A direct numerical simulation analysis of coherent structures in bubble-laden channel flows

Haßlberger, Josef; Cifani, Paolo; Chakraborty, Nilanjan; Klein, Markus

doi:10.1017/jfm.2020.780

Cited by 13 publications

(8 citation statements)

References 45 publications

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“…34 The average relative velocity between the two phases in stream-wise direction is defined as u rel = ⟨u⟩ l − ⟨u⟩ g , where the phase-conditional averaging ⟨⋅⟩ l,g is limited to the bulk region 0.5 < y∕H < 1.5 to exclude the relatively bubble-free wall boundary layers. 7 The higher Eötvös number of Eo = 3.75 is prescribed by decreasing the surface tension coefficient, while retaining all other parameters. Here, the bubble Reynolds number is approximately Re b ≈ 358, which in combination with Eo leads to ellipsoidal and wobbling bubbles.…”

Section: Case Definitionmentioning

confidence: 99%

“…Since experimental techniques such as non‐intrusive imaging are usually limited to very dilute void fractions, 1,2 numerical investigations play a major role in improving the fundamental understanding of such flows. The increase in computational resources has allowed first large‐scale direct numerical simulations (DNS) of turbulent bubble‐laden channel flows 3–8 . While the pioneering studies of Lu and Tryggvason 9–11 featured relatively small‐scale channel flows with up to 72 bubbles, recently developed massively parallel solvers 5,12 are able to perform DNS with up to

𝒪 (1 0^{4})

bubbles in full‐scale channels, while maintaining excellent scalability.…”

Section: Introductionmentioning

confidence: 99%

“…The increase in computational resources has allowed first large-scale direct numerical simulations (DNS) of turbulent bubble-laden channel flows. [3][4][5][6][7][8] While the pioneering studies of Lu and Tryggvason [9][10][11] featured relatively small-scale channel flows with up to 72 bubbles, recently developed massively parallel solvers 5,12 are able to perform DNS with up to  (10 4 ) bubbles in full-scale channels, while maintaining excellent scalability. However, due to the computational cost, DNS will remain limited to reduced-complexity bubbly flows at moderate Reynolds numbers for the foreseeable future.…”

mentioning

confidence: 99%

“…Therefore, in the recent years, first large-scale simulations of freely deformable bubbles in turbulent flow have been performed. Compared to previous studies, [5][6][7]42 the utilization of the volume conservation methods allows to study particularly challenging setups combining high Reynolds and Eötvös numbers and coarse grid resolutions, which have been out of reach for this numerical framework previously. This is a first step towards LES of turbulent bubble-laden flows in realistic industrial applications.…”

mentioning

confidence: 99%

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Enforcing accurate volume conservation in VOF‐based long‐term simulations of turbulent bubble‐laden flows on coarse grids

Trautner,

Hasslberger,

Cifani

et al. 2024

Numerical Methods in Fluids

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This study proposes two different strategies to enforce accurate volume conservation in volume‐of‐fluid (VOF)‐based simulations of turbulent bubble‐laden flows on coarse grids. It is demonstrated that, without a correction, minimal volume errors on a time‐step level, caused by the under‐resolution of the interface, can accumulate to significant deviations from the intended flow conditions despite the comparably good volume conservation properties of the geometric VOF method. In particular, large volume errors are observed for challenging setups combining coarse grid resolutions and comparably high Reynolds and Eötvös numbers. The problem is reinforced for long‐term simulations in periodic domains, which are often performed to collect flow statistics of bubbly flows. The first proposed volume conservation method simply corrects the volume error of a bubble by uniformly adding or removing the respective amount of gas volume in the interface cells. The second proposed method performs an additional reconstruction and advection step of the VOF field using a non‐divergence‐free velocity field, which can be interpreted as a slight dilatation or contraction of the bubble. A comparison between the global flow statistics as well as the individual bubble dynamics for both volume conservation methods reveals that the results are quasi‐identical for a number of challenging test cases, while the gas volume is accurately conserved. The proposed methods allow to perform numerical simulations of freely deformable bubbles in turbulent flows for setups that have previously been out of reach for this numerical framework.

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Section: Case Definitionmentioning

confidence: 99%

𝒪 (1 0^{4})

bubbles in full‐scale channels, while maintaining excellent scalability.…”

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Enforcing accurate volume conservation in VOF‐based long‐term simulations of turbulent bubble‐laden flows on coarse grids

Trautner,

Hasslberger,

Cifani

et al. 2024

Numerical Methods in Fluids

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“…This choice is related to studies carried out at low Re number (Bunner & Tryggvason 2002). A very recent study characterising the topological properties of the agitation induced by two bubbles (Hasslberger et al 2020) is also worth mentioning. This work uses a higher resolution (Δx = d b /40), but for a flow at very high Reynolds number, larger than 900.…”

Section: Introductionmentioning

confidence: 99%