Near-wall behaviour of transient flow in a channel with distributed pyramid roughness

Mehdi Seddighi*, Shuisheng He, Dubravka Pokrajac, Tom O'Donoghue, Alan Vardy

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

DNS has been performed to investigate near-wall behaviour of turbulence for a rapid 'turbulent-to-turbulent' transient flow in a channel with a smooth top surface and a rough bottom surface made of close-packed pyramids. The transient flow is studied following a rapid change in flow rate from Re = 2800 to Re = 7400. The equivalent roughness heights normalised by the wall units, k+ s, of the initial and final flows are, respectively, 14.5 and 41. The results show that near-wall behaviour of turbulence in the early stages of the transient process for the rough wall differs significantly from that over the smooth-wall. The early transient process over the rough-wall is in the form of a single cycle of birth, evolution and eventually breakdown of strong primary counter-rotating hairpin structures in the region very close to the roughness crests. Similar to that in a steady flow, the direct effect of roughness in a transient flow is confined to a region up to approximately three times of roughness height above the crest. Though the transient process starts from an initially fully-developed turbulent flow, the early transient process exhibits a roughness-induced laminar-turbulent transition. Various statistical quantities, including the three components of r.m.s. of velocity fluctuations and also turbulent shear stress, confirm the visualisation results.

Original languageEnglish
Title of host publication9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015
PublisherTSFP-9
Volume1
ISBN (Electronic)9780000000002
Publication statusPublished - 1 Jan 2015
Event9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015 - Melbourne, Australia
Duration: 30 Jun 20153 Jul 2015

Conference

Conference9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015
CountryAustralia
CityMelbourne
Period30/06/153/07/15

Fingerprint

Surface roughness
Turbulence
Confined flow
Steady flow
Turbulent flow
Shear stress
Visualization
Flow rate

ASJC Scopus subject areas

  • Fluid Flow and Transfer Processes

Cite this

Seddighi, M., He, S., Pokrajac, D., O'Donoghue, T., & Vardy, A. (2015). Near-wall behaviour of transient flow in a channel with distributed pyramid roughness. In 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015 (Vol. 1). TSFP-9.

Near-wall behaviour of transient flow in a channel with distributed pyramid roughness. / Seddighi, Mehdi; He, Shuisheng; Pokrajac, Dubravka; O'Donoghue, Tom; Vardy, Alan.

9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015. Vol. 1 TSFP-9, 2015.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Seddighi, M, He, S, Pokrajac, D, O'Donoghue, T & Vardy, A 2015, Near-wall behaviour of transient flow in a channel with distributed pyramid roughness. in 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015. vol. 1, TSFP-9, 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015, Melbourne, Australia, 30/06/15.
Seddighi M, He S, Pokrajac D, O'Donoghue T, Vardy A. Near-wall behaviour of transient flow in a channel with distributed pyramid roughness. In 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015. Vol. 1. TSFP-9. 2015
Seddighi, Mehdi ; He, Shuisheng ; Pokrajac, Dubravka ; O'Donoghue, Tom ; Vardy, Alan. / Near-wall behaviour of transient flow in a channel with distributed pyramid roughness. 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015. Vol. 1 TSFP-9, 2015.
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