An Overview of the Lagrangian Dispersion Modeling of Heavy Particles in Homogeneous Isotropic Turbulence and Considerations on Related LES Simulations
Round 1
Reviewer 1 Report
Please see the attached report for comments.
Comments for author File: 
Comments.pdf
Author Response
Dear Reviewer,
You will find my modifications in the attached pdf file
Best Regards
Author Response File: Author Response.pdf
Reviewer 2 Report
This is an extensive survey on turbulent dispersion modelling of inertial particles in turbulence. It clearly demonstrates the Author's experience on the topic. The paper focuses on a historical perspective, starting with the seminal paper by Taylor (1921) and presenting various aspects of dispersion models (EIM, DRW, CRW, rtc.) referring to the state of knowledge up to the early 2000s, basically. Personally, I would welcome some more details on recent findings. In particular, the PDF-based approaches, started in the 1990s and continued till today, are far less detailed in the paper. I know the work is already very long but some comment would be welcome, emphasising the fact that the random-walk models, and other proposals setup in the discrete time, have been shown (see papers by Minier & coworkers) to be rooted in the continuous-time Langevin equation for fluid evolution (GLM, etc.). That model has then been extended (building on some analogy, and not necessarily unique) for the fluid velocity "seen" by particles. This move remedied earlier problems with proper formulations for inhomogeneous turbulence, spurious drifts, etc.
The value of the paper is a relatively smooth narrative, quite self-contained, even a bit like of the textbook, particularly in its first part. The bibliographic coverage is rich as well. If the paper is deemed suitable for "Fluids" (because of its length which is over 50 pages), then I am rather favourable towards its publication. However, a major revision would be necessary, inluding a number of technical points as listed below. Also, the English language imperfections call for a proofreading.
Remarks, suggestions (listed in the order of appearance):
- Title: "... and considerations on…" I am not convinced whether the second part of the title is justified. Actually, the LES part is relatively short as compared to the main thrust of the paper which focuses on RANS-based models.
-Abstract: references are discouraged in the Summary; typically, either remove them altogether or provide the full bibliographic info directly in the Abstract - but see with the copy-Editor of "Fluids" for their policy;
- Most Lagrangian models" should be followed by "in the RANS setting" or "in the statistical approach to turbulence" or alike, for clarity. In the point-particle DNS of HIT, for example, no such nodels are needed. Also in the LES, the situation is quite different.
- "computation results ... are proposed" - English: suggest "are reported" instead;
- "with more computer time consuming" - awkward in English;
20: "models based on LES and pref. conc." - unclear; the same in lines 83-84;
32: unclear - "gas-solid flows" can also be dilute;
36: "M-C process" unclear; the same in line 61 and 481: to me, M-C is a computational method, perhaps also to simulate a process, but not a process as such; Refs. 60 and 183 have this phrase in the title - perhaps, that meaning can somehow be explained in the present text;
37: "an average ensemble" --> "ensemble average"
- why are we told about "spreading" in line 86 and "spreading and mixing" in line 89?
94=95: in general (beyond HIST), this statement is not true, as in the near-wall regions of turbulent flows the molecular transport effects dominate and are difficult for proper modelling;
106: "statistics in time" - unclear;
112: this line repeats Eq.4;
151: when talking about microscale" it is worthwhile to add "(also called the Taylor scale)" or alike; the same in line 169;
191: "Taylor's microscale marks the transition from..." - how do we know this? Can this be proven/demonstrated? Any reference?
205: citations are welcome to substantiate the statement;
219: incorrect English;
222: u_i^p - wrong notation;
225: "kinematic viscosity of density" - awkward English;
263: I would add "the drag correction factor" before "f" for clarity;
236 vs. 275: \tau_s or \tau_p ?
- I suggest adding a comment that Table 1 is setup in the spirit of RANS and, in particular, for lines 1 & 2 of the Table, the point-particle approximation (as expressed through u^p in Eqs.23-24) is no longer valid in DNS; it may be risky even in LES with a filter scale D, depending on the d_p/D ratio;
315: "negligible inertia" - add a comma in-between;
319: typical of; the same in line 330;
340: "is quite unclear in transport processes" unclear (Nota Bene);
419: What is "turbulent continuity equation"?
450: "As expected" - twice;
484: "development of computer performance" does not sound well in English;
496: "several" - ?
567: "constant dt controls the process" - unclear;
731: "according to be able" possibly incorrect English;
823: One of the aimS; "is order to" - ?
862: Wand;
880: althougth;
Figure 5, caption: I guess it should be Normalised variance of particle velocity (?); the same for Figs. 7 and 11;
Figs.9-10, caption: What is "Lagr. dispersion"? (It is a process, not a measurable quantity). Did the Author mean "diffusivity" or "dispersion coefficient"?
892: are Figs. 4 and 5 referred to in the text? (I have not found it); please also check this for some other Figures;
1008: "performant" sounds French;
1107-8: equation seems incorrect;
- Ref.8: correct name is "Podgorska"
- Ref.43: correct name is "Nijhoff"
- Refs. 224 and 229 are the same; the correct publication year is 2009;
- Ref. 265: book title in italics;
Author Response
Dear Reviewer,
You will find my modifications in the attached pdf file
Best Regards
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
In the revised manuscript, the Author has carefully addressed all the concerns raised in the review - thank you. The paper is now stronger and it is my pleasure to recommend it for publication.
A few minor points that are left for the Autor's discretion:
L45: rather "The ensemble average"
L117/8: suggest: "the time average equal to the ensemble average"
L318: just a remark - this choice of \tau_L is not quite clear: the Kolmogorov time scale is quite often used to define the Stokes number;
L1084/5: "pehaps", then ".."
L1221: "coupling" - did the author mean "two-way momentum coupling" or "interphasial coupling"?
Author Response
Dear Reviewer,
Enclosed my modifications and comments to your suggestions.
Best Regards
- Huilier
Comments and Suggestions for Authors
In the revised manuscript, the Author has carefully addressed all the concerns raised in the review - thank you. The paper is now stronger and it is my pleasure to recommend it for publication.
A few minor points that are left for the Author's discretion:
L45: rather "The ensemble average" Correction made
L117/8: suggest: "the time average equal to the ensemble average" Correction made
L318: just a remark - this choice of \tau_L is not quite clear: the Kolmogorov time scale is quite often used to define the Stokes number;
Author’s comment : The Stokes number St is the ratio of the particle's momentum response time to a flow-field time scale, thes the ratio of a characteristic length L and velocity U of the flow. Referring to Clayton Crowe and his textbooks, one classical timescale refers the ‘turnover’ timescale, Tf = Le/Ue, where Le and ue are the characteristic length and velocity scales of the eddy, respectively. How St is chosen depends on several factors, on the simulation method (RANS, LES, DNS,…) and as indicated in the manuscript (line 284 to 297) several Stokes numbers can be defined and one has to be careful when reading a paper in multiphase flows on how a Stokes number is defined. But of course, Kolmogorov based Stokes numbers or, in LES, SGS Stokes numbers based on a cut-off time-scale are often used too.
L1084/5: "pehaps", then ".." Correction made
L1221: "coupling" - did the author mean "two-way momentum coupling" or "interphasial coupling"?
Author’s comment : The review proposed by Balachandar & Eaton discusses several aspects of coupling, turbulence modulation by the dispersed phase, effect of carrier-phase turbulence on interphase coupling, one-way and two-way coupling including also momentum exchanges between the carrier and dispersed phase.
In the paper :
focusing on preferential concentration and different coupling mechanisms (e.g. interphase, two-way momentum coupling),..
Author Response File: Author Response.pdf
