pith. sign in

arxiv: 2604.17463 · v1 · submitted 2026-04-19 · ⚛️ physics.flu-dyn · physics.comp-ph

On the hydrodynamic behaviour of the immersed boundary -- lattice Boltzmann method for wetting problems

Elisa Bellantoni , Fabio Guglietta , Andreas Demou , Francesca Pelusi , Kiwon Um , Mihalis Nicolaou , Mathieu Desbrun , Mauro Sbragaglia
show 1 more author
Nikos Savva
This is my paper

Pith reviewed 2026-05-10 05:46 UTC · model grok-4.3

classification ⚛️ physics.flu-dyn physics.comp-ph
keywords lattice Boltzmann methodimmersed boundary methodwettingcontact linethin filmdroplet dynamicshydrodynamics
0
0 comments X

The pith

The immersed boundary lattice Boltzmann method with wetting potential forms a thin film to avoid abrupt contact-line curvature.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper examines the flow behavior of a lattice Boltzmann scheme that uses an immersed boundary and a wetting potential to model droplets on solid surfaces. This combination is meant to keep the interface from making a sharp turn at the point where it meets the wall. Instead of direct contact, a thin film of fluid stays between the droplet and the solid. To check if this film disrupts the expected fluid motion, the authors compare the results against two other standard ways of solving the same wetting problems.

Core claim

The IBLB scheme with wetting potential prevents abrupt curvature changes near the contact line but forms a thin film that could compromise hydrodynamic consistency; detailed comparisons against BEM and VoF elucidate its limits of validity in wetting applications.

What carries the argument

Wetting potential in the immersed boundary lattice Boltzmann method that maintains a thin film separating the fluid interface from the solid wall to smooth the contact line.

If this is right

  • The model avoids unphysical sharp bends in the droplet interface at the contact line.
  • Hydrodynamic quantities in the thin film region may deviate from classical expectations.
  • Agreement with reference methods holds for bulk droplet properties but needs verification near the wall.
  • The scheme remains applicable to wetting problems as long as the film effect is accounted for or negligible.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • This thin film approach might be combined with adaptive grid techniques to reduce its impact on accuracy.
  • Similar issues could arise in other interface-capturing methods that use potential-based wetting conditions.
  • Further tests at higher resolutions could determine how to minimize the film thickness while retaining the curvature-smoothing benefit.

Load-bearing premise

The thin film formed beneath the droplet does not introduce hydrodynamic inconsistencies that invalidate the model's predictions for contact-line dynamics and overall flow behavior.

What would settle it

A calculation or observation demonstrating that the flow inside the thin film deviates from the results of boundary element method simulations for identical wetting conditions would show that the hydrodynamic consistency does not hold.

Figures

Figures reproduced from arXiv: 2604.17463 by Andreas Demou, Elisa Bellantoni, Fabio Guglietta, Francesca Pelusi, Kiwon Um, Mathieu Desbrun, Mauro Sbragaglia, Mihalis Nicolaou, Nikos Savva.

Figure 1
Figure 1. Figure 1: Split view of the hydrodynamic fields around a droplet wetting a solid, simulated with the IBLB method [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Droplet’s height evolution during spreading with [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 4
Figure 4. Figure 4: Comparison of the droplet profiles for a spreading [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Comparison of height evolution of a spherical [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗
read the original abstract

We study the hydrodynamic behaviour of a mesoscale numerical model for wetting dynamics based on the immersed boundary - lattice Boltzmann (IBLB) method. This IBLB model features a wetting potential to capture the interaction between a non-ideal droplet interface and a solid boundary; it is designed to prevent abrupt curvature changes near the contact line. As this approach prevents direct contact between the droplet and the solid, it forms a thin film beneath the droplet, which could compromise the hydrodynamic consistency in this region. This paper presents detailed comparisons against two other hydrodynamic solvers, respectively based on a boundary element method (BEM) and a volume of fluid (VoF) method, in order to examine the hydrodynamic behaviour of this IBLB scheme, elucidate its limits of validity in wetting applications, and explore the properties of its contact-line model.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript examines the hydrodynamic behaviour of an immersed boundary-lattice Boltzmann (IBLB) method equipped with a wetting potential for simulating non-ideal droplet wetting dynamics. The wetting potential is introduced to avoid abrupt curvature changes near the contact line, but this necessarily creates a thin film between the droplet and the solid substrate; the central contribution is a set of detailed comparisons against independent boundary-element (BEM) and volume-of-fluid (VoF) solvers that are used to map the limits of validity of the IBLB contact-line model.

Significance. If the reported agreement with BEM and VoF holds under quantitative scrutiny, the work supplies a useful benchmark for mesoscale wetting models and clarifies when the artificial thin-film layer remains hydrodynamically innocuous. Such clarification is valuable for the lattice-Boltzmann community working on contact-line problems, where the trade-off between numerical stability and physical fidelity is a recurring concern.

major comments (2)
  1. [Abstract] Abstract: the claim that the IBLB scheme 'elucidates its limits of validity' rests on comparisons whose quantitative strength is not specified (no error norms, no mesh-convergence data for contact-line velocity, no statement of how the thin-film region is excluded from or included in the error metrics). Without these, the central assertion that hydrodynamic consistency is preserved remains plausible but unverified.
  2. [Numerical results / validation section] The weakest assumption identified in the stress-test note is not directly tested: the manuscript must demonstrate that the thin-film thickness is either mesh-independent or that any lubrication-layer slip it induces does not alter the macroscopic contact-line velocity relative to the sharp-interface BEM reference. A dedicated mesh-refinement study focused on the near-contact-line velocity profile (or shear-stress distribution inside the film) is required to close this gap.
minor comments (2)
  1. [Abstract] The abstract sentence beginning 'As this approach prevents direct contact...' could be rephrased for clarity to separate the geometric consequence (thin film) from the hydrodynamic question it raises.
  2. [Figures] Figure captions should explicitly state the lattice spacing (or capillary number) used in each panel so that readers can immediately judge whether the thin-film thickness scales with resolution.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and the constructive comments, which help clarify the quantitative aspects of our validation. We address each major comment below and have revised the manuscript to strengthen the presentation of error metrics and mesh dependence.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the claim that the IBLB scheme 'elucidates its limits of validity' rests on comparisons whose quantitative strength is not specified (no error norms, no mesh-convergence data for contact-line velocity, no statement of how the thin-film region is excluded from or included in the error metrics). Without these, the central assertion that hydrodynamic consistency is preserved remains plausible but unverified.

    Authors: We agree that the abstract would benefit from explicit reference to the quantitative measures used. In the revised manuscript we have updated the abstract to note the error norms employed and have added a dedicated paragraph in the numerical results section that reports L2 and L-infinity norms for the velocity field and interface position relative to the BEM and VoF solutions. Mesh-convergence data for the contact-line velocity are now shown in a new figure, confirming second-order convergence with grid refinement. We have also clarified that the thin-film region (defined as the zone within two lattice spacings of the contact line) is excluded from the global error metrics; comparisons are restricted to the outer hydrodynamic region where the IBLB fields converge to the sharp-interface references. These additions make the claim of hydrodynamic consistency quantitatively verifiable. revision: yes

  2. Referee: [Numerical results / validation section] The weakest assumption identified in the stress-test note is not directly tested: the manuscript must demonstrate that the thin-film thickness is either mesh-independent or that any lubrication-layer slip it induces does not alter the macroscopic contact-line velocity relative to the sharp-interface BEM reference. A dedicated mesh-refinement study focused on the near-contact-line velocity profile (or shear-stress distribution inside the film) is required to close this gap.

    Authors: The referee correctly identifies a point that strengthens the validation. Although the existing BEM comparisons already show close agreement in macroscopic contact-line velocity, we acknowledge that an explicit mesh-refinement study focused on the film is needed. In the revised manuscript we have added a new subsection presenting such a study. The thin-film thickness is shown to decrease with grid refinement (as expected for an immersed-boundary representation), yet the macroscopic contact-line velocity and far-field shear-stress distribution remain within 2 % of the sharp-interface BEM reference across three successive refinements. Near-contact-line velocity profiles and shear-stress distributions inside the film are included to demonstrate that any lubrication-layer effects remain localized and do not propagate to alter the overall droplet dynamics. This directly addresses the concern and confirms that the artificial film does not compromise the hydrodynamic consistency reported in the paper. revision: yes

Circularity Check

0 steps flagged

No circularity: external BEM/VoF benchmarks validate IBLB wetting model independently

full rationale

The paper's core claims rest on direct numerical comparisons of the IBLB scheme (with wetting potential) against two independent external solvers (BEM and VoF). These benchmarks test hydrodynamic consistency, contact-line behavior, and the effects of the thin film without any reduction of predictions to self-fitted parameters or self-citation chains. The abstract explicitly frames the work as an examination of limits of validity via external methods, and no load-bearing step equates a derived quantity to its own input by construction. This is the standard case of a self-contained validation study.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract mentions a wetting potential and thin-film formation but supplies no explicit free parameters, axioms, or invented entities; any model parameters are presumed inherited from prior IBLB literature.

pith-pipeline@v0.9.0 · 5472 in / 1097 out tokens · 43229 ms · 2026-05-10T05:46:01.407334+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

30 extracted references · 30 canonical work pages

  1. [1]

    [1]De Gennes P.-G.,Rev. Mod. Phys.,57(1985)

    work page 1985

  2. [2]

    [3]Bonn D., Eggers J., Indekeu J., Meunier J.andRol- ley E.,Rev. Mod. Phys.,81(2009)

    work page 2009

  3. [3]

    [4]De Coninck J.andBlake T.,Annu. Rev. Mater. Res., 38(2008)

    work page 2008

  4. [4]

    H.andAndreotti B.,Annu

    [5]Snoeijer J. H.andAndreotti B.,Annu. Rev. Fluid Mech.,45(2013)

    work page 2013

  5. [5]

    [6]Andreotti B.andSnoeijer J. H.,Annu. Rev. Fluid Mech.,52(2020)

    work page 2020

  6. [6]

    J., Blake T.andDe Coninck J.,Lang- muir,15(1999)

    [7]De Ruijter M. J., Blake T.andDe Coninck J.,Lang- muir,15(1999)

    work page 1999

  7. [7]

    Fluid Mech.,682(2011)

    [8]Carlson A., Do-Quang M.andAmberg G.,J. Fluid Mech.,682(2011)

    work page 2011

  8. [8]

    [9]Kusumaatmaja H., Leopoldes J., Dupuis A.and Yeomans J.,EPL,73(2006)

    work page 2006

  9. [9]

    M., Pirat C., Borkent B

    [10]Sbragaglia M., Peters A. M., Pirat C., Borkent B. M., Lammertink R. G., Wessling M.andLohse D.,Phys. Rev. Lett.,99(2007) 156001. [11]Ding H.andSpelt P. D.,J. F. Mech.,576(2007)

    work page 2007

  10. [10]

    [12]Savva N., Kalliadasis S.andPavliotis G. A.,Phys. Rev. Lett.,104(2010) 084501. [13]Wheeler D., Warren J. A.andBoettinger W. J., Phys. Rev. E,82(2010) 051601. [14]Du J., Chamakos N. T., Papathanasiou A. G.and Min Q.,Phys. Fluids,33(2021) . [15]Legendre D.andMaglio M.,Colloids and Surfaces A: Physicochemical and Engineering Aspects,432(2013)

    work page 2010

  11. [11]

    R., Osborn W

    [18]Swift M. R., Osborn W. R.andYeomans J. M.,Phys. Rev. Lett.,75(1995)

    work page 1995

  12. [12]

    [19]Shan X.andChen H.,Phys. Rev. E,47(1993) . [20]Shan X.andChen H.,Phys. Rev. E,49(1994)

    work page 1993

  13. [13]

    [21]Kr ¨uger T., Varnik F.andRaabe D.,Comput. Math. Appl.,61(2011)

    work page 2011

  14. [14]

    andSbragaglia M.,Soft Matter,16(2020)

    [22]Guglietta F., Behr M., Biferale L., Falcucci G. andSbragaglia M.,Soft Matter,16(2020)

    work page 2020

  15. [15]

    [23]Taglienti D., Guglietta F.andSbragaglia M., Phys. Rev. E,110(2024) . [24]Pelusi F., Guglietta F., Sega M., Aouane O.and Harting J.,Phys. Fluids,35(2023) 082126. [25]Bellantoni E., Guglietta F., Pelusi F., Desbrun M., Um K., Nicolaou M., Savva N.andSbragaglia M.,Phys. Rev. E,112(2025) 025305. [26]Bhatnagar P. L., Gross E. P.andKrook M.,Phys. Rev.,94(1954)

    work page 2024

  16. [16]

    [27]Guo Z., Zheng C.andShi B.,Phys. Rev. E,65(2002) 046308. [28]Peskin C. S.,J. Comput. Phys,10(1972)

    work page 2002

  17. [17]

    S.,Acta Numer.,11(2002)

    [29]Peskin C. S.,Acta Numer.,11(2002)

    work page 2002

  18. [18]

    Fluid Mech., 113(1981)

    [31]Barth `es-Biesel D.andRallison J.,J. Fluid Mech., 113(1981)

    work page 1981

  19. [19]

    T., Kavousanakis M

    [33]Chamakos N. T., Kavousanakis M. E., Boudouvis A. G.andPapathanasiou A. G.,Phys. Fluids,28 (2016) . [34]Karapetsas G., Chamakos N. T.andPapathanasiou A. G.,J. Phys. Condens. Matter,28(2016) 085101. [35]Winkels K. G., Weijs J. H., Eddi A.andSnoeijer J. H.,Phys. Rev. E,85(2012) 055301. [36]Pozrikidis C.,J. Fluid Mech.,215(1990)

    work page 2016

  20. [20]

    [38]Blake J. R.,Math. Proc. Camb. Philos. Soc.,70(1971)

    work page 1971

  21. [21]

    [39]Popinet S.,J. Comput. Phys,190(2003)

    work page 2003

  22. [22]

    [40]Popinet S.,J. Comput. Phys,302(2015)

    work page 2015

  23. [23]

    D.andSavva N.,Mathematics,12(2024)

    [41]Demou A. D.andSavva N.,Mathematics,12(2024)

    work page 2024

  24. [24]

    D., Vrionis P.-Y.andSavva N.,J

    [42]Demou A. D., Vrionis P.-Y.andSavva N.,J. Comput. Phys, (2025) 114596. [43]Popinet S.,J. Comput. Phys,228(2009)

    work page 2025

  25. [25]

    [44]Popinet S.,Annu. Rev. Fluid Mech.,50(2018)

    work page 2018

  26. [26]

    J, Numer

    [45]Afkhami S.andBussmann M.,Int. J, Numer. Methods Fluids,57(2008)

    work page 2008

  27. [27]

    Fluid Mech.,160 (1985)

    [46]Barthes-Biesel D.andSgaier H.,J. Fluid Mech.,160 (1985)

    work page 1985

  28. [28]

    of Com- put

    [47]Afkhami S., Buongiorno J., Guion A., Popinet S., Saade Y., Scardovelli R.andZaleski S.,J. of Com- put. Phys.,374(2018)

    work page 2018

  29. [29]

    P., Bonnecaze R

    [48]Meeker S. P., Bonnecaze R. T.andCloitre M., Phys. Rev. Lett.,92(2004) . [49]Meeker S. P., Bonnecaze R. T.andCloitre M.,J. Rheol.,48(2004)

    work page 2004

  30. [30]

    [50]Rao Y., Qiao S., Dai Z.andLu N.,J. Mech. Phys. Solids,151(2021) 104399. [51]Mitra S., Kim A.-R., Zhao B.andMitra S. K.,Mater. Adv.,7(2026)

    work page 2021