Antennas on circular cylinders
Knudsen, H. L.
1959-01-01
antenna in a circular cylinder. By a procedure similar to the one used by Silver and Saunders, expressions have been derived for the field radiated from an arbitrary surface current distribution on a cylinder surface coaxial with a perfectly conducting cylinder. The cases where the space between the two...... cylindrical surfaces have the sane characteristic constants and different constants are treated separately. Extensive numerical computations of the field radiated from the slot antennas described here are being carried out, but no numerical results are yet available...
Progress on LES of Flow Past a Circular Cylinder
Mittal, R.
1996-01-01
The objective of the present research is to assess the usefulness of large-eddy simulation (LES) methodology for flows in complex geometries. Flow past a circular cylinder has been calculated using a central-difference based solver, and the results have been compared to those obtained by a solver that employs higher-order upwind biased schemes (Beaudan & Moin, 1994). This comparison allows us to assess the suitability of these schemes for LES in complex geometry flows.
Electromagnetic Casimir Forces in Elliptic Cylinder Geometries
Graham, Noah
2013-01-01
The scattering theory approach makes it possible to carry out exact calculations of Casimir energies in any geometry for which the scattering T-matrix and a partial wave expansion of the free Green's function are available. We implement this program for the case of a perfectly conducting elliptic cylinder, thereby completing the set of geometries where electromagnetic scattering is separable. Particular emphasis is placed on the case of zero radius, where the elliptic cylinder reduces to a st...
Failure of Non-Circular Composite Cylinders
Hyer, M. W.
2004-01-01
In this study, a progressive failure analysis is used to investigate leakage in internally pressurized non-circular composite cylinders. This type of approach accounts for the localized loss of stiffness when material failure occurs at some location in a structure by degrading the local material elastic properties by a certain factor. The manner in which this degradation of material properties takes place depends on the failure modes, which are determined by the application of a failure criterion. The finite-element code STAGS, which has the capability to perform progressive failure analysis using different degradation schemes and failure criteria, is utilized to analyze laboratory scale, graphite-epoxy, elliptical cylinders with quasi-isotropic, circumferentially-stiff, and axially-stiff material orthotropies. The results are divided into two parts. The first part shows that leakage, which is assumed to develop if there is material failure in every layer at some axial and circumferential location within the cylinder, does not occur without failure of fibers. Moreover before fibers begin to fail, only matrix tensile failures, or matrix cracking, takes place, and at least one layer in all three cylinders studied remain uncracked, preventing the formation of a leakage path. That determination is corroborated by the use of different degradation schemes and various failure criteria. Among the degradation schemes investigated are the degradation of different engineering properties, the use of various degradation factors, the recursive or non-recursive degradation of the engineering properties, and the degradation of material properties using different computational approaches. The failure criteria used in the analysis include the noninteractive maximum stress criterion and the interactive Hashin and Tsai-Wu criteria. The second part of the results shows that leakage occurs due to a combination of matrix tensile and compressive, fiber tensile and compressive, and inplane
Numerical simulation for flow around two circular cylinders in tandem
Kondo, Norio; Matsukuma, Daisuke
2005-05-01
We use a third-order upwind finite element scheme in order to perform numerical stabilization of solutions of the Navier Stokes equations and present numerical results of flow around two circular cylinders in tandem arrangement by two- and three-dimensional computations. The two circular cylinders are arranged with some spacings between the cylinders. It is well known from experimental data that the flow around two circular cylinders denotes very complicated phenomena with the variation of spacing between two cylinders. In addition, the time-averaged drag coefficients of two circular cylinders suddenly change at a certain spacing between the cylinders. We, therefore, make an investigation of such phenomena at the Reynolds number of 1000 by the use of a numerical approach, and the obtained numerical results are also qualitatively compared with experimental data.
Identification of Plasmonic Modes in Parabolic Cylinder Geometry by Quasi-Separation of Variables
KURIHARA, Kazuyoshi; Otomo, Akira; Yamamoto, Kazuhiro; TAKAHARA, Junichi; Tani, Masahiko; Kuwashima, Fumiyoshi
2014-01-01
This paper describes the plasmonic modes in the parabolic cylinder geometry as a theoretical complement to the previous paper (J Phys A 42:185401) that considered the modes in the circular paraboloidal geometry. In order to identify the plasmonic modes in the parabolic cylinder geometry, analytic solutions for surface plasmon polaritons are examined by solving the wave equation for the magnetic field in parabolic cylindrical coordinates using quasi-separation of variables in combination with ...
INTERACTION OF A FLOATING ELLIPTIC CYLINDER WITH A VIBRATING CIRCULAR CYLINDER
SUN Ren; CHWANG Allen T.
2006-01-01
The nonlinear hydrodynamic interaction between a floating elliptic cylinder and a vibrating circular cylinder immersed in an infinite fluid was investigated. By taking the added masses of the two-cylinder system into account, the dynamical equations of motion were formulated from the Lagrange equations of motion. The dynamical behaviors of these two cylinders were analyzed numerically for some typical situations, and the results show that the presence of a vibrating circular cylinder has a significant influence on the planar motion of a floating elliptic cylinder. The hydrodynamic interaction between them results in complicated nonlinear behaviors of the floating cylinder. It is found that oscillatory motion of the elliptic cylinder takes place in response to the vibrating mode of the circular one.
PLANAR MOTION OF A SLIGHTLY DISTORTED CIRCULAR CYLINDER AROUND ANOTHER CIRCULAR ONE
SUN Ren; CHWANG Allen T.
2004-01-01
Accurate prediction of the motion of a body moving around another one in an unbounded fluid and determi-nation of the hydrodynamic interaction between them are im-portant in the coastal and offshore engineering. For two-dimensional cases, most of the previous studies were focused on the interaction between circular cylinders without considering the non-circular situation. To break through the limitation of"circular" bodies, in the present paper the boundary perturbation method was employed to investigate the motion of a slightly distorted circular cylinder around a circular one. An approximate complex velocity potential in terms of double infinite series expanded at two singular points was derived using the method of continued fractions. The hydrodynamic interaction between two cylinders was computed by solving the dynamical equations of motion. In a relative coordinate system moving with the uniform stream, the kinetic energy of the fluid was expressed as a function of fifteen added masses. Approximate analytical solutions of added masses in the series form were obtained and applied to determine the trajectories of the slightly distorted circular cylinder around a fixed circular one. Numerical results show that the presence of the circular cylinder affects the planar motion of the slightly distorted cirular cylinder and the initial configuration of the slightly distorted circular cylinder has a decisive influence on the development of its rotational motion.
FORCES ON A NEAR-WALL CIRCULAR CYLINDER
ZHAN Jing-xia; WANG Jin-jun; ZHANG Pang-feng
2004-01-01
The pressure distribution around a near-wall smooth circular cylinder in cross-flow was mainly investigated. The experiment was conducted at the sub-critical Reynolds number ranging from 2.24·104 to 8.94·104,at which the regular vortex separation exists on an isolated circular cylinder. The experimental results indicate that the forces on a circular cylinder near a plane wall are different from those on an isolated circular cylinder. Drag and lift coefficients of a near-wall circular cylinder strongly depend on gap ratio. The increase of gap ratio results in the increase of drag coefficient and the declination of lift coefficient, drag coefficient ranges from 0.5 to 1.0, and lift coefficient from 0.25 to 0 when gap ratio gradually increases from 0 to 1.0, and then the forces tend to be nearly constant with the increase of gap ratio. The attraction between a cylinder and a plane wall, i.e., downward force, occurs when gap ratio lies in certain range. The existence of cylinder changes the pressure gradient on the plane wall, and the influence extends to the location where x/D＜-3.0 and x/D＞5.0.
Vibrations of Circular Cylinders of a Perfectly Conducting Elastic Material
K. S. Sarma
1972-07-01
Full Text Available The problems of radial vibrations of a long circular solid cylinder with a transverse magnetic field and rotary vibrations of a hollow cylinder with radial magnetic field are solved. The results of the case of an infinite medium with a cylinderical cavity are given. The frequency equation in each case, is solved in particular cases approximately.
Inflation of polymer melts into elliptic and circular cylinders
Rasmussen, Henrik Koblitz; Christensen, Jens Horslund; Gøttsche, Søren
2000-01-01
A thin sheet (membrane) of the polymeric material is clamped between a Teflon-coated thermostated plate and a thermostated aluminium cylinder. By applying thermostated air through the plate, the polymer membrane deforms into an elliptic or a circular cylinder. The position of the top of the...
Wake instability issues: From circular cylinders to stalled airfoils
Meneghini, J. R.; Carmo, B. S.; Tsiloufas, S. P.; Gioria, R. S.; Aranha, J. A. P.
2011-07-01
Some recent results regarding the global dynamical behaviour of the wake of circular cylinders and airfoils with massive separation are reviewed in this paper. In order to investigate the effect of interference, the three-dimensional instability modes are analysed for the flow around two circular cylinders in tandem. In the same way, the flow around a stalled airfoil is investigated in order to provide a better understanding of the three-dimensional characteristics of wakes forming downstream of a lifting body with massive separation. These results are compared with those found for an isolated cylinder. Some fundamental differences among these flows are discussed.
Numerical Simulations of Viscous Flow Around Stepped Circular Cylinder
Bjørkli, Rune
2012-01-01
A stepped cylinder could be a desired design for an offshore buoy or SPAR platform. The geometry of a stepped cylinder consists of a small diameter cylinder (d) placed on top of a large diameter cylinder (D). This master thesis has investigated numerically the flow around a stepped cylinder with different diameter ratios (d/D) for a Reynolds number, ReD = 150. The commercial software Fluent v13.0 by Ansys was used for the numerical investigation.The aim of the study has been exploring the nea...
Flow control behind a circular cylinder via a porous cylinder in deep water
Akilli H.
2013-04-01
Full Text Available In this present work, the effects of surrounding outer porous cylinder on vortex structure downstream of a circular inner cylinder are investigated experimentally in deep water flow. The porosity of outer cylinder were selected as β = 0.4, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8 and 0.85. Porosity is defined as the ratio of the gap area on the body to the whole body surface area. The ratio of outer cylinder diameter to inner cylinder diameter, Do/Di was selected as 2.0, i.e. the inner cylinder diameter is Di = 30 mm where the outer cylinder diameter is Do = 60 mm. All experiments were carried out above a platform. The water height between the base of the platform and the free surface was adjusted as 340 mm. Free stream velocity is U = 156 mm/s, which corresponds to the Reynolds number of Rei = 5,000 based on the inner cylinder diameter. It has been observed that the outer porous cylinders have influence on the attenuation of vortex shedding in the wake region for all porosities. The turbulent intensity of the flow is reduced at least 45% by the presence of outer porous cylinder compared to the bare cylinder case. The porosities β = 0.4 and 0.5 are most suitable cases to control the flow downstream of the circular cylinder.
Two circular cylinders in cross-flow: A review
Sumner, D.
2010-08-01
Pairs of circular cylinders immersed in a steady cross-flow are encountered in many engineering applications. The cylinders may be arranged in tandem, side-by-side, or staggered configurations. Wake and proximity interference effects, which are determined primarily by the longitudinal and transverse spacing between the cylinders, and also by the Reynolds number, have a strong influence on the flow patterns, aerodynamic forces, vortex shedding, and other parameters. This paper reviews the current understanding of the flow around two “infinite” circular cylinders of equal diameter immersed in a steady cross-flow, with a focus on the near-wake flow patterns, Reynolds number effects, intermediate wake structure and behaviour, and the general trends in the measurements of the aerodynamic force coefficients and Strouhal numbers. A primary focus is on the key experimental and numerical studies that have appeared since the last major review of this subject more than 20 years ago.
Analysis of Aerodynamic Noise Generated from Inclined Circular Cylinder
YasutakeHaramoto; ShoujiYasuda; 等
2000-01-01
Making clear the generation mechanism of fluid dynamic noise is essential to reduce noise deriving from turbomachinery.The analysis of the aerodynamic noise generated from circular cylinder is carried out numerically and experimentally in a low noise wind tunnel.in this study,aerodynamic sound radiated from a circular cylinder in uniform flow is predicted numericaslly by the following two step method,First,the three-dimensional unsteady incompressible Navier-Stokes equation is solved using the high order accurate upwind scheme.Next.the sound pressure level at the observed point is calculated from the fluctuating surface pressure on the cylinder.based on modified Lighthill-Curl's equation.It is worth to note that the noise generated from the model is reduced rapidly when it is inclined against the mean flow.In other works,the Peak level of the radiated noise decreases apidly with inclination of the circular cylinder.The simulated SPL for the inclined circular cylinder is compared with the measured value .and good agreement is obtained for the peak spectrum fequency of the sound pressue level and tendency of noise reduction,So we expect that the change of flow structures makes reduction of the aerodynamic noise from the inclined models.
This paper describes an effect of spacing between two adjoining circular cylinders on flow around two-dimensional circular cylinder bundles. The experiment was carried out in an N.P.L blow-down type wind-tunnel with a working section of 500 mm x 500 mm x 2000 mm, and under the Reynolds number 1.3 x 104. The surface-pressure distributions on the circular cylinder were measured and the drag coefficient was determined from these measurements. The flow-pattern around circular cylinders was observed. The power spectrum in the turbulent wake behind circular cylinders was also measured. It was found that the pressure on the rear surface of circular cylinders becomes lower and the drag coefficient increases as the spacing ratio decreases, while the step-change in the drag coefficient occurs at the spacing ratio where the flow pattern around the downstream circular cylinder changes. (author)
Flow instability in flow past O-grooved circular cylinder
This study was devoted to elucidating the change in the flow characteristics of a laminar flow past a circular cylinder by modifying the cylinder shape with O-grooves. A numerical analysis was performed in a two-dimensional framework. The cylinder was represented using an immersed boundary method and marker particles on a Cartesian grid system. The number and locations of the O-grooves were the key parameters. An analysis of the flow pattern and flow induced forces was performed at Re = 40 and 50. In addition, we calculated the critical Reynolds number depending on the number of O-grooves and their locations
Inflation of polymer melts into elliptic and circular cylinders
Rasmussen, Henrik Koblitz; Christensen, Jens Horslund; Gøttsche, Søren
2000-01-01
A thin sheet (membrane) of the polymeric material is clamped between a Teflon-coated thermostated plate and a thermostated aluminium cylinder. By applying thermostated air through the plate, the polymer membrane deforms into an elliptic or a circular cylinder. The position of the top of the...... inflating membrane is detected by fibreoptic sensors positioned in the cylinder. The pressure difference across the inflating membrane is measured as well. Measurements were performed on a polyisobutylene melt. As the deformation in this device is highly non-uniform, the response of the material is modelled...
Elliptic cylinder geometry for distinguishability analysis in impedance tomography.
Saka, Birsen; Yilmaz, Atila
2004-01-01
Electrical impedance tomography (EIT) is a technique that computes the cross-sectional impedance distribution within the body by using current and voltage measurements made on the body surface. It has been reported that the image reconstruction is distorted considerably when the boundary shape is considered to be more elliptical than circular as a more realistic shape for the measurement boundary. This paper describes an alternative framework for determining the distinguishability region with a finite measurement precision for different conductivity distributions in a body modeled by elliptic cylinder geometry. The distinguishable regions are compared in terms of modeling error for predefined inhomogeneities with elliptical and circular approaches for a noncircular measurement boundary at the body surface. Since most objects investigated by EIT are noncircular in shape, the analytical solution for the forward problem for the elliptical cross section approach is shown to be useful in order to reach a better assessment of the distinguishability region defined in a noncircular boundary. This paper is concentrated on centered elliptic inhomogeneity in the elliptical boundary and an analytic solution for this type of forward problem. The distinguishability performance of elliptical cross section with cosine injected current patterns is examined for different parameters of elliptical geometry. PMID:14723501
Scattering of SH Waves by Fixed-Rigid Nearly Circular Cylinder
Abdul; Ibrahim BAKIRTAS
2001-01-01
A solution for the two-dimensional scattering and diffraction of plane SH waves by fixed-rigid cylinder of arbitrary shape in an elastic infinite medium is presented. The wave field for arbitary geometry in this paper is computed numericaly by the method weighted residues (moment method). Dynamic stress concentration factors around the arbitrary obstacles are obtained with respect to various dimensionless wave numbers. When the cavity is circular, results obtained from the analytical solution...
Fluid dynamic effects of grooves on circular cylinder surface
Kimura, Takeyoshi; Tsutahara, Michihisa
1991-12-01
It is shown that a groove on the surface of a circular cylinder affects movement of the separation point backward and reduces drag even at Reynolds numbers of about a few thousand. Several types of circular-arc cross-section grooves are studied using flow visualizations and numerical simulations. Whether these grooves are effective depends strongly on their positions, and the most effective positions are about 80 deg, measured from the foremost point. When they are effective, cavity flows are developed inside the grooves. This effect corresponds to that of dimples on golf balls and will explain unique characteristics of the drag curve.
Circular cylinders and pressure vessels stress analysis and design
Vullo, Vincenzo
2014-01-01
This book provides comprehensive coverage of stress and strain analysis of circular cylinders and pressure vessels, one of the classic topics of machine design theory and methodology. Whereas other books offer only a partial treatment of the subject and frequently consider stress analysis solely in the elastic field, Circular Cylinders and Pressure Vessels broadens the design horizons, analyzing theoretically what happens at pressures that stress the material beyond its yield point and at thermal loads that give rise to creep. The consideration of both traditional and advanced topics ensures that the book will be of value for a broad spectrum of readers, including students in postgraduate, and doctoral programs and established researchers and design engineers. The relations provided will serve as a sound basis for the design of products that are safe, technologically sophisticated, and compliant with standards and codes and for the development of innovative applications.
Laminar vortex shedding behind a cooled circular cylinder
Trávníček, Zdeněk; Wang, A. B.; Tu, W.Y.
2014-01-01
Roč. 55, č. 2 (2014), s. 1-12. ISSN 0723-4864 R&D Projects: GA ČR GA14-08888S Institutional support: RVO:61388998 Keywords : vortex shedding * cooled circular cylinder * thermal effect Subject RIV: JU - Aeronautics, Aerodynamics, Aircrafts Impact factor: 1.670, year: 2014 http://link.springer.com/journal/348/55/2/page/1
Numerical simulation of laminar flow past an oscillating circular cylinder
The problem of unsteady, two dimensional laminar flow past a circular cylinder which performs recti-linear oscillations at an arbitrary angle η with respect to the oncoming uniform flow is considered. The governing Navier-Stokes equations are expressed in terms of a stream-function/vorticity formulation are solved numerically for a fixed Reynolds number R=855. The calculations are performed when the maximum displacement amplitude-to-cylinder radius ratio is 0.26. The recti-linear oscillations are only allowed when η=45o. A boundary-layer type transformation is adopted to scale out the singular nature in the vorticity at the start of the motion. The object of this study is to examine the effect of increase of frequency of the recti-linear oscillations on the near wake structure as well as the hydrodynamic forces acting on the cylinder. The results of this study are in good agreement with previous experimental predictions. (author)
Numerical Simulation of Flow Interference Between Two Circular Cylinders
Gao, F.; Mingham, C. G.; Causon, D. M.
2011-09-01
Viscous flow past two circular cylinders in tandem and side-by-side arrangements is investigated numerically. The solution to the Navier-Stokes equations is obtained by means of a cell-centred finite volume method (FVM) based on a structured Cartesian grid with collocated variable arrangement. The pressure-velocity coupling is evaluated by using the SIMPLE algorithm. The 2D Cartesian cut cell mesh is generated on the horizontal plane, which is extended vertically to form the 3D grid. The simulations are based on the Reynolds number of 200, and the gap between the two cylinders are 1.5-3D for side-by-side arrangement and 3-4D for tandem. Instantaneous velocity contours of the flow around the cylinders and time histories of force coefficients are presented.
Synthesis of antenna arrays radiation patterns on random geometry cylinders
Gabriel'yan, D. D.; Kalchenko, O. V.
2007-01-01
Synthesis algorithm for gain-phase radiation patterns formed by linear electrical vibrators antenna arrays located on random geometry cylinders is discussed. The results of numerical calculations are presented.
Passive jet control of flow around a circular cylinder
Chen, Wen-Li; Gao, Dong-Lai; Yuan, Wen-Yong; Li, Hui; Hu, Hui
2015-11-01
In the present study, a passive flow control method, which is featured by passive windward suction combined with leeward jet over a circular cylinder for drag reduction and dynamic wind loading suppression, was experimentally investigated to manipulate unsteady wake vortex shedding from a circular cylinder. Four perforated pipe designs with different numbers of suction/jet holes (i.e., from 2 to 24 suction/jet holes) were used to create flow communicating channels between the windward and leeward stagnation points of a cylindrical test model. The experimental study was performed in a wind tunnel at a Reynolds number of Re = 4.16 × 104 based on the cylinder diameter and oncoming airflow speed. In addition to measuring surface pressure distributions to determine the dynamic wind loads acting on the test model, a digital particle image velocimetry (PIV) system was also used to quantify the wake flow characteristics in order to assess the effectiveness of the passive jet control method with different perforated pipe designs, in comparison with a baseline case without passive jet control. It was found that the passive jet control method is very effective in manipulating the wake vortex shedding process from the circular cylinder. The perforated pipe designs with more suction/jet holes were found to be more effective in reducing drag and suppressing fluctuating amplitude of the dynamic wind loads acting on the test model. With 24 suction/jet holes evenly distributed over the cylindrical test model (i.e., the N13 design of the present study), the passive jet control method was found to be able to achieve up to 33.7 % in drag reduction and 90.6 % in fluctuating wind loading suppression, in comparison with the baseline case. The PIV measurement results revealed clearly that the passive jet control method would cause airflow jets into the cylinder wake and change the shedding modes of the wake vortex structures from the cylindrical test model. Because of the dynamic
Effect of plasma actuator and splitter plate on drag coefficient of a circular cylinder
Akbıyık, Hürrem; Erkan Akansu, Yahya; Yavuz, Hakan; Ertuğrul Bay, Ahmet
2016-03-01
In this paper, an experimental study on flow control around a circular cylinder with splitter plate and plasma actuator is investigated. The study is performed in wind tunnel for Reynolds numbers at 4000 and 8000. The wake region of circular cylinder with a splitter plate is analyzed at different angles between 0 and 180 degrees. In this the study, not only plasma actuators are activated but also splitter plate is placed behind the cylinder. A couple electrodes are mounted on circular cylinder at ±90 degrees. Also, flow visualization is achieved by using smoke wire method. Drag coefficient of the circular cylinder with splitter plate and the plasma actuator are obtained for different angles and compared with the plain circular cylinder. While attack angle is 0 degree, drag coefficient is decreased about 20% by using the splitter plate behind the circular cylinder. However, when the plasma actuators are activated, the improvement of the drag reduction is measured to be 50%.
Effect of plasma actuator and splitter plate on drag coefficient of a circular cylinder
Akbıyık Hürrem
2016-01-01
Full Text Available In this paper, an experimental study on flow control around a circular cylinder with splitter plate and plasma actuator is investigated. The study is performed in wind tunnel for Reynolds numbers at 4000 and 8000. The wake region of circular cylinder with a splitter plate is analyzed at different angles between 0 and 180 degrees. In this the study, not only plasma actuators are activated but also splitter plate is placed behind the cylinder. A couple electrodes are mounted on circular cylinder at ±90 degrees. Also, flow visualization is achieved by using smoke wire method. Drag coefficient of the circular cylinder with splitter plate and the plasma actuator are obtained for different angles and compared with the plain circular cylinder. While attack angle is 0 degree, drag coefficient is decreased about 20% by using the splitter plate behind the circular cylinder. However, when the plasma actuators are activated, the improvement of the drag reduction is measured to be 50%.
Acoustic band gaps in two-dimensional square arrays of semi-hollow circular cylinders
T.; Kim
2009-01-01
Concave surfaces focus sound while convex surfaces disperse sound. It is therefore interesting to know if it is possible to make use of these two opposite characteristics to enhance the band gap performance of periodic arrays of solid cylinders in air. In this paper, the band gap characteristics of a 2-D square array of semi-hollow circular cylinders embedded in air are investigated, both experimentally and theoretically. In comparison with the types of inclusion studied by previous researchers, a semi-hollow circular cylinder is unique in the sense that it has concave inner surfaces and convex outer surfaces. The finite difference time domain (FDTD) method is employed to study the propagation behavior of sound across the new phononic crystal of finite extent, and the influences of sample size and inclusion orientation on band gap characteristics are quantified in order to obtain the maximum band gap. For reference, the band gap behaviors of solid circular cylinder/air and hollow circular cylinder/air systems are considered and compared with those of semi-hollow circular cylinder/air systems. In addition to semi-hollow circular cylinders, other inclusion topologies such as semi-hollow triangular and square cylinders are also investigated. To validate the theoretical predictions, experimental measurements on square arrays of hollow Al cylinders in air and semi-hollow Al cylinders in air are carried out. The results demonstrate that the semi-hollow circular cylinder/air system has the best overall band gap performance.
Standing torsional waves in a fully saturated, porous, circular cylinder
Solorza, S; 10.1111/j.1365-246X.2004.02198.x
2004-01-01
For dynamic measurement of the elastic moduli of a porous material saturated with viscous fluid using the resonance-bar technique, one also observes attenuation. In this article we have carried out the solution of the boundary-value problem associated with standing torsional oscillations of a finite, poroelastic, circular cylinder cast in the framework of volume-averaged theory of poroelasticity. Analysing this solution by eigenvalue perturbation approach we are able to develop expressions for torsional resonance and temporal attenuation frequencies in which the dependence upon the material properties are transparent. It shows how the attenuation is controlled by the permeability and the fluid properties, and how the resonance frequency drops over its value for the dry solid-frame due to the drag effect of fluid mass. Based upon this work we have a firm basis to determine solid-frame shear modulus, permeability, and tortuosity factor from torsional oscillation experiments.
Movement of a horizontal vortex ring in a circular cylinder
In this paper, we report the numerical and experimental solutions of the vortical flows driven by an impingement of fluid from the bottom wall of a circular cylinder. We managed to visualize successfully the flow pattern shown on the vertical plane through the container axis. The numerical results are shown to compare well with the experimental results for the case of infinity Rossby number. The satisfactory agreement between the two results was possible when in the numerics the free surface was treated as a solid wall so that a no-slip condition was applied on the surface. The numerical solutions reveal that inertial oscillation plays an important role at small Rossby numbers, or at a large background rotation
Fermionic Casimir interaction in cylinder-plate and cylinder-cylinder geometries
Teo, L P
2015-01-01
In this work, we consider the Casimir effect due to massless fermionic fields in the presence of long cylinders. More precisely, we consider the interaction between a cylinder parallel to a plate, between two parallel cylinders outside each other, and between a cylinder lying parallelly inside another cylinder. We derive the explicit formulas for the Casimir interaction energies and compute the leading and the next-to-leading order terms of the small separation asymptotic expansions. As expected, the leading order terms coincide with the proximity force approximations. We compare the results of the next-to-leading order terms of different quantum fields, and show that our results support the ansatz of derivative expansions.
Oki, M. [Tokai University, Tokyo (Japan); Aoki, K. [Tokai University, Tokyo (Japan). Faculty of Engineering; Nakayama, Y.
1998-09-25
In the flow around a circular cylinder, the sudden decrease in the drag force occurs at around Reynolds number Re = 3 times 10{sup 5}, but the same phenomenon occurs at a lower Reynolds number in the case where there exist grooves or roughness on the circular cylinder surface. In this paper, in order to make clear the flow characteristics around a circular cylinder with grooves, the unsteady flow was analyzed by applying the RNG (Renormalization Group) {kappa}-{epsilon} turbulent model to a flow around a circular cylinder with grooves each of whose section shapes being as same as that of a dimple an a golf ball, with changing Reynolds number. This result made clear the characteristics of lift and drag, Strouhal number, flow pattern behind the circular cylinder, pressure distribution and separation points. Moreover, the time averages of these values almost agreed with the experimental values. 20 refs., 10 figs.
Dual Circularly Polarized Omnidirectional Antenna with Slot Array on Coaxial Cylinder
Bin Zhou; Junping Geng; Zhe Li; Wenzhi Wang; Xianling Liang; Ronghong Jin
2015-01-01
A dual circularly polarized (CP) omnidirectional antenna based on slot array in coaxial cylinder structure is presented in this paper. It is constructed by perpendicular slot pairs around and along the axis of the coaxial cylinder to realize the omnidirectional CP property, and two ports are assigned in its two sides as left hand circularly polarized (LHCP) port and right hand circularly polarized (RHCP) port, respectively. The proposed antenna achieves a bandwidth of 16.4% ranging from 5.05 ...
An experimental investigation was performed in a low-speed wind tunnel in which an elastically mounted circular cylinder was fitted with two accelerometers and surrounded by from one to six identical cylinders in order to study the fluid flow characteristics and predict the possibility of suppressing flow-induced vibration excitation in the test cylinder. The spectral diagram, amplitude and orbital motion of the test cylinder were used to analyze the vibration excitation under differing free stream velocities, natural frequencies of the test cylinder, and number of surrounding cylinders. In this study, for the test cylinder with the same natural frequency as the adjacent cylinders (24 Hz) the amplitude response showed that when the fluid flow velocity exceeded a critical value, which depends on the arrangement of the cylinders, fluid elastic instability occurred. Beyond the critical velocity the cylinder became excited and vibrated in a figure-of-eight pattern along with the line-dominated spectrum, which implies that by having the same frequency along with a phase shift, the characteristic behavior of the cylinder is observed to be like an oscillator with the cross-wise and stream-wise response. From the assessment of the amplitude response of the test cylinder it was observed that the upstream cylinders had a greater influence on the amplitude response than the downstream cylinders. On the other hand, when the test cylinder had a natural frequency different to the adjacent cylinders it was observed that the frequency had a minimal effect on the critical velocity, and yet beyond the critical velocity it had a significant influence on the vibration amplitude response. (paper)
Wang, X. H.; Zhu, W. F.; He, Z. Y.
It is well known that the steady flow past a circular cylinder loses stability at Re takes the value about 50 (Y. Ding et al, 1999). Most papers about the characterization and understanding of the stability for the flow past blunt bodies are mainly carried out for such flow past one circular cylinder. And there is a large variation in the values of Re cr and correspondingly the values of St cr reported by different reseachers. Bhascar and Sunjay (2006) have attributed it to the effect of blockage (here, it means the ratio of the diameter of cylinder to the lateral width of domain). And for high Re cr first decreases and then increases with the increase of the blockage. And the correspondingly values of St cr are quite sensitive to the blockage. In this paper, we attampt to estimate the critical Re for the flow past one square cylinder. It is obviously that geometry symmetry or attack degree will not change just with rotation of the circular cylinder, but for the square cylinder, the symmetry or the degree will not keep for the rotation. So the numerical estimation of the critical Re for the flow past square cylinders should be carried out for the symmetric or unsymmetric geometry boundary conditions separately. Based on the calculation of the lid driven cavity flow at Re=100 and 1000, a second order Euler-Taylor-Galerkin finite element method was used to estimate the critical Reynolds number for flow past one square cylinder with zero attact degree through direct time integration of the NS equationes. The role of blockage on such flow was analysed at Re=100. It was found that the averged St tend to be constant as blockage took the value larger than 50. The critical Reynolds number is then computed. As the result shown, it was estimated that Re Cr =40.11. And the computation for unsymmetric geometry condition will discussed laterly.
Streamwise forced oscillations of circular and square cylinders
Tudball-Smith, Daniel; Leontini, Justin S.; Sheridan, John; Lo Jacono, David
2012-01-01
International audience The modification of a cylinder wake by streamwise oscillation of the cylinder at the vortex shedding frequency of the unperturbed cylinder is reported. Recent numerical simulations [J. S. Leontini, D. Lo Jacono, and M. C. Thompson, "A numerical study of an inline oscillating cylinder in a free stream," J. Fluid Mech. 688, 551-568 (2011)] showed that this forcing results in the primary frequency decreasing proportionally to the square of the forcing amplitude, before ...
Plane Wall Effect of Flow around Two Circular Cylinders in Tandem Arrangement
Triyogi Yuwono,; Wawan Aries Widodo; Heru Mirmanto; Fahmi Fahreza
2011-01-01
The flow characteristic around two circular cylinders in tandem arrangement located near a plane wall were investigated experimentally in a uniform flow at a Reynolds Number of 5.3 x 104. The center to center spacing between the two cylinders relative to the cylinder diameter was constantly maintained at P/D = 1.5. The pressure distributions along the surface of the cylinder and the plane wall were measured by varying the gap-to-diameter of cylinder ratio (G/D) in the range of 0 < G/D < 0.467...
Ahmed W. Mustava
2013-04-01
Full Text Available The effect of a semi-circular cylinders in a two dimensional channel on heat transfer by forced convection from two heat sources with a constant temperature has been studied numerically. Each channel contains two heat sources; one on the upper surface of the channel and the other on the lower surface of the channel. There is semi-circular cylinder under the source in upper surface and there is semi-circular cylinder above the source in lower surface. The location of the second heat source with its semi-cylinder has been changed and keeps the first source with its semi- cylinder at the same location. The flow and temperature field are studied numerically with different values of Reynolds numbers and for different spacing between the centers of the semi-cylinders. The laminar flow field is analyzed numerically by solving the steady forms of the two-dimensional incompressible Navier- Stokes and energy equations. The Cartesian velocity components and pressure on a collocated (non-staggered grid are used as dependent variables in the momentum equations, which discretized by finite volume method, body fitted coordinates are used to represent the complex channel geometry accurately, and grid generation technique based on elliptic partial differential equations is employed. SIMPLE algorithm is used to adjust the velocity field to satisfy the conservation of mass. The range of Reynolds number is (Re= 100 – 800 and the range of the spacing between the semi-cylinders is(1-4 and the Prandtl number is 0.7.The results showed that increasing the spacing between the semi-cylinders increases the average of Nusselt number of the first heat source for all Reynolds numbers. As well as the results show that the best case among the cases studied to enhance the heat transfer is when the second heat source and its semi-cylinder located on at the distance (S=1.5 from the first half of the cylinder and the Reynolds number is greater than (Re ≥ 400 because of the
Kitagawa, T.; Ohta, H.
2008-07-01
Three-dimensional fluid computations have been performed to investigate the flows around two circular cylinders in tandem arrangements at a subcritical Reynolds number, Re=2.2×104. The center-to-center space between the cylinders was varied from twice the cylinder diameter to five times that, and the flows and fluid-dynamic forces obtained from the simulations are compared with the experimental results reported in the literature. Special attention is paid to the characteristics of the vortices shed from the upstream cylinder such as the convection, the impingement onto the downstream cylinder and the interaction with the vortices from the downstream cylinder. The effects of the vortices from the upstream cylinder on the fluid-dynamic forces acting on the downstream cylinder are discussed.
A cell boundary element method applied to laminar vortex shedding from circular cylinders
Farrant, T; Tan, M; Price, W.G.
2001-01-01
The two-dimensional unsteady incompressible Navier–Stokes equations are solved for flows around arrangements of circular cylinders at Reynolds number 100 and 200. A hybrid boundary element/finite element method is used to discretise the spatial domain together with a second order implicit finite difference approximation in time. The numerical scheme of study is validated for a uniform stream past an isolated circular cylinder by comparing findings with experimental and numerical studies. Both...
Water Wave Scattering by a Nearly Circular Cylinder Submerged Beneath an Ice-cover
Rumpa Chakraborty; Birendra Nath Mandal
2015-01-01
Assuming linear theory, the two-dimensional problem of water wave scattering by a horizontal nearly circular cylinder submerged in infinitely deep water with an ice cover modeled as a thin-elastic plate floating on water, is investigated here. The cross-section of the nearly circular cylinder is taken as r=a(1+δC(θ)), wherea is the radius of the corresponding circular cross-section of the cylinder,δ is a measure of small departure of the cross-section of the cylinder from its circularity andC(θ) is the shape function. Using a simplified perturbation technique the problem is reduced to two independent boundary value problems up to first order inδ. The first one corresponds to water wave scattering by a circular cylinder submerged in water with an ice-cover, while the second problem describes wave radiation by a submerged circular cylinder and involves first order correction to the reflection and transmission coefficients. The corrections are obtained in terms of integrals involving the shape function. Assuming a general Fourier expansion of the shape function, these corrections are evaluated approximately. It is well known that normally incident wave trains experience no reflection by a circular cylinder submerged in infinitely deep water with an ice cover. It is shown here that the reflection coefficient also vanishes up to first order for some particular choice of the shape function representing a nearly circular cylinder. For these cases, full transmission occurs, only change is in its phase which is depicted graphically against the wave number in a number of figures and appropriate conclusions are drawn.
Kang, XiuYing; Su, YanPing
2012-10-01
Cross-flows around two, three and four circular cylinders in tandem, side-by-side, isosceles triangle and square arrangements are simulated using the incompressible lattice Boltzmann method with a second-order accurate curved boundary condition at Reynolds number 200 and the cylinder center-to-center transverse or/and longitudinal spacing 1.5 D, where D is the identical circular cylinder diameter. The wake patterns, pressure and force distributions on the cylinders and mechanism of flow dynamics are investigated and compared among the four cases. The results also show that flows around the three or four cylinders significantly differ from those of the two cylinders in the tandem and side-by-side arrangements although there are some common features among the four cases due to their similarity of structures, which are interesting, complex and useful for practical applications. This study provides a useful database to validate the simplicity, accuracy and robustness of the Lattice Boltzmann method.
Effect of Inner Circular Cylinder Size on Three-Dimensional Natural Convection in Cubical Enclosure
This study evaluates the effect of a heated circular cylinder's size on three-dimensional natural convection in a cubical enclosure. The Rayleigh number was varied between 103 and 105, and the Prandtl number was maintained at 0.7. In this study, the radius of the circular cylinder was changed by 0.1 L within a range of 0.1.0.4 L. The thermal and fluid flow characteristics were regarded to be independent of time in the range of the Rayleigh number and cylinder radius considered in this study. The surface-averaged Nusselt numbers of the cylinder and the enclosure were found to increase with the increase in the radius of the cylinder. The effect of the cylinder's size on natural convection in the enclosure was analyzed across the thermal and flow fields, and the distributions of the Nusselt numbers
Forcing of a bottom-mounted circular cylinder by steep regular water waves at finite depth
Paulsen, Bo Terp; Bredmose, Henrik; Bingham, Harry B.;
2014-01-01
Forcing by steep regular water waves on a vertical circular cylinder at finite depth was investigated numerically by solving the two-phase incompressible Navier–Stokes equations. Consistently with potential flow theory, boundary layer effects were neglected at the sea bed and at the cylinder...
Poiseuille flow-induced vibrations of two tandem circular cylinders with different mass ratios
Jiang, Ren-Jie; Lin, Jian-Zhong
2016-06-01
Flow-induced vibrations of two tandem circular cylinders with different mass ratios confined between two parallel walls are numerically studied via a lattice Boltzmann method. With fixed Reynolds number Re = 100 and blockage ratio β = 1/4, the effects of mass ratio m* = [0.0625, 16] and streamwise separation between two cylinders S/D = [1.125, 10] on the cylinder motions and vortex wake modes are investigated. A variety of distinct cylinder motion regimes involving the symmetric periodic vibration, biased quasi-periodic vibration, beating vibration, and steady regimes, with the corresponding wake structures, e.g., two rows of alternately rotating vortices, a single row of same-sign vortices, and steady wake, are observed. For each current case, the cylinder motion type is exclusive and in the binary oscillation regime, both cylinders always vibrate at a common primary frequency. The lighter cylinder usually oscillates at a larger amplitude than the heavier one, while the heavier cylinder undergoes larger lift force than the lighter one. The lift force and cylinder displacement always behave as an out-of-phase state. In the gap-interference region, large-amplitude oscillations could be produced extensively and in the wake-interference region, the cylinder motions and fluid flows are mainly dependent on the upstream cylinder. When the separation is large enough, both cylinders behave as two isolated ones. The mechanisms for the excitations of cylinder vibrations have also been analysed.
WANG; JinJun; FENG; LiHao; XU; ChaoJun
2007-01-01
Circular cylinder separation control and flow structure influenced by the synthetic jet have been experimentally investigated in a water channel. The synthetic jet issues from a slot and ejects toward upstream from the front stagnation point of the cylinder. It has been found that, similar to the traditional synthetic jet which is positioned near the separation point or inside the separation region, the present synthetic jet arrangement constitutes an efficient way to control flow separation of the circular cylinder, but with a different control mechanism. The present synthetic jet leads to an upstream displacement of the front stagnation point and the formation of a vortex pair near both sides of the exit orifice. When ReU based on the synthetic jet average exit orifice velocity is about lower than 43, a closed envelope forms in front of the windward side of the cylinder during the blowing cycle of synthetic jet, which acts as an apparent modification for the cylinder configuration. When ReU is high enough, an open envelope forms upstream of the cylinder, and the flow around the cylinder becomes much energetic. Thus, regardless of ReU, the present synthetic jet can improve separation for flow around a circular cylinder. With regard to the leeward side, as ReU increases, the flow separation region behind the cylinder gradually disappears. The flow over cylinder may be fully attached when the open envelope forms upstream of the cylinder and ReU is greater than 344. Then, the flow past the cylinder will converge near the back stagnation point of the cylinder, where a new vortex pair shedding periodically is generated due to the high shear layer.
Eskandari Jam Jafar
2014-12-01
Full Text Available In this paper, by using a semi-analytical solution based on multi-layered approach, the authors present the solutions of temperature, displacements, and transient thermal stresses in functionally graded circular hollow cylinders subjected to transient thermal boundary conditions. The cylinder has finite length and is subjected to axisymmetric thermal loads. It is assumed that the functionally graded circular hollow cylinder is composed of N fictitious layers and the properties of each layer are assumed to be homogeneous and isotropic. Time variations of the temperature, displacements, and stresses are obtained by employing series solving method for ordinary differential equation, Laplace transform techniques and a numerical Laplace inversion.
Upper bounds on packing density for circular cylinders with high aspect ratio
Kusner, Wöden
2013-01-01
In the early 1990s, A. Bezdek and W. Kuperberg used a relatively simple argument to show a surprising result: The maximum packing density of circular cylinders of infinite length in $\\mathbb{R}^3$ is exactly $\\pi/\\sqrt{12}$, the planar packing density of the circle. This paper modifies their method to prove a bound on the packing density of finite length circular cylinders. In fact, the maximum packing density for unit radius cylinders of length $t$ in $\\mathbb{R}^3$ is bounded above by $\\pi/...
Seal whisker-inspired circular cylinders reduce vortex-induced vibrations
Beem, Heather; Triantafyllou, Michael
2012-11-01
Recent work shows that the undulatory, asymmetric geometry of harbor seal whiskers passively reduces vortex-induced vibration (VIV) amplitudes to less than 0.1 times the whisker diameter. This reduction holds in frontal flows, but due to the elliptical cross-section of the whisker, flows that approach from large angles of attack generate significant vibrational response. The present study investigates the possibility of extending the vibration reduction to unidirectional bodies, such that flows from all angles cause reduced VIV. A method for developing a new geometry that incorporates the ``whisker'' features into bodies with uniform, circular cross-section is presented. This geometry and multiple variations on it are fabricated into rigid models. Forces are measured on the models while they undergo imposed oscillations and are towed down a water tank. Contour plots of CL , v show peak VIV amplitudes to decrease as much as 28% from that of a standard cylinder. This result holds promise for applications where vibration reduction is desired, regardless of the angle of oncoming flow.
Interaction of oblique waves with an array of long horizontal circular cylinders
NG; Chiu-On
2007-01-01
The scattering and radiations of linear oblique waves by multiple long horizontal circular cylinders submerged in water of finite depth are investigated using the multipole expansion method. Analytical expressions for the diffracted and radiated potentials are given as a linear combination of infinite multipoles. The unknown coefficients in the expressions are determined by using the addition theorem of the Bessel function and the cylinder boundary conditions. Also analytical expressions for wave forces, hydrodynamic coefficients and reflection and transmission coeffi-cients are derived. The present analytical solution is verified through the boundary element method and applied to investigate three different cases of the interaction of oblique waves with multiple submerged horizontal circular cylinders. The results show that the number of cylinders, the arrangement and spacing between cylinders play an important role in wave forces, hydrodynamic coefficients and reflection and transmission coefficients. Some interesting and important phenomena are ob-served in numerical experiments.
Interaction of oblique waves with an array of long horizontal circular cylinders
SHEN YongMing; ZHENG YongHong; NG Chiu-On
2007-01-01
The scattering and radiations of linear oblique waves by multiple long horizontal circular cylinders submerged in water of finite depth are investigated using the multipole expansion method. Analytical expressions for the diffracted and radiated potentials are given as a linear combination of infinite multipoles. The unknown coefficients in the expressions are determined by using the addition theorem of the Bessel function and the cylinder boundary conditions. Also analytical expressions for wave forces, hydrodynamic coefficients and reflection and transmission coefficients are derived. The present analytical solution is verified through the boundary element method and applied to investigate three different cases of the interaction of oblique waves with multiple submerged horizontal circular cylinders. The results show that the number of cylinders, the arrangement and spacing between cylinders play an important role in wave forces, hydrodynamic coefficients and reflection and transmission coefficients. Some interesting and important phenomena are observed in numerical experiments.
Numerical Simulation of Flow Around a Row of Circular Cylinders Using the Lattice Boltzmann Method
S. Ul Islam; C.Y. Zhou
2009-01-01
This study describes a numerical study of flow past a row of circular cylinders at different Reynolds numbers with different distances between the cylinders using the Lattice Boltzmann Method (LBM). Numerical simulations are performed to investigate the blockage effect for the ranges of Re≤200 and B = W[R]≤25R , where, Re, R and W are the Reynolds numbers, the radius of the cylinders and the distance between the center of the cylinders, respectively. The Strouhal number and drag forces exerte...
Numerical analysis of two and three dimensional buoyancy driven water-exit of a circular cylinder
Moshari Shahab
2014-06-01
Full Text Available With the development of the technology of underwater moving bodies, the need for developing the knowledge of surface effect interaction of free surface and underwater moving bodies is increased. Hence, the two-phase flow is a subject which is interesting for many researchers all around the world. In this paper, the non-linear free surface deformations which occur during the water-exit of a circular cylinder due to its buoyancy are solved using finite volume discretization based code, and using Volume of Fluid (VOF scheme for solving two phase flow. Dynamic mesh model is used to simulate dynamic motion of the cylinder. In addition, the effect of cylinder mass in presence of an external force is studied. Moreover, the oblique exit and entry of a circular cylinder with two exit angles is simulated. At last, water-exit of a circular cylinder in six degrees of freedom is simulated in 3D using parallel processing. The simulation errors of present work (using VOF method for maximum velocity and height of a circular cylinder are less than the corresponding errors of level set method reported by previous researchers. Oblique exit shows interesting results; formation of waves caused by exit of the cylinder, wave motion in horizontal direction and the air trapped between the waves are observable. In 3D simulation the visualization of water motion on the top surface of the cylinder and the free surface breaking on the front and back faces of the 3D cylinder at the exit phase are observed which cannot be seen in 2D simulation. Comparing the results, 3D simulation shows better agreement with experimental data, specially in the maximum height position of the cylinder.
Mathematic modelling of circular cylinder deformation under inner grouwth
A. V. Siasiev
2009-09-01
Full Text Available A task on the intensive deformed state (IDS of a viscoelastic declivous cylinder, which is grown under the action of inner pressure, is considered. The process of continuous increase takes a place on an internal radius so, that a radius and pressure change on set to the given law. The special case of linear law of creeping is considered, and also numeral results are presented as the graphs of temporal dependence of tensions and moving for different points of cylinder.
Prebuckling, Buckling, and Postbuckling Response of Segmented Circular Composite Cylinders
Riddick, Jaret Cleveland
2001-01-01
Discussed is a numerical and experimental characterization of the response of small-scale fiber-reinforced composite cylinders constructed to represent a fuselage design whereby the crown and keel consist of one laminate stacking sequence and the two sides consist of another laminate stacking sequence. This construction is referred to as a segmented cylinder. The response to uniform axial endshortening is discussed. Numerical solutions for the nonlinear prebuckling, buckling, and postbuckling...
Circular Cylinders by Four or Five Points in Space
Devillers, Olivier; Mourrain, Bernard; Preparata, Franco ,; Preparata, Franco P.; Trebuchet, Philippe
2002-01-01
We are interested in computing effectively cylinders through 5 points, and in other problems involved in metrology. In particular, we consider the cylinders through 4 points with a fix radius and with extremal radius. For these different problems, we give bounds on the number of solutions and exemples show that these bounds are optimal. Finally, we describe two algebraic methods which can be used here to solve efficiently these problems and some experimentation results.
On circular Cylinders by Four or Five Points in Space
Devillers, Olivier; Mourrain, Bernard; Preparata, Franco ,; Trebuchet, Philippe
2001-01-01
We are interested in computing effectively cylinders through 5 points, and in other problems involved in metrology. In particular, we consider the cylinders through 4 points with a fix radius and with extremal radius. For these different problems, we give bounds on the number of solutions and exemples show that these bounds are optimal. Finally, we describe two algebraic methods which can be used here to solve efficiently these problems and some experimentation results.
Flow-induced vibrations of two tandem circular cylinders in a parallel-wall channel
Jiang, Ren-Jie; Lin, Jian-Zhong; Ku, Xiao-Ke
2014-10-01
Flow-induced vibrations of one and two tandem circular cylinders in the flow around cylinders in a parallel-wall channel are numerically studied by the lattice Boltzmann method. Within a range of Reynolds number Re = [1, 160], the effects of streamwise separation between two cylinders S/D = [1.25, 3], mass ratio M = [0.05, 5], and blockage ratio β = [1/2, 1/8] on the motions of cylinders and fluids are investigated, respectively. For the case of an isolated cylinder, as the mass ratio is 1, no large-amplitude oscillation is observed, and as the mass ratio is 0.1, the cylinder motion translates from the steady regime to the biased periodic vibration with a large oscillation amplitude gradually as Reynolds number is increased from 1 to 160. For the case of two cylinders in tandem, two steady regimes and a variety of distinct oscillation regimes with the corresponding flow structures are observed. The critical mass ratio of the two tandem cylinders in the strong coupling regime is about an order of magnitude larger than that of an isolated cylinder. For blockage ratio is more than 1/5, the vibration type of the cylinders is exclusive, while for blockage ratio is less than 1/6, the cylinder oscillation state is bistable. The mechanisms of the observed phenomena are also discussed.
Plane Wall Effect of Flow around Two Circular Cylinders in Tandem Arrangement
Triyogi Yuwono,
2011-02-01
Full Text Available The flow characteristic around two circular cylinders in tandem arrangement located near a plane wall were investigated experimentally in a uniform flow at a Reynolds Number of 5.3 x 104. The center to center spacing between the two cylinders relative to the cylinder diameter was constantly maintained at P/D = 1.5. The pressure distributions along the surface of the cylinder and the plane wall were measured by varying the gap-to-diameter of cylinder ratio (G/D in the range of 0 < G/D < 0.467. Surface oil-film techniques were used to investigate the flow patterns on the cylinder. The result showed that for upstream cylinder, in the gap-to-diameter ratio G/D < /D, there is no stagnation point at front side of the upstream cylinder; it is gradually raised as the gap increase. For the downstream cylinder, a peak on the lower side of the front side of the cylinder is apparent in each of the pressure distributions. This peak represents the reattachment of shear layer that separates from lower side of the upstream cylinder. The reattachment point tends to move forward close to the angular position of = 0o as the gap ratio increase. The shear layer bifurcates into two shear layers. One shear layer continues in the downstream direction, and the other shear layer flows in the upstream direction.
Experimental Study on Local Scour Around A Large Circular Cylinder Under Irregular Waves
周益人; 陈国平
2004-01-01
A series of physical model tests are conducted for local scour around a circular cylinder of a relatively large diameter (0.15 ＜ D/L ＜ 0.5) under the action of irregular waves. The laws of change of the topography around the cylinder are systematically studied. The effects of wave height, wave period, water depth, sediment grain size and cylinder diameter are taken into account. The mechanism of formation of the topography around the cylinder is analyzed. A detailed analysis is given to bed sediment grain size, and it is considered that the depth of scour around the cylinder under wave action is not inversely proportional to the sediment grain diameter. On such a basis, an equation is proposed for calculation of the maximum depth of scour around a cylinder as well as its position under the action of irregular waves.
A numerical analysis of the effect of the position of a circular cylinder in a 45 .deg. tilted enclosure on natural convection in the enclosure is presented. The location of the cylinder is changed between -0.4 and 0.4. The Rayleigh number is varied between 103 and 105. The effect of the location of the cylinder on natural convection in the enclosure is analyzed by the isothermal line, stream line, and surface-averaged Nusselt number. The flow and heat transfer characteristics are independent of time in the range of the Rayleigh number and cylinder location that is considered in this study. The surface-averaged Nusselt number of the cylinder and enclosure increases as the cylinder gets closer to the wall of the enclosure
In this study, we experimentally examined the vibration response characteristics of two tandem circular cylinders of uniform diameter (d) and relatively low structural damping. Experiments were carried out with inline tandem cylinders in a water channel with two degrees-of-freedom, varying the natural frequency ratio of upstream cylinder to downstream cylinder. The cylinders were cantilever mounted with a low natural frequency in the inline and cross-flow directions (around 50Hz). The spacing between the cylinders was 4.0d. The Reynolds number of the experiments was from 3000 to 22000, varying the reduced velocities from around 1.0 to about 4.5. The oscillating frequencies of the cylinders and the surrounding flow were measured simultaneously using high temporal resolution particle image velocimetry (PIV), which is non-intrusive with respect to the flow, and has high spatial and temporal resolutions. As a result, the closer the value of natural frequencies, the stronger the influence from the upstream cylinder to downstream cylinder was. Also, it was changed by the difference of structural damping between two cylinders. (author)
In this study, we consider the heat transfer characteristics of channel flow in the presence of an infinite streamwise array of equispaced identical rotating circular cylinders. This flow configuration can be regarded as a model representing a micro channel or an internal heat exchanger with cylindrical vortex generators. A numerical parametric study has been carried out by varying Reynolds number based on the bulk mean velocity and the cylinder diameter, and the gap between the cylinders and the channel wall for some selected angular speeds. The presence of the rotating circular cylinders arranged periodically in the streamwise direction causes a significant topological change of the flow, leading to heat transfer enhancement on the channel walls. More quantitative results as well as qualitative physical explanations are presented to justify the effectiveness of varying the gap to enhance heat transfer from the channel walls
Simulation of Viscous Flow Around a Circular Cylinder with OpenFOAM
Finserås, Live Reiten
2013-01-01
Flow around a circular cylinder has been extensively studied, both numerically and experimentally, for a number of years. With the increase in flow-structure interactions around marine structures such as platform legs/columns, pipelines and risers, the study of the complex flow mechanisms that is caused around cylinders at high Reynolds numbers has become increasingly important. The use of computational fluid dynamics (CFD) have proved to be an important tool in order to understand these mech...
Lift of a rotating circular cylinder in unsteady flows
Carstensen, Stefan; Mandviwalla, Xerxes; Vita, Luca;
2012-01-01
A cylinder rotating in steady current experiences a lift known as the Magnus effect. In the present study the effect of waves on the Magnus effect has been investigated. This situation is experienced with the novel floating offshore vertical axis wind turbine (VAWT) concept called the DEEPWIND co...
Investigation of drag reduction through a flapping mechanism on circular cylinder
Asif, Md. Asafuddoula; Gupta, Avijit Das; Rana, M. D. Juwel; Ahmed, Dewan Hasan
2016-07-01
During flapping wing, a bird develops sufficient lift force as well as counteracts drag and increases its speed through different orientations of feathers on the flapping wings. Differently oriented feathers play a significant role in drag reduction during flying of a bird. With an objective to investigate the effect of installation of such flapping mechanism as a mean of drag reduction in case of flow over circular cylinder, this concept has been implemented through installation of continuous and mini flaps, made of MS sheet metal, where flaps are oriented at different angles as like feathers of flapping wings. The experiments are carried out in a subsonic wind tunnel. After validation and comparison with conventional result of drag analysis of a single cylinder, effects of flapping with Reynolds number variation, implementation of different orientations of mini flaps and variation of different interspacing distance between mini flaps are studied to find the most effective angle of attack of drag reduction on the body of circular cylinder. This research show that, installation of continuous flap reduces value of drag co-efficient, CD up to 66%, where as mini flaps are found more effective by reducing it up to 73%. Mini flaps of L/s=6.25, all angled at 30O, at the 30O angular position on the body of circular cylinder has been found the most effective angle of attack for drag reduction in case of flow over circular cylinder.
Unsteady flow around two-dimensional circular cylinder bundles in fluid elastic vibration
We describe the unsteady flow around two-dimensional circular cylinder bundles supported by the leaf spring in the fluid-elastic vibration. The experiment was carried out in a circuit-type wind tunnel having a 200 mm x 200 mm working section of 2,000 mm length at the Reynolds number Re of 6,300. Two-dimensional circular cylinders with diameter D = 20 mm were aligned at regular spaces S in the square array of three rows. The spacing ratio between two adjoining circular cylinders was constant as S/D = 1.5. The time-mean velocity, turbulent intensities and Reynolds stress were measured by use of a laser Doppler velocimeter. The unsteady flow pattern around an oscillating cylinder was observed by the flow visualization in a water channel. Consequently, it was found that the occurrence of the fluid-elastic vibration is caused by the phenomenon of wake-switch for the circular cylinder bundles of three rows. (author)
Das, Pramode K.; Mathew, Sam; Shaiju, A. J.; Patnaik, B. S. V.
2016-02-01
The control of vortex shedding behind a circular cylinder is a precursor to a wide range of external shear flow problems in engineering, in particular the flow-induced vibrations. In the present study, numerical simulation of an energetically efficient active flow control strategy is proposed, for the control of wake vortices behind a circular cylinder at a low Reynolds number of 100. The fluid is assumed to be incompressible and Newtonian with negligible variation in properties. Reflectionally symmetric controllers are designed such that, they are located on a small sector of the cylinder over which, tangential sliding mode control is imparted. In the field of modern controls, proportional (P), integral (I) and differential (D) control strategies and their numerous combinations are extremely popular in industrial practice. To impart suitable control actuation, the vertically varying lift force on the circular cylinder, is synthesised for the construction of an error term. Four different types of controllers considered in the present study are, P, I, PI and PID. These controllers are evaluated for their energetic efficiency and performance. A linear quadratic optimal control problem is formulated, to minimise the cost functional. By performing detailed simulations, it was observed that, the system is energetically efficient, even when the twin eddies are still persisting behind the circular cylinder. To assess the adaptability of the controllers, the actuators were switched on and off to study their dynamic response.
EXPERIMENTAL STUDY OF FLOW STRUCTURE BEHIND A CIRCULAR CYLINDER WITH WAVY SURFACE BY PIV
无
2006-01-01
The wake behind a circular cylinder with wavy surface was investigated using single-frame PIV technique at Re=5200. The mean flow field and spatial distribution of turbulence statistics in the nodal, saddle and middle planes were presented and compared with those of a smooth cylinder. The near wake behind the wavy cylinder shows pronounced spanwise periodicity of flow structures. Compared with a smooth cylinder, the vortex formation region considerably expands in the streamwise direction, particularly reaching maximum in the saddle plane of the wavy cylinder. However, the longitudinal vortices in the nodal plane were noticeably suppressed in the transverse direction. In addition, the wake in the nodal plane contains the peak value of turbulent kinetic energy and the Reynolds shearing stress due to the intensive entrainment of free flow and the momentum exchange in the spanwise direction.
Carmo, Bruno S.; Assi, Gustavo R. S.; Meneghini, Julio R.
2013-08-01
In this work, we considered the flow around two circular cylinders of equal diameter placed in tandem with respect to the incident uniform flow. The upstream cylinder was fixed and the downstream cylinder was completely free to move in the cross-stream direction, with no spring or damper attached to it. The centre-to-centre distance between the cylinders was four diameters, and the Reynolds number was varied from 100 to 645. We performed two- and three-dimensional simulations of this flow using a Spectral/hp element method to discretise the flow equations, coupled to a simple Newmark integration routine that solves the equation of the dynamics of the cylinder. The differences of the behaviours observed in the two- and three-dimensional simulations are highlighted and the data is analysed under the light of previously published experimental results obtained for higher Reynolds numbers.
Re-examination of laminar flow over twin circular cylinders in tandem arrangement
Viscous fluid flow past two identical circular cylinders in a tandem arrangement is numerically investigated at a typical Reynolds number of 200. By considering a large span of spacing ratio (0.1 ⩽ G/D ⩽ 6.0) with a fine interval of 0.1 or less, the dependences on the spacing ratio of the drag force, lift force, lift fluctuation frequency, torque on the cylinder pair and phase difference between the lift fluctuations of the two cylinders are investigated in detail, where D is the diameter of the cylinder and G the surface-to-surface distance between the cylinders. The phase difference between the lift fluctuations of the two cylinders is addressed based on correlation analysis together with the phase diagram, which has received scarce attention before. The phase difference provides further understanding to the dependence of the wake evolutions behind the twin circular cylinders. The numerical investigations show that diverse regimes can be identified according to the dependence of the hydrodynamics on the spacing ratio. The hydrodynamic discontinuities at G/D = 0.9, which have previously been ignored, are reported in this work. The physical correlations between the hydrodynamic discontinuities and the wake patterns are presented. (paper)
Numerical Simulation of Circular Cylinders in Free-Fall
Romero Gomez, Pedro DJ; Richmond, Marshall C.
2016-02-05
In this work, we combined the use of (i) overset meshes, (ii) a 6 degree-of-freedom (6- DOF) motion solver, and (iii) an eddy-resolving flow simulation approach to resolve the drag and secondary movement of large-sized cylinders settling in a quiescent fluid at moderate terminal Reynolds numbers (1,500 < Re < 28,000). These three strategies were implemented in a series of computational fluid dynamics (CFD) solutions to describe the fluid-structure interactions and the resulting effects on the cylinder motion. Using the drag coefficient, oscillation period, and maximum angular displacement as baselines, the findings show good agreement between the present CFD results and corresponding data of published laboratory experiments. We discussed the computational expense incurred in using the present modeling approach. We also conducted a preceding simulation of flow past a fixed cylinder at Re = 3,900, which tested the influence of the turbulence approach (time-averaging vs eddy-resolving) and the meshing strategy (continuous vs. overset) on the numerical results. The outputs indicated a strong effect of the former and an insignificant influence of the latter. The long-term motivation for the present study is the need to understand the motion of an autonomous sensor of cylindrical shape used to measure the hydraulic conditions occurring in operating hydropower turbines.
THE INTERACTION OF A COLD ATOMISED SPRAY WITH A CIRCULAR CYLINDER
A. AROUSSI
2010-09-01
Full Text Available The development of non-intrusive diagnostic techniques has significantly increased with the introduction of lasers. Laser based anemometry, such as Laser Doppler (LDA, Phase Doppler (PDA, and Particle Image Velocimetery (PIV can provide an accurate description of flows without interference. This study determines experimentally the fluid motion resulting from the interaction of a liquid spray with a circular cylinder. Two experimental settings were examined: the first is a discharging spray into free air and the second is a spray impinging on a circular cylinder placed 25 cylinder diameters downstream of the nozzle. These sprays were quantified using PIV. A non-intrusive droplet sizing technique was used to characterise the spray. This has shown that, within the spray, the average droplet diameter increases when the circular cylinder is introduced and so does the frequency of occurrence of these large droplets. In the wake behind the cylinder, the smaller droplets were quickly entrained and recirculated, while the larger droplets continued in the general direction of the spray cone.
Vortex shedding of a heated circular cylinder at low Reynolds number
Wang, A. B.; Trávníček, Zdeněk; Wu, M. H.
Taiwan: National Cheng Kung University, 2001 - (Hsiao, F.), s. 49-54 [The 4th Pacific International Conference on Aerospace Science and Technology (PICAST 4). Kaohsiung (TR), 22.05.2001] R&D Projects: GA ČR GA101/99/0059 Keywords : heated circular cylinder * laminar flow * vortex shedding Subject RIV: BK - Fluid Dynamics
Modelling the Inflation of Polyisobutylene Into an Elliptic and a Circular Cylinder
Rasmussen, Henrik Koblitz; Gøttsche, Søren; Kjær, Erik Michael
2000-01-01
The isothermal inflation of a sheet of a Polyisobutylene melt into a circular and an elliptic cylinder is modelled using the 3D Lagrangian Integral Method. The non-linear properties of the Polyisobutylene are modelled with the Factorized K-BKZ constitutive equation, using a potential function bas...... on the potential function from the Doi-Edwards reptation theory....
无
2007-01-01
In the present study, analyzed are the variation of added mass for a circular cylinder in the lock-in (synchronization) range of vortex-induced vibration (VIV) and the relationship between added mass and natural frequency. A theoretical minimum value of the added mass coefficient for a circular cylinder at lock-in is given. Developed are semi-empirical formulas for the added mass of a circular cylinder at lock-in as a function of flow speed and mass ratio. A comparison between experiments and numerical simulations shows that the semi-empirical formulas describing the variation of the added mass for a circular cylinder at lock-in are better than the ideal added mass. In addition, computation models such as the wake oscillator model using the present formulas can predict the amplitude response of a circular cylinder at lock-in more accurately than those using the ideal added mass.
Accelerated micropolar fluid--flow past an uniformly rotating circular cylinder
Siddiqui, Abuzar Abid
2016-01-01
In this paper, we formulated the non-steady flow due to the uniformly accelerated and rotating circular cylinder from rest in a stationary, viscous, incompressible and micropolar fluid. This flow problem is examined numerically by adopting a special scheme comprising the Adams-Bashforth Temporal Fourier Series method and the Runge-Kutta Temporal Special Finite-Difference method. This numerical scheme transforms the governing equation for micropolar fluids for this problem into system of finite-difference equations. This system was further solved numerically by point SOR-method. These results were also further extrapolated by the Richardson extrapolation method. This scheme is valid for all values of the flow and fluid-parameters and for all time. Moreover the boundary conditions of the vorticity and the spin at points far from the cylinder are being imposed and encountered too. The results are compared with existing results (for non-rotating circular cylinder in Newtonian fluids). The comparison is good. The ...
Vortex-Induced Vibration Suppression of a Circular Cylinder with Vortex Generators
Shi-bo Tao
2016-01-01
Full Text Available The vortex-induced vibration is one of the most important factors to make the engineering failure in wind engineering. This paper focuses on the suppression method of vortex-induced vibration that occurs on a circular cylinder fitted with vortex generators, based on the wind tunnel experiment. The effect of the vortex generators is presented with comparisons including the bare cylinder. The experimental results reveal that the vortex generators can efficiently suppress vortex-induced vibration of the circular cylinder. Vortex generator control can make the boundary layer profile fuller and hence more resistant to separation. The selections of skew angles and the angular position have a significant influence on the vortex generator control effect. By correlation analysis, it can be concluded that the vortex generators can inhibit the communication between the two shear layers and produce streamwise vortices to generate a disturbance in the spanwise direction.
VANISHING OF THREE-DIMENSIONALITY IN THE WAKE BEHIND A ROTATIONALLY OSCILLATING CIRCULAR CYLINDER
无
2007-01-01
The flow behind a three-dimensional rotationally oscillating circular cylinder was studied by a numerical method. The computations were performed at a Reynolds number of 260, which is at a level that the flow wake has developed into a three-dimensional state called Mode-B. The purpose of this paper is to examine the influence of various rotational amplitudes (0.1-0.7) on the wake instability of the flow, while the oscillation frequency is fixed to the value of that measured in the wake of a stationary cylinder. The results show that the rotation with sufficiently high amplitude brings the flow back to its nominal two-dimensional state. Moreover, it is found that the value of the time-averaged drag and the RMS value of the lift are larger than those of a stationary circular cylinder.
RANS-VOF solver for solitary wave run-up on a circular cylinder
Cao, Hong-jian; Wan, De-cheng
2015-04-01
Simulation of solitary wave run-up on a vertical circular cylinder is carried out in a viscous numerical wave tank developed based on the open source codes OpenFOAM. An incompressible two-phase flow solver naoe-FOAM-SJTU is used to solve the Reynolds-Averaged Navier-Stokes (RANS) equations with the SST k- ω turbulence model. The PISO algorithm is utilized for the pressure-velocity coupling. The air-water interface is captured via Volume of Fluid (VOF) technique. The present numerical model is validated by simulating the solitary wave run-up and reflected against a vertical wall, and solitary wave run-up on a vertical circular cylinder. Comparisons between numerical results and available experimental data show satisfactory agreement. Furthermore, simulations are carried out to study the solitary wave run-up on the cylinder with different incident wave height H and different cylinder radius a. The relationships of the wave run-up height with the incident wave height H, cylinder radius a are analyzed. The evolutions of the scattering free surface and vortex shedding are also presented to give a better understanding of the process of nonlinear wave-cylinder interaction.
RANS-VOF Solver for Solitary Wave Run-up on A Circular Cylinder
曹洪建; 万德成
2015-01-01
Simulation of solitary wave run-up on a vertical circular cylinder is carried out in a viscous numerical wave tank developed based on the open source codes OpenFOAM. An incompressible two-phase flow solver naoe-FOAM-SJTU is used to solve the Reynolds-Averaged Navier–Stokes (RANS) equations with the SST k-wturbulence model. The PISO algorithm is utilized for the pressure-velocity coupling. The air-water interface is captured via Volume of Fluid (VOF) technique. The present numerical model is validated by simulating the solitary wave run-up and reflected against a vertical wall, and solitary wave run-up on a vertical circular cylinder. Comparisons between numerical results and available experimental data show satisfactory agreement. Furthermore, simulations are carried out to study the solitary wave run-up on the cylinder with different incident wave height H and different cylinder radius a. The relationships of the wave run-up height with the incident wave height H, cylinder radius a are analyzed. The evolutions of the scattering free surface and vortex shedding are also presented to give a better understanding of the process of nonlinear wave-cylinder interaction.
Oscillation-induced sand ripples in a circular geometry.
Rousseaux, Germain; Kruithof, Joachim; Jenffer, Patrice; Wesfreid, José Eduardo
2008-07-01
This study deals with the observation of sand ripples in a circular geometry under oscillatory flow. We characterize the observed patterns as a function of the excitation parameters. We report the time evolution of the corrugated front invading the flat bed. These experiments reveal unambiguously, because of the gradient of shear stress, the existence of two separated thresholds: one for grain motion and the other for the appearance of ripples. In addition, we display the phase diagram of this instability as a function of the Froude number and a Reynolds number. PMID:18764045
Dual Circularly Polarized Omnidirectional Antenna with Slot Array on Coaxial Cylinder
Bin Zhou
2015-01-01
Full Text Available A dual circularly polarized (CP omnidirectional antenna based on slot array in coaxial cylinder structure is presented in this paper. It is constructed by perpendicular slot pairs around and along the axis of the coaxial cylinder to realize the omnidirectional CP property, and two ports are assigned in its two sides as left hand circularly polarized (LHCP port and right hand circularly polarized (RHCP port, respectively. The proposed antenna achieves a bandwidth of 16.4% ranging from 5.05 to 5.95 GHz with an isolation higher than 15 dB between the two CP ports, and the return loss (RL is higher than 10 dB within the bandwidth in both of the two ports. From the measured results, the average axial ratio (AR of the proposed antenna in omnidirectional plane is lower than 1.5 dB.
Experiments on Sphere Cylinder Geometry Dependence in the Electromagnetic Casimir Effect
Mukhopadhyay, Shomeek; Noruzifar, Ehsan; Wagner, Jeffrey; Zandi, Roya; Mohideen, Umar
2013-03-01
We report on ongoing experimental investigations on the geometry dependence of the electromagnetic Casimir force in the sphere-cylinder configuration. A gold coated hollow glass sphere which forms one surface is attached to a Silicon AFM cantilever. The cylinder, which is constructed from tapered optical fiber is also gold coated. The resonance frequency shift of the cantilever is measured as a function of the sphere-cylinder surface separation. The sphere-cylinder electrostatic force is used for alignment of the sphere and the cylinder and also for calibrating the system. The results are compared to numerical simulations in the framework of the Proximity Force Approximation (PFA).
Ishimatsu, Takuto; Morishita, Etsuo; Okunuki, Takeo; Koyama, Hisao
Flows over two circular cylinders in tandem, side-by-side, and staggered arrangements were analyzed using the overset grid method, which is capable of handling a variety of sizes and arrangements. The Reynolds number was 100 based on the cylinder diameter. The present computation code was validated by comparison with benchmark solutions for flow around a single cylinder. Wind-tunnel experiments were conducted for the side-by-side cylinder flow for comparison with numerical simulations. Calculation showed two critical spacings in the tandem arrangement where the aerodynamic forces and Strouhal number change discontinuously. Three critical spacings and four distinct flow patterns were found numerically in the side-by-side arrangement. Similar critical spacings were found in the staggered arrangement calculation and formed critical lines. Furthermore, a pocket region was found for a staggered arrangement surrounded by the critical line.
Experimental Study of the Flow Field around a Circular Cylinder Using Plasma Actuators
Siavash Tabatabaeian
2015-01-01
Full Text Available In this paper different configurations of plasma actuator for controlling the flow around a circular cylinder made of Quartz were experimentally investigated. Three thin plasma actuator electrodes were flush-mounted on the surface of the cylinder and were connected to a DC high voltage power supply for generation of electrical discharge. Different configurations of plasma actuator were used for this study and pressure distribution experiments showed that the existence of the plasma decreases the pressure coefficient of the cylinder and the variation of the pressure coefficient can change the behavior of the lift and drag coefficient of the cylinder for all configurations. According to the pressure distribution data, two configurations of the plasma actuators made the best influence on the aerodynamic performance and also on the drag reduction.
Scattering from a Buried Circular Cylinder Illuminated by a Three-Dimensional Source
Hansen, T.B.; Meincke, Peter
2002-01-01
We employ plane and cylindrical wave expansions with the fast Fourier transform to solve scattering problems involving a circular cylinder buried in soil. The illumination is provided by a three-dimensional source located in air above ground. Plane wave expansions describe transmitted and reflected...... fields at the air-soil interface, and cylindrical wave expansions describe the fields scattered by the cylinder. The two types of expansions are joined by employing explicit expressions that relate cylindrical and plane waves. We neglect multiple interactions between the cylinder and the interface. The...... cylinder and soil can have frequency-dependent permittivities and conductivities. With the formulas cast in a special form the scattered fields can be computed rapidly for fixed-offset configurations in which the location of the source is different for each observation point. Fixed offset is the most...
Yingnan Fu
2015-01-01
Full Text Available Viscous flow past an upstream in-line forced oscillating circular cylinder with a stationary cylinder downstream at Reynolds number of 100 is investigated using a CIP model. The model is established in a Cartesian coordinate system using a high-order difference method to discretise the Navier-Stokes equations. The fluid-structure interaction is treated as a multiphase flow with fluid and solid phases solved simultaneously. An immersed boundary method is used to deal with the fluid-body coupling. The CFD model is firstly applied to the computation of flow past a fixed circular cylinder for its validation; then flow over two stationary tandem cylinders is investigated and good agreements are obtained comparing with existing ones. Computations are then performed with flow past two tandem cylinders with an upstream in-line oscillating cylinder with a small spacing L=2D. Considerable attention is paid to the spectrum characteristics and vortex modes.
Flow-induced vibration of a circular cylinder subjected to wake interference at low Reynolds number
Carmo, B. S.; Sherwin, S. J.; Bearman, P. W.; Willden, R. H. J.
2011-05-01
Two- and three-dimensional numerical simulations of the flow around two circular cylinders in tandem arrangements are performed. The upstream cylinder is fixed and the downstream cylinder is free to oscillate in the transverse direction, in response to the fluid loads. The Reynolds number is kept constant at 150 for the two-dimensional simulations and at 300 for the three-dimensional simulations, and the reduced velocity is varied by changing the structural stiffness. The in-line centre-to-centre distance is varied from 1.5 to 8.0 diameters, and the results are compared to that of a single isolated flexible cylinder with the same structural characteristics, m*=2.0 and ζ=0.007. The calculations show that significant changes occur in the dynamic behaviour of the cylinders, when comparing the flow around the tandem arrangements to that around an isolated cylinder: for the tandem arrangements, the lock-in boundaries are wider, the maximum displacement amplitudes are greater and the amplitudes of vibration for high reduced velocities, outside the lock-in, are very significant. The main responsible for these changes appears to be the oscillatory flow in the gap between the cylinders.
FLOW PAST TWO ROTATING CIRCULAR CYLINDERS IN A SIDE-BY-SIDE ARRANGEMENT
GUO Xiao-hui; LIN Jian-zhong; TU Cheng-xu; WANG Hao-li
2009-01-01
Measurements were performed using Particle Image Velocimetry (PIV) to analyze the modification of flow by the combined effects of the rotation and the Reynolds number on the flow past two rotating circular cylinders in a side-by-side-arrangement at a range of , (α is the rotational speed) at one gap spacing of (T and d are the distance between the centers of two cylinders and the cylinder diameter, respectively). A new Immersed-Lattice Boltzmann Method (ILBM) scheme was used to study the effect of the gap spacing on the flow. The results show that the vortex shedding is suppressed as rotational speed increases. The flow reaches a steady state when the vortex shedding for both cylinders is completely suppressed at critical rotational speed. As the rotational speed further increases, the separation phenomenon in the boundary layers disappears at the attachment rotational speed. The critical rotational speed and attachment rotational speed become small as Reynolds number increases. The absolute rotational speed of cylinders should be large at same critical rotational speed and attachment rotational speed in the case of large Reynolds number. The gap spacing has an important role in changing the pattern of vortex shedding. It is very different in the mechanism of vortex shedding suppression for the flows around two rotating cylinders and single rotating cylinder.
Hu, J. C.; Zhou, Y.
Flow structures, Strouhal numbers and their downstream evolutions in the wake of two-staggered circular cylinders are investigated at Re=7000 using hot-wire, flow-visualization and particle-image velocimetry techniques. The cylinder centre-to-centre pitch, P, ranges from 1.2d to 4.0d (d is the cylinder diameter) and the angle ( ~ 90 10 (x is the downstream distance from the mid-point between the cylinders), i.e. two single-street modes (S-I and S-II) and two twin-street modes (T-I and T-II), based on Strouhal numbers, flow topology and their downstream evolution. Mode S-I is further divided into two different types, i.e. S-Ia and S-Ib, in view of their distinct vortex strengths. Mode S-Ia occurs at P/d and P/d > 1.5. Shear layers separated from the upstream cylinder reattach on or roll up to form vortices before reaching the downstream cylinder, resulting in postponed flow separation from the downstream cylinder. A single vortex street thus formed is characterized by significantly weakened vortices, compared with Mode S-Ia. Mode S-II is identified at P/d=1.2~2.5 and or 1.54.0 and 10, where both cylinders generate vortices, with vortex shedding from the upstream cylinder at a much higher frequency than from the downstream, producing two streets of different widths and vortex strengths at x/d10. The vortices generated by the downstream cylinder are significantly stronger than those, originating from the upstream cylinder, in the other row. Mode T-I occurs at P/d=20; the two cylinders produce two streets of different vortex strengths and frequencies, both persisting beyond x/d=10. At P/d, the two cylinders generate two coupled streets, mostly anti-phased, of the same vortex strength and frequency (St≈0.21), which is referred to as Mode T-II. The connection of the four modes with their distinct initial conditions, i.e. interactions between shear layers around the two cylinders, is discussed.
M. Nicolet
2011-11-01
Full Text Available Computations of the phase matrix elements for single water droplets and ice crystals in fixed orientations are presented to determine if circular depolarization δ_{±C} is more accurate than linear depolarization for phase discrimination. T-matrix simulations were performed to calculate right-handed and left-handed circular depolarization ratios δ_{+C}, respectively δ_{−C} and to compare them with linear ones. Ice crystals are assumed to have a circular cylindrical shape where their surface-equivalent diameters range up to 5 μm. The circular depolarization ratios of ice particles were generally higher than linear depolarization and depended mostly on the particle orientation as well as their sizes. The fraction of non-detectable ice crystals (δ < 0.05 was smaller considering a circular polarized light source, reaching 4.5%. However, water droplets also depolarized light circularly for scattering angles smaller than 179° and size parameters smaller than 6 at side- and backscattering regions. Differentiation between ice crystals and water droplets might be difficult for experiments performing at backscattering angles which deviate from 180° unlike lidar applications. If the absence of the liquid phase is confirmed, the use of circular depolarization in single particle detection is more sensitive and less affected by particle orientation.
Experiment on smooth, circular cylinders in cross-flow in the critical Reynolds number regime
Miau, J.J.; Tsai, H.W.; Lin, Y.J.; Tu, J.K.; Fang, C.H.; Chen, M.C. [National Cheng Kung University, Department of Aeronautics and Astronautics, Tainan (China)
2011-10-15
Experiments were conducted for 2D circular cylinders at Reynolds numbers in the range of 1.73 x 10{sup 5}-5.86 x 10{sup 5}. In the experiment, two circular cylinder models made of acrylic and stainless steel, respectively, were employed, which have similar dimensions but different surface roughness. Particular attention was paid to the unsteady flow behaviors inferred by the signals obtained from the pressure taps on the cylinder models and by a hot-wire probe in the near-wake region. At Reynolds numbers pertaining to the initial transition from the subcritical to the critical regimes, pronounced pressure fluctuations were measured on the surfaces of both cylinder models, which were attributed to the excursion of unsteady flow separation over a large circumferential region. At the Reynolds numbers almost reaching the one-bubble state, it was noted that the development of separation bubble might switch from one side to the other with time. Wavelet analysis of the pressure signals measured simultaneously at {theta} = {+-}90 further revealed that when no separation bubble was developed, the instantaneous vortex-shedding frequencies could be clearly resolved, about 0.2, in terms of the Strouhal number. The results of oil-film flow visualization on the stainless steel cylinder of the one-bubble and two-bubble states showed that the flow reattachment region downstream of a separation bubble appeared not uniform along the span of the model. Thus, the three dimensionality was quite evident. (orig.)
Şibliyev, Orxan
2012-01-01
ABSTRACT: In this work, a computer program is written for solving the turbulent flow equations on unstructured grids using a Large Eddy Simulation (LES) model in C++ language. To test the code, two cases are considered: laminar, periodic flow past a circular cylinder at Reynolds number, ReD = 100 which is based on the diameter of the cylinder and turbulent flow at ReD = 3900. The turbulence or sub-grid scale (SGS) model is chosen as Smagorinsky model due to its simplicity compared with dy...
M. Nicolet
2012-05-01
Full Text Available Computations of the phase matrix elements for single water droplets and ice crystals in fixed orientations are presented to determine if circular depolarization δ_{C} is more accurate than linear depolarization for phase discrimination. T-matrix simulations were performed to calculate right-handed and left-handed circular depolarization ratios δ_{+C}, respectively δ_{−C} and to compare them with linear ones. Ice crystals are assumed to have a circular cylindrical shape where their surface-equivalent diameters range up to 5 μm. The circular depolarization ratios of ice particles were generally higher than linear depolarization and depended mostly on the particle orientation as well as their sizes. The fraction of non-detectable ice crystals (δ<0.05 was smaller considering a circular polarized light source, reaching 4.5%. However, water droplets also depolarized light circularly for scattering angles smaller than 179° and size parameters smaller than 6 at side- and backscattering regions. Differentiation between ice crystals and water droplets might be difficult for experiments performed at backscattering angles which deviate from 180° unlike LIDAR applications. Instruments exploiting the difference in the P_{44}/P_{11} ratio at a scattering angle around 115° are significantly constrained in distinguishing between water and ice because small droplets with size parameters between 5 and 10 do cause very high circular depolarizations at this angle. If the absence of the liquid phase is confirmed, the use of circular depolarization in single particle detection is more sensitive and less affected by particle orientation.
Wave Forces on Linear Arrays of Rigid Vertical Circular Cylinders in Regular Wave
V.J. Kurian
2014-06-01
Full Text Available The present investigation aims to experimentally determine the variation of forces and force coefficients acting on circular cylinders, which are arranged in a linear array along the direction of the waves. Most commonly used structural and non-structural elements in the construction of offshore platforms are circular cylindrical members. In many cases, these members are found in very close neighbourhood of each other, thus modifying the surrounding flow and wave forces acting on them. Model tests were conducted in the wave tank on a maximum of four cylinders of the same diameter. A reasonable scale factor was chosen considering the pertinent factors such as water depth, wave generating capability and accuracy of measurements. The cylinders were installed inside the wave tank as vertical cantilevers fixed at the top. Wave forces acting on the cylinders were measured using special wave force sensors exclusively designed and fabricated for the present project, while the wave profiles were recorded using wave probes installed in the wave basin. The results confirmed the presence of a force shielding effect on the trailing cylinders by the leading cylinders with few exceptions. The findings also substantiated the significant modification of the forces on cylinders when they are present in a linear array. A common practice adopted for the design of offshore platforms was identified with a possibility of underestimating the wave forces acting on the cylindrical elements. In many cases, the experimentally computed hydrodynamic force coefficients were found to be lower than the standard values adopted by various design codes. These findings portray the significance of the present work in achieving economy in the design of jacket platforms and risers.
Large eddy simulation of the subcritical flow over a V grooved circular cylinder
Alonzo-García, A. [Instituto Politécnico Nacional, SEPI-ESIME Zacatenco, U.P. Adolfo López Mateos Edif. 5, 3er. Piso, LABINTHAP, Av. Instituto Politénicno Nacional s/n, Col. Lindavista, C.P. 07738, México D.F., México (Mexico); Gutiérrez-Torres, C. del C., E-mail: cgutierrezt@ipn.mx [Instituto Politécnico Nacional, SEPI-ESIME Zacatenco, U.P. Adolfo López Mateos Edif. 5, 3er. Piso, LABINTHAP, Av. Instituto Politénicno Nacional s/n, Col. Lindavista, C.P. 07738, México D.F., México (Mexico); Jiménez-Bernal, J.A. [Instituto Politécnico Nacional, SEPI-ESIME Zacatenco, U.P. Adolfo López Mateos Edif. 5, 3er. Piso, LABINTHAP, Av. Instituto Politénicno Nacional s/n, Col. Lindavista, C.P. 07738, México D.F., México (Mexico); and others
2015-09-15
Highlights: • We compared numerically the turbulent flow over a smooth circular cylinder and a V grooved cylinder in the subcritical regime. • Turbulence intensities in both streamwise and normal direction suffered attenuations. • The swirls structures on grooves peaks seemed to have a cyclic behavior. • The evolution of the flow inside grooves showed that swirls structures located in peaks suffered elongations in the normal direction. • The secondary vortex structures formed in the grooved cylinder near wake were smaller in comparison of the smooth cylinder flow. - Abstract: In this paper, a comparative numerical study of the subcritical flow over a smooth cylinder and a cylinder with V grooves (Re = 140,000) is presented. The implemented technique was the Large Eddy Simulation (LES), which according to Kolmogorov's theory, resolves directly the most energetic largest eddies and models the smallest and considered universal high frequency ones. The Navier-Stokes (N-S) equations were solved using the commercial software ANSYS FLUENT V.12.1, which applied the finite volume method (FVM) to discretize these equations in their unsteady and incompressible forms. The grid densities were 2.6 million cells and 13.5 million cells for the smooth and V grooved cylinder, respectively. Both meshes were composed of structured hexahedral cells and close to the wall of the cylinders, additional refinements were employed in order to obtain y{sup +<5} values. All cases were simulated during at least 15 vortex shedding cycles with the aim of obtaining significant statistical data. Results: showed that for both cases (smooth and V grooved cylinder flow), the numerical code was capable of reproducing the most important physical quantities of the subcritical regime. Velocity distribution and turbulence intensity in the flow direction suffered a slight attenuation along the wake, as a consequence of grooves perturbation, which also caused an increase in the pressure
Large eddy simulation of the subcritical flow over a V grooved circular cylinder
Highlights: • We compared numerically the turbulent flow over a smooth circular cylinder and a V grooved cylinder in the subcritical regime. • Turbulence intensities in both streamwise and normal direction suffered attenuations. • The swirls structures on grooves peaks seemed to have a cyclic behavior. • The evolution of the flow inside grooves showed that swirls structures located in peaks suffered elongations in the normal direction. • The secondary vortex structures formed in the grooved cylinder near wake were smaller in comparison of the smooth cylinder flow. - Abstract: In this paper, a comparative numerical study of the subcritical flow over a smooth cylinder and a cylinder with V grooves (Re = 140,000) is presented. The implemented technique was the Large Eddy Simulation (LES), which according to Kolmogorov's theory, resolves directly the most energetic largest eddies and models the smallest and considered universal high frequency ones. The Navier-Stokes (N-S) equations were solved using the commercial software ANSYS FLUENT V.12.1, which applied the finite volume method (FVM) to discretize these equations in their unsteady and incompressible forms. The grid densities were 2.6 million cells and 13.5 million cells for the smooth and V grooved cylinder, respectively. Both meshes were composed of structured hexahedral cells and close to the wall of the cylinders, additional refinements were employed in order to obtain y+<5 values. All cases were simulated during at least 15 vortex shedding cycles with the aim of obtaining significant statistical data. Results: showed that for both cases (smooth and V grooved cylinder flow), the numerical code was capable of reproducing the most important physical quantities of the subcritical regime. Velocity distribution and turbulence intensity in the flow direction suffered a slight attenuation along the wake, as a consequence of grooves perturbation, which also caused an increase in the pressure coefficient
Ahmed W. Mustava
2013-01-01
The effect of a semi-circular cylinders in a two dimensional channel on heat transfer by forced convection from two heat sources with a constant temperature has been studied numerically. Each channel contains two heat sources; one on the upper surface of the channel and the other on the lower surface of the channel. There is semi-circular cylinder under the source in upper surface and there is semi-circular cylinder above the source in lower surface. The location of the second heat source wit...
Numerical study of turbulent flow separation over a wall mounted circular cylinder
Yu, Taejong; You, Donghyun
2015-11-01
Flow over a wall-mounted circular cylinder with a finite span and a free end is numerically studied at a range of Reynolds numbers. Separated flow behind a wall-mounted cylinder is characterized by dominant vortical structures developed around and behind the cylinder: i.e., Karman vortices and tip-shedding vortices. The formation and interaction among the vortices are found to be distinct depending on the aspect ratio of the span length to the diameter of the cylinder as well as the Reynolds number. It is also found that drag and lift forces on the cylinder show different dominance of Karman vortices and tip vortices for different span-to-diameter ratios. A detailed analysis of the mean and fluctuating velocity, pressure fields, and spectral characteristics of separated flow is presented for laminar-to-transitional flows over cylinders with different aspect ratios. Supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning Grant NRF-2014R1A2A1A11049599.
Effect of Mach number on transonic flow past a circular cylinder
XU ChangYue; CHEN LiWei; LU XiYun
2009-01-01
The effect of Mach number on transonic flow past a circular cylinder is investigated numerically for the free-stream Mach number M∞from 0.85 to 0.98 and the Reynolds number 2×105 based on the diameter of the cylinder. The work provides an insight into several salient features, including unsteady and quasi-steady flow state, formation of local supersonic zone, and evolution of turbulent shear layer. Results show that there exist two flow states dependent of a critical Mach number Mcr around 0.9. One is an unsteady flow state characterized by moving shock waves interacting with the turbulent flow in the near region of the cylinder for M∞Mcr, and the other is a quasi-steady flow state with nearly sta-tionary shock waves formed in the near wake for M∞>Mcr, suppressing vortex shedding from the cylin-der. Some flow behaviors in the unsteady and quasi-steady flow states are revealed. From time evolu-tion of flow structures, local supersonic zones are identified in the wake and generated by two typical processes, i.e. reverse flow behind the cylinder and shed vortices in the near wake. The convective Mach number Mc of turbulent shear layers shed from the cylinder is identified nearly as Mc 1 in the quasi-steady flow regime, resulting in different evolutions of the shear layers.
Self-excited oscillations of a closely spaced row of circular cylinders in cross-flow
Experiments were carried out to examine the vibratory motion of a single, closely spaced row of circular cylinders or tube arrays, in which flexible cylinders, free to respond in the streamwise direction, are placed alternatively between fixed cylinders. For a transverse cylinder spacing T less than about 2--2.2D, the fluid jets formed in the wake pair up and switch when the flexible cylinders are displaced far enough upstream or downstream. The bistable situation of the jet switching introduces a hysteretic effect which extracts energy from the flow and can excite and maintain large amplitude oscillations. Therefore, self-excited in-line oscillations occur about a mean position upstream of the initial row position. Amplitude and frequency measurements for an oscillating row of T/D = 1.5 were conducted for various free stream velocities yielding Reynolds numbers from 700 to 1,200. Large cylinder response was recorded for reduced velocities based on oscillation frequency ranging between 50 and 61
Computation of Viscous Uniform and Shear Flow over A Circular Cylinder by A Finite Element Method
赵明; 滕斌
2004-01-01
The incompressible viscous uniform and shear flow past a circular cylinder is studied. The two-dimensional NavierStokes equations are solved by a finite element method. The governing equations are discretized by a weighted residual method in space. The stable three-step scheme is applied to the momentum equations in the time integration. The numerical model is firstly applied to the computation of the lid-driven cavity flow for its validation. The computed results agree well with the measured data and other numerical results. Then, it is used to simulate the viscous uniform and shear flow over a circular cylinder for Reynolds numbers from 100 to 1000. The transient time interval before the vortex shedding occurs is shortened considerably by introduction of artificial perturbation. The computed Strouhal number, drag and lift coefficients agree well with the experimental data. The computation shows that the finite element model can be successfully applied to the viscous flow problem.
Computational study of subcritical response in flow past a circular cylinder
Cantwell, Christopher D.; Barkley, Dwight
2013-01-01
Flow past a circular cylinder is investigated in the subcritical regime, below the onset of Benard-von Karman vortex shedding at Re_c ~ 47. The transient response of infinitesimal perturbations is computed. The domain requirements for obtaining converged results is discussed at length. It is shown that energy amplification occurs as low as Re=2.2. Throughout much of the subcritical regime the maximum energy amplification increases approximately exponentially in the square of Re reaching 6800 ...
THREE-DIMENSIONAL FLOW AROUND TWO TANDEM CIRCULAR CYLINDERS WITH VARIOUS SPACING AT Re=220
无
2006-01-01
The flow around two tandem circular cylinders was studied by a three-dimensional numerical simulation of the Navier-Stokes equations at Re=220. The improved virtual boundary method was applied to model the no-slip boundary condition of the cylinders. The results show that as the spacing ratio L/D ≥4, the three dimensionality occurs in the wake. When L/D≤3.5 the wake keeps a two-dimensional state at the Reynolds number Re=220. The critical spacing for the appearance of three-dimensional instability obtained is at the range 3.5＜L/D＜4, similar to the critical spacing found in two-dimensional case. Two sources of instability from upstream and downstream cylinder generate a complicated vortex structures in the wake, investigated by streamlines topology analysis in the streamwise plane. Many other interesting problems were also addressed in this paper.
Unsteady Numerical Simulation of Flow around 2-D Circular Cylinder for High Reynolds Numbers
Yanhui Ai; Dakui Feng; Hengkui Ye; Lin Li
2013-01-01
In this paper,2-D computational analyses were conducted for unsteady high Reynolds number flows around a smooth circular cylinder in the supercritical and upper-transition flow regimes,i.e.8.21×104＜Re＜l.54×106.The calculations were performed by means of solving the 2-D Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with a k-ε turbulence model.The calculated results,produced flow structure drag and lift coefficients,as well as Strouhal numbers.The findings were in good agreement with previous published data,which also supplied us with a good understanding of the flow across cylinders of different high Reynolds numbers.Meanwhile,an effective measure was presented to control the lift force on a cylinder,which points the way to decrease the vortex induced vibration of marine structure in future.
Soret and Dufour effects in steady flow of a viscous conducting fluid through a circular cylinder
This paper presents an exact solution to the problem of the steady laminar fully developed free convective mass transfer flow of a viscous incompressible electrically conducting fluid through a circular cylinder under constant pressure gradient influenced by a magnetic field in the azimuthal direction in presence of constant heat source and chemical reaction. The Soret and Dufour effects are considered but the electrical and the induced magnetic fields are neglected. The effects of different physical parameters entering into the problem on the velocity, temperature and concentration fields and on the coefficient of the skin friction, the rates of heat and mass transfer at surface of the cylinder and mass flux across a normal section of the cylinder are discussed through graphs. (author)
Nemeth, Michael P.
2014-01-01
Nonlinear and bifurcation buckling equations for elastic, stiffened, geometrically perfect, right-circular cylindrical, anisotropic shells subjected to combined loads are presented that are based on Sanders' shell theory. Based on these equations, a three-parameter approximate Rayleigh-Ritz solution and a classical solution to the buckling problem are presented for cylinders with simply supported edges. Extensive comparisons of results obtained from these solutions with published results are also presented for a wide range of cylinder constructions. These comparisons include laminated-composite cylinders with a wide variety of shell-wall orthotropies and anisotropies. Numerous results are also given that show the discrepancies between the results obtained by using Donnell's equations and variants of Sanders' equations. For some cases, nondimensional parameters are identified and "master" curves are presented that facilitate the concise representation of results.
CALCULATION OF VISCOUS FLOW AROUND CIRCULAR CYLINDER WITH THREE-DIMENSIONAL NUMERICAL SIMULATION
无
2001-01-01
Three-dimensional numerical simulation of a uniform incompressible viscous flow around a stationary circular cylinder was conducted. The CFX-4 software was used to calculate the hydrodynamic characteristics of the flow and the finite volume method for incompressible Navier-Stokes equations was employed in the program. The simulation of the flow was performed for Re=103 and Re=104 respectively within the sub-critical region. In order to overcome numerical instability for the high Reynolds number flows, a quadratic upwind scheme was incorporated for the Navier-Stokes equations. The periodicity boundary condition was used at the ends of the cylinder. It was found that the evolution of the lift and drag coefficients in each plane along the cylinder span is different. Comparison between the predicted results based on the three-dimensional and the two-dimensional analysis was also given. It is concluded that at the high Reynolds number the effect of three-dimensionality of the flow around the circular cylinder is remarkable, and in addition hydrodynamic coefficients with of 3-D simulation are less than those given by 2-D simulation.
Mathematical Modeling of Partial-Porous Circular Cylinders with Water Waves
Min-Su Park
2015-01-01
Full Text Available The interaction of water waves with partially porous-surfaced circular cylinders was investigated. A three-dimensional numerical modeling was developed based on the complete mathematical formulation of the eigenfunction expansion method in the potential flow. Darcy’s law was applied to describe the porous boundary. The partial-porous cylinder is composed of a porous-surfaced body near the free surface, and an impermeable-surfaced body with an end-capped rigid bottom below the porous region. The optimal ratio of the porous portion to the impermeable portion can be adopted to design an effective ocean structure with minimal hydrodynamic impact. To scrutinize the hydrodynamic interactions in N partial-porous circular cylinders, the computational fluid domain is divided into three regions: an exterior region, N inner porous body regions, and N regions beneath the body. Wave excitation forces and wave run-up on multibodied partial-porous cylinders are calculated and compared for various porous-portion ratios and wave conditions, all of which significantly influence the hydrodynamic property.
An Approximate Method for Calculation of Fluid Force and Response of A Circular Cylinder at Lock-in
WANG Yi
2008-01-01
In this paper, equations calculating lift force of a rigid circular cylinder at lock-in in uniform flow are deduced in detail. Besides, equations calculating the lift force on a long flexible circular cylinder at lock-in are deduced based on mode analysis of a multi-degree freedom system. The simplified forms of these equations are also given. Furthermore, an approximate method to predict the forces and response of rigid circular cylinders and long flexible circular cylinders at lock-in is introduced in the case of low mass-damping ratio. A method to eliminate one deficiency of these equations is introduced. Comparison with experimental results shows the effectiveness of this approximate method.
Flow patterns and heat transfer around six in-line circular cylinders at low Reynolds number
Fornarelli, Francesco; Lippolis, Antonio
2014-01-01
The flow field and the heat transfer around six in-line iso-thermal circular cylinders has been studied by mean of numerical simulations. Two values of the center to center spacing ($s=3.6d$ and $4d$, where $d$ is the cylinder diameter) at Reynolds number of $100$ and Prandtl number of $0.7$ has been investigated. Similarly to the in-line two cylinder configuration, in this range a transition in the flow and in the heat transfer occurs. Two different flow patterns have been identified: the stable shear layer (SSL) mode and the shear layer secondary vortices (SLSV) mode, at $3.6$ and $4$ spacing ratio ($s/d$), respectively. At $s/d=3.6$ the flow pattern causes the entrainment of cold fluid on the downstream cylinders enhancing the heat transfer. On the other hand at $s/d=4$ two stable opposite shear layer prevent the cold fluid entrainment over the downstream cylinders reducing their heat exchange. The overall time average heat transfer of the array is enhanced up to 25% decreasing the spacing ratio from $4$ t...
Secondary instability in the wake of the flow around two circular cylinders in tandem arrangements
Carmo, Bruno; Meneghini, Julio; Sherwin, Spencer
2008-11-01
The stability of three-dimensional perturbations about two-dimensional time-periodic vortex wakes of the flow around two identical circular cylinders in tandem arrangements is investigated. The centre-to-centre separation is varied from 1.5 to 5 cylinder diameters. Direct linear stability analysis is employed to determine the shape, wavelength and onset of unstable three-dimensional perturbations. In addition the non-linear character of the bifurcations is identified through three-dimensional direct numerical simulations performed in the vicinity of the critical points. It is found that, for configurations with large cylinder separations, the first stages of the wake transition are similar to those observed in the flow around an isolated cylinder, although the onset of the secondary instability occurs at a lower Reynolds number. In contrast, for small separations the transition route is significantly different, resembling that of the flow in a periodically driven cavity. For these configurations the onset of the first instability arises at a higher Reynolds number than in the case of an isolated cylinder.
Kharlamov, Alexander A.; Filip, Petr
2012-01-01
Roč. 77, č. 1 (2012), s. 77-85. ISSN 0022-0833 Institutional research plan: CEZ:AV0Z20600510 Keywords : circular cylinders * cylinder between two walls * generalised method of images * ideal fluid * potential flow Subject RIV: BK - Fluid Dynamics Impact factor: 1.075, year: 2012
Transition to turbulence in the separated shear layers of yawed circular cylinders
Spatial and temporal resolution of transition to turbulence inside the free-shear layers of two yawed circular cylinders is the subject of the present investigation. These physics were resolved using the large-eddy simulation (LES) methodology. An O-type grid was implemented such that the spatial scales of the LES computation fully resolved the energy range physics of the shear layers at Reynolds number ReD = 8000 based on the cylinder diameter. The two test cases modeled the cylinder span skewed at angles 45o and 60o from the horizontal axis. Observations revealed the same transition process as the normal cross-flow state. Soon after separation, Tollmien-Schlichting disturbances were predicted that evolved into Kelvin-Helmholtz (K-H) eddies before absorption by the large-scale Karman-type vortices. These eddies defaulted to a spanwise wavy pattern similar to a normal cross-flow due to their three-dimensional instability. No mixed modes were found between the K-H (Bloor) and Strouhal frequencies. The effect of yaw angle shortened the transition process. As a result, peak turbulence levels inside the wake formation zone approach the downstream cylinder periphery. In addition, the dimensionless frequencies of the K-H eddies lie above the normal cross-flow relationship as formulated by . Disparity between the yawed and normal cross-flow states was further emphasized by the shear-layer transition characteristics. Although each property displayed the expected exponential growth during transition to turbulence, their dimensionless form was miss-aligned with those of the normal cross-flow case. Based on the present evidence, additional simulations (and/or experimental measurements) are necessary to form conclusive arguments regarding the expected behavior of the transition characteristics within the free-shear layers of yawed circular cylinders.
Plane section of cone and cylinder in computer geometry
Obradović Ratko M.; Milojević Zoran
2005-01-01
In this paper a mathematical apparatus for determination of plane section of cone and cylinder was formed. By using the descriptive geometric approach the contour lines of these quadrics were determined. The fact that the tangent lines of a circle could be transformed to the tangent lines of an ellipse using affinity was employed. In that way surfaces are represented by contour lines (tangent lines of basic ellipse in oblique projection) and thus they have a realistic view. Intersecting plane...
Energetically efficient Proportional-Integral control of flow past a circular cylinder
Kesavadas, Pramode; Anand, Vijay; Patnaik, B. S. V.; Shaiju, A. J.
2015-11-01
In this numerical study, we present an energetically efficient Proportional (P) and Integral (I) control strategy for the cessation of vortex shedding behind a circular cylinder. Reflectionally symmetric controllers are designed such that, they are located on a small sector of the cylinder over which, tangential sliding mode control is imparted. Energetically efficient optimal parameters for the P, I and PI controls have been numerically assessed. An estimation of the time-averaged kinetic energy of different flow regimes using Proper Orthogonal Decomposition (POD) is also carried out. These values are obtained with and without the optimal controllers. The Navier-Stokes equations along with an evolution equation for the PI controller, is numerically solved using finite volume method. The optimization procedure is formulated as a standard Linear Quadratic (LQ) problem and the time-averaged kinetic energy is obtained by summation of POD eigenvalues. The energetic efficiency for the, I controller was observed to be superior compared to the other two classes of controllers. By performing detailed fluid flow simulations, it was observed that, the system is energetically efficient, even when the twin eddies are still persisting behind the circular cylinder. The first author wishes to acknowledge the Ministry of Human Resource Development, Govt. of India.
Huang, Zhu
2015-03-01
The periodic unsteady natural convection flow and heat transfer in a square enclosure containing a concentric circular cylinder is numerically studied. The temperature of the inner circular cylinder fluctuates periodically with time at higher averaged value while the temperature of the enclosure keeps lower constant, and the natural convection is driven by the temperature difference. The two-dimensional natural convection is simulated with high accuracy temporal spectral method and local radial basis functions method. The Rayleigh number is studied in the range 103 ≤ Ra ≤ 106, the temperature pulsating period ranges from 0.01 to 100 and the temperature pulsating amplitudes are a = 0.5, 1.0 and 1.5. Numerical results reveal that the fluid flow and heat transfer is strongly dependent on the pulsating temperature of inner cylinder. Comparing with the steady state natural convection, the heat transfer is enhanced generally for the time-periodic unsteady natural convection, and the local maximum heat transfer rate is observed for Ra = 105 and 106. Moreover, the phenomenon of backward heat transfer is discussed quantitatively. Also, the influence of pulsating temperature on the unsteady fluid flow and heat transfer are discussed and analyzed.
Bifurcation of cylinders for wetting and dewetting models with striped geometry
López, Rafael
2011-01-01
We show that some pieces of cylinders bounded by two parallel straight-lines bifurcate in a family of periodic non-rotational surfaces with constant mean curvature and with the same boundary conditions. These cylinders are initial interfaces in a problem of microscale range modeling the morphologies that adopt a liquid deposited in a chemically structured substrate with striped geometry or a liquid contained in a right wedge with Dirichlet and capillary boundary condition on the edges of the ...
Study of Flowrate Measurement Characteristics of a Circular Cylinder with a Slit%带狭缝圆柱钝体流量测量特性研究
王慧; 黄咏梅
2013-01-01
The flowrate characteristics of vortex flowmeter is closely related to the size and geometry shape of vortex bluff body. A new kind of circular cylinder with a slit structure is proposed and applied to vortex flowmeter. Theoretical analysis shows that the slit can be regarded as a feedback channel, which can effectively accelerate vortex shedding and increase vortex intensity. Experiments were carried out in a water pipe with a diameter of 50 mm. Vortex signals produced by circular cylinder with a slit and trapezoidal cylinder respectively at different flowrate were collected. This paper mainly focuses on analyzing the low flowrate measurement performance of circular cylinder with a slit. Experimental results show that compared with trapezoidal cylinder circular cylinder with a slit possesses following characteristics:vortex signal intensity is stronger, signal-to-noise ratio is higher, the Reynolds number of measurement range can be as low as 9. 5í103 and linearity of Strouhal number is better as well. Theoretical analysis and experimental results manifest that circular cylinder with a slit possesses good flowrate meas-urement features and can be applied to vortex flowmeter successfully.%涡街流量计的流量特性与旋涡发生体的形状和几何尺寸密切相关,提出了一种新型的带狭缝圆柱发生体结构并应用于涡街流量计。理论分析表明狭缝可以看作是一个反馈通道,可有效加快旋涡脱落并增强旋涡强度。在内径为50 mm的管道中进行实验,采集不同流量下带狭缝圆柱与梯形柱绕流产生的涡街信号,重点讨论带狭缝圆柱的小流量测量性能。实验表明,与梯形柱相比,带狭缝圆柱涡街信号更强,信噪比高,雷诺数测量范围可低至9.5×103,斯特劳哈尔数线性度更好。理论分析与实验结果表明,带狭缝圆柱具有较好的流量测量特性,可应用于涡街流量计。
MULTI-MODE OF VORTEX-INDUCED VIBRATION OF A FLEXIBLE CIRCULAR CYLINDER
XIE Fang-fang; DENG Jian; ZHENG Yao
2011-01-01
The vortex-induced vibration of a flexible circular cylinder is investigated at a constant Reynolds number of 1 000.The finite-volume method on moving meshes is applied for the fluid flow,and the Euler-Bemoulli beam theory is used to model the dynamic response of a flexible cylinder.The relationship between the reduced velocity and the amplitude response agrees well with the experimental results.Moreover,five different vibrating modes appear in the simulation.From the comparisons of their vortex structures,the strength of the wake flow is related to the exciting vibrating mode and different vortex patterns arise for different vibrating modes.Only 2P pattern appears in the first vibrating mode while 2S-2P patterns occur in the other vibrating modes if monitoring at different sections along the length of the cylinder.The vibration of the flexible cylinder can also greatly alter the three-dimensionality in the wake,which needs further studies in our future work,especially in the transition region for the Reynolds number from 170 to 300.
Numerical Simulation of Wave Scour Around A Large-Scale Circular Cylinder
赵明; 滕斌; 柳淑学
2002-01-01
A numerical model is developed for estimation of local scour around a large circular cylinder under wave action. The model includes wave diffraction around structures, bed shear stress calculation inside the wave boundary layer and topographical change model. The wave model is based on the improved Boussinesq equations for varying depth. The wave boundary layer is calculated by solving the integrated momentum equation over the boundary layer. The bed shear stress due to streaming, an important factor affecting the sediment transport around a large-scale cylinder, is calculated. The Lagrangian drift velocity is included in calculation of the suspended sediment transport rates. The model is implemented by a finite element method and the results from the present model, which agree well with experimental data, are compared with those from other methods.
Stokes ﬂow past a swarm of porous circular cylinders with Happel and Kuwabara boundary conditions
Satya Deo
2004-08-01
The problem of creeping ﬂow past a swarm of porous circular cylinders with Happel and Kuwabara boundary conditions is investigated. The Brinkman equation for the ﬂow inside the porous cylinder and the Stokes equation outside the porous cylinder in their stream function formulations are used. The force experienced by each porous circular cylinder in a cell is evaluated. Explicit expressions of stream functions are obtained for both the inside and outside ﬂow ﬁelds. The earlier results reported by Happel and Kuwabara for ﬂow past a solid cylinder in Happel’s and Kuwabara’s cell model, have been deduced. Analytical expressions for the velocity components, pressure, vorticity and stress- tensor are also obtained.
A numerical study of flow about fixed and flexibly mounted circular cylinders
Meling, Trond Stokka
1998-12-31
Motivated by the needs of the offshore oil industry, this thesis studies flow around a circular cylinder that is either fixed or flexibly mounted. The latter configuration is susceptible to vortex-induced vibrations. To predict the results numerically, a two-dimensional procedure was developed to handle the fluid domain, the structural problem and the non-linear interaction between the two media. The arbitrary Lagrangian-Eulerian approach was employed in order to handle moving boundaries. The fluid forces and the cylinder kinematics are solved in a staggered fashion. A velocity-correction method is employed to solve the incompressible Navier-Stokes equations where the Galerkin finite element method is used for the spatial discretization of the fluid domain. The second-order equation of motion of the cylinder is solved by a 4th order Rung-Kutta scheme. Various numerical schemes for solving the convection-diffusion equation involved are tested. All the schemes, except the rational Runge-Kutta, were found to smear the vortex street. To predict the flow field at high Reynolds number several turbulence models were tested. The modified 2-layer K-epsilon model with all elements in the boundary layer was found to predict results in remarkably good agreement with experimental results. Self-excited vibration tests of circular cylinders are also performed showing that the presented model is able to capture the lock-in phenomenon with reasonable accuracy, both in the laminar- and in the subcritical Reynolds number regime. 136 refs., 67 figs., 13 tabs.
Reynolds and froude number effect on the flow past an interface-piercing circular cylinder
Koo Bonguk
2014-09-01
Full Text Available The two-phase turbulent flow past an interface-piercing circular cylinder is studied using a high-fidelity orthogonal curvilinear grid solver with a Lagrangian dynamic subgrid-scale model for large-eddy simulation and a coupled level set and volume of fluid method for air-water interface tracking. The simulations cover the sub-critical and critical and post critical regimes of the Reynolds and sub and super-critical Froude numbers in order to investigate the effect of both dimensionless parameters on the flow. Significant changes in flow features near the air-water interface were observed as the Reynolds number was increased from the sub-critical to the critical regime. The interface makes the separation point near the interface much delayed for all Reynolds numbers. The separation region at intermediate depths is remarkably reduced for the critical Reynolds number regime. The deep flow resembles the single-phase turbulent flow past a circular cylinder, but includes the effect of the free-surface and the limited span length for sub-critical Reynolds numbers. At different Froude numbers, the air-water interface exhibits significantly changed structures, including breaking bow waves with splashes and bubbles at high Froude numbers. Instantaneous and mean flow features such as interface structures, vortex shedding, Reynolds stresses, and vorticity transport are also analyzed. The results are compared with reference experimental data available in the literature. The deep flow is also compared with the single-phase turbulent flow past a circular cylinder in the similar ranges of Reynolds numbers. Discussion is provided concerning the limitations of the current simulations and available experimental data along with future research
Reynolds and froude number effect on the flow past an interface-piercing circular cylinder
Koo, Bonguk; Yang, Jianming; Yeon, Seong Mo; Stern, Frederick
2014-09-01
The two-phase turbulent flow past an interface-piercing circular cylinder is studied using a high-fidelity orthogonal curvilinear grid solver with a Lagrangian dynamic subgrid-scale model for large-eddy simulation and a coupled level set and volume of fluid method for air-water interface tracking. The simulations cover the sub-critical and critical and post critical regimes of the Reynolds and sub and super-critical Froude numbers in order to investigate the effect of both dimensionless parameters on the flow. Significant changes in flow features near the air-water interface were observed as the Reynolds number was increased from the sub-critical to the critical regime. The interface makes the separation point near the interface much delayed for all Reynolds numbers. The separation region at intermediate depths is remarkably reduced for the critical Reynolds number regime. The deep flow resembles the single-phase turbulent flow past a circular cylinder, but includes the effect of the free-surface and the limited span length for sub-critical Reynolds numbers. At different Froude numbers, the air-water interface exhibits significantly changed structures, including breaking bow waves with splashes and bubbles at high Froude numbers. Instantaneous and mean flow features such as interface structures, vortex shedding, Reynolds stresses, and vorticity transport are also analyzed. The results are compared with reference experimental data available in the literature. The deep flow is also compared with the single-phase turbulent flow past a circular cylinder in the similar ranges of Reynolds numbers. Discussion is provided concerning the limitations of the current simulations and available experimental data along with future research
Reynolds and froude number effect on the flow past an interface-piercing circular cylinder
Koo Bonguk; Yang Jianming; Yeon Seong Mo; Stern Frederick
2014-01-01
The two-phase turbulent flow past an interface-piercing circular cylinder is studied using a high-fidelity orthogonal curvilinear grid solver with a Lagrangian dynamic subgrid-scale model for large-eddy simulation and a coupled level set and volume of fluid method for air-water interface tracking. The simulations cover the sub-critical and critical and post critical regimes of the Reynolds and sub and super-critical Froude numbers in order to investigate the effect of both dimensionless param...
Acampora, Antonio; Georgakis, Christos T.
2013-01-01
vary from those estimated through use of aerodynamic coefficients of single circular cylinders, as reported in literature. To address this issue, wind tunnel tests were performed on a 1:2.3 scale section model of the Øresund Bridge cables, with and without the presence of helical fillets. In this paper......Moderate vibrations continue to be recorded on the Øresund Bridge twin-stay cables. System identification techniques have been applied to investigate the aerodynamic characteristics of the cables based on ambient vibration measurements. As might be expected, the measured aerodynamic damping ratios...
Numerical Simulation of Polymer Injection in Turbulent Flow Past a Circular Cylinder
Richter, David
2011-01-01
Using a code developed to compute high Reynolds number viscoelastic flows, polymer injection from the upstream stagnation point of a circular cylinder is modeled at Re = 3900. Polymer stresses are represented using the FENE-P constitutive equations. By increasing polymer injection rates within realistic ranges, significant near wake stabilization is observed. Rather than a turbulent detached shear layer giving way to a chaotic primary vortex (as seen in Newtonian flows at high Re), a much more coherent primary vortex is shed, which possesses an increased core pressure as well as a reduced level of turbulent energy. © 2011 American Society of Mechanical Engineers.
Stabilization of vortices in the wake of a circular cylinder using harmonic forcing
Chamoun, George Chaouki; Schilder, Frank; Brøns, Morten
2011-01-01
We explore whether vortex flows in the wake of a fixed circular cylinder can be stabilized using harmonic forcing. We use Fo¨ppl's point vortex model augmented with a harmonic point source-sink mechanism which preserves conservation of mass and leaves the system Hamiltonian. We discover a region of...... Lyapunov-stable vortex motion for an appropriate selection of parameters. We identify four unique parameters that affect the stability of the vortices: the uniform flow velocity, vortex equilibrium positions, forcing amplitude, and forcing frequency. We assess the robustness of the controller using a...
Cohen, Raymond; Iaccarino, Gianluca
2005-11-01
Previously published exprimental data of the flow around two circular cylinders arranged in tandem have shown that for small spacings between the cylinders, the shear layer from the upstream cylinder reattaches to the downstream cylinder, hence creating a recirculation region in between the two cylinders. The experimental data was obtained at Re=65,000 and it was found that beyond a critical spacing (L/D ˜ 4.0), the upstream shear layer ceases to attach to the downstream cylinder, resulting in a dramatic change in the flow mechanisms. Previous numerical studies using two-dimensional RANS and URANS were unsatisfactory at predicting the length of the recirculation region of the upstream cylinder and consequently badly predicted the hydrodynamic forces between the two cylinders. In this study, Large Eddy Simulation with a dynamic Smagorinsky subgrid-scale model was used to investigate the flow around two circular cylinders arranged in tandem. Results from high Reynolds numbers simulations will be presented and practical considerations in using LES in such a flow configuration will be discussed.
LARGE-EDDY AND DETACHED-EDDY SIMULATIONS OF THE SEPARATED FLOW AROUND A CIRCULAR CYLINDER
无
2007-01-01
The separated turbulent flow around a circular cylinder is investigated using Large-Eddy Simulation (LES), Detached-Eddy Simulation (DES, or hybrid RANS/LES methods), and Unsteady Reynolds-Averaged Navier-Stokes (URANS). The purpose of this study is to examine some typical simulation approaches for the prediction of complex separated turbulent flow and to clarify the capability of applying these approaches to a typical case of the separated turbulent flow around a circular cylinder. Several turbulence models, I.e. Dynamic Sub-grid Scale (SGS) model in LES, the DES-based Spalart-Allmaras (S-A) and Shear-Stress- Transport (SST) models in DES, and the S-A and SST models in URANS, are used in the calculations. Some typical results, e.g., the mean pressure and drag coefficients, velocity profiles, Strouhal number, and Reynolds stresses, are obtained and compared with previous computational and experimental data. Based on our extensive calculations, we assess the capability and performance of these simulation approaches coupled with the relevant turbulence models to predict the separated turbulent flow.
Second-order wave diffraction by a circular cylinder using scaled boundary finite element method
The scaled boundary finite element method (SBFEM) has achieved remarkable success in structural mechanics and fluid mechanics, combing the advantage of both FEM and BEM. Most of the previous works focus on linear problems, in which superposition principle is applicable. However, many physical problems in the real world are nonlinear and are described by nonlinear equations, challenging the application of the existing SBFEM model. A popular idea to solve a nonlinear problem is decomposing the nonlinear equation to a number of linear equations, and then solves them individually. In this paper, second-order wave diffraction by a circular cylinder is solved by SBFEM. By splitting the forcing term into two parts, the physical problem is described as two second-order boundary-value problems with different asymptotic behaviour at infinity. Expressing the velocity potentials as a series of depth-eigenfunctions, both of the 3D boundary-value problems are decomposed to a number of 2D boundary-value sub-problems, which are solved semi-analytically by SBFEM. Only the cylinder boundary is discretised with 1D curved finite-elements on the circumference of the cylinder, while the radial differential equation is solved completely analytically. The method can be extended to solve more complex wave-structure interaction problems resulting in direct engineering applications.
RICHTER, DAVID
2010-03-29
The results from a numerical investigation of inertial viscoelastic flow past a circular cylinder are presented which illustrate the significant effect that dilute concentrations of polymer additives have on complex flows. In particular, effects of polymer extensibility are studied as well as the role of viscoelasticity during three-dimensional cylinder wake transition. Simulations at two distinct Reynolds numbers (Re = 100 and Re = 300) revealed dramatic differences based on the choice of the polymer extensibility (L2 in the FENE-P model), as well as a stabilizing tendency of viscoelasticity. For the Re = 100 case, attention was focused on the effects of increasing polymer extensibility, which included a lengthening of the recirculation region immediately behind the cylinder and a sharp increase in average drag when compared to both the low extensibility and Newtonian cases. For Re = 300, a suppression of the three-dimensional Newtonian mode B instability was observed. This effect is more pronounced for higher polymer extensibilities where all three-dimensional structure is eliminated, and mechanisms for this stabilization are described in the context of roll-up instability inhibition in a viscoelastic shear layer. © 2010 Cambridge University Press.
Dynamic response of a clamped/free hollow circular cylinder under travelling torsional impact loads
Impact-induced vibrations in the casing of a gas centriguge due to a sudden failure of the spinning rotor (crash) can cause structural disintegrity of the casing. In order to study the influence of the rotor failure bahaviour and the impact load histories on the dynamic response of the casing, a simple crash model is proposed in this paper to analyse the transient torsional response due to tangential components of the impact loads. The casing is modeled as a linear-elastic hollow circular cylinder, clamped at the lower end and free at the upper end. The rotor is thought to breakup in identical sections in a sequence determined by its fracture behaviour. Each section is assumed to cause an axi-symmetric load distribution at the inner surface of the casing. Therefore the problem is essentially reduced to the analysis of a clamped/free cylinder under travelling torsional impact loads. The problem is solved by representing the impact loads as local pulses acting over the length of the sections. A perturbation method is used to show that the general two-dimensional theory of axi-symmetric torsional wave propagation in circular cylinders, for the problem under consideration, may be approximated by the elementary one-dimensional theory. Solutions are obtained according to the usual modal expansion approach. Measurements of transient torsional responses are shown to be in good agreement with the calculated responses by choosing a suitable shape of the pulses. The effects of travelling velocity and pulse shape are investigated. Finally the transfer of kinetic energy in the rotor to vibrational energy of torsion in the casing is studied. (orig.)
Plane section of cone and cylinder in computer geometry
Obradović Ratko M.
2005-01-01
Full Text Available In this paper a mathematical apparatus for determination of plane section of cone and cylinder was formed. By using the descriptive geometric approach the contour lines of these quadrics were determined. The fact that the tangent lines of a circle could be transformed to the tangent lines of an ellipse using affinity was employed. In that way surfaces are represented by contour lines (tangent lines of basic ellipse in oblique projection and thus they have a realistic view. Intersecting plane α is a plane normal to a frontal plane. For determination of intersecting points of intersecting curve between the plane α and the quadrics, the lock of auxiliary planes, which contain the vertex of quadrics, was used. Each auxiliary plane from the observed lock intersect the surface in two lines which intersect the given plane α in two points. By using a sufficient number of auxiliary planes the intersecting curve as a set of pairs of points for all auxiliary planes is determined and the intersecting curve was drawn by lightening of these pairs of points on the graphical screen.
This experimental study investigated the characteristics of flow induced vibration of two elastically supported circular cylinders in a side by side arrangement. In particular, the characteristics of the flow induced vibration of the two cylinders are investigated by changing the flow speed at each spacing ratio L/D (L is the space between two cylinders and D is the diameter of the cylinder). To clarify the mechanism generating the flow induced vibration of the cylinders, the flow patterns around the two vibrating cylinders are also investigated using a flow visualization test that reproduces the flow induced vibration of the cylinders with a forced vibration apparatus. As a result, it is clarified that the flow induced vibration characteristics of the two cylinders arranged side by side switch among four patterns as the flow between the two cylinders is switched. Among the three arrangements considered (tandem, staggered, and side by side), the arrangement that generates flow induced vibration of the two cylinders most easily is the side by side arrangement
On vortex shedding and prediction of vortex-induced vibrations of circular cylinders
Halse, Karl Henning
1997-12-31
In offshore installations, many crucial components can be classified as slender marine structures: risers, mooring lines, umbilicals and cables, pipelines. This thesis studies the vortex shedding phenomenon and the problem of predicting vortex-induced vibrations of such structures. As the development of hydrocarbons move to deeper waters, the importance of accurately predicting the vortex-induced response has increased and so the need for proper response prediction methods is large. This work presents an extensive review of existing research publications about vortex shedding from circular cylinders and the vortex-induced vibrations of cylinders and the different numerical approaches to modelling the fluid flow. The response predictions from different methods are found to disagree, both in response shapes and in vibration amplitudes. This work presents a prediction method that uses a fully three-dimensional structural finite element model integrated with a laminar two-dimensional Navier-Stokes solution modelling the fluid flow. This solution is used to study the flow both around a fixed cylinder and in a flexibly mounted one-degree-of-freedom system. It is found that the vortex-shedding process (in the low Reynolds number regime) is well described by the computer program, and that the vortex-induced vibration of the flexibly mounted section do reflect the typical dynamic characteristics of lock-in oscillations. However, the exact behaviour of the experimental results found in the literature was not reproduced. The response of the three-dimensional structural model is larger than the expected difference between a mode shape and a flexibly mounted section. This is due to the use of independent hydrodynamic sections along the cylinder. The predicted response is not unrealistic, and the method is considered a powerful tool. 221 refs., 138 figs., 36 tabs.
3D UTD Modeling of a Measured Antenna Disturbed by a Dielectric Circular Cylinder in WBAN Context
Plouhinec, Eric; Uguen, Bernard; Mhedhbi, Meriem; Avrillon, Stéphane
2014-01-01
This paper describes a work realized for On-Body antennas characterization: the 3D deterministic modeling of a measured antenna disturbed by a dielectric circular cylinder of finite length. This prediction model is based on the ray-tracing technique for the electromagnetic wave paths search and the Uniform Theory of Diffraction (UTD) for the modeling of the electromagnetic waves interactions with the cylinder. After a detailed description, the model is validated in 3D with measurements made f...
Limiting Geometries of Two Circular Maldacena-Wilson Loop Operators
Arutyunov, G.; Plefka, J.; Staudacher, M.
2001-01-01
We further analyze a recent perturbative two-loop calculation of the expectation value of two axi-symmetric circular Maldacena-Wilson loops in [Script N] = 4 gauge theory. Firstly, it is demonstrated how to adapt the previous calculation of anti-symmetrically oriented circles to the symmetric case. By shrinking one of the circles to zero size we then explicitly work out the first few terms of the local operator expansion of the loop. Our calculations explicitly demonstrate that circular Mald...
Maeda, G. (University of the Ryukyus, Okinawa (Japan))
1992-09-01
Concerning the pressure distribution around a circular cylinder placed in uniform flow, there is a big difference between theoretical analysis and test results of potential flow. This is because vortex street is formed due to boundary layer separation in real viscous flow. In this study, placing a circular cylinder in the middle of uniform flow between two parallel walls, the potential flow around the cylinder was analyzed in the case where Karman vortex street is formed behind the cyinder. Static pressure on the surface of the cylinder near the positions where vortex is formed is supposed to decrease because of energy transfer to the vortex. Magnitude of the pressure drop is then calculated from the strength of the vortex obtained in the test. The pressure distribution around the circular cylinder without vortex has minimum pressure coefficient of about [minus]3 and occurs at 90[degree]. When Karman vortex street is placed downstream, minimum pressure coefficient is about [minus]2 and its position is around 80[degree]. It is also clarified that the profile of the pressure distribution around the cylinder almost agrees with the test result. 4 refs., 10 figs.
Sobera, M.P.; Kleijn, C.R.
2008-01-01
We study flow and heat transfer to a cylinder in cross flow at Re = 3,900–80,000 by means of three-dimensional transient RANS (T-RANS) simulations, employing an RNG k − ε turbulence model. Both the case of a bare solid cylinder and that of a solid cylinder surrounded at some fixed distance by a thin porous layer have been studied. The latter configuration is a standard test geometry for measuring the insulating and protective performance of garments. In this geometry, the flow in the space be...
Numerical investigation of flow and scour around a vertical circular cylinder
Baykal, Cüneyt; Sumer, B. Mutlu; Fuhrman, David R.;
2015-01-01
Flow and scour around a vertical cylinder exposed to current are investigated by using a three-dimensional numerical model based on incompressible Reynoldsaveraged Navier–Stokes equations. The model incorporates (i) k-ω turbulence closure, (ii) vortexshedding processes, (iii) sediment transport...... (both bed and suspended load), as well as (iv) bed morphology. The influence of vortex shedding and suspended load on the scour are specifically investigated. For the selected geometry and flow conditions, it is found that the equilibrium scour depth is decreased by 50% when the suspended sediment...
An unsteady thermoelastic study, taking consideration of the length effects, was made of a finite short circular cylinder under an arbitrary heat supply along its cylindrical surface in the longitudinal direction. The analysis was treated by the thermoelastic potential method using a general form of the Love's displacement function which has not so far been used. The results obtained were compared with those of an approximate solution for the finite cylinder using Saint-Venant's principle. From the results the effects of the length-to-diameter ratio evidently appear in the transient thermal stress distributions for the finite short cylinder. (Auth.)
Lei Shi; Chengchun Zhang; Jing Wang; Luquan Ren
2012-01-01
Flow control can effectively reduce the aerodynamic noise radiated from a circular cylinder.As one of the flow control methods,a bionic method,inspired by the serrations at the leading edge of owls' wing,was proposed in this paper.The effects of bionic serrated structures arranged on the upper and lower sides of a cylinder on the aerodynamic and aeroacoustic performance of the cylinder were numerically investigated.At a free stream speed of 24.5 m·s-1,corresponding to Reynolds number of 1.58 × 104,the simulation results indicate that the bionic serrated structures can decrease the frequency of the vortex shedding and control the fluctuating aerodynamic force acting on the cylinder,thus reduce the aerodynamic noise.A qualitative-view of the vorticity in the wake of the cylinder suggest that the serrated structures reduce aerodynamic sound by suppressing the unsteady motion of vortices.
Limiting geometries of two circular Maldacena-Wilson loop operators
We further analyze a recent perturbative two-loop calculation of the expectation value of two axi-symmetric circular Maldacena-Wilson loops in N=4 gauge theory. Firstly, it is demonstrated how to adapt the previous calculation of anti-symmetrically oriented circles to the symmetric case. By shrinking one of the circles to zero size we then explicitly work out the first few terms of the local operator expansion of the loop. Our calculations explicitly demonstrate that circular Maldacena-Wilson loops are non-BPS observables precisely due to the appearance of unprotected local operators. The latter receive anomalous scaling dimensions from non-ladder diagrams. Finally, we present new insights into a recent conjecture claiming that coincident circular Maldacena-Wilson loops are described by a Gaussian matrix model. We report on a novel, supporting two-loop test, but also explain and illustrate why the existing arguments in favor of the conjecture are flawed. (author)
Edge properties of principal fractional quantum Hall states in the cylinder geometry
Soulé, Paul; Jolicoeur, Thierry
2012-01-01
We study fractional quantum Hall states in the cylinder geometry with open boundaries. We focus on principal fermionic 1/3 and bosonic 1/2 fractions in the case of hard-core interactions. The gap behavior as a function of the cylinder radius is analyzed. By adding enough orbitals to allow for edge modes we show that it is possible to measure the Luttinger parameter of the non-chiral liquid formed by the combination of the two counterpropagating edges when we add a small confining potential. W...
Piezoelectric energy harvesting from vortex-induced vibrations of circular cylinder
Mehmood, A.; Abdelkefi, A.; Hajj, M. R.; Nayfeh, A. H.; Akhtar, I.; Nuhait, A. O.
2013-09-01
The concept of harvesting energy from a circular cylinder undergoing vortex-induced vibrations is investigated. The energy is harvested by attaching a piezoelectric transducer to the transverse degree of freedom. Numerical simulations are performed for Reynolds numbers (Re) in the range 96≤Re≤118, which covers the pre-synchronization, synchronization, and post-synchronization regimes. Load resistances (R) in the range 500 Ω≤R≤5 MΩ are considered. The results show that the load resistance has a significant effect on the oscillation amplitude, lift coefficient, voltage output, and harvested power. The results also show that the synchronization region widens when the load resistance increases. It is also found that there is an optimum value of the load resistance for which the harvested power is maximum. This optimum value does not correspond to the case of largest oscillations, which points to the need for a coupled analysis as performed here.
Bouakkaz, R.; Talbi, K.; Khelil, Y.; Salhi, F.; Belghar, N.; Ouazizi, M.
2014-01-01
The heat transfer and air flow around an unconfined heated rotating circular cylinder is investigated numerically for varying rotation rates ( α = 0-6) in the Reynolds number range of 20-200. The numerical calculations are carried out by using a finite volume method based commercial computational fluid dynamics solver FLUENT. The successive changes in the flow pattern are studied as a function of the rotation rate. Suppression of vortex shedding occurs as the rotation rate increases ( α > 2). A second kind of instability appears for higher rotation speed where a series of counter-clockwise vortices is shed in the upper shear layer. The rotation attenuates the secondary instability and increases the critical Reynolds number for the appearance of this instability. Besides, time-averaged (lift and drag coefficients and Nusselt number) results are obtained and compared with the literature data. A good agreement has been obtained for both the local and averaged values.
Experimental study of ice accretion on circular cylinders at moderate low temperatures
Koss, Holger H.; Gjelstrup, Henrik; Georgakis, Christos T.
For the assessment of aerodynamic instability of iced bridge cables various calculation models are available. Input for these models are amongst others aerodynamic load coefficients usually determined in wind tunnel tests on generic or simplified models of iced cable sections. Even though icing of...... structures is widely studied, the particular climatic boundary conditions regarding bridge cable vibrations have so far been omitted. The presented study was performed in March 2009 in the Altitude Icing Wind Tunnel at the National Research Council of Canada (NRC) in Ottawa with the purpose of establishing...... detailed knowledge on the shape characteristics of ice accretion on circular cylinders under the specific conditions where large amplitude vibration of iced bridge have been observed in nature. Hence, the study shall serve as a reference and the results will be used for validation of numerical and...
A PIV study of the wake of a circular cylinder subjected to low amplitude flow perturbations
The 'locked-on' vortex shedding patterns resulting from the interaction of a fixed circular cylinder and an approaching flow with low-amplitude perturbations superimposed on it was studied by means of PIV measurements. The forced wake exhibits two different wake modes or states for a perturbation frequency below twice that of the natural vortex shedding frequency; the first one is a Karman-like vortex street formed by shedding of two single vortices per cycle (2S mode), whereas the other is most appropriately characterised by the splitting of the shed vortices into pairs (2P mode). For a perturbation frequency above twice that of the natural shedding frequency only the 2S mode is observed. Proper orthogonal decomposition is employed to further elucidate the existence of the two wake modes. (authors)
Torsion of Noncircular Composite Cylinders
Rouse, Marshall; Hyer, Michael W.; Haynie, Waddy T.
2005-01-01
The paper presents a brief overview of the predicted deformation and failure characteristics of noncircular composite cylinders subjected to torsion. Using a numerical analysis, elliptical cylinders with a minor-to-major diameter ratio of 0.7 are considered. Counterpart circular cylinders with the same circumference as the elliptical cylinders are included for comparison. The cylinders are constructed of a medium-modulus graphite-epoxy material in a quasi-isotropic lay-up. Imperfections generated from the buckling mode shapes are included in the initial cross-sectional geometry of the cylinders. Deformations until first fiber failure, as predicted using the maximum stress failure criterion and a material degradation scheme, are presented. For increasing levels of torsion, the deformations of the elliptical cylinders, in the form of wrinkling of the cylinder wall, occur primarily in the flatter regions of the cross section. By comparison the wrinkling deformations of the circular cylinders are more uniformly distributed around the circumference. Differences in the initial failure and damage progression and the overall torque vs. twist relationship between the elliptical and circular cylinders are presented. Despite differences in the response as the cylinders are being loaded, at first fiber failure the torque and twist for the elliptical and circular cylinders nearly coincide.
Strouhal number effect on synchronized vibration range of a circular cylinder in cross flow
Synchronized vibrations were measured for a circular cylinder subjected to a water cross flow in the subcritical Reynolds numbers in order to compare the synchronized vibration range between the subcritical and supercritical regions and clarify the effect of the Strouhal number on it. A small peak vibration in the lift direction was found when the Karman vortex shedding frequency was about 1/5 of the cylinder natural frequency in only the subcritical region. The ratio of the Karman vortex frequency to the natural frequency where the self-excited vibration in the drag direction by the symmetrical vortices began was about 1/4 in the subcritical region, and increased to 0,32 at the Strouhal number of 0,29 in the supercritical region. The frequency ratio at the beginning of the lock-in vibration in the drag direction by the Karman vortex was about 1/2, and that in the lift direction decreased from 1 to about 0,8 with decreasing Strouhal number. (author)
Three-dimensional flow around two circular cylinders in tandem arrangement
Deng, Jian; Ren, An-Lu; Zou, Jian-Feng; Shao, Xue-Ming
2006-06-01
The spatial evolutions of vortices and transition to three dimensionality in the wake of two tandem circular cylinders are numerically studied. The virtual body method developed from virtual boundary method is applied to model the no-slip boundary condition of the cylinders. Two different aspects of this problem are considered. Firstly, the spacing ratio L/D is varied from 1.5 to 8 and the Reynolds number is set unchanged at Re=220. It is shown that three dimensionality appears in the wake for L/D⩾4, whereas the flow wake keeps a two-dimensional state for L/D⩽3.5. The critical spacing for the appearance of three-dimensional instability is deduced at the range of 3.5two-dimensional case. For L/D=3.5, a mode of small-scale three-dimensional instability, named mode A, is observed to appear at Re=250 and persists over the Reynolds number range of 250-270. The three-dimensional results are compared with the two-dimensional flow with the same configuration.
Numerical investigation of the flow around two circular cylinders in tandem
Carmo, B. S.; Meneghini, J. R.
2006-08-01
The incompressible flow around pairs of circular cylinders in tandem arrangements is investigated in this paper. The spectral element method is employed to carry out two- and three-dimensional simulations of the flow. The centre-to-centre distance (l) of the investigated configurations varies from 1.5 to 8 diameters (D), and results thus obtained are compared to the isolated cylinder case. The simulations are in the Reynolds number (Re) range from 160 to 320, covering the transition in the wake. Our analysis focuses on the small-scale instabilities of vortex shedding, which occurs in the Re range investigated. With the aid of Strouhal data and vorticity contours, we propose mechanisms to explain the interference phenomenon and its interaction with the three-dimensional vortical structures present in the flow field. It is found that, for Re>190, when three-dimensional structures are present in the flow field, two-dimensional simulations are not sufficient to predict the (Re,l) pair of drag inversion.
Energy Harvester Based on the Synchronization Phenomenon of a Circular Cylinder
Junlei Wang
2014-01-01
Full Text Available A concept of generating power from a circular cylinder undergoing vortex-induced vibration (VIV was investigated. Two lead zirconate titanate (PZT beams which had high power density were installed on the cylinder. A theoretical model has been presented to describe the electromechanical coupling of the open-circuit voltage output and the vibration amplitudes based on a second-order nonlinear Van der pol equation and Gauss law. A numerical computation was applied to measure the capacity of the power generating system. The lift and drag coefficient and the vortex shedding frequency were obtained to verify how the nondimensional parameter reduced velocity Ur affects the fluid field. Meanwhile, a single-degree of freedom system has been added to describe the VIV, presynchronization, and synchronization together with postsynchronization regimes of oscillating frequencies. And the amplitudes of the vibration have been obtained. Finally, the vibrational amplitudes and the voltage output could go up to a high level in the synchronization region. The maximum value of the voltage output and the corresponding reduced velocity Ur were 8.42 V and 5.6, respectively.
Guo-qiang Tang
2015-10-01
Full Text Available Fluid flow past twin circular cylinders in a tandem arrangement placed near a plane wall was investigated by means of numerical simulations. The two-dimensional Navier-Stokes equations were solved with a three-step finite element method at a relatively low Reynolds number of Re = 200 for various dimensionless ratios of and , where D is the cylinder diameter, L is the center-to-center distance between the two cylinders, and G is the gap between the lowest surface of the twin cylinders and the plane wall. The influences of and on the hydrodynamic force coefficients, Strouhal numbers, and vortex shedding modes were examined. Three different vortex shedding modes of the near wake were identified according to the numerical results. It was found that the hydrodynamic force coefficients and vortex shedding modes are quite different with respect to various combinations of and . For very small values of , the vortex shedding is completely suppressed, resulting in the root mean square (RMS values of drag and lift coefficients of both cylinders and the Strouhal number for the downstream cylinder being almost zero. The mean drag coefficient of the upstream cylinder is larger than that of the downstream cylinder for the same combination of and . It is also observed that change in the vortex shedding modes leads to a significant increase in the RMS values of drag and lift coefficients.
Wei, Q; Mazzitelli, F C Lombardo F D; Onofrio, R
2011-01-01
We report on measurements performed on an apparatus aimed to study the Casimir force in the cylinder-plane configuration. The electrostatic calibrations evidence anomalous behaviors in the dependence of the electrostatic force and the minimizing potential upon distance. We discuss analogies and differences of these anomalies with respect to those already observed in the sphere-plane configuration. At the smallest explored distances we observe frequency shifts of non-Coulombian nature preventing the measurement of the Casimir force in the same range. We also report on measurement performed in the parallel plane configuration, showing that the dependence on distance of the minimizing potential, if present at all, is milder than in the sphere-plane or cylinder-plane geometries. General considerations on the interplay between the distance-dependent minimizing potential and the precision of Casimir force measurements in the range relevant to detect the thermal corrections for all geometries are finally reported.
Continuous dependence on initial geometry in linear elastodynamics on a half cylinder
Knops, R.J.; Quintanilla de Latorre, Ramón
2009-01-01
Continuous dependence on the initial time geometry is established for the mean-square integral of the displacement in a linear inhomogeneous anisotropic elastic semi-infinite cylinder in motion subject to a prescribed time-dependent base displacement and initial data. A bound, newly derived for the total energy, in conjunction with backward continuation in time of the unperturbed and perturbed displacements, is employed to obtain the result. Peer Reviewed
Ghazanfarian, Jafar; Saghatchi, Roozbeh; Gorji-Bandpy, Mofid
2015-12-01
This paper studies the two-dimensional (2D) water-entry and exit of a rotating circular cylinder using the Sub-Particle Scale (SPS) turbulence model of a Lagrangian particle-based Smoothed-Particle Hydrodynamics (SPH) method. The full Navier-Stokes (NS) equations along with the continuity have been solved as the governing equations of the problem. The accuracy of the numerical code is verified using the case of water-entry and exit of a nonrotating circular cylinder. The numerical simulations of water-entry and exit of the rotating circular cylinder are performed at Froude numbers of 2, 5, 8, and specific gravities of 0.25, 0.5, 0.75, 1, 1.75, rotating at the dimensionless rates of 0, 0.25, 0.5, 0.75. The effect of governing parameters and vortex shedding behind the cylinder on the trajectory curves, velocity components in the flow field, and the deformation of free surface for both cases have been investigated in detail. It is seen that the rotation has a great effect on the curvature of the trajectory path and velocity components in water-entry and exit cases due to the interaction of imposed lift and drag forces with the inertia force.
2008-01-01
In our previous study, the effects of the interval between the cylinder and the airfoil on the aerodynamic sound were investigated and compared with the cases of single circular and single airfoil. In this study, the effects of the attack angle of the airfoil located downstream on the characteristics of aerodynamic sound and the wake structure are investigated at a given interval between the cylinder and the airfoil. It is found that the sound pressure level of DFN and the peak frequency decrease with increasing attack angle of airfoil because of the diffusive wake structure due to the increased back pressure of circular cylinder, which is caused by the blocking effect of airfoil. It is shown that the sound sources are corresponded to the attack points of shedding vortex form the upstream circular cylinder to the downstream airfoil. We conclude that the pressure fluctuation at the airfoil surface effects on the sound pressure level, from the flow visualizations and the exploration test of sound source.
Todorov, M D
1998-01-01
The classical Helmholtz problem is applied for modelling and numerical investigation of inviscid cusp-ended separated flow around circular cylinder. Two coordinate systems are used: polar for initial calculations and parabolic as topologically most suited for infinite stagnation zone. Scaling by the shape of the unknown free line renders the problem to computational domain with fixed boundaries. Difference schemes and algorithm for Laplace equation and for Bernoulli integral are devised. A separated flow with drag coefficient $C_x=0$ like the so called ``critical'' flow is obtained. The pressure distribution on the surface of cylinder and the detachment point compares quantitatively very well with the predictions of the hodograph method.
A Comparison of Ultrasound Tomography Methods in Circular Geometry
Leach, R R; Azevedo, S G; Berryman, J G; Bertete-Aquirre, H R; Chambers, D H; Mast, J E; Littrup, P; Duric, N; Johnson, S A; Wuebbeling, F
2002-01-24
Extremely high quality data was acquired using an experimental ultrasound scanner developed at Lawrence Livermore National Laboratory using a 2D ring geometry with up to 720 transmitter/receiver transducer positions. This unique geometry allows reflection and transmission modes and transmission imaging and quantification of a 3D volume using 2D slice data. Standard image reconstruction methods were applied to the data including straight-ray filtered back projection, reflection tomography, and diffraction tomography. Newer approaches were also tested such as full wave, full wave adjoint method, bent-ray filtered back projection, and full-aperture tomography. A variety of data sets were collected including a formalin-fixed human breast tissue sample, a commercial ultrasound complex breast phantom, and cylindrical objects with and without inclusions. The resulting reconstruction quality of the images ranges from poor to excellent. The method and results of this study are described including like-data reconstructions produced by different algorithms with side-by-side image comparisons. Comparisons to medical B-scan and x-ray CT scan images are also shown. Reconstruction methods with respect to image quality using resolution, noise, and quantitative accuracy, and computational efficiency metrics will also be discussed.
Critical heat flux in circular tube geometries using Freon-12
Experimental and analytical investigations on critical heat flux have been performed in circular tubes of different diameters ranging from 2 mm to 16 mm. More than 1500 data points have been obtained in a large range of parameters: pressure 1.0 MPa to 3.0 MPa, mass flux 1.0 Mg/m2s to 6.0 Mg/m2s and exit steam quality -0.75 to +0.60. The effect of different parameters on CHF have been discussed. The test data have been compared with different CHF prediction methods. A very good agreement between the test data in the 8 mm diameter tube and the CHF look-up table shows that the test results in Freon-12 can be well transferred to water conditions by using fluid-to-fluid scaling laws available. The experimental data reveal that the effect of the tube diameter on CHF is governed mainly by exit steam quality and tube diameter itself. None of the equations or models available in the literature can reproduce the measured diameter effect with sufficient accuracy. (author)
Kirkil, Gokhan; Constantinescu, George
2015-07-01
The turbulent horseshoe vortex (HV) system and the near-wake flow past a circular cylinder mounted on a flat bed in an open channel are investigated based on the results of eddy-resolving simulations and supporting flow visualizations. Of particular interest are the changes in the mean flow and turbulence statistics within the HV region as the necklace vortices wrap around the cylinder's base and the variation of the mean flow and turbulence statistics in the near wake, in between the channel bed and the free surface. While it is well known that the drag crisis induces important changes in the flow past infinitely long circular cylinders, the changes are less understood and more complex for the case of flow past a surface-mounted cylinder. This is because even at very high cylinder Reynolds numbers, ReD, the flow regime remains subcritical in the vicinity of the bed surface due to the reduction of the incoming flow velocity within the bottom boundary layer. The paper provides a detailed discussion of the changes in the flow physics between cylinder Reynolds numbers at which the flow in the upstream part of the separated shear layers (SSLs) is laminar (ReD = 16 000, subcritical flow regime) and Reynolds numbers at which the transition occurs inside the attached boundary layers away from the bed and the flow within the SSLs is turbulent (ReD = 5 ∗ 105, supercritical flow regime). The changes between the two regimes in the dynamics and level of coherence of the large-scale coherent structures (necklace vortices, vortex tubes shed in the SSLs and roller vortices shed in the wake) and their capacity to induce high-magnitude bed friction velocities in the mean and instantaneous flow fields and to amplify the near-bed turbulence are analyzed. Being able to quantitatively and qualitatively describe these changes is critical to understand Reynolds-number-induced scale effects on sediment erosion mechanisms around cylinders mounted on a loose bed, which is a problem of
Dynamic viscoelastic effects on sound wave scattering by an eccentric compound circular cylinder
Hasheminejad, Seyyed M.; Kazemirad, Siavash
2008-12-01
The classical method of separation of variables in conjunction with the translational addition theorem for cylindrical wave functions are employed to obtain an exact solution for two-dimensional interaction of a harmonic plane acoustic wave with an infinitely long (visco)elastic circular cylinder which is eccentrically coated by another (visco)elastic material and is submerged in an ideal unbounded acoustic medium. The novel features of Havriliak-Negami model for dynamic viscoelastic material behaviour are used to take the rheological properties of the coating (and/or core) material into consideration. The analytical results are illustrated with numerical examples in which a steel rod eccentrically coated with (an eccentric steel shell filled with) dissipative materials of distinct viscoelastic properties is insonified by plane sound waves at selected angles of incidence. The effects of incident wave frequency, angle of incidence, core eccentricity and dynamic viscoelastic material properties on the backscattered form function spectra are examined. Limiting cases are considered and fair agreements with available solutions are obtained.
Turbulence statistics of flow over scoured cohesive sediment bed around circular cylinder
Debnath, K.; Manik, M. K.; Mazumder, B. S.
2012-06-01
The effect of clay content on the mean flow, turbulence intensities, Reynolds shear stress and conditional statistics of the Reynolds shear stress was investigated within and above the equilibrium scour hole around circular cylinder embedded in cohesive sediment bed having clay fractions 0.1 and 0.2. Detailed three dimensional velocity components were measured at three different cross-sections: upstream, sideward and downstream of the pier covering flow regions within and above the scour hole using 3D Micro acoustic Doppler velocimeter (ADV). It is observed that within the scour hole region the sweeping events play a dominant role at both the side and the front of the pier while the ejection events play a dominant role in the outer flow region. At the scour hole surface a thin layer of ejection dominant pocket is seen both at the pier front and the side. This resulted in kolk-boils phenomenon at the interface layer of sweep and ejection dominance which probably instigated the scouring process. In addition, the mean time interval of the turbulent bursting events within and above the scour hole is presented.
Analytical study of heat transfer from circular cylinder in liquid metals
Khan, W. A.; Culham, J. R.; Yovanovich, M. M.
2006-09-01
In this study the influence of a thin hydrodynamic boundary layer on the heat transfer from a single circular cylinder in liquid metals having low Prandtl number (0.004 0.03) is investigated under isothermal and isoflux boundary conditions. Two separate analytical heat transfer models, viscous and inviscid, are developed to clarify the discrepancy between previous results. For both models, integral approach of the boundary layer analysis is employed to derive closed form expressions for the calculation of the average heat transfer coefficients. For an inviscid model, the energy equation is solved using potential flow velocity only whereas for a viscous model, a fourth-order velocity profile is used in the hydrodynamic boundary layer and potential flow velocity is used outside the boundary layer. The third-order temperature profile is used inside the thermal boundary layer for both models. It is shown that the inviscid model gives higher heat transfer coefficients whereas viscous flow model gives heat transfer results in a fairly good agreement with the previous experimental/numerical results.
Analytical study of heat transfer from circular cylinder in liquid metals
Khan, W.A.; Culham, J.R.; Yovanovich, M.M. [University of Waterloo, Microelectronics Heat Transfer Laboratory, Department of Mechanical Engineering, Waterloo, ON (Canada)
2006-09-15
In this study the influence of a thin hydrodynamic boundary layer on the heat transfer from a single circular cylinder in liquid metals having low Prandtl number (0.004-0.03) is investigated under isothermal and isoflux boundary conditions. Two separate analytical heat transfer models, viscous and inviscid, are developed to clarify the discrepancy between previous results. For both models, integral approach of the boundary layer analysis is employed to derive closed form expressions for the calculation of the average heat transfer coefficients. For an inviscid model, the energy equation is solved using potential flow velocity only whereas for a viscous model, a fourth-order velocity profile is used in the hydrodynamic boundary layer and potential flow velocity is used outside the boundary layer. The third-order temperature profile is used inside the thermal boundary layer for both models. It is shown that the inviscid model gives higher heat transfer coefficients whereas viscous flow model gives heat transfer results in a fairly good agreement with the previous experimental/numerical results. (orig.)
Dinarvand Saeed; Abbassi Abbas; Hosseini Reza; Pop Ioan
2015-01-01
This article deals with the study of the steady axisymmetric mixed convective boundary layer flow of a nanofluid over a vertical circular cylinder with prescribed external flow and surface temperature. By means of similarity transformation, the governing partial differential equations are reduced into highly non-linear ordinary differential equations. The resulting non-linear system has been solved analytically using an efficient technique namely homotopy a...
Král, Radomil
2014-01-01
Roč. 77, October (2014), s. 906-914. ISSN 0017-9310 R&D Projects: GA MŠk(CZ) ED1.1.00/02.0060; GA ČR(CZ) GBP105/12/G059 Institutional support: RVO:68378297 Keywords : circular cylinder * unsteady heat transfer * temperature distribution * wind tunnel experiment * porous material Subject RIV: JN - Civil Engineering Impact factor: 2.383, year: 2014 http://www. science direct.com/ science /article/pii/S0017931014005171
García Aguilar, Andrés; Sipus, Zvonimir; Sierra Pérez, Manuel
2012-01-01
A novel formulation for the surface impedance characterization is introduced for the canonical problem of surface fields on a perfect electric conductor (PEC) circular cylinder with a dielectric coating due to a electric current source using the Uniform Theory of Diffraction (UTD) with an Impedance Boundary Condition (IBC). The approach is based on a TE/TM assumption of the surface fields from the original problem. Where this surface impedance fails, an optimization is performed to minimize t...
Král, Radomil
2014-01-01
Roč. 77, October (2014), s. 906-914. ISSN 0017-9310 R&D Projects: GA MŠk(CZ) ED1.1.00/02.0060; GA ČR(CZ) GBP105/12/G059 Institutional support: RVO:68378297 Keywords : circular cylinder * unsteady heat transfer * temperature distribution * wind tunnel experiment * porous material Subject RIV: JN - Civil Engineering Impact factor: 2.383, year: 2014 http://www.sciencedirect.com/science/article/pii/S0017931014005171
NUMERICAL SIMULATION OF AN OSCILLATING FLOW PAST A CIRCULAR CYLINDER IN THE VICINITY OF A PLANE WALL
SHAH Syed Bilai Hussain; LU Xi-yun
2008-01-01
Oscillating flow around a circular cylinder in the vicinity of a plane wall was investigated by solving the two-dimensional incompressible Navier-Stokes equations with a finite element Galarkin residual method. The effect of the gap G/D between the cylinder surface and the wall on the flow behavior was studied. For the case of G/D ≤ 0.25, the periodicity in the flow is attributed to both the outer shear layer instability and the oscillating frequency. As G/D > 0.25, vortex shedding occurs and the periodicity in the flow is mainly due to the competition of the oscillating frequency and the vortex shedding frequency from an isolated stationary cylinder.
Ding, H.; Shu, C.; Yeo, K. S.; Xu, D.
2007-01-01
In this paper, the mesh-free least square-based finite difference (MLSFD) method is applied to numerically study the flow field around two circular cylinders arranged in side-by-side and tandem configurations. For each configuration, various geometrical arrangements are considered, in order to reveal the different flow regimes characterized by the gap between the two cylinders. In this work, the flow simulations are carried out in the low Reynolds number range, that is, Re=100 and 200. Instantaneous vorticity contours and streamlines around the two cylinders are used as the visualization aids. Some flow parameters such as Strouhal number, drag and lift coefficients calculated from the solution are provided and quantitatively compared with those provided by other researchers.
3-D CFD simulation of natural convection of air over a circular cylinder in a cuboidal box
The objective of this study is to investigate the transient 3-D numerical simulations of natural convection of air around a circular cylinder (76.2 mm OD and 560 mm length) enclosed in a cuboidal box of 1000 mm X 600 mm X 1200 mm. The value of Ra number is 1.3 X 106. The 2-D numerical simulations are also performed and the comparison between the 2-D and 3-D numerical simulations has been presented in terms of Nusselt number. The effect of top wall to cylinder distance on the flow pattern has also been investigated for the case of conducting ceiling. The flow becomes unstable and oscillating depending on the distance between cylinder and ceiling. The time varying behavior of the Nu number has also shown. (author)
SOME OBSERVATIONS OF TWO INTERFERING VIV CIRCULAR CYLINDERS OF UNEQUAL DIAMETERS IN TANDEM
HUANG Shan; SWORN Andy
2011-01-01
Analysis of model test results was carried out to investigate the hydrodynamic interaction between a pair of elastically-supported rigid cylinders of dissimilar diameters in a water flume.The two cylinders are placed in tandem with one situated in the wake of the other.The diameter of the upstream cylinder is twice as large as that of the downstream cylinder.The spacing between the two cylinders ranges from 1 to 10 times the larger cylinder diameter.The Reynolds numbers are within the sub-critical range.The cylinders are free to oscillate in both the in-line and the cross-flow directions.The reduced velocity ranges from 1 to 10 and the low damping ratio of the model test set-up at 0.006 gives a combined m.ass-damping parameter of 0.02.It is found that the lift on and the cross-flow motion of the downstream cylinder have the frequency components derived from the upstream cylinder's vortex shedding as well as from its own vortex shedding,and the relative importance of the two sources of excitation is influenced by the spacing between the two cylinders.The downstream cylinder's VIV response appears to be largely dependent upon the actual reduced velocity of the cylinder.
Numerical investigation of flow and scour around a vertical circular cylinder.
Baykal, C; Sumer, B M; Fuhrman, D R; Jacobsen, N G; Fredsøe, J
2015-01-28
Flow and scour around a vertical cylinder exposed to current are investigated by using a three-dimensional numerical model based on incompressible Reynolds-averaged Navier-Stokes equations. The model incorporates (i) k-ω turbulence closure, (ii) vortex-shedding processes, (iii) sediment transport (both bed and suspended load), as well as (iv) bed morphology. The influence of vortex shedding and suspended load on the scour are specifically investigated. For the selected geometry and flow conditions, it is found that the equilibrium scour depth is decreased by 50% when the suspended sediment transport is not accounted for. Alternatively, the effects of vortex shedding are found to be limited to the very early stage of the scour process. Flow features such as the horseshoe vortex, as well as lee-wake vortices, including their vertical frequency variation, are discussed. Large-scale counter-rotating streamwise phase-averaged vortices in the lee wake are likewise demonstrated via numerical flow visualization. These features are linked to scour around a vertical pile in a steady current. PMID:25512595
Interaction theory of hypersonic laminar near-wake flow behind an adiabatic circular cylinder
Hinman, W. Schuyler; Johansen, C. T.
2015-12-01
The separation and shock wave formation on the aft-body of a hypersonic adiabatic circular cylinder were studied numerically using the open source software OpenFOAM. The simulations of laminar flow were performed over a range of Reynolds numbers (8× 10^3 < Re < 8× 10^4 ) at a free-stream Mach number of 5.9. Off-body viscous forces were isolated by controlling the wall boundary condition. It was observed that the off-body viscous forces play a dominant role compared to the boundary layer in displacement of the interaction onset in response to a change in Reynolds number. A modified free-interaction equation and correlation parameter has been presented which accounts for wall curvature effects on the interaction. The free-interaction equation was manipulated to isolate the contribution of the viscous-inviscid interaction to the overall pressure rise and shock formation. Using these equations coupled with high-quality simulation data, the underlying mechanisms resulting in Reynolds number dependence of the lip-shock formation were investigated. A constant value for the interaction parameter representing the part of the pressure rise due to viscous-inviscid interaction has been observed at separation over a wide range of Reynolds numbers. The effect of curvature has been shown to be the primary contributor to the Reynolds number dependence of the free-interaction mechanism at separation. The observations in this work have been discussed here to create a thorough analysis of the Reynolds number-dependent nature of the lip-shock.
Jordan, Stephen A.
2016-05-01
Long thin circular cylinders commonly serve as towed sonar tracking devices, where the radius-of-curvature along the longitudinal axis is quite low [ρr = O(10-4)]. Because no understanding presently exists about the direct impact of longitudinal curvature on the turbulent statistics, the long cylinder is simply viewed as a chain of straight segments at various (increasing then decreasing) small inclinations to the freestream direction. Realistically, even our statistical evidence along straight thin cylinders at low incidence angles is inadequate to build solid evidence towards forming reliable empirical models. In the present study, we address these shortcomings by executing Large-Eddy Simulations (LESs) of straight and longitudinally curved thin cylinders at low to moderate turbulent radius-based Reynolds numbers (500 ≤ Rea ≤ 3500) and small angles-of-incidence (α = 0° → 9°). Coupled with the previous experimental measurements and numerical results, the new expanded database (311 ≤ Rea ≤ 56 500) delivered sufficient means to propose power-law expressions for the longitudinal evolution of the skin friction, normal drag, and turbulent boundary layer (TBL) length scales. Surprisingly, the LES computations of the curved cylinders at analogous geometric and kinematic conditions as the straight cylinder showed similar character in terms of the longitudinal skin friction. Beyond incidence 1°-3° (upper end corresponds to the highest simulated Rea), the skin friction was directly proportional to the yaw angle and monotonically shifted downward with higher Rea. Conversely, the flow structure, normal drag, TBL length scales, Reynolds stresses, and the separation state of the transverse shear layers towards regular vortex shedding for the curved cylinder were highly dissimilar than the straight one at equivalent incidence angles.
Machynia, Adam
Analytic solutions to the static and stationary boundary value field problems relative to an arbitrary configuration of parallel cylinders are obtained by using translational addition theorems for scalar Laplacian polar functions, to express the field due to one cylinder in terms of the polar coordinates of the other cylinders such that the boundary conditions can be imposed at all the cylinder surfaces. The constants of integration in the field expressions of all the cylinders are obtained from a truncated infinite matrix equation. Translational addition theorems are available for scalar cylindrical and spherical wave functions but such theorems are not directly available for the general solution of the Laplace equation in polar coordinates. The purpose of deriving these addition theorems and applying them to field problems involving systems of cylinders is to obtain exact analytic solutions with controllable accuracies, thereby, yielding benchmark solutions to validate other approximate numerical methods.
Suppression of Flow Separation Around A Circular Cylinder by Utilizing Lorentz Force
ZHANG Hui; FAN Bao-chun; CHEN Zhi-hua; ZHOU Ben-mou
2008-01-01
Both experimental and numerical investigations on the flow past a cylinder under the influence of Lorentz force (electromagnetic force) were conducted in an electrically low-conducting fluid. The Lorentz force is applied both locally, wholly and periodically on the surface of the cylinder, and their control effects for flow separation were investigated Both experimental and numerical results show that Lorentz force can suppress the flow separation with Lorentz force applied on both local and whole surface of the cylinder. However, when the periodic and opposite Lorentz force adopted, the cylinder wake cannot be stabilized.
LUO Lin-cong; ZHANG Guan-min; PAN Ji-hong; TIAN Mao-cheng
2013-01-01
This paper presents a two-dimensional CFD study of the falling film evaporation of horizontal tubes with different shapes applied in the seawater desalination.The flow and heat transfer characteristics of the falling water film on one circular tube and two non-circular shaped tubes,a drop-shaped tube and an oval-shaped tube,are analyzed,respectively.The Volume Of Fluid (VOF)method is employed to investigate the influence of the mass flow rate and the feeder height on the distribution of the film thickness and the heat transfer performance.The numerical results show that the minimum value of the film thickness appears approximately at the angular positions of 125°,160° and 170° for the smooth circular,oval-and drop-shaped tubes,respectively.The film thickness grows with the increase of the mass flow rate and the decrease of the feeder height,while the variation pattern varies for different tubes.Moreover,compared with the circular tube,the drop-and oval-shaped tubes have a lower dimensionless temperature and a thinner thermal boundary layer,which means a better heat transfer performance.Finally,the numerical results correlate well with the experimental and predicted data in literature.
Singha, Sintu; Nagarajan, Kaushik Kumar; Sinhamahapatra, K. P.
2016-05-01
Incompressible flows at low Reynolds numbers over two identical side-by-side circular cylinders have been investigated numerically using unstructured finite volume method. The gap between the cylinders (g) and Reynolds number (Re) considered in the study lies respectively in the range of 0.2 ≤ g/D ≤ 4.0 (D being the diameter of the cylinder) and 20 ≤ Re ≤ 160. Low Reynolds number steady flows are given considerable importance. Two types of wakes are observed in the steady flow regime; the first type is characterized by attached vortices as in the case of an isolated cylinder and the other type is identified by detached standing vortices in the downstream. Reynolds number at which flow turns unsteady is quantified for each gap width. Five different types of wake patterns are observed in the unsteady flow regime: single bluff body wake, deflected wake, flip-flopping wake, in-phase synchronized, and anti-phase synchronized wakes. Present simulations of the evolution of single bluff-body wake demonstrate presence of vortices in the gap side too. The very long time simulations show that below a limiting Re depending on the gap, there is a transition of fully developed initial anti-phase flow to the in-phase flow at a later time. The limiting Reynolds number for this phase bifurcation phenomenon is evaluated in the (Re, g/D) space. A properly calibrated reduced order model based stability analysis is carried out to investigate the phase transition.
Gunnoo, Hans; Abcha, Nizar; Ezersky, Alexander
2016-02-01
The influence of harmonic surface wave on non-regular Karman Vortex Street is investigated. In our experiments, Karman Street arises behind a vertical circular cylinder in a water flow and harmonic surface waves propagating upstream. It is found that surface waves can modify regimes of shedding in Karman Street: frequency lock-in and synchronization of vortex shedding can arise. Intensive surface waves can excite symmetric vortex street instead of chess-like street, and completely suppress shedding behind the cylinder. It is shown experimentally that such effects occur if frequency of harmonic surface wave is approximately twice higher than the frequency of vortex shedding. Region of frequency lock-in is found on the plane amplitude-frequency of surface wave.
Mansour, M A; El-Kabeir, S M
2000-01-01
Steady laminar boundary layer analysis of heat and mass transfer characteristics in magnetohydrodynamic (MHD) flow of a micropolar fluid on a circular cylinder maintained at uniform heat and mass flux has been conducted. The solution of the energy equation inside the boundary layer is obtained as a power series of the distance measured along the surface from the front stagnation point of the cylinder. The results of dimensionless temperature, Nusselt number, wall shear stress, wall couple stress and Sherwood number have been presented graphically for various values of the material parameters. The results indicate that the micropolar fluids display a reduction in drag as well as heat transfer rate when compared with Newtonian fluids.
Mansour, M. A.; El-Hakiem, M. A.; El Kabeir, S. M.
2000-10-01
Steady laminar boundary layer analysis of heat and mass transfer characteristics in magnetohydrodynamic (MHD) flow of a micropolar fluid on a circular cylinder maintained at uniform heat and mass flux has been conducted. The solution of the energy equation inside the boundary layer is obtained as a power series of the distance measured along the surface from the front stagnation point of the cylinder. The results of dimensionless temperature, Nusselt number, wall shear stress, wall couple stress and Sherwood number have been presented graphically for various values of the material parameters. The results indicate that the micropolar fluids display a reduction in drag as well as heat transfer rate when compared with Newtonian fluids.
Steady laminar boundary layer analysis of heat and mass transfer characteristics in magnetohydrodynamic (MHD) flow of a micropolar fluid on a circular cylinder maintained at uniform heat and mass flux has been conducted. The solution of the energy equation inside the boundary layer is obtained as a power series of the distance measured along the surface from the front stagnation point of the cylinder. The results of dimensionless temperature, Nusselt number, wall shear stress, wall couple stress and Sherwood number have been presented graphically for various values of the material parameters. The results indicate that the micropolar fluids display a reduction in drag as well as heat transfer rate when compared with Newtonian fluids
Nemati Hasan
2011-01-01
Full Text Available A numerical investigation of the two-dimensional laminar flow and heat transfer a rotating circular cylinder with uniform planar shear, where the free-stream velocity varies linearly across the cylinder using Multi-Relaxation-Time Lattice Boltzmann method is conducted. The effects of variation of Reynolds number, rotational speed ratio at shear rate 0.1, blockage ratio 0.1 and Prandtl number 0.71 are studied. The Reynolds number changing from 50 to 160 for three rotational speed ratios of 0, 0.5, 1 is investigated. Results show that flow and heat transfer depends significantly on the rotational speed ratio as well as the Reynolds number. The effect of Reynolds number on the vortex-shedding frequency and period-surface Nusselt numbers is overall very strong compared with rotational speed ratio. Flow and heat conditions characteristics such as lift and drag coefficients, Strouhal number and Nusselt numbers are studied.
Guo, Li; Zhang, Xing; He, Guowei
2016-02-01
The flows past a circular cylinder at Reynolds number 3900 are simulated using large-eddy simulation (LES) and the far-field sound is calculated from the LES results. A low dissipation energy-conserving finite volume scheme is used to discretize the incompressible Navier-Stokes equations. The dynamic global coefficient version of the Vreman's subgrid scale (SGS) model is used to compute the sub-grid stresses. Curle's integral of Lighthill's acoustic analogy is used to extract the sound radiated from the cylinder. The profiles of mean velocity and turbulent fluctuations obtained are consistent with the previous experimental and computational results. The sound radiation at far field exhibits the characteristic of a dipole and directivity. The sound spectra display the -5/3 power law. It is shown that Vreman's SGS model in company with dynamic procedure is suitable for LES of turbulence generated noise.
Wang Ye-Long
2012-01-01
Full Text Available A direct forcing method for the simulation of particulate flows based on immersed boundary-lattice Boltzmann method is used to study the flow of power-law fluid through an infinite array of circular cylinders with cylinder separations of 20a (a is the cylinder radius with laminar shedding behind cylinders. Time averaged drag coefficient, maximum of lift coefficient and Strouhal number are given out with the power-law index in the range of 0.4 ≤ n ≤ 1.8 and Re in the range of 50 ≤ Re ≤ 140.
This paper presents a study of the bistable phenomenon which occurs in the turbulent flow impinging on circular cylinders placed side-by-side. Time series of axial and transversal velocity obtained with the constant temperature hot wire anemometry technique in an aerodynamic channel are used as input data in a finite mixture model, to classify the observed data according to a family of probability density functions. Wavelet transforms are applied to analyze the unsteady turbulent signals. Results of flow visualization show a predominantly two-dimensional behavior. A double-well energy model is suggested to describe the behavior of the bistable phenomenon in this case. (author)
Johansson, Jens; Nielsen, Mogens Peter
The uniform flow around a circular cylinder at Reynolds number 1e5 is simulated in a three dimensional domain by means of the newly developed Self-induced angular Moment Method, SMoM, turbulence model. The global force coefficients, Strouhal number, pressure distributions and wall shear stress...... distributions are compared to experimental findings reported in literature. The SMoM turbulence model is found to provide maximum, minimum and time-mean pressure coefficient distributions in very good agreement with experimental findings....
B. Harshavardhan; Mallikarjuna, J. M.
2013-01-01
In this investigation, a CFD analysis has been carried out on in-cylinder fluid flows and air-fuel interaction in Direct Injection Spark Ignition (DISI) engine by changing combustion chamber geometry during intake and compression stroke at an engine speed of 1500 rpm for four different types of piston profiles viz., flat piston, flat piston with centre bowl, dome piston with centre bowl and pentroof offset bowl piston. A polyhedral trimmed cell has been taken for meshing of the geometries usi...
Electromagnetic Casimir Forces of Parabolic Cylinder and Knife-Edge Geometries
Graham, Noah; Emig, Thorsten; Rahi, Sahand Jamal; Jaffe, Robert L; Kardar, Mehran
2011-01-01
An exact calculation of electromagnetic scattering from a perfectly conducting parabolic cylinder is employed to compute Casimir forces in several configurations. These include interactions between a parabolic cylinder and a plane, two parabolic cylinders, and a parabolic cylinder and an ordinary cylinder. To elucidate the effect of boundaries, special attention is focused on the "knife-edge" limit in which the parabolic cylinder becomes a half-plane. Geometrical effects are illustrated by considering arbitrary rotations of a parabolic cylinder around its focal axis, and arbitrary translations perpendicular to this axis. A quite different geometrical arrangement is explored for the case of an ordinary cylinder placed in the interior of a parabolic cylinder. All of these results extend simply to nonzero temperatures.
Pankaj Thakur
2014-01-01
Full Text Available Thermal stress and strain rates in a thick walled rotating cylinder under steady state temperature has been derived by using Seth’s transition theory. For elastic-plastic stage, it is seen that with the increase of temperature, the cylinder having smaller radii ratios requires lesser angular velocity to become fully plastic as compared to cylinder having higher radii ratios The circumferential stress becomes larger and larger with the increase in temperature. With increase in thickness ratio stresses must be decrease. For the creep stage, it is seen that circumferential stresses for incompressible materials maximum at the internal surface as compared to compressible material, which increase with the increase in temperature and measure n.
Bifurcation of Vortex Breakdown Patterns in a Circular Cylinder with two Rotating Covers
Brøns, Morten; Bisgaard, Anders
2006-01-01
We analyse the topology of vortex breakdown in a closed cylindrical container in the steady domain under variation of three parameters, the aspect ratio of the cylinder, the Reynolds number, and the ratio of the angular velocities of the covers. We develop a general post-processing method to obtain...
Optimal non-circular fiber geometries for image scrambling in high-resolution spectrographs
Stürmer, Julian; Grimm, Stephan; Kalide, Andre; Sutherland, Adam P; Seifahrt, Andreas; Schuster, Kay; Bean, Jacob L; Quirrenbach, Andreas
2016-01-01
Optical fibers are a key component for high-resolution spectrographs to attain high precision in radial velocity measurements. We present a custom fiber with a novel core geometry - a 'D'-shape. From a theoretical standpoint, such a fiber should provide superior scrambling and modal noise mitigation, since unlike the commonly used circular and polygonal fiber cross sections, it shows chaotic scrambling. We report on the fabrication process of a test fiber and compare the optical properties, scrambling performance, and modal noise behavior of the D-fiber with those of common polygonal fibers.
Geometry effects on magnetization dynamics in circular cross-section wires
Three-dimensional magnetic memory design based on circular-cross section nanowires with modulated diameter is the emerging field of spintronics. The consequences of the mutual interaction between electron spins and local magnetic moments in such non-trivial geometries are still open to debate. This paper describes the theoretical study of domain wall dynamics within such wires subjected to spin polarized current. We used our home-made finite element software to characterize the variety of domain wall dynamical regimes observed for different constriction to wire diameter ratios d/D. Also, we studied how sizeable geometry irregularities modify the internal micromagnetic configuration and the electron spin spatial distribution in the system, the geometrical reasons underlying the additional contribution to the system's nonadiabaticity, and the specific domain wall width oscillations inherent to fully three-dimensional systems
Numerical Study on the Charge Transport in a Space between Concentric Circular Cylinders
Suh, Y. K.; Baek, K H
2014-01-01
Electrification is one of the key factors to be considered in the design of power transformers utilizing dielectric liquid as a coolant. Compared with enormous quantity of experimental and analytical studies on electrification, numerical simulations are very few. This paper describes essential elements of numerical solution methods for the charge transport equations in a space between concentric cylinders. It is found that maintaining the conservation property of the convective terms in the g...
Mechanism of Tonal Noise Generation from Circular Cylinder with Spiral Fin
Ryo Yamashita; Hidechito Hayashi; Tetsuya Okumura; Hiromitsu Hamakawa
2014-01-01
The pitch of the spiral finned tube influences seriously to the acoustic resonance in the heat exchanger.In this research,the flow characteristics in relating to the aeolian tone from the finned cylinder are studied by the numerical simulation.It is observed that the tonal noise generated from the finned tube at two pitch spaces.The ratio of the fin pitch to the cylinder diameter is changed at 0.11 and 0.27.The tone level increases and the frequency decreases with the pitch shorter.The separation flow from the cylinder generates the span-wise vortices,Karman vortices,and the separation flow from the fin generates the stream-wise vortices.When the fin pitch ratio is small,the stream-wise vortices line up to span-wise and become weak rapidly.Only the Karman vortices are remained and integrate in span.So the Karman vortex became large.This causes the low frequency and the large aeolian tone.
The Flow Field Downstream of a Dynamic Low Aspect Ratio Circular Cylinder: A Parametric Study
Gildersleeve, Samantha; Dan, Clingman; Amitay, Michael
2015-11-01
Flow past a static, low aspect ratio cylinder (pin) has shown the formation of vortical structures, namely the horseshoe and arch-type vortex. These vortical structures may have substantial effects in controlling flow separation over airfoils. In the present experiments, the flow field associated with a low aspect ratio cylinder as it interacts with a laminar boundary layer under static and dynamic conditions was investigated through a parametric study over a flat plate. As a result of the pin being actuated in the wall-normal direction, the structures formed in the wake of the pin were seen to be a strong function of actuation amplitude, driving frequency, and aspect ratio of the cylinder. The study was conducted at a Reynolds number of 1875, based on the local boundary layer thickness, with a free stream velocity of 10 m/s. SPIV data were collected for two aspect ratios of 0.75 and 1.125, actuation amplitudes of 6.7% and 16.7%, and driving frequencies of 175 Hz and 350 Hz. Results indicate that the presence and interactions between vortical structures are altered in comparison to the static case and suggest increased large-scale mixing when the pin is driven at the shedding frequency (350 Hz). Supported by the Boeing Company.
Mandal, A. C.; Waechter, R. T.
1994-01-01
Waechter and Philip (1985) obtained the asymptotic expansion of the mean infiltration rate for large s from a buried circular cylinder using a scattering analog. Here s(= αl/2) is defined as the ratio of the characteristic length l of the water supply surface (in fact, its radius) to the sorptive length 2α-1 of the soil and a satisfies the relationship K(ψ) = K(0) eαψ, where K is the hydraulic conductivity, and ψ is the moisture potential. This exact solution cannot be used directly to obtain the separate contributions to the mean infiltration rate from the top and the bottom halves of the cylinder; our analysis is based on a new class of special functions derived from the modified Bessel equation with a forcing term. In this paper, we obtain the separate asymptotics for the two halves for large s to make a comparison with the results of the trench problem (Waechter and Mandal, 1993). The asymptotic expansions for top and bottom halves are (2/π)(0.69553s-2/3) and (2/π)(1+0.30066s-2/3), respectively, whereas for a semicircular trench, the mean infiltration rate is given by (2/π)(1+0.30066s-2/3).
This paper presents a study of the bistable phenomenon which occurs in the turbulent flow impinging on circular cylinders placed side-by-side. Time series of axial and transversal velocity obtained with the constant temperature hot wire anemometry technique in an aerodynamic channel are used as input data in a finite mixture model, to classify the observed data according to a family of probability density functions. Wavelet transforms are applied to analyze the unsteady turbulent signals. Results of flow visualization show that the flow is predominantly two-dimensional. A double-well energy model is suggested to describe the behavior of the bistable phenomenon in this case. -- Highlights: ► Bistable flow on two parallel cylinders is studied with hot wire anemometry as a first step for the application on the analysis to tube bank flow. ► The method of maximum likelihood estimation is applied to hot wire experimental series to classify the data according to PDF functions in a mixture model approach. ► Results show no evident correlation between the changes of flow modes with time. ► An energy model suggests the presence of more than two flow modes
Lift forces on a circular cylinder in cross flow resulting from heat/mass transfer
Trávníček, Zdeněk; Maršík, F.; Vít, Tomáš; Broučková, Zuzana; Pavelka, Miroslav
Southampton: WIT Press, 2013 - (Carlomagno, G.; Brebbia, C.; Hernández, S.), s. 149-159 ISBN 978-1-84564-732-2. ISSN 1746-4064. [Computational Methods and Experimental Measurements (CMEM) 2013. Coruna (ES), 02.07.2013-04.07.2013] R&D Projects: GA ČR(CZ) GCP101/11/J019; GA AV ČR(CZ) IAA200760801 Institutional support: RVO:61388998 Keywords : cylinder in cross flow * magnus effect * active flow control Subject RIV: JU - Aeronautics, Aerodynamics, Aircrafts http://library.witpress.com/pages/paperinfo.asp?PaperID=24858
无
2009-01-01
We analyze thickness-shear vibration of an axially poled circular cylindrical tube with unattached electrodes and air gaps. Both free and electrically forced vibrations are studied. Exact solutions are obtained from the equations of linear piezoelectricity. Resonant frequencies and the impedance of the transducer are calculated from the solution. Results show that the resonant frequencies are sensitive to the dimensions of the air gaps when the gaps are thin. The impedance depends strongly on the air gaps.
Lockwood, Vernard E.; McKinney, Linwood W.
1960-01-01
A two-dimensional lifting circular cylinder has been tested over a Mach number range from 0.011 to 0.32 and a Reynolds number range from 135,000 to 1,580,000 to determine the force and pressure distribution characteristics. Two flaps having chords of 0.37 and 6 percent of the cylinder diameter, respectively, and attached normal to the surface were used to generate lift. A third configuration which had 6-percent flaps 1800 apart was also investigated. All flaps were tested through a range of angular positions. The investigation also included tests of a plain cylinder without flaps. The lift coefficient showed a wide variation with Reynolds number for the 6-percent flap mounted on the bottom surface at the 50-percent-diameter station, varying from a low of about 0.2 at a Reynolds number of 165,000 to a high of 1.54 at a Reynolds number of 350,000 and then decreasing almost linearly to a value of 1.0 at a Reynolds number of 1,580,000. The pressure distribution showed that the loss of lift with Reynolds number above the critical was the result of the separation point moving forward on the upper surface. Pressure distributions on a plain cylinder also showed similar trends with respect to the separation point. The variation of drag coefficient with Reynolds number was in direct contrast to the lift coefficient with the minimum drag coefficient of 0.6 occurring at a Reynolds number of 360,000. At this point the lift-drag ratios were a maximum at a value of 2.54. Tests of a flap with a chord of 0.0037 diameter gave a lift coefficient of 0.85 at a Reynolds number of 520,000 with the same lift-drag ratio as the larger flap but the position of the flap for maximum lift was considerably farther forward than on the larger flap. Tests of two 6-percent flaps spaced 180 deg apart showed a change in the sign of the lift developed for angular positions of the flap greater than 132 deg at subcriti- cal Reynolds numbers. These results may find use in application to air- craft using
Experimental Study of Wave Forces on Vertical Circular Cylinders in Long and Short Crested Sea
Høgedal, Michael
in the transverse wave forces on the structure, whereas the vertical forces generally are unaffected. In this study the effect from wave directionality on the horizontal wave forces on a slender vertical cylinder in a laboratory environment is investigated. In addition wave forces from regular waves......The three-dimensional structure of ocean waves is generally ignored in favour of two-dimensional waves, which are easier to handle from a theoretical and computational point of view. For design fixed structures where horizontal in-line and resultant wave forces are important, this is normally on...... the safe side, as the directional spreading of the wave field Ieads to reduced horizontal velocities and acceleration; in the fluid and hence a reduction of the resultant and in-line wave forces on the structure. The directional spreading of the horizontal velocity field generally causes an increase...
Gao, Shaoyan; Li, Pengbo; Li, Fuli
2013-03-01
The plasmon resonance-induced near electric field focusing and enhancement of three-layered silver nano-cylinder has been studied by quasi-static electricity. A field enhancement factor of more than 102 times can be obtained in the middle dielectric wall between the inner silver wire and outer tube around the resonance wavelengths of 400-500 nm. Because of the anti-symmetric coupling between the bonding tube plasmon and the wire plasmon, the incident electric field could be fine focused between the two metallic surfaces by decreasing the middle wall thickness. As a result of the curvature-dependent surface charge concentration, thinner dielectric wall with small diameter provides stronger local field enhancement. It provides the potential applications of plamonic nano-structures for high-density and high-contrast optical data storage under the diffraction limit.
Waka, R.; Yoshino, F.; Hayashi, T.
1985-06-01
An experiment was carried out to understand effects of the slot shape at the cylinder-side-wall juncture and the angular location of a blowing slot on the spanwise distributions of various characteristic values near the side-wall of a circular cylinder with tangential blowing. The range of the side-wall effects and the characteristic values near the side-wall are much influenced by the slot shape and the location of the slot. When the slot shaped like a knife edge, termed 'Edge', is used, the range of the side-wall effects becomes narrower as the angular location of the blowing slot is farther downstream.
Steady mixed convection boundary layer flow from an isothermal horizontal circular cylinder embedded in a porous medium filled with a nano-fluid has been studied for both cases of a heated and cooled cylinder using the Buongiorno-Darcy mathematical nano-fluid model. The resulting system of nonlinear partial differential equations is solved numerically using an implicit finite-difference scheme. The solutions for the flow and heat transfer characteristics are evaluated numerically for various values of the governing parameters, namely the constant mixed convection parameter λ, the traditional Lewis number Le, the buoyancy ratio parameter Nr, the Brownian motion parameter Nb and the thermophoresis parameter Nt. It is found that in the present case of the porous medium flow, the separation is always suppressed at negative values of λ. When λ changes from -2.1 to 0, one has a 'heating' of the cylinder, but a heating in the negative range of λ (λ 0) delays the separation of the boundary layer and if the cylinder is hot enough (large values of λ > 0), then it is suppressed completely at a positive value of λ, somewhere between 0.88 and 0.89. On the other hand, cooling the cylinder (λ < 0) brings the boundary layer separation point nearer to the lower stagnation point and for a sufficiently cold cylinder (large values of λ < 0) there will not be a boundary layer on the cylinder. (authors)
Wang, Chenglei; Tang, Hui; Yu, Simon C. M.; Duan, Fei
2016-05-01
This paper studies the control of two-dimensional vortex-induced vibrations (VIVs) of a single circular cylinder at a Reynolds number of 100 using a novel windward-suction-leeward-blowing (WSLB) concept. A lattice Boltzmann method based numerical framework is adopted for this study. Both open-loop and closed-loop controls are implemented. In the open-loop control, three types of actuation arrangements, including the pure suction on the windward side of the cylinder, the pure blowing on the leeward side, and the general WSLB on both sides, are implemented and compared. It is found that the general WSLB is the most effective, whereas the pure suction is the least effective. In the closed-loop control, the proportional (P), integral (I), and proportional-integral (PI) control schemes are applied to adjust the WSLB velocities according to the flow information obtained from a sensor. The effects of four key control parameters including the proportional gain constant, the integral gain constant, the length of data history used for the feedback, and the location of the sensor are investigated. It is found that the use of only P control fails to completely suppress the VIV, the use of only I control can achieve the complete suppression, and the PI control performs the best in terms of both the control effectiveness and efficiency. In the PI control, there exists an optimal length of data history for the feedback, at which the VIV control is the most efficient. There also exist the minimum required WSLB velocities for the VIV suppression, independent of the control schemes. Moreover, it is found that the VIV control is independent of the sensor location.
Premnath, Kannan N [Department of Mechanical Engineering, University of Colorado Denver, 1200 Larimer Street, Denver, CO 80217 (United States); Pattison, Martin J [HyPerComp Inc., 2629 Townsgate Road, Suite 105, Westlake Village, CA 91361 (United States); Banerjee, Sanjoy, E-mail: kannan.premnath@ucdenver.edu, E-mail: kannan.np@gmail.com [Department of Chemical Engineering, City College of New York, City University of New York, New York, NY 10031 (United States)
2013-10-15
Lattice Boltzmann method (LBM) is a kinetic based numerical scheme for the simulation of fluid flow. While the approach has attracted considerable attention during the last two decades, there is a need for systematic investigation of its applicability for complex canonical turbulent flow problems of engineering interest, where the nature of the numerical properties of the underlying scheme plays an important role for their accurate solution. In this paper, we discuss and evaluate a LBM based on a multiblock approach for efficient large eddy simulation of three-dimensional external flow past a circular cylinder in the transitional regime characterized by the presence of multiple scales. For enhanced numerical stability at higher Reynolds numbers, a multiple relaxation time formulation is considered. The effect of subgrid scales is represented by means of a Smagorinsky eddy-viscosity model, where the model coefficient is computed locally by means of a dynamic procedure, providing better representation of flow physics with reduced empiricism. Simulations are performed for a Reynolds number of 3900 based on the free stream velocity and cylinder diameter for which prior data is available for comparison. The presence of laminar boundary layer which separates into a pair of shear layers that evolve into turbulent wakes impose particular challenge for numerical methods for this condition. The relatively low numerical dissipation introduced by the inherently parallel and second-order accurate LBM is an important computational asset in this regard. Computations using five different grid levels, where the various blocks are suitably aligned to resolve multiscale flow features show that the structure of the recirculation region is well reproduced and the statistics of the mean flow and turbulent fluctuations are in satisfactory agreement with prior data. (paper)
Premnath, Kannan N.; Pattison, Martin J.; Banerjee, Sanjoy
2013-10-01
Lattice Boltzmann method (LBM) is a kinetic based numerical scheme for the simulation of fluid flow. While the approach has attracted considerable attention during the last two decades, there is a need for systematic investigation of its applicability for complex canonical turbulent flow problems of engineering interest, where the nature of the numerical properties of the underlying scheme plays an important role for their accurate solution. In this paper, we discuss and evaluate a LBM based on a multiblock approach for efficient large eddy simulation of three-dimensional external flow past a circular cylinder in the transitional regime characterized by the presence of multiple scales. For enhanced numerical stability at higher Reynolds numbers, a multiple relaxation time formulation is considered. The effect of subgrid scales is represented by means of a Smagorinsky eddy-viscosity model, where the model coefficient is computed locally by means of a dynamic procedure, providing better representation of flow physics with reduced empiricism. Simulations are performed for a Reynolds number of 3900 based on the free stream velocity and cylinder diameter for which prior data is available for comparison. The presence of laminar boundary layer which separates into a pair of shear layers that evolve into turbulent wakes impose particular challenge for numerical methods for this condition. The relatively low numerical dissipation introduced by the inherently parallel and second-order accurate LBM is an important computational asset in this regard. Computations using five different grid levels, where the various blocks are suitably aligned to resolve multiscale flow features show that the structure of the recirculation region is well reproduced and the statistics of the mean flow and turbulent fluctuations are in satisfactory agreement with prior data.
Seismic response of liquid sloshing in the annular region formed by coaxial circular cylinders
As to the sloshing of liquid in the storage tanks having free surface in earthquakes, there have been many reports, but these are limited to those of relatively simple structures and forms. As the cxamples of complex structures, there are chemical reaction towers, stress removal tanks for BWRs, reactor vessels for FBRs and so on. In these structures, annular parts are formed inside, and as to the sloshing in such annular parts, there is only the report of Aslam et al. In this study, examination was carried out on the earthquake response of the liquid sloshing in the annular part of a double walled cylinder which appears relatively frequently among complex structures. In the analysis, attenuation was taken into account in addition to the method of Aslam et al., the walls of an axisymmetric vessel were regarded as rigid, and infinitesinal displacement and incompressible invicid fluid were assumed. The velocity potential satisfying boundary conditions was determined assuming irrotational flow, and the solution of transient response when n sine waves resonating with the sloshing of first order mode were inputted was derived. Two kinds of double walled vessels were vibrated with a large vibrating table, and the response was measured. (Kako, I.)
2-D Urans Simulations of Vortex Induced Vibrations of Circular Cylinder at Trsl3 Flow Regime
Omer Kemal Kinaci
2016-01-01
Full Text Available Research on vortex-induced vibrations (VIV mainly involves experimental science but building laboratory setups to investigate the flow are expensive and time consuming. Computational fluid dynamics (CFD methods may offer a faster and a cheaper way to understand this phenomenon depending on the solution approach to the problem. The context of this paper is to present the author’s computational approach to solve for vortex-induced vibrations which cover extensive explanations on the mathematical background, the grid structure and the turbulence models implemented. Current computational research on VIV for smooth cylinders is currently restricted to flows that have Reynolds numbers below 10,000. This paper describes the method to approach the problem with URANS and achieves to return satisfactory results for higher Reynolds numbers.The computational approach is first validated with a benchmark experimental study for rather low Reynolds number which falls into TrSL2 flow regime. Then, some numerical results up to Re=130,000, which falls into TrSL3 flow regime,are given at the end of the paper to reveal the validity of the approach for even higher Reynolds numbers.
Direct Numerical Simulation of Flow around a Circular Cylinder Controlled Using Plasma Actuators
Taichi Igarashi
2014-01-01
by means of direct numerical simulation (DNS. The Reynolds number based on the freestream velocity and the cylinder diameter is set at ReD=1000. The plasma actuators are placed at ±90° from the front stagnation point. Two types of forcing, that is, two-dimensional forcing and three-dimensional forcing, are examined and the effects of the forcing amplitude and the arrangement of plasma actuators are studied. The simulation results suggest that the two-dimensional forcing is primarily effective in drag reduction. When the forcing amplitude is higher, the mean drag and the lift fluctuations are suppressed more significantly. In contrast, the three-dimensional forcing is found to be quite effective in reduction of the lift fluctuations too. This is mainly due to a desynchronization of vortex shedding. Although the drag reduction rate of the three-dimensional forcing is slightly lower than that of the two-dimensional forcing, considering the power required for the forcing, the three-dimensional forcing is about twice more efficient.
Asymmetrical boundary layer separation at the base of a two cylinder geometry
Boyle, M. T.; Langston, L. S.
1989-01-01
This paper reports on the experimental description of the three-dimensional horseshoe vortex system occurring at the base of two cylinder mounted side by side on an endwall. The spacing between the two cylinders is adjusted to generate a family of viscous flows. Flow visualization performed in a water tunnel provides a qualitative understanding of the flow over a range of flow variables. A detailed wind tunnel experiment provides a quantitative description of the flow at a single test condition. At Re(D) = 2.5 x 10 to the 5th the measurements show an asymmetrical primary vortex with a wide flat cross section. A small counterrotating vortex is found between the primary vortex and the cylinder leading edge.
Dinarvand Saeed
2015-01-01
Full Text Available This article deals with the study of the steady axisymmetric mixed convective boundary layer flow of a nanofluid over a vertical circular cylinder with prescribed external flow and surface temperature. By means of similarity transformation, the governing partial differential equations are reduced into highly non-linear ordinary differential equations. The resulting non-linear system has been solved analytically using an efficient technique namely homotopy analysis method (HAM. Expressions for velocity and temperature fields are developed in series form. In this study, three different types of nanoparticles are considered, namely alumina (, titania (, and copper ( with water as the base fluid. For copper-water nanofluid, graphical results are presented to describe the influence of the nanoparticle volume fraction on the velocity and temperature fields for the forced and mixed convection flows. Moreover, the features of the flow and heat transfer characteristics are analyzed and discussed for foregoing nanofluids. It is found that the skin friction coefficient and the heat transfer rate at the surface are highest for copper-water nanofluid compared to the alumina-water and titania-water nanofluids.
无
2006-01-01
The structure of double diffusive convection in a circular cylinder cavity has been numerically studied. The numerical results exhibit some new characters of non-horizontal stratifications of thermal and solutal fields: in the stratification state, the isothermal lines near the sidewall are higher than that near the symmetry axis, while the isoconcentration lines near the symmetry axis are relatively high. The mechanism of these non-horizontal stratifications is illustrated by comparing double-diffusive convection with natural convection driven by thermal buoyancy or solutal buoyancy alone. The effects of Lewis number Le and buoyancy ratio N on the non-hor- izontal stratifications of thermal and solutal fields are also investigated. The results show that: at a given time (t = 0.2), with an increase in Le (Le = 0-15), the area influenced by solute diffusion decreases; for isothermal line, the gradients of it initially increase, but it tends to be horizontal at the top of the cavity when the Lewis number is higher than 10. When N varies from 0 to 2, the isoconcentration lines tend to be horizontal while the gradients of isothermal line increase.
Peer, Petra; Filip, Petr; Stěnička, M.; Pavlínek, V.
2014-01-01
Roč. 59, č. 3 (2014), s. 221-235. ISSN 0001-7043 R&D Projects: GA ČR(CZ) GAP105/11/2342 Institutional support: RVO:67985874 Keywords : electrorheology * parallel plates * concentric cylinders * silicone oil * PANI powders Subject RIV: BK - Fluid Dynamics
Trávníček, Zdeněk; Wang, A.B.
2011-01-01
Roč. 25, č. 8 (2011), s. 1881-1884. ISSN 1738-494X R&D Projects: GA ČR(CZ) GCP101/11/J019 Institutional research plan: CEZ:AV0Z20760514 Keywords : heated circular cylinder * effective temperature * vortex shedding Subject RIV: BK - Fluid Dynamics Impact factor: 0.448, year: 2011 http://www.springerlink.com/content/2131l38t2u0504u6/
Hussain Ahmad; Tariq Javed; Abuzar Ghaffari
2016-01-01
In the present article, radiation effect on mixed convection boundary layer flow of a viscoelastic fluid over a horizontal circular cylinder with constant heat flux has been numerically analyzed. The governing boundary layer equations are transformed to dimensionless nonlinear partial differential equations. The equations are solved numerically by using Keller-box method. The computed results are in excellent agreement with the previous studies. Skin friction coefficient and Nusselt number ar...
Numerical Analysis and Optimization of Engine Cylinder Fins of Varying
Saravanan
2014-01-01
The main aim of the project is to analyze the thermal properties by varying geometry, material and thickness of cylinder fins. Parametric models of cylinder with fins have been developed to predict the transient thermal behavior. The models are created by varying the geometry, rectangular, circular and curved shaped fins and also by varying thickness of the fins. The 3D modeling software used is Pro/Engineer.The analysis is done using ANSYS. Presently Material used for manufac...
Yokoi Y.
2014-03-01
Full Text Available In this study, the flow features of vortex shedding from a circular cylinder forced-oscillating in the in-line direction were investigated by use of flow visualization experiment and numerical simulation at the Reynolds number Re=620, with varied amplitude ratio and varied frequency ratio. As a result of the experiments, it was found that although the flow structure around the circular cylinder is two-dimensional in the lock-in state of simultaneous vortex shedding, the large scale three-dimensional instability is observed in the lock-in state of alternate vortex shedding through a time lag in the boundary layer separation along the cylinder span. As a result of calculations, two typical flow patterns of the lock-in were shown, and it was confirmed that the calculated flow patterns were in reasonable agreement with previous experimental results. The fluid force act on the oscillating cylinder was investigated. It was clarified that the amplitude of the lift coefficient was larger than the amplitude of the drag coefficient in the lock-in of alternate vortex shedding, and the amplitude of the drag coefficient was larger than the amplitude of the lift coefficient in the lock-in of simultaneous vortex shedding. When the amplitude ratio 2a/d grows, this tendency becomes remarkable.
Towards a precision measurement of the Casimir force in a cylinder-plane geometry
Brown-Hayes, Michael; Dalvit, Diego A. R.; Mazzitelli, Francisco D.; Kim, Woo-Joong; Onofrio, Roberto
2005-01-01
We report on a proposal aimed at measuring the Casimir force in a cylinder-plane configuration. The Casimir force is evaluated including corrections due to finite parallelism, conductivity, and temperature. The range of validity of the proximity force approximation is also discussed. An apparatus to test the feasibility of a precision measurement in this configuration has been developed, and we describe both a procedure to control the parallelism and the results of the electrostatic calibrati...
Lockwood, Vernard E.
1961-01-01
A wind-tunnel investigation has been made to determine the ground effect on the aerodynamic characteristics of a lifting circular cylinder using tangential blowing from surface slots to generate high lift coefficients. The tests were made on a semispan model having a length 4 times the cylinder diameter and an end plate of 2.5 diameters. The tests were made at low speeds at a Reynolds number of approximately 290,000, over a range of momentum coefficients from 0.14 to 4.60, and over a range of groundboard heights from 1.5 to 10 cylinder diameters. The investigation showed an earlier stall angle and a large loss of lift coefficient as the groundboard was brought close to the cylinder when large lift coefficients were being generated. For example, at a momentum coefficient of 4.60 the maximum lift coefficient was reduced from a value of 20.3 at a groundboard height of 10 cylinder diameters to a value of 8.7 at a groundboard height of 1.5 cylinder diameters. In contrast to this there was little effect on the lift characteristics of changes in groundboard height when lift coefficients of about 4.5 were being generated. At a height of 1.5 cylinder diameters the drag coefficients generally increased rapidly when the slot position angle for maximum lift was exceeded. Slightly below the slot position angle for maximum lift, the groundboard had a beneficial effect, that is, the drag for a given lift was less near the groundboard than away from the groundboard. The variation of maximum circulation lift coefficient (maximum lift coefficient minus momentum coefficient) obtained in this investigation is in general agreement with a theory developed for a jet-flap wing which assumes that the loss in circulation is the result of blockage of the main stream beneath the wing.
Sobera, M.P.; Kleijn, C.R.
2008-01-01
We study flow and heat transfer to a cylinder in cross flow at Re = 3,900–80,000 by means of three-dimensional transient RANS (T-RANS) simulations, employing an RNG k − ε turbulence model. Both the case of a bare solid cylinder and that of a solid cylinder surrounded at some fixed distance by a thin
Sharma, B.R. [Dibrugarh University, Department of Mathematics, Dibrugarh, Assam (India); Singh, R.N. [Marwari Hindi High School, Dibrugarh (India)
2010-08-15
The effect of a radial magnetic field on separation of a binary mixture of incompressible viscous thermally and electrically conducting fluids confined between two concentric rotating circular cylinders with different angular velocity is examined. The equations governing the motion, temperature and concentration in cylindrical polar coordinate are solved analytically. The solution obtained in closed form for concentration distribution is plotted against the radial distances from the surface of the inner circular cylinder for various values of non-dimensional parameters. It is found that the non-dimensional parameters viz. the Hartmann number, thermal diffusion number, baro diffusion number, rotational Reynolds number, the product of Prandtl number and Eckert number, magnetic Prandtl number and the ratio of the angular velocities of inner and outer cylinders affects the species separation of rarer and lighter component significantly. The problem discussed here derives its application in the basic fluid dynamics separation processes to separate the rarer component of the different isotopes of heavier molecules where electromagnetic method of separation does not work. (orig.)
Supramolecular Chemistry: Induced Circular Dichroism to Study Host-Guest Geometry
Mendicuti, Francisco; Gonzalez-Alvarez, Maria Jose
2010-01-01
In this laboratory experiment, students obtain information about the structure of a host-guest complex from the interpretation of circular dichroism measurements. The value and sign of the induced circular dichroism (ICD) on an achiral chromophore guest when it complexes with a cyclodextrin can be related to the guest penetration and its…
Kawamura, T.; Nakao, T.; Takahashi, M.; Hayashi, M.; Goto, N. [Hitachi, Ltd., Tokyo (Japan)
1999-07-25
Vortex-induced vibrations were measured for a circular cylinder subjected to a water cross flow at supercritical Reynolds numbers for a wide range of reduced velocities. Turbulence intensities were changed from 1% to 13% in order to investigate the effect of the Strouhal number on the region of synchronization by symmetrical and Karman vortex shedding. The reduced damping of the test cylinder was about 0.1 in water. The surface roughness of the cylinder was a mirror-polished surface. Strouhal number decreased from about 0.48 to 0.29 with increasing turbulence intensity. Synchronized vibrations were observed even at supercritical Reynolds numbers where fluctuating fluid force was small. Reduced velocities at which drag and lift direction lock-in by Karman vortex shedding were initiated decreased with increasing Strouhal number. When Strouhal number was about 0.29, the self-excited vibration in drag direction by symmetrical vortex shedding began at which the frequency ratio of Karman vortex shedding frequency to the natural frequency of cylinder was 0.32. (author)
Park, Han G.
An experimental investigation is carried out on the processes of heat transfer associated with a heated circular cylinder in crossflow. Two studies are made. First, a study of the transport of heat in the near wake (x/Dthermochromic liquid crystal (TLC) particles which change their reflected wavelength as function of temperature. By calibrating reflected wavelength versus temperature using a color multi-CCD camera, the local temperature of the flow may be deduced. The velocity is measured by using the same particles as Lagrangian flow tracers, and local velocity or displacement of the flow may be measured by cross-correlating two sequential images. A limitation of DPIV/T, which is the low level of precision (5% - 20% of the temperature span of TLC particles), may be overcome by a process in which the temperature at a given location is computed by averaging the temperatures of the particles within a specified sampling window. This process increases the precision to 2% - 10%.In the study of the heat transport in the near wake, the velocity and temperature measurements obtained from DPIV/T are decomposed into their mean, coherent, and incoherent components using the triple decomposition. It is found that the heat from the cylinder is transported down the wake mostly by the mean heat flux and is laterally transported out of the wake by the coherent and the incoherent heat fluxes. In examining the direction of the turbulent heat flux vectors, the vectors are found not to be co-linear with the gradient of mean temperature. This misalignment implies that the gradient transport models are inappropriate for modeling the turbulent heat transport in the near wake of a circular cylinder. In examining the production of turbulence, it is found that that kinetic energy fluctuations are produced in the saddle regions (regions where the fluid is being stretched in one direction and compressed in another) while the temperature fluctuations are produced at the edges of center regions
陈瑞志; 黄华; 詹杰民; 朱梦华; 郭宗晓
2015-01-01
基于 Biot 渗流固结理论和水波绕射理论，应用特征函数展开法，推导了对应透空复合圆柱的绕射波势和波浪引起的海床内渗流压力分布的解析解式，由此计算了作用于固立透空复合圆柱底部上由波浪渗流压力所导致的浮托力和倾覆力矩，并与水平和垂直绕射波浪力和力矩进行了相应比较。计算结果表明，复合柱上部圆柱侧表面的透空性对水平方向的波浪直接作用有明显的减弱效应，对波浪渗流倾覆力矩也有一定的减弱效应，而对垂直方向的波浪直接作用及波浪渗流浮托力影响较小。海况条件和复合圆柱几何条件等因素的相对变化对波浪渗流作用均存在一定的影响，其中对渗流倾覆力矩的影响更为明显。在一定条件下，波浪渗流作用与绕射波浪作用可以具有相同的量级。%Based on Biot seepage consolidation theory and wave diffraction theory,the analytical solu-tions to the diffracted water wave potentials and the wave-induced seepage pressures referring to porous compound vertical circular cylinder resting on permeable elastic seabed are derived by applying the eigen-function expansion approach,and then the wave-induced lift force and overturn moment caused by the seepage pressure on the bottom of compound vertical circular cylinder are accordingly evaluated and are compared with direct diffracted wave force and moment.The results demonstrate that the porosity of the lateral surface of the circular column resting on a circular base will lead an obvious reduction in direct horizontal wave loads on compound cylinder and certain reduction in seepage overturn moment on the bot-tom of compound cylinder,and having slight influence on direct vertical wave loads and wave-induced seepage uplift force on compound cylinder .The variation of ocean condition and structure geometry con-dition may have some influence on wave-induced seepage loads,especially on seepage
Carmo, B. S.; Meneghini, J. R.; Sherwin, S. J.
2010-05-01
The possible states in the flow around two identical circular cylinders in tandem arrangements are investigated for configurations in the vicinity of the drag inversion separation. By means of numerical simulations, the hysteresis in the transition between the shedding regimes is studied and the relationship between (three-dimensional) secondary instabilities and shedding regime determination is addressed. The differences observed in the behavior of two- and three-dimensional flows are analyzed, and the regions of bistable flow are delimited. Very good agreement is found between the proposed scenario and results available in the literature.
Pankaj Thakur
2014-01-01
Full Text Available The non-homogeneity is assumed due to variation of modulus of compression. It has seen that in the presence of temperature, a cylinder made of non-homogeneous material k<0 (Non-homogeneity is less at internal surface than at outer surface require high pressure to become fully plastic as is required for initial yielding and this pressure goes on increasing with the increases in temperature, showing that a cylinder made of non-homogeneous material k<0 is on the safer side of design. For homogeneous case, it has been observed that the circumferential stress has maximum value at the external surface of the cylinder made of incompressible material as compared to compressible material. For Homogeneous case, with effects of temperature reduces the stresses at the external surface of the cylinder in comparison to pressure effects only. Strain rates are found to be maximum at the internal surface of the cylinder made of compressible material and they decrease with the radius. With the introduction of temperature effect, the creep rates have higher values at the internal surface but lesser values at the external surface as compare to a cylinder subjected to pressure only.
An incompressible unsteady viscous two-dimensional finite volume Navier-Stokes solver is developed using 'consistent flux reconstruction' technique on a collocated unstructured mesh comprising of triangular cells. In this solver, the full Navier-Stokes equations have been solved numerically in the physical plane itself without using any transformation to the computational plane. The cell face centre velocities are reconstructed explicitly by solving the momentum equations on flux reconstruction control volumes defined judiciously around the respective cell face centres. This is followed by solution of the cell centre pressure field using a discrete Poisson equation developed from the reconstructed velocities and updating the cell centre velocities by using an explicit scheme. In the present investigation, the solver has been applied to unconfined flow past a single cylinder, two cylinders and three cylinders for Reynolds number (Re) = 100 and 200. To validate the numerical code the present results for single and two cylinder arrangements were compared with results available from literature and found to be agreeing well. For the two and three cylinder configurations flow has been computed for various gaps between cylinders and for both side-by-side and tandem arrangements. Different wake patterns like in-phase and anti-phase synchronized wake patterns, flip-flopping, deflected wake patterns and steady wake patterns are observed depending on the Reynolds number and the gap spacing.
Numerical Simulation of Flow-induced Vibration of Tandem Circular Cylinders%串列双圆柱流致振动数值模拟
及春宁; 杨立红; 黄继露; 刘爽
2014-01-01
基于开源程序OpenFOAM和动网格技术，利用切应力平衡法建立水流作用下的海上风电基础局部冲刷数学模型。通过模拟结果与实验数据的对比发现，所建立的冲刷数学模型能够合理反映圆柱型单桩基础周围的水流结构，冲刷深度与实验结果吻合较好。%Numerical simulation is carried out for the flow-induced vibrations(FIV)of the elastically-mounted tandem cylinders in laminar flow by using immersed boundary method in the process of harvesting VIVACE ocean current energy (Vortex Induced Vibration Aquatic Clean Energy). The research results show the crosscurrent displacement of the upstream and downstream cylinders,vortex shedding frequency,lift-drag coefficient and the curve of the phase difference between lift force and displacement being affected by reduced flow velocity. In addition,analysis is made for the influence of cylinder’s spacing ratio on the hydrodynamic and FIV response characteristics of the tandem circular cylinders.
About the basic laws of non-isothermal cross-flow past of a circular cylinder with beads mix
The influence of mechanical impurities in the fluid on the structure of the flow near a stationary, rotating cylinder, on its hydrodynamic characteristics and the heat exchange with the stream was investigated numerically. It was shown that the presence of impurities in the liquid leads to a significant change in the pattern of the flow, to increase in the resistance and heat transfer of a stationary cylinder, reducing the lifting force. The emissivity of the rotating cylinder in a fluid flow with an admixture of substantially depends on the dimensionless velocity of the surface. If the speed is less critical, equal to 3.0, the heat is intensified. At higher values, on the contrary, the heat transfer deteriorates. The necessity of considering these circumstances when developing technologies for deposition of functional coatings is evidential
Demartino, Cristoforo; Koss, Holger; Ricciardelli, Francesco
2013-01-01
temperatures are considered. The tested cylinder is a specimen of a HDPE tube used for bridge hanger protection. The wind tunnel tests shall serve as a reference, and the results can be used for the evaluation of possible aerodynamic instability phenomena. A preliminary evaluation of possible galloping...
This note describes the development of a short program for a personal computer to calculate the solid angle subtended by a right cylinder detector to a circular or rectangular, plane or thick source at any position and orientation to the cylinder. The program also calculates the number of hits on the cylinder side and on each end, and the average path-length through the detector volume (assuming no scattering or absorption). The current performance of personal computers makes it realistic to model the order of 109 simulations of radiation emission and achieve accuracies of solid angle estimates typically better than 0.03%. (authors)
Rayleigh-Bénard convection at high Prandtl numbers in circular and square geometry
Johnston, Stephen R.; Fonda, Enrico; Sreenivasan, Katepalli R.; Ranjan, Devesh
2015-11-01
Experiments using water and simulations have shown that flow structures and turbulent fluctuations in Rayleigh-Bénard convection are affected by the shape of the container. We study the effect of the geometry in both square and cylindrical test cells of aspect ratio of order unity in high Prandtl fluids (up to 104). Flow visualization using a photochromic dye seeded throughout the fluid allows us to uninvasively study the evolution of the large scale structures. We discuss the observations in the two geometries and compare them with previous observations at low Prandtl numbers.
杨锦文; 何意; 鲍锋
2014-01-01
The flow around cylinder is one of the classic research issues of fluid mechanics.The modifica-tion of the cylindrical geometry will affect the cylinder’s pressure distribution and near wake flow structures. The present study on slotted cylinder has some certain values in engineering applications such as vortex gen-erator in flow meters and heat convection.Large eddy stimulation based on 3-D Fluent code was carried out for cylinders with slit,with respect to test model of ratio of slit width to diameter s/d =0.15 on five different Reynolds numbers (Re =1500、3000、4400、5837、7200).By the means of qualitative flow visualization and quantitative PIV experiments,the flow patterns between the slit and the shedding vortex of the baseline and slotted cylinder were carefully investigated,measuring and predicting of the shedding vortex frequency were included.The results of numerical simulation agreed well with the experimental measurement.The experi-mental and computational results show that the flow in the slit demonstrated periodic motion,this oscillating vent-flow has greatly altered the near wake flow features.The periodic oscillation in the slit has enhanced the periodicity of the flow around circular cylinder;consequently,the slotted cylinder exhibited an increase in shedding vortex frequency and Strouhal number compared with their baseline case at the same Reynolds numbers.Meanwhile,The wake of the slotted cylinder presented obvious three dimensional features.%基于 Fluent 软件平台采用大涡模拟（LES）的方法对开缝圆柱绕流进行了三维数值仿真，计算了五组不同雷诺数（Re ＝1500、3000、4400、5837、7200）情况下缝宽比 s/d ＝0．15的开缝圆柱绕流流场。通过定性的流动显示和定量的 PIV 实验，对 s/d ＝0．15情况下开缝圆柱内部缝隙流动以及旋涡脱落情况进行了细致研究，并测量了基准圆柱与开缝圆柱的脱落涡频率。数值模拟与实验测量结果符合
Bai, Xiao-Dong; Zhang, Wei; Guo, An-Xin; Wang, Yong
2016-04-01
A global stability analysis is performed for the flip-flopping wake pattern behind two side-by-side cylinders with emphasis on the unstable vorticity field. The combination of direct numerical simulation with the state-of-art lattice Boltzmann method and dynamic mode decomposition is used to analyse such wake pattern for the first time. The vorticity mode of the secondary instability is extracted from the flow. Such mode is found to be symmetrical with respect to the geometric axis of symmetry. Furthermore, a new scenario is found for the high order harmonics that there is a pair of two tertiary modes as a result of nonlinear interaction between the mode related to the secondary instability and the global mode of the in-phase synchronized vortex shedding base flow. Besides, the reason for the Fourier spectra of the lift on the two cylinders being the same is also illustrated for this case.
A proper orthogonal decomposition (POD) method is applied to the problem of a two-dimensional flow past two side-by-side circular cylinders. Based on the POD bases, which are constructed by a snapshot method, a low-dimensional model is established for representing two-dimensional incompressible Navier-Stokes equations. Coupled with the low-dimensional model, the Chiba method is used to analyze the global stability of the basic flow. Different bifurcation paths at three major regions are revealed, in good agreement with the available results by other methods. However, the computation amount in the POD method is low, which shows the availability and advantage of the POD method. (fundamental areas of phenomenology(including applications))
AHMED N A
2006-01-01
A comprehensive hot wire investigation of the flow around a circular cylinder is carried out in an 18" × 18" wind tunnel to look into the dominant frequencies at the stagnation, separation and separated shear layers in the transition Reynolds number range. The majority of the experiments are carried out at Reynolds number of 4.5 × 104, with additional transition frequency tests at Reynolds numbers of 2.9 × 104, 3.3 × 104 and 9.7 × 104 respectively. The results are analysed in terms of power spectral density. While the frequency associated with stagnation is found to be essentially due to vortex shedding, frequency doubling of vortex shedding is also evident in the separated shear layers.Two peaks associated with transition frequencies are detected and their possible implications are presented.
Penland, Jim A
1954-01-01
Pressure-distribution and force tests of a circular cylinder have been made in the Langley 11-inch hypersonic tunnel at a Mach number of 6.86, a Reynolds number of 129,000 based on diameter, and angles of attack up to 90 degrees. The results are compared with the hypersonic approximation of Grimminger, Williams, and Young and with a simple modification of the Newtonian flow theory. The comparison of experimental results shows that either theory gives adequate general aerodynamic characteristics but that the modified Newtonian theory gives a more accurate prediction of the pressure distribution. The calculated crossflow drag coefficients plotted as a function of crossflow Mach number were found to be in reasonable agreement with similar results obtained from other investigations at lower supersonic Mach numbers. Comparison of the results of this investigation with data obtained at a lower Mach number indicates that the drag coefficient of a cylinder normal to the flow is relatively constant for Mach numbers above about 4.
Wang, Kun
2012-01-01
Photoacoustic computed tomography (PACT), also known as optoacoustic tomography, is an emerging imaging modality that has great potential for a wide range of biomedical imaging applications. In this Note, we derive a hybrid reconstruction formula that is mathematically exact and operates on a data function that is expressed in the temporal frequency and spatial domains. This formula explicitly reveals new insights into how the spatial frequency components of the sought-after object function are determined by the temporal frequency components of the data function measured with a circular or spherical measurement geometry in two- and three-dimensional implementations of PACT, respectively. The structure of the reconstruction formula is surprisingly simple compared with existing Fourier-domain reconstruction formulae. It also yields a straightforward numerical implementation that is robust and two orders of magnitude more computationally efficient than filtered backprojection algorithms.