Vortex Eccentricity Research Articles

Numerical investigation on the swirling vortical characteristics of a Stairmand cyclone separator with slotted vortex finder

The slotted vortex finder (SVF) represents a novelly modified cyclone vortex finder, which is validated to be valuable and prospective for industrial applications. The main purpose of present study is to illustrate the effect of slotted vortex finder on the swirling turbulent flow characteristics of cyclone separator in comparison with conventional vortex finder (CVF). Based on three cyclone models (CVF, SVF_D1, SVF_D2), the differences of swirling vortical characteristics between SVF and CVF models are comprehensively tested and the influence of SVF insertion length on the cyclone performance was discussed. The overall detailed features and variations of flow pattern, such as velocity profile distribution, unsteady particle tracking, swirl number comparison and special flow phenomena of vortex eccentricity in the whole cyclone separator body, are analyzed in detail. Specifically, The SVF_D2 model could improve the cyclone separation efficiency (about 20% reduction of pressure drop and 4.2% reduction of cut off size) and also reduce 40% of central vortex rotation frequency compared with CVF model at vin = 16.1 m/s. The current study is beneficial to further clarify the influence of SVF on the mechanism of the particle separation motion in cyclone separator and identify the characterization differences between traditional cyclone separator and cyclone with installation of SVF.

Vortex and its implication on separation performance in an electro-swirling coupling device

ABSTRACT An electro-swirling coupling device coupled with electric field and centrifugation can achieve demulsification and dewatering of emulsion efficiently and economically. But, the vortex structure and its implication on separation performance under the coupling condition are unclear. Accordingly, a vortex analysis for the coupling separator was conducted numerically, and the effect of eccentricity on the efficiency was investigated. The results show that the iso-vortex surface is twisted and fluctuates. And there is a vibrational radial deviation between the vortex core and central axis, and increasing inlet velocity and voltage amplitude can increase the radial deviation of the vortex at the z-coordinate range from 250 to 550 mm. Furthermore, the underlying reason for the increase in vortex eccentricity is different where the electric coalescence is for the increase in voltage amplitude and the fluid kinetic energy is for the increase in inlet velocity. Moreover, the separation efficiency increases with the increase in vortex eccentricity at the case that the coalescence is dominant, but the separation efficiency gradually decreases with the increase in breakage rate and the droplet breakup is dominant.

Effect of number of inlets on performance and flow field of large‐scale cyclone separators

AbstractThe performance and flow field of large‐scale cyclones with different inlet numbers were investigated by using computational fluid dynamics methods. The results show that the efficiency, pressure drop, and performance factor of cyclones increase with the increase in the number of inlets, and the quadruple inlet cyclone having the best overall performance is supposed to adopt. The number of inlets of the cyclone increases, the tangential velocity increases, and the short‐circuit flow rate decreases; however, when the number of inlets is greater than 2, both variations are lessened. In this study, the vortex eccentricity of the quadruple inlet cyclone is the smallest, the vortex eccentricity of the double and triple inlet cyclone is comparable, and the vortex eccentricity of the single inlet cyclone is the most significant.

Vortex characteristics of a gas cyclone determined with different vortex identification methods

This paper characterizes the vortex flow field in a gas cyclone based on different vortex identification methods, including vorticity method, Q criterion, λ2 criterion, Ω method and Liutex method. Analysis and comparison of isosurfaces of different vortex identification methods indicate that except vorticity method, the vortex core, the eddy flow and the short-circuit flow can be identified directly by other methods. But the small scale vortices, such as top ash ring, can only be fully recognized by Liutex method. The contours demonstrate that the magnitude of five vortex parameters is the largest in the vortex core, followed by the short-circuit flow, and the eddy flow is the smallest. But only Liutex method can predict the vortex core center and identify the most severe vortex eccentricity is in the bottom of vortex finder, the lower part of the cone and the hopper. The work not only improves the understanding of the vortex structure in a gas cyclone, which can critically affects cyclone performance, but also reveals the differences in the commonly used vortex characterization methods.

Vortex Solution in Elliptic Coordinates

Abstract Vortices (flows with closed elliptic streamlines) are exact nonlinear solutions to the compressible Euler equation. In this contribution, we use differential geometry to derive the transformations between Cartesian and elliptic coordinates, and show that in elliptic coordinates a constant vorticity flow reduces to μ ˙ = 0 and ν ˙ = const along the streamline μ 0 that matches the vortex eccentricity.

Numerical study of vortex eccentricity in a gas cyclone

This paper presents a numerical study of the vortex eccentricity in a gas cyclone and its effect on the performance of the cyclone. The gas flow in the cyclone was modeled as an unsteady flow by the Navier–Stokes equations with the Reynolds Stress Model (RSM) as the turbulence model. The particles were modelled by the Lagrangian particle tracking (LPT) approach in an unsteady gas flow. Gas cyclones with the same dimensions and total flow rates but different numbers of inlets were simulated with the inlet velocity varying from 12 to 20 m/s. The vortex eccentricities in different cases were analyzed in terms of radial deviation and angular deviation. In addition, the frequency of the precessing vortex core (PVC) was analyzed by the fast Fourier transform (FFT). The results show that the vortex center in the single inlet cyclone has a great eccentricity and its precession center is also different from the geometric center, which reduces the particle collection efficiency. The increase in the symmetry of the inlet causes only a very small increase in the pressure drop in the simulated cases, but it can significantly reduce the vortex eccentricity, particularly by eliminating the eccentricity of the PVC center. The improvement of the vortex eccentricity can generally increase the collection efficiency for particles greater than 2.0 µm. The increase of the collection efficiency is mainly because the symmetrical vortex can restrain the short-circuiting flow of particles. The results can improve the understanding of the vortex flow in gas cyclones which may guide the optimization of gas cyclones.

An Aerodynamic Investigation of an Isolated Rotating Formula 1 Wheel Assembly

The flowfield around a 60% scale rotating Formula 1 tire in contact with the ground in a closed wind tunnel at a Reynolds number of 500,000 was examined computationally and experimentally. The goal of this study was to assess the accuracy of unsteady Reynolds-averaged Navier–Stokes (URANS) equations and confirm the existence of large scale vortical and flow recirculating features. A replica deformable F1 tire model that includes four tire treads and all brake components was used to determine the sensitivity of the wake to cross flow within the tire hub as well as the flow blockage caused by the brake assembly. Several turbulence closures were employed and the one that matched closest to the experimental PIV data was the Reynolds stress model. The variability between the six turbulence closures is shown by comparing velocity profiles, pressure distributions, and vortex eccentricity. The sensitivity of the wake to four different hub geometries, contact patch boundary conditions, multiple reference frame (MRF) rotor and spoke treatment, and time step size are also discussed.

Contraction of the 300 mbar north circumpolar vortex during 1963–1997 and its movement into the eastern hemisphere

The size of the 300 mbar north circumpolar vortex, and its partition into western and eastern hemispheres and quadrants 0°–90°W, 90°W–180°, 90°E–180°, and 0°–90°, is estimated by planimetering the area poleward of contours in the main belt of westerlies on the polar stereographic mean‐monthly analyses of the Institute of Meteorology of the Free University of Berlin. During 1963–1997 the trend in annual vortex size is a significant − 1.4%/decade (vortex contraction), but with the trend in the western hemisphere portion of the vortex a significant −2.1%/decade compared to −0.7%/decade in the eastern hemisphere portion, signifying a movement of the vortex farther into the eastern hemisphere. Thus, while on average 52% of the vortex was in the eastern hemisphere during 1963–1997, this value increased by a significant 0.4%/decade during the period, resulting in a substantial increase in vortex eccentricity. In winter and spring the vortex has moved mainly into the Asian quadrant 90°E–180°, whereas in summer the vortex has become elliptical with less of a decrease in size of quadrants 90°E–180° and 0°–90°W, and in autumn there has been a decrease in size of quadrant 90°W–180° relative to the other quadrants. The standard deviation of the annual quadrant‐size anomalies has decreased significantly during 1963–1997, indicating a decrease in the annual displacements of the vortex center from its mean location as the eccentricity increases and the vortex contracts. On the basis of a 41‐station northern hemisphere radiosonde network, during 1963–1997 the annual 850–300 mbar temperature increased by a significant 0.12°C/decade in the northern hemisphere as a whole, and by a significant 0.17°C/decade in the western half and by 0.06°C/decade in the eastern half of the hemisphere. The resulting association of a 1%/decade decrease in 300 mbar vortex size, with about an 0.1°C/decade increase in 850–300 mbar temperature, differs by a factor of 2 from what would be expected hydrostatically, a difference that would be eliminated by an 0.4 mbar/decade increase in midlatitude surface pressure during 1963–1997.

Vortex ring dynamics at a free surface

The results of a flow visualization study of the evolution of vortex rings near a free surface are presented. The vortex rings were formed underwater with their axis parallel to the free surface one ring diameter below the surface. It is shown that vortex lines in the ring open during the interaction with the surface. The resulting flow field consists of vortex lines, beginning and terminating at the free surface. Data are reported on several features of the vortex ring evolution, which show a large reduction of the propagation speed and an oscillation of the vortex eccentricity as it propagates downstream after the interaction.

Studies on the Flow of Cross-Flow Impellers : 2nd Report, Analytical Study

Using an actuator model, velocity and pressure distributions of a flow around a cross-flow impeller are derived, which are in good agreement with experimental results on impellers with radial blades. Under the assumption that the stability of an eccentric vortex in the radial direction inside an impeller is achieved when an input furnished to the flow by impeller-bladings balances with energy dissipation by fluid viscosity, the stability conditions are discussed. Critical Reynolds number of stability for an axisymmetric vortical flow is given as a function of eccentricity of vortex. Performance of a fan with a simple casing around an impeller is obtained by numerical computation and influences of several parameters on it are clarified. It is found that only one circumferential location of stability of a vortex to make input maximum exists for a given eccentricity.