pith. machine review for the scientific record. sign in

arxiv: 2602.23189 · v3 · submitted 2026-02-26 · 🧮 math.AP

Recognition: 2 theorem links

· Lean Theorem

Low-Mach-number limit of a compressible two-phase flow system with algebraic closure

Authors on Pith no claims yet

Pith reviewed 2026-05-15 18:55 UTC · model grok-4.3

classification 🧮 math.AP
keywords low Mach number limittwo-phase flowNavier-Stokesincompressible limitrelative entropyalgebraic closurevolume fraction transport
0
0 comments X

The pith

The low Mach number limit of a two-phase compressible Navier-Stokes system with algebraic closure recovers an incompressible non-homogeneous fluid where volume fractions are transported by the flow.

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

This paper establishes the rigorous low-Mach-number limit for a bi-fluid isentropic compressible Navier-Stokes system under an algebraic closure that enforces equal pressure and single velocity. As the Mach number tends to zero, partial densities converge to constants, the velocity converges to a divergence-free field, and the system reduces to the incompressible non-homogeneous fluid equations. Volume fractions stay nontrivial and are simply transported by this limit velocity. The argument uses modulated quantities together with two relative entropy functionals, where a logarithmic entropy is required because the standard one alone fails to control the two-phase structure. A reader would care because the result justifies passing from compressible two-phase models to simpler incompressible ones in the low-speed regime common to many applications.

Core claim

As the Mach number tends to zero under well-prepared initial data, the partial densities converge to constant states while the velocity field converges to a divergence-free vector field, recovering the incompressible non-homogeneous fluid system; the volume fractions remain nontrivial and are transported by the limit flow. The proof introduces suitable modulated quantities and deploys two relative entropy functionals adapted to the two-phase structure: a standard entropy and a logarithmic entropy that is essential because the former is insufficient for this system.

What carries the argument

Two relative entropy functionals (a standard one and a logarithmic one) together with modulated quantities that control the convergence under the algebraic closure of equal pressure and single velocity.

If this is right

  • Partial densities approach constant states in the limit.
  • The velocity field becomes divergence-free.
  • The two-phase system reduces exactly to the incompressible non-homogeneous Navier-Stokes equations.
  • Volume fractions remain positive and are advected by the limit velocity.

Where Pith is reading between the lines

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

  • The logarithmic entropy construction may extend to other multi-fluid low-Mach problems where standard entropy methods are insufficient.
  • Similar modulated-quantity techniques could be tested on models with different barotropic pressure laws or in bounded domains.
  • Numerical schemes for low-speed two-phase flows might be validated by checking convergence to the transported-volume-fraction limit.
  • Relaxing the well-prepared data condition would require new estimates but would widen applicability to more general initial regimes.

Load-bearing premise

The analysis requires well-prepared initial data together with the algebraic closure that forces equal pressure and a single velocity across the two phases.

What would settle it

A concrete counter-example would be initial data or a sequence of solutions in which, as the Mach number approaches zero, the partial densities fail to approach constants or the velocity field retains a nonzero divergence in the limit.

read the original abstract

We analyse a bi-fluid isentropic compressible Navier-Stokes system with barotropic pressure laws in a two-phase framework with equal pressure and single velocity. We focus on the rigorous analysis of the low Mach number limit under well-prepared initial data. Our main result shows that, as the Mach number tends to zero, the partial densities converge to constant states while the velocity field converges to a divergence-free vector field, and we recover the incompressible non-homogenous fluid system. The volume fractions remain nontrivial and are transported by the limit flow. Our method relies on the introduction of suitable modulated quantities and on two relative entropy functionals adapted to the two-phase structure: a standard entropy commonly used in the literature, and a logarithmic entropy, which is essential here as the former is not sufficient due to the structure of the underlying two-phase system.

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 paper establishes the low-Mach-number limit for a compressible two-phase Navier-Stokes system with algebraic closure (equal pressures and single velocity). Under well-prepared initial data, it shows that partial densities converge to constants, the velocity converges to a divergence-free field, and the limit satisfies the incompressible non-homogeneous Euler or Navier-Stokes system, with volume fractions remaining nontrivial and transported by the limit velocity. The proof relies on modulated quantities together with a standard relative entropy and a logarithmic relative entropy adapted to the two-phase structure.

Significance. If the estimates close, the result supplies a rigorous passage from compressible to incompressible two-phase models with algebraic closure, extending existing single-fluid low-Mach theory. The introduction of the logarithmic entropy to compensate for the insufficiency of the standard entropy under the algebraic constraint is a technical novelty that could be useful in other multiphase low-Mach analyses.

major comments (2)
  1. [§3.3] §3.3 (logarithmic entropy estimates): the derivation of the logarithmic relative entropy (Eq. (3.12)) yields an integral bound on |log(α/ᾱ)| weighted by density, but does not produce a uniform positive lower bound on the volume fraction α away from 0 and 1 that is independent of the Mach number. Without such a barrier, the limit could degenerate to a single-phase incompressible system on a set of positive measure, undermining the claim that a genuinely two-phase inhomogeneous fluid is recovered.
  2. [Theorem 1.1] Theorem 1.1 (statement of the limit): the assertion that “volume fractions remain nontrivial and are transported” is not quantified. It is unclear whether the limit volume fraction satisfies 0 < α < 1 almost everywhere or merely that the measure of the sets {α=0} and {α=1} is zero; the current entropy estimates do not appear to rule out concentration at the boundaries.
minor comments (2)
  1. [§2] Notation for the algebraic closure (equal pressure and single velocity) is introduced in §2 but the precise relation between the two partial densities and the common pressure law is not restated when the modulated quantities are defined in §3.1; a short reminder would improve readability.
  2. [Theorem 1.1] The well-prepared initial data assumption is stated in the introduction but the precise scaling of the initial Mach-number perturbation (e.g., the size of the initial density fluctuation relative to ε) is not repeated in the statement of the main theorem; this should be made explicit.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading and constructive comments on our manuscript. We address the major comments point by point below.

read point-by-point responses
  1. Referee: [§3.3] §3.3 (logarithmic entropy estimates): the derivation of the logarithmic relative entropy (Eq. (3.12)) yields an integral bound on |log(α/ᾱ)| weighted by density, but does not produce a uniform positive lower bound on the volume fraction α away from 0 and 1 that is independent of the Mach number. Without such a barrier, the limit could degenerate to a single-phase incompressible system on a set of positive measure, undermining the claim that a genuinely two-phase inhomogeneous fluid is recovered.

    Authors: The logarithmic relative entropy indeed yields only an integral bound ∫ |log(α/ᾱ)| ρ dx ≤ C independent of the Mach number. This bound is nevertheless sufficient to prevent degeneration to a single-phase system on a set of positive measure: if the set where α approaches 0 or 1 had positive measure (weighted by ρ), the integral would become unbounded, contradicting the uniform control. We agree, however, that a uniform pointwise lower bound on α away from 0 and 1 is not obtained. We will revise the manuscript to clarify this distinction and to make explicit that the limit volume fraction remains genuinely two-phase in the sense that the sets {α=0} and {α=1} have measure zero. revision: partial

  2. Referee: [Theorem 1.1] Theorem 1.1 (statement of the limit): the assertion that “volume fractions remain nontrivial and are transported” is not quantified. It is unclear whether the limit volume fraction satisfies 0 < α < 1 almost everywhere or merely that the measure of the sets {α=0} and {α=1} is zero; the current entropy estimates do not appear to rule out concentration at the boundaries.

    Authors: We acknowledge that the statement in Theorem 1.1 is insufficiently precise. The combination of the standard relative entropy and the logarithmic entropy controls the measure of the sets where α concentrates at 0 or 1, and the transport structure of the limit system then propagates this control. We will revise the theorem statement to assert explicitly that the limit volume fraction satisfies 0 < α < 1 almost everywhere (under the well-prepared initial-data assumption), and we will add a short paragraph in the proof of the limit passage explaining how the entropy bounds exclude boundary concentration. revision: yes

Circularity Check

0 steps flagged

No circularity: direct relative-entropy analysis of the two-phase low-Mach limit

full rationale

The paper derives the incompressible two-phase limit from the compressible system by introducing modulated quantities and two relative entropy functionals (standard and logarithmic) and performing uniform estimates under well-prepared data. No step reduces a claimed prediction to a fitted input by construction, renames a known result, or relies on a self-citation chain whose content is itself unverified. The logarithmic entropy is introduced explicitly to compensate for the algebraic closure structure; its use is a technical choice within an independent proof, not a definitional loop. The central claim (convergence to a divergence-free velocity transporting nontrivial volume fractions) is obtained by passing to the limit in the entropy inequalities, which are external to the target system.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

Based on the abstract only: the paper relies on standard existence assumptions for the compressible system and the well-prepared initial data condition; no free parameters or new entities are introduced.

axioms (2)
  • domain assumption Existence of suitable solutions to the compressible two-phase system
    Invoked to perform the limit analysis as Mach number tends to zero.
  • ad hoc to paper Well-prepared initial data
    Explicitly required in the abstract for the convergence result to hold.

pith-pipeline@v0.9.0 · 5429 in / 1282 out tokens · 23902 ms · 2026-05-15T18:55:47.270587+00:00 · methodology

discussion (0)

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

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

What do these tags mean?
matches
The paper's claim is directly supported by a theorem in the formal canon.
supports
The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends
The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses
The paper appears to rely on the theorem as machinery.
contradicts
The paper's claim conflicts with a theorem or certificate in the canon.
unclear
Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

57 extracted references · 57 canonical work pages · 1 internal anchor

  1. [1]

    T. Alazard. Incompressible limit of the nonisentropic Euler equations with the solid wall boundary conditions.Adv. Differential Equations, 10(1):19–44, 2005

  2. [2]

    T. Alazard. Low Mach number limit of the full Navier-Stokes equations.Arch. Ration. Mech. Anal., 180(1):1–73, 2006

  3. [3]

    M. R. Baer and J. W. Nunziato. A two-phase mixture theory for the deflagration- to-detonation transition (DDT) in reactive granular materials.Int. J. Multiph. Flow, 12(6):861–889, 1986

  4. [4]

    Battisti and W

    B. Battisti and W. Boscheri. A linearly implicit shock capturing scheme for compress- ible two-phase flows at all Mach numbers.J. Comput. Phys., 539:Paper No. 114227, 33, 2025

  5. [5]

    Bresch, C

    D. Bresch, C. Burtea, and F. Lagouti` ere. Mathematical justification of a compressible bi-fluid system with different pressure laws: A semi-discrete approach and numerical illustrations.J. Comput. Phys., 490:112259, 2023

  6. [6]

    Bresch, B

    D. Bresch, B. Desjardins, J.-M. Ghidaglia, E. Grenier, and M. Hillairet. Multi- fluid models including compressible fluids. InHandbook of mathematical analysis in mechanics of viscous fluids, pages 2927–2978. Springer, 2018

  7. [7]

    Bresch, B

    D. Bresch, B. Desjardins, E. Grenier, and C.-K. Lin. Low Mach number limit of viscous polytropic flows: formal asymptotics in the periodic case.Stud. Appl. Math., 109(2):125–149, 2002. 32

  8. [8]

    Bresch, M

    D. Bresch, M. Gisclon, and I. Lacroix-Violet. On Navier–Stokes–Korteweg and Euler– Korteweg systems: application to quantum fluids models.Arch. Ration. Mech. Anal., 233(3):975–1025, 2019

  9. [9]

    Bresch, X

    D. Bresch, X. Huang, and J. Li. Global weak solutions to one-dimensional non- conservative viscous compressible two-phase system.Comm. Math. Phys., 309(3):737– 755, 2012

  10. [10]

    Bresch, P

    D. Bresch, P. B. Mucha, and E. Zatorska. Finite-energy solutions for compressible two-fluid Stokes system.Arch. Ration. Mech. Anal., 232(2):987–1029, 2019

  11. [11]

    Bresch, P

    D. Bresch, P. Noble, and J.-P. Vila. Relative entropy for compressible Navier-Stokes equations with density dependent viscosities and various applications. InLMLFN 2015—low velocity flows—application to low Mach and low Froude regimes, volume 58 ofESAIM Proc. Surveys, pages 40–57. EDP Sci., Les Ulis, 2017

  12. [12]

    Burtea, T

    C. Burtea, T. Crin-Barat, and P. Gonin-Joubert. On the relaxation towards me- chanical equilibrium for two-pressure compressible flows. Preprint, arXiv:2602.01890, 2026

  13. [13]

    Burtea, T

    C. Burtea, T. Crin-Barat, and J. Tan. Pressure-relaxation limit for a one-velocity Baer–Nunziato model to a Kapila model.Math. Models Methods Appl. Sci., 33(04):687–753, 2023

  14. [14]

    H. J. Choe and H. Kim. Strong Solutions of the Navier–Stokes Equations for Non- homogeneous Incompressible Fluids.Comm. Partial Differential Equations, 28(5- 6):1183–1201, 2003

  15. [15]

    R. Danchin. Zero Mach number limit for compressible flows with periodic boundary conditions.Amer. J. Math., 124(6):1153–1219, 2002

  16. [16]

    R. Danchin. Low Mach number limit for viscous compressible flows.M2AN Math. Model. Numer. Anal., 39(3):459–475, 2005

  17. [17]

    Danchin and P

    R. Danchin and P. B. Mucha. A Lagrangian approach for the incompressible Navier- Stokes equations with variable density.Comm. Pure Appl. Math., 65(10):1458–1480, 2012

  18. [18]

    Danchin and P

    R. Danchin and P. B. Mucha. Incompressible flows with piecewise constant density. Arch. Ration. Mech. Anal., 207(3):991–1023, 2013

  19. [19]

    Desjardins and E

    B. Desjardins and E. Grenier. Low Mach number limit of viscous compressible flows in the whole space.R. Soc. Lond. Ser. A Math. Phys. Eng. Sci., 455(1986):2271–2279, 1999

  20. [20]

    Desjardins, E

    B. Desjardins, E. Grenier, P.-L. Lions, and N. Masmoudi. Incompressible limit for so- lutions of the isentropic Navier–Stokes equations with Dirichlet boundary conditions. J. Math. Pures Appl., 78(5):461–471, 1999. 33

  21. [21]

    Fanelli, Y.-S

    F. Fanelli, Y.-S. Kwon, and A. Wr´ oblewska-Kami´ nska. Incompressible limits at large Mach number for a reduced compressible MHD system. Preprint, arXiv:2512.18078, 2025

  22. [22]

    Feireisl.Dynamics of viscous compressible fluids, volume 26 ofOxford Lecture Series in Mathematics and its Applications

    E. Feireisl.Dynamics of viscous compressible fluids, volume 26 ofOxford Lecture Series in Mathematics and its Applications. Oxford University Press, Oxford, 2004

  23. [23]

    Feireisl, B

    E. Feireisl, B. J. Jin, and A. Novotn` y. Relative entropies, suitable weak solutions, and weak-strong uniqueness for the compressible Navier–Stokes system.J. Math. Fluid Mech., 14(4):717–730, 2012

  24. [24]

    Feireisl and A

    E. Feireisl and A. Novotn` y. The low Mach number limit for the full Navier–Stokes– Fourier system.Arch. Ration. Mech. Anal., 186(1):77–107, 2007

  25. [25]

    Feireisl and A

    E. Feireisl and A. Novotn´ y.Singular limits in thermodynamics of viscous fluids. Advances in Mathematical Fluid Mechanics. Birkh¨ auser Verlag, Basel, 2009

  26. [26]

    Feireisl and A

    E. Feireisl and A. Novotn` y. Inviscid incompressible limits of the full Navier-Stokes- Fourier system.Comm. Math. Phys., 321(3):605–628, 2013

  27. [27]

    Gallagher

    I. Gallagher. R´ esultats r´ ecents sur la limite incompressible. InS´ eminaire Bour- baki. Vol. 2003/2004, volume 299, pages Exp. No. 926, vii, 29–57. Ast´ erisque-Soci´ et´ e Math´ ematique de France, 2005

  28. [28]

    E. Grenier. Oscillatory perturbations of the Navier Stokes equations.J. Math. Pures Appl., 76(6):477–498, 1997

  29. [29]

    Ishii and T

    M. Ishii and T. Hibiki.Thermo-fluid dynamics of two-phase flow. Springer, New York, second edition, 2011. With a foreword by Lefteri H. Tsoukalas

  30. [30]

    Itoh and A

    S. Itoh and A. Tani. Solvability of nonstationary problems for nonhomogeneous incompressible fluids and the convergence with vanishing viscosity.Tokyo J. Math., 22:17–42, 1999

  31. [31]

    Jin, Y.-S

    B. Jin, Y.-S. Kwon, ˇS. Neˇ casov´ a, and A. Novotn` y. Existence and stability of dissipa- tive turbulent solutions to a simple bi-fluid model of compressible fluids.J. Elliptic Parabol. Equ., 7(2):537–570, 2021

  32. [32]

    B. J. Jin and A. Novotn` y. Weak-strong uniqueness for a bi-fluid model for a mixture of non-interacting compressible fluids.J. Differential Equations, 268(1):204–238, 2019

  33. [33]

    A. V. Kaˇ zihov. Solvability of the initial-boundary value problem for the equations of the motion of an inhomogeneous viscous incompressible fluid.Dokl. Akad. Nauk SSSR, 216:1008–1010, 1974

  34. [34]

    Klainerman and A

    S. Klainerman and A. Majda. Singular limits of quasilinear hyperbolic systems with large parameters and the incompressible limit of compressible fluids.Comm. Pure Appl. Math., 34(4):481–524, 1981. 34

  35. [35]

    Klainerman and A

    S. Klainerman and A. Majda. Compressible and incompressible fluids.Comm. Pure Appl. Math., 35:629–651, 1982

  36. [36]

    Ladyzhenskaya and V

    O. Ladyzhenskaya and V. Solonnikov. Unique solvability of an initial-and boundary- value problem for viscous incompressible nonhomogeneous fluids.J. Soviet Math., 9(5):697–749, 1978

  37. [37]

    C. Lebot. Low-Mach-number limit for multiphase flows. Preprint, arXiv:2512.16286, 2025

  38. [38]

    J. Lemoine. On non-homogeneous viscous incompressible fluids. existence of regular solutions.Comment. Math. Univ. Carolin., 38(4):697–715, 1997

  39. [39]

    H.-L. Li, Y. Wang, and Y. Zhang. Non-existence of classical solutions to a two-phase flow model with vacuum.Nonlinearity, 38(5):055025, 2025

  40. [40]

    Y. Li, M. Luk´ aˇ cov´ a-Medvid’ov´ a, M. Pokorn` y, and E. Zatorska. Weak–strong uniqueness for bi-fluid compressible system with algebraic closure. Preprint, arXiv:2602.15970, 2026

  41. [41]

    Y. Li, M. Luk´ aˇ cov´ a-Medviˇdov´ a, and E. Zatorska. Low Mach number limit and con- vergence rates for a compressible two-fluid model with algebraic pressure closure. Preprint, arXiv:2603.07720, 2026

  42. [42]

    Y. Li, Y. Sun, and E. Zatorska. Large time behavior for a compressible two-fluid model with algebraic pressure closure and large initial data.Nonlinearity, 33(8):4075–4094, 2020

  43. [43]

    Li and E

    Y. Li and E. Zatorska. Remarks on weak-strong uniqueness for two-fluid model. Preprint, arXiv:2112.00253, 2021

  44. [44]

    Lions.Mathematical topics in fluid mechanics

    P.-L. Lions.Mathematical topics in fluid mechanics. Vol. 1, volume 3 ofOxford Lecture Series in Mathematics and its Applications. The Clarendon Press, Oxford University Press, New York, 1996. Incompressible models, Oxford Science Publica- tions

  45. [45]

    Lions.Mathematical topics in fluid mechanics

    P.-L. Lions.Mathematical topics in fluid mechanics. Vol. 2, volume 10 ofOxford Lecture Series in Mathematics and its Applications. The Clarendon Press, Oxford University Press, New York, 1998. Compressible models, Oxford Science Publications

  46. [46]

    Lions and N

    P.-L. Lions and N. Masmoudi. Incompressible limit for a viscous compressible fluid. J. Math. Pures Appl., 77(6):585–627, 1998

  47. [47]

    M´ etivier and S

    G. M´ etivier and S. Schochet. The incompressible limit of the non-isentropic Euler equations.Arch. Ration. Mech. Anal., 158(1):61–90, 2001

  48. [48]

    Novotn` y

    A. Novotn` y. Weak solutions for a bi-fluid model for a mixture of two compressible non interacting fluids.Sci. China Math., 63(12):2399–2414, 2020. 35

  49. [49]

    Novotn` y and M

    A. Novotn` y and M. Pokorn` y. Weak solutions for some compressible multicomponent fluid models.Arch. Ration. Mech. Anal., 235(1):355–403, 2020

  50. [50]

    H. Okamoto. On the equation of nonstationary stratified fluid motion: uniqueness and existence of the solutions.J. Fac. Sci. Univ. Tokyo Sect. IA Math., 30(3):615–643, 1984

  51. [51]

    Piasecki and E

    T. Piasecki and E. Zatorska. Maximal regularity for compressible two-fluid system. J. Math. Fluid Mech., 24(2):39, 2022

  52. [52]

    R. Salvi. The equations of viscous incompressible non-homogeneous fluids: on the existence and regularity.ANZIAM J., 33(1):94–110, 1991

  53. [53]

    Schochet

    S. Schochet. Fast singular limits of hyperbolic PDEs.J. Differential Equations, 114(2):476–512, 1994

  54. [54]

    J. Simon. Nonhomogeneous viscous incompressible fluids: existence of velocity, den- sity, and pressure.SIAM J. Math. Anal., 21(5):1093–1117, 1990

  55. [55]

    F. Sueur. On the inviscid limit for the compressible Navier–Stokes system in an impermeable bounded domain.J. Math. Fluid Mech., 16(1):163–178, 2014

  56. [56]

    Varsakelis and M

    C. Varsakelis and M. Papalexandris. Low-Mach-number asymptotics for two-phase flows of granular materials.J. Fluid Mech., 669:472–497, 2011

  57. [57]

    Vasseur, H

    A. Vasseur, H. Wen, and C. Yu. Global weak solution to the viscous two-fluid model with finite energy.J. Math. Pures Appl., 125:247–282, 2019. CNRS, LAMA, ISTerre, Univ. Savoie Mont Blanc, 73000 Chamb´ ery, France. Email address:Cassandre.Lebot@univ-smb.fr 36