Cylinder Of Square Cross-section Research Articles

Vortex shedding suppression for laminar flow past a square cylinder near a plane wall: a two-dimensional analysis

A numerical study on the uniform shear flow past a long cylinder of square cross-section placed parallel to a plane wall has been made. The cylinder is considered to be within the boundary layer of the wall. The maximum gap between the plane wall to the cylinder is taken to be 0.25 times the cylinder height. We investigated the flow when the regular vortex shedding from the cylinder is suppressed. The governing unsteady Navier-Stokes equations are discretized through the finite volume method on staggered grid system. A pressure correction based iterative algorithm, SIMPLER, has been used to compute the discretised equations iteratively. We found that the critical value of the gap height for which vortex shedding is suppressed depends on the Reynolds number, which is based on the height of the cylinder and the incident stream at the surface of the cylinder. At high Reynolds number (Re ≥ 500) however, a single row of negative vortices occurs for wall to cylinder gap height L ≥ 0.2. The shear layer that emerges from the bottom face of the cylinder reattaches to the cylinder itself at this gap hight.

Vortex shedding around a heated square cylinder under the influence of buoyancy

The influence of buoyancy on vortex shedding and heat transfer from a cylinder of square cross-section exposed to a horizontal stream has been studied.Unsteady Navier-Stokes and energy equations are solved numerically using a control volume approach. Flow field has been analysed for a wide range of Reynolds number (which is based on the cross-sectional height of the cylinder) and Grashof number with Richardson number between 0 to 1. Our results show that the centerline symmetry of the wake is lost and the cylinder experiences a downwards lift when the buoyancy effect is considered. Vortex shedding suppression doesn’t occur in the present case in which the cylinder is exposed to a horizontal cross-flow. Heat transfer from the cylinder increases due to increase in Reynolds number and Grashof number.

Implicit multigrid computation of unsteady flows past cylinders of square cross-section

An implicit, multigrid scheme has been extended to treat unsteady flows using the concept of temporal subiteration (or dual-time stepping, as it sometimes is called). The efficiency and accuracy of the subiterated, multigrid approach has been discussed in a previous paper. Here, the scheme is applied to compute the unsteady flow past fixed cylinders of square cross-section at moderate Reynolds numbers. The observed pattern of periodic vortex shedding is computed and the dimensionless frequency of this phenomenon (the Strouhal number) is compared with experimentally determined values. Results of coupled aeroelastic computations also are presented that illustrate a hysteresis phenomenon as the structural frequency is varied.

Nonlinear flow in porous media

The flow of an incompressible liquid at nonzero Reynolds number Re in a two-dimensional model porous medium is studied via numerical simulation. The geometry is a random array of cylinders of square cross section and spectral element methods are used. We find a transition from linear Darcy flow at vanishing Re, to a cubic transitional regime at low Re, and then a quadratic Forchheimer when Re=O(1). In addition, some general remarks on scaling behavior and the form of the flow equation at finite Re are presented. {copyright} {ital 1998} {ital The American Physical Society}

Discrete vortex model of flow over a square cylinder

Abstract The discrete vortex method (DVM) is used to numerically study the velocity field in the near wake of a 2-D cylinder of square cross-section. Vortex panels are used to model the cylinder surface, at which a no-penetration boundary condition was imposed. The DVM uses a series of individual vortex elements to model the separated shear layers of the cylinder. The discrete-vortex elements interact to form clusters in the wake region, which represent the larger vortical structures present in such flows. By careful choice of numerical parameters, good agreement is obtained with experimental measurements for the mean and fluctuating velocity fields in the near-wake region. The method is especially effective in modelling the unsteady, quasi-periodic motions associated with the large-scale vortex structures in the wake.

Unsteady flow and heat transfer for cylinder pairs in a channel

The incompressible, two-dimensional, unsteady flow past a pair of cylinders of square cross-section, placed in tandem normal to the flow in a channel, has been investigated by dye visualization and direct numerical simulation. The objective has been to evaluate the effect of cylinder separation distance, λ, on the flow behavior and heat transfer, for cylinder diameter ratios, D d , of 1 and 2 over a range of Reynolds numbers 200 ⩽ Re ⩽ 1600, based on the larger (downstream) cylinder diameter. A comparison between the experimental and numerical results for cylinders of equal cross-section dimensions shows very good agreement. The results for D d = 1 reveal three distinct flow patterns as a function of λ and Re which, apparently, have not been previously reported: (1) For 0.25 ⩽ λ ⩽ 4 with Re ⩽ 200, the inter-cylinder flow consists of a pair of steady counter-rotating eddies which do not exchange fluid with the surrounding flow and eddy shedding is observed only for the downstream cylinder. (2) For 0.25 ⩽ λ ⩽ 1.0 with 400 ⩽ Re ⩽ 1600, vertical flow oscillations arise in the inter-cylinder space, and the periodic ingestion of backward-jetting fluid from the top and bottom walls of the downstream cylinder into the inter-cylinder space is observed. For fixed λ the unsteadiness increases with Re but only the downstream cylinder sheds large eddies. (3) At a critical inter-cylinder spacing related to Re according to λ c ∼ Re − 2 3 , the shedding of large eddies also occurs at the upstream cylinder and this results in a highly mixed inter-cylinder flow. For a cylinder diameter ratio of D d = 2 , with the smaller cylinder located upstream of the larger heated cylinder, it is shown that for Re fixed an optimal location exists for the upstream cylinder such that the heat transfer from the downstream cylinder is maximized. The optimal location corresponds to a spacing smaller than the critical inter-cylinder spacing.

Interference in the wake of two square-section cylinders arranged perpendicular to each other

The flow around two cylinders of square cross-section arranged perpendicular to each other has been investigated in a steady, low-turbulence, uniform flow at Reynolds numbers of 2×10 4 and 1×10 4 (based on cylinder diameter and freestream velocity). Complex three-dimensional interference effects were found to exist in the wake of the cylinders, the precise nature of which is dependent upon their spacing. If the distance between the axis of each cylinder is less than three diameters, the interference effects are dominated by secondary flows associated with horseshoe vortex structures generated at the centre of the configuration, wheareas at spacings beyond this critical value, the disturbance is largely confined to the wake of the downstream cylinder. The paper examines these interference effects in detail for axis spacings up to a maximum of ten diameters.

The use of a forebody plate to reduce the drag and to improve the aerodynamic stability of a cylinder of square cross-section

The use of an upstream plate attached to a square bar is shown to reduce the drag of the original bar by up to 81%, depending on plate size and location. The plate serves to stabilize the bar against galloping by reversing the sign of the lift curve slope at small wind angles and also acts to reduce or eliminate vortex shedding excitation. The price paid for these benefits is an approximate doubling of the cross-wind response to turbulence at small wind angles due to the increased magnitude of the side force coefficient curve slope.

A model of the combined effects of vortex-induced oscillation and galloping

In this paper, the interactions of two forms of wind-induced oscillation of a cylinder of square cross-section in cross flow are modelled by simply combining the mathematical models of each form taken separately. The Hartlen-Currie model for vortex-induced oscillation is added to Parkinson and Smith's quasi-steady model for galloping and the resulting nonlinear oscillator equations are solved by a perturbation technique, the method of multiple scales. The results are compared with recent experimental data.

The calculation of the effective thermal conductivity of media with regularly dispersed parallel cylinders.

In treating problems of thermal conduction in dispersive media, it is necessary to calculate the effective thermal conductivity instead of analyzing the detailed thermal field. The present paper aims to estimate the effective thermal conductivity of two-dimensional media with regularly dispersed materials by applying the boundary element method. Media with parallel cylinders dispersed at square lattice points are considered. It is assumed that two-dimensional thermal conduction takes place in the plane normal to these cylinders. In the case of regularly arranged circular cylinders, the present authors have also developed an exact analytical method. The present method is compared with the previous one by carrying out numerical calculation and the result is satisfactory. The method is also applied to analyze the case of cylinders of square cross section.

Turbulent disruptions from the Strauss equations

The Strauss equations of reduced resistive magnetohydrodynamics are solved pseudo-spectrally, inside a cylinder of square cross-section. Conducting, free-slip, boundary conditions are imposed at the boundaries normal to the direction of the imposed d.c. magnetic field and net current, and periodic boundary conditions are imposed in the third direction. The emphasis is on the development of disruptions. Initial conditions are not analytical equilibria, and are characterized by wide-band noise perturbations in many Fourier modes. Typical spatial resolution is 32 × 32 × 16. At this resolution, the code takes approximately 0·7 seconds per time step on a CRAY-1 computer. Lundquist numbers are limited by the need to resolve the small-scale turbulence which develops. Disruptions are characterized by (i) a burst of kinetic fluid activity which is roughly equipartitioned with the magnetic fluctuations at the small scales, but which involves overall kinetic energies which are much less than the magnetic energies; (ii) a helical ‘m = l, n = 1’ current filament which develops out of the wide-band turbulent noise and wraps itself around the magnetic axis; and (iii) relatively mild disturbances of the magnetic field lines, at least at these low values of Lundquist number (S ≃ 100). The results are compared with those from similar codes which solve the linearized Strauss equations.

Part II: Spanwise Correlation and Loading

SummaryThe influence of spanwise correlation of fluctuating pressures due to vortex shedding on the total oscillatory loading of a long bluff cylinder in cross-flow is considered. Experimentally determined pressure correlation lengths on a stationary and vibrating cylinder of square cross section are then combined with previously obtained chordwise pressure distributions to demonstrate the amplification of the oscillatory lift on a long bluff cylinder during cross-flow vibrations.

Resonant solutions involved in the integral equation approach to scattering from conducting and dielectric cylinders

Resonant solutions involved in the integral equation formulation for analyzing the scattering problems and the elimination of these erroneous solutions are investigated. The parameter ranges where the resonant solutions are mixed into the correct ones and the degree of errors caused by the resonant solutions are checked on through numerical computation of matrix condition numbers and scattering cross sections for dielectric cylinders of square cross section with side width/wavelength ratio being less than about 1.27. As a of removing the resonant solutions, the taking some lower order equations of the so-called extended boundary condition (EBC) method into consideration is proposed.

Field behavior near a dielectric wedge

A review of the theory of field behavior near a dielectric wedge is presented. An overview of the static results is given, and it is shown that the series of Meixner for the dynamic case in general is nonexisting. Numerical results for scattering by a dielectric cylinder of square cross section indicate that the static results give an accurate account for the rate of growth of the fields in the singular cases, but some disagreement in nonsingular cases.

角柱周辺の気流および風圧力に関する数値解析的研究 (第 2 報)

A method is investigated for the solution of time-dependent problems concerning wind flow and wind pressure around a structure in two-dimensional, turbulent, airflow at large Reynolds numbers. The method is numerical, using a computer, for the solution of a finite-difference approximation to the governing equations of motion, with subgrid scale effects simulated with eddy coefficients proportional to the local velocity deformation. The computational example is given about a long cylinder of square cross-section with a front angle of attack, and the result seems to be in good agreement with the experimental data. It is concluded that the numerical approach to the problem of such as a Building scale phenomenon is already profitable.

Stagnation and Reattachment Lines on a Cylinder of Square Cross-section in Smooth and Turbulent Flows

Flow visualization experiments have been performed to ascertain the positions of stagnation and reattachment lines on a cylinder of square cross-section at various angles of incidence with and without turbulence in the ambient flow. Vickery1 found that the introduction of turbulence into the ambient flow caused a significant increase in base pressure coefficient at low angles of incidence. He tentatively explained this effect by supposing that the turbulence caused reattachment. McLaren et al.2 explained their data by the same supposition and it is also accepted in the discussion of Hunt3 on flow around buildings. Kavur4 found, however, that no reattachment occurred at zero angle of incidence even for extremely high levels of turbulence. This disagreement is discussed by Bearman5. My investigation was intended, in part, to throw light on this problem.

Spectral and dosimetric characteristics of soft X rays for studies in radiobiology.

A DEMOUNTABLE x-ray generator has been developed to investigate the radiobiological effects of soft x rays (1). This generator (Fig. 1) is capable of operating with high D.C. currents at relatively low potentials (e.g., up to 500 MA at 6 kV). I t consists of a Pierce type electron gun (2) and a water-cooled target. The use of the gun permits a large current even at an 11.5-cm target-cathode spacing. This large spacing is required to prevent deposition on the target of a significant amount of tungsten evaporated from the filamentary cathode. Such a deposit would change the target from the selected material to tungsten. The target is constructed from a hollow copper cylinder of square cross section. Each face of the cylinder forms one target and the target material is applied to the copper by vacuum evaporation. The design permits the use of each of the four different target materials without disturbing the vacuum. A thin composite window formed by a beryllium foil and a Mylar film isolates the high vacuum ...

Fluctuating lift and drag on a long cylinder of square cross-section in a smooth and in a turbulent stream

The paper presents the results of measurements of fluctuating lift and drag on a long square cylinder. The measurements include the correlation of lift along the cylinder and the distribution of fluctuating pressure on a cross-section. The magnitude of the fluctuating lift was found to be considerably greater than that for a circular cross-section and the spanwise correlation much stronger.It was found that the presence of large-scale turbulence in the stream had a marked influence on both the steady and the fluctuating forces. The most significant changes were at small angles of attack (%alpha; < 10°) and included a reduction in base suction and a decrease in fluctuating lift of about 50%.