining oscillations.

정면에 정방형주를 가진 원주의 항력저감 특성실험

The Characteristics of the drag reduction of a circular cylinder having a small square prism at the upstream side was investigated by measuring of drag on the circular cylinder and by visualization of the flow fields using PIV. The experimental parameters were the width ratios(H/B=0.2~0.6) of square prisms to the circular cylinder’s diameter and the gap ratios(G/B=0~3) between the circular cylinder and the square prism. The drag reduction rate of the circular cylinder was increased and then decreased with G/B in case of the same H/B. The drag reduction rate was increased with H/B in case of the same G/B. The maximum drag reduction rate was represented by 90.8% at H/B=0.6 and G/B=1.0. In case of a circular cylinder having a small square prism, the stagnation regions were represented in the upstream and downstream sides of the circular cylinder, the size of that region in the upstream side was increased with H/B but that in the down stream side was almost same.

Synthetic and Continuous Jets Impinging on a Circular Cylinder

ABSTRACTSynthetic and continuous water jets impinging onto an electrically heated circular cylinder were experimentally investigated. The slot nozzle width was 0.36 mm, the cylinder diameter was 1.2 mm, and the cylinder-to-nozzle spacing related to the slot width was 5–21. Two optical methods were used: qualitative laser-induced fluorescence (LIF) visualization and laser Doppler vibrometry (LDV) measurements. Simultaneously with the optical experiments, the overall convective heat transfer from the circular cylinder was evaluated. The LDV quantified the velocity of the oscillating piezo-driven diaphragm at frequencies from 30 to 68 Hz. A majority of the study was performed at the near-resonant frequencies from 46 to 49 Hz. For all investigated jets, the Reynolds numbers based on the nozzle width ranged from 36 to 171. The LIF visualization revealed a dominant flow separation occurring on the windward cylinder side. This result is attributed to the effect of the miniscales, a relatively small ratio of the nozzle width to the cylinder diameter, and low Reynolds numbers. An increase in the Reynolds number changes the flow pattern from a steady jet-flow separation to a vortex shedding wake-flow regime. The heat transfer experiments were validated in a natural convection regime. An enhancement of the average Nusselt numbers by 4.2–6.2 times by means of the synthetic jets was quantified by comparison with the natural convection regime. A correlation for the average Nusselt number was proposed for both the continuous and synthetic jets.

Exploring the electrical potential inside cylinders beyond the Debye-Hückel approximation: a computer code to solve the Poisson-Boltzmann equation for multivalent electrolytes

Exploring the electrical potential inside cylinders beyond the Debye-Hückel approximation: a computer code to solve the Poisson-Boltzmann equation for multivalent electrolytes

Modeling of fluid flow in a biological reactor of rotational type

The technology using for the replacement of damaged tissues the own cells of the patient, which are placed in a three-dimensional frame - scaffold, is promising for solving the problem of the bone tissue regeneration. A new biological reactor of the rotational type, in which the scaffold tissue rotates in a medium for cultivating the cells, was designed for the development of this technique. A numerical algorithm based on the ANSYS program was developed, which enables one to estimate in a new bioreactor the level of the mechanical load on the cells, which affects their pro-perties. The algorithm enables the computation of the values of the shear stress and static pressure acting on the scaf-fold surface. The computations have shown that the necessary shear stress is reached in the proposed rotational biore-actor on the outer side of the inner cylinder (0.002−0.1 Pa) in the range of rotation frequencies 0.083 < f < 0.233 Hz. At the same time, computational results have revealed the presence of an inhomogeneity in the mechanical action distribution along the scaffold tissue, which is due to the appearance of two Taylor vortices with opposite rotation directions in the gap between the cylinders. The experiments on the flow field visualization inside the rotational bio-logical reactor have shown a qualitative agreement of the flow character with computational results. The proposed numerical algorithm may simulate with sufficient accuracy the fluid flow in a real system. The obtained dependencies can be used in practice for creating an optimal microenvironment of the cells cultivated in the biological reactor.

Observer-based nonlinear precise control of pneumatic servo systems

Pneumatic systems are used in a wide range of industrial robotic and automation systems due to their interesting properties. However, air compressibility, friction, and the other nonlinear characteristics of a servo pneumatic system are difficulties, which contribute to use modern controllers. Conventional linear controllers face steady-state error and uncertainty. Nonlinear modeling with model-based control is a good choice to deal with this problem. In this paper, behavior equation of flow and pressure, friction, and other nonlinear factors are studied. Afterward to reach precise position tracking and low steady error, sliding mode control is proposed. In this way, measurement of pressures and other states of system is required. To reduce the cost of using pressure sensor, observation of pressure with nonlinear high gain observer is suggested. It was seen that the new proposed approach solved the observability problem of servo pneumatic systems. Pressure signal of each sides of cylinder are observed simultaneously by measurement of piston position. Finally, stability of designed controller is studied in the presence of observed states. Experimental results validate the advantage of using designed controller-observer instead of conventional proportional–integral–derivative controller with different input signals in the presence of high friction actuator.

Numerical investigation of the vibration effect of a flexible membrane on the flow behaviour around a circular cylinder

Active control of the flow behind a bluff body is obtained by integrating a vibrating membrane. A numerical study has been conducted to investigate the effect of the vibration of a flexible membrane, stuck to the rear side of a circular cylinder, on the global flow parameters such as the Strouhal number, the drag and lift coefficients. The shape of the membrane is evolving as a vibrating chord using a dynamic mesh. The governing equations of 2D and laminar flow have been solved using ANSYS Fluent 16.0 as a solver and the Gambit as a modeler. The motion of the membrane is managed by two parameters: frequency f and amplitude A. The effect of the flexible membrane motion is studied for the range of conditions as 0.1 Hz ≤ f ≤ 6 Hz and 5 × 10−4 m ≤ A ≤ 10−3 m at a fixed Reynolds number, Re = 150. Three different sizes of the flexible membrane have been studied. Results show that a beat phenomenon affects the drag coefficient. The amplitude does not affect significantly the Strouhal number as well as drag and lift coefficients. By increasing the size of the flexible membrane, we show a lift enhancement by a growth rate equal to 39.15% comparing to the uncontrolled case.

Two-Dimensional Simulation of the Navier-Stokes Equations for Laminar and Turbulent Flow around a Heated Square Cylinder with Forced Convection

Few studies jointly investigate thermal and turbulent effects. In general, these subjects are treated separately. The purpose of this paper is to use the Immersed Boundary Method (IBM) coupled with the Virtual Physical Model (VPM) to investigate incompressible two-dimensional Newtonian flow around a heated square cylinder at constant temperature on its surface with forced convection and turbulence. The VPM model dynamically evaluates the force that the fluid exerts on the immersed surface and the thermal exchange between both in the Reynolds numbers (Re) window 40 ≤ Re ≤ 5×103 . For simulations of turbulence the Smagorinsky and Spalart-Allmaras models are used. The first model uses the Large Eddy Simulation (LES) methodology and is based on the local equilibrium hypothesis for small scales associated with the Boussinesq hypothesis, such that the energy injected into the spectrum of the turbulence balances the energy dissipated by convective effects. The second model uses the concept Unsteady Reynolds Averaged Navier-Stokes Equations (URANS), with only one transport equation for turbulent viscosity, being calibrated in pressure gradient layers. The goal of this work is to analyse the combination of the heat-transfer phenomena with the turbulence for the thermo-fluid-structure interaction in a square cylinder. For this, it was developed a C/C++ code that requires low computational costs in regards to memory and computer facilities. It is observed that, with the increase of the Reynolds number, an increase of the drag coefficient occurs, as well as reinforces the influence of the pressure distribution downstream of the cylinder, which is strongly influenced by the formation and detachment of vortices on the upper and lower sides of the square cylinder.

Experimental investigation of flow over a square cylinder with an attached splitter plate at intermediate reynolds number

The present work is an experimental investigation of flow control over a square cylinder using an attached splitter plate. The experiments are mainly conducted at a Reynolds number of 485. A splitter plate of varying length from 0 to 6 times of the cylinder width is attached to the rear side of the square cylinder to control the flow. The thickness of the splitter plate is kept constant at 10% of cylinder width. The flow interference of a square cylinder with an attached splitter plate is observed using PIV, Hot wire and flow visualization techniques. The primary focus is given on the flow structure and related forces. From the experiments, it has been observed that a secondary vortex appears at the tail edge of the plate after a particular length of the splitter plate. This vortex rotation is opposite to the main vortex and it influences the primary vortex shedding as well as shear layer formation. As a result, the plate modifies the wake size and flow structure behind the cylinder. The drag coefficient and the Strouhal number decrease with an increase in splitter plate length. A correlation is found between the splitter plate length, Reynolds number, and the drag coefficient. The effect of the splitter plate length on the flow field is also studied in terms of velocity, vorticity, streamlines, recirculation length, and turbulence statistics.

Lattice Boltzmann simulations of flow and heat transfer from a permeable triangular cylinder under the influence of aiding buoyancy

Mesoscopic numerical simulations have been carried out to learn about the flow and heat transfer characteristics of a 2-D permeable triangular cylinder, aligned at two different orientations under the influence of aiding buoyancy. Objective of this study is to investigate the effects of Darcy number and forebody shape on the hydrodynamic and thermal behaviour of the porous cylinder, under forced convection (i.e.Ri=0) and aiding buoyancy conditions (Ri = 0.5 and 1) for a Prandtl number value of 0.71 (air). The ranges of Reynolds number (Re) and Darcy number (Da) considered in this study are 1⩽Re⩽40 and 10-6⩽Da⩽10-2, respectively. Lattice Boltzmann method with two distribution functions is employed to perform the numerical experiments. Alongwith BGK collision operator, a body force term with viscous and inertial effects of the porous medium is employed at the porous zone. Detailed results are exhibited in the form of wake length, drag coefficient, streamlines, isotherm contours, heat transfer enhancement ratio and mean Nusselt number. Furthermore, a comparative investigation of drag coefficient and mean Nusselt number of permeable triangular cylinder (apex and side facing flow) with that of the square cylinder is carried out at Da=10-6 for different buoyancy levels. Under aiding buoyancy condition (i.e.Ri>0), the side facing triangular cylinder experiences less drag force than the apex facing for all values of Da. A significant thermal dissipation is observed for increasing values of non-dimensional permeability (or Da) and Richardson number. Furthermore, simple expressions for mean Nusselt number, valid for the range of parameters embraced in the present study, are also provided. The appropriate selection of non-dimensional permeability under different buoyancy conditions is important while applying porous media modeling technique in diverse fields of engineering.