My field of expertise is in problems involving the interaction of turbulence with reactive multiphase flows. More recently I have extended my research to flows through porous media as well as bubble formation in ultra-high pressure injection systems.
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.
Enriching the energy mix with 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 microscale porous materials
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.