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Peer-Review Record

Numerical Analysis of Unsteady Characteristics of the Second Throat of a Transonic Wind Tunnel

Aerospace 2023, 10(11), 956; https://doi.org/10.3390/aerospace10110956
by Chenghua Cong 1,2, Honggang Qin 2,* and Xingyou Yi 2
Reviewer 1: Anonymous
Reviewer 2:
Aerospace 2023, 10(11), 956; https://doi.org/10.3390/aerospace10110956
Submission received: 11 August 2023 / Revised: 8 September 2023 / Accepted: 15 September 2023 / Published: 13 November 2023
(This article belongs to the Section Aeronautics)

Round 1

Reviewer 1 Report

Authors, I recommend the following modifications to your well-organized manuscript. 

1) Abstract has the following two sentences: " Under 1% 21 of the pressure disturbance, the fluctuation amount reaches 16%. The pressure disturbance near 22 the shock wave had obvious amplification effect, and its fluctuation amount reached 16% under 23 the pressure disturbance of 1%." 

Condense this to one sentence, as the same information is conveyed.

2) Introduction - Add some of the classical references from the 1920's to bolster the importance of your work in a historical context. 

3) Some English editing needed for sentence starting on line 72

4) Add a heading to the Introduction Section. Current manuscript has Section 1 as Numerical Methods

5) Strengthen the last paragraph of the Introduction within the context of all the references you discuss briefly in the Introduction paragraphs immediately preceding. Tell the reader why your work is important, and point out the type of problems you can address by applying your methodology prior to constructing a new tunnel. 

6) Recommend the addition of a Methodology Section to the paper. This section should explain the cases that were run. Move the discussion about the pressure pulse application at the outlet this introductory paragraph since it applies to all results. Give the reader an example case to follow through so the understanding is established as to how you applied the pressure pulses at the outlet to examine the flow. Further, explain the notation such as (0-T/4) in the methodology to explain how you picked out the cycle time in the results. 

7) Additional discussion is required in my opinion to explain why you present several pages of results for the 5Hz case and only one plot and 2 paragraphs for the 10-2500Hz cases. I understand this is due to the pressure fluctuation frequency exceeding the ability of the flow dynamics to propagate the disturbance upstream, but this is only treated cursorily on line 419. I think this is an important result, that may be able to be related to the length of the duct downstream of the shock wave. It would be interesting to propose a methodology for other wind tunnel geometries to select the downstream pressure fluctuations that need to be considered by a designer. 

Overall, very little issues with the English language detected. Some recommendations were provided in the comments.

Author Response

  1. The modifications have been made according to the comments.
  2. Relevant literature has been added.
  3. The sentence in line 72 has been adjusted.
  4. Title has been added to the first part
  5. According to the requirements, the importance of this article's work and the problems that can be solved through this article's work were described.
  6. As requested, a section has been added to the paper that introduces the application of pulsating pressure at the outlet of the computational domain and how to determine the position of the shock wave. An explanation was also provided on how the flow cycle is defined.
  7. The selection of downstream pressure pulsation frequency here has certain empirical properties, including the references cited in the paper [17]. Chan measured the axial force pulsation of the balance in NTF, with the main components concentrated below 3Hz. The pulsation affecting wind tunnel flow was mainly low-frequency and long-period components (Chan D T, Balakrishna S, Walker E L, et al. Mach stability improvements using an existing second stroke capability at the national transitional facility [R]. AIAA paper 2015-0622, 2015.). In other relevant literature mentioned the issue of pulsation frequency in wind tunnels, mainly consisting of low-frequency pressure pulsations below 10Hz.( Jones G, Balakrishna S, Demoss J, et al. Influences of models on the unsteady pressure characteristics of the NASA national transitional facility [R]. AIAA paper 2015-1557, 2015. 2. Owen F K, Stainback P C, Harvey W D. Evaluation of flow quality in two NASA transitional wind tunnels [J]. Journal of Aircraft, 1981, 18 (6): 451-457.3.Pugh P G, Graue r-Carstensen H, Quemard C An investment of the quality of the flow generated by three types of wind tunnel [R] AGARD AG-240, 1:1-23, 1980.).The magnitude of the frequency may be related to the length of the downstream pipeline of the second throat, but based on experience, it is boldly speculated that it should be below 20Hz. Further research on the impact of frequency will continue, which is a systematic work that will consume a lot of computational resources and time.

Reviewer 2 Report

Dear authors, 

please find my comments in the attached file.

Comments for author File: Comments.pdf

Overall, the quality of English is high; in some cases, the sentences are too complex, or they can be improved grammatically (please see my comments in the attached review report).

Author Response

Major points 

  1. According to the review comments, the abstract has been reduced. The repeated sentences have been modified, and the current summary word count is 300 words.
  2. In the paper, details on the measurement of experimental results were added. And added an explanation on the number of grid cells in the figure.

Minor recommendations

  1. In the name of a wind tunnel, it is generally referred to as the cross-sectional size of the test section of the wind tunnel. For example, a 5m * 4m wind tunnel refers to a test section with lengths of 5m and 4m in both directions of the cross-section. If the dimensions in both directions are the same, such as a 5m * 5m wind tunnel, it is usually referred to as a 5m wind tunnel. If readers are unfamiliar with this field, they can obtain relevant explanations from the original literature.
  2. The dimensions in both directions of the cross-section of the test section are marked in the figure.
  3. The sentence has been modified. Due to changes in the paper, the line number has changed.
  4. The “ideal”in the figure represents the situation when fully following the distribution of sinusoidal pressure pulsation at the outlet, which has been explained in the paper.
  5. The sentence has been adjusted. Due to modifications in the paper, the line number has changed.
  6. The statement has been adjusted. Due to changes in the paper, the line number may have changed.
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