Simulations of rib-roughened rough-to-smooth turbulent channel flows Ismail, Umair Zaki, Tamer Durbin, Paul Durbin, Paul
dc.contributor.department Aerospace Engineering 2018-11-17T19:44:46.000 2020-06-29T22:45:28Z 2020-06-29T22:45:28Z Mon Jan 01 00:00:00 UTC 2018 2018-11-25 2018-05-25
dc.description.abstract <p>High-fidelity simulations of turbulent flow through a channel with a rough wall, followed by a smooth wall, demonstrate a high degree of non-equilibrium within the recovery region. In fact, the recovery of all the flow statistics studied is incomplete by the streamwise exit of the computational domain. Above a thin wall layer, turbulence intensities significantly higher than fully developed, smooth-wall levels persist in the developing region. Within the thin wall layer, the profile shapes for turbulence stresses recover very quickly and wall-normal locations of characteristic peaks are established. However, even in this thin layer, complete recovery of magnitudes of turbulence stresses is exceptionally slow. A similar initially swift but eventually incomplete and slow relaxation behaviour is also shown by the skin friction. Between the turbulence shear and streamwise stresses, the turbulence shear stress shows a comparatively quick rate of recovery above a thin wall layer. Over the developing smooth wall, the balance is not merely between fluxes due to pressure and shear stresses. Strong momentum fluxes, which are directly influenced by the upstream roughness size, contribute significantly to this balance. Approximate curve fits estimate the streamwise distance required by the outer peaks of Reynolds stresses to attain near-fully-developed levels at approximately 20 delta-25 delta,with delta being the channel half height. An even longer distance, of more than 50 ffi, might be needed by the mean velocity to approach near-fully-developed magnitudes. Visualizations and correlations show that large-scale eddies that are created above the roughness persist downstream, and sporadically perturb the elongated streaks. These streaks of alternating high and low momentum appear almost instantly after the roughness is removed. The mean flow does not re-establish an equilibrium log layer within the computational domain, and the velocity deficit created by the roughness continues throughout the domain. On the step change in roughness, near the wall, profiles for turbulence kinetic energy dissipation rate, epsilon, and energy spectra indicate a sharp reduction in energy at small scales. Despite this, reversion towards equilibrium smooth-wall levels is slow, and ultimately incomplete, due to a rather slow adjustment of the turbulence cascade. The non-dimensional roughness height, k(+) ranges from 42 to 254 and the friction velocity Reynolds number at the smooth wall, Re-tau S, ranges from 284 to 1160 in the various simulations.</p>
dc.description.comments <p>This is a manuscript of an article published as Ismail, Umair, Tamer A. Zaki, and Paul A. Durbin. "Simulations of rib-roughened rough-to-smooth turbulent channel flows." <em>Journal of Fluid Mechanics</em> 843 (2018): 419-449. DOI: <a href="" target="_blank">10.1017/jfm.2018.119</a>. Posted with permission.</p>
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dc.identifier archive/
dc.identifier.articleid 1134
dc.identifier.contextkey 13305872
dc.identifier.s3bucket isulib-bepress-aws-west
dc.identifier.submissionpath aere_pubs/130
dc.language.iso en
dc.source.bitstream archive/|||Fri Jan 14 19:42:06 UTC 2022
dc.source.uri 10.1017/jfm.2018.119
dc.subject.disciplines Aerodynamics and Fluid Mechanics
dc.subject.disciplines Aerospace Engineering
dc.title Simulations of rib-roughened rough-to-smooth turbulent channel flows
dc.type article
dc.type.genre article
dspace.entity.type Publication
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relation.isOrgUnitOfPublication 047b23ca-7bd7-4194-b084-c4181d33d95d
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