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.

A major design consideration for offshore wave energy devices is survivability under extreme wave loading. The aim of this project is to predict loading and response of two floating wave energy devices in extreme waves using CFD (computational fluid dynamics), in which fluid viscosity, wave breaking and the full non-linearity of Navier-Stokes and continuity equations are included. Two classes of device will be considered: Pelamis (of Ocean Power Delivery Ltd.), the prototype having already successfully generated electricity into the grid, and a floating buoy device responding in heave, known as the Manchester Bobber (Manchester University), which is being tested at 1/10th scale. Both classes of device are thought to be competitive with other renewable energy sources, being economically roughly equivalent to onshore wind energy. The CFD simulations will be undertaken in three ways: by commercial codes, CFX and COMET (STAR-CD); by recent advanced surface-capturing codes; and by the novel SPH (smoothed particle hydrodynamics) method. In order to address the uncertainties in the CFD approaches, such as the accuracy of prediction and the magnitude of computer resources required, a staged hierarchical approach of increasing computer demand will be taken in: mathematical formulation (from an inviscid single fluid to a two-fluid viscous/turbulence approach); wave description (from regular periodic to focussed wave groups including NewWave); and complexity of structure (from a fixed horizontal cylinder parallel to wave crests to the six degrees of freedom of Pelamis). At each stage, numerical results will be compared with experimental data. The significance of the inviscid v. viscous formulations, wave nonlinearity, non-breaking v. breaking conditions, and the dynamic response of the body will thus be assessed for extreme conditions. Designs for survivability should thus be better evaluated. The resulting CFD methodology will also benefit analysis of extreme wave interaction with ships, other marine vehicles and structures in general. For example interaction with freak waves and the 'green' water problem have yet to be resolved.

A major design consideration for offshore wave energy devices is survivability under extreme wave loading. The aim of this project is to predict loading and response of two floating wave energy devices in extreme waves using CFD (computational fluid dynamics), in which fluid viscosity, wave breaking and the full non-linearity of Navier-Stokes and continuity equations are included. Two classes of device will be considered: Pelamis (of Ocean Power Delivery Ltd.), the prototype having already successfully generated electricity into the grid, and a floating buoy device responding in heave, known as the Manchester Bobber (Manchester University), which is being tested at 1/10th scale. Both classes of device are thought to be competitive with other renewable energy sources, being economically roughly equivalent to onshore wind energy. The CFD simulations will be undertaken in three ways: by commercial codes, CFX and COMET (STAR-CD); by recent advanced surface-capturing codes; and by the novel SPH (smoothed particle hydrodynamics) method. In order to address the uncertainties in the CFD approaches, such as the accuracy of prediction and the magnitude of computer resources required, a staged hierarchical approach of increasing computer demand will be taken in: mathematical formulation (from an inviscid single fluid to a two-fluid viscous/turbulence approach); wave description (from regular periodic to focussed wave groups including NewWave); and complexity of structure (from a fixed horizontal cylinder parallel to wave crests to the six degrees of freedom of Pelamis). At each stage, numerical results will be compared with experimental data. The significance of the inviscid v. viscous formulations, wave nonlinearity, non-breaking v. breaking conditions, and the dynamic response of the body will thus be assessed for extreme conditions. Designs for survivability should thus be better evaluated. The resulting CFD methodology will also benefit analysis of extreme wave interaction with ships, other marine vehicles and structures in general. For example interaction with freak waves and the 'green' water problem have yet to be resolved