Dear Prof. Sznitman,

Thank you very much for submitting your manuscript "In vitro−in silico correlation of three-dimensional turbulent flows in an idealized mouth-throat model" for consideration at PLOS Computational Biology.

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Sincerely,

Alison L. Marsden

Academic Editor

PLOS Computational Biology

Edwin Wang

Section Editor

PLOS Computational Biology

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Reviewer's Responses to Questions

Comments to the Authors:

Please note here if the review is uploaded as an attachment.

Reviewer #1: The study by Nof et al. provides exciting 3D maps of velocity fields from Tomographic Particle Image Velocimetry (TPIV), RANS simulations, and LES simulations of an idealized mouth-throat geometry of a healthy adult. This is the first study to provide 3D TPIV measurements, which can be used to validate computational models. Notably, the authors provide the 3D data through an online repository, which can be used by the community. This is a well written paper and I have just a few minor comments that should be addressed prior to publication.

Thank you for providing the particle relaxation time. Can you provide us with how much a particle is expected to drift during an experiment?

The no-slip wall boundary condition is hard to observe on the cutouts in Fig. 3. Is this because of near wall averaging of the experimental data?

It would be great to include a brief discussion on how the flow profile differences between RANS and LES might lead to differences in particle deposition. Specifically, is it expected that the unresolved TKE might under-estimate deposition?

Reviewer #2: The manuscript describes a comparison of Tomogaphic (3D) PIV measurements with LES and RANS in a mouth throat model. Although the authors report about limitations of already existing studies, their results do not much contribute to new knowledge. It is rather another Benchmark study which shows good agreement between LES and TPIV and larger deviations for the RANS simulations as already reported in their reference [23 - Koullapis et al.]. The advantage of 3D measurements which was emphasized as new in the paper could not be found. The authors showed again detailed comparisons for the mid-sagittal plane and one cross section. The results could have been received also from Stereo PIV (if pure secondary flows had been presented in Fig. 5, 2D planar PIV would have been sufficient to gain the same results). Although additional planes are roughly shown in Fig. 3, their details are not given or discussed. Thus, introduction and conclusion should be changed accordingly.

The following points need to be furthermore addressed:

1. The introduction is too long and should concentrate on the main goal of the paper

2. Important information in the description of the experimental methods are missing. These are

1. The time delay between successive images used for the PIV measurements (for all 3 flow rates)

2. What was the field of view (FOV) in mm and what pixel and vector resolution could have been achieved (see next comment)?

3. The size of the FOV (for each camera) is probably something in the range of 100 x 80 mm^2. With the camera pixels given, one would achieve a resolution of about 80µm/Px. It is mentioned that tracers in the size of 10µm have been used. That means, they do not even cover a pixel. How were the measurements possible and more important, what errors/uncertainties can be expected? Peak locking must have been a big issue. Please elaborate on these discrepancies. This becomes furthermore important when differences to the CFD results are discussed.

4. What was the reason for the use of fluorescent tracers? – as no optical filters have been mentioned.

5. Obviously, the side walls of the mouth throat model were not illuminated anymore but the light was cut off by the knife edges. Please explain why this was done as flow information seems to be missing then for Fig. 5

3. RANS details: the lines 163 – 181 only repeat texbook knowledge. This passage can be omitted

4. Fig 1: The camera lenses are not oriented perpendicular to the phantom model wall. Please elaborate on possible errors due to optical distortions. E.g. Buchmann et al. (Exp Fluids (2011) 50:1131–1151) have used prisms to exclude any optical distortions. Why were these not necessary here?

5. Fig. 3 and 4: The mid-sagittal plane was significantly wider for the TPIV than for CFD. Please elaborate

6. Secondary Flows: In this section Fig. 5 should show secondary flow. However, color coded is again the velocity magnitude. It would be more interesting to visualize only the in plane velocity components to show only the secondary flow. The described dean vortices can be identified only with difficulty.

7. There must be something wrong with the scaling in Fig. 5 for the TPIV. It is mentioned though that only a rectangular cross sectional view could be shown here, but the dimensions do not agree at all with the CFD model. The horizontal extension is much wider than the actual model geometry, the vertical structures seem to be squeezed. i.e. the vertical extension of the low speed region is much smaller for PIV than for the CFD results. At least the characteristic round geometry cannot be recognized for the PIV. This needs correction.

8. In the suppl. Mat. S3 Files, the authors mention a repository for the measured 3D vector field source files. These data could not be found. Please add or correct this.

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Have the authors made all data and (if applicable) computational code underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data and code underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data and code should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data or code —e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: No: 

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Reviewer #1: Yes: Jessica M Oakes

Reviewer #2: No

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Dear Prof. Sznitman,

We are pleased to inform you that your manuscript 'In vitro−in silico correlation of three-dimensional turbulent flows in an idealized mouth-throat model' has been provisionally accepted for publication in PLOS Computational Biology.

Before your manuscript can be formally accepted you will need to complete some formatting changes, which you will receive in a follow up email. A member of our team will be in touch with a set of requests.

Please note that your manuscript will not be scheduled for publication until you have made the required changes, so a swift response is appreciated.

IMPORTANT: The editorial review process is now complete. PLOS will only permit corrections to spelling, formatting or significant scientific errors from this point onwards. Requests for major changes, or any which affect the scientific understanding of your work, will cause delays to the publication date of your manuscript.

Should you, your institution's press office or the journal office choose to press release your paper, you will automatically be opted out of early publication. We ask that you notify us now if you or your institution is planning to press release the article. All press must be co-ordinated with PLOS.

Thank you again for supporting Open Access publishing; we are looking forward to publishing your work in PLOS Computational Biology. 

Best regards,

Alison L. Marsden

Academic Editor

PLOS Computational Biology

Edwin Wang

Section Editor

PLOS Computational Biology

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Please make the one minor correction requested by the reviewer prior to submitting the final version of the paper for publication.

Reviewer's Responses to Questions

Comments to the Authors:

Please note here if the review is uploaded as an attachment.

Reviewer #2: Almost all issues have been accordingly addressed. Only one discrepancy remains (Lines 112 – 115): It is mentioned that image acquisition was done using a single frame mode with 1250fps and 800us image separation. It the next sentence a pulse time separation of 25 – 40us has been mentioned. This can only apply to double pulse mode, i.e. with double images. As only one of these methods could have been applied, this requires correction.

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Have the authors made all data and (if applicable) computational code underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data and code underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data and code should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data or code —e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #2: Yes

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PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

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Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #2: No