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| 4. |
- Fuchs, Laszlo, et al.
(författare)
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Rena rusningen i gaser och vätskor
- 2003
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Ingår i: Hett om kalla fakta. - 9173070335 ; , s. 169-178
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Bokkapitel (populärvet., debatt m.m.)
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| 5. |
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| 6. |
- Lazarkov, Mikhail, et al.
(författare)
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Simulations of flow around a confined oscillating circular cylinder using a virtual boundary method
- 2003
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Ingår i: Advances in Fluid Mechanics. - 1353-808X. ; 36, s. 343-352
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Konferensbidrag (refereegranskat)abstract
- In this paper streamwise and transverse oscillations of a rigid circular cylinder in a rectangular channel are investigated using the Virtual Boundary method. Numerical study of the three-dimensional flow around the cylinder is done for the uniform Cartesian grid. All computations are performed at Reynolds numbers of Re=500 and 1000 based on the mean flow velocity. The Keulegan-Carpenter number (Kc) of cylinder forced oscillation is equal to 6 and the excitation frequencies considered are higher, lower and equal to the vortex shedding frequency. The locked-on state of the wake for the transverse and streamwise oscillations of a cylinder in uniform flow are obtained. The force coefficients spectra show the presence of a dominating component that is equal to the excitation frequency.
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| 7. |
- Moghaddas, Jafar Sadegh, et al.
(författare)
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A comparison of the mixing characteristics in single- and two-phase grid-generated turbulent flow systems
- 2004
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Ingår i: Chemical Engineering & Technology. - : Wiley. - 1521-4125 .- 0930-7516. ; 27:6, s. 662-670
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Tidskriftsartikel (refereegranskat)abstract
- The mixing process is studied in grid-generated turbulent flow for single- and bubbly two-phase flow systems. Concentration and mixing characteristics in the liquid phase are measured with the aid of a PLIF/PLIF arrangement. A nearly isotropic turbulent flow field is generated at the center of the vertical pipe by using a honeycomb, three grids and a contraction. In two-phase flow experiments, air bubbles were injected into the flow from a rectangular grid, with mesh size M = 6 mm, which is placed midway between two circular grids each with a mesh size of M = 2 mm. For single-phase flow, the normalized mean concentration cross-stream profiles have rather similar Gaussian shapes, and the cross-stream profiles of the normalized root-mean-square (RMS) values of concentration were found to be quite similar. Cross-stream profiles of the mean concentration, for bubbly two-phase flow, were also found to be quite similar, but they did not have the Gaussian shape of the profiles for single-phase flow. Almost self-similar behavior was also found for the RMS values of the concentration in two-phase systems. The turbulent diffusion coefficient in the liquid phase was also calculated. At the center of the plume, the flow was found to have a periodic coherent structure, probably of vortex shedding character. Observations showed that the period of oscillation is higher in the case of two-phase flow than in single-phase flow.
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| 8. |
- Revstedt, Johan
(författare)
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A virtual boundary method with improved computational efficiency using a multi-grid method
- 2004
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Ingår i: International Journal for Numerical Methods in Fluids. - : Wiley. - 1097-0363 .- 0271-2091. ; 45:7, s. 775-795
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Tidskriftsartikel (refereegranskat)abstract
- The flow around spherical, solid objects is considered. The boundary conditions on the solid boundaries have been applied by replacing the boundary with a surface force distribution on the surface, such that the required boundary conditions are satisfied. The velocity on the boundary is determined by extrapolation from the flow field. The source terms are determined iteratively, as part of the solution. They are then averaged and are smoothed out to nearby computational grid points. A multi-grid scheme has been used to enhance the computational efficiency of the solution of the force equations. The method has been evaluated for flow around both moving and stationary spherical objects at very low and intermediate Reynolds numbers. The results shows a second order accuracy of the method both at creeping flow and at Re = 100. The multi-grid scheme is shown to enhance the convergence rate up to a factor 10 as compared to single grid approach. Copyright (C) 2004 John Wiley Sons, Ltd.
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| 9. |
- Revstedt, Johan, et al.
(författare)
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Handling complex boundaries on a Cartesian grid using surface singularities
- 2001
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Ingår i: International Journal for Numerical Methods in Fluids. - 0271-2091 .- 1097-0363. ; 35:2, s. 125-150
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers flow around arbitrarily shaped objects. The boundary conditions on the solid boundaries have been applied by replacing the boundary with a surface force distribution on the surface, such that the required boundary conditions are satisfied. The velocity on the boundary is determined by interpolation or by local (Gaussian space) average. The source terms are determined iteratively as part of the solution. They are then averaged and are smoothed out to nearby computational grid points. The method has been applied both to test problems as well as to more complex engineering problems, where there are not many real competitive alternatives to the proposed method. Simulations of creeping flow around a sphere were studied in order to evaluate the performance of different, competitive approaches of imposing boundary conditions. Using local averaging first-order accuracy is obtained; this can be improved by using a Lagrangian polynomial instead, although the convergence is then considerably slower. Simulations of flows around spheres in the Reynolds number range 1-1000 have been carried out. Finally, the approach was used to describe the impellers in a turbine agitated mixer. For these cases, the results show overall good agreement with other computational and experimental results.
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| 10. |
- Revstedt, Johan, et al.
(författare)
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Influence of impeller type on the flow and mixing in a stirred reactor
- 2000
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Ingår i: AIChE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 46:12, s. 2373-2382
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Tidskriftsartikel (refereegranskat)abstract
- Large eddy simulations (LES) of a stirred reactor with a liquid volume of 0.64 m3 were performed. The tank was stirred by either two standard Rushton impellers or two Scaba 6SRGT impellers. The LES can provide details of the flow field that cannot be obtained with so‐called Reynolds‐averaged equations and the corresponding models. The unsteady spatially filtered incompressible Navier‐Stokes equations were solved together with a transport equation for the concentration of an inert additive using a multigrid finite difference code with a staggered grid. The unresolved turbulent scales were modeled using a scale similarity model. The aim of this investigation has been to study the influence of impeller type on the flow structure and scalar transport. The results show that, compared at equal power input, the center plane velocities and the volume flow in the impeller stream do not differ much for the impeller types. Also, for the 6SRGT the periodic fluctuations associated with the blade passing is less pronounced
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