The minimal-span channel for rough-wall turbulent flows
Boundary layers; Pressure gradient; Quay walls; Reynolds number; Shear stress; Turbulence; Turbulent flow; Wall flow; Computational time; Hydraulic behaviour; Improving performance; Pressure-gradient parameters; Statistical uncertainty; Stream-wise velocities; Turbulence simulation; Turbulent bounda...
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2023
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my.uniten.dspace-232562023-05-29T14:38:51Z The minimal-span channel for rough-wall turbulent flows MacDonald M. Chung D. Hutchins N. Chan L. Ooi A. Garci�-Mayoral R. 56611327100 34976574800 15925318900 57139456500 7005905452 37088430100 Boundary layers; Pressure gradient; Quay walls; Reynolds number; Shear stress; Turbulence; Turbulent flow; Wall flow; Computational time; Hydraulic behaviour; Improving performance; Pressure-gradient parameters; Statistical uncertainty; Stream-wise velocities; Turbulence simulation; Turbulent boundary layers; Shear flow; channel flow; flow modeling; pressure gradient; Reynolds number; shear stress; surface roughness; turbulence; turbulent boundary layer; turbulent flow Roughness predominantly alters the near-wall region of turbulent flow while the outer layer remains similar with respect to the wall shear stress. This makes it a prime candidate for the minimal-span channel, which only captures the near-wall flow by restricting the spanwise channel width to be of the order of a few hundred viscous units. Recently, Chung et al. (J. Fluid Mech., vol. 773, 2015, pp. 418-431) showed that a minimal-span channel can accurately characterise the hydraulic behaviour of roughness. Following this, we aim to investigate the fundamental dynamics of the minimal-span channel framework with an eye towards further improving performance. The streamwise domain length of the channel is investigated with the minimum length found to be three times the spanwise width or 1000 viscous units, whichever is longer. The outer layer of the minimal channel is inherently unphysical and as such alterations to it can be performed so long as the near-wall flow, which is the same as in a full-span channel, remains unchanged. Firstly, a half-height (open) channel with slip wall is shown to reproduce the near-wall behaviour seen in a standard channel, but with half the number of grid points. Next, a forcing model is introduced into the outer layer of a half-height channel. This reduces the high streamwise velocity associated with the minimal channel and allows for a larger computational time step. Finally, an investigation is conducted to see if varying the roughness Reynolds number with time is a feasible method for obtaining the full hydraulic behaviour of a rough surface. Currently, multiple steady simulations at fixed roughness Reynolds numbers are needed to obtain this behaviour. The results indicate that the non-dimensional pressure gradient parameter must be kept below 0.03-0.07 to ensure that pressure gradient effects do not lead to an inaccurate roughness function. An empirical costing argument is developed to determine the cost in terms of CPU hours of minimal-span channel simulations a priori. This argument involves counting the number of eddy lifespans in the channel, which is then related to the statistical uncertainty of the streamwise velocity. For a given statistical uncertainty in the roughness function, this can then be used to determine the simulation run time. Following this, a finite-volume code with a body-fitted grid is used to determine the roughness function for square-based pyramids using the above insights. Comparisons to experimental studies for the same roughness geometry are made and good agreement is observed. � 2017 Cambridge University Press. Final 2023-05-29T06:38:50Z 2023-05-29T06:38:50Z 2017 Article 10.1017/jfm.2017.69 2-s2.0-85014044349 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85014044349&doi=10.1017%2fjfm.2017.69&partnerID=40&md5=1401fa66a9a10f2cd2e6a45b0554b6f2 https://irepository.uniten.edu.my/handle/123456789/23256 816 5 42 All Open Access, Green Cambridge University Press Scopus |
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| description |
Boundary layers; Pressure gradient; Quay walls; Reynolds number; Shear stress; Turbulence; Turbulent flow; Wall flow; Computational time; Hydraulic behaviour; Improving performance; Pressure-gradient parameters; Statistical uncertainty; Stream-wise velocities; Turbulence simulation; Turbulent boundary layers; Shear flow; channel flow; flow modeling; pressure gradient; Reynolds number; shear stress; surface roughness; turbulence; turbulent boundary layer; turbulent flow |
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56611327100 |
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56611327100 MacDonald M. Chung D. Hutchins N. Chan L. Ooi A. Garci�-Mayoral R. |
| format |
Article |
| author |
MacDonald M. Chung D. Hutchins N. Chan L. Ooi A. Garci�-Mayoral R. |
| spellingShingle |
MacDonald M. Chung D. Hutchins N. Chan L. Ooi A. Garci�-Mayoral R. The minimal-span channel for rough-wall turbulent flows |
| author_sort |
MacDonald M. |
| title |
The minimal-span channel for rough-wall turbulent flows |
| title_short |
The minimal-span channel for rough-wall turbulent flows |
| title_full |
The minimal-span channel for rough-wall turbulent flows |
| title_fullStr |
The minimal-span channel for rough-wall turbulent flows |
| title_full_unstemmed |
The minimal-span channel for rough-wall turbulent flows |
| title_sort |
minimal-span channel for rough-wall turbulent flows |
| publisher |
Cambridge University Press |
| publishDate |
2023 |
| _version_ |
1806424521550331904 |
| score |
13.18916 |