Numerical Modelling of Complex Buoyancy-Driven Flows

Applied Science

Numerical analysis of blood flow in realistic arteries subjected to strong non-uniform magnetic fields

The paper reports on a comprehensive mathematical model for simulations of blood flow under the presence of strong non-uniform magnetic fields. The model consists of a set of Navier–Stokes equations accounting for the Lorentz and magnetisation forces, and a simplified set of Maxwell’s equations (Biot–Savart/Ampere’s law) for treating the imposed magnetic fields. The relevant hydrodynamic and electromagnetic properties of human blood were taken from the literature. The model is then validated for different test cases ranging from a simple cylindrical geometry to real-life right-coronary arteries in humans. The time-dependency of the wall-shear-stress for different stenosis growth rates and the effects of the imposed strong non-uniform magnetic fields on the blood flow pattern are presented and analysed. It is concluded that an imposed non-uniform magnetic field can create significant changes in the secondary flow patterns, thus making it possible to use this technique for optimisations of targeted drug delivery.MSP/Multi-Scale PhysicsApplied Science

Turbulence anisotropy and coherent structures in electromagnetically generated vortex patterns

Chemical EngineeringApplied Science

Applications of an Embedded Seamless Hybrid RANS/LES Approach for Turbulent Dispersion over Complex Urban Areas

This work presents an application of a RANS/LES hybrid approach in simulating flows and turbulent dispersion in complex urban areas. It is demonstrated that thehybrid approach correctly captures the time-dependent behavior of the wake regions behind buildings, resulting in improvements of the total turbulent kinetic energy and, consequently, the turbulent dispersion of pollutants.The seamless variant of the hybrid RANS/LES approach proposed here, based on a dynamic evolution of the local interface zone, in combination with a generic-reaction set atmospheric chemistry model, proved to be numerically efficient and robust, and is recommended for future investigations of turbulent dispersion in real-scale city domains.ChemE/Transport Phenomen

On Electromagnetic Modulation of Flow Instabilities, Mixing and Heat Transfer in Conducting and Magnetized Fluids

In the present paper we give a concise review of some recent highlights of our research dealing with electromagnetic control of flow, mixing and heat transfer of electrically conductive or magnetized fluids. We apply a combination of state-of-art numerical (DNS and LES) and experimental (PIV and LIF) techniques to provide fundamental insights into the complex phenomena of interactions between imposed (or induced) electromagnetic fields and underlying fluid flow. Our analysis covers an extensive range of working fluids, i.e. weakly- and highly-electrically-conductive, as well as magnetized fluids. These interactions are defined through the presence of different types of body forces acting per volume of fluid. A fully closed system of governing equations containing an extended set of the Navier-Stokes and a simplified set of the Maxwell equations is presented. The four characteristic examples are selected: the electromagnetic control of self-sustained jet oscillations, the electromagnetic enhancement of heat transfer in thermal convection, the wake interactions behind magnetic obstacles and finally, the thermo-magnetic convection in differentially heated cubical enclosure. The comparative assessment between experimental and numerical results is presented. It is concluded that generally good agreement between simulations and experiments is obtained for all cases considered, proving the concept of electromagnetic modulation, which can be used in numerous technological applications.ChemE/Transport Phenomen

Large eddy simulations of targeted electromagnetic control of buoyancy-driven turbulent flow in a slender enclosure

We conducted a large eddy simulation (LES) of a locally applied electromagnetic control of turbulent thermal convection of an electrically conductive fluid (electrolyte solution) inside of a slender enclosure. Generic configurations, consisting of two or three magnets of opposite polarities located below the lower wall, and two oppositely charged electrodes along the side walls, are considered. The neutral situation (pure thermal convection) is selected to be in turbulent regime at Ra = 107, Pr = 7. A magnetically extended Smagorinsky type model for the subgrid turbulent stresses and a simple-gradient diffusion model for the subgrid turbulent heat fluxes are used. Different intensities of applied DC current through electrodes are imposed. The effects of the resulting Lorentz force on flow, turbulence reorganisation and wall-heat transfer are analysed. It is demonstrated that significant flow and turbulence structure reorganisation takes place in the proximity of the lower horizontal wall and in the central parts of the enclosure—even for weak DC current of I = 1 A. Significant turbulence increase, generated by the elevated electromagnetic mixing, produced significant enhancements of the wall-heat transfer—up to 70% for the 2-magnet configuration.Multi-Scale PhysicsApplied Science

Electromagnetic enhancement of turbulent heat transfer

We performed large eddy simulations (LES) of the turbulent natural convection of an electrically conductive fluid (water with 7% Na2SO4 electrolyte solution) in a moderate (4:4:1) aspect ratio enclosure heated from below and cooled from above and subjected to external nonuniformly distributed electromagnetic fields. Different configurations with permanent magnets (located under the lower thermally active wall, B0=1 T) and different strengths of imposed dc electric currents (I=0–10 A) were compared to the case of pure thermal convection in the turbulent regime, Ra=107, Pr=7. It is demonstrated that the electromagnetic forcing of the boundary layers caused significant reorganization of flow and turbulence structures producing significant enhancement of the wall-heat transfer (up to 188% for a configuration with 35 magnets and an applied dc current of 10 A).Multi-Scale PhysicsApplied Science

Numerical insights into magnetic dynamo action in a turbulent regime

We report on hybrid numerical simulations of a turbulent magnetic dynamo. The simulated set-up mimics the Riga dynamo experiment characterized by Re ? 3.5 × 106 and (Gailitis et al 2000 Phys. Rev. Lett. 84 4365–8). The simulations were performed by a simultaneous fully coupled solution of the transient Reynolds-averaged Navier–Stokes (T-RANS) equations for the fluid velocity and turbulence field, and the direct numerical solution (DNS) of the magnetic induction equations. This fully integrated hybrid T-RANS/DNS approach, applied in the finite-volume numerical framework with a multi-block-structured nonorthogonal geometry-fitted computational mesh, reproduced the mechanism of self-generation of a magnetic field in close accordance with the experimental records. In addition to the numerical confirmation of the Riga findings, the numerical simulations provided detailed insights into the temporal and spatial dynamics of flow, turbulence and electromagnetic fields and their reorganization due to mutual interactions, revealing the full four-dimensional picture of a dynamo action in the turbulent regime under realistic working conditions.Applied Science

Electromagnetically driven dwarf tornados in turbulent convection

Motivated by the concept of interdependency of turbulent flow and electromagnetic fields inside the spiraling galaxies, we explored the possibilities of generating a localized Lorentz force that will produce a three-dimensional swirling flow in weakly conductive fluids. Multiple vortical flow patterns were generated by combining arrays of permanent magnets and electrodes with supplied dc current. This concept was numerically simulated and applied to affect natural convection flow, turbulence, and heat transfer inside a rectangular enclosure heated from below and cooled from above over a range of Rayleigh numbers. The large-eddy simulations revealed that for low- and intermediate-values of Ra, the heat transfer was increased more than five times when an electromagnetic forcing was activated. In contrast to the generally accepted view that electromagnetic forcing will suppress velocity fluctuations and will increase anisotropy of turbulence, we demonstrated that localized forcing can enhance turbulence isotropy of thermal convection compared to its neutral state.Multi-Scale PhysicsApplied Science

Numerical Modeling of the Macroscopic Behavior of a Crowd of People under Emergency Conditions Triggered by an Incidental Release of a Heavy Gas: an Integrated Approach

In the present study, we focus on modeling and simulations of macroscopic behavior of a crowd of people under emergency conditions. We present a newly developed integrated numerical approach, which combines the time-dependent RANS method in predicting the temporal and spatial evolution of a heavy gas turbulent dispersion with the macroscopic model of a crowd movement. The coupling is imposed through locally determined concentration of the heavy gas which directly impacts the movement of the crowd of people. The potential of the developed approach is demonstrated in a series of cases that include the crowd behavior on an open railway platform and inside a train station, as well as predictions of field studies of turbulent dispersion of a heavy gas under windy conditions. Finally, various scenarios have been analyzed of the coupling between the local concentration of a potentially harmful heavy gas on crowd behavior through different forms of the cost functions. In conclusion, the version of the integrated model is recommended for future optimization studies of crowd dynamics following an incidental release of heavy gas.ChemE/Transport Phenomen