Flow visualization studies of a swirling flow in a cylinder (original) (raw)
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Three-dimensional turbulent swirling flow in a cylinder: Experiments and computations
2007
Dynamics of the three-dimensional flow in a cyclone with tangential inlet and tangential exit were studied using particle tracking velocimetry (PTV) and a three-dimensional computational model. The PTV technique is described in this paper and appears to be well suited for the current flow situation. The flow was helical in nature and a secondary recirculating flow was observed and well predicted by computations using the RNG k-e turbulence model. The secondary flow was characterized by a single vortex which circulated around the axis and occupied a large fraction of the cylinder diameter. The locus of the vortex center meandered around the cylinder axis, making one complete revolution for a cylinder aspect ratio of 2. Tangential velocities from both experiments and computations were compared and found to be in good agreement. The general structure of the flow does not vary significantly as the Reynolds number is increased. However, slight changes in all components of velocity and pressure were seen as the inlet velocity is increased. By increasing the inlet aspect ratio it was observed that the vortex meandering changed significantly.
Investigation of the flow in a flat bottom cyclone
The main objective of this investigation was to determine the velocity profiles of a swirling flow in a flat bottom cyclone, a cylindrical vessel with central discharges used for classifying or separating particles in industrial processes. A two component laser Doppler velocimeter was used to measure the axial and the tangential component of velocity. A perspex model of a flat bottom cyclone 310,5 mm high and with a diameter of 102 mm was installed in an experimental rig under controlled water flow conditions. The velocity profiles were measured for two different overflow tube (vortex finder) diameters and three different values of pressure drop p Δ in the cyclone. For each cyclone, three different values of both under flowrate through the apex tube and over flowrate through the vortex finder were thus originated, the Reynolds number Re varying in the range 4 10 37
Swirling Flows Characteristics in a Cylinder Under Effect of Buoyancy
2021
Swirling flows have been investigated extensively aiming at providing further insight into the conditions that cause abrupt flow stagnation and associated breakdown. This latter complex feature may be evidenced, for instance, in the benchmark model flow driven by one end disk of an upright cylinder of given aspect ratio [1, 2]. Several prior studies provided means of controlling breakdown onset as it can be harmful / beneficial, depending upon the application considered. Hereafter, are presented selected investigations based on kinematic, geometric and thermal means of vortex flows control. Of note, Mullin et al. [3] demonstrated the effects of including a tapered center body and showed it to alter significantly breakdown onset and location. In particular, they argued that the inhibition / suppression of the vortex structure depended on the axial pressure gradient sign, induced by the conical axial rod, whose circular base is sealed to either the rotating or the stationary disk of t...
A Study of Vortex Structure in the Shear Layer between Main Flow and Swirling Backflow
JSME International Journal Series B, 2004
The present paper describes the vortex structure and the flow field of model experiments simulating the inlet flow of turbomachines at low flow coefficients. A new experimental apparatus was devised to freely set the axial velocity of the main flow and the axial and tangential components of the swirling backflow. The vortex structure was visualized by small air bubbles. It occurs in the shear layer between the main flow and the backflow. The number and the radial location of vortices are determined mainly by the axial and tangential velocities of the backflow normalized by the axial velocity of the main flow. These characteristics agree with those of the backflow vortex structure of real turbomachines. This shows that the vortex structures are caused by the roll-up of the shear layer between the axial main flow and swirling backflow, not associated with the flow interaction with individual blade of the impeller. It was shown that a two-dimensional linear stability analysis can reasonably predict the relation between the number of vortices and their radial location.
The three dimensional swirling flow has been obtained by solving Navier Stokes equations, expressed in cylindrical coordinate system, using finite difference technique on a staggered grid. An explicit finite difference method using pressure correction technique, for the solution of Navier-Stokes has been implemented to solve three dimensional flows. Present study explores the 3-D axisymmetric nature of stratified swirling flow and vortex breakdown in a cylindrical annulus cavity with top rotating lid. The annulus is obtained by inserting a thin coaxial rod in cylindrical cavity. This rod may be stationary or rotating depending on the particular study. Three dimensional swirling flows in annuli have also been studied subjected to axial temperature gradient or under the influence of axial magnetic field. Influence of governing parameters Re, Ri and Ha on the overall heat transfer has been investigated through variation of the average Nusselt number with these parameters. Further, the present numerical results are shown to be in good agreement with the available benchmark solutions under the limiting conditions. INTRODUCTION There has been interest to study swirling flow for last many decades. The swirling flow occurs in various flow devices: ranging from centrifuges used for particle separation and collection to vortex tubes used for cooling to furnaces and combustion chambers. Flow with swirl occurs in draft tubes of hydraulic turbines, as well as in the casing of the compressors and axial turbines. Practical application of study of swirling flow and vortex breakdown also ranges from vortex control on modern aircraft to mixing in combustion chambers and to chemical reactions. In another application strong magnetic field can be used in lithium-lead alloys cooling system of fusion reactor. This application can be realized by creating a liquid metal flow in a closed cylindrical cavity by rotating end wall under the influence a strong axial magnetic field. Several investigators have focused on the issue of the axial symmetry or lack of it in the lid driven swirling flow-field. Experiments conducted by Escuder[1] indicate a small degree of asymmetry in the flow field but did not addressed this aspect adequately. Hourigan et al. [2] argued that the asymmetry seen in the experimental results, Escuder[1], is perhaps due to some unidentified errors remained in the observation techniques. However, more accurate flow visualization photographs, Steven et al.[3]; Fujimura et al.[4] ; Spohn et al.[5], too have revealed such asymmetric behavior in the swirling flow field. As an outcome of these experimental observations it has been claimed that the vortex breakdown could be physically an asymmetric phenomenon and hence argued that previous 2-D axisymmetric simulations are unable to capture the 3-D asymmetric flow features. In some of the studies, Blackburn & Lopez[6]; Sotiropoulos & Ventikos[7]; Sotiropoulos et al.[8]; Gelfgat et. al.[9]; Serre & Bontoux[10], numerical simulations of the swirling flow have included a fully 3-dimensional model. The 3D simulations by Sotiropoulos & Ventikos[7], reconfirmed the observation of Spohn et al.[5]that the boundary layer separation along the sidewall is basically asymmetric and concluded that the dynamics of the vortex breakdown bubble is indeed a 3-D,asymmetric and unsteady phenomenon. Escudier [1] observed the vortex breakdown phenomenon in swirling flows in a cylindrical container with a rotating lid utilizing a laser-induced-fluorescence technique. Escudier's experimental results are the extension of those obtained earlier by Vogel[8]and Ronnenberg [9]. One of the major contributions of his study was to observe and report that multiple vortex breakdown bubbles can exist in the closed cylindrical geometry. These recirculation vortex breakdown bubbles were observed to be axisymmetric and steady over a large range of the governing parameters i.e. aspect ratio (AR) and Reynolds Number (Re).
2021
A study about the influence of geometry simplification on the swirling flow of a cyclone was performed by comparing CFD results with experimental data. The numerical results were obtained by solving the mass and momentum equations with the Reynolds Stress Model (RSM) for the turbulence closure. On other hand, the experimental data were obtained in the literature, the authors used the Particle Image Velocimetry (PIV) technique to measure the velocity fields and a differential manometer to measure the pressure drop. In this work, different test facility geometries configurations were simulated: the complete test facility; and others with some simplifications downstream and upstream of the cyclone. The boundary condition for both numerical and experimental analysis was performed with inlet velocity in 10.5 and 12.25 m/s. Results showed a decrease in the gas vortex velocity in the cyclone center when simplifications in the test facility geometry are made. These bring significant consequ...
The Persistence of Vortex Structures Between Rotating Cylinders in the 106 Taylor Number Range
International Review of Aerospace Engineering (IREASE), 2015
The flow in the annular gap d = R oR i between a stationary outer cylinder of radius R o and a co-axial rotating inner cylinder of radius R i is characterised at large gap, over the radius ratio (η) range 0.44 ≤ η ≤ 0.53 and aspect ratio (Γ) range 7.81 ≤ Γ ≤ 11.36. These configurations are more representative of turbomachinery bearing chambers and large rotating machinery than the journal bearing geometries of narrow gap commonly reported in the literature. Particle Image Velocimetry measurements are taken across the full meridional plane over the Taylor number (Ta) range 258 × 10 3 ≤ Ta ≤ 10.93 × 10 6 , which is 1000 times higher than the critical Taylor number for the onset of the first axisymmetric Taylor instability. Well-defined azimuthal vortex structures persist over this high Taylor number range, characterised by a constant number of vortices at a given aspect ratio, vortex core axial and radial motion over time, and mixing between neighbour vortices. This regime, with wavy Taylor vortex flow like features, is defined over the range 1.18 × 10 6 ≤ Ta ≤ 6.47 × 10 6. These results form a body of experimental evidence from which further progress in the understanding of the wavy Taylor vortex dynamics can be sought, through advanced flow dynamic models that reproduce the persistence of the observed flow features.
An experimental and numerical study of turbulent swirling flow in gas cyclones
Chemical Engineering Science, 1999
Experimental results on the turbulent, strongly swirling #ow "eld in a reverse #ow gas cyclone separator are presented, and used to evaluate the performance of three turbulence closure models. Mean and #uctuating velocity components were measured for gas cyclones with di!erent geometric swirl numbers by means of laser-Doppler velocimetry. The experimental data show the strong e!ect of the geometric swirl number on mean #ow characteristics, in particular with respect to vortex core size and the magnitude of the maximum tangential velocity. It is shown that the forced vortex region of the #ow is dominated by the so-called precessing vortex core. Numerical calculation of the cyclonic #ow shows that turbulence models based on the eddy-viscosity approach fail to predict the combined vortex observed experimentally. Predictions with the Reynolds stress transport model are in reasonable agreement with measured pro"les for all three swirl numbers, though the turbulent normal stresses are generally overpredicted. : S 0 0 0 9 -2 5 0 9 ( 9 8 ) 0 0 3 7 3 -X
Study of flow behaviour in a three-product cyclone using computational fluid dynamics
Minerals Engineering, 2006
Simplicity in design and minimal floor space requirements render the hydrocyclone the preferred classifier in mineral processing plants. Empirical models have been developed for design and process optimisation but due to the complexity of the flow behaviour in the hydrocyclone these do not provide information on the internal separation mechanisms. To study the interaction of design variables, the flow behaviour needs to be considered, especially when modelling the new three-product cyclone. Computational fluid dynamics (CFD) was used to model the three-product cyclone, in particular the influence of the dual vortex finder arrangement on flow behaviour. From experimental work performed on the UG2 platinum ore, significant differences in the classification performance of the three-product cyclone were noticed with variations in the inner vortex finder length. Because of this simulations were performed for a range of inner vortex finder lengths. Simulations were also conducted on a conventional hydrocyclone of the same size to enable a direct comparison of the flow behaviour between the two cyclone designs. Significantly, high velocities were observed for the three-product cyclone with an inner vortex finder extended deep into the conical section of the cyclone. CFD studies revealed that in the three-product cyclone, a cylindrical shaped air-core is observed similar to conventional hydrocyclones. A constant diameter air-core was observed throughout the inner vortex finder length, while no air-core was present in the annulus.
Nonlinear vortex development in rotating flows
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2008
We present the results of a combined experimental and numerical investigation into steady secondary vortex flows confined between two concentric right circular cylinders. When the flow is driven by the symmetric rotation of both end walls and the inner cylinder, toroidal vortex structures arise through the creation of stagnation points (in the meridional plane) at the inner bounding cylinder or on the mid-plane of symmetry. A detailed description of the flow regimes is presented, suggesting that a cascade of such vortices can be created. Experimental results are reported, which visualize some of the new states and confirm the prediction that they are stable to (mid-plane) symmetry-breaking perturbations. We also present some brief results for the flows driven by the rotation of a single end wall. Vortex structures may also be observed at low Reynolds numbers in this geometry. We show that standard flow visualization methods lead to some interesting non-axisymmetric particle paths in...