Single Bluff Body Research Articles

Spacing effects on flows around two square cylinders in staggered arrangement via LBM

This study presents a computational analysis of fluid flow characteristics around two staggered arranged square cylinders using the Lattice Boltzmann Method (LBM). With Reynolds number (Re) fixed at 200, numerical simulations explore the influence of varying gap ratios (G) ranging from 0 to 10 times the cylinder size. Emphasis is placed on understanding the impact of cylinders spacing on flow structure mechanisms and induced forces. Investigation of fluid flow parameters includes vorticity behavior, pressure streamlines, and variations in drag and lift coefficients alongside the Strouhal number under different values of G. From the results, four distinct flow patterns emerge: single bluff body flow, flip flopping flow, modulated synchronized flow, and synchronized flow, each exhibiting unique characteristics. This study reveals the strong dependence of fluid forces on G, with low spacing values leading to complex vortex structures and fluctuating forces influenced by jet flow effects. At higher spacing values, proximity effects between cylinders diminish, resulting in a smoother periodic flow. The Strouhal number, average drag force and the rms values of drag and lift force coefficients vary abruptly at narrow gaps and become smooth at higher gap ratios. Unlike the tandem and side-by-side arrangements the staggered cylinders arrangement is found to have significant impact on the pressure variations around both cylinders. Overall, this research could contribute to a comprehensive understanding of staggered cylinder arrangements and their implications for engineering applications.

On the prediction of the turbulent flow behind cylinder arrays via echo state networks

This study aims at the prediction of the turbulent flow behind cylinder arrays by the application of Echo State Networks (ESN). Three different arrangements of arrays of seven cylinders are chosen for the current study. These represent different flow regimes: single bluff body flow, transient flow, and co-shedding flow. This allows the investigation of turbulent flows that fundamentally originate from wake flows yet exhibit highly diverse dynamics. The data is reduced by Proper Orthogonal Decomposition (POD) which is optimal in terms of kinetic energy. The Time Coefficients of the POD Modes (TCPM) are predicted by the ESN. The network architecture is optimized with respect to its three main hyperparameters, Input Scaling (INS), Spectral Radius (SR), and Leaking Rate (LR), in order to produce the best predictions in terms of Weighted Prediction Score (WPS), a metric leveling statistic and deterministic prediction. In general, the ESN is capable of imitating the complex dynamics of turbulent flows even for longer periods of several vortex shedding cycles. Furthermore, the mutual interdependencies of the TCPM are well preserved. However, optimal hyperparameters depend strongly on the flow characteristics. Generally, as flow dynamics become faster and more intermittent, larger LR and INS values result in better predictions, whereas less clear trends for SR are observable.

Aerodynamic characteristics and wake formation behind a pair of side-by-side rectangular cylinders using the lattice Boltzmann method

In this work, the lattice Boltzmann method is used to numerically analyze the interactions of flowing fluid with two side-by-side rectangular cylinders at a fixed Reynolds number of 150. The gap ratios between the cylinders are varied from 0.5 to 5 while the aspect ratios of both cylinders are varied from 0.25 to 4. The deflected, bistable, flip-flopping, chaotic, single bluff body, two pairs’ street of anti-phase vortex shedding, anti-phase synchronized, and in-phase non-synchronized wake patterns are observed upon varying the aspect ratios as well as the gap ratios. The observed results show that the mean drag coefficients of both side-by-side rectangular cylinders, as well as that of the single cylinder, exhibit decreasing trends till the aspect ratio = 2 and become almost constant afterward. The Strouhal number varies abruptly at the gap ratio of 0.5 and becomes steady for gap ratios = 2 and 5. The root-mean-square values of lift coefficients of two side-by-side rectangular cylinders exhibit variations till the aspect ratio equal to 1.5 and then becomes constant afterward. This study also reveals that an increment in aspect ratios results in the minimization of the drag force and controls the wake, while the increment in gap ratio results in stabilizing the chaos produced in the flow structure due to jet flow influence. The wake patterns in this study are found to be consistent with the numerical and experimental work of other researchers.

Numerical analysis of the flow over four side-by-side square cylinders with different gaps

This study conducts two-dimensional numerical simulations of the flow over four square cylinders arranged side by side at a low Reynolds number (Re) of 100. The investigation primarily centers on the influence of the gap to a square cylinder width ratio (g*) on the flow. The range of g* spans from 0.1 to 7.0. Within this parameter range, three distinct flow regimes emerge based on the inherent flow characteristics. These regimes are defined as follows: (1) single bluff body flow (g* ≤ 0.3), (2) flip-flopping flow (0.3 < g* < 2.0), and (3) modulated periodic flow (g* ≥ 2.0). Additionally, the modulated periodic flow is further categorized into three distinct flow patterns. Various aspects of these different flow regimes are examined, including vortex contours, velocity fields, and liquid force coefficients around the cylinders. Moreover, detailed illustrations are provided for the modulation behaviors in vortex structures and liquid force coefficients. Finally, the proper orthogonal decomposition technique is employed to identify and analyze the underlying spatial coherent structures in the flow field, offering further insights into the dynamic features of wakes.

Enhancement of piezoelectric energy harvesting by the elliptical cylinder interference

The performance of the piezoelectric energy harvester (PEH) driven by a single bluff body is not entirely satisfactory in wind environment. However, the wake excitation generated by the interference cylinder can intensify the vibration and subsequently increase the harvested energy. This paper presents a piezoelectric energy harvester which uses an elliptical cylinder for interference (ECI). The extended Hamilton’s principle and the Gauss’s law is applied to obtain the electro-mechanical coupling model. Following this, the analytical solution is derived by employing the Galerkin procedure. Experiments pertaining to this study were conducted in a DC wind tunnel, where ECIs of varying aspect ratios were positioned directly upstream of the PEH. The experimental results not only verify the model accuracy, but also identify the distance between the ECI and the bluff body in terms of the proximity interference region, induced galloping region, and wake interference region. Only when the system is located in the induced galloping region, does the harvester’s output power significantly increase and the system stability improve. Furthermore, as the aspect ratio of the elliptical cylinder decreases, the harvested energy increases, and when the wind speed reaches 18 m/s, with the aspect ratio and the spacing ratio being 0.4 and 13 respectively, the harvester can yield a power density of 10.93 kW/m3. This is 624% higher than that without wake excitation. Numerical simulations demonstrate that the wake, generated by ECI, interferes with the positive pressure region in front of the funnel-shaped bluff body. This interference shifts the location of the positive pressure region to the sides of the bluff body and reduces its area.

Vortex shedding characteristics and hydrodynamic forces of stationary and elastically mounted side-by-side cylinders fitted with small diameter control rods

Vortex shedding behind bluff bodies can induce noise and vibration problems when it engages in a feedback cycle of oscillations with an acoustic or structural mode. Therefore, several passive and active flow control techniques have been developed to suppress vortex shedding behind a single bluff body. However, less attention was given to the case of multiple bluff bodies in cross-flow. Therefore, in this paper, a numerical investigation is performed to study the effect of adding small diameter control rods in the vicinity of two side-by-side cylinders on the vortex shedding characteristics, the hydrodynamic fluid forces, as well as the suppression of vortex-induced vibration. The simulations are conducted at a Reynolds number of Re = 200 and the side-by-side cylinders have a spacing ratio of T∗=2.5. The number of control rods and their angular positions around the main cylinders are varied. Fitting the side-by-side cylinders with control rods has resulted in three different flow regimes compared to the base case with no control rods. These flow regimes depend on the angular positions of the control rods and they are classified as; bistable flow, stable biased flow, and merged wake flow regimes. The stable biased flow regime has resulted in the maximum reduction of the fluctuating lift coefficient of the side-by-side cylinders, especially when the control rods are placed at θ=135° from the flow stagnation point. Increasing the number of control rods around the cylinders has further reduced the fluctuating lift coefficient and produced a more symmetric wake at the rod angles which produce the stable biased flow, and the merged wake flow regimes. The vortex-induced vibration of the side-by-side cylinders is investigated when the control rods are placed at the angular position that results in a stable biased flow regime. It is revealed that fitting the cylinders with control rods at an angular position of θ=135° has resulted in reducing the vibration amplitude over the whole range of the simulated reduced flow velocities, which makes this technique a viable one to control the vortex shedding and the vortex-induced vibration of side-by-side cylinders.

Flow structure and dynamics behind cylinder arrays at Reynolds number ∼100

The flow behind nine different arrays of cylinders is experimentally investigated via Particle Image Velocimetry (PIV) at a Reynolds number of Re ∼100 based on the diameter of the cylinders. Each array consists of a column of four cylinders in front and three in the rear. The horizontal distance between the two columns and the vertical distance between the cylinders within each column are varied for H/D=[2,4,8] and V/D=[2,4,6], resulting in nine different arrays denoted as mVnH, where m corresponds to V/D and n stands for H/D. The PIV measurements are conducted for 15 s at 200 Hz frequency, corresponding to 39 to 360 vortex shedding events for the wakes in this study. Then, proper orthogonal decomposition is applied to the velocity fields to analyze the flow dynamics. All arrays show unsteady flow, and based on their flow structures, they are classified in to three main categories of single bluff body (SBB), transitional (TR), and co-shedding (CS) flow. SBB characteristics can be seen for 2V2H and 2V4H arrays, but the latter has more steady vortex shedding as the H/D increases from 2 to 4. Then, 2V8H and 4V2H have an asymmetric flow with several vortex streets and act as an intermediary stage in the shift from SBB to CS flow structure when the distances are increased. The highest total kinetic energy values and widest probability density functions of the velocity components are observed for this group. The five remaining arrays in the CS group have symmetric flow, with three or five vortex streets present behind. However, based on the distances, the frequency and phase synchronization of the vortex streets change considerably, which might have an important effect on, for example, the heat transfer or the structural load of the cylinders.

Research on flow around two tandem rectangular cylinders

Uniform flow around two identical rectangular cylinders arranged in tandem has been investigated via the lattice Boltzmann method. With a fixed Reynolds number of 100, the effects of side ratio (γ = 1/2, 1/4, 1/8 and 1/16) and spacing ratio (S* = 0.25–12) on the fluid dynamics are investigated. Results indicate that both side ratio and spacing ratio have significant influences on the flow structure, vortex shedding frequency and hydrodynamic force. Several distinct vortex wake modes including the single bluff-body (SBB), shear-layer reattachment (SLR) and secondary vortex formation (SVF) modes are observed. The variations of Strouhal number, drag and lift coefficients versus spacing ratio are similar between all the current side ratios. In the branches of small and large spacing ratios, the fluid dynamics are obviously different and there is a critical spacing ratio, beyond which the relevant mechanical parameters jump suddenly as a result of the flow mode transition. A phenomenon of two-stage drag frequency separation between two cylinders occurs in the region of low side ratio and large spacing ratio, and its formation mechanism has also been analysed on the basis of flow characteristics and frequency spectra of force coefficients.

Large eddy simulation of flow around two side-by-side circular cylinders at Reynolds number 3900

This paper investigates the flow dynamics around two circular cylinders in a side-by-side arrangement with different spacing ratios (T/D, T is the center-to-center cylinder spacing and D is the diameter) under a subcritical Reynolds number condition (Re = 3900). A three-dimensional (3D) numerical model was developed with Large Eddy Simulation (LES) technique. The model was well validated against published data of flow around a single cylinder at Re = 3900. Numerical simulations were conducted for flow around two side-by-side circular cylinders with T/D = 1.2, 1.5, 1.75, 2, 2.5, 3, 3.5, and 4. Based on the LES results, three wake regimes were identified: single bluff body regime (T/D = 1.2), biased flow regime (T/D = 1.5–2), and parallel vortex streets regime (T/D = 2.5–4). In the single bluff body regime with T/D = 1.2, the stable deflection of gap flow is also observed which indicates that there may exist a transition state from the single bluff body regime to the biased flow regime. In biased flow regime, the pairing and merging process of the outer vortices with the inner vortices are analyzed. The occurrence of the flip-flopping phenomenon is found to be related to the merging tendency between gap-side vortices in narrow wake region and free-flow-side vortices in wide wake region, and the relative phase of gap side vortices in transient state. In the parallel vortex streets regime, the phase relation of the vortex shedding process was analyzed. The time proportions of the in-phase mode and anti-phase mode are found to be varied with spacing ratio. As the spacing ratio increases, the wakes behind the cylinders lose their dependency on the anti-phase mode. The results of the present study were compared with the existing results at other Reynolds numbers. It is found that vortex shedding manner during the flip-over transitions is closely related to the spacing ratios and is independent of the Reynolds number.

Cross flow over two heated cylinders in tandem arrangements at subcritical Reynolds number using large eddy simulations

This study analyses the heat transfer and flow characteristics of cross-flow over two heated infinite cylinders in a tandem (in-line) configuration. Non-isothermal Large Eddy Simulations (LES) using the dynamic Smagorinsky model were conducted at a fixed Reynolds number of 3,000 (based on the free stream velocity and the cylinder diameter). A range of cylinder gap ratios (1.0≤L/D≤5.0) was investigated (in increments of 0.25) with two different Prandtl numbers Pr=0.1 and 1.0. Results show that the flow structures vary according to the order of the patterns: (i) Extended body regime: without attachment for low L/D (1.0-1.25) where cylinders behave as a single bluff body with top–bottom vortex shedding, (ii) Shear layer reattachment regime: with reattachment for moderate L/D (1.5-3.75) where the detached shear layer from the upstream cylinder reattaches to the downstream cylinder, and (iii) Co-shedding regime: for high gap ratios (3.75≤L/D≤5.0) a phenomenon called “jumping”, where the two cylinders behave as isolated bluff bodies. Furthermore, it was observed that the average Nusselt number of both cylinders experience a drastic variation at a critical spacing ratio (between 3.75≤L/D≤4.0). For L/D≤3.0, the average Nusselt number of the upstream cylinder was found to be higher than that of the downstream one. However, for spacing ratios L/D>3.0, the average Nusselt number was similar for both cylinders. For the downstream cylinder, the maximum Nusselt number was located at the separation angle and was found to be independent of the spacing ratio.

From snapshots to manifolds – a tale of shear flows

We propose a novel nonlinear manifold learning from snapshot data and demonstrate its superiority over proper orthogonal decomposition (POD) for shedding-dominated shear flows. Key enablers are isometric feature mapping, Isomap, as encoder and,$K$-nearest neighbours ($K$NN) algorithm as decoder. The proposed technique is applied to numerical and experimental datasets including the fluidic pinball, a swirling jet and the wake behind a couple of tandem cylinders. Analysing the fluidic pinball, the manifold is able to describe the pitchfork bifurcation and the chaotic regime with only three feature coordinates. These coordinates are linked to the vortex-shedding phases and the force coefficients. The manifold coordinates of the swirling jet are comparable to the POD mode amplitudes, yet allow for a more distinct and less noise-sensitive manifold identification. A similar observation is made for the wake of two tandem cylinders. The tandem cylinders are aligned and located at a streamwise distance which corresponds to the transition between the single bluff body and the reattachment regimes of vortex shedding. Isomap unveils these two shedding regimes while the Lissajous plot of the first two POD mode amplitudes features a single circle. The reconstruction error of the manifold model is small compared with the fluctuation level, indicating that the low embedding dimensions contain the coherent structure dynamics. The proposed Isomap–$K$NN manifold learner is expected to be of great importance in estimation, dynamic modelling and control for a large range of configurations with dominant coherent structures.

Passive Flow Control around Two Side‐by‐Side Square Cylinders Using a Control Plate

This article is concerned with the numerical analysis of reduction of fluid forces (drag and lift) and suppression of vortex shedding around two side‐by‐side square cylinders using the lattice Boltzmann method. For this purpose, a passive flow control methodology is adopted in which a flat plate (termed as the control plate) is placed at the upstream position of cylinders. The gap ratio (g) between the cylinders and the plate is varied from 0 to 4 while the height of the control plate is varied from 0.2 to 0.8 at fixed Reynolds number of 150. Different flow patterns are found in this study depending on the gap ratios and different heights of the control plate. These flow patterns are single bluff body flow, flip‐flopping flow, and antiphase vortex shedding flow patterns. The narrow gap ratio (g = 0.5) is found to have more impact in terms of force reduction and flow control as compared to larger gap ratios. This article also shows that the fluid flow parameters such as the mean drag coefficient, the Strouhal number, and rms values of drag and lift coefficients of both cylinders reduce considerably due to the control plate as compared to without the control plate. In this regard, it is found that the mean drag coefficient of upper cylinder reduces upto 45.94%, the Strouhal number of both cylinders reduces upto 18.66%, while a maximum reduction of 83.47% and 95.39% is observed in root‐mean‐square values of drag and lift coefficients of upper cylinder, respectively. Another important finding of this article is that the control plate does not suppress forces and control flow at all gap ratios and heights of control plate considered in this article. In some cases, the flow‐induced forces were found to be increasing as compared to without the control plate, and this generally happened at higher gap ratios.

Experimental Investigation of the Effect of Single and Twin Bluff Bodies on the Turbulent Flow in an Asymmetric Rectangular Diffuser

Experimental investigation of the effect of bluff bodies on the turbulent flow through an asymmetric diffuser has been carried out. The rectangular diffuser is designed and made keeping similarity to that used by Buice and Eaton, [1], having an inclination angle of 10°. Three geometrical configurations have been selected for the experimentation. (I) At first the experiment has been carried out for the validation of the present results with Buice and Eaton, [1], placing no bluff body at all. (II) Thereafter measurements have been carried out by placing a single bluff body on the horizontal floor of the diffuser to estimate the effect of the bluff body on the downstream flow. (III) Finally, two identical bluff bodies are placed on the horizontal floor of the diffuser and experimental work has been carried out in order to investigate the effect of the existence of two bluff bodies on the downstream flow through the diffuser. The present results agree well with the results of Buice and Eaton, [1], to show that the recirculation zone appears just adjacent to the inclined plane when there is no bluff body in a diffuser. Also, the detailed investigation for velocity of flow field, distribution of skin friction factor along with uncertainty analysis as well as the correlation between friction factor and Reynolds Number have been carried out in the research paper.

Numerical Study on the Flow Past Three Cylinders in Equilateral-Triangular Arrangement at Re = 3 × 106

One of the most common systems in engineering problems is the multi-column system in the form of an equilateral-triangular arrangement. This study used three-dimensional numerical simulations to investigate the flow around three cylinders in this arrangement at the super-critical Reynolds number Re=3×106, concentrating on the influence on the spacing ratio (L/D) among cylinders. The instantaneous vortex structures, Strouhal numbers, fluid force coefficients, and pressure distributions are analyzed thoroughly. The present study demonstrated that fluid dynamics is sensitive to L/D, by which five different flow patterns are classified, namely single bluff body flow (L/D≤1.1), deflected gap flow (1.2≤L/D≤1.4), anti-phase flow (1.5≤L/D≤2.3), in-phase flow (2.5≤L/D<3.5), and co-shedding flow (L/D≥3.5). Critical bounds are identified by significant transitions in the flow structure, discontinuous drop and jump of St, and force coefficients.

Numerical computations of flow around three equilateral-triangular square cylinders with rounded corners using momentum exchange-based IB-LBM at low Reynolds numbers

In this study, the flow around three square cylinders with rounded corners in equilateral-triangular arrangements were investigated using the momentum exchange-based immersed boundary-lattice Boltzmann method (IB-LBM) at low Reynolds (Re) numbers. The influences of Re number and gap ratio δ to the flow characteristics, force coefficients, and Strouhal (St) number were examined by selecting one hundred different gap ratios δ and forty different Re numbers. The wake flow patterns are divided into six distinct categories according to the gap ratio, these are single bluff-body, deflected, flip-flopping, anti-phase, anti-phase & in-phase coexist, and fully developed in-phase flow patterns. In addition, the Re number was also found to have a significant impact on the vortex shedding frequencies and flow properties. The drag coefficients, lift coefficients, and St number were calculated to demonstrate the relationship between vortex shedding properties, gap ratio, and Re numbers. The results revealed that the wake flow pattern, flow characteristics, and force coefficients depended significantly on the gap ratio and Re numbers. In addition, the power spectral density of the upstream cylinder were significantly lower than those of downstream cylinders for low gap ratios, and the mutual interference between each cylinders vanished as the gap ratio increased.

Investigation on fine particle agglomeration and separation promoted by different bluff bodies

Using particle agglomeration to help separate fine particles receives increasing attention in air purification processes. Recent studies suggested that enhanced turbulence using bluff bodies can significantly improve the agglomeration of fine particles. However, since micron-sized particles are difficult to measure, the current exploration of flow fields and particles is mainly based on simulations and lacks experimental validation. This paper innovatively used a phase doppler particle analyzer to measure the flow field in terms of velocity, streamline and turbulence intensity, as well as particle size and number concentration in an agglomeration chamber with a bluff body located at the center. Different shaped bluff bodies were also considered. It was found that low-velocity recirculation region with different shapes appeared in the wake, and vortex flow with special structures were observed. From the perspective of particles, the development of the flow field generated by a single bluff body effectively caused an increase in particle size and a decrease in particle number, which is because that the flow field promotes collisional agglomeration. More specifically, for V-structure bluff body, the particle size improved from 6 μm to a maximum of 13 μm and the particle number concentration decreased by 8 times. The agglomeration efficiency for PM2.5 and PM10 reached 89.06% and 87.38% respectively. Furthermore, by analyzing the velocity of different sized particles, it was reasonable to assume that different sized particles appeared to have velocity differences due to recirculating vortex flow, while the overlapping trajectories of positive and negative moving particles was mainly responsible for the collision probability enhancement. This paper presents new insights into particle agglomeration separation for this environment-friendly and low-cost technology.

Fast fluid dynamics simulation of airflow around a single bluff body under different turbulence models and discretization schemes

Fast and accurate simulation of outdoor airflow distribution is important for studying urban microclimate. Choosing a reasonable turbulence model and discretization scheme is not only related to the computational accuracy but also to efficiency. However, conventional CFD methods are computationally intensive and slow for unsteady problems, and thus cannot meet the demand for fast simulation of urban microclimate. In this paper, three pressure-correction schemes (i.e., NIPC, SIPC, and NSPF) for solving the N–S equation item by item are implemented in OpenFOAM, and then the differences are compared when applying different turbulence models and discretization schemes to quickly simulate the airflow distribution around a single 1:1:2 bluff body. All pressure-correction schemes can accurately predict the main airflow characteristics around the bluff body. The three schemes are about 2.5–3.5 times faster than the PISO algorithm, and they take the shortest computational time when applying RKE, followed by SQKE and RNG, while the longest computational time is required when applying SKE and LBKE. NIPC and SIPC have similar computational speeds, while NSPF is about 10–16% faster than them. The pressure-correction scheme with the first-order upwind scheme is about 6–10% faster than the second-order discretization scheme. Considering both computational accuracy and efficiency, the combination of NSPF with RNG or SQKE turbulence model and first-order upwind scheme may be a reasonable choice to quickly simulate the urban airflow distributions.

Large volume scanning laser induced fluorescence measurement of a bluff-body stabilised flame in an annular combustor

This study outlines a variant of three-dimensional OH planar laser-induced fluorescence and its application in characterising a single bluff body stabilised flame inside a 12 burner annular combustor. In this variant of the method a relatively large volume was scanned slowly in order to calculate the full three-dimensional Flame Surface Density (FSD) distribution. The method used a combination of two scanning directions to overcome bias errors associated with laser sheet positions close to the flame edges. The source of this bias error was confirmed numerically through a complimentary synthetic PLIF study, which was also used to refine the experimental setup. The bias error resulted in a reduction of FSD magnitude, although the method was still capable of capturing the flame structure. This was demonstrated by comparing the reconstructions from the two independent scan directions. Combining the data from both directions overcame the bias, and allowed flame asymmetry due to the confinement to be assessed. The FSD was used to determine the heat release rate of the flame with varying local azimuthal angle for different downstream regions. This highlighted the highly asymmetric structure, produced by the asymmetric confinement.Graphical abstract

Topology of flow and heat transfer from prisms in square array

Structures in an array with multiple rows and columns may undergo both inline and side-by-side interferences. A system of nine square prisms in a 3 × 3 square array is numerically investigated for pitch ratio L/D = 1.2 – 7.0 at a Reynolds number of 150, where L is the spacing between the centers of two adjacent prisms, and D is the side width of a square prism. The focus is given on investigating the effect of L/D on flow topology, fluid forces, heat transfer, vortex shedding, and recirculation bubbles. An increase in L/D from 1.2 to 7.0 leads to evolutions of five distinct flows: single bluff body flow (L/D < 1.6), reattachment flow (1.6 < L/D < 3.3), lateral-interaction-induced coshedding flow (3.3 < L/D < 4.1), mixed flow (4.1 < L/D < 4.6) and free coshedding flow (4.6 < L/D < 7.0). The reattachment flow corresponds to small fluid forces while the lateral-interaction-induced coshedding flow induces large fluid forces. The time-mean drag force coefficient of the center prism drastically increases from 0.09 to 1.0 as the flow evolves from the reattachment flow to the lateral-interaction-induced coshedding flow. The maximum heat transfer from the center prism, 10% higher than that from a standalone prism, occurs for the lateral-interaction-induced coshedding flow where the flow around the center prism resembles creeping flow, no recirculation bubble forming on the front or rear surface of the prism. The coherence between heat transfer and flow patterns is discussed, including the impacts of shear layer reattachment, flow recirculation, and vortex shedding on heat transfer.

Flow and mass transfer characteristics for interacting side-by-side cylinders.

This study investigates the local and global flow structures and mass transfer characteristics for a group of interacting side-by-side cylinders in unbounded flow. Configurations with 2, 3, 4, and 5 members are considered for a range of pitch-ratios ( ) at the Reynolds number Re = 90. The focus is laid on the time-averaged and instantaneous local flow features including wake field, jet flow, vortical structures, λ 2, pressure coefficient, and mass transfer coefficient as well as integral variables including hydrodynamic forces. Four flow regimes are identified based on the vortical structures and average stream-wise velocity field. At low pitch-ratio, the whole structure behaves like a single bluff body, while each member in the configuration behaves like an independent isolated bluff body when the pitch-ratio is large. Between these two regimes, asymmetrically and symmetrically deflected wake regimes are observed. Flow regimes dictate hydrodynamic and mass transfer characteristics such that a jump in the hydrodynamic forces and mass transfer coefficient is observed as the flow regime evolves from a single body to a deflected wake. The configuration's size and the position of member cylinders in the structure have more profound effects on hydrodynamic forces and mass transfer characteristics at small pitch-ratio. For all configurations, drag increases as one progresses deeper into the structure, while lift forces are always repulsive between any two neighboring cylinders. Member cylinders have comparable mass transfer coefficients at intermediate and high pitch-ratios, while exterior cylinders exhibit a higher mass transfer coefficient at low pitch-ratio. Overall, the structure's size has a more profound effect on the values of scalars at low pitch-ratios.