Concerning Dynamic Effects in Pipe Systems with Two-Phase Flows: Pressure Surges, Cavitation, and Ventilation

Round 1

Reviewer 1 Report

The paper focuses on the dynamic effects of two-phase flows in the pipeline systems. A collection of unsteady two-phase flows phenomena associated with the pressurized pipelines operations (e.g. filling and draining) are summarized in the manuscript. Both numerical and experimental investigations of the dynamic effects induced by two-phase flows in pipeline systems are presented. It is emphasized that the behavior of pipeline systems during unstable two-phase flows is often counter-intuitive and difficult to predict. It is shown in the manuscript that the air management strategy in the pressured pipelines through the type selection and placement of protection devices and their maintenance is the key element for the operation during filling, drainage and transient events. The research issues selected in the manuscript correspond to a hot topic for both the research community and the industry. The manuscript is well written with a good scientific level. I am recommending that the manuscript to be MINOR REVISED. A few suggestions are included in my review report to improve the clarity of the manuscript.

1. Please include the main purpose and the synoptic view of the research in the last paragraph of the introduction section. This paragraph will help the reader to easily follow the manuscript.

2. Please provide quantitative references instead of qualitative references where possible. What does high turbulence mean in this case? Could you provide a quantitative reference on what a high degree of air-water mixture means in this case?

Page 6/1st paragraph/ lines 147-150: “For the case in Figure 4a, as the expansion phase starts, HIGH turbulence takes place with a HIGH degree of air-water mixture. Such behaviour is typical when the air pocket is RELATIVELY LARGE, the differential pressure ΔHp is also LARGE, and the initial air pocket pressure is REDUCED.”

It is appreciated that the experience gained by the authors in their valuable investigations is shared with readers. However, the reader can use them in cases he encounters if he has some quantitative landmarks. The behavior associated with relatively large air pockets can be misinterpreted by the reader if it does not have a quantitative reference that means relatively large air pockets. Please provide a quantitative reference or quantity range to make the reader understand what you mean by relatively large air pockets.

3. The air-water interface in the vertical pipe segment during pipe filling obtained in the numerical investigations is shown in Figure 4b together with experimental snapshots. I would like to point out that both numerical investigations and experimental tests to determine the air-water interface are very valuable.

The following statement is included on page 6/lines 152-153: “Overall, the agreement between the numerical results and the experimental data is EXCELLENT.”

Please explain how the excellent agreement between the numerical results and the experimental data is determined in this case? Did you apply any data processing procedure to extract the interface from experimental snapshots? Then was this interface compared to the numerical results obtained with VOF?

4. Two types of cavitation (gaseous and vaporous) are known in literature. In this case, reference is made to the gaseous cavitation (Page 17/ lines 507-511). Please explain more clearly the term used by “macro-cavitation”. Could you provide a few quantitative references to characterize the “macro-cavitation”?

Page 17/ lines 507-511: “Cavities formed from water column separation events are generally assumed to be localized. In terms of modelling, it is usual (and a conservative analysis) to neglect the effect of air release upon cavity formation and the possibility of a GAS cavity is admitted in all calculation sections. In this way, macro-cavitation can be characterized by the existence of a volume of GAS that will be obtained through the continuity equation. Importantly, system response to macro-cavitation is dependent on pipe material [61,62].”

5. Page 13/ lines 351-352: “Such curves show the relationship between AIR FLOW and differential pressure across the device.”

It is suggested to be considered “air flow rate” instead of “air flow”.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

In general, the present is well prepared and written. The present paper summarized the experimental and numerical study on the unsteady two-phase air-water flow in pipelines. It is a very important topic in many engineering fields. Thus, the reviewer suggests accepting the present manuscript. However, some minor comments should be addressed before the final submission. Please see the below comments.

1. Please increase the figure resolution since some notations are hardly seen. 

2. Pease add additional information on the CFD method. For instance, did the authors use their code or commercial code? 

3. Page 2, line 153. The reviewer disagrees that the comparison between CFD and experimental is excellent. It is reasonable but not excellent. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf