Relaminarization by steady modification of the streamwise velocity profile in a pipe Journal Article


Author(s): Kühnen, Jakob; Scarselli, Davide; Schaner, Markus; Hof, Björn
Article Title: Relaminarization by steady modification of the streamwise velocity profile in a pipe
Affiliation IST Austria
Abstract: We show that a rather simple, steady modification of the streamwise velocity profile in a pipe can lead to a complete collapse of turbulence and the flow fully relaminarizes. Two different devices, a stationary obstacle (inset) and a device which injects fluid through an annular gap close to the wall, are used to control the flow. Both devices modify the streamwise velocity profile such that the flow in the center of the pipe is decelerated and the flow in the near wall region is accelerated. We present measurements with stereoscopic particle image velocimetry to investigate and capture the development of the relaminarizing flow downstream these devices and the specific circumstances responsible for relaminarization. We find total relaminarization up to Reynolds numbers of 6000, where the skin friction in the far downstream distance is reduced by a factor of 3.4 due to relaminarization. In a smooth straight pipe the flow remains completely laminar downstream of the control. Furthermore, we show that transient (temporary) relaminarization in a spatially confined region right downstream the devices occurs also at much higher Reynolds numbers, accompanied by a significant local skin friction drag reduction. The underlying physical mechanism of relaminarization is attributed to a weakening of the near-wall turbulence production cycle.
Keywords: pipe flow; Relaminarization; turbulence control; drag reduction
Journal Title: Flow Turbulence and Combustion
ISSN: 1573-1987
Publisher: Springer  
Date Published: 2018-01-01
Start Page: Epub ahead of print
Copyright Statement: CC BY
Sponsor: The project was partially funded by the European Research Council under the European Union’s Seventh Framework Program (FP/2007-2013)/ERC grant agreement 306589.
DOI: 10.1007/s10494-018-9896-4
Notes: We thank George H. Choueiri for friendly help and useful discussions. We thank M. Schwegel for a Matlab-code to post process experimental data.
Open access: yes (OA journal)