Cylinder Of Finite Height Research Articles

Structure of dense plumes from a finite-height cylinder in laminar crossflow

Structure of dense plumes from a finite-height cylinder in laminar crossflow

Taking inspiration from the natural tubular sponge to enhance momentum exchange in marine environments

Coral reefs consist of various alive elements with specific biological functions. Tubular sponges, as the main coral reefs' constituents, have a marvelous mechanism. They receive nutrients by suctioning from the perforated body (Ostia) and pumping the un-digested materials through the water column from the top mouth (Osculum). This mechanism can be an inspiration for making a device to control or improve sediment/pollutant transport. In the current study, an attempt has been made to evaluate an inspired concept's effects on flow hydrodynamics. In this regard, OpenFOAM® V. 1812 (interFOAM solver) and image processing technique were deployed. The perforated finite-height cylinders (height to diameter ratio of 2.5) with various suction/pump discharges (i.e., J = 150, 300, 350, 400, 450, and 600 lit/h) were considered. The results indicated that increasing the outflow discharge (J ≥ 600 lit/h) could widen the wake by flapping the shear layer. In the vertical plane, the results showed that dipole vortices turned into quadrupole vortex. On the free surface, tip-vortices and counter-rotating vortex pairs (CRVP) generated saw-toothed vortices on two sides of the cylinder. Generating these unique vortices is proof of enhancing the momentum exchange through the water column.

Direct numerical simulations on oscillating flow past surface-mounted finite-height circular cylinder

In this work, a surface-mounted circular cylinder with a fixed aspect ratio (ratio of height of the cylinder to its diameter) of 5 is subjected to a non-zero mean oscillating flow with a range of frequencies and amplitudes. Three-dimensional direct numerical simulations are then conducted on this finite-height cylinder. The mass and momentum equations are resolved using the finite volume-based Open Source Field Operation and Manipulation (OpenFOAM). A fixed Reynolds number Re=UoD/ν of 250 is used in this study, which is defined based on mean velocity at the inlet ( Uo ) and cylinder diameter (D). Here ν is the kinematic viscosity of the working fluid. Non-dimensional velocity oscillation amplitude ( A∗=a/Uo ) is varied from 0.1 to 0.3, while the non-dimensional oscillation frequency ( f∗=f/fo ) takes the values of 0.33, 0.5, 1, 2, and 3. Here a and f are the dimensional oscillation amplitude and frequency, respectively and fo is the vortex shedding frequency corresponding to a uniform flow at Re = 250. The three-dimensional vortex structures, presented with the help of iso-Q surfaces, show that the oscillating flow changes the size and shape of the hairpin-shaped vortices. Wake is found to be synchronized with the oscillation frequency at f* = 2 for each value of the A* and results in the maximum lift force on the cylinder. Hilbert Huang transformation analysis of the transverse velocity signals at a specific point in the wake reveals that the wake is more complex and aperiodic in nature for f* values of 0.33, 0.5, and 1, whereas it is periodic for f* = 2 and 3. In order to further disclose the nonlinearity associated with the oscillating flow, the degree of stationarity is discussed corresponding to each value of A* and f*. Dynamic mode decomposition is exploited to obtain information about the coherent vortical structures and their spatial and temporal behavior in the wake with a change in the value of f*. Effects of A* and f* on the dynamic characteristics are also investigated.

Aspect ratio influence on the vortex induced vibrations of a pivoted finite height cylinder at low Reynolds number

The effect of the aspect ratio on the vortex induced vibrations (VIV) of a pivoted finite length circular cylinder is investigated. A fixed value of the Reynolds number Re = 100 with four values of the aspect ratio AR=2, 3, 5, 7 is considered. Different values of the reduced velocity ur* in the range 2≤ur*≤11 were used for each AR value with a fixed value of the reduced mass mr*=5. Results on the oscillatory response of the cylinder, hydrodynamic forces, and wake structures are reported. In order to compare the VIV of the different length cylinders, the displacement of the center of mass (which coincides on each case) was analyzed. It is found that the maximum oscillation amplitudes, the extent of the synchronization region, and the wake structures are influenced by the aspect ratio. Also, a steady symmetrical flow is obtained for the small AR=2, 3 cases with relatively low values of ur*, which is found to be unstable when increasing ur*.

Macroscopic turbulent kinetic energy budget in flow through a wall-bounded compact bank of cylinders

The flow in devices, such as heat exchangers, can be idealized as turbulent flow past an array of regularly spaced obstacles. Engineering calculations in such devices are easily handled if the flow can be represented by its volume-average quantities. This paper reports an investigation into the volume-averaged flowfield in a regular array of cylinders of finite height in crossflow at two Reynolds numbers (ReD). The investigation is based on scale-resolving computations and is thus the first to analyze the true form of the macroscopic turbulent kinetic energy (TKE) conservation law in the presence of macroscopic shear. Volume-averaging is performed parallel to the end walls in order to obtain profiles of macroscopic flow quantities. In inner coordinates, the macroscopic velocity profiles are similar to the canonical turbulent channel flow profiles, but with different values of the von Kármán constant and log-law y-intercept. The volume-averaged TKE is defined so as to include contributions from both the macroscopic and microscopic components of the flow. While the macroscopic TKE profile is very different to that of channel flow, the macroscopic TKE budget terms are remarkably similar. One notable exception is that the production rate stays large throughout the domain rather than attenuating rapidly after a near-wall peak. An extension to a widely used macroscopic turbulence model is proposed, which enables it to match the volume-averaged TKE production rate predicted by the large eddy simulations.

Vortex induced vibrations of a pivoted finite height cylinder at low Reynolds number

The vortex induced vibrations (VIVs) of a pivoted cylinder with finite height have been numerically investigated. A mathematical model is introduced and described, and the resulting equations are numerically solved for low Reynolds number Re = 100, 200 and several combinations of the governing parameters. Results on the solid body trajectories, the maximum amplitude of the oscillations, the hydrodynamic force coefficients, the wake structure, and details on the vortex shedding near the cylinder are presented and discussed. The numerical results compare reasonably well with the canonical system of VIV of two-degrees of freedom circular cylinder in the laminar regime. Also, qualitative similarities with closely related VIV systems at larger Re suggest interesting lines of future research. Analytical approximations for limiting cases are done and an excellent agreement with the numerical results is obtained.

Application of the Variational Method of Homogeneous Solutions for the Determination of Axisymmetric Residual Stresses in a Finite Cylinder

We consider the problem of determination of axisymmetric residual stresses caused by incompatible residual strains in a circular cylinder of finite height. The solution of this problem is reduced to: (i) evaluation of residual stresses in an infinite cylinder and (ii) determination of perturbed stresses caused by the free surfaces of end faces of the cylinder. The variational method of homogeneous solutions is used to solve the second problem. We also perform the numerical analysis of residual stresses formed in a solid for two given distributions of incompatible strains depending on the radial coordinate. The proposed approach can be used for the evaluation of residual stresses formed in cylindrical bodies in the course of their heat treatment.

Characteristics of the free-end mean pressure distribution for a surface-mounted finite-height cylinder

Wind tunnel experiments at a Reynolds number of Re = 6.5 × 104 were used to study the effect of aspect ratio and boundary layer thickness on the mean static pressure distribution on the free end of a surface-mounted finite-height cylinder. The cylinder's aspect ratio was changed in small increments from AR = 0.5 to AR = 11. Two different boundary layer thicknesses (relative to the cylinder diameter) were employed, δ/D = 0.6 and δ/D = 1.9. From analysis of the mean pressure contour plots, it was found that the sizes and locations of regions of lower pressure, adverse pressure gradient, and higher pressure, and the appearance of “eye-like spots”, are sensitive to both AR and δ/D. The adverse pressure gradient occurs just ahead of the mean reattachment line while the eye-like spots are related to termination points of the legs of the arch vortex within the free-end mean recirculation zone. The total normal force coefficient experienced by the cylinder is strongly influenced by the contribution of the wall shear stress on the sides of the cylinder, with a change in direction of the net vertical shear stress contribution occurring between AR = 7 and AR = 8 for both boundary layers.

Influence of the free end flow on the bistability phenomenon after two side by side finite height cylinders with aspect ratios of 3 and 4 and high blockage

This work presents an experimental study of the bistability phenomenon downstream of pairs of finite cylinders with aspect ratios h/d of 3 and 4. In finite cylinders, bistability is still poorly explored and understood. The wake flow around a single finite cylinder with Red = 2.00 × 104 was studied. After that, the flow around two finite cylinders with diameters of 25 and 32 mm and aspect ratios of 3 and 4 was studied (3.86 × 103 ≤ Red ≤ 4.81 × 104). Hot wire anemometry in an aerodynamic channel and flow visualization by ink injection in water in a hydraulic channel were employed. Analysis of hot wire data employed statistics, spectral, and wavelet tools. Video analysis was made with editing software and statistical tools. The flow visualization technique strengthens the interpretation of the results obtained through the hot wire anemometer technique. In this work three concomitant flows are considered: the upward flow, from the cylinder base; the downward flow, from the top; and the so-called main flow, by the vortex shedding at half height of the cylinders. The results show the existence of two different levels of mean velocity in time series, corresponding to two flow modes confirming the presence of the phenomenon of bistability for two finite cylinders placed side by side. Downward flow from the top of the cylinders with an aspect ratio of h/d = 4 studied also presents bistable characteristics.

Wake interference effects for two finite cylinders: A brief review and some new measurements

A brief review of the literature for the flow around two surface-mounted finite-height cylinders in a staggered configuration illustrates some of the additional complexity associated with changes in the cylinder aspect ratio (AR), the effects of downwash, the three-dimensional structure of the wake, and the presence of additional vortex structures. To date, however, few extensive systematic studies of centre-to-centre pitch ratio (P/D), incidence angle ( α), aspect ratio, boundary layer thickness on the ground plane (δ/D) and Reynolds number (Re) have been reported for two finite cylinders. Some new measurements of the mean drag and lift coefficients (CD and CL) and the Strouhal numbers (St) for two staggered finite cylinders, for AR = 9, 7, 5, and 3, P/D=1.125–4.5, and α = 0∘–90°, at Re = 6.5×104 and δ∕D=1.4, illustrate the moderating effect of the three-dimensional flow on the wind loading and vortex shedding behaviour compared to the flow around two infinite cylinders. These new results suggest some changes to the flow pattern boundaries and uncover some new trends in the CD, CL and St data with P/D and/or α; there is a need for new flow visualization, flow field measurements, and numerical simulations to advance physical interpretation.

FAST INVERSION OF UAV MAGNETIC FIELD DATA ON THE EXAMPLE OF SYNTHETIC MODELS WITH THE TOPOGRAPHY

High-performance algorithm for an unmanned magnetometer complex data inversion is proposed. We provide numerical tests for tomographic inversion of data for the different-height magnetic surveying. We show the results of calculations for a test model with a magnetic object in the form of a cylinder of finite height. We propose the recommendations for the method application for the inversion of the observed data.

The effect of aspect ratio on the aerodynamic forces and bending moment for a surface-mounted finite-height cylinder

Wind tunnel experiments were performed at Re = 6.5 × 104 to measure the mean drag and normal forces, mean bending moment, and vortex shedding frequency for surface-mounted finite-height cylinders. The cylinder aspect ratio was varied in small increments between AR = 0.5 and 11, and two different boundary layer thicknesses were used, δ/D = 0.6 and 1.9. Small increments in AR and use of a single Re helped clarify some AR effects for finite cylinders. The data allowed a more precise definition of the familiar critical aspect ratio to be set, based on the behaviour of the mean aerodynamic forces and the point of action of the mean drag force. A second change in behaviour of the aerodynamic forces with AR was also identified; this transition was related to changes in the vortex formation length, the development of the near-wake recirculation zone, and the influence of the two main near-wake vortex structures, with AR. The general effects of increasing δ/D are to lower the force and moment coefficients and Strouhal number, increase the critical AR, and increase the AR where the second transition occurs.

DES of the turbulent flow around a circular cylinder of finite height

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.

Investigation of short‐range, broadband, on‐body electromagnetic wave propagations

Electromagnetic wave propagation over a broad frequency band (300 MHz – 3 GHz) and within short ranges (<40 cm) was investigated for on-body wireless channel communications. Experimental and modelling methods were used to examine two scenarios: along the body surface [line-of-sight (LOS)] and around the body torso [non-LOS (NLOS)]. The LOS scenario was modelled simply as an infinitely-large ground plane, and the NLOS scenario as a finite-height cylinder. Homogeneous muscle tissue properties were assumed for both models. The propagation characteristics were extracted using signal-processing techniques. The results show that the space wave is the dominant wave for the LOS scenario and the creeping wave for the NLOS scenario over the short ranges of the body's surface. The analytical models based on the ground wave theories of Bannister and Wait were derived and shown to agree well with the experimental and simulation data.

A Kinematic Description of the Key Flow Characteristics in an Array of Finite-Height Rotating Cylinders

Experimental data are presented for large arrays of rotating, finite-height cylinders to study the dependence of the three-dimensional (3D) mean flows on the geometric and rotational configurations of the array. Two geometric configurations, each with two rotational configurations, were examined at a nominal Reynolds number of 600 and nominal tip-speed ratios of 0, 2, and 4. It was found that the rotation of the cylinders drives the formation of streamwise and transverse flow patterns between cylinders and that net time–space averaged transverse and vertical flows exist within the developed flow region of the array. This net vertical mean flow provides an additional mechanism for the exchange of momentum between the flow within the array and the flow above it, independent from the turbulent exchange mechanisms which are also observed to increase by almost a factor of three in a rotating array. As an array of rotating cylinders may provide insight into the flow kinematics of an array of vertical axis wind turbines (VAWTs), this planform momentum flux (both mean and turbulent) is of particular interest, as it has the potential to increase the energy resource available to turbines far downstream of the leading edge of the array. In the present study, the streamwise momentum flux into the array could be increased for the rotating-element arrays by up to a factor of 5.7 compared to the stationary-element arrays, while the streamwise flow frontally averaged over the elements could be increased by up to a factor of four in the rotating-element arrays compared to stationary-element arrays.

Influence of aspect ratio on the flow above the free end of a surface-mounted finite cylinder

The flow above the free end of a surface-mounted finite-height cylinder was studied in a low-speed wind tunnel using particle image velocimetry (PIV). Velocity measurements were made in vertical and horizontal measurement planes above the free end of finite cylinders of aspect ratios AR=9, 7, 5 and 3, at a Reynolds number of Re=4.2×104. The relative thickness of the boundary layer on the ground plane was δ/D=1.7. Flow separating from the leading edge formed a prominent recirculation zone on the free-end surface. The legs of the mean arch vortex contained within the recirculation zone terminate on the free-end surface on either side of the centreline. Separated flow from the leading edge attaches onto the upper surface of the cylinder along a prominent attachment line. Local separation downstream of the leading edge is also induced by the reverse flow and arch vortex circulation within the recirculation zone. As the cylinder aspect ratio is lowered from AR=9 to AR=3, the thickness of the recirculation zone increases, the arch vortex centre moves downstream and higher above the free-end surface, the attachment position moves downstream, and the termination points of the arch vortex move upstream. A lowering of the aspect ratio therefore results in accentuated curvature of the arch vortex line. Changes in aspect ratio also influence the vorticity generation in the near-wake region and the shape of the attachment line.

Flow Behavior in a Curved Converging Diverging Duct Employed in a Dye Laser

In this paper the flow behavior in a converging diverging curve duct used in a high stability dye laser pumped by Copper Vapour Laser(CVL) is presented at different angular positions. The flow duct is formed by two eccentric cylinders of finite height. The channel aspect ratio and effective curvature ratio varies from 1 to 50, and 1 to 81, respectively, along the flow path. The flow behaviors at different sections of test duct are studied numerically and experimentally using a dye solvent mixture of 70 % glycol and 30 % ethanol. It is shown that the average values and variation of eddy sizes gradually reduces along the flow path till CVL pump position and then gradually increases. A non linear CFD turbulence model is used to get enhanced numerical results for accelerating curved flow. The numerically estimated average values of turbulent kinetic energy and its dissipation rate at different angular positions are compared with the intensity variation of He Ne laser passing through the flow. The flow field tends to become more stable at higher Reynolds number and at lowest hydraulic diameter (CVL pump position). The average variation of flow and temperature inhomogeneities in boundary layer at CVL pump position reduces with the increase in flow rate. The variation in dye laser band width and wave length is correlated with flow and temperature induced inhomogeneities for different flow speed.

Juncture flows around cylinders of unequal finite-height and diameter in tandem arrangement

This experimental study examines the effects of placing a control cylinder of small diameter and height in the upstream region of a main cylinder at a gap of 0.75 D in tandem arrangement on laminar junction flow at Re $$_D$$ = 1.3 $$\times $$ 10 $$^3$$ . The study is performed using 2D particle image velocimetry (PIV). The experiment clearly visualizes the changes in flow pattern with this arrangement and gives insight into the new flow pattern.

Broadband electromagnetic metamaterials with reconfigurable fluid channels

We present the design, characterization, and experimental verification of broadband and tunable metamaterials based on reconfigurable fluid channels. We demonstrate through simulation that a finite-height cylinder of water in a background medium behaves as a nonresonant metamaterial. By changing liquid type or adjusting liquid level, we tune the effective material parameters of the metamaterial through altering the composition and amount of water used. We verify the efficacy of the metamaterial through experiment, demonstrating a design procedure for a metamaterial with broadband and tunable properties.

Forced Convection Heat Transfer from a Finite-Height Cylinder

This paper presents a large eddy simulation of forced convection heat transfer in the flow around a surface-mounted finite-height circular cylinder. The study was carried out for a cylinder with height-to-diameter ratio of 2.5, a Reynolds number based on the cylinder diameter of 44 000 and a Prandtl number of 1. Only the surface of the cylinder is heated while the bottom wall and the inflow are kept at a lower fixed temperature. The approach flow boundary layer had a thickness of about 10% of the cylinder height. Local and averaged heat transfer coefficients are presented. The heat transfer coefficient is strongly affected by the free-end of the cylinder. As a result of the flow over the top being downwashed behind the cylinder, a vortex-shedding process does not occur in the upper part, leading to a lower value of the local heat transfer coefficient in that region. In the lower region, vortex-shedding takes place leading to higher values of the local heat transfer coefficient. The circumferentially averaged heat transfer coefficient is 20 % higher near the ground than near the top of the cylinder. The spreading and dilution of the mean temperature field in the wake of the cylinder are also discussed.