Circular Cylinder Of Finite Length Research Articles

Numerical analyses of the flow past a short rotating cylinder

This work studies the three-dimensional flow dynamics around a rotating circular cylinder of finite length, whose axis is positioned perpendicular to the streamwise direction. Direct numerical simulations and global stability analyses are performed within a parameter range of Reynolds number $Re=DU_\infty /\nu <500$ (based on cylinder diameter $D$ , uniform incoming flow velocity $U_\infty$ ), length-to-diameter ratio ${\small \text{AR}}=L/D\leq 2$ and dimensionless rotation rate $\alpha =D\varOmega /2U_\infty \leq 2$ (where $\varOmega$ is rotation rate). By solving Navier–Stokes equations, we investigated the wake patterns and explored the phase diagrams of the lift and drag coefficients. For a cylinder with ${\small \text{AR}}=1$ , we found that when the rotation effect is weak ( $0\leq \alpha \lesssim 0.3$ ), the wake pattern is similar to the unsteady wake past the non-rotating finite-length cylinder, but with a new linear unstable mode competing to dominate the saturation state of the wake. The flow becomes stable for $0.3\lesssim \alpha \lesssim 0.9$ when $Re<360$ . When the rotation effect is strong ( $\alpha \gtrsim 0.9$ ), new low-frequency wake patterns with stronger oscillations emerge. Generally, the rotation effect first slightly decreases and then sharply increases the $Re$ threshold of the flow instability when $\alpha$ is relatively small, but significantly decreases the threshold at high $\alpha$ ( $0.9<\alpha \leq 2$ ). Furthermore, the stability analyses based on the time-averaged flows and on the steady solutions demonstrate the existence of multiple unstable modes undergoing Hopf bifurcation, greatly influenced by the rotation effect. The shapes of these global eigenmodes are presented and compared, as well as their structural sensitivity, visualising the flow region important for the disturbance development with rotation. This research contributes to our understanding of the complex bluff-body wake dynamics past this critical configuration.

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*.

Effects of floating ice on the flow drag of a circular cylinder with finite length

In present paper, free surface is covered with artificial ice of uniform size. Effects of characteristic sizes of ice, i.e. DL/D = 0.28, 0.56 and 1.08 (DL is diameter of equivalent circle of ice block section and D cylinder diameter), local coverage ratio n and cylinder draught H on drag of ice-water flows around finite length circular cylinder are investigated experimentally. Two hydrodynamic states when Froude number Fr=0.50 in subcritical and Fr=0.99 in supercritical are selected, where Fr=V/gD, V is towing speed and g gravitational acceleration. When Fr=0.99, wave-making increases drag coefficient by 0.1–0.2. For DL/D = 0.56 and 1.08, cross-correlation coefficient between n and drag coefficient exceeds 0.85. Higher n results in greater drag. With H/D increasing from 0.4 to 2.0, momentum transferred from water pushed by cylinder to ice increases, making relative velocity between ice and cylinder decrease and collision contribution to total drag be reduced. While DL/D = 0.28, ice blocks follow water flow closely due to small inertia, making collision between cylinder and ice blocks weak and drag caused by collision insignificant. Also ice-water mixture is more like single phase flow of higher viscosity than water, with drag coefficient almost not affected by draught.

Hygrothermoelastic response of a finite hollow circular cylinder

In this paper, a hollow circular cylinder of finite length with finite extent occupying the space is considered. Based on the hygrothermoelasticity theory, the transient response of a hollow circular cylinder subjected to the hygrothermal loading at the surface is analyzed. The analytical solution for the coupling and uncoupling effects of temperature, moisture, and thermal stresses is obtained by using the integral transform technique. The numerical results of the transient response of the hygrothermoelasticity field are presented graphically for a graphite fiber–reinforced epoxy matrix composite material (T300/5208).

Effects of reattachment and three-dimensionality on the aerodynamics of a circular cylinder in the critical Reynolds number range

Details of the aerodynamic characteristics of a circular cylinder in the critical Reynolds number range remain unclear. A significant influencing factor is the occurrence of reattachment. A series of pressure measurements on a circular cylinder of finite length in the critical Reynolds number range, Re = 1.0 × 105–4.6 × 105, is carried out in a wind tunnel to reveal the three-dimensional effects of reattachment on the aerodynamics, which cannot be observed by the two-dimensional simulation and significantly influence the estimation of the aerodynamics of slender structures. The results show that the flow can reattach along only a certain length of the cylinder instead of the entire length, inducing a strong three-dimensional flow state and corresponding aerodynamic force distribution. The reattachment also induces an unsteady variation in the aerodynamic force; the lift coefficient is mainly dependent on the occurrence of a separation bubble and the motion of the reattachment point.

Electrophoresis of tightly fitting spheres along a circular cylinder of finite length

Electrophoresis of a tightly fitting sphere of radius $a$ along the centreline of a liquid-filled circular cylinder of radius $R$ is studied for a gap width $h_0=R-a\ll a$ . We assume a Debye length $\kappa ^{-1}\ll h_0$ , so that surface conductivity is negligible for zeta potentials typically seen in experiments, and the Smoluchowski slip velocity is imposed as a boundary condition at the solid surfaces. The pressure difference between the front and rear of the sphere is determined. If the cylinder has finite length $L$ , this pressure difference causes an additional volumetric flow of liquid along the cylinder, increasing the electrophoretic velocity of the sphere, and an analytic prediction for this increase is found when $L\gg R$ . If $N$ identical, well-spaced spheres are present, the electrophoretic velocity of the spheres increases with $N$ , in agreement with the experiments of Misiunas & Keyser (Phys. Rev. Lett., vol. 122, 2019, 214501).

Flow structure and loads over inclined cylindrical rodlike particles and fibers

The flow past a fixed finite-length circular cylinder, the axis of which makes a nonzero angle with the incoming stream, is studied through fully-resolved simulations, from creeping-flow conditions to strongly inertial regimes. The investigation focuses on the way the body aspect ratio $\chi$ (defined as as the length-to-diameter ratio), the inclination angle $\theta$ with respect to the incoming flow and the Reynolds number $\text{Re}$ (based on the cylinder diameter) affect the flow structure past the body and therefore the hydrodynamic loads acting on it. The configuration $\theta=0^\circ$ (where the cylinder is aligned with the flow) is considered first, from creeping-flow conditions up to $\text{Re}=400$, with aspect ratios up to $20$ ($10$) for $\text{Re}\leq10$ ($\text{Re}\geq10$). In the low-to-moderate Reynolds number regime ($\text{Re}\lesssim5$), influence or the aspect ratio, inclination (from $0^{\circ}$ to $30^{\circ}$), and inertial effects is examined by comparing numerical results for the axial and transverse force components and the spanwise torque with theoretical predictions based on the slender-body approximation, possibly incorporating finite-Reynolds-number corrections. Semiempirical models based on these predictions and incorporating finite-length and inertial corrections extracted from the numerical data are derived. For large enough Reynolds numbers ($\text{Re}\gtrsim10^2$), separation takes place along the upstream part of the lateral surface of the cylinder, deeply influencing the surface stress distribution. Numerical results are used to build empirical models for the force components and the torque, valid for moderately inclined cylinders ($|\theta|\lesssim30^\circ$) of arbitrary aspect ratio up to $\text{Re}\approx300$ and matching those obtained at low-to-moderate Reynolds number.

Scattering by a uniaxially anisotropic chiral object under electromagnetic beam illumination

ABSTRACT We propose a semi-analytical scheme for investigating the electromagnetic beam scattering by a uniaxially anisotropic chiral object. The scattered and internal fields are expanded in terms of appropriate spherical vector wave functions, and the method of moments procedure is employed for determining the unknown expansion coefficients. Normalized differential scattering cross sections are evaluated for a uniaxially anisotropic chiral spheroid and circular cylinder of finite length, respectively illuminated by a Gaussian beam, Hermite-Gaussian beam and zero-order Bessel beam. The scattering properties are analyzed briefly.

Dynamics of the Tip Vortices in the Wake Behind a Circular Cylinder of Finite Length

The dynamics of the tip vortices in the wake behind a wall-mounted finite-length circular cylinder of the aspect ratio 2 was studied experimentally using time resolved stereo PIV technique. The cylinder was mounted normal to a ground plane and it was subjected to a cross-flow with thin boundary layer developed on the wall, the Reynolds number based on inflow velocity and cylinder diameter was 9.7 thousands. The dynamics of tip vortices were analysed using the POD method applied to the plane perpendicular to the flow close to the cylinder. Besides the decaying power spectrum, slower that the Kolmogorov-type one, the two distinct frequencies were detected on Strouhal numbers 0.09 and 0.15. These frequencies could be linked to the vortical structures dynamics in the wake. The frequency Sh = 0.15 corresponds to predominantly spanwise vortices dynamics with anti-symmetrical patterns with respect to the cylinder axis, while the frequency Sh = 0.09 corresponds to mainly streamwise vortical structures dynamics with symmetrical patterns respectively. Thus, the von Kármán vortex street was detected on Strouhal frequency 0.15.

Hygrothermoelastic response of a finite solid circular cylinder

PurposeIn this paper, a solid circular cylinder of finite length occupying the space 0⩽r⩽1, 0⩽z⩽h is considered. The purpose of this paper is to adopt a linear hygrothermal effect to analyze the unsteady state responses in a finite long solid cylinder subjected to axisymmetric hygrothermal loading T=TR and C=CR at the surface. The analytical solution of temperature, moisture and thermal stresses is obtained by using the integral transform technique. The coupling and uncoupling effects of temperature, moisture and thermal stresses are discussed for a graphite fiber-reinforced epoxy matrix composite material (T300/5208). The numerical results of transient response hygrothermoelastic field are presented graphically.Design/methodology/approachIn the present problem, hygrothermoelastic response of a finite solid circular cylinder has been investigated by integral transform technique consisting of Laplace transform, Hankel transform and Fourier-cosine transform. The problem is investigated subjected to prescribed sources. Numerical algorithm has been developed for numerical computation.FindingsThe analytical solution of temperature, moisture and thermal stresses is obtained by using the integral transform technique. The coupling and uncoupling effects of temperature, moisture and thermal stresses are discussed for a graphite fiber-reinforced epoxy matrix composite material (T300/5208). The numerical results of transient response hygrothermoelastic field are presented graphically.Research limitations/implicationsThe work presented here is mostly hypothetical in nature and totally mathematical.Practical implicationsIt may be useful for composite materials, composite laminated plates in hygrothermal environment. Also it is having the applications in hygrothermal field where porous media exposed to heat and moisture. The problem investigated will be beneficial for the researcher working in the field thermoelastic diffusion and hygrothermoelastic materials.Originality/valueTill date, the other authors did the research work on hygrothermal effect of an infinitely long cylinder without thickness. In this paper, the authors consider finite solid cylinder with finite length and discuss the hygrothermal effect within a small range. Second, the material properties are both homogenous and isotropic and are independent of both temperature and moisture.

Vortex-induced vibration of finite-length circular cylinders with spanwise free-ends: Broadening the lock-in envelope

The unsteady response of finite-length rigid circular cylinders with spanwise free-ends undergoing vortex-induced vibration (VIV) has been experimentally investigated in a large-scale wind tunnel. The model consists of a cylinder mounted on the upstream tip of an elastic cantilever beam, thus allowing the investigation of the effects of the aspect-ratio on the VIV dynamic response of the system. Models with different aspect-ratios have been tested, and the time dependent oscillation amplitude of the cylinder has been determined from the analysis of images obtained with a high-speed camera. The solid body rotation of the vibrating cylinder and the vorticity flux generated by this moving boundary, entering the flow field, are associated with the formation of large vortical structures and increased forcing on the cylinder. Surprisingly, the results show an unexpected broadening of the lock-in envelope by about 200% as the aspect-ratio decreases from 28.8 to 5 and an almost 230% increase in the peak oscillation amplitude. The reduced damping parameter known as the Skop-Griffin parameter has been used to interpret these novel results. The Griffin plot shows a reasonably good agreement between the present experimental data of different aspect-ratio cylinders and those of other investigators.

Arbitrary shaped beam scattering from a chiral-coated conducting object with arbitrary monochromatic illumination

An exact semi-analytical method of calculating the scattered fields from a chiral-coated conducting object under arbitrary shaped beam illumination is developed. The scattered fields and the fields within the chiral coating are expanded in terms of appropriate spherical vector wave functions. The unknown expansion coefficients are determined by solving an infinite system of linear equations derived using the method of moments technique and the boundary conditions. For incidence of a Gaussian beam, circularly polarized wave, zero-order Bessel beam and Hertzian electric dipole radiation on a chiral-coated conducting spheroid and a chiral-coated conducting circular cylinder of finite length, the normalized differential scattering cross sections are evaluated and discussed briefly.

Axisymmetric equilibrium of an isotropic elastic solid circular finite cylinder

Axisymmetric equilibrium of an elastic solid circular finite cylinder is one of the oldest problems in the theory of linear elasticity. Crosswise superposition is a well-known method that is used to solve this boundary value problem (BVP); however, technical realization of its underlying ideas still seems to be vague and the solution obtained by this method suffers from some convergence issues. In this study, we follow two main objectives via analyzing a benchmark problem where an isotropic elastic solid circular cylinder of finite length is subjected to normal lateral loading. The first goal is to add more insight into the method of crosswise superposition by extending the ideas that are used for solving classical BVPs via the superposition principle. For this purpose, a new unified approach that naturally gives rise to the subtle concept of corner conditions (CCs) in the context of crosswise superposition method is introduced. Another goal is to demonstrate the influence of CCs on the convergence of the solution obtained by the method of crosswise superposition. In this avenue, the Love function approach is used to convert the Navier equations for an isotropic elastic material to a single axisymmetric biharmonic equation. Next, a general solution for the axisymmetric biharmonic equation consisting of separable and non-separable solutions is presented in cylindrical coordinates. These two classes of solutions are used to construct the Love function and associated elastic fields through the unified approach. Numerical results reveal that considering the CCs can significantly affect the convergence rate of the solution on the boundaries of the cylinder. Furthermore, it is observed that the solution does not converge to the boundary data at the rims without considering the CCs. Far enough from the boundaries of the cylinder, the solution does not seem to be much different with or without taking the CCs into account.

Numerical investigations on drag coefficient of circular cylinder with two free ends in roller bearings

Abstract In high speed roller bearings, the drag force due to the oil-air mixture present in the bearing cavity – that is acting against the roller movement – is usually computed with a two-dimensional model of flow around a cylinder of infinite length. However rollers are of finite length, and the flow is perturbed by the two free ends, the surrounding rings, the cage and other rolling elements. In this article, the Computational Fluid Dynamics (CFD) method is employed to analyze first the flow around one finite-length circular cylinder with two free ends in an open space. Then the model is changed to one finite cylinder and then several in-line circular cylinders sandwiched by two flat walls, which represents a simplified approach. The results indicate that both the flow pattern around the cylinder and its drag coefficient are modified in comparison with the two-dimensional model. Finally a relationship between the drag coefficient and the Reynolds number suitable for circular cylinder in roller bearings is proposed.

Model formulation of churning losses in cylindrical roller bearings based on numerical simulation

Abstract A numerical-based fluid mechanics model is proposed to predict churning losses in cylindrical roller bearings, which is caused by the rotation and the translation of the rollers in the bearing cavity. The Computational Fluid Dynamics (CFD) method is conducted to quantify the influence of various factors on churning losses, including operating conditions, roller geometry parameters, and fluid properties. One configuration with several in-line finite-length circular cylinders sandwiched by two flat walls is analyzed in one-phase environment, which represents a simplified approache. The results indicate that the roller orbital speed, the presence of adjacent rollers, and the rings have a significant impact on the churning moments. Finally a formulation is proposed for churning losses prediction in cylindrical roller bearings. This is of particular interest for high-speed applications where churning losses may represent up to 50 % of the total power dissipated.

Scattering of electromagnetic beam by a chirally coated object

We present a semi-analytical solution to the electromagnetic scattering by a chirally coated object with arbitrary monochromatic illumination. The scattered fields and the internal fields in different regions are expanded in terms of appropriate spherical vector wave functions, and the unknown expansion coefficients are determined using the boundary conditions and the method of moments scheme. As examples, for a Gaussian beam, zero-order Bessel beam and Hertzian electric dipole radiation incident on a chirally coated spheroid and circular cylinder of finite length, numerical results of the normalized differential scattering cross section are provided to illustrate the validity and capability of the proposed method, and the scattering characteristics are discussed concisely.

Prediction of flow induced sound generated by cross flow past finite length circular cylinders.

The paper presents aeroacoustic results for the flow around finite-length circular cylinders at Reynolds number 84 770 for various length-to-diameter (L/D) ratios (= 3, 9, 20, 25, 30, and 35). The incompressible Navier-Stokes equations are solved using the large eddy simulation model of turbulence followed by acoustic predictions in the far field using Ffwocs Williams and Hawkings method. The comparisons of numerical and anechoic wind tunnel measurements show good agreement in terms of the aerodynamic forces and acoustic parameters such as tonal frequency, tonal sound pressure level, and overall sound pressure level. The cylinder L/D ratio was observed to be a significant parameter that controls vortex shedding and consequently the flow induced sound generation.

Shaped beam scattering by an anisotropic particle

An exact semi-analytical solution to the electromagnetic scattering from an optically anisotropic particle illuminated by an arbitrarily shaped beam is proposed. The scattered fields and fields within the anisotropic particle are expanded in terms of spherical vector wave functions. The unknown expansion coefficients are determined by using the boundary conditions and the method of moments scheme. For incidence of a Gaussian beam, zero-order Bessel beam and Hertzian electric dipole radiation, numerical results of the normalized differential scattering cross section are given to a uniaxial, gyrotropic anisotropic spheroid and circular cylinder of finite length. The scattering properties are analyzed concisely.

Scattering of arbitrarily shaped beam by a chiral object

An exact semi-analytical solution to the arbitrarily shaped beam scattering by a chiral object is proposed through expanding the scattered and internal fields in terms of appropriate spherical vector wave functions. By using the boundary conditions and the method of moments technique, the unknown expansion coefficients are determined. For incidence of a Gaussian beam, zero-order Bessel beam and Hertzian electric dipole radiation, numerical results of the normalized differential scattering cross section are given to a chiral spheroid and a chiral circular cylinder of finite length, and the scattering characteristics are discussed concisely.

Semi-analytical solution to arbitrarily shaped beam scattering

Based on the field expansions in terms of appropriate spherical vector wave functions and the method of moments scheme, an exact semi-analytical solution to the scattering of an arbitrarily shaped beam is given. For incidence of a Gaussian beam, zero-order Bessel beam and Hertzian electric dipole radiation, numerical results of the normalized differential scattering cross section are presented to a spheroid and a circular cylinder of finite length, and the scattering properties are analyzed concisely.