Semi-circular Cylinder Research Articles

Wake transitions of flow past two tandem semi-circular cylinders near a moving wall

Wake transitions of flow past two tandem semi-circular cylinders near a moving wall were numerically investigated using the lattice Boltzmann method at the Reynolds number of 150 with various gap ratios (G/D, where G and D are the spacing between the cylinder and wall and the cylinder diameter, respectively) and spacing ratios (L/D, where L is the distance between the cylinder centers). The analysis aims to clarify the effects of L/D and G/D on wake structures, hydrodynamic forces, Strouhal number, and spectral energy of the flow exerted on both cylinders. This study reveals five distinct flow regimes in the L/D-G/D space, such as overshoot, continuous reattachment, pair-wise, quasi-coshedding, and coshedding. These regimes are identified using plots of vorticity contour, time history of drag and lift coefficients (CD and CL), power spectral density, and proper orthogonal decomposition of the vorticity fluctuation into deterministic spatial structures. Furthermore, the flow regime maps and diagrams of time-averaged pressure coefficients on the surface of the cylinders are given to analyze the influence of the moving wall. A significant change in CD and CL is observed for both cylinders, depending on the L/D and G/D ratios. The time-averaged drag coefficient of the downstream cylinder is remarkably lower than that of the upstream cylinder. A significant increase in the time-averaged lift coefficient of the upstream cylinder is observed when the G/D is small due to near-moving wall effects. The root-mean-squared value of the lift and drag coefficients of the downstream cylinder is lower than that of the upstream cylinder as a result of the proximity effect. Meanwhile, the Strouhal number for both cylinders remains mostly the same.

Heat transfer inside a horizontal circular enclosure with a heated semi-circular cylinder at different orientations

Natural convection inside a cylindrical enclosure is important in many industrial applications. Laminar natural convective heat transfer in the annular space between heated semi-circular cylinder in a horizontal concentric cylindrical enclosure, which has relevance to cooling of electronic components, is studied in this work. Constant wall temperature (CWT) and constant wall heat flux (CWHF) boundary conditions are considered on the inner cylinder, whereas the outer cylindrical enclosure is maintained at a fixed lower temperature. The Finite Volume Method (FVM) is used for the computations. The effect of the Rayleigh number ( Ra = 10 2 to 10 5 ) and the angular orientation of the semi-circular cylinder on the convective heat transfer is investigated. The fluid flow, temperature profile, and heat flow are visualized via streamlines, isotherms, and heatlines. Further, the overall heat transfer is explained based on the local and average Nusselt number on the inner cylinder wall. The effect of the angular orientation of the inner cylinder is noticeable for Ra ≥ 10 3 . The angular orientation ϕ = 90 ° greatly enhances the heat transfer as compared to all other orientations for all Ra ≥ 10 3 for both CWT and CWHF boundary conditions. The correlation between the average Nusselt and Rayleigh numbers for a particular orientation is proposed.

Investigating the Turbulent Flow around Semi-Circular Cylinder

The Spalart-Allmaras turbulence model is used to study the flow patterns around a semi-circular cylinder surrounded by water in two dimensions with various angles of strike owing to rotating the cylinder by an angle. The rotation angle ranges from zero to 360° and the ANSYS Fluent software is employed to implement the required simulation. The Spalart-Allmaras turbulence model is used to determine the flow velocity vector, velocity contours, and pressure contours. Moreover, this turbulent model is used to calculate three different non-dimensional parameters, the drag coefficient, lift coefficient, and skin friction factors. Two different Reynolds numbers (Re) are adopted in the calculation of the three non-dimensional parameters with various values for the angle of the cylinder rotation. Here, the semi-circular cylinder is considered stationary but it is placed in a water domain in various positions. Due to the scarcity in information about using the Spalart-Allmaras turbulence model as compared with other models, which are widely used to investigate the flow around the cylinder, three turbulent models are employed to verify the results obtained by the Spalart-Allmaras model, these models are (standard), (RNG), and (Realizable). Results show an excellent agreement between the four turbulent models compared, where there is no significant variation in the obtained results, all results are very similar.

Significance of a permeable semi-circular body and magnetic field on thermo-solutal natural convection and irreversibilities

This study explores the intriguing phenomenon of thermo-solutal buoyancy-driven traits in the presence of a magnetic force within a square cold enclosure housing a soluted and heated permeable semi-circular cylinder. The amalgamation of flat and curved edges, alongside the permeable characteristics, serves as the driving motivation behind this investigation. The primary objective is to scrutinize the impact of magnetic force and its orientation, buoyant force, permeability on the thermo-solutal convection occurring within and around the permeable body. To achieve this, a thorough parametric investigation is carried out, focusing on the significance of Hartmann number (Ha), magnetic field angle (γM), buoyancy ratio (BR), and Darcy number (Da), concerning flow, heat, concentration transfer, and the variation in irreversibilities. The Darcy-Brinkmann-Forchheimer equation as a source term in lattice Boltzmann technique is utilized to accurately solve the intricate porous medium flow. The investigation reveals that escalating the buoyant force, and permeability, and magnetic field angle yields favourable heat and concentration traits. Additionally, aligning the magnetic force opposite to gravity diminishes the inhibitory effects on the thermal and solutal transfers exerted by the magnetic force. Notably, unsteady behaviour is predominantly observed when the BR assumes a negative value, with the amplitude and frequency of these phenomena amplified by the Da and γM. Also, a few anomalous spikes in the NuM and ShM are witnessed, attributed to the development of a robust uni-vortex in the top region of the cavity. Interestingly, the irreversibilities induced by the magnetic field diminish as the BR increases. Among these irreversibilities, entropy generation due to concentration emerges as the dominant contributor, with the exception of cases exhibiting atypical rises, where fluid entropy resulting from friction takes precedence.

Wake-induced vibration and heat transfer characteristics of three tandem semi-circular cylinders

This paper studies the wake-induced vibration (WIV) and heat convection of the downstream tandem bluff bodies under the influence of an upstream bluff body at Re = 200 and Pr = 0.7. For the reduced fluidic velocity (Ur) in the range of 1–16 and different bluff body diameter ratios (d/D), three wake interference patterns, namely, the quasi-co-shedding (QCS) pattern, the co-shedding (CS) pattern, and the coupling between QCS and CS (QCS-CS) are formed due to the interference between the shear layer and vortex shedding process. The occurrence conditions of the three patterns are closely related to Ur and d/D. The vibration response of the midstream bluff body is roughly consistent with that of a heat-isolated semi-circular cylinder (HISC) if d/D is small. By increasing d/D, the vibration amplitude of the midstream bluff body first increases, then decreases with Ur. The vibration amplitude of the downstream bluff body starts to increase from small d/D and then can maintain a high value with the increase of Ur, even at large d/D. Compared with the HISC, the tandem configurations can help reduce the drag force. Because of the wake interference and the ‘blocking effect’ from the upstream bluff body, although the heat convection of the midstream and downstream bluff bodies can be effectively strengthened through WIV, the time-averaged Nusselt numbers (NuA) of the midstream and downstream bluff bodies are still lower than that of the HISC. Besides, heat transfer efficiency has been found to correlate with the transverse vibration amplitude of bluff bodies. Moreover, it is revealed that there is a trade-off between the heat transfer efficiency of the equipment and its service lifespan because increasing the vibration amplitude enhances convection but also increases the risk of potential damage to the structural integrity.

Investigation on the influence of electro thermo hydrodynamics (ETHD) on semi-circular cylinder

Investigation on the influence of electro thermo hydrodynamics (ETHD) on semi-circular cylinder

Mimicking the Mechanism of Lift Generation in Dragonflies

Human pursuit of flight has learnt many lessons from nature and a few adaptations have led to phenomenal progress. Insect flight uses complex unsteady aerodynamics to generate lift in addition to producing thrust. A close look at the dragonfly provides some clues to mimic its flight using passive means by separating propulsion and lifting mechanisms. Though the dragonfly can independently flap each of its wings to generate lift and thrust, during forward flight, fore-wings alone flap while the aft-wings remain nearly steady. We adopt this as basis for new passive configurations to generate steady lift. Conceptually, we replace fore-wings with a cylinder that is known to shed vortices, to mimic flapping. A simple plate replaces the aft-wings. Flow analysis of such a configuration at Reynolds Number of 7500 revealed a steady flow topology featuring a trapped vortex over the plate, resulting in steady lift to drag ratio of 3. A further optimized configuration consisting of a semi-circular cylinder upstream and a cambered plate downstream resulted in lift to drag ratio of 14.5, which is considerable for these flow regimes, opening up new possibilities for design of nano-flight vehicles.

Large-eddy simulations of the flow past a bluff-body with active flow control based on trapped vortex cells at Re = 50000

We investigate a novel flow control concept, which allows to govern bluff-body wake dynamics and the laminar–turbulent transition by suppressing vortex shedding and obtaining the mostly detached flow. Large-eddy simulations past a bluff-body (BB) with and without an active flow control (AFC) system at a Reynolds number of 50000 and zero angle of attack are presented. The BB is designed of a semicircular cylinder of the finite span-wise length with two hemispheres attached to its lateral sides. The BB has a negative lift force because of detached and attached massive recirculation zones, which respectively, originate from separation of the laminar boundary layers from its upper side and the leading edge. AFC is based on the two trapped vortex cells implemented at the upper side of BB to control the behavior of boundary layers. The chosen AFC demonstrates almost the detached flow and suppresses the vortex street. The lift-to-drag ratio of BB with integrated AFC is calculated as ≈1.5 (compared to ≈−1 obtained for the simple BB) coupled with reasonable energy losses of 10% in terms of the total drag coefficient. Finally, present findings demonstrate the potential of the concept and provide the basis for its further development.

Investigating the effect of the flow direction on heat transfer and energy harvesting from induced vibration in a heated semi-circular cylinder

The present study examines the flow and heat around low-mass arched forebodies (AF), flat forebodies (FF) and a circular cylinder (CC) in the presence of buoyancy. The Richardson number prescribed in this investigation varies from 0 to 1.5 for the Prandtl number of 0.71 and Reynolds numbers of 100 and 200. Selecting five semi-circular cylinders with various length-to-diameter ratios (L* = L/D) aims to investigate the influence of L* on energy harvesting. The arched and flat surfaces exposed to the incoming flow can result in experiencing heat transfer augmentation due to the separating shear layers. The functional dependence of drag coefficient, lift coefficient, non-dimensional maximum vibration amplitude, and output power are analyzed and examined in detail. The main novelty introduced in current investigation is to determine a bluff body that generates a substantial amount of vibration in order to capture maximum energy. Another connotation of this study regards the possibility of employing a numerical approach to combine the effects of geometry and buoyancy to alter heat transfer as well as extracted flow energy. Increasing the Richardson number results in increased heat transfer and energy harvesting. This is because the interaction between fluid and bluff body in the presence of buoyancy can cause disruption of the thermal boundary layer, thereby augmenting heat transfer. In the absence of buoyancy force, the circular cylinders with L* of 0.5 and 0.6 for the flat forebody configuration gain the highest extracted power at Reynolds numbers of 100 and 200, respectively, resulting in 3.5 and 5.3 times more extracted power compared to the circular cylinder. Considering extracted power, it is shown that a D-shaped configuration is less dependent on buoyancy force compared to an inverted D-Shaped configuration. The flat forebody configuration always harvests more energy than the same body with opposite flow direction. These results are capable of providing deeper insight into configuring the thermal systems, which are able to dissipate heat loads as well as produce maximum power. Having compared some of the outcomes of present work with other studies, a good agreement has been achieved to validate the simulations.

Computational investigation of magneto-hydrodynamic flow of newtonian fluid behavior over obstacles placed in rectangular cavity

The magneto hydro-dynamic flows are of great importance in the industries such as food processing, power generation and in investigating the behavior of boundary layer convection. In this article, the magneto hydrodynamic flow of Newtonian fluid in rectangular cavity under the effect of applied magnetic filed is investigated. In the rectangular cavity, three semi circular cylinders are placed as obstacles to create unsteadiness in the flow path. Computational fluid dynamics model is built to analyze and observe the flow behavior in presence of 10 Ampere per meter. Furthermore, velocity profiles in vertical and horizontal directions, streamlines patterns, pressure distribution profile, vorticity profile, and viscous stress are presented. These profiles are discussed with and without the presence of strong magnetization force and flow behavior is investigated. The model is designed and compute in COMSOL-Multiphysics. It is concluded that presence of high magnetization force enhance the surface velocity to 1.87 m/s in horizontal direction and 0.86 m/s in vertical direction. Swirling flow pattern in streamlines increase with high magnetic force. The exerted pressure on wall of cavity has augmented to 2.39 Pa with increment in magnetic field. Moreover, obtained results are in complete agreement with already published work.

Unsteady forced convection flow and heat transfer past a blunt headed semicircular cylinder at low Reynolds numbers

A numerical analysis is performed to study the forced convective fluid flow and heat transfer past an unconfined semicircular cylinder. The two-dimensional simulations are carried out for Reynolds number ranging 10 ≤ Re ≤ 200 and operating fluid is air (Pr = 0.71) for Newtonian constant property fluid. Continuity, Navier-Stokes, and energy equations with appropriate boundary conditions are solved using computational fluid dynamics solver Ansys Fluent. Various parameters flow such as lift, drag, skin friction coefficient, pressure coefficient, Nusselt (Nu) number, Strouhal (St) number, and vortex strength are calculated. The transition from steady to time periodic flow occurs between Re = 60 and 80. The effect of Reynolds number on heat transfer is discussed. Finally, a developed correlation of Nu and St numbers are presented.

Spin-up in a semicircular cylinder

We report experimental and theoretical results on how a fluid (homogeneous or continuously stratified) is spun up in a closed, semicircular cylinder. Experiments were performed for Rossby numbers $Ro=0.02$, 0.2 and 1 (the latter corresponding to the limiting case of spin-up from rest), with the Ekman number $E=O({10^{-5}})$, and the Burger number ($S$) varied between 0 and 10. There are two key processes: Ekman pumping that drives the core flow; and the formation and breakdown of the vertical-wall boundary layers, with respective characteristic time scales $t\sim E^{-1/2}$ and $Ro^{-1}$. When these time scales are comparable, the observed flow is dominated by the gradual spin-up of the initial anticyclone that forms when the rotation rate is increased, which fills the container's interior; vorticity generated adjacent to the vertical walls throughout remains confined to the neighbourhood of the container's walls and corners. Conversely, when ${E^{1/2}/Ro\ll 1}$, the vertical-wall boundary layers rapidly break down, resulting in the formation of cyclonic vortices in the container's vertical corners, which grow and interact with the initial anticyclone, leading to the formation of a three-cell flow pattern. For $Ro=0.02$, our theoretical description of the flow generally agrees well with experiments, and the computation of the eruption times for the unsteady boundary layers is consistent with the observations for both $Ro=0.02$ and $Ro=0.2$.

Responses of cyprinid (Ancherythroculter nigrocauda) to flow with a semi-circular cylinder patch.

Flows in river habitats are characterized by unsteady turbulence due to the existence of woody debris, boulders and vegetation. As a representative aquatic species, fish is important for the riverine ecosystems, with its complex behavioural responses to turbulent flows. Previous studies investigated the fish-vortices interaction with vortex streets by placing objects with simplified geometries centred at the flow. Nonetheless, complex river morphology in natural rivers results in much more spatially heterogeneous flows due to randomly distributed obstructions. Thus, a semi-circular cylinder patch located on one side of the flume is used to mimic a vegetation patch at the riverbank. The patch varies in diameter (D0 =16, 20 and 24 cm) and density (φ=0.04 and 0.1), whereas the flow velocity is fixed at 25 cm s-1 . Fish are observed to swim in three typical patterns, which are "swim around" (pattern 1), "spill" (pattern 2) and "swim through" (pattern 3). For flow with a dense patch, all three patterns are recorded, but only patterns 1 and 2 are observed in sparse patches. It is noticed that in patterns 1 and 2, fish prefer to hold place in zones of low velocity and low turbulence. Moreover, variations in patch diameter have little influence on pattern selection. Results showed that tail beat amplitude (TBA*) in each zone displayed more variations compared with tail beat frequency (TBF). In addition, Spearman's rank tests revealed that TBA* is affected by none of the four hydrodynamic variables ( ), whereas flow velocity imposes the most influence on TBF. Both diameter and density of the patch displayed no significant influence on TBA* and TBF.

Modeling Open Channel Flows of a Viscous Fluid: Critical Transition and Apparent Bottom

The Shallow Water model (SWM) provides a simplification of the Navier–Stokes model (NSM) for stratified flows over a topography when the depth of the fluid layer is small compared to the horizontal scale of the flow. Nevertheless, the application of SWM is limited to the case of slowly variable bottoms and fails in describing the fluid flow over steep obstacles. In this work, we propose to extend the applicability of SWM when the topography is no longer slowly variable with space, by replacing the topography with an “apparent bottom”. This methodology is tested for the laminar flow of a two-layer fluid over a semi-circular cylinder. Sixteen different steady configurations are investigated in order to assess the influence of the Froude number and the blocking factor corresponding to the ratio between the obstacle height and the fluid layer normal height. Here, the apparent bottom required for SWM is obtained by enforcing the liquid height profile to be the one obtained from full resolution (NSM).

Numerical investigation on vortex-induced vibration energy harvesting of a heated circular cylinder with various cross-sections

This study describes a two-dimensional numerical investigation of the flow and heat transfer around inverted D-shaped cylinders. The effects of thermal buoyancy force over the bluff bodies are considered numerically based on the flow field around circular and semi-circular cylinders. The operating Richardson numbers (Ri) are 0, 0.5, 1, and 1.5 with a Reynolds number (Re) of 100. Five cylinders with a length -to -diameter ratio of L* = (L/D) = 0.5, 0.6, 0.7 0.8, 0.9 are selected to investigate the effect of L* on energy harvesting. The functional dependence of drag coefficient, lift coefficient, resultant force coefficient, dimensionless maximum vibration amplitude, and output power is analyzed and studied. To validate the present study, some of the results are compared with other numerical and experimental investigations, and reasonable agreement is obtained. The results show that in the absence of buoyancy force, the history of the contours, and streamlines are periodic, and vortices created at the back of the body detach similarly from either side of the body; however, this behavior is not seen for other values of the Richardson numbers. Moreover, when the temperature contours are examined, a higher heat transfer is observed when a higher value of the Richardson is prescribed. Finally, the analysis shows that the output power of the bluff bodies under the condition of Ri =1.5 increases by 7.02, 10.4, 15.6, 21.2, and 25.4 as the L* increases, and the maximum extracted power is 26.2 at L* = 1 in relation to not applying buoyancy.

Free convection heat transfer from a semi-circular cylinder inside a square enclosure: Orientation effects

The numerical investigation has been carried out for the buoyancy driven flow (free convection) from a cylinder of semi-circular cross-section at three orientation angles (i.e., φ=0°,45°and90°) to stagnant power-law fluids inside a square cavity. The coupled governing equations were solved for the given range of the pertinent dimensionless parameters of Rayleigh number (102⩽Ra⩽105), Prandtl number (10⩽Pr⩽100), and power-law index (0.3⩽n⩽1.8). At different orientation angles of the semi-circular cylinders, the numerical results were visualized in terms of velocity and temperature profiles near the cylinder and, gross engineering parameters (e.g., average Nusselt numbers). If all other factors are equal, the rate of heat transfers from a semi-circular cylinder at φ=90° is higher than for the other orientations. The rate of heat transfer can also be increased by increasing the value of Ra and decreasing the value of Pr. In the power-law fluids, the heat transfer rate is always higher in shear-thinning fluids under the same condition. In the end, the average Nusselt number for different orientation angles of the cylinder has been correlated by simple expression.

Mixed convection from semi-circular cylinder in Bingham plastic fluids: Adding buoyancy

Mixed convection heat transfer from a heated semi-circular cylinder in Bingham plastic fluids with adding buoyancy configuration has been studied numerically. Extensive results of fluid flow and heat transfer characteristics are presented in terms of the velocity and temperature profiles, shape and size of yield/unyielded zone. In the steady flow regime, Reynolds number, Prandtl number, and Richardson number are expected to be positively dependent on the average Nusselt number (which decreases the convection boundary layer). In contrast, the average Nusselt number decreases as the value of the Bingham number increases from its maximum value in Newtonian media to its conduction limit when most of the fluid is frozen.. Finally, using a simple expression, the numerical results of average Nusselt number have been predicted in terms of the j-factor for new applications.

Simulation of Non-Isothermal Turbulent Flows Through Circular Rings of Steel

This article is intended to examine the fluid flow patterns and heat transfer in a rectangular channel embedded with three semi-circular cylinders comprised of steel at the boundaries. Such an organization is used to generate the heat exchangers with tube and shell because of the production of more turbulence due to zigzag path which is in favor of rapid heat transformation. Because of little maintenance, the heat exchanger of such type is extensively used. Here, we generate simulation of flow and heat transfer using non-isothermal flow interface in the Comsol multiphysics 5.4 which executes the Reynolds averaged Navier stokes equation (RANS) model of the turbulent flow together with heat equation. Simulation is tested with Prandtl number (Pr = 0.7) with inlet velocity magnitude in the range from 1 to 2 m/sec which generates the Reynolds number in the range of 2.2 × 105 to 4.4 × 105 with turbulence kinetic energy and the dissipation rate in ranges (3.75 × 10−3 to 1.5 × 10−2) and (3.73 × 10−3−3 × 10−2) respectively. Two correlations available in the literature are used in order to check validity. The results are displayed through streamlines, surface plots, contour plots, isothermal lines, and graphs. It is concluded that by retaining such an arrangement a quick distribution of the temperature over the domain can be seen and also the velocity magnitude is increasing from 333.15% to a maximum of 514%. The temperature at the middle shows the consistency in value but declines immediately at the end. This process becomes faster with the decrease in inlet velocity magnitude.

The effect of second order slip condition on MHD nanofluid flow around a semi-circular cylinder

Abstract Steady forced convection of non-Newtonian nanofluids around a confined semi-circular cylinder subjected to a uniform magnetic field is carried out using ANSYS FLUENT. The numerical solution is obtained using the finite volume method. The user-defined scalar (UDS) is used for the first time to calculate the second order velocity slip boundary condition in semi-circular curved surface and the calculated results are compared with those of the first order velocity slip boundary condition. Besides, the effects of volume fraction, size, type of nanoparticles and magnetic field strength on heat transfer are studied. The present study displays that adding nanoparticles in non-Newtonian fluids significantly enhances heat transfer. In addition, it is observed that the heat transfer rate decreases first and then increases with the increase of Hartmann number. The effects of blocking rate on Nusselt number, wake length and heat transfer effect are shown in the form of graphs or tables.

Wake evolution and vortex structure characteristics of flow over two tandem semi-circular cylinders with flat surfaces facing each other

This paper reports the results of a numerical investigation into the flow over two tandem semi-circular cylinders with flat surfaces facing each other and the associated wake flow characteristics. The effect of spacing ratio (L/D, L is the in-line spacing between two flat surfaces and D is the diameter of cylinders) ranging from 1 to 16 is examined in a low Reynolds number range of Re = 60–180. Five flow patterns are identified including the over-shoot, continuous reattachment, alternate reattachment, quasi-co-shedding, and co-shedding regimes. The difference between quasi-co-shedding and co-shedding regimes depends on the origin of the vortices shed from the downstream cylinder. Unlike the vortices generated due to the roll-up of shear layers detached from both upstream and downstream cylinders in the co-shedding regime, the vortices shed from the downstream cylinder come from upstream instead of the roll-up of shear layers for the quasi-co-shedding regime. The wake flow characteristics are discussed in terms of the vortex formation and shedding, wake structure and evolution, boundary layer separation and shear layer development, the occurrence of secondary vortex street, and the associated migrating vortex modes. The variations of hydrodynamic coefficients and Strouhal number are associated with the flow regime transition. When the alternate reattachment and quasi-co-shedding regimes emerge, a small pair of peaks of the root-mean-squared streamwise flow velocity (u*rms) fixedly occurs at the two corners of the downstream cylinder, illustrating the strong velocity fluctuation caused by vortices impingement and the secondary separation. Three types of vortex street are observed in the wake, where the secondary vortex street region is further divided into three parts in terms of the vortex structure, including S + P (a single vortex and a pair of vortices are formed per cycle in the secondary vortex street), P (a pair of vortices is formed per cycle in the secondary vortex street), and 2S (two vortices in opposite directions are formed per cycle in the secondary vortex street) modes. Two partitions in Re–L/D map (Re and L/D as the vertical and horizontal ordinates, respectively) are proposed in this work for the flow regime as well as the vortex street.