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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... more
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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Research Interests: Materials Science and Wit
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The wake flow behind a cantilever beam of quadratic cross-section at a Reynolds number of 50,000 is investigated using detailed simulations. Two cases are considered, the first one using a stiff beam and the second one with a beam... more
The wake flow behind a cantilever beam of quadratic cross-section at a Reynolds number of 50,000 is investigated using detailed simulations. Two cases are considered, the first one using a stiff beam and the second one with a beam allowing for elastic deformation due to the hydrodynamic forces. The flow is simulated using an implicit large eddy simulation (ILES) approach in OpenFOAM and the structural deformation of the beam is found from a non-linear finite element approach using OOFEM. The motion of the fluid mesh due to the structural deformation is handled by an ALE method. The wake structures are investigated using proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) of the flow field. The results show that apart from the wake structures originating from the vortex shedding there is also a low frequency mode, which is an oscillatory motion in the stream-wise direction, present.
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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... more
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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Research Interests: Engineering, Mechanical Engineering, Chemical Engineering, Computer Science, Materials Science, and 12 moreParticle Image Velocimetry, Power, Computation Fluid Dynamics, PIV, LES, Continuous stirred tank reactor, Mixing Time, Stirred Tank, Large Eddy Simulation(LES), Cfd, Experimental Method, and Rushton Turbine
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SUMMARY A numerical and an experimental study of the flow of an incompressible fluid in a polar cavity is presented. The experiments included flow visualization, in two perpendicular planes, and quantitative measurements of the velocity... more
SUMMARY A numerical and an experimental study of the flow of an incompressible fluid in a polar cavity is presented. The experiments included flow visualization, in two perpendicular planes, and quantitative measurements of the velocity field by a laser Doppler anemometer. Measurements were done for two ranges of Reynolds numbers; about 60 and about 350. The stream function-vorticity form of the governing equations was approximated by upwind or central finite-differences. Both types of finite-difference approximations were solved by a multi-grid method. Numerical solutions were computed on a sequence of grids and the relative accuracy of the solutions was studied. Our most accurate numerical solutions had an estimated error of 0 1 per cent and 1 per cent for Re = 60 and Re = 350, respectively. It was also noted that the solution to the second order finite difference equations was more accurate, compared to the solution to the first order equations, only if fine enough meshes were used. The possibility of using extrapolations to improve accuracy was also considered. Extrapolated solutions were found to be valid only if solutions computed on fine enough meshes were used. The numerical and the experimental results were found to be in very good agreement.
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Among the first important observations concerning the role of fluid mechanics in atherogenesis were those made by Hugh and Fox [1] more than 20 years ago from carotid angiographies. From the angiograms they not only described the... more
Among the first important observations concerning the role of fluid mechanics in atherogenesis were those made by Hugh and Fox [1] more than 20 years ago from carotid angiographies. From the angiograms they not only described the localization of the atherosclerotic plaques at the origin of the internal carotid artery, but also drew conclusions regarding flow phenomena in the vessel. What they described as zones of contrast stasis supported the theory that hemodynamic factors contribute to atherosclerosis.
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Accurate numerical prediction of the flow in an IC-engine is a complex and demanding task. Besides the obvious problem of solving for the flow one must also be able to treat the geometry in a flexible manner and once there is combustion... more
Accurate numerical prediction of the flow in an IC-engine is a complex and demanding task. Besides the obvious problem of solving for the flow one must also be able to treat the geometry in a flexible manner and once there is combustion one has to include the interaction between turbulence and the combustion process. Using more or less ’standard’ methods and models, the ’state of the art’ offers the possibility of predicting, to a certain level of accuracy, the features and behaviour of the flow in the engine.
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LES computations have been carried out in a geometry involving three coannular swirling jets. Three explicit models are compared to the case without any explicit model. The influence on the mean values have found to be small, while the... more
LES computations have been carried out in a geometry involving three coannular swirling jets. Three explicit models are compared to the case without any explicit model. The influence on the mean values have found to be small, while the fluctuations are influenced in the developing region of the jets. The magnitude of the dissipation effect is dominating over other effects of the sub-grid scales (such as backscatter and non-local effects). Using implicit dissipation (based upon the numerical scheme) is not a problem if the spatial resolution is adequate and when the inertial sub-range is well resolved. Three SGS models for the scalar transport equations have also been evaluated. The passive scalar is affected both by the momentum SGS terms as well as the SGS term of the scalar equation.
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Transonic flows imply that the flow is subsonic in certain parts of the domain of interest and is supersonic in others. In most cases the flow decelerates from the supersonic speed to the subsonic one through a fast compression layer.... more
Transonic flows imply that the flow is subsonic in certain parts of the domain of interest and is supersonic in others. In most cases the flow decelerates from the supersonic speed to the subsonic one through a fast compression layer. This compression layer is often very thin (of the order of several mean distance among the air molecules). The thin layer is called a shock-wave. Naturally, within the shock layers the continuum approximation of the fluid is not very good. However, if one uses the weak formulation (i.e. one seeks a weak solution) the continuum formulation, which accomodates discontinuities becomes a very good approximation to real flows. Transonic flows are non-linear in their character, and hence the location of shocks is unknown a-priori. Therefore, computing flows with shocks implies that one has to compute also the position of the shock. Computing a weak solution (in a strict sense) implies that the governing equations are valid only when the flow is smooth while across shocks one has to use the shock-jump (Rankine-Hugoniot, R-H) relations. As a consequence, the basic approach until the beginning of the seventies, was to use a so called “shock-fitting” technique. Shock fitting implies that the shape of the shock is adjusted so that the R-H relations aresatisfied. The approach is less complex for 2-D cases but becomes impractical for 3-D shocks. Thus, the competitive approach of “shock capturing” became the method of choice when computing general transonic flows. Shock capturing is possible by relaxing the assumption of computing the weak solution in the strict sense.
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... The model equations include the mass-averaged Navier-Stokes equations, the energy equation, the k-~ turbulence model and Magnussen-Hjertager's chemcial reaction model. ... 7. A. Brandt, Multi-level adaptive solutions... more
... The model equations include the mass-averaged Navier-Stokes equations, the energy equation, the k-~ turbulence model and Magnussen-Hjertager's chemcial reaction model. ... 7. A. Brandt, Multi-level adaptive solutions to boundary-value problems. Maths Comput. ...
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ABSTRACT
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ABSTRACT
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The flow around two wind turbines with constant axial but varying lateral spacing is computed to evaluate their interaction. The solver is based on finite differences on a cartesian grid. Turbulence is accounted for by Large Eddy... more
The flow around two wind turbines with constant axial but varying lateral spacing is computed to evaluate their interaction. The solver is based on finite differences on a cartesian grid. Turbulence is accounted for by Large Eddy Simulations whereas the solid objects are modeled using the Immersed Boundary Method. The computations revealed no major influence of the placement of downstream wind turbine on the right or left side of the upstream one. Furthermore, the wake generated by the upstream wind turbine was found to have significant impact up to a lateral spacing of approximately one rotor diameter.
A lifted turbulent flame in a vitiated co-flow is studied using Large Eddy Simulation together with a perfectly stirred reactor based closure. The closure generates chemical look-up tables that are further used to close the filtered... more
A lifted turbulent flame in a vitiated co-flow is studied using Large Eddy Simulation together with a perfectly stirred reactor based closure. The closure generates chemical look-up tables that are further used to close the filtered temperature equations and to compute local radical concentrations throughout the computational domain. The two-scalar approach has been used to simulate a lifted turbulent flame. The numerical predictions are compared to detailed experimental data obtained by Cabra et al. (2002). The agreement between the two sets of data is very good indicating that the present approach predicts successfully the flame lift-off and the combustion process. The LES data is also used to study the unsteady flame stabilization. The influence of the large scale turbulent structures on the fuel/air mixing as well as on the combustion is highlighted. INTRODUCTION Turbulent combustion is a difficult topic involving non-linear multi-scale phenomena. As a result, turbulent flames a...
ABSTRACT This paper considers the effects of intermittent injection of a liquid jet or spray on the initial break-up and mixing of one fluid with the surrounding ambient fluid. The aim of the analysis is to describe the physical process... more
ABSTRACT This paper considers the effects of intermittent injection of a liquid jet or spray on the initial break-up and mixing of one fluid with the surrounding ambient fluid. The aim of the analysis is to describe the physical process and indicate the mechanisms that control the mixing under different flow conditions (time-dependent injection and its frequency relative to the time scales of the flow) and fluid properties (density ratio, Schmidt number for a single phase case which is studied for comparison, or the Weber number for the two-phase cases. The computations use Large Eddy Simulation (LES) to account for turbulence, and either Volume Of Fluid (VOF) for the initial break-up or Lagrangian Particle Tracking (LPT) with droplet break-up model in the case of liquid droplets injected into the ambient gas. The results show that, depending on the physical properties of the liquid and ambient gas, the initial break-up and turbulent mixing can be enhanced substantially with intermittent injection. The numerical modeling is validated by recovering key results of experimental and analytical works. It can be observed that a main effect during the mixing is the suction of ambient fluid at the tail of the injected liquid, which depends on the fluid properties. Increased injection frequency shows to increase the mixing significantly during the initial transient phase.
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ABSTRACT In this paper, numerical studies are reported on the effect of flow-flame interaction at large and medium scales and its impact on flame stabilization in a lean premixed low swirl stabilized methane/air flame. The numerical... more
ABSTRACT In this paper, numerical studies are reported on the effect of flow-flame interaction at large and medium scales and its impact on flame stabilization in a lean premixed low swirl stabilized methane/air flame. The numerical simulations are based on a large eddy simulation (LES) approach with a three-scalar flamelet model with equations for mixture fraction and fuel mass fraction and the level-set G-equation to account respectively for stratification of the mixture, fuel leakage at the trailing edge of the flame, and tracking of the flame front. Distinct frequencies, associated with the flame stabilization process, are identified from point data of LES in the outer and inner shear layers of the burner induced flow field. To understand the effect of the spatial structures related to the observed flow frequencies, a dynamic mode decomposition (DMD) is performed. Based on the analysis of LES data, frequency specific coherent flow structures are extracted along with associated flame structures through an extended version of DMD. The inner shear layer generated vortices are associated with recurring frequency specific coherent structures of both flow and flame and contribute to the flame stabilization in the outer regions of the flow.