UK Turbulence Consortium

Lead Research Organisation: University of Southampton
Department Name: Faculty of Engineering & the Environment

Abstract

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.

Planned Impact

The research to be carried out in the UK turbulence consortium is relevant to the transportation, energy supply/generation, biomedical and process sectors in the UK and the world. In addition to creating new knowledge and training for the next generation of engineers and scientists (as outlined in academic impact), research carried out in this HEC consortium will deliver benefits to the economy and allow us to realize our societal goals.
Despite being the largest contributors to harmful emissions, the transportation, energy generation/supply and process sectors are experiencing unprecedented growth around the world. For example, it is estimated that air transport will contribute an additional 200 Billion Euros to the EU economy over the next twenty years. Moreover, most applications generate aero/hydrodynamic noise that is a significant nuisance (and sometimes harmful) to local communities. For increases in production efficiencies the process industry needs improved prediction of transition and better ways of mixing fluid substances that reduce the very significant amounts of power used. These sectors have an enormous impact on the environment and the global energy budget and any improvements in aero-/hydrodynamic, mixing and heat transfer efficiencies as well as reducing noise rely in large parts on a better understanding of the overarching subject of turbulence. A large number of projects to be carried out within the UKTC will contribute to resolving all of the above-mentioned issues and hence will have a significant impact in our quest towards a greener future. Even a 1% reduction in drag can save at least 25,000 gallons of fuel per year per aircraft. Worldwide, this reduction could translate to fuel savings of more than $1 billion per year. The resulting reduction in emissions into the air is equally as impressive.
Our consortium also has economic benefits as it creates new opportunities for industries in the UK and worldwide. This is clearly identified by our industrial partners who are all keen to follow and where possible adopt our technologies. Our project partner CD-adapco (U.K.) specialises in turbulent flow modelling and believes that work within UKTC constitutes a very important contribution to developing knowledge of turbulence and therefore new avenues for modelling turbulence in a very wide range of engineering applications. As a project partner, CD-adapco will have first-hand access to any information, understanding or guidance from our fundamental DNS/LES research that can filter into their commercial CFD software. Both Rolls-Royce (U.K.), in the context of aero-engines, and GE Global Research (Germany), in the context of aero-engines and energy, express how LES and CFD methods utilising UKTC resources are crucial to gain insights into turbulence physics and have enabled them to better understand limitations of their current CFD approaches and how to devise improvement strategies to take a competitive lead. GE GR also have a strong interest in our WP7 activities, in particular in strategies to exploit future HEC architectures. This interest is shared by an F1 team who, despite their focus on applied aerodynamics, emphasize that they need to embrace leading edge simulation techniques that help gain a fundamental understanding of the transient flow environments that dictate the performance of road and race cars in order to maintain their position as a UK based, world leading engineering company. Airbus Germany/EADS Innovation Works (Germany, U.K.) is particularly interested in the WP2 activities on the physics of turbulent drag reduction as improved understanding is the prerequisite for developing flow control devices for drag reduction, and hence reduced fuel consumption and emissions of aeroplanes. Siemens (U.K.) is interested in our work on the fundamental understanding of instabilities for energy generation.

Publications

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Sandham N (2016) Effects of Compressibility and Shock-Wave Interactions on Turbulent Shear Flows in Flow, Turbulence and Combustion

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Seddighi M (2015) Turbulence in a transient channel flow with a wall of pyramid roughness in Journal of Fluid Mechanics

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Simmonds N (2018) Low-Mach number treatment for Finite-Volume schemes on unstructured meshes in Applied Mathematics and Computation

 
Description Examples taken from the 2015,2016 and 2017 report to EPSRC:
1. Hi-fidelity turbulence simulations have been shown to have direct relevance to industry designs in turbomachinery applications. Simulations have demonstrated the sensitivity to inflow disturbances and enabled the development of boundary conditions to accurately reproduce experimental studies of low-pressure turbines. Losses of low-pressure turbines blades can be significantly increased by wake distortion. This mechanism is not accounted for by steady control volume analysis. This insight has led to consideration of new designs by industry (see also the associated impact case study)
2. Wall-resolved large-eddy simulation of shock-wave boundary-layer interactions have been extended to fully three-dimensional interaction, including swept fins and oblique shock interactions with sidewalls. These simulations have shown in great detail the physics of the interaction, linking large-scale separation features with near-wall and corner flow. Datasets of pressure fluctuations have been extracted for long run times, covering low-frequency motions in addition to boundary-layer turbulence.
3. State of the art simulations on Archer are continuing to provide insight into the fundamentals of turbulence in canonical flows. The non-equilibrium nature of axisymmetric turbulent wakes generated by various types of plates has shown the presence of well-defined non-equilibrium (non-Kolmogorov) dissipation scalings and of resulting hitherto undocumented basic mean flow profile properties. Shear-flow dispersion has been shown to be the dominant mixing mechanism in unsteady scalar transfer in jets and plumes.
4. Engineering rough surfaces have been simulated for the first time using DNS. Archer has been used to extend the number of surfaces covering a wide range of surface parameters. As well as illuminating the physics of flow over and around roughness features this database is providing for the first time an opportunity to link surface properties to surface drag. In addition, transient flow over roughness is being studied for the first time.
5. Implicit LES of a wing tip vortex has been extended to Re=1.2 million, representing the highest Reynolds number for which correlations have been made with experiment. The development of these vortices in the near wake, in combination with the large Reynolds numbers present in these cases, makes these types of test cases particularly challenging to investigate numerically.

From Jan 2017 report:
Key research findings:

• In contrast to the conventional view of laminarisation, He et al (2016) have shown that applying a streamwise body force to a turbulent flow while keeping the pressure force unchanged causes little changes to the key characteristics of the turbulence. In particular, the mixing characteristics of the turbulence represented by the turbulent viscosity remain largely unaffected. The so-called flow laminarisation due to a body force is in effect a reduction in the apparent Reynolds number of the flow, based on an apparent friction velocity associated with only the pressure force of the flow (i.e. excluding the contribution of the body force).

• Recent studies on multiscale generated turbulence by Laizet et al have revealed a highly increased transverse turbulent scalar flux downstream of multiscale objects compared to regular objects. This phenomenon is called the space-scale unfolding mechanism (SSU) and it is now studied in various institutions worldwide (Imperial College in the UK, Nagoya in Japan, Ottawa in Canada, Napoli in Italy). This mechanism is playing a decisive role in environmental, atmospheric, ocean, and river transport processes wherever turbulence originates from multiscale objects such as trees, forests, mountains, rocky riverbeds, and coral reefs. It also ushers in the concept of multiscale design of turbulence which may hold the power of setting entirely new mixing and cooling industrial standards.

• Obligado et al (2016) have demonstrated that nonequilibrium turbulent wake scalings are not the preserve of irregular (fractal-like/multiscale) plates but appear to be universal, as they also hold for regular plates over a very substantial downstream distance. These scalings are currently absent from all textbooks on turbulent flows even though they are more relevant to most applications and equally fundamental as the equilibrium scalings which are in these textbooks."

• A sequence of papers have been published that document significant progress in the aeroacoustics of airfoil/gust interactions. Kim et al (2016) is the first paper that presents a fully resolved 3D calculation of aerofoil-turbulence interaction noise and provides fundamental understandings of noise reduction mechanisms due to undulated leading edges. Turner & Kim (2016) presents the detailed aeroacoustic source mechanisms of undulated aerofoils which have not before been understood or investigated. Perez-Torro & Kim (2016) provides a solid ground on which the leading-edge geometry can be optimised for effective control of the radiated noise

• Bao et al (2016) have proposed a new "thick" strip theory for prediction of vortex induced vibration relevant to the off shore engineering prediction of riser pipes. This is a significant extension to the well-established 2D strip theory which incorporate important flow physics into the modelling whilst maintaining the ability to massively scale through parallelism.

• This year has seen further journal publication of our work on rough surfaces, in which fully-resolved simulations are carried out on filtered surface scans of real engineering material surfaces. Busse et al (2016) carried out simulations up to the fully rough regime and observed the formation of a new 'blanketing' layer close to the surface, that remains intact up to the fully rough regime and is responsible for a significant (and unexpectedly large) viscous contribution to drag from a rough surface. Meanwhile Thakkar et al (2016) used DNS data for a range of rough surface to propose new corrections based on measurable surface properties that can help with engineering prediction of rough-surface drag.

• In airfoils with blunt trailing edges, bluntness results in periodic vortex shedding. For the conditions examined in Thomareis & Papadakis (2016), this frequency was found to be close to the subharmonic of the natural frequency of the shear layer separating close to the leading edge. The shedding, resulting from a global instability, has an upstream effect and forces the separating shear layer. Under such conditions, a locking mechanism was discovered: due to forcing, the shear layer frequency locks onto the shedding frequency while the natural frequency (and its subharmonic) are suppressed.

• Tucker and Tyacke (2016) considers jets with flight stream effects and jet-wing interaction that are currently critical issues in jet noise prediction. To be able to control jet noise, the link between the turbulent flow and noise generated requires a deep understanding of numerous interactions. By using high fidelity LES to understand complex flow physics, jet noise can be predicted accurately and provide a wealth of data for lower order modelling. These simulations are at the forefront of international jet-noise research, the scientific outcomes of which, will enable future jet noise reductions.

• Lyu et al (2017) have used large eddy simulation of various single stream and co-axial jets to study their acoustic properties and noise generation. It provides data to perform analysis of jet noise production mechanisms, which will be helpful in the reduction of jet engine noise. This work is also aimed at the establishment of standard practice for industry to implement LES in a consistent manner to predict far-field noise from aero engines.

• Work at Cambridge has continued to expand the range of applications of LES in turbomachinery contexts. Scillitoe et al (2016) use high fidelity wall resolved large eddy simulation to study the three dimensional separation that occurs in the endwall region of a compressor. It demonstrates how large eddy simulation with advanced sub-grid scale models can be used to predict complex transitional flows. The study highlights the importance of unsteady inflow conditions and boundary-layer transition to the three dimensional separation. This information will be useful for future experimental and computation studies of such flows. Cui and Tucker (2016) is the first ever LES study for the hub leakage flow in low pressure turbines, giving a more accurate estimation of the amount of loss generated by the hub leakage flow.

• Aghdam and Ricco (2016) studied laminar and turbulent flows over hydrophobic surfaces featuring shear-dependent slip length. For the first time, a conceptual link between the slip-length model for hydrophobic surfaces and the feedback law extracted through the Lyapunov stability analysis has been advanced, thereby providing a precise physical interpretation for a feedback law proposed by other authors. The turbulent drag reduction is measured as a function of the hydrophobic-surface parameters and the power spent by the turbulent flow on the hydrophobic walls is computed for the first time. It is found to be a non-negligible portion of the power saved through drag reduction, thereby introducing a novel definition of the passive-absorbing drag-reduction method.
Exploitation Route Please see impact case studies on ARCHER for examples.
Sectors Aerospace, Defence and Marine,Energy,Environment

URL http://www.turbulence.ac.uk/
 
Description The UK Turbulence Consortium facilitates the use of high performance computer for engineering problems. A number of the project work with industry, including Rolls-Royce, GE, McLaren Racing etc. A number of impact case studies of the work are available via the ARCHER website.
First Year Of Impact 2015
Sector Aerospace, Defence and Marine,Energy,Environment
 
Title Incompact3D - CFD code 
Description Incompact3d is a powerful numerical tool for academic research. It can combine the versatility of industrial codes with the accuracy of spectral codes. Thank to a very successful project with NAG and HECToR (UK Supercomputing facility), Incompact3d can be used on up to hundreds of thousands computational cores to solve the incompressible Navier-Stokes equations. This high level of parallelisation is achieved thank to a highly scalable 2D decomposition library and a distributed Fast Fourier Transform (FFT) interface. This library is available at http://www.2decomp.org and can be freely used for your own code. 
Type Of Technology Software 
Year Produced 2013 
Open Source License? Yes  
Impact A large (approx 100) number of international users are now using the code. 
URL https://code.google.com/p/incompact3d/
 
Title PyFR - CFD code 
Description PyFR is an open-source Python based framework for solving advection-diffusion type problems on streaming architectures using the Flux Reconstruction approach of Huynh. The framework is designed to solve a range of governing systems on mixed unstructured grids containing various element types. It is also designed to target a range of hardware platforms via use of an in-built domain specific language derived from the Mako templating engine. 
Type Of Technology Software 
Year Produced 2013 
Impact This open source code has only just been released - thus impact is not known at this stage. 
URL http://www.pyfr.org/