Cylinder Separation Research Articles

Flow past two diamond-section cylinders in tandem arrangement at a low Reynolds number

The unsteady flow surrounding two fixed diamond cylinders is analyzed at Reynolds number 100 over normalized center-to-center spacing ratios 2−15. By analyzing the contours of instantaneous vorticity, variations of recirculation length, surface pressure, and fluid forcing of cylinders, the value of normalized critical spacing is found to be 3.4. In the reattachment zone below critical spacing, vortex-shedding from the upstream (UC) and downstream (DC) cylinders is anti-phase. At the critical spacing, regular vortex-shedding commences also from the UC, and vortex-shedding from the cylinders becomes phase synchronized for the first time. The analysis of a vortex-shedding cycle at the critical spacing reveals that the cylinders shed vortices at the same frequency, but with a time delay. Impingement of vortices shed from the UC on the DC strengthens vorticity around the DC and shifts the instantaneous position of its forward stagnation point from the leading edge. The understanding that locations of stagnation points govern the direction and magnitude of lift force comes from the analysis of flow at the critical gap. When the surface bounded by stagnation points is occupied mostly with negative vorticity, the instantaneous lift is negative and vice versa. At critical spacing, mean streamlines show the emergence of an anti-wake at forward stagnation point of the DC for the first time. Over the entire range of cylinder separation, nine distinct patterns of separation topologies are identified. Below critical spacing, both pressure and viscous drag components, and hence, total drag of the DC are negative or upstream-acting.

Experimental investigation of thermal characteristics of slot synthetic jet impingement on a circular cylinder: Free and constrained environment

The present study aimed to comprehensively investigate the thermal behavior of a slot synthetic jet (SJ) interacting with a circular cylinder in both free and constrained environments through experimental analysis. By traversing the cylinder along the jet centerline across a range of non-dimensional distances (H/w = 5-50), spanning from the near-field to the fully developed region, the research aimed to elucidate the factors governing heat transfer performance. Key parameters such as Reynolds number, jet-cylinder separation distance, and excitation frequency were scrutinized to understand their influence on thermal performance. The SJ was found to perform better in the constrained environment, attributed to relatively higher flow fluctuations developed by the complex interaction of the vortex with the sidewall boundary layer and the cylinder. Almost 12% higher average heat transfer was observed in the case of the constrained environment over the range of parameters employed in the current work. Moreover, a strong dependence of heat transfer on the jet cylinder separation distance was also found. In contrast to the SJ impinging on flat target surfaces where the maximum heat transfer was attained in the intermediate field, at H/w = 14 to 18, for SJ impingement on the circular cylinder, however, this was consistently achieved in the near field, i.e., H/w = 5. Also, the thermal performance as a function of the flow Reynolds number was comparable to the uniform flow case when the Reynolds number was based on the approach flow velocity (i.e., local velocity based on the cylinder location) instead of the velocity at the slot exit.

Study on radial segregation of whole and broken rice in an indented cylinder separator

Indented cylinder separators are often used to complete the grading of rice, but there is radial segregation which affects the screening performance. To clarify the cause of its radial segregation, the rice data required for simulation were first obtained through experiments, and then discrete element method (DEM) was used to analyze the segregation process of whole and broken rice at low filling levels. The results showed that with the intensification of segregation, the screening efficiency decreased gradually. Increasing the filling level will increase segregation. Segregation core to form in the center of the left half of the bed. The radial segregation mechanism of whole and broken rice is “percolation”, which is the result of a combination of particle size and shape driving forces. This study is helpful to improve the screening efficiency of rice and provides some reference for exploring segregation of multi-component mixture with multi-attribute differences.

An Analysis of the Spelt Dehulling Process in a Cylinder Separator

Abstract Spelt is one of unprofitable wheat types and requires an additional hulling process, in which the husks are removed from the grain. A device for dehulling spelt kernels was proposed. The described solution consists of a stainless-steel wire mesh cylinder with 4×20 mm and 4×30 mm longitudinal openings and a rotor with adjustable blade angles. Kernels were dehulled at the following angular speeds of the shaft: 16.76, 23.04, 29.32, 35.60, and 41.89 rad·s−1, and the following rotor blade angles: 50°, 60°, 70°, 80°, and 90°. The efficiency of glume and glumelle removal, the proportion of damaged kernels, and kernel and husk separation efficiency were evaluated during the experiment. The highest of kernel separation efficiency η z was 81.86% using a wire mesh cylinder with 4×30 mm longitudinal openings and 81.60% for a wire mesh cylinder with 4×20 mm longitudinal openings.

DEM Study of the Motion Characteristics of Rice Particles in the Indented Cylinder Separator.

The precise separation of rice particles is an important step in rice processing. In this paper, discrete element simulations of the motion of rice particles of different integrity in an indented cylinder separator were carried out using numerical simulation methods. The effects of single factors (cylinder rotation rate, cylinder axial inclination angle, and collection trough inclination angle) on the motion trajectories of particles are investigated and the probability distribution functions of particles are obtained. The statistical method of Kullback-Leibler divergence is used to quantitatively evaluate the differences in the probability distribution functions of the escape angles of particles of different degrees of integrity. The purpose of this paper is to determine the optimum parameters for an indent cylinder separator by understanding the material cylinder separating process from particle scale and to provide a basis for the numerical design of a grain particle cylinder separators.

Numerical investigation on buoyancy-driven flow over a circular cylinder in a channel with nonparallel walls

The flow over a stationary cylinder is destabilized mainly in the separated shear layer (SSL) and wake regions and transverse shedding forms downstream of the cylinder. It has been revealed that aiding/opposing buoyancy or diverging/converging channel could stabilize/destabilize the separated and wake flows, while their joint effect has not been investigated. In this numerical investigation, the low-Re buoyancy-driven flow over a circular cylinder placed in a channel consists of diverging or converging walls is studied. We aim to reveal the effects of two parameters, i.e. Richardson number Ri representing buoyancy and channel angle α, on the flow dynamics and heat transfer. The cases of aiding (Ri > 0) and opposing (Ri < 0) buoyancy, and diverging (α > 0) and converging (α < 0) channels are considered in this work. The effects of Ri and α are presented in terms of the instantaneous flow field, global characteristic quantities, heat transfer between the fluid and cylinder surface, separation and shearing of wake flow, and temperature variations of the channel walls. We found that the flow transits to steady subjected to aiding buoyancy at a lower value of Ri where the fluctuations of force and heat transfer rate reduces to zero; however, the mean drag and Nusselt number do not exhibit monotonic variations with Ri. The convection heat transfer is prone to be notably affected by Ri rather than α on the leeward side of the cylinder, and its fluctuation is significant in the separation zone downstream of the separation point. Depending on the value of Ri, the steady and unsteady wake flow present different velocity profile as well as the shearing; the deficit wake flow recovers more rapidly for the steady flow cases.

Numerical simulation and instability analysis of particles in liquid–solid concave‐wall jet using DPM‐RSM

AbstractThe liquid–solid concave‐wall jet existed in the vertical cylinder separator with tangential inlet; the instability near concave‐wall was the key factor for centrifugal separation. The effects of jet flowrate and wall curvature radius on the instability of solid‐particles were explored by experiment and numerical simulation. The results showed that the separation efficiency of particles decreased with the increase of centrifugal separation factor. The liquid–solid concave‐wall jet flow in separator was unstable in this study. The decay rate of jet maximum velocity on the concave‐wall was larger than that on plane‐wall jet. The ratio of half‐width value to wall curvature radius was about 0.08 at the circumferential direction 90°, which coincided with the critical value of centrifugal instability in strongly concave‐wall jet. The pressure, velocity, and vorticity fluctuated periodically along streamwise direction in separator. The fluctuation period was linearly related to the wall curvature, and the radial range of fluctuation was only half of jet width. The paired longitudinal vortices formed along the flow direction, and the longitudinal vortices merged at length 0.74 m from the inlet cross‐section along circumferential direction. After the position of vortices merged, the particle trajectory oscillated obviously.

Separation characteristics of white rice in an indented cylinder separator with a baffle

Broken rice can gather in the core of a cylinder during rice grain separation because it is wrapped by whole rice and cannot contact the indents causing low separation efficiency. To improve contact with the indented cylinder by broken rice the actions of a baffle were simulated using the discrete element method. By analysing rice movement in the mixing area under the action of baffle, the mechanism of reducing the segregation of grains, and therefore lack of contact with the indents, was clarified. The simulations showed that effects of blade length on separation characteristics were more obvious, compared with that of the rotational speed of the baffle. Shorter blade lengths and lower rotational speeds were more favourable for separation. Optimal parameters of the baffle were obtained after a comprehensive evaluation of the separation efficiency and loss rate was determined by the intercriteria correlation (CRITIC) method. This study provides a foundation for the design of the baffle and improving separation efficiency of the indented cylinder rice separators. • Separation of indented cylinder with baffle was simulated by discrete element method. • The motion behaviors of rice with or without a baffle were investigated. • Effect of blade length and rotation speed on separation characteristics was analyzed. • The CRITIC method was used to evaluate separation ability comprehensively. • Blade length of 0.54 h and rotational speed of 0.5 v are the optimum.

Intensification of the rate of diffusion-controlled reactions involved in wastewater treatment by using a rotating array of vertical cylinders reactor

The mass transfer behavior of a circular rotating array of vertical cylinders was studied using an electrochemical technique which involves measuring the limiting current of the cathodic reduction of potassium ferricyanide. Variables studied were: array rotation speed, cylinder diameter, cylinder separation, and physical properties of the solution. It was found that the rate of mass transfer at the cylinder array increases with increasing rotation speed while increasing cylinder diameter decreased the rate of mass transfer, cylinder spacing within the array was found to have little effect. The data were correlated by a dimensionless equation including all affecting parameters. The reactor was tested in removing copper ions from dilute solutions and found to be promising. Possible applications of the rotating cylinder array in building electrochemical reactors and catalytic reactors e.g., photocatalytic and immobilized cell (or enzyme) biochemical reactions suitable for wastewater treatment were highlighted.

The concave-wall jet characteristics in vertical cylinder separator with inlet baffle component

The concave-wall jet was formed in the vertical cylinder separator with inlet baffle component. The effect of curvature of radial baffle on the jet flow in the separator was investigated by the experiment of concentration and the numerical simulation of species transport. The results show that the concave-wall jet was confined within the narrow region near the concave-wall and the flow disturbance in the center of separator was weakened. The distribution of concentration and the flow region of wall jet depended on the curvature of radial baffle ( K ). Compared with the turbulent intensity of the plate baffle ( K = 0), that of concave baffle ( K = 2) reduced by 6.1% and the turbulent intensity of convex baffle ( K = −2) increased by 13.5%. The best flow stability was obtained by the concave baffle because the baffle outlet was similar to convergent nozzle. The outlet convergent angle was between 0° and 19.5° when 0 ≤ K ≤ 2. The secondary vortices were caused by the tangential velocity irregularity on the cross-section of two axial baffles in the separator with convex baffle. The baffle with K ≥ 0 was more suitable in separator inlet than that with K < 0.

Numerical Computation of Low Reynolds Number Viscous Flow Past Bluff Bodies

This article presents a two-dimensional steady viscous flow simulation past circular and square cylinders at low Reynolds numbers (based on the diameter) by the finite volume method with a non-orthogonal body-fitted grid. Diffusive fluxes are discretized using central differencing scheme, and for convective fluxes upwind and central differencing schemes are blended using a ‘deferred correction’ approach. A simplified pressure correction equation is derived, and proper under-relaxation factors are used so that computational cost is reduced without adversely affecting the convergence rate. The governing equations are expressed in Cartesian velocity components and solution is carried out using the SIMPLE algorithm for collocated arrangement of variables. The mesh yielding grid-independent solution is then utilized to study, for the very first time, the effect of the Reynolds number on the separation bubble length, separation angle, and drag coefficients for both circular and square cylinders. Finally, functional relationships between the computed quantities and Reynolds number (Re) are proposed up to Re = &lt;i&gt;40&lt;/i&gt;. It is found that circular cylinder separation commences between Re= &lt;i&gt;6.5-6.6&lt;/i&gt;, and the bubble length, separation angle, total drag vary as Re, Re&lt;i&gt;−0.5&lt;/i&gt;, Re&lt;i&gt;−0.5&lt;/i&gt; respectively. Extrapolated results obtained from the empirical relations for the circular cylinder show an excellent agreement with established data from the literature. For a square cylinder, the bubble length and total drag are found to vary as Re and Re&lt;i&gt;−0.666&lt;/i&gt;, and are greater than these for a circular cylinder at a given Reynolds number. The numerical results substantiate that a square shaped cylinder is more bluff than a circular one.

Wheat cleaning and milling technologies to reduce DON toxin contamination

Mycotoxicosis caused by Fusarium fungi holds a huge risk considering economic and food safety issues worldwide. By applying milling technologies, we attempted to reduce the concentrates of DON toxin, as it is the most often found toxin in wheat.&#x0D; The processes of sieving, aspiration and combination had been used on wheat with high DON toxin concentration. As a next step, grains were sorted using a horizontal cylinder separator, assorted by an optical and a gravity separator, and finally, the products were scoured and ground. The contamination level of the wheat and flour samples were defined by the HPLC-MS method.&#x0D; Regarding the results, it can be stated that toxin concentration was most effectively reduced by optical separation and scouring, and by applying these milling techniques, food safety can be increased significantly.

The development of instability of Richtmyer–Meshkov in the interaction of a shock wave with a two-component medium consisting of light and heavy gas

On the basis of the previously formulated mathematical model of the mechanics of a two-speed two-temperature mixture of light and heavy gases, the evolution of a system of two cylinders of heavy gas after the passage of a shock wave through it is numerically investigated. The analysis of the obtained data on the dependence of the spatial expansion on time, as well as the kinematic characteristics of the system showed their satisfactory compliance with the experimental data for all initial separations of the cylinders. The influence of the initial separation of cylinders on the flow morphology is investigated.

Flow characteristics at low Reynolds number around two in-line circular cylinders with slits

This study investigated numerically the characteristics of laminar flow around two identical circular cylinders placed in tandem, with slits of the same width through their respective axis. The center to center distance between the cylinders and the slit orientation were varied to study their effects on the flow structure, lift and drag, and vortex shedding characteristics. It was found that three flow regimes could be distinguished, the transitions between which could be indicated by the sudden changes in drag and lift. Asymmetrically, configured slits destabilized the stagnant region between cylinders; whereas in-line slits connect the two cylinders to act as a single elongated bluff body, even at large cylinder separation, by stabilizing the stagnant region in between. These in turn strongly modified the transition between flow regimes. Vortex shedding was also strongly influenced by both slit configuration and cylinder separation.

DEM study of white rice separation in an indented cylinder separator

The precise separation of whole and broken rice is an issue of great significance in rice processing industry. This paper presents a numerical study on the rice separation in an indented cylinder separator based on the discrete element method. The probability density function of escape angle of whole and broken rice was investigated at 10% filling level for various rotational speeds and indent numbers. Hellinger distance, a statistical estimate used to quantify the difference between two probability distributions, was adopted to measure the separation ability. It was found that the Hellinger distance appears to initially increase to a maximum and then decrease with the increase in rotational speed. While the Hellinger distance increases to a maximum value then keeps stable with the increase in indent number. After obtaining the optimal operating condition for the best separation, the position of trough was decided based on the boundary of parabolic trajectories of whole rice after leaving indents. The aim of this work is to determine the best parameters for the indented cylinder separator based on the understanding of separation progress at a particle scale, providing a foundation for the numerical investigation of indented cylinder separator.

A high-order hybrid turbulence model with implicit large-eddy simulation

A new hybrid turbulence modelling algorithm combining Implicit Large-Eddy Simulation and Reynolds-Averaged Navier–Stokes has been developed. This variable-resolution algorithm consists of a continuous, non-zonal approach with a hybrid blending function operating at the edge of boundary layers and separated flow regions. This algorithm is informed by an auxiliary transport variable B˜, implemented in a compressible, high-order computational solver Flamenco. The model parameters and the hybrid blending mechanisms are developed for a zero-pressure gradient flat plate boundary layer. Secondly, the flow around a NACA4412 aerofoil in a near-stall configuration is used to evaluate its predictive capability in adverse pressure gradients. Finally, a fully turbulent flow around a circular cylinder at a Reynolds number of Re=1.4×105 is simulated at three different grid-refinement levels. Mean and unsteady results were compared to experimental measurements for validation. Results are critically evaluated against state-of-the-art Detached-Eddy Simulation variants (DES, DDES), Partially-Averaged Navier–Stokes (PANS) and Large-Eddy Simulation (LES). The influence of spanwise sizing, resolution and the choice of an effective characteristic length-scale for the blending functions are discussed. The model responds favourably with increased resolution and also agreed well with the experimental measurements for the wake profiles. Predicted cylinder separation angles were within the expected range, despite the challenges in accurately capturing the recirculation lengths.

Interaction between Charged Cylinders in Electrolyte Solution; Excluded Volume Effect.

Electrostatic interactions govern the physical properties of charged cylindrical structures in electrolyte solutions. Besides the surface charge on the cylinders, another factor influencing the electrostatic interactions are the mobile ions. The finite size of the mobile ions is included by the excluded volume effect within the lattice statistics, while the electrostatic interactions are considered by means of the mean electrostatic field. In this article we consider charged parallel cylinders embedded into an electrolyte solution of mobile monovalent ions. A modified nonlinear Poisson-Boltzmann equation is proposed via variational procedure, and we implement the finite element method to solve it numerically. Excluded volume effect of the system containing two and multiple charged parallel cylinders are taken into account. Numerical results show that the excluded volume effect decreases the concentration of counterion and increases the electrostatic potential near the charged cylinders. The angular distribution of counterion around the particular cylinder is asymmetric. The study of the electrostatic interaction between two parallel equally charged cylinders reveals that an increase in the free energy is seen when the ionic strength is decreased. The free energy decreases as a function of the cylinders separation distance. On the contrary for two oppositely charged cylinders, the free energy increases with increasing cylinder separation distance, while for two cylinders with different charged density it shows nonmonotonic variation with the increasing cylinders separation distance.

A DPIV study on the effects of separation distance upon the vortical behaviour of jet–cylinder impingements

An experimental investigation based on laser-induced fluorescence (LIF) and digital particle image velocimetry (DPIV) was conducted to provide a better understanding into the effects of jet–cylinder separation distance on the vortical structures and dynamic behaviour resulting from jet impingements upon convex cylinders. Separation distances of 1, 2 and 4 jet diameters were investigated, while cylinder–jet diameter ratio was maintained at 2 throughout. LIF and DPIV results show that jet ring-vortex initiation, wall-separated vortex initiation, vortex dipole formation and vortex separation occur further away from the impingement point as the separation distance decreases. Varying the separation distance also influences the recirculating wake region size at the cylinder lee sides, as well as producing two distinct flow modes between adjacent vortex dipoles along the cylinder straight edges. Mean and instantaneous skin friction coefficient distributions determined from DPIV results not only showcase the different effects of separation distance on the wall shear stress, but also illustrate how the flow dynamics influence the local wall shear stress levels. On the other hand, wall-separated vortex initiation, vortex dipole formation and separation events incur little distinctive changes upon the local wall shear stress distributions that may ease their unique identification.

Simultaneous Wake- and Vortex-Induced Vibrations of a Cylinder With Two Degrees of Freedom in Each Direction

The flow-induced vibration of one cylinder in the wake of another is the subject of continuing interest in connection with interactions between vertical tension risers in deep water. When one riser is downstream of another, it is likely to be subject to wake-induced and vortex-induced excitations at different frequencies simultaneously. Both are complex mechanisms, and it is reasonable to assume that they interact. To begin to understand this complicated process, it is desirable that any modeling should incorporate some features of a multidegree-of-freedom structural response. With this aim, this paper describes experiments in which one cylinder was free to undergo simultaneous wake- and vortex-induced vibrations downstream of a similar but stationary cylinder in a steady flow. The downstream cylinder was mounted on an elastic system that had two natural frequencies in both the in-line and cross-flow directions. Mass ratios were almost the same in all four modes. Measurements are presented of simultaneous wake- and vortex-induced vibrations for cylinder separations of 5 and 10 diameters in the in-line direction, and up to 4 diameters transversely. At a reduced velocity of 83 (based on the cylinder's lower submerged natural frequency) and a separation of 5 diameters, excursions of wake-induced vibrations peaked at almost 5 diameters, when the downstream cylinder was near the edge of the upstream cylinder's wake.

Analysis of Broken Rice Separation Efficiency of a Laboratory Indented Cylinder Separator

Purpose: Using a laboratory indented cylinder separator, broken rice separation experiments were conducted and the characteristics of the separation process were studied to provide information for developing a prototype indented cylinder broken rice separator. Methods: Rice (Ilmi variety) milled in a local RPC was used for the experiment. Rice kernels were classified into four groups according to their length l; whole kernels (l > 3.75 mm), semi-whole kernels (2.5 < l < 3.75 mm), broken kernels (1.75 < l < 2.5 mm), and foreign matters (l < 1.75 mm). A laboratory grain cleaner, Labofix ’90 (Schmidt AG, Germany) was used for the experiments. Experiments were designed as a 4 × 4 factorial arrangement in randomized blocks with three replications. Cylinder rotational speeds (17, 34, 51, 68 rpm) and trough angles (15, 37.5, 60, 82.5°) were the two factors and feed rates (25, 50 kg/h), indent shapes (Us, S1 type), and indent sizes (2.5, 3.75 mm) were treated as the blocks. Two 125 g samples and one 125 g sample were taken at the cylinder outlet and from the trough, respectively. The whole, semi-whole, and broken kernel weight ratio of the samples and feed was determined by a rice sizing device. From these weight ratios, purities, degrees of extraction and coefficient of separation efficiency were calculated. Results: Trough angle, cylinder speed, and their interaction on the coefficient of separation efficiency were statistically significant. Cylinder speed of 17, 34, and 51 rpm made the most effective separation when t he trough angle was 15° or 37.5°, 60°, and 82.5°, respectively. Maximum values of coefficient of separation efficiency were in the range of 60 to 70% except when the indent size was 2.5 mm and were recorded for the combinations of low cylinder speed (17 rpm) with medium trough angle (37.5° or 60°). Indent shape did not appear to make any noticeable difference in separation efficiency. Conclusions: Due to the interaction effect, the trough angle needs to be increased appropriately when an increase in cylinder speed is made if a rapid drop of effectiveness of separation should be avoided. In commercial applications, S1 type indents are preferred because of their better manufacturability and easier maintenance. For successful separation of broken kernels, the indent size should be set slightly bigger than the actual sizes of broken kernels: an indent size of 3.0 mm for separating broken kernels shorter than 2.5 mm.