Row Of Cylinders Research Articles

Stability of a row of noncircular cylinders in an elastic matrix with finite strains

Stability of a row of noncircular cylinders in an elastic matrix with finite strains

Fluid flow behavior around a circular cylinder perpendicular arrangement of circular cylinders.

Fluid flow behavior around a circular cylinder placed downstream of and perpendicular to a single row of cylinders in a uniform flow was investigated varying the distance (L) between upstream and downstream cylinders. Flow visualization techniques (oil-film and smoke-wire methods) and a near-surface flow direction judgement (flow direction probe method) were used, and time-averaged and fluctuating pressure distributions on a circular cylinder were measured under the constant Reynolds number, Re=5×104. It was clarified that the flow structure could be divided as a border of L/D=2.5. In the connection with the vortex transfer, especially, the three-dimensional separation bubble formed at L/D≤2.5 was the result of the stretching of separating shear layers due to the horseshoe-like vortex and inner secondary vortex. At this distance, the span-averaged drag of the downstream cylinder was less than 1.15 times that of a single cylinder.

The particle collection efficiency of a cascade of cylinders

AbstractThe entry flow and the trajectories of small solid particles into a fibrous filter, which is modelled as a single row or cascade of cylinders, is examined. Both large (potential) and small (creeping) Reynolds number flows through the cascade of cylinders are treated using the Boundary Element Method (BEM). Results for the collection efficiency are presented as functions of the Stokes number for both types of flow and are shown to be in excellent agreement with existing published results. An asymptotic expansion of the flow is developed both upstream and downstream of the cascade and it is shown to significantly affect the collection efficiency.

Stability of particle motions in a narrow channel flow.

Single rows or two rows of identical circular cylinders spaced regularly in a narrow channel flow have been shown to be capable of steady flow provided the cylinders are located at equal lateral positions and with equal spacings in the flow direction. The stability of such steady flows of circular cylinders is studied for periodic perturbations of the particle positions, assuming that every other cylinder is equally perturbed in lateral position and spacing along the channel. This results in two rows which are not symmetrically placed. The suspending fluid is assumed to be an incompressible Newtonian fluid. It is assumed that no external forces or moments act on the cylinders and the effects of inertia forces on the motion of the fluid and the cylinders are negligible. The velocity field of the suspending fluid and the instantaneous velocities of the cylinders are computed by the finite element method. The translational velocities of the cylinders are obtained for a large number of particle positions, from which the trajectories of their relative motion are determined for various initial positions near the regular single-file and two-file arrangements. It is shown that when the initial arrangements of the cylinders are slightly perturbed from the regular (alternating) two-file flows, the trajectories of their relative motions become small closed loops around the regular two-file arrangements. In contrast, such small closed trajectories are not obtained when they start from the arrangements near the regular single-file flows or regular (symmetric) double-file flows, suggesting that these flows are unstable under the conditions examined.

Stability effects in a normal triangular cylinder array

Fluid-elastic vibrations in tube bundles are often responsible for major damage and very high shutdown costs. The onset is manifested by a rapid increase in the tube vibration amplitude at a particular critical flow velocity and is strongly dependent upon various physical parameters. In this paper, experimental results showing a second stability boundary for a flexibly mounted cylinder in an otherwise fixed cylinder array are presented. It is shown that minor variations of the array geometry affect its vibration mode. The stability boundaries, for various configurations of flexibly mounted and fixed cylinders in the array, have been measured. The resulting stability boundaries are plotted as functions of the mass-damping parameter and amplitude-diameter ratio in stability diagrams. The results are critically compared with known results from the literature. A closed-circuit wind tunnel with a 1·5 m diameter, 2·1 m long test section is used for the tests. The eighteen 80 mm × 800 mm aluminium cylinders in the multi-row normal triangular array have a pitch-to-diameter ratio of 1·25 and are, when not fixed, linear iso-viscoelastically mounted. Additionally, the linear damping of nine cylinders (4, 3 and 2 cylinders in the first, second and third cylinder row, respectively) can be continuously varied over the wide mass-damping parameter range of 10 2

Forward Scattered Sound Field by Parallel Cylinders

The sound fields scattered in the forward direction by a line row of parallel cylinders are measured in a water tank and calculated theoretically. The effects of diameter, spacing, and materials on the sound fields are investigated. The fields are calculated using a multiple scattering formula. Theoretical and experimental studies have confirmed that the sound shielding effects are large in cylinders with a pressure release wall with a small spacing. This result appears to be useful for the design of sound shielding walls in water.

Local heat transfer characteristics from a circular cylinder placed downstream of and perpendicular to a single row of cylinders.

Local heat transfer characteristics from a circular cylinder placed downstream of and perpendicular to a single row of cylinders.

Unsteady fluid dynamic forces acting on a single row of cylinders vibrating in a cross flow

This paper examines the vibrational characteristics of a single row of three circular cylinders, of small aspect ratio (1-93), subjected to a water cross flow, and clarifies the unsteady fluid force acting on the cylinders. The cylinder system, having a pitch-to-diameter ratio of 1.33 and mass-damping parameter of about 0-5, exhibits two kinds of instability, i.e., an out-of-phase mode instability and an in-phase mode instability, occurring at the low, reduced velocity of 2.9 and the high, reduced velocity of 12.6, respectively. An unsteady fluid force, measured by forcing the central cylinder to oscillate sinusoidally in water at the natural frequency of the two nearby cylinders which are free to vibrate, reveals a phase-lead of the force with respect to displacement. This phase-lead reaches about 30 degrees, for an oscillation amplitude of 10% of the cylinder diameter. Wake flow patterns show an oscillation of the flow separation points with a phase-lead to the cylinder motion; this may be considered as a major reason for the phase-lead of the unsteady force to displacement, generating, in turn, a negative damping in the cylinder system.

FLOW THROUGH A ROW OF CLOSELY-SPACED CIRCULAR CYLINDERS NORMAL TO A COLD WATER STREAM

Flow near a row of parallel circular cylinders standing normal to a cross flow has been investigated experimentally. The cylinders spanned the height of the test section in a water tunnel in which the temperature was maintained close to the freezing point. Reynolds numbers, based on the mean bulk water velocity and the cylinder diameter, ranged between 3 x 103 and 3 x 104. The gap-diameter ratio g/D was set at five nominal values: 0.49, 0.20, 0.15, 0.10 and 0.06. For this range of conditions, static pressure readings were taken around the cylinder surfaces and at points well upstream and downstream of the cylinders. The overall static pressure change was converted into a pressure loss coefficient whose dependency on Reynolds number and gap-diameter ratio has been studied. The cylinder surface pressure profiles were used to determine flow behaviour in the gap region and in the wake. A critical transition at free stream Reynolds numbers much lower than that corresponding to a single cylinder was evident; a gap-diameter ratio near to 0.15 appeared to separate two different flow regimes. A cellular wake was often observed and found to be either metastable or bistable.

WATER WAVE SCATTERING BY ROWS OF CIRCULAR CYLINDERS

The scattering of waves by a finite number of rows of circular cylinders is examined. Reflection and transmission coefficients are obtained and compared to Kakuno's experimental data. Following Twersky (1962), the scattering from a single row of cylinders (or the single grating problem) is numerically solved. The wide-spacing approximation is used to find the effect of multiple gratings.

Heat transfer between gas-liquid spray stream flowing perpendicularly to the row of the cylinders

Experimental investigation and analysis of heat transfer process between a gas-liquid spray flow and the row of smooth cylinders placed in the surface perpendicular to the flow has been performed. Among others, there was taken into account in the analysis the phenomenon of droplets bouncing and omitting the cylinder as well as the phenomenon of the evaporation process from the liquid film surface.

Small vesicle bouton synapses on the distal half of the lateral dendrite of the goldfish Mauthner cell: freeze-fracture and thin section study.

To understand principles of synaptic integration, it is necessary to define the types of synapses on a particular neuron and their distribution. Thin sectioning and double replica freeze-fracture techniques were employed to characterize the small vesicle bouton (SVB) synapses on the distal half of the Mauthner (M) cell lateral dendrite, which probably mediate a remote dendritic inhibition. Three morphologically distinct SVB synapses, types A, B, and C, were found. These three SVB synapses form roughly 90% of the synapses on the distal half of the lateral dendrite, with types A and B being most common. The SVB A synapse is characterized by mostly oval and round synaptic vesicles, a discrete presynaptic active zone with a highly variable shape, and a postsynaptic active zone with no apparent particle aggregate in either the E or P face. At the SVB B synapse, most of the synaptic vesicles are flat. A very high particle density is present throughout the presynaptic P face, and vesicle attachment sites are dispersed over much of the presynaptic membrane. Postsynaptic P face particle aggregates are subjacent to the presynaptic vesicle attachment sites, and are often large and anastomosing. The SVB C synapse is characterized by synaptic vesicle profiles that vary from flattened to round. The SVB C cytoplasm was unclouded by the flocculent material that characterized SVBs A and B. The presynaptic active zones at the SVB C synapse are discrete, and macular or oblong. No particle aggregates are apparent in the postsynaptic active zone. Small, macular particle aggregates were found in nonactive zone regions of the postsynaptic E face of all three types of SVBs. Small subsurface cisterns were also observed underlying the M cell membrane at all three types of SVB synapses. Neither the postsynaptic E face aggregates nor the subsurface cisterns were ever observed directly subjacent to presynaptic active zones, but were often seen adjacent to active zones. Short, straight rows of particles and short cylinders were often seen in both pre- and postsynaptic surrounding zone regions of SVB A and C synapses. These structures are thought to represent tight junctions.

加熱円柱・円柱列周囲の流れの数値計算

It is investigated to predict heat transfer and to visualize air flows around a cylinder and a single row of cylinders. Direct numerical simulation of Boussinesq approximated NavierStokes equation is carried, and upwind finite defference method with third order accuracy is used. Generalized cordinate system is adopted to give flexibility on treating objects to calculate.The results of calculations are visualized on a computer graphic display and made into animations. The results are successfully coincident with experiments, and some visualizations of the air flows are shown in this report.

Vibrations of circular cylindrical structures subjected to two-phase cross flows.

This paper reviews a vibration problem relating to industrial energy equipment such as steam generators, heat exchangers. and condensers. It focuses on unstable vibrations in circular cylindrical structures immersed in two-phase cross flows, which are caused by unsteady fluid forces induced by the interaction between structural vibration and the fluid flow. Added mass and fluid damping induced by a vibrating circular cylinder in a two-phase bubble fluid are introduced, and then the effects of air bubbles on vortex-induced vibrations such as in-line and cross-flow oscillations of a single circular cylinder are reviewed experimentally. Finally, fluidelastic vibrations in a single row of cylinders as well as in cylinder arrays are discussed in relatlon to air bubble effects on instability criteria with respect to reduced velocity and mass-damping parameters.

Mass transfer in creeping flow past periodic arrays of cylinders.

Creeping flow past a square and an equilateral triangular array of cylinders and mass transfer between the fluid and the surface of the cylinders were studied theoretically. A numerical solution for the drag coefficient of the cylinders was obtained and found to be in good agreement with the asymptotic analytical solutions for very small and very large values of the dimensionless pitch respectively. A numerical solution for the Sherwood number was obtained as a function of the Peclet number, the dimensionless pitch, and the number of rows of cylinders in square and triangular arrays. Theoretical predictions for the drag coefficient of the cylinders and the Sherwood number were compared with approximate analytical solutions based on the free-surface model by Happel.

Aerodynamic characteristics of an airfoil in periodic gusts. Effects of separation bubble's behavior on airfoil performance.

The effects of periodic gusts on the performance of an airfoil are investigated. Periodic gusts were generated by the movement of a row of cylinders crossing in front of an airfoil. Total pressure loss, unsteady pressure distribution on the airfoil surface and velocity fluctuation were measured. The airfoil investigated here has a separation bubble on its suction surface, which increases total pressure loss even if the angle of attack is small. But as either frequency or solidity of cylinders increases, the separation bubble tends to disappear, followed by recovery of total pressure.

Numerical calculation of particle collection by a row of cylinders in a viscous fluid

AbstractA method for calculating the collection efficiency of particles by a row of cylinders in a viscous fluid is presented. The Navier‐Stokes equation is solved by the finite element method to determine the carrier gas velocity field. Then, the particle equation of motion is also solved by the finite element method to find the particle velocity of impact. Finally, the collection efficiency is obtained by integration of the intercepted particles on the cylinder surface. Results of this model are compared with other theoretical models as well as with some experimental data.

A constrained-mode analysis of the fluidelastic instability of a double row of flexible circular cylinders subject to cross-flow: A theoretical investigation of system parameters

A new method of solution is proposed for a previously developed stability analysis of a double row of flexible cylinders subject to a fluid cross-flow. The double row of flexible cylinders may either be by itself or positioned in an array of rigid cylinders, the latter case being more representative of heat exchanger tube arrays. This new method of solution enables a long double row of fluid-dynamically coupled flexible cylinders to be adequately represented, from a stability viewpoint, by a two-cylinder kernel. This is done by prescribing a specific inter-cylinder modal pattern, and this is the reason for calling this the constrained-mode solution. A comparison of the critical flow velocities obtained via (i) this solution and (ii) the more complete long-row solution shows that the agreement between them is excellent. It is also shown that for some combinations of cylinder array geometry and mass-damping parameter the theoretical stability boundary of a single flexible cylinder surrounded by rigid cylinders is sensibly the same as that for a full array of flexible cylinders, the instability mechanism for these cases being virtually entirely due to negative fluid damping. However, for other cases where fluidelastic-stiffness effects are important, the flexibility of adjacent cylinders has a significant effect on the stability. The constrained-mode solution is capable of dealing with both of these instability mechanisms. By using the constrained-mode analysis, theoretical stability boundaries are obtained and compared with experimental data from similar cylinder arrays, plotted in terms of the critical reduced flow velocity versus the mass-damping parameter. Although the shape of the theoretical curve agrees well with the experimental data, theory consistently under estimates the experimental data points, by a factor of approximately 2. It is shown that the discrepancy may be partly due to small frequency differences between cylinders, which will inevitably be present in any cylinder array, raising the critical flow velocity of the experimental data points and bringing them closer to the theoretical values. This effect of frequency detuning is particularly important for high values of the mass parameter and low cylinder mechanical damping; however, it becomes less important for low values of the mass parameter and high values of cylinder mechanical damping.

WAVE DIFFRACTIONS BY ROWS OF VERTICAL CYLINDERS OF ARBITRARY CROSS SECTION

Wave diffractions by a number of (a group of or a row of) vertical cylinders have been investigated in connection with, e.g., multilegged offshore structures (Spring and Monkmeyer(1974), Ohkusu(1974), Chakrabarti(1978), Mciver and Evans(1984), etc.); Wave-Power absorption devices (Miles (1983), Falnes(1984) , Kyllingstad(1984) , etc.); Wave barrier systems (Massel(1976), Kakuno and Oda(1986), etc.). Most of the previous works were, however, mainly aimed at the wave diffractions by cylinders of circular cross section and/or by cylinders of relatively small dimensions compared to wave length. In this paper, we describe a simple yet versatile analytical method to solve wave diffractions by infinite rows of vertical cylinders. In the method, it is assumed, in addition to usual linearised small amplitude assumptions, that: the row of cylinders is composed of infinite number of surface-piercing evenly spaced equal cylinders fixed on sea bottom; incident wave direction is perpendicular to the row; the number of rows may be arbitrary, at least in principle; the cross sectional shape of the cylinders may be arbitrary as long as it is symmetrical with respect to the incident wave ray; and the cylinders are relatively large compared to incident wave length so that inertial forces are predominant to drag forces.

Efects of air bubbles on flow-induced vibrations and unsteady fluid force in a single row of circular cylinders.

We studied experimentally the characteristics of unsteady fluid forces in single-phase water and two-phase air-water flows using one sinusoidally oscillating and two elastically supported circular cylinders. We also studied the effects of air bubbles in suppressing vibration in a single-row of cylinders. Adding air bubbles reduced cross-flow-induced, unstable vibrations occurring at a reduced velocity of about 3 in a water flow. Unsteady fluid forces were very large and led to displacement in the phase angle when the single-row cylinder system was vibrationally unstable. The two-phase flow-induced fluid forces became small and rather random when the displacement was small. We discussed the vibration suppression mechanism by comparing the unsteady fluid force characteristics of single-and two-phase flows.