Diameter Of Circular Cylinder Research Articles

Coupled effects of variable permeability and adiabatic undulating walls on natural convective flow in a trapezoidal cavity: Finite element analysis

Investigation of hydrothermal characteristics and entropy produced by change in diameter of circular cylinder positioned at the center of trapezoidal enclosure with undulated upper wall is conducted. Natural convection phenomenon is considered along with physical aspects of inclining magnetic field and permeable medium. Envisioning all these factors combined no such study is available which makes current problem novel. So, the premier intends to commence this artifact is to fill the existing gap by comprehensively disclosing the influence of governing transport parameters attained after mathematical modeling in dimensionless format. Entropy phenomenon is analyzed by estimating total entropy and average Bejan number. The numerical solution of modeled mathematical framework is attained by utilizing finite element based open-source software renowned as COMSOL. Wide range of flow concerning parameters are considered for instance, diameter of cylinder (0.10≤D1≤0.20), Prandtl number (0.015≤Pr≤7.00), Rayleigh number (103≤Ra≤105), Darcy number (10-5≤Da≤10-3) and Hartmann number (0≤Ha≤10) while, remaining parameters like angle of inclination (γ) and irreversibility ratio (ω) are fixed at 45° and 10-2 respectively. The influence of these parameters on distributions is interpreted by displaying streamlines and isotherms. After scrutinization of outcomes, it is deduced that average Nusselt number, total entropy and average Bejan number enhances up to 3.49 %, 1.86 % and 2.70 % respectively for situation when diameter of cylinder is increased from 0.10 to 0.20. Furthermore, 28.35 %, 43.06 % and 59.55 % decrement in previously stated quantities is revealed in comparative manner for hydrodynamic (Ha =0) and hydromagnetic (Ha ≠0) cases.

Flow structures around a circular cylinder with bilateral splitter plates and their dynamic characteristics

Flow structures around a circular cylinder with bilateral splitter plates and their dynamic characteristics are numerically investigated at a low Reynolds number of 100. The two splitter plates with the same length as the half of cylinder diameter are symmetrically placed beside the cylinder. In this work, three gap ratios of G/D = 0, 0.5 and 1.0 (G is the gap distance between the cylinder surface and the near end of plate, D is the diameter of circular cylinder) and inclination angle (α, between splitter plate and wake centerline) ranging from 0° to 90° are examined. According to flow characteristics, five vortex shedding regimes are identified, including "2S" (two vortices are alternatively shed per cycle) regime, single-sided regime, wake-flapping regime, steady regime and irregular regime. Apart from the main vortices, some special vortices such as subordinate vortices, tip vortices and persisted vortices are recognized. Additionally, local "2S″ and "4S" (four vortices are shed per cycle) regimes are observed behind the cylinder and the plates, respectively. The dynamic mode decomposition (DMD) results show that the first mode possesses the majority of energy of the flow field. As α increases, the splitter plates contribute to the lift reduction, especially when a gap is introduced. By contrast, the bilateral plates lead to a significant growth in the drag coefficient when α ≥ 15°.

Harvesting airflow energy from circular cylinder wake via a thin polyvinylidene fluoride film

To improve the characteristics of airflow energy harvesting, this paper presents a new piezoelectric wind energy harvester (PWEH), in which a polyvinylidene fluoride (PVDF) film was directly located in the wake of the circular cylinder. Four important parameters were independently varied for detailed experimental investigations: wind speed, spacing ratio for the distance between the center of the circular cylinder and the tip of the PVDF film to the circular cylinder diameter, diameter of the circular cylinder, and load resistance. The results indicated that the designed PWEH performed optimally with the occurrence of resonance, maintaining a relatively high output when significantly exceeding the resonance wind speed. The PVDF film inhibited the vortex shedding of the circular cylinder, which weakened with increasing spacing ratio. The optimum value of the spacing ratio should be approximately 2.5, which yields an effective coupling between the vortex and structure. The diameter of the circular cylinder played an important role in determining the output power. The match between the load resistance and PWEH also contributed to the high-level performance. Moreover, with an increase in the diameter of the circular cylinder, the increasing blockage ratio unexpectedly enhanced the vortex shedding frequency and decreased the theoretical resonance wind speed, which provided a new orientation for improving the performance of such PWEHs.

Investigation of the influence of cylinder span length on vortex shedding from an in-line oscillating circular cylinder

In order to investigate the dependability of the circular cylinder span length of a lock-in phenomenon, closed circuit water channel experimental apparatus was used, and the visualization experiment was performed. In the visualization experiment, the aspect of the vortex shedding from the circular cylinder which is carrying out the in-line forced oscillation was observed by varying the water level of a test section. In the experiment, adjustment was carried out so that flow velocity might constitute about 0.06 m/s every water level. Main experiment parameters are a circular cylinder diameter (6 mm, 10 mm and 16 mm), amplitude ratio (2a/d=0.5 and 1.0),oscillation frequency ratio (range of f/fK is from 0 to 6), and circular cylinder span length (200 mm, 150 mm and 100 mm). As a result, although changes of the configuration of the lock-in corresponding to the variation of circular cylinder oscillating frequency were the same, it was found that the appearance ranges differ. Distribution of the lock-in range was classified into three groups by the aspect ratio. In the closed circuit water channel experiment, sunken span length was required 150 mm or more, and the aspect ratio L/d obtained the indicator in which the circular cylinder diameter which becomes 15 or more was selected.

Dynamics and stability of the wake behind a circular cylinder in the vicinity of a plane moving wall

This paper identifies and characterizes modes of the three-dimensional instability of the flow over a circular cylinder of diameter D near a plane moving wall with a gap height of G=0.1D beyond the onset of vortex shedding through the Floquet stability analysis. The associated effects of the transitions on the hydrodynamic forces of the cylinder are examined by performing direct numerical simulations. Six distinct three-dimensional modes are identified and their characteristics are discussed in detail. It is found that the physical mechanism responsible for the synchronous mode 1 appears to be associated to an elliptic instability. The quasi-periodic mode 4 is observed to transform to a synchronous mode (mode 6) on increasing the Reynolds number, indicating that they are likely to be resulted from the same physical mechanism. For mode 6, its physical nature seems to be a hyperbolic instability. Fully three-dimensional simulations show that the wake undergoes a rapid transition to complex chaotic flow state after the most dominant mode starts to saturate, due to the strongly nonlinear interactions of many modes with different spanwise wavelengths.

Flow Characteristics of a Circular Cylinder behind an Impinging Airfoil Near Wake with Different Lateral Spacing

A computational model is formulated to investigate the unsteady flow characteristics of a circular cylinder behind an impinging airfoil near-wake at Re=200. The distance between the airfoil trailing edge and the downstream cylinder axis is fixed at 1.5D where D is the diameter of circular cylinder and the lateral spacing is varied from 5 to 5 so as to numerically investigate the effect of lateral spacing on the flow characteristics. The present work is concerned on the following aspects: the general flow patterns, the vortex shedding frequency, force fluctuations and spectra, as well as the effect of lateral spacing on the flow features at low Reynolds number and small axial spacing. The calculated flow pattern and its comparison with the visualization by Laser-Induced Fluorescence (LIF) technique are conducted. It is determined that three regimes can be defined in terms of H/D, where H is the distance between the cylinder center and the line extended from the airfoil leading edge to trailing edge. And four kinds of typical flow pattern associated with the three regimes can be identified accordingly. It is interesting to find that both the fluctuations of lift and drag forces on the circular cylinder exhibit symmetric features centered at H/D=0 and the dump distribution of C′SUBD/SUB is found as well.

Influence of coverage of fin-shaped rods on flow-induced vibration and power extraction of cylinder-based wind energy harvester

Wind-induced vibration (WIV) and power extraction performances of a circular cylinder with symmetrically installed fin-shaped rods (FSR) were experimentally and numerically investigated under different coverages. The FSR coverage which is expressed as an angle (α) is measured from the upstream edge to the downstream edge of the rod. The effect of FSR installation angle (θ) which is the angle from the stagnation point of cylinder to the upstream edge of the rod was also considered in this work. The FSR cylinder is exposed in uniform wind and allowed to vibrate in cross-flow direction. The output electric power is realized by piezoelectric patch. It is found that, for most cases, the output power of FSR cylinder increases monotonously with the rise of α for a given wind velocity (U). In addition, the tendency of output voltage varies with the wind velocity is highly similar to that of output power. The maximum values of output voltage and power are 19.70 V and 1.90 mW can be obtained when α= 20° (θ= 60°). The WIV responses of FSR cylinder show that the amplitudes of FSR cylinder increase with the rise of α for low installation angle (θ= 0°, 30°) and the maximum amplitudes exceed 2D (D: diameter of circular cylinder) can be observed for α= 40°/50° (θ= 30°) and α= 20° (θ= 60°). The reduced frequency of cylinder for θ= 0° and 30° does not sensitive to the coverage (α). It is worth noting that multiple frequencies can be captured for high coverage. Due to the boundary layer separating point moves in downstream direction with the increase of U and α, the vortex pattern switches from 2S to 2P.

Impact damage protection mechanisms for elastomer-coated concrete

Cost-efficient strategies for protecting structural elements against the effects of explosive detonations are of interest for vulnerable infrastructure. Dynamic loading due to both blast pressures and impact from fragments are of concern. This investigation focuses on the protection of concrete structural elements against impact damage. A recent experimental study by the authors demonstrated that an elastomer coating can provide a significant impact mitigating effect when applied to the impacted face of a concrete substrate. Preliminary numerical results have indicated that the elastomer serves to alter the details of damage initiation in the concrete, though there remains a limited understanding of the protective effects at play. In this work, a numerical investigation is performed to determine the mechanisms of impact damage initiation exhibited by a concrete circular cylinder of diameter, 100 mm and height, 100 mm when impacted by a 0.1 kg circular cylindrical (i.e. blunt) projectile, travelling at velocities in the range 5–150 m s−1. The influence of applying a 5 mm elastomer coating on these damage mechanisms is assessed. At the lowest impact velocities, the concrete remains undamaged, though the sub-surface stress state is influenced by the polymer coating. At higher impact velocities, two distinct damage initiation mechanisms are observed. Damage Mechanism 1 is characterised by immediate, severe concrete damage initiating under the indenter corner. Damage Mechanism 2 is characterised by more diffuse, sub-surface damage. Adding a polymer coating serves to shift damage initiation from Damage Mechanism 1–2, delaying the onset of severe concrete damage. Simplified 1D and 2D numerical models are employed to interrogate how the elastomer achieves this effect. Two protective effects are identified: (i) a temporal effect causing a reduction in the magnitude of peak acceleration and an increase in contact duration between projectile and target and (ii) a spatial effect where the stress concentration under the indenter corner is removed.

Experimental study on aerodynamic characteristics of a large-diameter ice-accreted cylinder without icicles

The aerodynamic characteristics of a circular cylinder (diameter ​= ​600 ​mm) with and without ice accretion (without icicles) were studied via wind tunnel tests (including simultaneous multi-pressure and force measurements) for Reynolds numbers (Re) of 1.29 ​× ​105–1.27 ​× ​106. The influences of wind angle of attack α, turbulence intensity Iu, relative surface roughness k, and accreted ice shape on the mean aerodynamic force coefficients (MAFCs), mean pressure coefficients, and pressure correlation coefficients were comprehensively investigated. Experimental results showed that the MAFCs of the ice-accreted cylinders exhibited significant Reynolds number effects, and the effects were closely related to the ice shape. The effects of Iu and k on the drag force of the ice-accreted and ice-free cylinders were similar. The remarkable lift force due to the asymmetric ice accretion could be reduced by increasing k and Iu. The effect of α on the MAFCs was related to the ice shapes and Re. The flow reattachments in the critical and supercritical regimes were examined to reveal the flow states around the finite ice-free and ice-accreted cylinders. The flow-fields around the finite ice-free and ice-accreted cylinders had significant three-dimensional effects, which could be weakened by introducing the Iu and k. The findings of this study could provide further understanding of the effect of ice accretion on the aerodynamic characteristics of circular cylinders. The results could be used as beneficial references in the wind-resistance design of ice-accreted circular cylinders.

Multi-Objective Optimization with Fuzzy Logic Analysis of Confined Flow Characteristics on Circular Cylinder

Two-dimensional, isothermal numerical computations are carried out using Ansys Fluent-18. Here, the flow is unsteady and incompressible past confined circular cylinder in a plane rectangular channel. A uniform inlet velocity profile is preferred; the Reynolds number varies in between 50 and 200. The blockage ratios (width of the channel to circular cylinder diameter) are 5, 10, 15 and 20. Flow characteristics like pressure and frictional drag coefficients, and Strouhal number (flow shedding frequency) are optimized. Fuzzy logic analysis has been used to model and predict the results of confined circular cylinder. A Mamdani fuzzy inference system with triangular membership function is used to be fuzzy sets. The results show that fuzzy model will predict the Strouhal number with 0.45% error. The present study recommends the lowest blockage ratio (highest blockage effect) and the highest Reynolds number combination is more suitable in flow shedding region in real-field applications.

The von Kármán street behind a circular cylinder: flow control through synthetic jet placed at the rear stagnation point

Abstract

Transition to chaos in the wake of a circular cylinder near a moving wall at low Reynolds numbers

Floquet stability analysis has been employed to identify modes of three-dimensional (3D) instability in the flow over a circular cylinder of diameter D above a moving wall at a gap height of G = 0.2D, beyond the onset of two-dimensional vortex shedding. Two subharmonic modes (mode C1 and mode C2) and one long-wavelength quasi-periodic mode (mode QPL) are revealed. The characteristics of these 3D modes are discussed in detail. The results of 3D direct simulations show that it is the intensively nonlinear modal interactions that lead to a chaotic final flow state at higher Reynolds numbers, rather than the interference of the shear layer caused by the no-slip moving wall.

Neural network and multi-objective optimization of confined flow characteristics on circular cylinder in standing double vortex region

The unsteady state and isothermal two dimensional numerical computations were carried out using Ansys Fluent-18 between the Reynolds number ranges 10 to 50. The blockage ratios (Domain height to the circular cylinder diameter) range 1.54–112. The flow characteristics such as drag coefficients and length of recirculation are optimized and correlated as a function of various Reynolds numbers at different blockage ratios. Gradual decrease in blockage ratio which means the increase in blockage effect postponed the flow separation, transition and reduces the length of recirculation and also makes the flow steady. In this study optimum flow characteristics exist at maximum blockage ratio, i.e. with minimum blockage effect and maximum Reynolds number. The artificial neural networks model proved to predict values of the total drag coefficient (R2 = 0.979) and length of recirculation (R2 = 0.992) closer to simulated data at 95% (α = 0.05) confident interval.

Vortex-induced vibrations of a confined circular cylinder for efficient flow power extraction

The effects of confinement on vortex-induced vibration (VIV) of a circular cylinder (diameter D) and its flow power extraction capability are presented. A two-dimensional numerical study is performed on VIV of a circular cylinder inside a parallel plate channel of height H at Reynolds numbers 100 and 150. The blockage ratio (b = D/H) is varied from 1/4 to 1/2. The cylinder is elastically mounted with a spring such that it can only vibrate transversely to the flow. It has a fixed non-dimensional mass (m*) of 10. The energy extraction process is modeled as a damper (damping ratio ζ) attached to the cylinder. With increasing blockage, the vibration amplitude of the cylinder decreases, the lock-in happens at a larger non-dimensional natural frequency of the cylinder, and the initial branch of the vibration response of the cylinder shrinks. There is a minimum value of the channel height and Reynolds number for the existence of the initial branch. The extracted power is found to increase rapidly with the blockage. For the maximum blockage (b = 1/2), the flow power extracted by the cylinder is an order of magnitude larger as compared to what it would extract in an open domain with free stream velocity equal to the channel mean velocity. The optimal mass-damping (α = m*ζ) for extracting the maximum power is found to lie between 0.2 and 0.3. An expression is derived to predict the maximum extracted power from the undamped response of a confined/unconfined cylinder.

Flow instabilities in the wake of a circular cylinder with parallel dual splitter plates attached

In this paper, instabilities in the flow over a circular cylinder of diameter $D$ with dual splitter plates attached to its rear surface are numerically investigated using the spectral element method. The key parameters are the splitter plate length $L$, the attachment angle $\unicode[STIX]{x1D6FC}$ and the Reynolds number $Re$. The presence of the plates was found to significantly modify the flow topology, leading to substantial changes in both the primary and secondary instabilities. The results showed that the three instability modes present in the bare circular cylinder wake still exist in the wake of the present configurations and that, in general, the occurrences of modes A and B are delayed, while the onset of mode QP is earlier in the presence of the splitter plates. Furthermore, two new synchronous modes, referred to as mode A$^{\prime }$ and mode B$^{\prime }$, are found to develop in the wake. Mode A$^{\prime }$ is similar to mode A but with a quite long critical wavelength. Mode B$^{\prime }$ shares the same spatio-temporal symmetries as mode B but has a distinct spatial structure. With the exception of the case of $L/D=0.25$, mode A$^{\prime }$ persists for all configurations investigated here and always precedes the transition through mode A. The onset of mode B$^{\prime }$ occurs for $\unicode[STIX]{x1D6FC}>20^{\circ }$ with $L/D=1.0$ and for $L/D>0.5$ with $\unicode[STIX]{x1D6FC}=60^{\circ }$. The characteristics of all the transition modes are analysed, and their similarities and differences are discussed in detail in comparison with the existing modes. In addition, the physical mechanism responsible for the instability mode B$^{\prime }$ is proposed. The weakly nonlinear feature of mode B$^{\prime }$, as well as that of mode A$^{\prime }$, is assessed by employing the Landau model. Finally, selected three-dimensional simulations are performed to confirm the existence of these two new modes and to investigate the nonlinear evolution of the three-dimensional modes.

Numerical Study of the Stagger Angle Effect of a Circular Cylinder Installed in Front of Returning Blade Toward the Vertical Axis Savonius Water Turbine Performance

This paper investigates numerically the effect of the circular cylinder’s stagger angle variation installed in front of the returning blade on the performance of Savonius vertical axis water turbine. The numerical simulation uses Computational Fluid Dynamics using ANSYS 17.0 to solve the incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS). Firstly, numerical model is verified by varying the grid size at TSR 1,078. Then numerical results are validated by existing experimental data, in this case the torque coefficients. The working fluid is in verification using air at Reynolds of 4.32 x105 and convert to water fluid. Ratio of circular cylinder diameter to the turbine diameter (ds/D) is 0.5 at gap (S/D) of 0.95 with varying TSR of 0.3, 0.5, 0.7, 0.9, 1.1 and 1.3 and stagger angle (α) of 0, 30, 60 and 90 degree. The results show that the maximum power coefficient increases about 29.84% at a TSR of 0.9 for stagger angle of 60 degree.

Experimental Review on Influence of Inlet Disturbance Body (IDB) at 30° Against Inhibitory Force Reduction on Three Circular Cylinders with Composed of Stagger (Variation L/D(constant=2), T/D = 1.5, 2, 3 & 4)

Research on the characteristics of the fluid flow across the bluff body has been carried out and placed in a variety / setting, let alone research on fluid flow across three circular cylinder arranged stagger by placing 2 (two) Inlet Disturbance Body (IDE) as a bully in front. This effort is usually done to reduce the normal force, shear force, and drag force that occurs in the bluff body of the three circular cylinders. This research was conducted experimentally in mechanics laboratories and fluid machines using subsonic wind tunnels and tested at Re = 2.2x104 based on the diameter of a circular cylinder. Variations used are longitudinal distance ratio (L/D) = 2 with a circular cylinder diameter (D = 25 mm) and transverse distance ratio (T/D) = 1.5, 2, 3 and 4 and IDE placement on the upper and lower sides from cylinder 1 (upstream) in the form of a cylinder with a diameter (d = 4mm) at 30 °. The results showed that the use of IDB at position 30° can reduce the drag force that occurs in cylinder 1 (upstream) 36 to 53% compared to with no IDE, while for cylinder 2 (upstream), the drag is higher for (T/D) = 1.5, 2 and 3 are 3.2 to 22% and at (T/D) = 4 the drag force is reduced to 9% again. About cylinder 3 (downstream - down) in the stagger configuration with IDB 30°, the drag is 4.8 to 44% higher for all distance variations (T/D) compared to the stagger configuration with no IDE. Variation in distance (T/D) also greatly affects the distribution of pressure coefficients that occur with the three circular cylinders with a stagger arrangement, causing a difference in the distribution of the drag pressure coefficient (Cdp) and also the velocity profile behind the 3 circular cylinders with the stagger arrangement.

An Overview of Different Possibilities to Master the Challenge of Coupling an AE-Sensor to an Object of Interest Partly Using Examples of Previous Investigations

Abstract Acoustic emission analysis is defined as a passive, non-destructive investigation method, which only listens for AE-waves (AEW), generated actively by an object of interest. Therefore, the AEW must have the possibility to propagate from their source to an acoustic emission sensor (AES). By virtue of the piezoelectric effect, the AEW transmitted into electrical signals inside of the AES. During the analysation of these electrical signals we earn–online–information about the object of interest, e.g. the operating characteristic of a machine or the strength of the friction of a tribolocical system. To enable the AEW to propagate into the AES, the sensor has to be fixed suitable onto the object of interest. Hereby has to be strictly respected, that the sensor is fixed in a reproducible mechanical way as well as to ensure that the through-transmission has a weak attenuation (couplant). Standard AES have the shape of a circular cylinder (diameter and height depend on the operation purpose), the AEW pass through one of the frontends into the sensor. The objects of interest can have different geometry of the surface (e.g. plane, cylindrical, unspecific) or temperatures which usually conflicting the operating range of the sensor. Depending on the operational purpose, there are many different couplants to use. This article offers help to master the different connecting challenges within the range of acoustic emission analysis.

Numerical simulation on improvement of a Savonius vertical axis water turbine performance to advancing blade side with a circular cylinder diameter variations

The use of fossil fuel will generate particulate gas in the atmosphere and forming the greenhouse effect. One of the ways to reducing greenhouse effect is used renewable energy as hydropower without generating particulate gas impacted in human life. The present study uses hydropower as the renewable energy by using a Savonius turbine. The main objective investigates the performance of Savonius water turbine numerically due to the installation of a circular cylinder beside of the advancing blade with circular cylinder diameter variations. The method used is numerically toward Savonius turbine disturbed a circular cylinder. The numerical simulation using two-dimensional (2D) analysis of Computational Fluid Dynamics (CFD) simulation by using ANSYS 17.0-Fluent and sliding Mesh technique used is to solve the incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) equations. The turbulence model uses Realizable k-epsilon (RKE) and transport equation uses the finite volume discretization method with the second-order upwind scheme and the SIMPLE algorithm. Firstly, the numerical model has been validated by the published experimental data toward the torque coefficient by using air fluid at Reynolds of 4.32.105. Then the fluid is changed the water fluid at the same Reynolds. The circular cylinder diameter relative to the turbine diameter (ds/D) is varied of 0.1, 0.3, 0.5, 0.7 and 0.9 at X/D of 0.5 and Y/D of 0.7 kept constant with TSR of 0.5, 0.7, 0.9, 1.1 and 1.3. The numerical simulation uses the transient and two dimensional (2D) simulations. The results show that the increase of disturbance diameter (ds/D) will improve the performance of the conventional Savonius turbine and the maximum power coefficient increase about 18.04% at ds/D of 0.7 with TSR of 0.7.

Influence of control cylinder placement on vortex shedding from a circular cylinder

Modifications to the vortex-shedding dynamics from a circular cylinder of diameter D are investigated experimentally in a free-surface water channel at $$Re_D$$ =9500. The vortex shedding is modified via the placement of a control cylinder of diameter D/8 in the vicinity of the main cylinder. A methodology is presented to link changes in the wake dynamics and loading on the main cylinder. The analysis combines fourier model decomposition, proper orthogonal decomposition, and phase averaging. Based on differences in the wake dynamics, the influence of the control cylinder can be classified according to its placement: (1) in the free stream outside the main cylinder shear layer; (2) within the main cylinder shear layer; (3) in the recirculation region. While fluctuating lift is significantly reduced in all the cases, the mean and fluctuating drag are affected differently.