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Influence of strong perturbations on wall-bounded flows

Influence of strong perturbations on wall-bounded flows
Influence of strong perturbations on wall-bounded flows
© 2018 American Physical Society. Single-point hot-wire measurements are made downstream of a series of spanwise repeating obstacles that are used to generate an artificially thick turbulent boundary layer. The measurements are made in the near field, in which the turbulent boundary layer is beginning to develop from the wall-bounded wakes of the obstacles. The recent paper of Rodríguez-López et al. [E. Rodríguez-López, Phys. Rev. Fluids 1, 074401 (2016)2469-990X10.1103/PhysRevFluids.1.074401] broadly categorized the mechanisms by which canonical turbulent boundary layers eventually develop from wall-bounded wakes into two distinct mechanisms, the wall-driven and wake-driven mechanisms. In the present work we attempt to identify the geometric parameters of tripping arrays that trigger these two mechanisms by examining the spectra of the streamwise velocity fluctuations and the intermittent outer region of the flow. Using a definition reliant upon the magnitude of the velocity fluctuations, an intermittency function is devised that can discriminate between turbulent and nonturbulent flow. These results are presented along with the spectra in order to try to ascertain which aspects of a trip's geometry are more likely to favor the wall-driven or wake-driven mechanism. The geometrical aspects of the trips tested are the aspect ratio, the total blockage, and the blockage at the wall. The results indicate that the presence, or not, of perforations is the most significant factor in affecting the flow downstream. The bleed of fluid through the perforations reenergizes the mean recirculation and leads to a narrower intermittent region with a more regular turbulent-nonturbulent interface. The near-wall turbulent motions are found to recover quickly downstream of all of the trips with a wall blockage of 50%, but a clear influence of the outer fluctuations, generated by the tip vortices of the trips, is observed in the near-wall region for the high total blockage trips. The trip with 100% wall blockage is found to modify the nature of the inner-wall peak of turbulent kinetic energy.
2469-990X
1-18
Buxton, O.R.H.
9b41844d-45ee-4508-8773-528f1fb0f97f
Ewenz Rocher, M.
d76617b8-9cc7-4152-b7e5-3fd302e1ea8f
Rodríguez-López, E.
0aef9cc6-1abf-48b6-bafb-e20201b44d6a
Buxton, O.R.H.
9b41844d-45ee-4508-8773-528f1fb0f97f
Ewenz Rocher, M.
d76617b8-9cc7-4152-b7e5-3fd302e1ea8f
Rodríguez-López, E.
0aef9cc6-1abf-48b6-bafb-e20201b44d6a

Buxton, O.R.H., Ewenz Rocher, M. and Rodríguez-López, E. (2018) Influence of strong perturbations on wall-bounded flows. Physical Review Fluids, 3 (1), 1-18, [014605]. (doi:10.1103/PhysRevFluids.3.014605).

Record type: Article

Abstract

© 2018 American Physical Society. Single-point hot-wire measurements are made downstream of a series of spanwise repeating obstacles that are used to generate an artificially thick turbulent boundary layer. The measurements are made in the near field, in which the turbulent boundary layer is beginning to develop from the wall-bounded wakes of the obstacles. The recent paper of Rodríguez-López et al. [E. Rodríguez-López, Phys. Rev. Fluids 1, 074401 (2016)2469-990X10.1103/PhysRevFluids.1.074401] broadly categorized the mechanisms by which canonical turbulent boundary layers eventually develop from wall-bounded wakes into two distinct mechanisms, the wall-driven and wake-driven mechanisms. In the present work we attempt to identify the geometric parameters of tripping arrays that trigger these two mechanisms by examining the spectra of the streamwise velocity fluctuations and the intermittent outer region of the flow. Using a definition reliant upon the magnitude of the velocity fluctuations, an intermittency function is devised that can discriminate between turbulent and nonturbulent flow. These results are presented along with the spectra in order to try to ascertain which aspects of a trip's geometry are more likely to favor the wall-driven or wake-driven mechanism. The geometrical aspects of the trips tested are the aspect ratio, the total blockage, and the blockage at the wall. The results indicate that the presence, or not, of perforations is the most significant factor in affecting the flow downstream. The bleed of fluid through the perforations reenergizes the mean recirculation and leads to a narrower intermittent region with a more regular turbulent-nonturbulent interface. The near-wall turbulent motions are found to recover quickly downstream of all of the trips with a wall blockage of 50%, but a clear influence of the outer fluctuations, generated by the tip vortices of the trips, is observed in the near-wall region for the high total blockage trips. The trip with 100% wall blockage is found to modify the nature of the inner-wall peak of turbulent kinetic energy.

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e-pub ahead of print date: 16 January 2018
Published date: January 2018

Identifiers

Local EPrints ID: 418704
URI: http://eprints.soton.ac.uk/id/eprint/418704
ISSN: 2469-990X
PURE UUID: ff2a8e6e-fdc5-4e8c-b588-573c845ac508
ORCID for E. Rodríguez-López: ORCID iD orcid.org/0000-0003-3927-8811

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Date deposited: 19 Mar 2018 17:30
Last modified: 16 Dec 2019 18:25

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