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- Arlov, Dragana, et al.
(författare)
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Large eddy simulation of an aerated Rushton stirred tank
- 2006
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Konferensbidrag (refereegranskat)abstract
- Simulations of aerated stirred reactor is performed using Large Eddy Simulation (LES). The gas phase is modelled using Lagrangian Particle Tracking (LPT). The reactor is stirred by a single impeller Rushton turbine, centred in the reactor. The air is introduced at the bottom wall through a circular sparger. The main focus is to investigate how the gas phase affects the liquid in the reactor. Effects of gas volume flow and stirrer speed are investigated. The results show that the time averaged liquid velocities in the radial and tangential directions as well as the pumping capacity decrease with increasing gas volume fraction. In the axial direction the gas redirects the radial jet upwards breaking the symmetry of the ring vortices.
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| 5. |
- Arlov, Dragana, et al.
(författare)
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Numerical simulation of a gas-liquid Rushton stirred reactor - LES and LPT
- 2008
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Ingår i: Computers & Fluids. - : Elsevier BV. - 0045-7930 .- 1879-0747. ; 37:7, s. 793-801
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Konferensbidrag (refereegranskat)abstract
- Simulations of aerated stirred reactor is performed using a combination of large eddy simulation (LES) and Lagrangian particle tracking (LPT). A single impeller Rushton turbine is positioned at the center of the reactor and air is introduced at the bottom through a circular sparger. Effects of the gas volume flow, stirrer speed and sparger dimension are investigated. The results show that the time averaged liquid velocities in radial and tangential directions decrease with increasing gas volume fraction. In the axial direction, the gas redirects the radial jet upwards, breaking the symmetry of the ring vortices. Especially, for a narrower sparger, a more concentrated tilt upwards is observed with a larger region of negative axial velocity. Although, low aeration number is used, the periodicity from the impeller is decreasing and interfering with the creation of the trailing vortex pair. The gas dispersion increases with decreasing the sparger diameter.
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- Duwig, Christophe, et al.
(författare)
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Large Scale Dynamics of a Jet in a Counter Flow
- 2009
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Ingår i: Advances in Turbulence XII - Proceedings of the 12th Euromech European Turbulence Conference. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 0930-8989. ; 132, s. 321-324
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Konferensbidrag (refereegranskat)
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| 7. |
- Fuchs, Laszlo, et al.
(författare)
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Direct measurement of the turbulent fluxes of a passive scalar in impinging jets using simultaneous PIV AND LIF
- 2009
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Ingår i: 39th AIAA Fluid Dynamics Conference. - 9781563479755 ; , s. 2009-4010-
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Konferensbidrag (refereegranskat)abstract
- Turbulent mixing of passive scalars in an impinging jet are studied experimentally and numerically. The experiments use simultaneous PIV/PLIF data to obtain data on the velocity and concentration fields in a circular impinging jet with nozzle to plate distance of five diameters. The distributions of the mean velocity, turbulent kinetic energy, mean concentration, concentration fluctuation, turbulent fluxes, turbulent diffusivity are obtained from the measured data. The information enables one to compare directly the validity of different models for the turbulent fluxes, e.g. GDM model, GGDM model. Large Eddy Simulation are used as complimentary for studying Schmidt number (Sc) effects. The results show that the simpler models for turbulent fluxes are inadequate for use in flows with large coherent structures. Also, under conditions turbulence that enhances mixing is not always adequate to maintain the homogeneity of the mixture, whereby Sc-number effects become evident. For such flows, models for turbulent fluxes that neglect Sc-effects are apparently inadequate.
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- Jadoon, Asim, et al.
(författare)
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Hydrodynamic interaction of a particle pair at Reynolds number 600
- 2009
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Ingår i: [Host publication title missing]. - 1901-7278. ; DCE technical memorandum No. 11, s. 261-264
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Konferensbidrag (refereegranskat)abstract
- In the current study the focus is on the flow and particle interaction effects in the chaotic regime. The influence on the forces (i.e drag and lift), wake structures and flow patterns from different inflow boundary conditions and varying separation distances of a particle pair in tandem is discussed at a particle Reynolds number of 600.
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- Jadoon, Asim, et al.
(författare)
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Interaction between fixed dual particles at moderate Reynolds numbers
- 2007
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Ingår i: Proceedings of the 6th International Conference on Multiphase Flow. - 9783860109137
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Konferensbidrag (refereegranskat)abstract
- Numerical simulations of 3D flow past two identical spheres which are held fixed relative to each other at different separation distances and angles (which describe the deviation from the centre line of the trailing particle) are carried out. Particle Re = 300 is used to investigate the dependency of drag and lift coefficients on the separation distances and the angles. The simulations are performed on a Cartesian grid using the Volume of Solid (VOS) method to represent the spherical particles. Comparison with experimental and numerical data shows that method can accurately resolve the flow field around the spheres and the forces they are subjected to. Results are focused on the behaviour of forces (drag and lift) affected by the presence of another particle. The drag of the reference and secondary sphere is greatly affected when they are placed in tandem arrangement at a gap of 2.5 - 3d and 1.5d respectively. Similarly the lift of the reference sphere is greatly affected in the arrangement when the spheres are placed in the symmetry plane at gap of 1.5d and angle of 45 degrees. The effect of both forces decrease as the gap is increased in all arrangements. The flow becomes unsteady and periodic at a separation distance of 3d for the tandem case. Irregular vortex shedding is observed at large separation distances 6 - 9d. The results for forces coefficients and the vortex shedding show great resemblance for the cases when the spheres are placed in symmetry plane and plane perpendicular to it at same gaps and angles. The characteristics of the flow, wake and the vortical structures are investigated in detail in the present study.
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| 10. |
- Lazarkov, Mikhail, et al.
(författare)
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Flow-induced motion of a short circular cylinder spanning a rectangular channel
- 2008
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Ingår i: Journal of Fluids and Structures. - : Elsevier BV. - 1095-8622 .- 0889-9746. ; 24:4, s. 449-466
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedFlow-induced oscillation of an elastically supported circular cylinder subject to an incompressible fluid at Re=100 and 400 has been studied using three-dimensional simulations. The cylinder is either subjected to a uniform flow in an unconfined surrounding or confined by rectangular channel, i.e. the cylinder is confined in both the span-wise and the cross-stream directions. The cylinder surface is represented by a virtual boundary method which replaces a solid object in flow by additional force distribution to satisfy local boundary condition. The simulations have been performed for nondamped cylinder with low mass ratio. For the unconfined cylinder, the effects of Reynolds number are studied. The effects of confinement have been investigated by varying the extent of the channel (and thereby also the cylinder length) in the span-wise direction. The maximal amplitude is found to be decreased by the confinement. For very strong confinement (short cylinder) the motion of the cylinder is governed by the natural frequency of the structure even beyond synchronisation range. The upper boundary of the synchronisation range exhibits no dependency on the confinement, only on Reynolds number.
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