A Comparison of Tidal Turbine Characteristics Obtained from Field and Laboratory Testing

Round 1

Reviewer 1 Report

Overall an interesting study, and good to see that results from different forms of testing (open water and tow-tank) give comparable results,  reinforcing that different forms of testing can be used. This builds well on the round-robin comparison of test facilities.

 

There are a few sections where the clarity of the manuscript should be improved, particularly the figure captions which are not comprehensible in themselves, and some of the abbreviations used are not fully explained.

 

The revisions required are each not too significant, but overall the manuscript needs further refinement before publication. 

 

Overall comments on the paper:

 

1. The Introduction should mention field testing and the real environment in which these experiments are trying to represent before discussing details of the MARINET tests.
2. More detail is required on how the structure of the barge (and its thrustors) might influence the tests. With a draft of 1.8m, the vessel would be below the level of the turbine, potentially influencing the flow. The paper also states the turbine was mounted at the bow, but the photographs appear to show it from the stern, was the vessel operated in reverse for the tests?
3. As one of the main findings reported is that the agreement was only good once the blockage correction was applied, it might be interesting to include a result without blockage correction.
4. The paper does not really discuss any limitations of the methodology or areas for further work.
5. The authors note that "self propelled platforms in the field can be an accurate and efficient way to test tidal turbines", it would be useful however to have some discussion on the relative costs of these methods, and possibly other considerations.
6. It would be useful to include a section in the introduction briefly introducing the measurement instruments, highlighting their operating principles, and any differences between them. This would address a few of the specific points below.
7. The conclusions section is not particularly well written compared to the rest of the paper. Possibly rewording some of the bullet points into more complete sentences would improve this. It also lacks an overall conclusion.
8. One important topic that is not really covered is how all of these tests relate to a full-scale device. I appreciate this is not the focus of this work, but it is nevertheless an important overall driver in conducting scale tests. Indeed, using an open water test would allow for larger-scale turbines, with presumably lesser influence of scaling.
9. The results plots do not all state which measurement location(s) they represent, making it difficult to interpret them, especially as the same instrumentation was used for both field and tank tests.
10. Does the discussion on inflow angle only reflect the open-water testing, or is this considered for the tow-tank as well? In Fig. 9 is this the absolute angle, or was there a directional bias to the inflow, as all values are positive? This should be elaborated on.

Specific points to address in the manuscript to improve clarity:

1. Line 23. not clear what "these tests" refer to
2. Line 32. This seems to be suggesting lab test are more expensive than the other way round, which goes counter to perceived wisdom
3. Line 33. Reference these examples? or note they are elaborated below if that is the case.
4. Line 58. Provide more detail here on what the Vector to measure inflow velocities is, similarly with Aquadopps below
5. Figure 1 - it would be helpful to show both a plan and side view, preferably a scale drawing, including how the barge might influence the flow, particularly on the elevation. Caption should include what A1,A2, V1, V2 are.
6. Fig. 2 - Caption should include what A1,A2, V1, V2 are. Applies throughout.
7. Table 1 - headings should be something like Parameter and Value
8. Revise colours and symbols in fig 6 so  PMV1 is a blue cross as per fig 5, and PMV1f is a different marker. Similarly with Fig 8.
9. Line 211 - incomplete sentence - complete this.
10. Line 221 - expand on what is meant by "no flow measurement information was available" - is this that the skipper was not able to monitor the instruments live, that the data was only available afterwards?
11. Line 249. clearer to write between -1.7 and -2.2m/s.
12. Fig 13. Consider using colour as well as symbols to help differentiate the markers. Caption needs to be re-written to make it clear what the figure shows. Aqdp1 abbreviation not needed. What is "binx"?
13. Fig 15  & 16  legend is not clear for last item, is it "PA1,s"? use a better resolution image/vector image.
14. Line 271. Can this sentence be reworded, as it is not clear.
15. Fig. 17 - Can this image be made higher resolution, as it is difficult to see the different lines, particularly the blue dashed Tank line (maybe use a different shade of blue?)
16. Figs. A20-23 - consider plotting these on a consistent colour scale (-300 to -2800)?. What are the units of the colour scale?  Consider also making these smaller in the vertical direction, allowing them to be placed on the same page to facilitate comparison. The Bins are very elongated in the vertical direction. As with other figures, captions need expanded to explain what the plot shows.

 

Author Response

Please see attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript “A Comparison of Tidal Turbine Characteristics obtained from Field and Laboratory Testing” presented the comparison of results of tidal characteristics of the power coefficient with speed ration in case of mechanical power output by and eclectrical power output, different position of velocities, different location of in-site or laboratory etc. The idea is innovative, and authors can find lots of data to do the analysis, which would be helpful to understand how much discrepancy between the experimental test and the in-site test on tidal turbine research. While there are some minor points need to be clear.

1.    What is the definition of the parameters of  and γ? Even though that definition ofγis described, what is the starting point for each slope in the data series like fig.A18?

2.     In fig.A20-fig.A23, the legend need explanation.

3.     In Fig.5 does the all run mean that either in laboratory and in-site?

4.     In fig.6, the flow dynamics induced data variable, a 30s section filter is applied, it is better to present how the filter is done. How much of a different filter will affect the result? Why apply 30s?

5.     In line 212, the blockage in laboratory is considered, how about in-site? If the blockage need consideration in laboratory, does that mean the similarity has problem between the test in laboratory and in-site?

6.     Why the fig.17 is presented. In the fig. Model results compared very well with tank and field results, while why the Cp is not scattered with larger λ compared with other figs you presented in the manuscript?

Author Response

Please see attached file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Reviewer’s report on the paper: A Comparison of Tidal Turbine Characteristics obtained from Field and Laboratory Testing

A 3-bladed horizontal axis turbine was used for those experiments. The rotor had a 113 diameter of 1.05m and the blade length was 0.35m. This paper presents 6 field tests of a tidal turbine, performed using a self-propelled barge in real tidal flow and still 7 water conditions, that are compared to a towing tank test.

Since the blockage effect will affect the flow velocity passing the turbine blade, thus, the velocity passing blade in a towed test is larger than it in a field water condition.

The paper is well written and the quality of the figures is good. I only have one question: The agreement between experimental and numerical results is too good to be true. A similar excellent agreement between field and lab tests is reported. I rarely have those experiences and no similar reports were found in the literature.

 

 

 

 

 

Author Response

Please see attached file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have addressed my main concerns with the manuscript, and I think the clarity of the work is significantly improved with this revised version. I still consider that a side elevation of the field experimental setup would add clarity, however the information is present within the manuscript.  

There are a few final minor points I would suggest, and these can possibly be fixed in the final editing/proofs.

1. I would suggest on line 135 the instrument sampled "at" the frequency, and this sentence is now somewhat of a fragment. 

2. On line 155, suggest changing to "where ^the^ water is"

3. Lines 152, 268, 278, and Fig 11 (legend & caption) - the Authors should be consistent with the use of either "narrows" or "channel", at present both are used inconsistently.

 

Author Response

1. I would suggest on line 135 the instrument sampled "at" the frequency, and this sentence is now somewhat of a fragment. 

We have amended the manuscript accordingly.

 

2. On line 155, suggest changing to "where ^the^ water is"

We have amended the manuscript accordingly.

3. Lines 152, 268, 278, and Fig 11 (legend & caption) - the Authors should be consistent with the use of either "narrows" or "channel", at present both are used inconsistently.

We have amended the manuscript accordingly.