Row Of Cylinders Research Articles

Analytical/Numerical Study of Fluid Flow and Heat Transfer Across In-Line Cylinders

An integral approach to boundary-layer analysis is employed to investigate the effects of the longitudinal-pitch ratio on fluid flow and heat transfer from a longitudinal row of circular cylinders immersed in an infinite medium. The momentum equation is solved using the modified von Kármán–Pohlhausen method, which employs a fourth-order velocity profile within the hydrodynamic boundary layer. The potential-flow velocity is obtained by complex potential theory outside the boundary layer. A third-order temperature profile is used in the thermal boundary layer to solve the energy integral equation for the isothermal boundary condition. Closed-form solution is obtained for the heat transfer coefficient for a longitudinal row of circular cylinders immersed in an infinite medium. In the second part of this research activity, a numerical model based on computational fluid dynamics is developed to validate the closed-form solution. The proposed numerical model has been successfully implemented for simulating the flowfield over a longitudinal row of circular cylinders. Numerical simulations have been carried out for various values of the freestream Reynolds number and longitudinal-pitch ratio. The results obtained from the analytical and numerical models have been found to be in good agreement. The maximum percentage error in values of the average Nusselt number obtained from the numerical and analytical solutions is less than 9% and reduces further to a value of less than 4% with an increase in values of the freestream Reynolds number.

Effect of gap spacings on flow past row of rectangular cylinders with aspect ratio 1.5

Two-dimensional numerical study has been carried out to investigate the effect of gap spacings for flow past five side-by-side rectangular cylinders using the lattice Boltzmann method at a Reynolds number of 150 and aspect ratio defined as AR=length/height=1.5. The gap spacing between the cylinders is varied systematically from g=0.5 to 4, so that the sensitivity of the flow and force statistics can be inspected. The gap spacings have strong effect on the hydrodynamic interaction of the cylinders wakes which significantly affects the flow structure. The flow behavior can be grouped into five patterns: (i) symmetric, (ii) flip-flopping, (iii) in-phase and anti-phase modulated deflected, (iv) in-phase modulated non-synchronized and (v) in-phase and anti-phase modulated synchronized. Calculations of mean drag coefficient, Strouhal number and root-mean-square value of drag and lift coefficients are carried out on each cylinder and compared with available literature. Each flow pattern will be studied in terms of wake structure, power spectra analysis of lift coefficients and time analysis of drag and lift coefficients. The average Strouhal number and average drag coefficient show significant variation against gap spacing.

一列加熱円柱列まわりの強制対流熱伝達

Forced convective heat transfer from a single row of cylinders placed in the longitudinal and the transverse direction to the flow was investigated experimentally. The average Nusselt numbers from the longitudinal row of six-cylinders were first measured in the range of Reynolds numbers Red =160-2000 and the spacing between cylinders G =5-70mm, where the cylinder diameter d were varied as d=8.4 and 14.4mm. Similar measurements were also carried out for the transverse row of multiple cylinders. It is found that the average Nusselt numbers NuG are well correlated with the non-dimensional parameter ReG (G/d) for both cases of the longitudinal and transverse row of cylinders, where NuG and ReG stand for the Nusselt and Reynolds numbers based on the cylinder spacing.

Numerical study on characteristics of flow and thermal fields of offset cylinder arrays in the middle Reynolds number range

In order to offer a detailed explanation for heat transfer enhancement caused by the instability, a computational model for offset cylinder arrays was established by using a compound grid system. The fully implicit forms of continuous equation, unsteady Navier–Stokes equations and energy equation were finite-differenced. The numerical results demonstrate that cylinder row pitch plays an important role on the flow effects, which enhance or deteriorate the heat transfer on cylinder surfaces. Among these flow effects, the acceleration effect and the instability effect are the main factors for enhancing the downstream cylinders. Moreover, heat transfer enhancement caused by the flow instability is an effective way to reach the aim of reducing flow resistance and promoting heat transfer.

DNS of unsteady effects on the control of laminar separated boundary layers

The main factor that determines the efficiency of a high-lift low-pressure-turbine operating at low Reynolds numbers is the size of the laminar separation bubble that forms on the suction side of the turbine blade. In this study, the suction side of a low-pressure gas-turbine blade is modeled as a flat plate with a streamwise pressure distribution. The combined effects of discrete surface roughness and periodic large-scale wake forcing on separation bubble transition and control are investigated numerically by direct numerical simulation. The laminar separation bubble is controlled by positioning the roughness element upstream of the separation bubble and introducing a low-frequency large-scale wake forcing. The three-dimensional discrete roughness with varying roughness height in the spanwise direction is modeled using immersed boundary method. The wake effect is numerically modeled as the mean wake deficit profile created by a linear row of cylinders moving in a direction perpendicular to the flat plate. Results indicate that the location of transition and hence the shape and extent of the separation bubble, largely depend on which of the above-noted passive control mechanisms dominates the unsteady transition process. It is shown that considering the mean flow properties, the roughness effect is found to be negligible compared to the individual wake effect.

Fluid flow and heat transfer of natural convection induced around a vertical row of heated horizontal cylinders

Natural convective flow and heat transfer induced around a vertical row of heated horizontal cylinders were investigated experimentally. The experiments were carried out with the 10-cylinder rows of diameters d=8.4, 14.4, 20.4mm. The cylinder rows were placed in air with vertical gaps ranging from G=3.6mm to 150.6mm. These enabled the experiments in the wide ranges of the modified Rayleigh numbers 5×102<Rad∗<105, and the non-dimensional gaps (G/d)=0.176–17.9. The flow fields around the row were first visualized using a smoke. The results depicted that the plumes arising from the upstream cylinders remain laminar throughout the rows when the gaps between cylinders are smaller than 20.6mm. While when the gaps are larger than 30.6mm, the plumes begin to sway and undergo the turbulent transition on the halfway of the rows. The average heat transfer coefficients from the individual cylinders in the row were subsequently measured. They showed a monotonous decrease toward downstream when the flow remains laminar. While when the turbulent transition occurs, they turn to increase. The coefficients were next arranged with various parameters to obtain non-dimensional heat transfer correlations. Among those parameters, the parameter RaG∗ (G/d) was found to best correlate the present Nusselt numbers NuG, where, RaG∗ and NuG are the gap-based modified Rayleigh and the average Nusselt numbers. Moreover, the non-dimensional heat transfer correlations were proposed both for the laminar and turbulent flows based on the data plots in NuG–RaG∗ (G/d) plane. The proposed correlations are very simple but can predict the Nusselt numbers quite satisfactory.

Sound Propagation in Rows of Cylinders of Infinite Extent: Application to Sonic Crystals and Thickets Along Roads

Sound Propagation in Rows of Cylinders of Infinite Extent: Application to Sonic Crystals and Thickets Along Roads

Inertial Deposition of Aerosol Particles in a Periodic Row of Porous Cylinders

The aerosol flow through a periodic row of parallel porous cylinders is investigated. The air flow field outside the cylinders is described by the Navier–Stokes equations of viscous incompressible fluid. The extended Darcy–Brinkman equations are used to calculate the flow velocity inside a porous cylinder. The dependence of the efficiency of the deposition of aerosol particles by inertial impaction and interception on the Stokes number for various values of the Darcy number is studied. Comparison of the results obtained from the numerical model and an approximate analytical model is given. The combined approximate formula for the deposition efficiency of a cylindrical fiber in a parallel array proposed by Müller et al. (2014) is extended for the porous cylindrical fiber. The aerosol flow through the porous body composed by a random array of cylinders is calculated to estimate the interior deposition.Copyright 2015 American Association for Aerosol Research

Modelling the Pore Level Heat Transfer in Porous Media Using the Immersed Boundary Method

This work presents the extension of a compact finite difference immersed boundary method for the detailed calculation of fluid flow and heat transfer in porous media. The unsteady incompressible Navier-Stokes and energy conservation equations are solved with fourth-order Runge-Kutta temporal discretization and fourth-order compact schemes for spatial discretization, which allows achieving highly accurate calculations. Verification proves that the method is higher than third-order accurate. Three test cases were used for the validation of the method: (i) isothermal flow around a square cylinder in a plane parallel channel, (ii) isothermal flow through an infinite row of square cylinders and iii) flow and heat transfer around a square cylinder in a plane parallel channel. The validation tests establish confidence in the application of the method to porous media. As an example of such an application, direct numerical simulations are conducted for a staggered array of equal size square cylinders. Although the problem is rather complex from the geometrical point of view, a Cartesian grid is employed, with all its advantages. The potential of applying an immersed boundary method to the solution of a multiphase problem with complex internal boundaries is demonstrated.

CFD Simulations to Determine Wave Forces on a Row of Cylinders

The open source Computational Fluid Dynamics (CFD) model REEF3D is used to simulate interaction of low steepness linear waves and high steepness 5th-order Stokes waves with a single cylinder and linear arrays of two, three, four and five large cylinders. The wave forces on any cylinder in the array is seen to generally increase with the inclusion of additional downstream cylinders in both cases. The wave forces on the downstream cylinders also reduce along the length of the array and the most downstream cylinder experiences the least forces in the array. The formation of standing waves in between the cylinders is observed in the case of low steepness incident waves. The wave forces on the most downstream cylinder in the array is almost equal to the force on a single cylinder in the case of low steepness incident waves and less than the force on a single cylinder in the case of high steepness incident waves.

Dynamic behavior of flow around rows of square cylinders kept in staggered arrangement

A two-dimensional numerical study is carried out to understand the vortex dynamics behind two rows of square cylinders arranged in a staggered fashion in an unbounded medium and at low Reynolds number (Re=100). A uniform cross flow of an incompressible fluid is considered. The transverse spacing between the cylinders is varied (S/d=1, 2, 3 and 5; with S and d are the transverse spacing and cylinder size) while the streamwise gap is fixed at L/d=1 (L being the streamwise gap). Computations are performed by a finite volume based CFD solver using PISO algorithm. An unsteady two-dimensional laminar model is used for all the computations. Effect of transverse spacing on flow characteristics and global fluid dynamic parameters are discussed. Furthermore, the establishment of the low-dimensional chaotic nature of the flow is predicted for relatively small transverse spacing of the cylinders. The transition to chaos is manifested through a quasi-periodic route. The quasi-periodic route to chaos is established through different characterization tools, such as the spectra, autocorrelation function, time-delay reconstruction and the Poincare section. The chaotic behavior of the flow system is quantified through the calculation of the Lyapunov exponent and fractal dimension.

Numerical study of aperiodic phenomena past two staggered rows of cylinders in cross-flow

The results of a numerical study of cross-flow past two staggered rows of cylinders are presented, at a fixed Reynolds number equal to 200. The upstream row comprised three and the downstream row four cylinders, for centre-to-centre pitch ratios in the streamwise direction, S/D, varying between 0 and 1. The distance between the centres of adjacent cylinders on the same row was equal to 3 cylinder diameters. The finite element method was employed for the solution. Significant fluctuations of the hydrodynamic forces, especially in the streamwise direction, were observed for all cylinders. Although for each longitudinal pitch ratio the variation of flow pattern with time appears almost chaotic, systematic attempt was made for the classification of the various flow regimes. A common characteristic of all longitudinal pitch ratios is the switch of wake width behind the cylinders of the downstream row. For S/D≤0.5 the formation of a large and symmetrical wake occurred intermittently past the downstream cylinders, with drastic impact on the entire flow domain. High shedding frequencies past the cylinders of the upstream row were detected for S/D≤0.5, which could reach two or even three times the shedding frequency past the cylinders of the downstream row.

Acoustic confinement and waveguiding in two-dimensional phononic crystals with material defect states

In this paper, we present the theoretical investigation of acoustic confinement and waveguiding in two-dimensional phononic crystals with material defect states. In contrast to the typical formation pattern of defect states, the proposed material defect states are created by replacing single cylinder in the core center or one row of cylinders in the perfect phononic crystal with different material cylinders. The dispersion relations and the power transmission spectra are studied by using the finite element method in combination with a supercell technique. With the introduction of material defects into perfect phononic crystals, defect states and bands appear, elastic waves of specific frequencies are localized in the point defects or along the line defects, respectively. The displacement fields of the eigenmodes are carried out to further intuitively illustrate the acoustic confinement and waveguiding in the material defect states phononic crystals. Furthermore, the effects of the material parameters of defects on the point defect states and waveguiding are further explored numerically. Numerical results show that, the location and number of defect states can be efficiently modulated by the material parameters of defects. The material defect states are more sensitive to the density parameters than the elastic constants when the elastic modulus of the defects is far higher than that of matrix.

Second-order resonance among an array of two rows of vertical circular cylinders

Experimental and theoretical works are conducted on the first-order and second-order wave interactions among an array of two rows of vertical circular cylinders.We show that both the first-order and the second-order resonance of dynamic free-surface displacement could in some cases be quite relevant among an array of two rows of vertical cylinders not only in theory but also in real phenomena. In some cases, on the other hand, we show that large free-surface displacement predicted theoretically is quite attenuated in reality probably due to viscous dissipation.

Prediction of Free Convection from Vertical and Inclined Rows of Horizontal Isothermal Cylinders Using ANFIS

The current study is conducted to predict the laminar free convection from horizontal isothermal cylinder sets in vertical and inclined rows, using an adaptive neuro-fuzzy inference system (ANFIS). The effects of the Rayleigh number, vertical and horizontal separation distances on average heat transfer from the rows are considered via this prediction. The training data for optimizing the ANFIS structure is based on available experimental data. A hybrid learning algorithm consisting of the gradient descends method and least-squares method is used for ANFIS training. In the view of the physics of the problem, it was observed that in the vertical row, by increasing the vertical separation spacing heat transfer increases. Moreover, the heat transfer increases by increasing the horizontal spacing ratio. In addition, according to good consistency obtained between the experimental and predicted results, it can be concluded that ANFIS can be used to predict the experimental results accurately.

海岸林に作用する波力特性と透過率と反射率の評価

Laboratory experiments were performed to study wave transmission and wave reflection capacity of circular Cylinders as coastal protection from waves. The energy dissipated in circular cylinders may be evaluated by using the drag forces acting on the cylinders and wave particle velocities. A theoretical analysis based on application of the continuity and energy equations to flow through the rows of circular cylinders were made to evaluate wave transmission and wave reflection capacity of mangroves and trees in coastal area. The reflection coefficient Kr is significant for large value of the ratio of the circular cylinders area to the unit bed area in the array of circular cylinders. The theoretical analysis were also made to evaluate wave transmission and wave reflection capacity of mangroves in coastal area. The significant wave reflection from mangroves with large and dense canopy was estimated.

0508 有限一列管群の表面圧力分布に及ぼす偏流パターンの影響

0508 有限一列管群の表面圧力分布に及ぼす偏流パターンの影響

Numerical and experimental study on confinement in Y-shaped post wall branching waveguide

Post wall waveguides consist of dielectric or metallic cylinders for microwave around 4 GHz were experimentally and numerically investigated. The structure attracts interests for application of transmission circuit for three-dimensionally integrated planar circuit in millimeter wavelength. In straight waveguide with dielectric cylinders, confinement of microwave is poor, when the post wall was composed of a pair of single row of cylinders. The confinement was improved as increase of rows of post wall. In metallic cylinders, microwave was well confined even when a pair of single row of cylinders composed the waveguide. After confirming confinement of the electromagnetic field, Y-shaped branches of post wall waveguide consisted of dielectric cylinders for microwave were similarly investigated for dielectric rods. The confinement was also improved by increase of post wall up to 3 layers. These results are applicable for fundamental design and fabrication of integrated circuit for microwave and millimeter wave.

10308 斜円柱群の伝熱特性に関する実験と数値計算

The present research investigated the effect of the obliqueness cylinder group on the heat transfer and pressure loss performances. The pressure loss and the temperature were measured by the pressure transducer and the thermal couple, respectively. The numerical simulation was performed to simulate the duct flow affected by the cylinder groups. The result shows that the heat transfer performance was improved by the obliqueness cylinder group as compared with the perpendicular cylinder group. Furthermore, the effect of the number of the cylinder row was examined. It was found that the cylinder group with the three rows is suitable for the heat transfer with minimum pressure loss.

Electro-optical channel drop switching in a photonic crystal waveguide-cavity side-coupling system

The electro-optical channel drop switching in a photonic crystal waveguide-cavity side-coupling system is reported. The line waveguide is formed by removing a single row of dielectric cylinders. The twin optical microcavities side coupled between linear waveguides is studied by solving Maxwell's equations. We determine the general characteristics of the coupling element required to achieve channel drop tunneling. By modulating the conductance of the twin microcavities, the electrical tunability of the resonant modes is observed in the transmission spectrum. The spectral characteristics suggest a potential application for this switching device as an efficient multichannel optical switch in the photonic integrated circuits.