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Large Eddy Simulations (LES) with Smagorinsky subgrid scale model have been performed for the flow past two circular cylinders in tandem placed in the vicinity of a horizontal plane wall at very small gap ratios, namely G ∕ D = 0 . 1 , 0 . 3 and 0.5, in three-dimension (3D). The ratio of cylinder center-to-center distance to cylinder diameter, or the pitch ratio, L ∕ D , considered in the simulations is L ∕ D = 2 and 5. This work serves as an extension of Abrahamsen Prsic et al. (2015). In essence, six sets of simulations have been performed in the subcritical Reynolds number regime at R e = 1 . 31 × 1 0 4 . Our major findings can be summarized as follows. (1) At both pitch ratios, the wall proximity has a decreasing effect on the mean drag coefficient of the upstream cylinder. At L ∕ D = 2 , the mean drag coefficient of the downstream cylinder is negative since it is located within the drag inversion separation distance. (2) At L ∕ D = 2 , a squarish cavity-like flow exists between the cylinders and the flow circulates within the cavity. A long lee-wake recirculation zone is found behind the downstream cylinder at G ∕ D = 0 . 1 . However, a much smaller lee-wake recirculation zone is noticed at L ∕ D = 5 with G ∕ D = 0 . 1 . (3) At L ∕ D = 2 , the reattachment is biased to the bottom shear layer due to the deflection from the plane wall, which leads to the formation of the slanted squarish cavity-like flow. At both pitch ratios, as G ∕ D becomes smaller, stronger vortices are found between the two cylinders. Less intense vortices are observed in the near wake of the downstream cylinder due to the vortex shedding suppression of the neighboring wall.

The flow around a twisted elliptic cylinder is numerically calculated using large eddy simulation (LES) at the Reynolds number of 2 × 104, along with a circular cylinder for comparison. The mean drag coefficient and the fluctuating lift coefficient of the twisted cylinder are 27.99% and 94.01% lower, respectively, than that of the circular cylinder. The twisted surface leads to more stable wake, longer vortex formation length, higher base pressure and three-dimensional separation. In addition, cluster-based reduced-order modelling (CROM) is performed to analyze phase-dependent variations of the wake flow and evaluate the relationship between derived characteristic flow structures and their impact on forces. It captures the oscillatory behavior of Karman vortex shedding in the wake of the circular cylinder. Meanwhile, two flow regimes, anti-phased and in-phase-dominated vortex shedding, generated by the twisted cylinder are extracted and distinguished. The two regimes prevail alternately with changing probability of occurrence along the spanwise of the twisted cylinder, which can be attributed to the different separation angles. The in-phase-dominated vortex shedding inhibits the effect of Karman vortex shedding and is subjected to a lower force compared with the anti-phased vortex shedding.

A series of experiments was carried out to study the flow behaviour behind a rotationally oscillating cylinder at a low Reynolds number (Re=300) placed in a recirculation water channel. A stepper motor was used to rotate the cylinder clockwise- and- counterclockwise about its longitudinal axis at selected frequencies. The particle image velocimetry (PIV) technique was used to capture the flow field behind a rotationally oscillating cylinder. Instantaneous and timeaveraged flow fields such as the vorticity contours, streamline topologies and velocity distributions were analyzed. The effects of four rotation angle and frequency ratios F r (F r=f n/f v, the ratio of the forcing frequency f n to the natural vortex shedding frequency f v) on the wake in the lee of a rotationally oscillating cylinder were also examined. The significant wake modification was observed when the cylinder undergoes clockwise-and-counterclockwise motion with amplitude of π, especially in the range of 0.6≤F r≤1.0.

Laminar flow past a rotating cylinder near a plane wall is studied numerically using a second-order accurate immersed boundary method. The wake-wall interactions are investigated in detail, for different wall heights and varying rotational rates. Flow patterns are classified based on the wake structure and the effect of rotation on critical wall heights is discussed for both clockwise and counterclockwise rotation. For the configuration studied i.e. rotating cylinder above a bottom plane wall, counterclockwise rotation of cylinder favors the wake-wall interactions, while clockwise rotation influences in an adverse manner. In addition to conventional analysis, the evolution of the vortical structures in the wake region are examined using Lagrangian analysis of individual vortical structures. The diffusion of the positive vortex shed from the wall facing side of the cylinder is accelerated due to the influence of boundary layer with net negative vorticity. The wall augmented diffusion of positive cylinder vortices is compensated by the creation of secondary wall vortices from the bottom wall boundary layer. Counterclockwise rotation of cylinder increases the shear inside boundary layer resulting in more pronounced diffusion.

Theoretical characteristics of the flow in scrolls of hydraulic turbines whose cross-sectional dimensions and shapes are determined using the equations of the potential flow induced by a vortex sink cylinder of finite length located on an impermeable cylinder of infinite length in an ideal fluid are calculated. The theoretical distributions of the components of the velocity and the directions of its horizontal and vertical projections (vertical turbine) are determined and plotted. They are favorable for hydraulic turbines and are in good agreement with the values set at the stator inlet, which confirms the effectiveness of the new approach to studying potential flows whose velocity potential cannot be expressed analytically.

The coupled evolution of an eroding cylinder immersed in a fluid within the subcritical Reynolds range is explored with scale resolving simulations. Erosion of the cylinder is driven by fluid shear stress. Karman vortex shedding features in the wake and these oscillations occur on a significantly smaller time scale compared to the slowly eroding cylinder boundary. Temporal and spatial averaging across the cylinder span allows mean wall statistics such as wall shear to be evaluated; with geometry evolving in 2-D and the flow field simulated in 3-D. The cylinder develops into a rounded triangular body with uniform wall shear stress which is in agreement with existing theory and experiments. We introduce a node shuffle algorithm to reposition nodes around the cylinder boundary with a uniform distribution such that the mesh quality is preserved under high boundary deformation. A cylinder is then modelled within an infinite array of other cylinders by simulating a repeating unit cell and their profile evolution is studied. A similar terminal form is discovered for large cylinder spacings with consistent flow conditions and an intermediate profile was found with a closely packed lattice before reaching the common terminal form.

A coupled viscous-inviscid interaction scheme combining the continuity equation for potential flow with the three-dimensional integral boundary layer equations is presented. The inviscid problem is ...

Within the framework of two-dimensional Euler equations, the stability is investigated of a system consisting of an inner unfastened round cylinder, an incompressible fluid flow around this cylinder with circular streamlines, and an outer fastened cylinder (vessel). An equation is obtained for the natural frequencies with different mean flows between the cylinders. Accurate solutions of this equation are derived and an analysis of these solutions is given. An energetic investigation of the loss of stability in the system is carried out.

The problem of flow of a viscous incompressible fluid in an axially symmetric pipe with small irregularities on the wall is considered. An asymptotic solution of the problem with the double-deck structure of the boundary layer and the unperturbed flow in the environment (the “core flow”) is obtained. The results of flow numerical simulation in the thin and “thick” boundary layers are given.

This note studies the accuracy of Isogeometric Analysis (IGA) applied in the simulation of incompressible flows around a cylinder in two and three dimensions. Quantities of interest, like the drag coefficient, the lift coefficient, and the difference of the pressure between the front and the back of the cylinder are monitored. Results computed with standard finite element methods are used for comparison.

The current research work investigates numerically the turbulent flow field characteristics around three dimensional circular cylinder of finite height at Reynolds number of 43000 using Detached Eddy Simulation (DES) turbulence model. Comparison of the numerical results with the experiment data has been taken place. The results reveals that the DES turbulence model is superior for predicting the flow past the circular cylinder of finite height at this Re. The numerical results of this study show the great potential of the presented DES for investigating the complicated flow structure in this case. DES is very accurate for predicting the flow characteristics in many sophisticated cases and can reduce the computational efforts during the simulation process in comparison with Large Eddy Simulation (LES) turbulence mathematical model.

A numerical investigation was performed on the reduction of the fluid forces acting on the square cylinder in the laminar flow regime with a perforated plate. The effects of geometric parameters such as the distance between the square cylinder and the perforated plate on the wake of the square cylinder were discussed. Furthermore, the flow characteristics such as the drag coefficient, lift coefficient, Strouhal number and flow pattern were obtained. It can be concluded that the drag force of the square cylinder reduces to some extent due to the addition of the perforated plate. The flow structure varies when the perforated plate is located behind the square cylinder. Moreover, the recirculation zone augments with the increase of L/D, and the vortex trace on the upper and lower surface of the square cylinder moves gradually backwards until a stable recirculation zone formed between the square cylinder and the perforated plate.

The study focuses on the effect of gap spacing (g) ranging g = 1–7, Reynolds numbers (Re) ranging Re = 80–200 and the size of the control plate (w) varied from 0.1d to 1d (where d is the size of the main cylinder) on the flow around a square cylinder with an upstream control plate. Two-dimensional multiple-relaxation-time lattice Boltzmann method is used to find the optimum condition, where the maximum reduction in drag force and suppression of vortex shedding occurs. It is observed that the drag is reduced significantly and the fluctuating lift is also suppressed. The detailed wake structure mechanism within gap spacing and near wake vortex structures around and behind the main square cylinder in the presence of the control plate are studied and compared with a plain square cylinder. In this study, the optimum conditions for maximum drag reduction in terms of control plate width, gap spacings and Reynolds numbers are found. The single bluff body, shear layer reattachment, critical flow, two-row single bluff body, fully developed two-row vortex shedding and quasi-steady-flow patterns are found. The time-trace analysis of drag and lift coefficients, power spectra analysis of lift coefficients, variation in force statistics and inclination angles are discussed in detail for all observed flow patterns. The maximum reductions on the drag force are 99.82, 99.8, 99.8, 99.9, 99.98, 100.4, 100.1, 100.05 and 100.1% for Re = 80, 100, 120, 140, 150, 160, 180, 190 and 200, respectively.

Laminar flow over a twisted cylinder is numerically simulated at a Reynolds number of 100. The flow past a smooth cylinder is calculated for comparison. Jung and Yoon (J. Fluid Mech., 759, 2014) showed the considerable suppression of force coefficients at the subcritical Reynolds number of 3000. The present results verify that the twisted shape of the cylinder can be used to reduce the force coefficients at a low Reynolds number containing the laminar flow. This suppression of the force coefficients is supported by a longer vortex formation length produced by the twisted cylinder. We investigated the characteristics of the local force coefficients for a twisted cylinder. The simple periodic oscillation of the time histories of total and local lift coefficients for the twisted cylinder exhibits the same pattern as that of a smooth cylinder. However, the time history of drag for the twisted cylinder reveals the presence of multi-frequency oscillations, resulting in harmonic behavior of the power spectra. This is confirmed by a time sequence of the instantaneous flow fields during the half-period of the time histories of force coefficients. The nature of the three-dimensional (3-D) twisted shape forms the 3-D vortical structures along the spanwise direction, which leads to the harmonic behavior of the drag time trace power spectra.

Direct numerical simulation is performed for flow past an isolated cylinder at R e = 1 , 000 . The corners of the cylinder are rounded at different radii, with the non-dimensional radius of curvature varying from R + = R / D = 0.000 (square cylinder with sharp corners) to 0.500 (circular cylinder), in which R is the corner radius and D is the cylinder diameter. Our objective is to investigate the effect of the rounded corners on the development of the separated and transitional flow past the cylinder in terms of time-averaged statistics, time-dependent behavior, turbulent statistics and three-dimensional flow patterns. Numerical results reveal that the rounding of the corners significantly reduces the time-averaged drag and the force fluctuations. The wake flow downstream of the square cylinder recovers the slowest and has the largest wake width. However, the statistical quantities do not monotonically vary with the corner radius, but exhibit drastic variations between the cases of square cylinder and partially rounded cylinders, and between the latter and the circular cylinder. The free shear layer separated from the R + = 0.125 cylinder is the most stable in which the first roll up of the wake vortex occurs furthest from the cylinder and results in the largest recirculation bubble, whose size reduces as R + further increases. The coherent and incoherent Reynolds stresses are most pronounced in the near-wake close to the reattachment point, while also being noticeable in the shear layer for the square and R + = 0.125 cylinders. The wake vortices translate in the streamwise direction with a convection velocity that is almost constant at approximately 80% of the incoming flow velocity. These vortices exhibit nearly the same trajectory for the rounded cylinders and are furthest away from the wake centerline for the square one. The flow past the square cylinder is strongly three-dimensional as indicated by the significant primary and secondary enstrophy, while it is dominated by the primary enstrophy ( ω z 2 ) for the rounded cylinders.

Potential flow is considered in a cylindrical coordinate system (r, z, θ), caused by a vortex filament located on the z-axis and a finite length vortex inflow-cylinder of uniform intensity distribution located on an infinite impermeable cylinder, the centerline of which coincides with the z axis, in infinite space filled with an ideal liquid. Equipotential surface (line) equations and flow surfaces (lines) are given, along with relations for determining velocity components. It is shown that the flow lines caused by a vortex inflow-cylinder lie on the flow surfaces created generated by the inflow-cylinder. Equations are given that allow lines of total flow to be projected onto planes normal to the z axis using the finite difference method. It is noted that the shape of the flow lines on the respective flow surfaces depend only on the ratio of the vortex filament intensity to inflow-cylinder flow rate.

The topology and evolution of three-dimensional flow past a cylinder of slenderness ratio SR=1 mounted in a wind tunnel is examined for 0.1≤Re≤325 (based on the diameter of the cylinder) where steady-state solutions have been obtained. Direct numerical simulations were computed using an in-house parallel finite element code. The three-dimensional theory of separation is used to analyze and interpret the flow phenomena. Results indicate that symmetry breaking occurs at Re=1, while the first prominent structure is a horseshoe vortex downstream from the cylinder. At Re=150, two foci are observed, indicating the formation of two tornadolike vortices downstream. Concurrently, another horseshoe vortex is formed upstream from the cylinder. For higher Reynolds numbers, the flow downstream is segmented to upper and lower parts, whereas the topology of the flow on the solid boundaries remains unaltered. Pressure distributions show that pressure, the key physical parameter in the flow, decreases everywhere except im...

A series of experiments was conducted in a re-circulating water tunnel with a uniform flow profile, in which a flexible tension-dominated cylinder was held fixed at both ends and placed perpendicular to the incoming flow direction. The circular cylinder had an aspect ratio of L / D =67 and a low mass ratio of m *=0.43. Dynamic response of the system was studied in the reduced velocity range of U *=2.9–14.5 and Reynolds numbers of Re =315–1580. The oscillations of the cylinder in the inline (IL) and crossflow (CF) directions were captured using two synchronized high speed cameras. Continuous response of the cylinder was reconstructed from limited number of measurement points based on modal expansion theorem modified using Modal Assurance Criterion (MAC). The MAC enhanced the response reconstruction by adjusting the contributions from each structural mode. A distinct advantage of implementing the MAC in this method compared with the previously used methods was reconstructing the VIV response accurately when the experimental measurement points were clustered in a small region along the length of the cylinder. Mono- and multi-frequency excitation responses as well as transition from a low mode number to a higher one were observed. Flow forces acting on the cylinder were calculated and a consistent relation between the regions where the cylinder was being excited by the flow and the counterclockwise figure-eight trajectories of oscillations was observed.

In the present study heat transfer and entropy generation analysis of boundary layer flow of an incompressible viscous fluid over hyperbolic stretching cylinder are taken into account. The governing nonlinear partial differential equations are normalized by using suitable transformations. The numerical results are obtained for the partial differential equations by a finite difference scheme known as Keller box method. The influence of emerging parameters namely curvature parameter and Prandtl number on velocity and temperature profiles, skin friction coefficient and the Nusselt number is presented through graphs. A comparison for the flat plate case is given and developed code is validated. It is seen that curvature parameter has dominant effect on the flow and heat transfer characteristics. The increment in the curvature of the hyperbolic stretching cylinder increases both the momentum and thermal boundary layers. Also skin friction coefficient at the surface of cylinder decreases but Nusselt number shows opposite results. Temperature distribution is decreasing by increasing Prandtl number. Moreover, the effects of different physical parameters on entropy generation number and Bejan number are shown graphically.

This research presents a computational fluid dynamics study for simulating a curved cylinder in ocean currents. A rigid curved cylindrical geometry with two bending directions was modelled in uniform and logarithmic flow profiles at a maximum Reynolds number of 1.5 × 105; the Realizable k–epsilon formulation is used as the turbulence closure model. An analysis of force coefficients and vortex structure are presented. The results show that a curved cylindrical structure will have different hydrodynamic behaviour depending on the oncoming flow direction. Bending the cylinder in a direction which is opposite to the predominant flow direction is recommended, as the maximum forcing amplitude is reduced in this case.

The characteristics of the flow field of a circular cylinder having a small vertical plate at the upstream side are investigated by measuring the fluid force on the circular cylinder and by visualizing the flow field using particle image velocimetry. The experimental parameters are the width ratios (H/B = 0.2–0.6) of the vertical plates to the circular cylinder's diameter, and the gap ratios (G/B = 0–3) between the circular cylinder and the vertical plate. The drag reduction rate and Strouhal number of the circular cylinder increased and then decreased with G/B in the case of the same H/B. The drag reduction rate increased with H/B in the case of the same G/B. In the case of a circular cylinder having a small vertical plate, the stagnation regions are represented on the upstream and downstream sides of the circular cylinder, and the size of that region on the upstream side increased with H/B.

Wake-induced vibration of a small cylinder in the wake of a large cylinder was investigated numerically. The focus of the study is to identify the effects of the spacing between the two cylinders on the wake mode and the vibration of the small cylinder. Simulations were conducted for a diameter ratio of 0.5, a low mass ratio of 3, a Reynolds number of 200 (based on the diameter of the large cylinder) and three spacing ratios of S =1.5, 2 and 3. Four response regimes (regimes 1, 2, 3 and 4) have been identified depending on the spacing ratio and the reduced velocity. For S =1.5 and 2, the four regimes can be clearly identified by the disconnections of the amplitude-versus-reduced-velocity curves. For the largest spacing ratio of S =3, only regimes 1 and 3 are observed. Regime 1 is the low reduced velocity range where the response amplitude is small. It can be further divided into regimes 1A and 1B based on the variation of the amplitude in the in-line direction with the reduced velocity. In regime 2, the small cylinder is trapped in the wake of the large cylinder and the vortex shedding frequency of the large cylinder is close to the natural frequency of the small cylinder instead of following the Strouhal law. The maximum response amplitude occurs in regime 3, where the small cylinder is downstream the vortex formation zone of large cylinder. In regime 4, the smaller cylinder is attracted towards the large cylinder and fully immersed in the main wake vortices. Hysteresis is observed near the boundary between regimes 1 and 2 and near the boundary between regimes 2 and 3. In the hysteresis regions, the response of the small cylinder depends on how the fluid velocity at the inlet fluid velocity is initiated.

The plane problem of a steady-state potential flow of an ideal fluid around an infinite fluid cylinder with surface tension is considered. A family of solutions is constructed. An approximate relation is found between the Weber number and the ratio of the sizes of the cross-sections of the cylinder along the normal and along the free stream velocity. (A ratio of 11/2 corresponds to the exact McLeod special solution.) The problem of the stability of this flow is solved in the sense of a relaxed Lyapunov definition. For a ratio of the density of the cylinder to the density of the fluid flowing around it of less than 26.35, the flow is stable, and, for a greater value, it is unstable. The conventional Lyapunov stability is proved when the ratio of the densities is less than 11.07.

In the present study, two-dimensional numerical investigation of flow past a square cylinder beneath the free surface has been performed to identify the effects of presence of the free surface. An immersed boundary method was adopted for implementation of the cylinder cross-section in a Cartesian grid system. Also, a level-set method was used to capture the interface of two fluids. To prevent transition to three-dimensional flow, Reynolds number chosen for this simulation was 150. The cases for Froude number 0.2 and gap ratio(h/D) between 0.25 and 5.00 were examined. At the specific Reynolds number, we study the effects of gap ratio on flow characteristics around a square cylinder by computing flow fields, force coefficients and Strouhal number.

Purpose – The purpose of this paper is to implement the numerical analysis based on finite volume method to compare the effects of stress-jump (SJ) and stress-continuity (SC) conditions on flow structure around and through a porous circular cylinder. Design/methodology/approach – In this study, a steady flow of a viscous, incompressible fluid around and through a porous circular cylinder of diameter “D,” using Darcy-Brinkman-Forchheimer’s equation in the porous region, is discussed. The SJ condition proposed by Ochoa-Tapia and Whitaker is applied at the porous-fluid interface and compared with the traditional interfacial condition based on the SC condition in fluid and porous media. Equations with the relevant boundary conditions are numerically solved using a finite volume approach. In this study, Reynolds and Darcy numbers are varied within the ranges of 1 < Re < 40 and 10-7 < Da < 10-2, respectively, and the porosities are e=0.45, 0.7 and 0.95. Findings – Results show that the SJ condition leads to a much smaller boundary layer within porous medium near the interface as compared to the SC condition. Two interfacial conditions yield similar results with decrease in porosity. Originality/value – There is no published research in the literature about the effects of important parameters, such as Porosity and Darcy numbers on different fluid-porous interface conditions for a porous cylinder and comparison the effects of SJ and SC conditions on flow structure around and through a porous circular cylinder.

Vortex-induced vibration (VIV) of a curved circular cylinder (a quarter of a ring, with no extension added to either end) free to oscillate in the crossflow direction was studied experimentally. Both the concave and the convex orientations (with respect to the oncoming flow direction) were considered. As expected, the amplitude of oscillations in both configurations was decreased compared to a vertical cylinder with the same mass ratio. Flow visualizations showed that the vortices were shed in parallel to the curved cylinder, when the cylinder was free to oscillate. The sudden jump in the phase difference between the flow forces and the cylinder displacement observed in the VIV of vertical cylinders was not observed in the curved cylinders. Higher harmonic force components at frequencies twice and three times the frequency of oscillations were observed in flow forces acting on the vertical cylinder, as well as the curved cylinder. Asymmetry in the wake was responsible for the 2nd harmonic force component and the relative velocity of the structure with respect to the oncoming flow was responsible for the 3rd harmonic force component. The lock-in occurred over the same range of reduced velocities for the curved cylinder in the convex orientation as for a vertical cylinder, but it was extended to higher reduced velocities for a curved cylinder in the concave orientation. Higher harmonic force components were found to be responsible for the extended lock-in range in the concave orientation. Within this range, the higher harmonic forces were even larger than the first harmonic force and the structure was being excited mainly by these higher harmonic forces.

A water drop-shaped fairing is applied to control the wake behind a circular cylinder and to suppress the formation of Karman vortex street in this paper. The results are evaluated using high resolution CFD technique. A finite-volume total variation diminishing (TVD) approach based upon the recently proposed elemental velocity vector transformation (EVVT) method, which aims at solving the incompressible turbulent flow for irregular boundary conditions with renormalization group (RNG) turbulence model, is used to simulate the flow field around circular cylinder systems. The calculations are carried out with cylinder systems with and without fairings, while the fairings have different top shape angles within the range of 30 ° ~ 90 ° . The Reynolds number ranges from 1000 to 50 000. It is shown that the simulation results of present numerical method reaches good agreement with the available experimental and numerical simulation data of typical circular cylinder flow and a fixed fairing cylinder system flow. Compared with bare cylinder, the faired bluff structures can obviously reduce the lift and drag forces and alter the vortex shedding frequency. Overall, the mean drag coefficient can be reduced up to about (10–31)% and the RMS lift coefficient can be reduced up to (30–99)% for all faired systems at given Reynolds numbers. The influence of Reynolds number and attack angles on the flow field characters of bare cylinder and faired cylinders is also discussed. The faired structures with shape angles within 30 ° ~ 45 ° under zero-attack-angle-inflow case are considered as the optimal structures, with which the mean drag coefficient and the RMS lift coefficient can be reduced up to (26–31)% and (98–99)%, respectively. Considering the influence of attack angles on lift and drag coefficients reduction, 75° shaped faired structure may be taken as a proper option.

This work is focused on the analytic solution of steady boundary layer axisymmetric flow of third-grade fluid over a continuously stretching cylinder in the presence of magnetic field. Suitable transformations are considered to reduce the partial differential equation into the ordinary differential equation. The obtained non-linear differential system is solved by homotopy analysis method (HAM). The effects of the emerging parameters such as third-grade parameter, second-grade parameters and Reynolds number on the velocity are displayed and discussed. The expression of skin-friction coefficient is computed and presented. It is found that velocity and momentum boundary layer thickness are increasing functions of curvature parameter. Velocity profile is higher for third-grade fluid when compared with Newtonian and second-grade fluids with and without MHD effects for the cases (i) stretching cylinder and (ii) flat plate.

The current study reports structural modifications imposed in fully developed, turbulent channel flow by an isolated wall-mounted circular cylinder. The cylinder extended into the logarithmic layer of the flow, perturbing the larger flow scales that embody a significant fraction of the turbulent kinetic energy and Reynolds shear stress. Hot-wire measurements were made in the wake of the wall-mounted circular cylinder at multiple wall-normal and streamwise positions. Besides observing the expected mean velocity deficit in the wake of the cylinder, a secondary peak in streamwise Reynolds normal stress away from the wall was observed, coupled with suppression of the near-wall peak native to the incoming unperturbed, turbulent flow. These observations are similar to those made by Ryan et al. (“Effects of Simple Wall-Mounted Cylinder Arrangements on a Turbulent Boundary Layer,” AIAA Journal, Vol. 49, No. 10, 2011, pp. 2210–2220) for a wall-mounted cylinder protruding into the logarithmic layer of a turbulent b...

The flow past a finite circular cylinder with a height-to-diameter ratio of 1.5 and an infinite circular cylinder of the same diameter at a Reynolds number Re = 3 900 is investigated using the large eddy simulation (LES). The objective of the present study is to explore the differences of the flow mechanisms between the finite and infinite circular cylinders. It is shown that the free end of the finite circular cylinders affects the wake region significantly. The mean drag coefficient and the fluctuating lift coefficient of the finite circular cylinder are smaller than those of the infinite circular cylinder. The three-dimensional separation and the separated shear layer instability of the finite circular cylinder can obviously be observed. The existence of an arch vortex in the average flow downstream of the free end is demonstrated.

This paper studies the wall-bounded flow around a cylindrical at a high Reynolds numbers body in a determined computational domain, with simulations of the 3-D, turbulent concentric annulus flow in a straight pipe. Numerical results show that a reversing zone, appearing as a tongue zone with nested velocities higher than the surrounding area, exists behind the cylindrical body. The annulus space is a region of high velocity and low pressure. The zero velocity, of combined the velocity and the velocity, exists in the cross sections and no vortex shedding is formed behind the attaching cylinders. Among all investigated effecting factors, the diameters of the attaching and the main cylinders affect the wake feature behind the cylindrical body while the main cylinder length does not affect the distribution tendency of the flow field. The diameters of the main cylinder and the pipe affect the pressure values and the distribution tendencies on the main cylinder surface. Obviously, the increase of the pipe diameter reduces the drag coefficient of the cylindrical body and the increase of the diameter of the main cylinder increases the drag coefficient greatly. The numerical investigation of the concentric annulus flow provides foundations for further improvements of the intricate flow studies.

This paper reports on the time-dependent axisymmetric flow of a viscous, incompressible fluid along a moving circular cylinder having infinite extent. A mathematical account is given to unsteady motion, in which the governing non-dimensional equations are obtained in the presence of a velocity-slip boundary condition near the cylinder wall. In the case where the cylinder is started impulsively from rest in (initially) still air, the Bingham number is obtained by means of Laplace transform techniques with particular emphasis regarding the cylinder in motion with uniform velocity and acceleration. The effects of the momentum slip length parameter on the shear stress are determined and presented.

In this paper, two-dimensional numerical simulations of the incompressible flow around an elastically mounted rigid circular cylinder in cross-flow have been accomplished with the finite difference method. The bluff body immersed in the flow is modeled by the Immersed Boundary Methodology combined with the Virtual Physical Model. The motion of the cylinder is described by the harmonic structural model which is solved using a fourth order Runge–Kutta method. The numerical simulations were performed for Reynolds number 8,000 and 10,000 and for the reduced velocity in the range 1 ≤ V r ≤ 15. The vortex shedding process, the time evolution of the dynamic coefficients, the cylinder response and the power spectra of the lift coefficient and of the cylinder displacement were investigated. It was found a reasonable agreement with numerical results for R e = 8,000. On the other hand, for R e = 10,000, the present results as well as other numerical simulations failed when compared with the experiments in the capture of the so-called upper branch. The absence of that in LES simulations can be explained by the existence of discrepancies between the experiments and the assumptions adopted in the present methodology.

A numerical study of two-dimensional incompressible shear flow past a square cylinder is presented in this paper. Numerical simulations are performed using the recently developed higher order compact (HOC) scheme for K = 0.0, 0.1 for Re = 100, 200, where Re is the Reynolds number and K is the shear rate based on cylinder side. We investigate the effect of shear rate on the vortex shedding phenomenon in terms of stream function and vorticity contours, lift and drag coefficients employed on the cylinder and corresponding power spectra. The results presented here show that the vortex shedding phenomenon strongly depends on the Reynolds number as well as on the shear rate. In general, average drag coefficient decreases with increase in the shear rate for fixed Re and for K = 0.0 − 0.1, this change is negligible. In contrary to shear flow around circular cylinder, Strouhal number for flow past square cylinder decreases with increase in K.

The plane problem of the potential irrotational motion of an ideal fluid, caused by a cylinder rotating about a fixed axis parallel to the generatrix, is considered. It is shown that the average fluid velocity far from the cylinder decreases in proportion to the fifth power of the distance from the cylinder, and, by a special choice of the position of the fixed axis, in proportion to the seventh power. An exact solution of the problem is presented for an elliptic cylinder.

A solution in the form of asymptotic series is obtained for the problem about the near wake behind a thin cylinder in an laminar incompressible flow. To find the solution, we use the method of expansion into series of the solutions for the inner and outer portions of the flow. The influence of the circulation flow is not taken into account. The so-obtained solution is applicable only within a limited distance from the afterbody. Some essential differences are observed between the axisymmetric flow and the corresponding problem about the two-dimensional wake after a flat plate.

The flows around a cylinder in infinite domain are simulated using CFD method. The simulation results are found to be in agreement with the data in literatures. The flow stability is investigated with the energy gradient theory. It is found that the two zero velocity gradient points at lateral sides of the cylinder lead to flow instability which causes vortex shedding. The flow transition to turbulence are dominated by two aspects, i.e. the zero velocity gradient at the lateral sides of the cylinder, and the zero velocity gradient inner the region of the vortex in the cylinder wake.

Author(s): Dai, SS; Younis, BA; Zhang, HY | Abstract: Predictions are reported of the two-dimensional turbulent flow around a square cylinder with rounded corners at high Reynolds numbers. The effects of rounded corners have proved difficult to predict with conventional turbulence closures, and hence, the adoption in this study of a two-equation closure that has been specifically adapted to account for the interactions between the organized mean-flow motions due to vortex shedding and the random motions due to turbulence. The computations were performed using OPENFOAM and were validated against the data from flows past cylinders with sharp corners. For the case of rounded corners, only the modified turbulence closure succeeded in capturing the consequences of the delayed flow separation manifested mainly in the reduction of the magnitude of the lift and drag forces relative to the sharp-edged case. These and other results presented here argue in favor of the use of the computationally more efficient unsteady Reynolds- averaged Navier-Stokes approach to this important class of flows provided that the effects of vortex shedding are properly accounted for in the turbulence closure.

Unsteady mixed convection heat transfer from a circular cylinder has been investigated in the presence of viscous dissipation. The isothermal horizontal cylinder is placed to the oncoming free stream whose direction is considered in the free convection flow (parallel flow) and opposite to it (contra flow). The system of dimensionless governing equations for unsteady, two-dimensional flow is reduced to a suitable form for integration, and the resulting equations are solved employing finite-difference method. For both parallel and contra flows, the influences of the viscous dissipation on the Nusselt number are found to be strong; however, it has rather weak effect on the vorticity distribution. In the presence of the viscous dissipation, the isotherms are significantly changed while there is less effect on the streamlines. Under the same conditions, the size of the vortex for the contra flow is larger than that for parallel flow.

A numerical study was conducted to examine the flow field around and heat transfer from an elliptical cylinder of AR=0.5 in two types of the annular boundary and rectangular one. The fluid near the surface separates from the cylinder surface and forms a steady recirculation bubble at the rear end of the cylinder at the first critical Reynolds (Rec1). The vortices begins the alternating separation at the second critical Reynolds (Rec2). Rec1 and Rec2 for the fluid in two boundary types are studied. The Nusselt numbers are compared at Rec1 and Rec2 respectively.

Flow around a circular cylinder is a classical problem in fluid mechanics. The flowing problem about three tandem cylinders with different diameter is numerical simulated by a finite volume method. Through the simulation, the variations of flow field with different distance between the adjacent cylinder and different Reynolds number are investigated. The simulation result shows that three tandem cylinders with different diameter can evidently small columns minish width and aggrandize length of cylinder wakes compared with single cylinder.

The flow characteristics around a cactus-analogue grooved cylinder and a smooth cylinder were extensively compared at Re D ==5.4×104 based on the free-stream velocity and cylinder diameter (D). Wall-pressure fluctuations on the cylinder surfaces and the fluid flows around the cylinders were measured using a microphone and planar particle image velocimetry, respectively. The influence of the cactus-analogue grooved cavities on the wake characteristics was assessed in terms of the circumferential distributions of the wall-pressure fluctuation intensity, the wall-pressure spectra, and the auto-correlation coefficient of the wall-pressure fluctuations. The global distributions of the time-averaged velocity field, reverse-flow intermittency, streamwise velocity fluctuation intensity, Reynolds shear stress, and spatial velocity correlation were also considered. The circumferential distributions of the wall-pressure fluctuation intensity showed that the wall-pressure fluctuations on the cactus-analogue cylinder were remarkably reduced by around 50% at most stations. On the grooved cylinder, the magnitude of the wall-pressure spectra at the characteristic frequency of the shedding from the large-scale vortical structures was considerably reduced by around 7 dB. This convincingly demonstrated that the unsteady aerodynamic forces on the cactus-analogue cylinder were significantly weakened. In contrast, the auto-correlation analysis of the wall-pressure fluctuations showed that the consecutive motion of the shedding from the large-scale vortical structures close to the grooved cylinder was much more organized. Inspection of the time-averaged velocity field around the cylinders disclosed that the velocity of the near-surface fluid around the grooved cylinder was increased by the small recirculation flows immersed inside the cavities. Near the grooved cylinder, the trace of the peaked streamwise velocity fluctuation intensity was highly localized at θ = 105 ° while in the smooth cylinder a very long, slender peaked region began at θ = 60 ° and extended to the leeside of the cylinder. Finally, a snapshot proper orthogonal decomposition analysis was performed on the velocity fields. The correlation map of the first two POD coefficients convincingly indicated that the vortex shedding process in the grooved cylinder system was more coherent but weaker than that in the smooth cylinder system, which is further confirmed by the phase-dependent contour plots of the swirling strength and its standard deviation.

Flow past a yawed circular cylinder in the vicinity of a plane boundary is investigated numerically by solving the three-dimensional Navier–Stokes equations using the Petrov–Galerkin finite element method. Simulations are carried out at a constant Reynolds number of 500, two gap ratios of 0.4 and 0.8 and six cylinder yaw angles (α) ranging from 0° to 60° with an increment of 15°. The gap ratio is defined as the ratio of the gap between the cylinder and the plane boundary to the cylinder diameter. The focus of the study is on the effects of α and the gap ratio on the vortex shedding flow and the hydrodynamic forces of the cylinder. It is found that increasing the cylinder yaw angle weakens three-dimensionality of the flow. The root mean square lift coefficient decreases at α=60°, indicating that the vortex shedding is suppressed more than that at small yaw angles. The independence principle, which states that the drag and lift coefficients based on the velocity component perpendicular to the cylinder axis are independent on the yaw angle of the cylinder, applies to the flow at the gap ratio of 0.8 better than that at the gap ratio of 0.4. Because of the strong influence from the plane boundary on the flow, the force coefficients for the gap ratio of 0.4 do not follow the independence principle if the yaw angle is greater than α>30°.

A discrete forcing based Cartesian grid method is presented. The non-staggered arrangement of velocity and pressure is considered. The pressure gradient in localized discrete form is added separately with the velocity making them explicitly coupled. The governing equation is time-integrated implicitly with both linearized and non-linear forms are investigated. Both linear and bi-linear reconstruction techniques are tested for extrapolation of velocity near a complex boundary. The present method is tested for vortical flow in an inclined cavity, flow past circular and inclined square cylinder. Both homogeneous and non-homogeneous Dirichlet forcing problems are tested. The parallelized version of the method is applied to 2D-to-3D transitional flow behind a single and multiple circular cylinders. The present numerical results compare well with the previously documented results.

In this research work, an experimental investigation of wind effect on pentagonal cylinders was carried out. The study was performed on the single cylinder in an open circuit wind tunnel at a Reynolds number of 4.22 x 104 based on the face width of the cylinder across the flow direction in a uniform flow velocity of 13.5 m/s. The test was carried out at various angles of attack from 0° to 63° at a step of 9°. The surface static pressures at the different locations of the cylinder were measured with the help of inclined multi-manometers. The wind velocity was kept constant at 13.5 m/s. The pressure coefficients were calculated from the measured values of the surface static pressure distribution on the cylinder. Later the drag and lift coefficients were obtained from the pressure coefficients by the numerical integration method. The results will enable the engineers and architects to design buildings more efficiently. Since the results will be expressed in the nondimensional form they may be applied for the prototype building. DOI: http://dx.doi.org/10.3329/jme.v44i1.19499

Using ANSYS-CFX, a general purpose fluid dynamics program, the vortex-induced vibration (VIV) of a variable cross-section cylinder is simulated under uniform current with high Reynolds numbers. Large eddy simulation (LES) is conducted for studying the fluid-structure interaction. The vortex shedding in the wake, the motion trajectories of a cylinder, the variation of drag and lift forces on the cylinder are analyzed. The results show that the vortices of variable cross-section cylinder are chaotic and are varying along the cylinder. In places where cross-sections are changing significantly, the vortices are more irregular. The motion trail of the cylinder is almost the same but irregular. The drag and lift coefficients of the cylinder are varying with the changes of diameters.

It is well known from a lot of experimental data that fluid forces acting on two tandem circular cylinders are quite different from those acting on a single circular cylinder. Therefore, we first p...

Laminar flow past a circular cylinder with multiple small-diameter control rods is numerically investigated in this study. The effects of rod-to-cylinder spacing ratio, rod and cylinder diameter ratio, cylinder Reynolds number, number of control rods and angle of attack on the hydrodynamics of the main circular cylinder are investigated. Four different flow regimes are identified based on the mechanism of lift and drag reduction. The range of rod-to-cylinder spacing ratio where significant force suppression can be achieved is found to become narrower as the Reynolds number increases in the laminar regime, but is insensitive to the diameter ratio. The numerical results for the case with six identical small control rods at Re=200 show that the lift fluctuation on the main cylinder can be suppressed significantly for a large range of spacing ratio and various diameter ratios, while the drag reduction on the main cylinder is also achieved simultaneously. The six-control-rod arrangement has shown better performance in flow control than the arrangements with less control rods, especially in terms of force reduction at various angles of attack.

This study performed numerical analysis for the characteristics of flow-induced forces and the flow instability depending on the cross-sectional shape of the cylinder in laminar flow. To implement the cylinder cross-section, we adopted an Immersed Boundary Method with marker particles. We analyzed flow characteristics based on the radius of corner curvature. Main parameters are corner radius and Reynolds number (). With = 40, 50, 150 we calculated the flow field, drag coefficient, RMS of lift coefficient, pressure coefficient and Strouhal number in conjunction with the corner radius variation. Also, we calculated critical Reynolds number (  ) depending on the corner radius variation.