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Taylor, P and Seddighi, M (2024) Turbulent–turbulent transient concept in pulsating flows. Journal of Fluid Mechanics, 982. A20-1-A20-43. ISSN 0022-1120
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Abstract
The turbulence behaviour of current-dominated pulsating flows has been investigated. Direct numerical simulations have been carried out for Stokes lengths over a range of l+s=5–26, and amplitudes spanning 90 % of the current-dominated regime, about a mean flow of Re=6275. The results show that the turbulence response in intermediate and low-frequency pulsations is governed by a multistage turbulent–turbulent transition process, which bears a strong similarity to the multistage response of non-periodic acceleration. During the early acceleration period, the flow enters a pretransition stage, in which a new laminar perturbation boundary layer forms at the wall, and the streamwise velocity streaks are stretched. If the low-speed streaks destabilise prior to the deceleration period, then the flow enters a transition stage in which the perturbation boundary layer undergoes a bypass-like transition process. A unique feature of pulsating flows is the ongoing mechanism of turbulence decay, which initiates during the deceleration period and constitutes the main transient turbulence mechanism for much of the cycle. For high-frequency pulsations, the perturbation boundary layer fails to reach the pretransition stage prior to the deceleration period. Instead, the flow alternates between two inertial stages which are characterised by two layers of amplified viscous force; one growing at the wall, and one detached and moving towards the core.
| Item Type: | Article |
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| Uncontrolled Keywords: | 01 Mathematical Sciences; 09 Engineering; Fluids & Plasmas |
| Subjects: | T Technology > TA Engineering (General). Civil engineering (General) |
| Divisions: | Engineering |
| Publisher: | Cambridge University Press |
| SWORD Depositor: | A Symplectic |
| Date Deposited: | 24 Nov 2023 13:40 |
| Last Modified: | 07 Mar 2024 13:45 |
| DOI or ID number: | 10.1017/jfm.2023.1025 |
| URI: | https://researchonline.ljmu.ac.uk/id/eprint/21940 |
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