Reynolds-number dependence of turbulence enhancement on collision growth

Onishi, Ryo; Seifert, Axel

doi:https://doi.org/10.5194/acp-16-12441-2016

Articles | Volume 16, issue 19

https://doi.org/10.5194/acp-16-12441-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-16-12441-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 16, issue 19

Research article

|

05 Oct 2016

Research article |

| 05 Oct 2016

Reynolds-number dependence of turbulence enhancement on collision growth

Ryo Onishi and Axel Seifert

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Final revised paper (published on 05 Oct 2016)
Supplement to the final revised paper
Preprint (discussion started on 05 Feb 2016)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Review of "Reynolds-number dependence of turbulence enhancement on collision growth" by Onishi & Seifert', Anonymous Referee #1, 07 Mar 2016
- RC2: 'Review on acp-2016-19', Anonymous Referee #2, 12 Apr 2016
  - AC2: 'Reply to Referee #2', Ryo Onishi, 09 May 2016
AC1: 'Reply to Referee #1', Ryo Onishi, 09 May 2016

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Ryo Onishi on behalf of the Authors (09 May 2016) Manuscript

ED: Referee Nomination & Report Request started (03 Jun 2016) by Patrick Chuang

RR by Lian-Ping Wang (13 Jun 2016)

RR by Anonymous Referee #1 (21 Jun 2016)

Suggestions for revision or reasons for rejection

The authors have made acceptable responses to most of the points I raised in my first review. However, there are some remaining issues to address:

Concerning Figure 2. First, I realized that the text in the paper does not actually refer to this figure at any point (that I could see). I wonder whether the line below equation 42 is supposed to be referring to figure 2 and not figure 3? Second, the results in Fig 2 suggest that in going from Re_lambda=O(100) to Re_lambda=O(10000), the RDF at contact can vary significantly if St is large enough. Yet the data for Re_lambda>O(1000) is based upon a model that attempts to capture the effects of intermittency, and not DNS data. Being a model, the results are open to question. On the other hand, in Ireland's recent JFM paper (Journal of Fluid Mechanics, Volume 796, June 2016, pp 617 - 658, which is the published version of the arXiv paper I referred to in my first review), in Fig 23, their DNS results show that the effect of Re_lambda on the RDF saturates as Re_lambda is increased. This is in contrast to the assertions of the present paper that claims in Fig 2 (using a model) that increasing Re_lambda continues to decrease the RDF up to Re_lambda=O(10000). The authors need to discuss this difference in detail. Since the Re_lambda dependence of the collision statistics is in fact the main topic of the present paper, the authors need to seriously consider how to explain the discrepancy between their results and those of Ireland, e.g. whether the effect of Re_lambda saturates or not etc. The authors should consider how the different numerical schemes employed in the two studies may be responsible for the discrepany etc.

Regarding section 2, the authors stated in response to my first review that section 2 is general, and is not specific to the equation of motion for the particles. But this is not correct, for example, as I pointed out in my initial review, equation 10 is only valid for monodisperse inertial particles, subject to Stokes drag only without gravity. So how then can section 2 be general, and not specific to the equation of motion for the particles?

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ED: Reconsider after major revisions (21 Jun 2016) by Patrick Chuang

AR by Ryo Onishi on behalf of the Authors (01 Aug 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (04 Aug 2016) by Patrick Chuang

ED: Publish as is (15 Sep 2016) by Patrick Chuang

AR by Ryo Onishi on behalf of the Authors (21 Sep 2016)

Short summary

This study includes massively parallel simulation results on droplet collisions in turbulence. The attained maximum Taylor-microscale-based Reynolds number (Re) exceeds 10³, which steps into the typical range (O(10³)–O(10⁴)) of observed Re in turbulent clouds. The results clearly show that the Re dependence of turbulence enhancement on droplet collision growth is relevant for cloud microphysics modeling. This will promote the discussion on the Re dependence of turbulent collision statistics.