To reduce the UK's greenhouse-gas emissions anywhere near the legally-binding 2050 targets, a major attack on both energy wastes and unsustainable forms of electricity production is essential. Owing to their appealing thermo-physical properties (e.g. large heat capacity relatively to the molecular weight, low boiling point, elevated density), molecularly-complex and dense gases (e.g. hydrocarbons, perfluorocarbons, siloxanes) are at the heart of realistic solutions for thermal power stations to operate efficiently on low-temperature heat sources (e.g. solar, biomass, geothermal), where they are used as substitute for water steam (e.g. organic Rankine cycle). Flow expanders in such power stations partially operate in the vicinity of the thermodynamic critical point, where the speed of sound is substantially reduced, turning the expander flow into a highly supersonic gas flow, inevitably leading to the formation of shock waves. Shock waves have the detrimental property of degrading the expander efficiency by dissipating kinetic energy into heat, and by promoting viscous losses through boundary-layer separation and thickening. Quite remarkably, and contrary to ideal gases, shock waves in molecularly-complex and dense gases can be made almost isothermal, therefore relieving part of the efficiency losses imparted by the shock wave. This remarkable property is a direct consequence of the exceptionally large number of active degrees of freedom of the gas molecule. While the prospect of efficient supersonic expanders is appealing, little is known on the implication near-isentropic shocks have on the amplification of turbulence fluctuations (which are always present in turbines). In particular, shock/turbulence interactions in dense gases can lead to the emission of energetic acoustic waves, which are significantly more powerful than in standard ideal gases. If present, such acoustic forcing can erode the expected turbine efficiency, generate vibrations and cause premature blade fatigue. The proposed research will establish a robust and fundamental understanding of sound emission from shock/turbulence interactions in dense gases, and provide a new understanding of the underlying physics, which will allow the development of predictive tools that can inform future design choices.

Aeronautics and air transport is a vital sector of our society and economy. Aviation currently accounts for about 2% of human-induced CO2 emissions with more than 3.12 billion passengers and 48 million tons of freight worldwide last year with an average of more than 100,000 flights every day. Worldwide traffic is predicted to grow at a rate of 4% to 5% per year for the next 30 years. It simply means that more than 16 billion passengers and 25 million flights are expected in 2050. Aviation will have to find ways to meet the growing demand for air transport whilst reducing its environmental impact, specifically the level of noise and of carbon emissions. Innovative solutions are also needed to deal with fuel consumption so that aviation does not become increasingly dependent on more and more expensive energy sources. It is clear that it requires a significant step change in the technologies of future aircraft. In recent years, the development of devices known as plasma actuators has advanced the promise of controlling flows in new ways that increase lift, reduce drag and improve aerodynamic efficiencies, advances that may lead to safer, more efficient and quieter aircraft. Dielectric barrier discharge (DBD) plasma actuators consist of two electrodes, one exposed to the ambient fluid and the other covered by a dielectric material. When an A.C. voltage is applied between the two electrodes the ambient fluid over the covered electrode ionizes. This ionized fluid is called the plasma and results in a body force vector which exchanges momentum with the ambient, neutrally charged, fluid. For this project, high-resolution simulations will be carried out on the most powerful supercomputers in Europe in order to demonstrate the potential of DBD plasma actuators for the control of turbulent jets. The problem of jet noise pollution has become more severe in the past few decades due to the ever increasing number of flights, the tightening of environmental impact regulations, and the development of urban/residential areas in close proximity to airports. The scientific objective of the present project is to advance our understanding of aeroacoustic mechanisms up to the point where we can propose targeted plasma control strategies for free shear flows to tackle the problem of jet noise pollution. This research project is a first step in the development of new technologies based on plasma actuators in the aeronautic sector not only for noise reduction purposes but also potentially for mixing enhancement and for a better efficiency of jet engines. As of today, active flow control technologies have not been implemented in commercial aircraft. The large number of parameters (location of the actuator, orientation, size, relative placement of the embedded and exposed electrodes, applied voltage, frequency) affecting the performance of plasma actuators makes their development, testing and optimisation a very complicated task. Experimental approaches require numerous high-cost and time consuming trial-and-error iterations. Computational Fluid Dynamics (CFD) can complement ideally experiments with the potential to investigate in detail plasma-actuator controlled turbulent flows.

An expanded high-end-computing (HEC) consortium is proposed to investigate fundamental aspects of the turbulence problem using numerical simulations. The proposed UK Turbulence Consortium (UKTC) will ensure that the UK's worldwide reputation of being at the forefront of turbulence research is maintained. Cases in this proposal include transitional and fully developed turbulent flows in canonical and complex geometries and a new work package on turbulence-particle interactions, with relevance to a wide range of engineering, environmental/geophysical and biological applications. The consortium will serve to coordinate, augment and unify the research efforts of its participants, and to communicate its expertise and findings to a national and international audience. Most of the staff resource to carry out the scientific work is already in place, funded by EPSRC or other sources, and in all cases the projects have qualified and available staff in place to complete them. This application is for: (a) a core allocation of HEC time to enable consortium members to carry out simulations of world-leading quality, (b) dedicated staff at STFC Daresbury Laboratory and the University of Southampton for software development projects that will open up new research areas and to ensure efficient use of HEC resources and progress on key projects, (c) travel and subsistence for regular management meetings and international visitors, and (e) support for annual progress reviews, including two expanded workshops to which members of other HEC consortia and the wider UK turbulence community will be invited. The software development projects are essential to maintain the UKTC's worldwide leadership in turbulence research and to provide cutting-edge HEC application software that will deliver internationally leading scientific research on the next national HEC service ARCHER.

Though many industrial problems involving gas/liquid flows can be simulated via fairly simple models, there are other cases where the number of different forces and their direction can not be handled by this approach. A typical example is that of flow in a bend. If it is just the pressure drop across the bend that is required, then there are simple methods, more or less accurate, which can be invoked. However, if more detailed information is required, such as how are the liquid and gas disposed about the bend, then more advanced methods are required, methods which hitherto are not available. Calculation methods for multiphase flow are not yet at a stage that they can handle all the problem industry has to solve. Therefore developments have to be produced. However, to achieve these developments there is a need for information from experiment to inform the modeling and to validate the product models. In spite of the extensive multiphase flow literature, such information if often limited and most certainly confined to pipe diameters far smaller than used in industry and with physical properties very different to those which industry is dealing with. The programme of work proposed here aims to push forward developments in modeling and provide experimental observations/measurement to help this development.

The advancement of numerous technologies has become increasingly reliant on the ability to dissipate large quantities of heat from small areas. Current designs in power electronics, supercomputers, lasers, X-ray medical devices, nuclear fusion reactor blankets, spacecraft, and hybrid vehicle electronics, and future improvements, rely on record high heat transfer rates. This rapid increase in heat dissipation rates required by such devices has led to a transition from more traditional fan-cooled heat-sink attachments to liquid cooling techniques. Liquid cooling techniques operating in single-phase, however, have now reached their limit being forced to run at very low inlet temperatures and exceedingly high mass flow rates, resulting in unacceptably high pressure drops and surface temperature gradients. Innovative approaches are urgently needed to overcome these significant shortcomings: one such approach is spray-cooling. Spray-cooling uses a nozzle to break up the liquid coolant into fine droplets that impinge individually on a heated surface. 'Low'- and 'high-temperature' spray-cooling applications involve surface temperatures below and above the critical heat flux (CHF), respectively. Single-phase spray-cooling (relies on liquid sensible heat rise only) provides greater operational stability and spatially uniform heat removal than liquid cooling, reducing the likelihood of large surface thermal gradients, particularly important for fragile electronic components. Two-phase spray-cooling (relies on liquid sensible heat rise and latent heat), are superior to single-phase systems and furthermore, compared to pool/flow boiling alternative systems, offer far less resistance to vapour removal from a heated surface enabling superior drop-surface contact . In fact, the CHF increases from 1.2 MW/m2 (for water pool boiling) to 10 MW/m2 for water sprays in two-phase applications. SANGRIA is an ambitious 3-year collaborative research programme aimed at investigating the fundamental mechanisms and transfer processes underlying spray-cooling. This project combines cutting-edge experimental techniques that furnish spatiotemporally-resolved diagnostics of the thermal, interfacial, and hydrodynamic fields, with multi-scale theory, modelling and 3-D high-fidelity numerical simulation that bridge the molecular and continuum-scales. The deep insights generated from SANGRIA will be harnessed to provide tools that are practically implementable by our industrial partners in order to maximise impact. Industrial and academic partners will provide additional technical support and feedback during the research programme plus pathways for direct industrial impact. The industrial partners include possible users of this technology: TMD Ltd (manufacturers of electronic equipment, high heat flux devices); Oxford naNosystems (manufacturers of enhanced heat transfer surfaces); ANSYS (Software development); Siemens (Software development); Spraying Systems Co. (Nozzle manufacturers); Syngenta (users of nozzles). LaVision offered a 15% discount on their Particle Master System. The academic partners from the University of Nottingham, Sorbonne University, Technical University of Darmstadt and Kyushu University are internationally recognised experts in single and two-phase thermal systems, including spray cooling. Participation and presentations during the HEXAG and PIN meetings will facilitate feedback and technology transfer.