Self-Sustaining Process of Townsend’s Attached Eddies in High-Reynolds-Number Wall Turbulence
Lead Research Organisation:
Imperial College London
Department Name: Aeronautics
Abstract
Over the past decade, significant progress on understanding the coherent structures in wall turbulence has been made, especially in twofold. One is discovery of the non-trivial exact solutions of the Navier-Stokes equation, known as exact coherent structures, which has allowed for tackling low-Reynolds-number turbulence with dynamical system approaches. The other, initiated by discovery of new coherent structures emerging much further from wall at high Reynolds numbers, is the emerging evidence supporting Townsend's attached eddy hypothesis, which views that all the coherent structures, the size of which varies from the inner to outer length scale, are self-similar and form a hierarchial organisation.
Recently, the single eddy entity in the hierarchial organisation, called attached eddy, has been computed by our group, providing compelling evidence on the existence of the attached eddy. It has been found that the computed attached eddies exhibit the physical features highly reminiscent of those of the exact coherent structures. The goal of the proposed research is therefore to establish a theoretical link between the Townsend's attached eddies and the exact coherent structures in high-Reynolds-number wall turbulence. To achieve this, two work packages are proposed, one of which is to examine the detailed physical processes of a single attached eddy (especially streak instability) and the other is to directly compute the exact coherent structures associated with the given attached eddy.
The proposed research will be an important step towards a consistent theoretical description of statistical and dynamical features of the coherent structures in a wide range of the Reynolds numbers, covering from transitional (especially bypass transition) to fully-developed turbulent regime. It will also have a great potential to contribute to understanding and controlling wall turbulence at high Reynolds numbers, crucial for development of next generation aeronautical and mechanical engineering devices.
Recently, the single eddy entity in the hierarchial organisation, called attached eddy, has been computed by our group, providing compelling evidence on the existence of the attached eddy. It has been found that the computed attached eddies exhibit the physical features highly reminiscent of those of the exact coherent structures. The goal of the proposed research is therefore to establish a theoretical link between the Townsend's attached eddies and the exact coherent structures in high-Reynolds-number wall turbulence. To achieve this, two work packages are proposed, one of which is to examine the detailed physical processes of a single attached eddy (especially streak instability) and the other is to directly compute the exact coherent structures associated with the given attached eddy.
The proposed research will be an important step towards a consistent theoretical description of statistical and dynamical features of the coherent structures in a wide range of the Reynolds numbers, covering from transitional (especially bypass transition) to fully-developed turbulent regime. It will also have a great potential to contribute to understanding and controlling wall turbulence at high Reynolds numbers, crucial for development of next generation aeronautical and mechanical engineering devices.
Planned Impact
The proposed research is concerned with the understanding of the fundamental physical processes of coherent structures in wall turbulence by establishing a link between two state-of-the-art theoretical ideas, Townsend's attached eddy hypothesis and exact coherent structures. Given the recent finding that the attached eddies (i.e. the coherent structures at all the length scales varying from the inner to outer units at high Reynolds numbers) are involved in a significant amount of turbulent skin-friction drag, the outcome of the proposed research will subsequently play an important role in illuminating the mechanism of turbulent skin-friction generation at high Reynolds numbers. The precise understanding of turbulent skin-friction generation mechanism is very important especially for design of novel wall-based control strategies for turbulent drag reduction, which can create direct impact on numerous engineering applications, such as design of aircraft wings, ship hulls and turbine blades, construction of pipelines for transport of gas and oil, onshore wind-energy farming, sediment and pollution transport, and many others.
The proposed research will therefore potentially contribute to the manufacturing sector, a crucial part of the UK economy. In particular, it will create a basic knowledge required for aeronautical and mechanical industries, contributing to the sector's international competitiveness. The proposed research will also train postgraduate and undergraduate students, and will be acting as a pipeline for producing internationally competent aeronautical engineers. A public engagement is finally proposed for a societal contribution through Imperial Science Festival and HEADSTART Summer School.
The proposed research will therefore potentially contribute to the manufacturing sector, a crucial part of the UK economy. In particular, it will create a basic knowledge required for aeronautical and mechanical industries, contributing to the sector's international competitiveness. The proposed research will also train postgraduate and undergraduate students, and will be acting as a pipeline for producing internationally competent aeronautical engineers. A public engagement is finally proposed for a societal contribution through Imperial Science Festival and HEADSTART Summer School.
People |
ORCID iD |
Yongyun Hwang (Principal Investigator) |
Publications
Hwang Y.
(2017)
The mesolayer of attached eddies in wall-bounded turbulent flows
in 10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017
Pausch M
(2019)
Quasilinear approximation for exact coherent states in parallel shear flows
in Fluid Dynamics Research
Cho M
(2018)
Scale interactions and spectral energy transfer in turbulent channel flow
in Journal of Fluid Mechanics
Yang Q
(2017)
Energy production and self-sustained turbulence at the Kolmogorov scale in Couette flow
in Journal of Fluid Mechanics
Hwang Y
(2016)
Invariant solutions of minimal large-scale structures in turbulent channel flow for up to 1000
in Journal of Fluid Mechanics
De Giovanetti M
(2017)
Streak instability in turbulent channel flow: the seeding mechanism of large-scale motions
in Journal of Fluid Mechanics
Yang Q
(2019)
Exact coherent states of attached eddies in channel flow
in Journal of Fluid Mechanics
Doohan P
(2019)
Shear stress-driven flow: the state space of near-wall turbulence as
in Journal of Fluid Mechanics
Ibrahim J
(2018)
Phase-space dynamics of opposition control in wall-bounded turbulent flows
in Journal of Fluid Mechanics
Hwang Y
(2016)
Self-sustaining process of minimal attached eddies in turbulent channel flow
in Journal of Fluid Mechanics
De Giovanetti M
(2016)
Skin-friction generation by attached eddies in turbulent channel flow
in Journal of Fluid Mechanics
Cassinelli A
(2017)
Streak instability in near-wall turbulence revisited
in Journal of Turbulence
Cossu C
(2017)
Self-sustaining processes at all scales in wall-bounded turbulent shear flows.
in Philosophical transactions. Series A, Mathematical, physical, and engineering sciences
Hwang Y
(2016)
Mesolayer of attached eddies in turbulent channel flow
in Physical Review Fluids
Description | The research funded by this grant enabled me to unveil the fundamental mechanism which makes turbulence in near-solid surface sustained. This has a huge range of applications, including wing and wind turbine design, ship hulls, train and aircraft, etc. |
Exploitation Route | The research has generated the valuable knowledge on the origin of turbulence and its sustaining mechanisms. Therefore, this knowledge can be used to design sufaces of wings of aircrafts, turbine blades, ship hull etc. This knowledge will particularly be useful to model and control the flows, and the on-going research in my group is dedicated to generate a novel turbulence model that can generate turbulent spectra combining with data-driven techniques. In the future, this model can be used how turbulence responds to external perturbation such as surface protrusion and external noise, which will be crucial in industrail applications. |
Sectors | Aerospace, Defence and Marine,Energy,Transport |
Description | EPSRC summer school on Modal Decompositions in Fluid Mechanics |
Geographic Reach | Multiple continents/international |
Policy Influence Type | Influenced training of practitioners or researchers |
Impact | Educated 60 PhD and postdoctoral researchers about the state-of-the-art data-driven analysis technique for fluid mechanics. |
URL | https://fluids.ac.uk/sig/FlowInstability |
Description | A dynamical systems analysis of high-Reynolds-number wall turbulence |
Amount | £414,596 (GBP) |
Funding ID | EP/T009365/1 |
Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
Sector | Public |
Country | United Kingdom |
Start | 08/2020 |
End | 07/2024 |
Description | Assessing attached eddy hypothesis using quasi-linear approximations |
Amount | £211,930 (GBP) |
Funding ID | RPG-2019-123 |
Organisation | The Leverhulme Trust |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 03/2020 |
End | 02/2023 |
Description | SIG on Flow instability, modelling and control |
Amount | £811,714 (GBP) |
Funding ID | EP/N032861/1 |
Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
Sector | Public |
Country | United Kingdom |
Start | 12/2016 |
End | 11/2019 |
Description | A spectral attached eddy model for finite Reynolds number |
Organisation | University of Melbourne |
Country | Australia |
Sector | Academic/University |
PI Contribution | Developed a novel statistical model of wall turbulence valid at finite Reynolds number (all the classical model work at infinite Reynolds numbers) |
Collaborator Contribution | Currently writing a new paper |
Impact | Visiting fellowship at the University of Melbourne. |
Start Year | 2019 |
Description | Quasi-linear approximation |
Organisation | Philipp University of Marburg |
Country | Germany |
Sector | Academic/University |
PI Contribution | Made some numerical calculation for a paper published together. |
Collaborator Contribution | Theoretical aspect was developed by the partner |
Impact | Paper publication: Quasi-linear approximation of exact coherent states in parallel shear flows, 2018. M. Pausch, Q. Yang, Y. Hwang & B. Eckhardt, Fluid Dyn. Res. (Invited Special Issue), 51, 011402. Attached eddy model revisited using a minimal quasi-linear approximation Y. Hwang & B. Eckhardt, J. Fluid Mech., 894, A23 |
Start Year | 2017 |
Description | Scale interaction in wall turbulence |
Organisation | University of Paris-Saclay |
Country | France |
Sector | Academic/University |
PI Contribution | We have just built contribution. We are currently writing a proposal together. |
Collaborator Contribution | We have just built contribution. We are currently writing a proposal together. |
Impact | Not yet. |
Start Year | 2019 |
Description | 10th International Symposium of Turbulent Shear Flow Phenomena |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | More than 500 researchers and students working on turbulence attended this international meeting, which led to active discussion and collaboration on the current and future research. |
Year(s) Of Engagement Activity | 2017 |
URL | http://tsfp10.org/ |
Description | A talk or presentation - Annual Meeting of Division of Fluid Dynamics, American Physical Society |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | More than 100 people attended my presentation and successfully delivered the research outcome to international research community |
Year(s) Of Engagement Activity | 2019 |
Description | Annual Meeting of Division of Fluid Dynamics in American Physical Society |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | This is the largest meeting in Fluid Mechanics -- More than 3000 researchers, students and industrial people attended this meeting to present and discuss their research progress and future direction. |
Year(s) Of Engagement Activity | 2017 |
URL | http://www.apsdfd2017.org/ |
Description | Annual Meeting of Division of Fluid Dynamics, American Physical Society |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Study participants or study members |
Results and Impact | A member of group, Patrick Doohan, delivered a presentation on dynamical systems analysis of the near-wall turbulence |
Year(s) Of Engagement Activity | 2018 |
Description | Annual Meeting of UK turbulence consortium |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Study participants or study members |
Results and Impact | About 60-70 academics, postdocs and PG students attended the meeting to discuss progress of their research activities through UK turbulence consortium (EP/L000261/1) |
Year(s) Of Engagement Activity | 2016 |
URL | http://www.turbulence.ac.uk/ |
Description | Annual meeting of American Physical Society Division of Fluid Dynamics |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Study participants or study members |
Results and Impact | About 3000 researchers, including academics, postdocs, postgraduate and undergraduate students attended for the conference, which sparked dissemination and discussions of my current research activities |
Year(s) Of Engagement Activity | 2016 |
URL | http://meetings.aps.org/Meeting/DFD16/Content/3199 |
Description | Euromech Colloquium 586 on Turbulent Superstructures in open and closed flows |
Form Of Engagement Activity | A formal working group, expert panel or dialogue |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | 60 international experts and their postgraduate students attended this meeting to discuss the current progress in turbulence research. I was invited one of the named speaker. |
Year(s) Of Engagement Activity | 2017 |
URL | http://586.euromech.org/ |
Description | Euromech Colloquium 591 on Three-dimensional instability mechanisms on transitional and turbulent flows |
Form Of Engagement Activity | A formal working group, expert panel or dialogue |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | More than 60 international experts and their postgraduate students were gather to discuss on progress in the area of transition and turbulence. A collaboration has been developed through this meeting (with Dr Yohann Duguet at LIMSI-CNRS, University of Paris-Saclay). |
Year(s) Of Engagement Activity | 2017 |
URL | http://591.euromech.org/ |
Description | Euromech Fluid Mechanics Conference |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Postgraduate students |
Results and Impact | A member of group, Patrick Doohan, delivered a presentation on dynamical systems analysis of the model of near-wall turbulence |
Year(s) Of Engagement Activity | 2018 |
Description | International Congress of Theoretical and Applied Mechanics (Montreal) |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Study participants or study members |
Results and Impact | More than 3000 researchers (academics, postdocs, PG and UG studentes) attended to the conference, which sparked active dissemination of my current research activities and development of future collaboration |
Year(s) Of Engagement Activity | 2016 |
URL | http://www.ictam2016.org/ |
Description | International Symposium on Turbulent Shear Flow Phenomena |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | More than 100 people attended my presentation and successfully delivered the research outcome to international research community |
Year(s) Of Engagement Activity | 2019 |
URL | http://tsfp11.org/ |
Description | Invited Talk in University of Philps Marburg |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | Give an invited seminar in Physics department at University of Marburg |
Year(s) Of Engagement Activity | 2017 |
Description | Invited seminar at Applied Mathematics in University of Leeds |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Study participants or study members |
Results and Impact | Delivered an invited talk on dynamical systems analysis on attached eddies in wall turbulence to research group in Leeds. |
Year(s) Of Engagement Activity | 2018 |
Description | Invited seminar for the University of Melbourne |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Professional Practitioners |
Results and Impact | More than 50 people attended my presentation and successfully delivered the research outcome to the fluid research group at the University of Melbourne (the fluid group is one of the world leaders in turbulence research). |
Year(s) Of Engagement Activity | 2019 |
Description | Invited talk - CNRS-LIMSI France |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Study participants or study members |
Results and Impact | Gave an invited seminar on coherent structures on wall-bounded turbulence and sparked interest in LIMSI |
Year(s) Of Engagement Activity | 2018 |
Description | Invited talk in the Department of Applied Mathematics and Theoretical Physics, University of Cambridge |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Other audiences |
Results and Impact | Gave an invited presentation to fluid mechanics community in DAMTP at University of Cambridge |
Year(s) Of Engagement Activity | 2018 |
Description | Organisation of Euromech Colloquium 598 on Coherent structures in wall-bounded shear flows: New Directions of a Classical Problem |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | About 60 world-leading experts in transition and turbulence met and presented their research. There was also a big discussion on future direction. |
Year(s) Of Engagement Activity | 2018 |
Description | Organisation of SIG on flow instability, modelling and control in the UK fluid network |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Study participants or study members |
Results and Impact | Organised a Special Interest Group |
Year(s) Of Engagement Activity | 2016 |
URL | https://www.ukfluids.net/ |
Description | SIG meeting on flow instability, modelling and control in UK fluid network |
Form Of Engagement Activity | A formal working group, expert panel or dialogue |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Professional Practitioners |
Results and Impact | 40 experts and postgraduate students working flow instability, modelling and control were gathered to discuss the recent advance in research in this area. Nationwide collaboration and future direction were discussed. |
Year(s) Of Engagement Activity | 2017 |
URL | https://fluids.ac.uk/sig/FlowInstability |
Description | UK Fluid conference |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Study participants or study members |
Results and Impact | About 300 researchers, including academics, postdocs, postgraduate and undergraduate students attended for the conference, which sparked dissemination of my current research activities with active discussions |
Year(s) Of Engagement Activity | 2016 |
URL | http://www.imperial.ac.uk/fluids-cdt/uk-fluids-conference-2016/ |
Description | UK fluid conference |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Professional Practitioners |
Results and Impact | Researchers and students in the UK participated in the national fluid conference to discuss their research and collaboration. |
Year(s) Of Engagement Activity | 2017 |
URL | https://engineering.leeds.ac.uk/events/event/210/uk_fluids_conference_2017 |
Description | Visit to specialist workshop in Kavli institute of theoretical physics in UC Santa Barbara by invitation (California) |
Form Of Engagement Activity | A formal working group, expert panel or dialogue |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Study participants or study members |
Results and Impact | The leading experts in turbulence and dynamical systems are invited to actively discuss the future direction of the field |
Year(s) Of Engagement Activity | 2017 |
URL | http://online.kitp.ucsb.edu/online/transturb_c17/ |