Evolution of Water Conveyance Capacity through Hydraulic Transition Processes in Circular Drop Manholes

Round 1

Reviewer 1 Report

The manuscript deals with the experimental investigation of flow transitions due to circular drop manholes. The manuscript details the experimental investigation along with the data analysis that motivates a novel classification of flow stages. The authors propose a series of empirical relationships useful to identify the stage of the flow as a function of dimensionless parameters: the drop parameter, pipe Froude number, diameter ratio for given drop ratios. The proposed relationships are intended to be used to infer either the dimensionless drop height (equations 1 and 2) or the relative water depth (equations 3 and 4).

I found the manuscript interesting, well-written, and well-structured. Before I can recommend the manuscript for publication I have only one major concern. It is related to the reliability of the experimental findings.

If I catch correctly the rationale behind the proposed classification, the identified flow stages (i.e., S1, S2, S3, and S4) are characterized by a two-phase flow for which the air entrainment plays a crucial role. On the other hand, the proposed relationships are given (in my opinion, correctly) in a dimensionless form. My concern is related to the scale effects on air entrainment processes related to the (absolute) size of the physical model. In few words: can the authors provide the readers with a more detailed analysis aimed to assess the scale effects on the reliability of the proposed formulation? Can the proposed formulations be used also for other diameters (i.e. for other absolute sizes) than the ones reproduced in the model? Indeed, it is well accepted that the interaction between air bubbles and turbulent structures can be hardly reproduced at the model scale. On the one hand, the Reynolds number affects the turbulence at the model scale; on the other hand, the reproduced Weber number influences the effects of the surface tension. This aspect should be discussed in the manuscript and related to the reliability of the proposed formulations.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Dear Authors,

Please see the attached document.

Thanks

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

I have no additional comments

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.