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Delay of Turbulence in Pipe Flow (Delaying Turbulence)
Start date: 01 Jun 2008, End date: 31 May 2010 PROJECT  FINISHED 

The objective of this proposal is to delay the transition to turbulence in pipe flow. The important motivation of reducing drag in fluid flows, and therefore to reduce the energy consumption required to drive them, has lead to significant breakthroughs in the study of flow control. Only last year for the case of flow over a flat plate, turbulence was successfully delayed in experiment by using small controlled streaky disturbances to suppress the development of more unstable disturbances downstream. Key factors enabling this progress have been a recognition of the sensitivity of strongly sheared flows to disturbances caused by streamwise rolls, and the improvement of stability associated with modifications to the underlying mean flow. Simultaneously in pipe flow, the discovery of exact solutions to the Navier-Stokes equations has driven a surge of interest in transitional turbulence. These travelling wave solutions are believed to form a separatrix between laminar and turbulent states. Together these developments form a framework about which to design a strategy to delay turbulence in pipe flow, by systematic analysis of the stability of disturbances in the presence of controlled streaky flows.
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