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Published May 19, 2016 | public
Journal Article

Streamwise-varying steady transpiration control in turbulent pipe flow


The effect of streamwise-varying steady transpiration on turbulent pipe flow is examined using direct numerical simulation at fixed friction Reynolds number Re_τ=314. The streamwise momentum equation reveals three physical mechanisms caused by transpiration acting in the flow: modification of Reynolds shear stress, steady streaming and generation of non-zero mean streamwise gradients. The influence of these mechanisms has been examined by means of a parameter sweep involving transpiration amplitude and wavelength. The observed trends have permitted identification of wall transpiration configurations able to reduce or increase the overall flow rate −36.1% and 19.3%, respectively. Energetics associated with these modifications are presented. A novel resolvent formulation has been developed to investigate the dynamics of pipe flows with a constant cross-section but with time-mean spatial periodicity induced by changes in boundary conditions. This formulation, based on a triple decomposition, paves the way for understanding turbulence in such flows using only the mean velocity profile. Resolvent analysis based on the time-mean flow and dynamic mode decomposition based on simulation data snapshots have both been used to obtain a description of the reorganization of the flow structures caused by the transpiration. We show that the pipe flows dynamics are dominated by a critical-layer mechanism and the waviness induced in the flow structures plays a role on the streamwise momentum balance by generating additional terms.

Additional Information

© 2016 Cambridge University Press. Received 12 October 2015; revised 2 March 2016; accepted 15 April 2016; first published online 19 May 2016. The authors acknowledge financial support from the Australian Research Council through the ARC Discovery Project DP130103103, from Australia's National Computational Infrastructure via Merit Allocation Scheme Grant d77, and from the US Office of Naval Research, grant no. N000141310739 (B.J.M.).

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