Projects per year
I am Reader (Associate Professor) at the University of Brighton, EPSRC Innovation Fellow and member of the Advanced Engineering Centre – a centre dedicated to high-efficiency thermal propulsion systems. My research within lies in the field of Computational Fluid Dynamics (CFD). I develop high fidelity numerical algorithms that can be used as part of virtual manufacturing tools of future energy systems as well as to the understanding of complex bio-systems. I have expertise both in RANS and LES simulations of multiphase flows and turbulent combustion. My aspiration is that my research can contribute towards the solution of the grand challenges of today in relation to climate change and sustainability of our planet using state of the art algorithms that help us analyse, understand, and eventually predict phenomena relevant to thermo fluids dynamics. I have published more than 50 high impact journal and conference papers and I has been involved in various projects with industrial support.
Large Eddy Simulations (LES) of in-nozzle flow, spray dynamics and ignition at ultra-high pressure devices
The efficiency of spray systems designed for various applications is determined by the size/shape distribution and velocity of the droplets formed. For example, in combustion process, smaller droplets imply higher vaporisation rates and subsequently more efficient combustion with fewer emissions. Despite the importance of droplet size and velocity distributions in industrial applications, there are fundamental questions which still remain unanswered. Given certain conditions, including fluid properties and geometry, it is unclear what size and shape of the droplets are expected to be generated. What is the effect of ultra-high pressure (up to 3000bars that modern automotive injectors operate) and turbulence on these structures? How do these liquid structures evolve? What is the effect of in-nozzle phenomena on the formation of sprays? What happens when the injected fluid exhibits super critical conditions.
My current research aims at answering these questions through the development of advanced numerical tools within Large Eddy Simulations context that will be capable of representing in a unified manner in-nozzle and subsequent spray formation mechanisms and will be valid for both sub- and supercritical conditions. With co-workers from Imperial College (Dr S. Navarro Martinez), Stuttgart University (Prof A. Kronenburg) and Melbourne University (Dr R. Gordon) we work on implementing a novel model for spray evolution based on the probabilistic modelling of sub-grid scale liquid surface evolution under sub-critical conditions. Parallel research is performed within our group towards understanding supercritical conditions based on experiments from the ECN network as well as complimentary experiments at ultra-high pressure performed in house (collaboration with Prof Crua). We try to understand the shock wave formation of high pressure jet tips and the effect these waves have to the surrounding turbulence. Moreover, the interaction of these waves with waves travelling from within the nozzle downstream to the nozzle exit because of cavitation collapse is of interest.
Multiple Mapping Conditioning (MMC)
An important part of my work has focused on a novel approach in turbulent combustion named Multiple Mapping Conditioning (MMC). MMC offers a new predictive framework based on conditional and probabilistic methodologies that can account for detailed chemical kinetics and turbulent mixing and thus offers more accurate prediction of emissions and efficiency of energy conversion systems. In the past seven years, I developed key model closures for MMC – both in a stochastic and deterministic context – and I pioneered the implementation of the model in real flames. MMC is not only a rigorous combustion model but can be used as a generalised mixing model for a variety of flow configuration that accurate prediction of mass and heat transfer is important. Mixing in reality determines the efficiency of the device and the production rate of pollutants and thus its accurate modelling is of interest. In collaboration with colleagues, I have developed a new turbulent mixing algorithm based on the extension of the ideas of MMC methodology to be applicable to any device where different fluids are injected separately and are required to mix. Although this model has mostly been implemented in the RANS context and simple jet flame configurations, part of my current research focuses on extending the model to the Large Eddy Simulations context and to test its applicability to a wider range of problems that combine mixing and chemical processes. More specifically, I am interested in exploring the applicability of the methodology in high pressure chambers that have application to automotive industry.
Alternative fuels (Hydrogen, Syngas, Bio-fuels)
The growth of the energy consumption due to population and economic growth represents a pressing problem for most countries both in financial and environmental terms. Electricity generation as well as transportation currently relies on hydrocarbons which are both running out and contribute tremendously to climate change. The use of alternative fuels mostly coming from renewable sources such as wind or solar energy has started to emerge as a promising solution although there are not yet the technologies available (or even if they are available, their cost is prohibitive) to completely replace the use of fossil fuels for large-scale energy generation. My current research within this field in collaboration with Dr R. Morgan and colleagues from MIT evolves around the idea of how traditional sources of energy can be supplemented by renewable forms of energy in large power plants. Our current focus is on synthetic fuels with various hydrogen context. We explore the effect of the fuel input on the combustion stability mechanisms
Cavitation and flashing
Microscopic bubbles are ubiquitous in nature and could interact significantly with their environment once excited. Extensive studies have elucidated these effects in diverse fields of application, eg. hydrodynamics, sound and erosion structure protection and environmental technologies. However, still many questions remain unanswered and the CFD modelling of their dynamics is a very challenging task mostly because of the lack of rigorous algorithms to track the full process from nucleation to bubble explosion and the release of energy to their surroundings. The problem I am currently interested in is relevant to bubble formation within ultra-high pressure injectors also known as cavitation. In our group (with collaborators from Stuttgart University), we are working on a project entitled: LES modelling of bubble collapse-induced spray atomisation for cryogenic fluids. Flashing is similar in nature to cavitation however it occurs when a liquid’s temperature exceeds a certain degree of superheat. Flashing also can accelerate the primary spray break-up when the bubbles – present in the superheated liquid because of the pressure changes through the process – explode and thus leads to smaller droplets. The resulting very fine droplets promote a quick evaporation of the liquid and lead to a rather homogeneous mixing with the carrier gas. The phenomena can be manifested in the chemical and process plants where liquid superheat is essential. The phenomenon is initially more violent at the surface and causes the liquid to acquire a very heterogeneous temperature composed of superheated, saturated, and sub-cooled liquid. The area of research we are interested in is how these temperature variations are affected by turbulence and how they can affect in turn the chemical processes taking place at the applications that flashing occurs.
Flows through porous media
This project is relevant to environmental fluid dynamics in the context of oil and gas interaction through tight porous media. We are performing high fidelity numerical simulations to explore the flow patterns of multiple phases (oil, water, gas) present in the primary and secondary extraction phase inside the complicated structures of rocks. We aspire to help designers and operators of large wells to solve flow problems, extend life of flow and, ultimately, assure the efficient and reliable delivery of the product. Our main challenge is to perform the simulations in a manner that accounts for interpenetrating or immiscible fluids that include effects of pressure, temperature and liquid/gas mass transfer in detail. We also target creating generalised algorithms that will allow us, in the future, to tackle a wider range of problems in porous materials such as Porous Media Combustion (PMC), storage of CO2, flow of fluids and solutes in biological tissues.
Recently there has been increased interest in the use of cryogenic fluids in existing and new technologies. Some of these cryogenic fluid dependent technologies include enhancement of superconductivity by cooling the materials to required temperatures using cryogenic fluids, cryosurgery based on cryogenic fluid jets used to tackle skin cancers, Magnetic Resonance Imaging (MRI) and cryopreservation.
In addition, cryogenic fluids such as liquid air, liquid nitrogen or liquified natural gas can serve as cost-effective energy vectors within power production units as well as transport “fuels” with zero emissions. For example, energy coming from renewable resources can be used in order to “cool” air or nitrogen, down to the point that they become liquids. Follow up injection of these liquids to a higher temperature environment causes rapid re-gasification and large expansion in volume. This can either drive a turbine or piston engine even without combustion or be used in novel ultra-low emission combustion systems in order to optimise the compression stroke and reduce emissions as in the case of the Cryopower split-cycle which has been developed in the University of Brighton and Dolphin N2
We are currently running multiple projects within the University of Brighton in order to understand the behavior of such fluids when they are injected in various environments or as they interact with surfaces.
I am interested in supervising research students (master and PhD level) in the following areas: modelling and simulation of multiphase flows for energy and medical systems. Emphasis on sprays and bubble dynamics (caviatation and flashing), interaction of fluids with porous media, turbulent, reacting flows, particulate flows, alternative fuels (hydrogen, syngas, dual fuel engines), cryogenic fluids.
We are also happy to support candidates to apply for fellowships to work within our group [Fellowships by the EPSRC, Royal Academy of Engineering, Royal Society (e.g. Newton International Fellowships), The Wellcome Trust, the Leverhulme Trust, and the European Union (MSC actions)]
Indicative PhD projects currently under development in our lab include
1. Linking in-nozzle flow with spray dynamics at high pressure injection based on probabilistic approaches, P. Mc Ginn
2. Development of a novel break up model for unconvational spray systems, F. Gerbino
3. Development of practical simulation tools for advanced combustion system design, D. Nsikane
4. LES modelling of atomisation from airblast atomisation for aero-engines. Imperial College London, UK, G. Tretola
5. A novel approach to zero emission combustion for ultra-high efficiency internal combustion engines, S Harvey
6. DNS simulation of flash evaporation of cryogenic liquids in rocket engine injectors, Stuttgart University, Germany, D. Loureiro
7. Injection and Droplet Dynamics of Cryogenic Fluids under Supercritical Conditions, J. Gopal
Approach to teaching
With a background in both applied mathematics and fluid mechanics, my teaching is characterised by a multidisciplinary approach. I am teaching a range of courses both at postgraduate and undergraduate level, such as thermodynamics, dynamics, advanced fluid mechanics and computational fluid dynamics. It is my priority to present educational material in an engaging and memorable manner that shows the elegance and beauty of the course as well as demonstrating solutions to common problems, which can be often found in engineering practice. Since my teaching directly relates to the areas that my group performs research on, I try to update my lectures with the most recent developments, practices and applications in the relevant fields. This helps the students to familiarise with the state-of-the-art technologies currently used, as well as extending their understanding on how the fundamental knowledge gained during their university studies can find application in their future role as engineers and project managers.
Selected Invited Talks
2017: University of Southampton: LES modelling of in nozzle flow and spray formation in modern energy system, 15th of November 2017
2017: SIG of Sprays in Engineering Applications: Modelling and Experimental studies: Investigation of the LES numerical parameters affecting the mixing field predictions for a spray, 13th June 2017
2015: Imperial College, London UK (UKTRFC meeting): Cavitation Characterisation at different back pressures, 23rd September 2015
2014: Cambridge University, Cambridge UK (UKTRFC meeting): CFD Modelling for Modern -Combustion based- Energy Conversion Systems, 11th September 2014
2013: Space Exploration Technologies Corporation (SpaceX), Hawthorne, CA, USA: Innovative Modeling of Energy Processes from Conventional and Renewable Sources, 11th June 2013
Membership in Scientific Commitees
Institute of Physics (elected member of the Combustion Physics group)
Combustion Institute (elected member)
Society of Industrial and Applied Mathematics (SIAM)
International Society of Porous Media
2018: Woman of Impact is Science (University of Brighton)
2017: Seal of Excellence (European Commission Horizon 2020), for high quality project proposal
2016:Hinshelwood Prize (Combustion Institute), awarded annually to a young member for work in any branch of Combustion
2010: Bernard Lewis Fellowship (Combustion Institute), for high quality research in combustion by young scientist
2007: Award for the Best Poster and the Best Oral Presentation (COCCFEA)
PhD, Imperial College London
Award Date: 1 Mar 2010
Bachelor, the National Technical University of Athens
Award Date: 1 Oct 2005
Visiting Academic, Imperial College London1 Sep 2016 → …
Research Scientist, Massachusetts Institute of Technology1 Jan 2012 → 1 Sep 2013
Research Associate, Imperial College London1 Jan 2010 → 31 Dec 2011
Research Associate , University of Stuttgart1 Feb 2009 → 30 Dec 2009
Unveiling the injection dynamics of cryogenic energy carriers for zero-emission high-efficiency systems
29/06/18 → 28/06/21
1/07/17 → 1/01/19
Tretola, G., Navarro-Martinez, S., Vogiatzaki, K., Duret, B., Reveillon, J. & Demoulin, F-X., 2020, In : Atomization and Sprays. 30, 4, p. 239-266 28 p.
Research output: Contribution to journal › Article
DNS and LES of primary atomization of turbulent liquid jet injection into a gaseous crossflow environmentMukundan, A. A., Tretola, G., Menard, T., Hermann, M., Navarro-Martinez, S., Vogiatzaki, K., Brandle de Motta, J. C. & Berlemont, A., 18 Sep 2020, In : Proceedings of the Combustion Institute.
Research output: Contribution to journal › Article
Vogiatzaki, K., 24 Jul 2020, In : International Journal of Multiphase Flow. 132, 103405.
Research output: Contribution to journal › ArticleOpen AccessFile
Tretola, G., Vogiatzaki, K. & Navarro-Martinez, S., 2020, ICLASS 2018 - 14th International Conference on Liquid Atomization and Spray Systems.
Research output: Chapter in Book/Conference proceeding with ISSN or ISBN › Conference contribution with ISSN or ISBN
Understanding Sub and Supercritical Cryogenic Fluid Dynamics in Conditions Relevant to Novel Ultra Low Emission EnginesMadana Gopal, M. J. V., Tretola, G., Morgan, R., De Sercey, G., Atkins, A. & Vogiatzaki, K., 12 Jun 2020, In : Energies. 13, 12, 3038.
Research output: Contribution to journal › ArticleOpen AccessFile