Row Of Cylinders Research Articles

Numerical study of heat transfer across in-line circular cylinders for low to moderate Reynolds numbers

A computational fluid dynamics (CFD) model is generated to study the fluid flow and heat transfer from a series of six cylinders arranged in a horizontal row. The momentum and energy equations were solved using the finite volume method, with convective terms discretized using a second-order upwind method and diffusion terms discretized using central differencing. A second-order implicit technique was used for time integration. Simulations were run with four different values of the free stream Reynolds numbers 100, 200, 300, 400 and three different values of the longitudinal pitch (SL ) 1.5D, 2D, 2.5D to analyze the heat transfer behavior with fluid flow over a series of horizontal cylinders. First the grid independence test and CFD model validation are performed with the exact relation available in the literature. Next, the numerical results obtained from the developed CFD model for the row of cylinders were compared with the previously published analytical model, and correlation available in the literature, and were found to be in good agreement. The average Nusselt number calculated from the analytical and numerical models falls in the range of 8 to 10 for free stream Reynolds number equal to 100 for all values of dimensionless longitudinal pitches. Moreover, for the free stream Reynolds number equal to 400 with longitudinal pitch of 2.5D, the values of the average Nusselt number reach up to double the above-mentioned range. The maximum percentage error between the average Nusselt number obtained from the numerical and analytical solutions was less than 20% for larger free stream Reynolds number. The study found that the average Nusselt number for the array of cylinders increases with both the free stream Reynolds number and the dimensionless longitudinal pitch ratio increments. This information can be used to design more efficient heat exchangers or other fluid systems involving arrays of cylinders.

A new variety of axial piston hydraulic machines with multi-row units and a dual oscillating unit

The possibility of increasing the working volume, power, specific energy capacity (energy efficiency), and acceleration response of hydraulic machines under reduced supply and torque pulsation is investigated. The research methodology included the geometric, kinematic, power, and energy analysis of a four-row axial piston hydraulic machine with a dual oscillating unit and without an end distribution system. As a result, a new type of compact rotary hydraulic machines with volumetric action was created. In the proposed model, each subsequent row of cylinders is located in the inter-cylinder space of the previous cylinders with smaller radii. Such a design provides for a 24.5-fold increase in the working capacity and power of a hydraulic machine compared to a single-row design, as well as an increase in the acceleration response in the hydraulic motor mode. The elimination of end distribution systems excludes the possibility of violation of joint tightness between blocks and distribution disks due to block overturning by piston centrifugal forces at high rotation speeds and a multiple reduction of supply and torque pulsation. It was established that the increase in the specific power capacity of a hydraulic machine depends on its particular implementation, potentially reaching 18–25 kW/kg. The abovementioned features of the proposed axial piston hydraulic machine with a dual oscillating unit ensure the compactness of oscillating units, minimum dimensions of the cylinder blocks, and the hydraulic machine as a whole, resulting in its minimum mass and maximum specific power capacity.

On the combined influence of Reynolds number and cylinder spacing for flow around a row of heated square cylinders

AbstractThe characteristics of forced convection heat transfer across a row of heated square cylinders kept in side‐by‐side arrangement are numerically investigated to examine the combined effects of Reynolds number and cylinder spacing for Ri = 0, 60 ≤ Re ≤ 160, Pr = .71, and s/d = 1.0–8.0, where the space between cylinder surfaces is s and the cylinder size is d. A numerical study was carried out using the thermal lattice Boltzmann method. The goal of this work is to explore the transitions in heat transfer phenomenon that occurs behind the cylinder and to report the corresponding regimes for heat transfer namely synchronous, quasiperiodic, and chaotic. The proposed regime of heat flow is a function of Reynolds number and spacing. The synchronous heat regime is obtained for s/d ≥ 5.0 and quasiperiodic, chaotic regimes are observed for 3.0 ≤ s/d < 5.0, s/d < 3.0, respectively at Re = 100. The instantaneous isotherms, the power spectra of the corresponding Nusselt number signals, and the significance of cylinder Nusselt number frequency are used to examine these heat flow regimes. The heat transfer regimes for a row of heated cylinders and flow regimes for a row of unheated cylinders both have comparable appearances except for the fact that the heat transfer regime is synchronous at s/d ≥ 5.0 and flow is synchronous at s/d ≥ 4.0. The chaotic or quasiperiodic heat transfer regimes occur due to merging and strong interactions between thermal blobs shed from the cylinders. Heat transfer is synchronous at a higher spacing and characterized by independent thermal blobs shedded from the cylinders. It is reported that as spacing reduces and Reynolds number increases, the mean value of the Nusselt number experienced by all cylinders increases. The important outcome of the present numerical work is that for understanding heat transfer from bluff body, the transitions that occur in heat transfer are useful.

Effect of splitter damper on airflow conduction for thermal management of a lithium-ion battery cooling system with plate and cylindrical batteries

BackgroundThis paper simulates a lithium-ion battery pack (BRK) with cylindrical and plate batteries in an air duct. The batteries are arranged in rows of cylinders and plates in the BRK. A splitter damper is used at the air inlet and outlet in the duct. MethodsThis study was performed in a laminar airflow by changing the length of the splitter damper from 0.2 to 0.5 m, for both oval and triangular shapes of the splitter damper. Effects of various splitter damper settings on the BRK temperature, output air temperature, and heat transfer coefficient have been investigated. The BRK is simulated using COMSOL 6.0 software. Significant findingsAccording to the study's findings, the BRK greatest and lowest mean temperatures were measured along the 0.4 and 0.2 m of the splitter damper's triangular form, respectively. The heat transfer coefficient for the oval shape of the splitter damper was higher than the triangular shape of the splitter damper at all lengths of the splitter damper. The highest heat transfer coefficient is recorded in the oval form of a splitter damper with a length of 0.5 m.

Discharge prediction in partly vegetated channel flows: Adaptation of IDCM method with a curved interface and large-scale roughness elements

This study provides new insight into how to predict flow discharges of partly vegetated channels with emergent vegetation. By adapting for the first time the Interacting Divided Channel Method (IDCM), applied with a curved interface approach and with the presence of large-scale roughness elements (not considered in previous studies), the total and zonal discharges of partly vegetated channels were predicted based on a series of experimental results in this study together with collected data from previous studies. Consideration of transverse momentum transfer in terms of apparent shear stress at curved interface plane showed better performance with IDCM than the Divided Channel Method (DCM) with both curved and classic vertical/diagonal divisions. In this study, we also proposed a series of expressions, easily applicable, to predict the zonal discharges of a partly vegetated channel.Many experiments were carried out in a physical model of a very large rectangular channel with the presence of rows of vertical, rigid, circular, and rough steel cylinders, representing emergent rigid vegetation. The rows of cylinders were partially mounted on the bottom of the channel, leaving lateral areas of free circulation near the walls. The three-dimensional components of the flow velocity were measured using a 3D Acoustic Doppler Velocimeter (ADV)-Vectrino.

Effective Diffusivity From Analytical Solution for Banks of Cylinders

Abstract Benchmarks are provided for the evaluation of the effective coefficient for species diffusion, or electrical/thermal conduction, in structured porous media. The cases considered corresponding to doubly periodic rows of circular cylinders, for which a power series solution has been previously obtained, from complex variable theory. Both inline and staggered geometries are considered for three common configurations: inline-square, rotated-square, and equilateral geometries. From these mathematical solutions, values for the effective conduction/diffusion coefficient are readily constructed. The results are presented in terms of correlations for the ratio of effective-to-bulk conductivity/diffusivity or microstructural parameter, as a function of porosity. It is shown that near identical results with the present analytical analysis are obtained using calculations based on a finite-volume method and also with a previous mathematical analysis for the case of inline-square geometry. The present analytical solutions are also compared with two well-known correlations for random porous media, based on effective medium and percolation theory. It is shown that agreement with the analytical solution is not in general particularly good and depends on the choice of fitting parameters. The present results may be used as canonical data for comparative studies with numerical procedures to enumerate microstructural parameters for arbitrary-shaped occlusions in random geometries.

Passive concentration dynamics incorporated into the library IB2d, a two-dimensional implementation of the immersed boundary method

In this paper, we present an open-source software library that can be used to numerically simulate the advection and diffusion of a chemical concentration or heat density in a viscous fluid where a moving, elastic boundary drives the fluid and acts as a source or sink. The fully-coupled fluid-structure interaction problem of an elastic boundary in a viscous fluid is solved using Peskin’s immersed boundary method. The addition or removal of the concentration or heat density from the boundary is solved using an immersed boundary-like approach in which the concentration is spread from the immersed boundary to the fluid using a regularized delta function. The concentration or density over time is then described by the advection-diffusion equation and numerically solved. This functionality has been added to our software library, IB2d, which provides an easy-to-use immersed boundary method in two dimensions with full implementations in MATLAB and Python. We provide four examples that illustrate the usefulness of the method. A simple rubber band that resists stretching and absorbs and releases a chemical concentration is simulated as a first example. Complete convergence results are presented for this benchmark case. Three more biological examples are presented: (1) an oscillating row of cylinders, representative of an idealized appendage used for filter-feeding or sniffing, (2) an oscillating plate in a background flow is considered to study the case of heat dissipation in a vibrating leaf, and (3) a simplified model of a pulsing soft coral where carbon dioxide is taken up and oxygen is released as a byproduct from the moving tentacles. This method is applicable to a broad range of problems in the life sciences, including chemical sensing by antennae, heat dissipation in plants and other structures, the advection-diffusion of morphogens during development, filter-feeding by marine organisms, and the release of waste products from organisms in flows.

Flow-induced vibrations in long rows of cylinders and their links to convective instabilities

Flows past rows of elastically mounted cylinders display a number of flow-induced vibration phenomena that hitherto have proven difficult to categorise in a way that is independent of the number of cylinders in the row. Here, we investigate the flow past six equispaced but independent elastically-mounted cylinders at Reynolds number Re=200 using direct numerical simulations over a wide range of stiffnesses and for three values of the inter-cylinder spacing or pitch p. We make a first attempt at categorising the responses observed in terms of the framework of flow states linked to convective instabilities in rows of rigidly mounted cylinders recently presented in Hosseini, Griffith and Leontini (2020). We show that regardless of pitch, this framework has some success in explaining and collating the flow-induced vibration response for high to moderate stiffnesses (corresponding to low to moderate reduced velocities U∗). Among others, one phenomenon observed that fits this framework is the fact that for some cases, the first and last cylinders in an array can vibrate, while the rest are almost stationary. However, at low stiffness/high U∗, the arrays behave more like a single flexible structure that exhibits waves, which is an inherent fluid-structure mode with no root in the rigidly mounted case.

Near-wake flow and thermal characteristics of three side-by-side circular cylinders for large temperature differences using large-eddy simulation

The trailing edge of a gas turbine blade contains rows of short circular cylinders which extract the heat from blade, with the help of the coolant. Large temperature differences exist between the incoming coolant and the blade, and its effect on the flow and thermal characteristics need to be understood. To this end, in the present work, non-isothermal flow over three side-by-side circular cylinders is investigated for a Reynolds number of 3900 using large-eddy simulation (LES). The numerical solver used is validated for isothermal flow using reference experimental data. Large temperature differences, ranging from 25∘C to 300∘C, between the incoming flow and the surface of the cylinders are considered and their effect on the flow and thermal characteristics in the near wake region of cylinders are analyzed. The cylinder-surface and wake characteristics are analyzed using instantaneous and mean quantities. The surface characteristics of the cylinders are studied using Nusselt number, wall shear stress, and lift and drag coefficients. The wake characteristics are studied using Reynolds stresses, turbulent heat flux, and turbulence anisotropy invariant maps. Phase-averaging is used to analyze the unsteady flow and topology of the wake. It is observed that, compared to the middle cylinder the production of turbulence and diffusion of heat is higher behind the two outer cylinders, and their location remains stationed independent of the time. Convection and diffusion of heat takes place along the free shear layer of the wake of the middle cylinder. The vortex shedding behind the cylinders are noted to have multiple frequencies. Further, the vortices shed by the outer cylinders contain more energy and at higher-frequencies when compared to those shed by the middle cylinder.

Balancing of the moments of the VR-5 type engine taking into account the desaxial and the cylinder camber angle

Recently, V-engines with a small angle of camber are more widely used as power units for passenger cars, especially because of the reduced engine length, and the transverse dimensions are almost the same as in-line ones. All this leads to an increase in overall engine power. However, due to the small camber angle between the parallel rows of cylinders, the intersection of the cylinders in their lower part may occur. To prevent the latter, significant multidirectional desaxial is used. Moreover, the calculation of the dynamics of similar engines introduces a number of features, including balancing the inertia forces and their moments from the reciprocating moving and rotating masses. The article discusses the balancing of 5-cylinder four-stroke VR type engines with desaxial crank mechanism and uniform flash alternation. The formulas allowing to find and analyze moments of the inertia forces of the reciprocating and rotating masses arising in VR-5 engines are given by the given value of the cylinder camber angle, the ratio of the crank radius to the connecting rod length and the relative displacement of the cylinder axis. A method of balancing the moments of inertia forces of the reciprocating and rotating masses is proposed and the results of the presented dynamic study of a VR-5 engine using analytical, software and graph-analytical methods.

Constructal design analysis of viscoplastic cross-flow over a row of cylinders

This work applies the Constructal Design Method to a row of circular tubes subjected to cross-flows of viscoplastic Bingham fluids to investigate how viscoplasticity affects the system performance and which are the best geometric shapes depending on fluid rheology. The heat transfer density for a fixed pressure drop was the performance indicator, and the step distance between tubes was the degree of freedom for the Constructal Design Method. Combinations of dimensionless parameters Bejan number (104 and 105) and Bigham number (1, 10, and 100) were examined. The dimensionless heat transfer density increased with the increase of Bejan number and decreased with the increase of Bingham number, showing that the increase in yield stress reduces heat transfer as it hinders the flow rate for a constant gauge pressure. The optimal step distance between tubes decreased with the increase of Bejan number as a result of decreasing the boundary layer thickness. The optimal step distance between tubes increased, on average, 25% with the increase in the Bingham number. The best configurations were always of greater step distance between tubes than those found for Newtonian fluids, indicating the gains in performance when applying the Constructal Design Method to systems of non-Newtonian fluids.

Flow states and transitions in flows past arrays of tandem cylinders

Abstract

Wave Guide Structures in an Electromagnetic Crystal with a Triangular Grid

In this paper, we study EBG-waveguides in an electromagnetic crystal in the form of a two-dimensionally periodic lattice of metal cylinders with a triangular grid. The dispersion characteristics of waveguides formed by removing one, two, and three rows of cylinders along the orthogonal axes of the crystal are obtained. A parametric analysis of the critical frequencies of the waveguide modes and eigenwaves of a homogeneous crystal is performed. Electrodynamic modeling was performed in the ANSYS HFSS system using the eigenwave mode. The optimal parameters of the electromagnetic crystal, which provide the maximal operating frequency bands of waveguides with various orientations in the grid, are obtained. The characteristics of waveguides in crystals with triangular and square grids are compared.

Particle Image Velocimetry (PIV) experiment of the buoyant flow field of a thermal chimney model designed for geothermal power plants

ABSTRACT To enhance the air-cooling process in geothermal power plants for economical utilization of the exhaust steam from expansion, a natural-draft thermal chimney design was proposed and studied here in this paper. In view of the necessity of accurate velocity field measurements which would provide further insight into the physics behind the evolving plumes above heated horizontal cylinders, Particle Image Velocimetry (PIV) was employed to experimentally investigate the buoyant flow in the thermal chimney system. Two configurations have been tested to understand the flow induced by the horizontally heated cylinders inside the thermal chimney. Firstly, flow field above a single row of cylinders was tested while they were isothermally heated to simulate of an air-cooled condenser. After that, a second row of cylindrical heaters (air-heater) was added above the first row to enhance the buoyant flow, aiming at enhancing the air side flow of the air-cooled condenser. Flow characteristics and velocity enhancement were studied for both configurations. The results show that significant flow unsteadiness occur near the cylindrical heaters because of the non-steady crossing flows between adjacent cylinders, and the unsteadiness attenuates in the downstream. The effects of cylinder row distance, surface temperature as well as downstream distance on the flow field were then analyzed. Flow velocity is increased by the air-heater as the buoyancy force is enhanced, proving the idea of flow enhancement of the thermal chimney configuration. It is also observed that the velocity fluctuation, turbulent kinetic energy and vorticity change significantly after adding the second row of heaters. The present study provides further insight into natural convection flow theory of heated cylinders for a Rayleigh number range of 1.3E4 to 2.2E4, which is fundamental for the flow enhancement designing of the proposed natural-convection-driven cooling system.

Waves in Diagonally-Oriented EBG Waveguides in Electromagnetic Crystals with a Square Lattice

Abstract—EBG waveguides in an electromagnetic crystal are studied in the form of a two-dimensionally periodic array of metal cylinders located between conducting screens. The dispersion characteristics of waveguides formed by removing one, two, and three rows of cylinders along the diagonal of a square crystal lattice are obtained. As a result of analyzing the frequency dispersion of the fundamental waveguide modes and eigenmodes of a homogeneous crystal, the factors limiting the operating frequency bands of the waveguides are determined and the lattice parameters optimal from the aspect of the band properties are obtained. The characteristics of waveguides oriented along the diagonal of the crystal lattice are compared with similar characteristics of waveguides formed along the principal axes in crystals with a square lattice.

The flow past large numbers of cylinders in tandem

The present study investigates the flow in a multi-cylinder tandem array. A primary aim is to build a framework for understanding the flow as the number of cylinders becomes large. Two-dimensional numerical simulations have been conducted of the flow past a row of identical and equispaced cylinders, at Reynolds number Re≤200, while the distance between cylinders or pitch varies in the range 1.1≤p≤10. The number of cylinders n in the array varies between n=2 and n=100. Three main regimes are identified as a function of p which are delineated by the behavior of the flow in the gap between the two most upstream cylinders, similar to the regimes in a two-cylinder array. These are a short-pitch or attached regime, with a fully attached and apparently steady flow in this gap, a medium-pitch or fluctuating regime, with some fluctuation in this gap, and a large-pitch or shedding regime, with full vortex formation similar to the wake of single-cylinder system in this gap. Large arrays show that these regimes actually occur as a geometric series, i.e. with progression downstream, the attached regime begins to fluctuate, and then form and shed vortices. This shedding regime is then followed by a region of convective instability which breaks the feedback of information upstream. The flow downstream of this convectively unstable region then goes through the same series of regimes with further downstream progression, but on a longer length scale. There is a self-similar “cascade” – development of fluctuation, established vortex shedding, convectively unstable flow – the self-similar units of which are separated by the regions of convective instability. While the length of each unit is a function of p and Re, the appearance of these units is common.

Research of hydrodynamics and heat transfer during the transverse air flow of a row of cylinders with screw grooves

Cylinder cross-flow is a common phenomenon in many fields of technology. Technological simplicity of tubular structures makes them attractive, especially when using working bodies that are under different pressure values. However, the cylinders belong to the category of «poorly streamlined» bodies, and there are many opportunities to improve their hydrodynamics and heat transfer. For a circular cylinder, there is a speed range in which its hydraulic resistance can decrease due to the deformation of the cylinder surface. This phenomenon can be used for the rational design of heat exchangers. In the open-type wind tunnel, heat transfer coefficients and hydraulic resistances of single-row cylinder bundles with several types of spiral grooves on the outer surface have been determined. The largest increase in heat transfer (64 %) was shown by the cylinder with the smallest pitch of the groove (10 mm), the second place was taken by the cylinder with a relatively large step – 40 mm. Using the best spiral groove allowed reducing the hydraulic resistance by 19 %. Visualization and computer simulation have been used to explain the effects. The conformity of computer simulations to the experimental results was determined by comparing the average heat transfer coefficient (calculated and determined using an ice calorimeter). As a result, the turbulence model RNG_ke has been chosen, which provides a better fit of the experimental model. Computer simulations have explained the physical picture of the flow around cylinders with spiral grooves, including their mutual influence with a different axial orientation in the bundle. It has been shown that the presence of a spiral groove, which on the one hand increases heat transfer and on the other hand reduces hydraulic resistance, can significantly increase thermohydraulic efficiency (Reynolds analogy factor).

Vertical-plate free convection boundary layer disturbed by a row of circular cylinders: RANS-based numerical simulation

This paper presents the results of RANS-based numerical simulation of 3D flow dynamics and heat transfer in the turbulent free-convection boundary layer disturbed by a transverse periodic row of finite-height cylindrical obstacles. The disturbing row elements are mounted on a vertical isothermally heated plate along which the free-convection flow develops starting from a 2D state prescribed at the computational domain inlet. The height-to-diameter ratio of the cylindrical obstacles is varied from 1 to 3, and their surface is treated as adiabatic or isothermal. Vortex flow structures and local heat transfer patterns in the front and in the rear of the introduced macroroughness are analyzed.

Experimental study of the self-excited resonance effect on the dynamic lift and flow structure around inline cylinders

The excitation of acoustic resonance by air flow around a row of inline cylinders is investigated experimentally using phase-locked particle image velocimetry and direct measurements of the dynamic lift forces. The experiments are performed during self-excited acoustic resonance for arrangements of two, three, four, and five inline cylinders with a spacing ratio L∕D=2.0, where L is the center-to-center distance between the cylinders and D is the cylinder diameter, to clarify the effect of increasing the number of cylinders on the resonance mechanism and the characteristics of the periodic flow cycle. The PIV measurements show that increasing the number of cylinders results in weaker and distorted periodic flow structures around the most downstream cylinders. However, the phase and strength of the flow structures within the most upstream gap are minimally affected. Intrinsic flow features, such as gap flow that is observed in some cases, lead to the disruption of the shear layer impingement on downstream cylinders. Moreover, direct measurements of the dynamic lift forces on all cylinders simultaneously identified the upstream gap as the location where most of the energy exchange between the flow and the acoustic fields occurs. Decomposition of the dynamic lift force with respect to the acoustic pressure revealed that the distorted flow structures were accompanied by weaker, sometimes negative, contribution to the acoustic resonance excitation. The findings presented in this article explain the observation that for inline configurations of cylinders, as well as inline tube bundles, increasing the number of cylinders in the flow direction does not result in stronger resonance, and demonstrate that countermeasures for resonance excitation should target the most upstream rows of cylinders.

Coupling Analysis of Adjacent Substrate-Integrated Waveguides Based on the Equivalent Transmission Line Model

This article presents a method for analyzing the coupling between two adjacent substrate-integrated waveguides (SIWs) sharing a common row of metallic cylinders, which is based on the concept of equivalent circuit and wavenumber calculation. When the specific sizes of two adjacent SIWs are known, the scattering parameters of the shared common row of metallic cylinders can be derived, and the equivalent transmission line model of the SIW coupling structure is extracted. The even-and odd-mode wavenumbers in both transverse and propagating directions are calculated for this equivalent circuit. For an ideal forward-wave directional coupler, the transmission and coupling coefficient are then derived directly from the wavenumber and the length of the structure. Based on the proposed method, three SIW directional couplers with different coupling levels are designed and fabricated for verification. Good agreements between the calculated and simulated coupling parameters are observed. The proposed method provides a simple and accurate approach to estimate the coupling between two closely spaced SIWs sharing one common row of metallic cylinders and is expected to use for the design of millimeter-wave SIW-based circuits and systems.