Hibernating Turbulence

Lead Research Organisation: University of Liverpool
Department Name: Centre for Engineering Dynamics


Recent Direct Numerical Simulations (DNS) of low Reynolds number (Re=3600) turbulent channel flow of dilute polymer solutions have discovered - even in the Newtonian limit - intervals of so-called "hibernating" turbulence (Xi and Graham (2010a)). In this state many features of fully drag-reduced flow are observed (i.e. features associated with Virk's Maximum Drag Reduction Asymptote MDRA Virk (1975)); weak streamwise structures, reduced Reynolds shear stresses and, as a consequence, enhanced mass flux (at constant driving pressure) i.e. drag reduction occurs. The aim of this project is to search for experimental verification of this hibernating turbulence and extract the coherent structures within it over a range of Reynolds numbers. Ultimately, enhanced knowledge of hibernation can pave the way for novel flow-control strategies to maintain this hibernating state and therefore substantially reduce skin friction drag.

Planned Impact

It is anticipated that the fundamental understanding gained from this project will subsequently be applied to a follow-on proposal to implement a number of possible flow control concepts. The intention here would be to devise strategies to encourage hibernating turbulence without recourse to polymer addition. If hibernating turbulence can be encouraged (at the expense of active turbulence) then this opens the door to numerous practical applications for skin-friction reduction and huge potential impact. Reduction of skin-friction drag has been a major goal for many decades and there are obviously huge and unlimited commercial potentials: the Alaskan pipe line is often cited as a major commercial example of reducing pumping costs but decreasing drag around ships and or submarines and improving efficiency in district heating and cooling systems or geothermal systems are a few other examples of vast commercial exploitability. In Japan, for example, district heating and cooling systems are becoming increasing widely used and there are now over 100 installations [Ref 6 in CfS]. The benefits of comparable reduction in frictional drag without recourse to polymer addition - through flow control to maintain hibernating turbulence for example - clearly offer an even greater avenue for net energy savings. An additional benefit of the increased understanding that this proposal will produce is that it may offer different routes for active control techniques. We anticipate that the fundamental understanding gained from this future project will subsequently be applied to practical engineering and we would look to the Knowledge Transfer Partnership (KTP) scheme in collaboration with industry, in the medium future (in 7-10 years time), to produce practical applications. As turbulence control and reduction has been a major scientific goal for many over the past 50 years or so, such ideas are at the high end of the high risk/high return spectrum of research. Without the fundamental experiments proposed in this study, future development in this exciting area (i.e. this recently discovered hibernating turbulence state) will be more limited.


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Description The aim of this project was to search for experimental verification of a so-called "hibernating turbulence" state where the amount of drag/energy consumed by a flowing liquid had been shown by simulation to be significantly lower during these intervals than might otherwise be expected. We were able to observe these states experimentally and so confirm that there are such states - embedded within the very complex chaotic turbulence motions - which consume significantly less energy than the turbulent state does on average. We were also able to image the flowfield during these states for a small range of flowrates and gain a better understanding of their structure in an extended spatial domain which is move relevant to "real" fluid systems.
Exploitation Route Ultimately, enhanced knowledge of the so-called "hibernating" state of turbulence can pave the way for novel flow-control strategies - e.g. to maintain this hibernating state - and therefore substantially reduce skin friction drag and pumping costs for fluid transport in pipelines etc.
Sectors Aerospace, Defence and Marine,Chemicals,Energy,Manufacturing, including Industrial Biotechology

Description EOARD White Paper
Amount $120,000 (USD)
Organisation European Office of Aerospace Research & Development (EOARD) 
Sector Public
Country United Kingdom
Start 05/2016 
End 05/2019