Imperial College London

ProfessorRaadIssa

Faculty of EngineeringDepartment of Mechanical Engineering

Professor of Practice (Computational Fluid Dynamics)
 
 
 
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Contact

 

+44 (0)20 7594 7038r.issa

 
 
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Location

 

662BCity and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

62 results found

Giustini G, Issa R, 2021, A method for simulating interfacial mass transfer on arbitrary meshes, Physics of Fluids, Vol: 33, ISSN: 1070-6631

This paper presents a method for modelling interfacial mass transfer in Interface Capturingsimulations of two-phase flow with phase change. The model enables mechanistic predictionof the local rate of phase change at the vapour-liquid interface on arbitrary computationalmeshes and is applicable to realistic cases involving two-phase mixtures with large densityratios. The simulation methodology is based on the Volume Of Fluid (VOF) representation ofthe flow, whereby an interfacial region in which mass transfer occurs is implicitly identified bya phase indicator, in this case the volume fraction of liquid, which varies from the valuepertaining to the ‘bulk’ liquid to the value of the bulk vapour. The novel methodologyproposed here has been implemented using the Finite Volume framework and solutionmethods typical of ‘industrial’ Computational Fluid Dynamics (CFD) practice. The proposedmethodology for capturing mass transfer is applicable to arbitrary meshes without the need tointroduce elaborate but artificial smearing of the mass transfer term as is often done in othertechniques. The method has been validated via comparison with analytical solutions for planarinterface evaporation and bubble growth test cases, and against experimental observations ofsteam bubble growth.

Journal article

Giustini G, Kim H, I Issa R, J Bluck Met al., 2020, Modelling microlayer formation in boiling sodium, Fluids, Vol: 5, Pages: 1-19, ISSN: 2311-5521

During boiling at a solid surface, it is often the case that a liquid layer of a few microns of thickness (’microlayer’) is formed beneath a bubble growing on the heated surface. Microlayers have been observed forming beneath bubbles in various transparent fluids, such as water and refrigerants, subsequently depleting due to evaporation, thus contributing significantly to bubble growth and possibly generating the majority of vapor in a bubble. On the other hand, boiling of opaque fluids, such as liquid metals, is not amenable to optical observations, and microlayers have not yet been observed in liquid metals. Among that class of fluids is sodium, suitable as a coolant for nuclear reactors and as the working fluid in phase-change solar power receivers. In order to support these applications, it is necessary to understand the boiling behavior of sodium and identify the parameters that might influence microlayer formation during boiling of this important fluid. This paper presents simulations of the hydrodynamics of sodium vapor bubble growth at a surface. An interface capturing flow solver has been implemented in the OpenFOAM code and used to predict the behavior of a sodium vapor bubble near a solid surface in typical boiling conditions. The methodology has been validated using recently reported direct experimental observations of microlayer formation in water and then applied to sodium boiling cases. Simulations indicate that microlayers are formed in sodium in a similar fashion to water. Comparison of simulation results with an extant algebraic model of microlayer formation showed good agreement, which increases confidence in the current predictions of microlayer formation. Typical values of microlayer thickness thus computed indicate that the microlayer is likely to play an important role during bubble growth in sodium.

Journal article

Sebilleau F, Issa R, Lardeau S, Walker SPet al., 2018, Direct Numerical Simulation of an air-filled differentially heated square cavity with Rayleigh numbers up to 10(11), INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, Vol: 123, Pages: 297-319, ISSN: 0017-9310

Journal article

Sebilleau F, Issa RI, Walker SP, 2015, Analysis of Turbulence Modelling Approaches to Simulate Single-phase Buoyancy Driven Counter-current Flow in a Tilted Tube, Flow Turbulence and Combustion, Vol: 96, Pages: 95-132, ISSN: 1573-1987

In the present paper, both Large Eddy Simulation (LES) and unsteady-RANS(uRANS) CFD studies of single-phase buoyancy-driven counter-current flow in a pipe arepresented for an Atwood number of 1.15 × 10−2 and an inclination angle of 15 degreesfrom the vertical. The basic flow phenomena involved are fundamentally the same as thoseencountered in various industrial applications including passive coolant flow in the loops ofa nuclear reactor. Earlier work on this type of flow was focused on its physical aspects usingboth experimental measurements and Direct Numerical Simulation (DNS). The presentwork investigates the performance of several commonly used LES eddy viscosity subgridscalemodels. The results show that LES is able to reproduce accurately the experimentalresults and that the dynamic Smagorinsky subgrid-scale model gives the best predictions.The results of those calculations were then used to obtain more information on the physicsof such flow. As regards uRANS simulations, a range of classic two-equation linear eddyviscosity models, based on low-y+ formulation at the wall and the single gradient diffusionhypothesis for the turbulent density fluxes were compared against experimental dataavailable in the literature. An elliptic blending Reynolds stresses model (EBRSM) with generalisedgradient diffusion hypothesis (GGDH) for the scalar fluxes was then implementedand compared with experiments. The latter showed very good agreement for the first ordermoment with the experimental data whereas all the two-equation eddy viscosity based modelsshowed rather high levels of discrepancy. The main cause of discrepancy was found tobe the underprediction of the axial turbulent buoyancy production effect, which has a moredetrimental impact on the eddy viscosity models than the second moment closure one

Journal article

Sebilleau F, Issa RI, Walker SP, Kansal A, Maheshwari NKet al., 2015, CFD and experimental analysis of single phase buoyancy driven counter-current flow in a pipe, Pages: 1275-1288

In the present paper, we study single-phase counter-current flow in a circular pipe as a model problem that is representative of flows occurring under various circumstances in a reactor primary loop, for example when emergency-cooling (ECCS) water is injected in the hot leg or when cooler fluid flows from the steam generator in the hot leg. In order to isolate the complexity of the turbulent mixing generated by buoyancy driven single-phase counter current flow, an experimental rig was built at the Bhabha Atomic Research Center (BARC) to validate CFD model predictions. This new rig is composed of two tanks of water linked by an inclined circular pipe. Initially the upper tank is filled with cold water and the lower one with heated water and the different-density fluids are allowed to mix under the influence of gravity. In this paper, thermocouple measurements of temperature at several locations in the rig are presented for several temperature differences and tilt angles. These experimental measurements are compared with state of the art highly-resolved large eddy simulation (LES). These LES computations (carried out with the commercial CFD package STAR-CCM+) give detailed information on the behaviour of the turbulence in such flow as well as serve to assess the performance of some uRANS two-equation eddy viscosity models that are also tested.

Conference paper

Cinosi N, Walker SP, Bluck MJ, Issa Ret al., 2014, CFD simulation of turbulent flow in a rod bundle with spacer grids (MATIS-H) using STAR-CCM+, Nuclear Engineering and Design: an international journal devoted to the thermal, mechanical, materials, and structural aspects of nuclear fission energy, Vol: 279, Pages: 37-49, ISSN: 0029-5493

This paper presents the CFD simulation of the turbulent flow generated by a model PWR spacer grid within a rod bundle. The investigation was part of the MATIS-H benchmark exercise, organized by the OECD-NEA, with measurements performed at the KAERI facilities in Daejeon, Korea. The study employed the CD-Adapco code Star-CCM+. An initial sensitivity study was conducted to attempt to assess the importance to the overall flow of components such as the outlet plenum and the end support grid; these were shown to be able to be safely neglected, but the tapered end portion of the rods was found to be significant, and this was incorporated in the model analyzed. A RANS model using any of K-epsilon, K-omega and Reynolds-stress turbulence models was found to be adequate for the prediction of mean velocity profiles, but they all three underestimate the time-averaged turbulent velocity components. Vorticity seems to be better predicted, although the measured values of vorticity are only presented via colored contour plots, making quantitative comparison rather difficult. Circulation, calculated via an integral for each channel, seems to be well predicted by all three models.

Journal article

Cinosi N, Walker SP, Bluck M, Issa RIet al., 2014, CFD ANALYSIS OF THE FLOW IN CRUD-COATED NUCLEAR ROD BUNDLES, 22nd International Conference on Nuclear Engineering (ICONE22), Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Sebilleau F, Kansal AK, Issa RI, Walker SPet al., 2014, CFD ANALYSIS OF SINGLE PHASE COUNTER-CURRENT BUOYANCY DRIVEN FLOWS AND ITS APPLICATIONS TO PASSIVE REACTOR DESIGN, 22nd International Conference on Nuclear Engineering (ICONE22), Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Lad B, Issa RI, 2012, A hybrid continuum/PDF model for the prediction of dispersed particulate flow, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 39, Pages: 148-158, ISSN: 0301-9322

Journal article

Issa RI, Montini M, 2010, Applicability of the Momentum-Flux-Parameter Closure for the Two-Fluid Model to Slug Flow, 6th International Symposium on Multiphase Flow, Heat Mass Transfer and Energy Conversion, Publisher: AMER INST PHYSICS, Pages: 712-722, ISSN: 0094-243X

Conference paper

Issa RI, 2010, Review of Applicability of the One-dimensional Two-fluid Model to the Prediction of Wave Growth and Slug Evolution in Horizontal Pipes, 6th International Symposium on Multiphase Flow, Heat Mass Transfer and Energy Conversion, Publisher: AMER INST PHYSICS, Pages: 74-80, ISSN: 0094-243X

Conference paper

Issa RI, Lad B, 2010, A PDF Based Approach For Modelling Dispersed Two-Phase Flows, 6th International Symposium on Multiphase Flow, Heat Mass Transfer and Energy Conversion, Publisher: AMER INST PHYSICS, Pages: 702-711, ISSN: 0094-243X

Conference paper

Issa RI, Barbeau S, Hale CP, Odozi U, Hewitt GF, Richardson SM, Wong WLet al., 2007, Measurement and prediction of slug characteristics in three-phase flows, 13th International Conference on Multiphase Production Technology, Pages: 153-169

This paper describes experimental and modelling studies of three-phase (oil-water-gas) flows in a 77.92mm diameter horizontal tube. Measurements were made of pressure gradient and of the spatial and temporal distribution of the contents of the respective phases. Phase content measurements were made using gamma- and X-ray systems capable of discriminating between the two liquid phases. Data were obtained for the time averaged liquid phase hold-ups and, by conditional sampling, the holdup in the bodies of the slugs. Data were also obtained on slug initiation and on the evolution of slug frequency along the (37m) channel. Slug evolution was found to be very different in water-continuous and oil-continuous systems. To predict the flows, the slug capturing methodology developed previously at Imperial College was extended to the prediction of gas entrainment in the liquid slugs. Here, the two-fluid model framework was retained for the three-phase flows by writing a single momentum equation for the combined liquid phases, taking account of the relative motion of the phases using a drift-flux model. Excellent agreement was obtained between the predictions and the experiments. © BHR Group 2007 Multiphase Production Technology 13.

Journal article

Issa RI, Bonizzi M, Barbeau S, 2006, Improved closure models for gas entrainment and interfacial shear for slug flow modelling in horizontal pipes, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 32, Pages: 1287-1293, ISSN: 0301-9322

Journal article

Behzadi A, Issa RI, Rusche H, 2004, Modelling of dispersed bubble and droplet flow at high phase fractions, CHEMICAL ENGINEERING SCIENCE, Vol: 59, Pages: 759-770, ISSN: 0009-2509

Journal article

Adechy D, Issa RI, 2004, Modelling of annular flow through pipes and T-junctions, COMPUTERS & FLUIDS, Vol: 33, Pages: 289-313, ISSN: 0045-7930

Journal article

Oliveira PJ, Issa RI, 2003, Numerical aspects of an algorithm for the Eulerian simulation of two-phase flows, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Vol: 43, Pages: 1177-1198, ISSN: 0271-2091

Journal article

Bonizzi M, Issa RI, 2003, A model for simulating gas bubble entrainment in two-phase horizontal slug flow, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 29, Pages: 1685-1717, ISSN: 0301-9322

Journal article

Bonizzi M, Issa RI, 2003, On the simulation of three-phase slug flow in nearly horizontal pipes using the multi-fluid model, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 29, Pages: 1719-1747, ISSN: 0301-9322

Journal article

Issa RI, Kempf MHW, 2003, Simulation of slug flow in horizontal and nearly horizontal pipes with the two-fluid model, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 29, Pages: 69-95, ISSN: 0301-9322

Journal article

Bonizzi M, Issa RI, Hewitt GF, Mendes-Tatsis A, Odozi Oet al., 2003, Studies of three phase oil-water-gas flow in pipelines, Cranfield, 11th international conference on multiphase; extending the boundaries of flow assurance, San Remo, Italy, Publisher: BHR Group, Pages: 407-426

Conference paper

Oliveira PJ, Issa RI, 2001, An improved PISO algorithm for the computation of buoyancy-driven flows, NUMERICAL HEAT TRANSFER PART B-FUNDAMENTALS, Vol: 40, Pages: 473-493, ISSN: 1040-7790

Journal article

Issa RI, Ubbink O, 1999, Numerical prediction of Taylor bubble dynamics using a new interface capturing technique, Pages: 1-6

Conference paper

Adechy D, Issa RI, 1999, Numerical modelling of horizontal annular flows, Pisa, Publisher: Edizioni ETS, Pages: 1607-1615

Conference paper

Ubbink O, Issa RI, 1999, A method for capturing sharp fluid interfaces on arbitrary meshes, Journal of Computational Physics, Vol: 153, Pages: 26-50, ISSN: 0021-9991

Journal article

Issa RI, Woodburn PJ, 1998, Numerical prediction of instabilities and slug formation in horizontal two-phase flows, Third international conference on multiphase flow ICMF '98 Lyon France, June 8-12 1998

Conference paper

Oliveira PJ, Issa RI, 1998, Numerical prediction of particle dispersion in a mixing layer using an Eulerian two-phase flow model, Proceedings of the ASME Fluids Engineering Division Summer Meeting Washington, DC June 21-25 1998 FEDSM98-5022, Publisher: American Society of Mechanical Engineers

Conference paper

Issa RI, Sadri MA, 1998, Numerical modelling of unsteady flow through a turbomachine stage, International Gas Turbine and Aeroengine Congress and Exhibition (Stockholm Sweden), Publisher: ASME, Pages: 1-9

Conference paper

Woodburn PJ, Issa RI, 1998, Well-posedness of one-dimensional transient, two-fluid models of two-phase flows, Proceedings of the ASME Fluids Engineering Division Summer Meeting Washington, DC June 21-25 1998, ASME Paper FEDSM98-5023, Publisher: American Society of Mechanical Engineers

Conference paper

Clayton RP, Leong WUA, Sanatian R, Issa RI, Xi Get al., 1998, A numerical study of the three dimensional turbulent flow in the impeller of a high speed centrifugal compressor, International gas turbine and aeroengine congress, Stockholm

Conference paper

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