Journal
JOURNAL OF FLUID MECHANICS
Volume 935, Issue -, Pages -Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1017/jfm.2022.14
Keywords
computational methods; turbulence simulation
Categories
Funding
- University of Saskatchewan Dean's Scholarship
- Department of Mechanical Engineering
- Natural Sciences and Engineering Research Council (NSERC) of Canada
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This study aims to investigate the characteristics of flow through a pipe with a sudden expansion at low Reynolds numbers, and the possible sources of perturbation in numerical simulations and their effect on transition to turbulence. The results suggest that perturbations need to be added in refined simulations in order to produce turbulence, and even without intentional perturbations, there can still be significant sources of numerical perturbation and error that trigger turbulence in simulations.
At low Reynolds numbers, the flow through a pipe with a sudden expansion is characterized by the localized occurrence of flow instabilities, with the formation of a so-called turbulence puff. In the literature, physical experiments typically predict earlier occurrence of turbulence than computational fluid dynamics simulations. However, the behaviour of 'natural' transition to turbulence without perturbations, and the dependence of transition to turbulence on perturbations, are not yet fully understood, particularly for the simulations. The purpose of the present study is therefore to investigate this flow, including possible sources of perturbation in numerical simulations, and to evaluate their effect on transition to turbulence. Through the exploration of different flow rates, numerical settings and inlet perturbation amplitudes, and by evaluating coarse and refined simulations, insights into low-Reynolds-number transitional turbulent flows are obtained. The turbulence kinetic energy budget of the turbulence puff or slug characteristic of this flow is also evaluated. In conclusion, even when perturbations are not intentionally added, there can still be significant sources of numerical perturbation and error that trigger turbulence in simulations, but perturbations will need to be added in refined simulations in order to produce turbulence. Finally, the results agree with the notion that there may not be a scenario where the flow transitions naturally to turbulence without any perturbation.
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