Members

IMMC

Miltiadis Papalexandris
Professor
Contact - Personnal web page
Recent publications

received an MSc degree in Naval Architecture & Marine Engineering from the National Technical University of Athens and MSc and PhD degrees in Aeronautics from the California Institute of Technology (Caltech). Soon after the completion of his PhD, he joined the Engineering Staff of NASA's Jet Propulsion Laboratory. While at NASA, he worked mainly on thermal control and optical modeling of space telescopes, including the James Webb Space Telescope (JWST) and the Laser Interferometry Space Antenna (LISA). In 2002 he became a member of the academic personnel (faculty) at UCL where he remains until now. He is the recipient of the William Balhaus Dissertation Prize of Caltech, NASA's Space Act Award, and the NOVA Award of Excellence of NASA. Prof. Papalexandris is an Associate Fellow of the American Institute of Aeronautics and Astronautics (AIAA).




The research activities of his group lie primarily on the fields of Theoretical and Computational Fluid Dynamics with particular emphasis on the fundamentals of multi-phase flows, complex fluids, and reacting flows. These activities cover: i) development of mathematical models for the flows of interest, ii) algorithm development and implementation for these models, iii) software verification and validation, and iv) detailed numerical studies and simulations via high performance computing.

IMMC main research direction(s):
Computational science
Energy
Fluid mechanics

Keywords:
non-equilibrium thermodynamics
reacting flows
two-phase flows

Research group(s): TFL

PhD and Post-doc researchers under my supervision:


A Comprehensive Study of Turbulent Natural Convection in a Pool heated from Below with an Evaporating Free Surface
William Andrew Hay

The PhD focuses on turbulent natural convection, thermal mixing and evaporation from the free surface of a Spent Fuel Pool (SFP) undergoing a Loss of Coolant (or Loss of Cooling) Accident (LOCA).

The physical phenomena will be better understood via CFD simulations using the openSource CFD code openFOAM. Simulation results will be validated against experimental results measuring PIV velocity an bulk and surface temperature measurements on a simplified geometry


Simulation of injection and combustion of Indian-origin biofuels in engines.
Constantin Sula

The topic of my research project is the modeling and simulation of turbulent reactive multiphase flows. The project is related to the application of bio-based fuels in combustion devices. The focus of the research is fuel injection and the combustion process in engines.

I am a member of the multi-phase and reacting flows group at the University of Louvain-la-Neuve, supervised by Professor Miltiadis V. Papalexandris. The research is conducted in close collaboration with an international consortium (including the University of Helsinki (Finland), Physikalisch-Technische Bundesanstalt (Germany), Goa University and Indian Institute of Technology Madras (both India)). The overall aim of the consortium is to research sustainable alternative energies. This involves the development of engines using efficient biofuels.

The aims of the doctoral research project are summarized as follows:

(i) Implementation of the biofuel properties and reaction kinetics

(ii) CFD modeling of the flow and combustion inside the engine

(iii) Validation of the simulations

(iv) Improvement the engine efficiency


Numerical Modeling and Simulation of Sediment Mobilisation and Transport due to Turbulent Currents
Anouk Riffard

The proposed doctoral research evolves around two principal axes. The first one is the

development of mathematical models and algorithms for flows of fluid-solid particles mixtures,

i.e. granular suspensions. The second one is the use of these algorithms for the study of

sediment mobilisation and transport due to turbulent currents.


Electric charge generation and transport in turbulent flows
Mathieu Calero

The general objective of this thesis is to advance the state-of-the-art in the mathematical modelling and numerical simulation of turbulent flows involving electrically charged fluids. The specific goals of the proposed research are the following. Firstly, the development of efficient numerical methodologies and related parallel computer codes for the prediction of electric charge transport in turbulent flows. Secondly,the development of a computational model for charge generation at fluid – solid wall interfaces. Then, the study of electric charge generation and transport in real-life industrial turbulent flows via numerical simulations, and comparisons with experiments. Finally, based on the findings, the improvement of safety for flows of electrically charged fluids that are used in the process industries.


Convection naturelle et ébullition dans et autour de milieux poreux immergés et exposés à des sources de chaleur internes
Victoria Hamtiaux

My doctoral research propose to advance the state-of-the-art in the modelling and simulation of natural convection in domains with immersed porous structures. Such flows are encountered in numerous natural phenomena (wind through urban areas, forest fires, and others) and technological applications (rapid heat-transfer devices, spent-fuel pools of nuclear power stations etc.) The motivation for my study comes from the need for improved understanding of convection and boiling phenomena that occur during a Loss of Cooling Accident (LOCA) in spent fuel pools of nuclear power stations; with this regard, the storage racks of used fuel are macroscopically modeled as a porous medium.
Concerning the model, the solid matrix and the fluid are modeled as two distinct continuous media. A single-domain approach is used, i.e. a single set of equations is employed for the fluid that is valid in both porous and pure-fluid subdomains. The model also considers the phase change of water.



Recent publications

See complete list of publications

Journal Articles


1. Varsakelis, Christos; Papalexandris, Miltiadis. Bridging the gap between the Darcy- Brinkman equations and the Nielsen model for tortuosity in polymer-filled systems. In: Chemical Engineering Science, Vol. 213, p. #115394 (2020). http://hdl.handle.net/2078.1/223098

2. Ceresiat, Lise; Grosshans, Holger; Papalexandris, Miltiadis. Powder electrification during pneumatic transport: The role of the particle properties and flow rates. In: Journal of Loss Prevention in the Process Industries, Vol. 58, no., p. 60-69 (2019). doi:10.1016/j.jlp.2019.01.010. http://hdl.handle.net/2078.1/213706

3. Hay, William Andrew; Papalexandris, Miltiadis. Numerical simulations of turbulent thermal convection with a free-slip upper boundary. In: Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, Vol. 475, p. #20190601 (2019). http://hdl.handle.net/2078.1/223105

4. Papalexandris, Miltiadis. On the applicability of Stokes’ hypothesis to low-Mach-number flows. In: Continuum Mechanics and Thermodynamics : analysis of complex materials and judicious evaluation of the environment, (2019). doi:10.1007/s00161-019-00785-z. http://hdl.handle.net/2078.1/219906

5. Grosshans, H.; Villafañe, L.; Banko, A.; Papalexandris, Miltiadis. Case study on the influence of electrostatic charges on particle concentration in turbulent duct flows. In: Powder Technology, Vol. 357, p. 46-53 (2019). doi:10.1016/j.powtec.2019.08.106. http://hdl.handle.net/2078.1/219922

6. Grosshans, Holger; Papalexandris, Miltiadis. Exploring the mechanism of inter-particle charge diffusion. In: The European Physical Journal - Applied Physics, Vol. 82, p. #11101 (2018). doi:10.1051/epjap/2018170360. http://hdl.handle.net/2078.1/198613

7. Monsorno, Davide; Dimas, Athanassios; Papalexandris, Miltiadis. Time-accurate calculation of two-phase granular flows exhibiting compaction, dilatancy and nonlinear rheology. In: Journal of Computational Physics, Vol. 372, p. 799-822 (2018). doi:10.1016/j.jcp.2018.06.061. http://hdl.handle.net/2078.1/199860

8. Grosshans, Holger; Szasz, Robert_Zoltan; Papalexandris, Miltiadis. Influence of the Rotor Configuration on the Electrostatic Charging of Helicopters. In: AIAA Journal : devoted to aerospace research and development, Vol. 56, no. 1, p. 368-375 (2018). doi:10.2514/I.J056242. http://hdl.handle.net/2078.1/187437

9. Georgiou, Michail; Papalexandris, Miltiadis. Direct numerical simulation of turbulent heat transfer in a T-junction. In: Journal of Fluid Mechanics, Vol. 845, p. 581-614 (2018). doi:10.1017/jfm.2018.256. http://hdl.handle.net/2078.1/197405

10. Schwindt, N.; von Pidoll, U.; Markus, D.; Klausmeyer, U.; Papalexandris, Miltiadis; Grosshans, Holger. Measurement of electrostatic charging during pneumatic conveying of powders. In: Journal of Loss Prevention in the Process Industries : the international journal of chemical and process plant safety, Vol. 49, no. B, p. 461-471 (2017). doi:10.1016/j.jlp.2017.05.028. http://hdl.handle.net/2078.1/185286


Conference Papers


1. Papalexandris, Miltiadis. Can we always neglect the bulk viscous pressure in variable- density flows. http://hdl.handle.net/2078.1/223101

2. Hay, William Andrew; Papalexandris, Miltiadis. Turbulent natural convection in a cavity with a free surface under non-Oberbeck-Boussinesq conditions. http://hdl.handle.net/2078.1/223103

3. Hay, William Andrew; Deledicque, Vincent; Papalexandris, Miltiadis. Numerical Simulations of Turbulent Rayleigh-Bénard Convection with a Free Surface. In: Proceedings of the 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH 2019). In: Proceedings of the 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH 2019), American Nuclear Society, 2019, 978-0-89448-767-5. http://hdl.handle.net/2078.1/219905

4. Grosshans, Holger; Susanti, N.; Papalexandris, Miltiadis. Experimental evaluation of deposit formation during powder transport. http://hdl.handle.net/2078.1/223104

5. Sula, Constantin; Papalexandris, Miltiadis; Grosshans, Holger. Numerical modeling of the secondary droplet break-up in spray flows. http://hdl.handle.net/2078.1/215242

6. Sula, Constantin; Grosshans, Holger; Papalexandris, Miltiadis. Modeling droplet evaporation and secondary breakup for simulations of spray combustion. http://hdl.handle.net/2078.1/215243

7. Ceresiat, Lise; Grosshans, Holger; Papalexandris, Miltiadis. The role of particle properties on powder electrification during pneumatic transport. http://hdl.handle.net/2078.1/202884

8. Grosshans, Holger; Papalexandris, Miltiadis. Influence of electrostatic charges and solid-mass loading on particle dynamics in duct flows. http://hdl.handle.net/2078.1/202887

9. Hay, William Andrew; Papalexandris, Miltiadis. A Numerical Study of Turbulent Thermal Convection in a Cavity with Evaporation at the Free Surface. http://hdl.handle.net/2078.1/202883

10. Grosshans, Holger; Villafãne, Laure; Banko, A.; Papalexandris, Miltiadis. Influence of electrostatic charges on the particle concentration in wall-bounded turbulent flows. In: Proceedings, 8th World Congress on Particle Technology, Orlando, FL, 2018, 978-0-8169-1105-9. http://hdl.handle.net/2078.1/197602


Books


1. Papalexandris, Miltiadis. Lecture Notes on Combustion and Fuels. 2017. 132 pages. http://hdl.handle.net/2078.1/191232

2. Papalexandris, Miltiadis. Unsplit numerical schemes for hyperbolic systems of conservation laws with source terms. 1997. 978-0-591-49445-7. 148 pages. http://hdl.handle.net/2078.1/70733