@article {Simula.sc.962,
	title = {MHD Flow Past a Circular Cylinder Using the Immersed Boundary Method},
	journal = {Computers \& Fluids},
	volume = {39},
	number = {2},
	year = {2010},
	note = {Appeared online 2009.},
	month = {February},
	pages = {345-358},
	abstract = {The immersed boundary method (IB hereafter) is an efficient numerical methodology for treating purely hydrodynamic flows in geometrically complicated flow-domains. Recently Grigoriadis et als. [1] proposed an extension of the IB method that accounts for electromagnetic effects near non-conducting boundaries in magnetohydrodynamic (MHD) flows. The proposed extension (hereafter called MIB method) integrates naturally within the original IB concept and is suitable for magnetohydrodynamic (MHD) simulations of liquid metal flows. It is based on the proper definition of an externally applied current density field in order to satisfy the Maxwell equations in the presence of arbitrarily-shaped, non-conducting immersed boundaries. The efficiency of the proposed method is achieved by fast direct solutions of the two poisson equations for the hydrodynamic pressure and the electrostatic potential. The purpose of the present study is to establish the performance of the new MIB method in challenging configurations for which sufficient details are available in the literature. For this purpose, we have considered the classical MHD problem of a conducting fluid that is exposed to an external magnetic field while flowing across a circular cylinder with electrically insulated boundaries. Two- and three-dimensional, steady and unsteady, flow regimes were examined for Reynolds numbers Red ranging up to 200 based on the cylinder{\textquoteright}s diameter. The intensity of the external magnetic field, as characterized by the magnetic interaction parameter N, varied from N=0 for the purely hydrodynamic cases up to N=5 for the MHD cases. For each simulation, a sufficiently fine Cartesian computational mesh was selected to ensure adequate resolution of the thin boundary layers developing due to the magnetic field, the so called Hartmann and sidewall layers. Results for a wide range of flow and magnetic field strength parameters show that the MIB method is capable of accurately reproducing integral parameters, such as the lift and drag coefficients, as well as the geometrical details of the recirculation zones. The results of the present study suggest that the proposed MIB methodology provides a powerful numerical tool for accurate MHD simulations, and that it can extend the applicability of existing Cartesian flow solvers as well as the range of computable MHD flows. Moreover, the new MIB method has been used to carrry out a series of accurate simulations allowing the determination of asymptotic laws for the lift and drag coefficients and the extent of the recirculation length as a function of the amplitude of the magnetic field. These results are reported herein.},
	doi = {10.1016/j.compfluid.2009.09.012},
	author = {D. G. E. {Grigoriadis} and I. E. {Sarris} and Stavros C. {Kassinos}}
}
@inproceedings {Simula.sc.1008,
	title = {Numerical Modeling of Turbulent Airflow and Particle Deposition in a Bifurcating Airway Model},
	journal = {World Congress on Medical Physics and Biomedical Engineering, September 7 - 12, 2009, Munich, Germany},
	volume = {25},
	number = {4},
	year = {2010},
	note = {Is listed in 2009 annual report},
	pages = {2089-2092},
	publisher = {Springer Berlin Heidelberg},
	type = {Conference},
	abstract = {Understanding transport and deposition of inhaled particles in the human airways plays a crucial role in the targeted therapy of pulmonary diseases, and the administration of inhaled medicines. Numerous researchers have studied the inhalation of particles using experiments or computer models. Even though experiments have shown that the airflow in the trachea and the upper branches of the lung is turbulent, the flow is taken to be laminar in most computer models. Only few recently published papers have looked at the turbulent transport of air in the human airways. Even fewer results have been published on the effect of the upper airway structures on the turbulent airflow in the lungs or on the effect of the turbulence on particle deposition. The previously published turbulent models have also mainly used RANS methods to predict the flow. To study the unsteady flow and particle deposition in a human lung, an LES model with a dynamic Smagorinsky sub-grid scale model was used. The model equations were solved to study steady inspirational flow at different flow rates for different particle sizes. Results indicate that the upper airway geometry produces turbulence in the flow and the deposition of particles is mainly affected by the particle size and Stokes number.},
	isbn = {978-3-642-03882-2},
	doi = {10.1007/978-3-642-03882-2\_554},
	author = {Radhakrishnan, Harikrishnan and Stavros C. {Kassinos}},
	editor = {D{\"o}ssel, Olaf and Wolfgang C. {Schlegel}}
}
@article {Simula.sc.992,
	title = {Analytic Models of Heterogenous Magnetic Fields for Liquid Metal Flow Simulations},
	journal = {Theoretical and Computational Fluid Dynamics},
	volume = {23},
	number = {6},
	year = {2009},
	pages = {571-578},
	abstract = {A physically consistent approach is considered for defining an external magnetic field as needed in computational fluid dynamics problems involving magnetohydrodynamics (MHD). The approach results in simple analytical formulae that can be used in numerical studies where an inhomogeneous magnetic field influences a liquid metal flow. The resulting magnetic field is divergence and curl-free, and contains two components and parameters to vary. As an illustration, the following examples are considered: peakwise, stepwise, shelfwise inhomogeneous magnetic fields, and the field induced by a solenoid. Finally, the impact of the streamwise magnetic field component is shown qualitatively to be significant for rapidly changing fields.},
	doi = {10.1007/s00162-009-0114-9},
	author = {E. V. {Votyakov} and Stavros C. {Kassinos} and Albets-Chico, X.}
}
@inproceedings {Simula.sc.1012,
	title = {CFD Modeling of Turbulent Flow and Particle Deposition in Human Lungs},
	journal = {Conference Proceedings of the International Conference of IEEE Engineering in Medicine and Biology Society (2009)},
	year = {2009},
	pages = {2867-2870},
	publisher = {IEEE Explore},
	type = {Conference},
	abstract = {Understanding transport and deposition of inhaled particles in the human airways plays a crucial role in the targeted therapy of pulmonary diseases, and the administration of inhaled medicines. Numerous researchers have studied the inhalation of particles using experiments or computer models. Even though experiments have shown that the airflow in the trachea and the upper branches of the lung is turbulent, the flow is taken to be laminar in most computer models. Only few recently published papers have looked at the turbulent transport of air in the human airways. Even fewer results have been published on the effect of the upper airway structures on the turbulent airflow in the lungs or on the effect of the turbulence on particle deposition. The previously published turbulent models have also mainly used RANS methods to predict the flow. To study the unsteady flow and particle deposition in a human lung, an LES model with a dynamic Smagorinsky sub-grid scale model was used. The model equations were solved to study steady inspirational flow at different flow rates for different particle sizes. Results indicate that the upper airway geometry produces turbulence in the flow and the deposition of particles is mainly affected by the particle size and Stokes number.},
	author = {Radhakrishnan, Harikrishnan and Stavros C. {Kassinos}}
}
@article {Simula.sc.974,
	title = {Direct Simulation of the Limiting Flux: I. Interpretation of the Experimental Results},
	journal = {Journal of Membrane Science},
	volume = {337},
	number = {1-2},
	year = {2009},
	month = {July},
	pages = {81-91},
	abstract = {Using a 2D fully coupled numerical model, the limiting flux phenomenon in the ultrafiltration of dextran was directly simulated assuming neither constant permeate velocity nor constant wall concentrations. It was found that the average permeate velocity agrees well with the permeate flux of Jonsson{\textquoteright}s experiment [G. Jonsson, Boundary layer phenomena during ultrafiltration of dextran and whey protein solutions, Desalination 51 (1984) 61-77], while significant axial variations of wall concentration and permeate velocity are maintained. This suggests that the limiting flux is actually the result of such axial variations, and therefore, assuming constant wall concentration or constant permeate velocity to interpret the experiment is inappropriate under the conditions investigated. The effects of osmotic pressure coefficients on permeate flux and wall concentrations, and the role of concentration-dependent viscosity in reaching the limiting flux, were further assessed. It was found that the permeate flux, and therefore the limiting flux, is not significantly affected by the osmotic pressure coefficients, although the magnitude of the wall concentration is considerably affected by osmotic pressure estimations. The concentration-dependent viscosity was found to be a critical factor for reaching the limiting flux under the simulation conditions. These findings imply that, in interpreting the results of limiting flux experiments, it is vital to include the axial variations of the wall concentration and permeate velocity and the impact of the variations of fluid properties.},
	doi = {10.1016/j.memsci.2009.03.031},
	author = {Ma, Shengwei and Stavros C. {Kassinos} and Kassinos, Despo}
}
@inproceedings {Simula.sc.1004,
	title = {Extension of the Immersed Boundary Method for Liquid-Metal Magnetohydrodynamics},
	journal = {Immersed Boundary Methods: Current status and Future Research Directions},
	year = {2009},
	type = {1},
	abstract = {Liquid-metal magnetohydrodynamics (MHD hereafter) are met in a variety of challenging industrial applications (metalheating, pumping, stirring, blankets of fusion reactors) as well as in geophysics whenever a magnetic field interacts with the motion of a conductive fluid. The present study forms the first attempt to simulate these flows using a non-boundary conforming methodology such as the immersed boundary method (IB hereafter). It is motivated by the belief that the IB method could bring to MHD simulations the same advantages it offers for hydrodynamics. We have recently presented [1] an extension of the IB methodology for efficient MHD simulations in geometrically complicated domains using a Cartesian flow solver and an identical, direct Poisson solver for both the hydrodynamic pressure and the electric potential fields. A projection scheme and a suitable forcing scheme for electric density currents in the vicinity of non-conducting immersed surfaces were suggested. The methodology has been extensively tested for several MHD flows at Hartmann numbers Ha=5-2000, reaching an excellent agreement with numerical or analytical solutions. The projection and forcing schemes for current densities were found capable of satisfying the charge conservation law in the presence of immersed boundaries. Finally, we demonstrate how the proposed extension can be used to extend the applicability of existing flow solvers using the IB concept, and extend the range of computable wall-bounded MHD flows.},
	author = {D. G. E. {Grigoriadis} and Stavros C. {Kassinos}}
}
@article {Simula.sc.966,
	title = {Immersed Boundary Method for the MHD Flows of Liquid Metals},
	journal = {Journal of Computational Physics},
	volume = {228},
	number = {3},
	year = {2009},
	note = {Is listed in 2008 Annual Report with incorrect year of publication.},
	month = {February},
	pages = {903-920},
	abstract = {Wall-bounded magnetohydrodynamic (MHD hereafter) flows are of great theoretical and practical interest. Even for laminar cases, MHD simulations are associated with very high computational cost due to the resolution requirements for the Hartmann and side layers developing in the presence of solid obstacles. In the presence of turbulence, these difficulties are further compounded. Thus, MHD simulations in complex geometries are currently a challenge. The immersed boundary (IB hereafter) method is a reliable numerical tool for efficient hydrodynamic field simulations in arbitrarily geometries, but it has not yet been extended for MHD simulations. The present study forms the first attempt to apply the IB methodology for the computation of both the hydrodynamic and MHD fields. A consistent numerical methodology is presented that is appropriate for efficient 3D MHD simulations in geometrically complicated domains using cartesian flow solvers. For that purpose, a projection scheme for the electric current density is presented, based on an electric potential correction algorithm. A suitable forcing scheme for electric density currents in the vicinity of non-conducting immersed surfaces is also proposed. The proposed methodology has been first extensively tested for Hartmann layers in fully-developed and developing channel and duct flows at Hartmann numbers Ha=500-2000. In order to demonstrate the potential of the method, the three-dimensional MHD flow around a circular cylinder at Reynolds number Re=200 is also presented. The effects of grid resolution and variable arrangement on the simulation accuracy and consistency were examined. When compared with existing numerical or analytic solutions, excellent agreement was found for all the cases considered. The proposed projection and forcing schemes for current densities were found capable of satisfying the charge conservation law in the presence of immersed non-conducting boundaries. Finally, we show how the proposed methodology can be used to extend the applicability of existing flow solvers that use the IB concept with a staggered variable arrangement.},
	author = {D. G. E. {Grigoriadis} and Stavros C. {Kassinos} and E. V. {Votyakov}}
}
@article {Simula.sc.970,
	title = {Lagrangian Particle Dispersion in Turbulent Flow Over a Wall Mounted Obstacle},
	journal = {International Journal of Heat and Fluid Flow},
	volume = {30},
	number = {3},
	year = {2009},
	pages = {462-470},
	abstract = {Large-eddy simulations (LES) of particle-laden turbulent flows are presented in order to investigate the effects of particle response time on the dispersion patterns of a space developing flow with an obstruction, where solid particles are injected inside the wake of an obstacle [Vincont, J.Y., Simoens, S., Ayrault M., Wallace, J.M., 2000. Passive scalar dispersion in a turbulent boundary layer from a line source at the wall and downstream of an obstacle. J. Fluid Mech. 424, 127-167]. The numerical method is based on a fully explicit fractional step approach and finite-differences on Cartesian grids, using the immersed boundary method (IBM) to represent the existence of solid obstacles. Two different turbulence models have been tested, the classical Smagorinsky turbulence model and the filtered structure function model. The dispersed phase was modelled either by an Eulerian approach or a Lagrangian particle tracking scheme of solid particles with Stokes numbers in the range St = 0-25, assuming one-way coupling between the two phases. A very good agreement was observed between the Lagrangian and Eulerian approaches. The effect of particle size was found to significantly differentiate the dispersion pattern for the inhomogeneous flow over the obstacle. Although in homogeneous flows like particle-laden turbulent channels near-wall particle clustering increases monotonically with particle size, for the examined flow over an obstacle, preferential concentration effects were stronger only for an intermediate range of Stokes numbers.},
	doi = {10.1016/j.ijheatfluidflow.2009.01.010},
	author = {D. G. E. {Grigoriadis} and Stavros C. {Kassinos}}
}
@inproceedings {Simula.sc.996,
	title = {Turbulent Effects of Liquid Metal Flow Under Strong Fringing Magnetic Fields},
	journal = {6th International Symposium on Turbulence and Shear Flow Phenomena},
	year = {2009},
	type = {Conference},
	author = {Albets-Chico, X. and D. G. E. {Grigoriadis} and Stavros C. {Kassinos} and Knaepen, B.}
}
@inproceedings {Simula.sc.1010,
	title = {Using LES to Model Turbulent Particle Transport in Human Lungs},
	journal = {The 6th International Symposium on Turbulence and Shear Flow Phenomena (TSFP6)},
	year = {2009},
	month = {June},
	type = {Conference},
	author = {Radhakrishnan, Harikrishnan and Stavros C. {Kassinos}}
}
@inproceedings {Simula.simula.78,
	title = {Efficient Simulations of Wall Bounded Magnetohydrodynamics Flows},
	journal = {6th GRACN International Congress on Computational Mechanics},
	year = {2008},
	type = {Conference},
	isbn = {978-960-6706-08-0},
	author = {D. G. E. {Grigoriadis} and Stavros C. {Kassinos}}
}
@inproceedings {Simula.sc.1034,
	title = {Lagrangian Particle Dispersion in Turbulent Flow Over a Wall Mounted Obstacle},
	journal = {7th international ERCOFTAC Symposium on Engineering Turbulence Modeling and Measurements},
	volume = {2},
	year = {2008},
	pages = {486-491},
	type = {Conference},
	author = {D. G. E. {Grigoriadis} and Stavros C. {Kassinos}}
}
@inproceedings {Simula.sc.1040,
	title = {Modeling Particle Deposition in the Human Lungs},
	journal = {6th GRACM International Congress on Computational Mechanics},
	year = {2008},
	type = {Conference},
	isbn = {978-960-6706-08-0},
	author = {Radhakrishnan, Harikrishnan and Stavros C. {Kassinos}}
}
@inproceedings {Simula.sc.1042,
	title = {Using LES to Model Turbulent Particle Transport in Lungs},
	journal = {7th international ERCOFTAC Symposium on Engineering Turbulence Modeling and Measurements},
	number = {3},
	year = {2008},
	pages = {856-861},
	type = {Conference},
	author = {Radhakrishnan, Harikrishnan and Stavros C. {Kassinos}}
}
