The members of the Experimental Fluid Dynamics Research Group, which the Government of Aragon granted “consolidated” status in 2002, include all scientific personnel from LIFTEC (Research Laboratory in Fluid Dynamics and Combustion Technologies), CSIC–University of Zaragoza joint centre, which performs experimental tasks. The work of this well-established group with wide-ranging experience covers virtually all the subjects included in LIFTEC’s lines and sublines of research.

General objective of the group’s research activity

The group’s main research activity shared by all members, and thus binding us together, focuses on the broadest variants of experimental fluid dynamics. We try to gain an understanding of the basic aspects of fluid mechanics and study applications of interest to industry.

Most of our research encompasses energy and environmental conservation areas, but the scope also includes other sectors. For organisational purposes, the subjects can be grouped into four lines of research coinciding with those of the Research Laboratory in Fluid Dynamics and Combustion Technologies (LIFTEC), CSIC–University of Zaragoza joint centre:

• Fluid engineering: this includes the study of multiphase flows, liquid atomisation and aerosol formation, design of sprays, bioengineering (design of medical and hospital components or biological flow models) and study of aerodynamics.
• Industrial combustion: study of gas, fuel oil and coal combustion, ash and slag formation, industrial control and measurements, characterisation of industrial facility components, real-time combustion measurement, monitoring and control systems, reduction of pollutant emissions, combustion improvement, design of burners, biomass and waste combustion, water treatment, ventilation and smoke extraction.
• Fuel cells: design and manufacture of bipolar plates, design, manufacture, assembly and testing of stacks of low- and medium-power polymer fuel cells, study of applications: power plants for vehicles, combined heat and power systems, uninterrupted power supply systems, etc.
• Hydrology and hydraulics: dam failure and floods, design of distribution and irrigation networks, basin monitoring.

Our research is based on experimental measurements performed at the facilities of LIFTEC and the Fluid Mechanics Department of the University of Zaragoza. Besides obtaining measurements, this work includes the design and construction of experimental assemblies and development of techniques. We use techniques that could be termed classic, although they are still robust and reliable, and the most advanced optical techniques whose use with the flows we study here is often highly innovative. Most the experimental facilities we have are unique in Spain.

We are a consolidated group for several reasons: our members have extensive experience and are highly productive, not just scientifically, demonstrated by the large number of publications in SCI journals and presentations at international conferences, but also in attracting resources through projects and contracts. As a result of participating in international projects and disseminating results in journals and conferences, this group is highly regarded in the scientific community both in Europe and worldwide. Without any doubt, we can confirm that the expertise of the Experimental Fluid Dynamics group is above national average in the scientific activity of fluid mechanics. The importance of the subjects we study in key sectors for scientific and economic development in Spain, and in particular in Aragon, mainly in energy and environmental areas, justify support for this type of research. Our lines of research are especially compliant with the priority subjects in PAID (Research and Development Plan of the Autonomous Community):

• Development of renewable energies and energy efficiency
• Water resources and quality
• Hydrogen technologies
• Clean use of coal

Description of the group’s research activity

Current main lines of research lines expected to continue in the near future are:

Fluid engineering

Fluid mechanics is a discipline present in many daily situations and in numerous industrial processes. Out of its many aspects, research in this area has recently focused on multiphase turbulent flows. This type of flow is often present in industrial applications and in nature, as aerosols of solid particles, drops or bubbles dispersed in a continuous medium. The transport of sediment in rivers, air pollution and the formation of liquid fuel aerosols are only some of the few examples that help us understand the importance of knowing this flow type. Multiphase flows take place in combustors, steam boilers, filter systems, medication dispensing devices (inhalers), flow in porous media, etc.

In this area, researchers and members of this group aim to study cases of basic and applied problems to further our knowledge of multiphase systems. Scientific equipment, experimental facilities and their scientific potential allow us to tackle a variety of tasks to comply with the general objectives we have outlined above. From the point of view of basic research, we aim to study the physical atomisation mechanisms of a liquid mass and phenomena describing the performance of drops and particles in gaseous jets and sprays. This line, well-established in the group, has led to several PhD theses in the past five years. Concerning basic aspects, we have completed the “Experimental Characterisation of Ultrasonic Atomisation in Systems with a Free Surface” (UZ2012-TEC-02) project, funded by the University of Zaragoza. Concerning the applied aspect, in this case industrial combustion, the “Development of air diffusers for injection burners” (ENE2008-03137/CON) project was concluded in 2012. Funded by the National Energy Plan of the DGICYT (Directorate General of Scientific and Technical Research), it formed the basis for a PhD thesis whose viva was in December 2014. Several research contracts have been completed related to these subjects. For example, the design of a nozzle for spraying disinfectant liquid for use in medical premises for the company Zobele España, and a patent has been submitted. The National Plan project “Methods of atomising micrometric drops for new applications” (DPI2013-45814-P), begun in December 2015, is still ongoing and in a development phase. It has focused on studying the ultrasound atomisation of suspensions in a solid phase in water and the formation of aerosols from various hydrocarbons.

Action Plan

The following tasks will be performed in the near future:

• Analysis of ultrasound atomisation and other alternatives for producing micrometric drops.
• Study of atomisation methods of high viscosity liquids.
• Study of hydrodynamic cavitation as an inducer of chemical reactions.
• Design and characterisation of nozzles and burners for industrial combustion applications.
• Detailed study and application of the stereoscopic particle image velocimetry technique (SPIV).

Industrial combustion

Combustion is an omnipresent process in our world and it is highly relevant for technology, the economy and the environment. It is also a field that poses major scientific and technological challenges since there are constant demands to improve its efficiency, to reduce its environmental impact, to use new fuels and to develop new applications. In this line of research, researchers and members of this group aim to cover a wide range of combustion science and technology aspects to gain further insight into the scientific challenges of this discipline and to develop new equipment and applications adapted to the industry's and society's new demands. We have unique facilities for that purpose: two combustors (500 kW and 150 kW), a laminar flow reactor, a gas turbine combustor, a test bench with cold-flow nozzles, etc. The activity fields worked in and in which the group has ample experience are:

• Design of atomizers for liquid fuels, with special attention paid to the requirements of ultra-heavy fuels and new fuels (derived from biomass and waste).
• Development of burners with low NOx emission to control the mixing pattern.
• Study of the combustion of particles, furthering the analysis of the combustion of pulverised coal and developing new procedures for studying solid biomass.
• Particle formation and emission in combustion systems, including submicron particle formation phenomena in coal and biomass combustion, which is especially relevant for the environment.
• Biomass combustion alone or in combination with other fuels.
• Fouling and slagging phenomena.
• Development of advanced monitoring and control systems of combustion systems.
• Combustion in gas turbines with an emphasis on the study of pulsation problems and the use of alternative fuels (biomass gasification, H2-enriched gases, etc).

This line of research includes several national and international projects in an implementation phase. They include: “Efficient and clean combustion of syngas to produce energy” (ENE2010-15445) and participation in the Consolider project “Sustainable combustion research (SCORE)” (CSD2010-00011). The main international project is “Development of high-efficiency CFB technology to provide flexible air/oxy operation for a power plant with CCS (FLEXIBURN)”, funded by the European Union. The outcome of these projects, and several others that have already concluded, is the vivas of three PhD theses this year. Several contracts are still in force with companies, for example with Gas Natural Fenosa (“Study of gas-focused solutions for climate control and DHW” and “Modification of GASESHOR to adapt to changes in the CTE—Spanish Technical Building Code—) or BSH Electrodomésticos España (“Experimental study of domestic burners with controlled primary aeration”).

Action Plan

The short-term tasks for this line are:

• Study of combustion conditions for various gaseous fuels, including hydrogen and synthetic gases with a high hydrogen content, in combination with air and oxygen in the gas turbine combustor.
• Combustion of biomass and other biofuels: study of particle development, formation of solid and gaseous pollutants, fouling and slagging problems.
• Design of complete burners for crude oil with high viscosity or distillation waste. Wind tunnel tests with flow display and speed measurements using particle image velocimetry.
• Active control of flame stability using image analysis and study of pressure signals and fluctuations.

Hydrology and Hydraulics

Efficient use of both pressure and open-channel irrigation systems or appropriate design of distribution and collection networks in urban areas are key issues in our community. They should be addressed using numerical calculations checked with experimental studies and on-site measurements to arrive at the end product, which is a distribution system with a protocol controlling management. The study of flooding is another issue to explore. Within this line of research, the Experimental Fluid Dynamics Group is responsible for:

• Field measurements of urban hydraulic conveyance systems (supply, discharge) and irrigation systems (gravity or pressure irrigation), acquiring parameters in real time, such as flow, speed, depth of channel or pressure, concentration of pollutants and suspended materials.
• Non-intrusive flow measurements (transit time ultrasounds) in pressure pipes.
• Calibration of simulation models of distribution systems with management and control proposals.
• GPS topography of water systems, channels, collectors, ditches, pipes, natural watercourses, sections, levels, etc.
• Study of floods in experimental laboratory models.

Part of these tasks take place in the context of projects funded by the DGICYT (Directorate General of Scientific and Technical Research) and the Government of Aragon (for example “Technologies and tools to save water and energy using localised irrigation in extensive crops” IPT-2012-0567-310000, “Advanced technologies for energy effectiveness in engineering and irrigation system management”, or “Engineering, analysis and management of irrigation systems to modernise irrigation”).

Action Plan

The future tasks for this line are:

• Precise topographical measurement of pressure irrigation systems using GPS technology.
• Determining pressure and flows in localised irrigation in conditions of strong topographical irregularities.
• Validating models developed in localised irrigation.
• Experimental validation of flood models with solute transport.

Fuel Cells

The increasing scarcity of fossil fuels and ever stricter regulations for pollutant and greenhouse-effect emissions have made it necessary to seek alternative systems to generate electricity. One possibility viewed as the most viable solution is the use of fuel cells using hydrogen as the energy vector. As this issue is complex, it needs to be addressed from a multidisciplinary standpoint since it includes chemical, mechanical and material science aspects, etc. Some of the problems to be solved specifically concern the field of fluid mechanics, and this is one of the aspects the research group covers. The subjects we are currently working on directly are:

• Study of flow distribution in bipolar plates of polymer fuel cells.
• Manufacture of medium-and low-power polymer fuel cells.
• Study and development of applications.

We recently completed the “Optimisation of the fluid dynamics and mechanical design of a high-temperature PEM fuel-cell system” (ENE2009-14750-C05-02/CON) and we are currently working on the project called “Design and manufacture of an ultralight medium-power PEM fuel cell for an energy unit of a UAV” (ENE2012-38642-C02-01), expected to result in a PhD thesis. Group members have also registered the patent “Bipolar plate for homogenous distribution of flow in fuel cells” (ES2315126B1) and they have requested two more patents related to this area.

Action Plan

The future tasks for this line are:

• Studying water formation and pooling problems.
• Studying appropriate cooling methods to dissipate the heat produced in the high-power stacks.
• Analysing the problem of potential inversion in isolated cells and checking its dependence on the homogeneity of the reagent supply.
• Optimising sealing and stack assembly processes.
• Developing an ultralight fuel cell to supply electricity to an unmanned aerial vehicle (UAV).

Scientific, technological and social impact of the group’s activity

All the research lines conducted by the Experimental Fluid Dynamics Group have a huge scientific and socioeconomic impact in the European and national context. But they also specifically address problems that might be especially relevant for the Autonomous Community of Aragon. Energy issues have always been extremely important, and this was heightened after the signing of the Kyoto Protocol. The severe limits on pollutant-gas and greenhouse-effect emissions are especially relevant in our community as it contains many coal plants whose operation is being limited by new restrictions. Combustion processes must be fully optimised to reduce pollutant emissions as far as possible. This includes improving the prior atomisation of fuels, optimising burners and controlling reactions precisely. All this is analysed in the research group. Alternative fuels (hydrogen, biomass, plant waste, etc.) also need to be studied. These issues impact directly on priority subjects in the II PAID (Research and Development Plan of the Autonomous Community) “Development of renewable energies and energy efficiency” and “Clean use of coal”. Alternative methods of electricity production also need to be found. A very attractive possibility so far, as we have already mentioned, is the use of fuel cells. This topic has a great deal of scientific, technological, economic and social relevance. The group’s participation in this line of research is essential since, together with the University of Zaragoza–LIFTEC Numerical Simulation Group, we are the only ones in Spain specifically dealing with the fluid mechanical problems of fuel cells, and the only ones currently working on medium-power stacks. Both the study of hydrogen-fed fuel cells and the study of direct hydrogen combustion in turbines or engines link directly with our region’s development plans for hydrogen-production systems based on wind energy through the Fundación para el Desarrollo de las Nuevas Tecnologías del Hidrógeno en Aragón (Foundation for the Development of New Hydrogen Technologies in Aragon).

Finally, there is the issue of the use of water resources, which everyone in Aragon recognises as important. Optimising irrigation systems, efficient management of distribution networks and leak detection are essential tasks for correct and rational use of an asset as precious as water.

Group structure and composition

Given that all the members work in the same scientific area— experimental fluid mechanics—the group does not have a rigid structure that must be adhered to. Members, especially permanent ones, collaborate on the basis of current projects and contracts, which means the organisation is horizontal rather than vertical.

The reason for this is that the research lines of many topics are difficult to define and they are also not independent as they overlap each other. Participation in research projects is often limited by administrative restrictions (for example you can only participate in a maximum of two National Plan projects), but collaboration is underscored in joint publications or presentations at conferences. The participation of non-permanent members is more rigid because, in most cases, their contracts are associated with a specific project that they must spend their time on exclusively.

The following are currently group members: