Pressure- and Size-Dependent Aerodynamic Drag Effects on Mach 0.3–2.2 Microspheres for High-Precision Micro-Ballistic Characterization

Round 1

Reviewer 1 Report

The authors derived drag coefficients for microspheres traveling in air at subsonic, transonic, and supersonic velocities from the measured trajectories of microspheres launched by laser-induced projectile acceleration. From my point of view, the work provides interesting results to the aerodynamic drag effects. I suggest minor modifications before it is accepted.

1. The section of the Introduction is too short. Breaking the Introduction down into several paragraphs for a more detailed description may be better.

2. The color bar in Figure 4 should be labeled from small to large.

 

3. When Eq 3 is defined, it is considered that the force on particles is completely derived from the drag force, and the additional mass force and other forces of particles are ignored. Has the author considered the influence of these forces?

Author Response

Reviewer #1

Reviewer #1 selected “Extensive editing of English language and style required.”

• The original manuscript was written with care by a native English speaker. In the revision, we have focused more on the English style and feel that our writing quality meets publishing standards.

“The section of the Introduction is too short. Breaking the -Introduction down into several paragraphs for a more detailed description may be better.”

• The Introduction was divided into multiple paragraphs to improve clarity. Further, discussions of the study’s significance in relation to two major areas of application (laser-induced projectile impact testing and projectile gene and drug delivery) have been broadened. With these revisions, we believe that the Introduction provides the context and background required to effectively communicates the motivation behind our study.

“The color bar in Figure 4 should be labeled from small to large.”

• The color bar in Figure 4 was revised according to the reviewer’s recommendation. The labels now read in ascending order.

“When Eq 3 is defined, it is considered that the force on particles is completely derived from the drag force, and the additional mass force and other forces of particles are ignored. Has the author considered the influence of these forces?”

• The additional mass force was neglected on the basis of the high density ratio between the particle and the surrounding gas. This has been noted in the manuscript at the introduction of Eq. 3.

Reviewer 2 Report

In this paper, drag coefficients for microspheres traveling in air at subsonic, transonic, and supersonic velocities have been acquired from the measured trajectories of microspheres launched by laser-induced projectile acceleration. The results is important for improving the drag coefficient model of supersonic microsphere motion considering rarefaction effect. The article is interesting and relevant. But some modifications are still needed.

1.     The main content of this paper is the aerodynamic drag effect on microspheres, and “projectile gene delivery” in the title has not been introduced.

2.     In “Introduction” the research significance needs to be more prominent.

3.     The coordinate system must be described.

4.     some variables are in bold and some are not. Please unify them.

Author Response

Reviewer #2

“The main content of this paper is the aerodynamic drag effect on microspheres, and ‘projectile gene delivery’ in the title has not been introduced.”

• We acknowledge that the inclusion of “projectile gene delivery” in the title of our manuscript may lead readers to believe that it is the focus of the work. Therefore, the title of the manuscript has been revised so as not to reference projectile gene delivery. Additionally, the introduction and discussion sections have been revised to consider the application of projectile gene delivery in more depth. The additional content emphasizes that, while the present experimental work did not include testing of projectile gene and drug delivery, subsequent studies of projectile gene and drug delivery will benefit from this work’s success in quantifying C_D with improved accuracy.

“In ‘Introduction, the research significance needs to be more prominent.”

• As noted in response to Reviewer #1’s feedback, the Introduction was extended to highlight why the study’s focus on quantifying C_D more accurately is beneficial to the applications of laser-induced projectile impact testing and projectile gene and drug delivery.

“The coordinate system must be described.”

• Figures 1(a) and (b) were revised to include the definition of the coordinate system’s z-direction. This addition should clarify subsequent references to z(t), including those in Figure 2.

“Some variables are in bold and some are not. Please unify them.”

• This inconsistency was rectified. All variables are now presented in standard formatting.

Reviewer 3 Report

Comments for author File: Comments.pdf

Author Response

Reviewer #3

“The referee wondering why the authors did not mentioned the works from Millikan [1] and more recent made in [2], where explicit expressions on the slip coefficient are provided.”

• To address the work of Millikan, the experimental space of interest in this work is high-M, low-Re. Millikan’s oil drop experiments studied the low-M experimental space. Today, there is little novelty in studying the low-M experimental space, as the accuracy of low-M drag models has been demonstrated. Therefore, Millikan’s work is not referenced in our manuscript.
• To address the work of Sharipov, his discussion of flow past a sphere focuses on Stokes flow, which applies to Re < 1. This represents a Reynolds number regime below the experimental space studied in our work. Further, the validity of Stokes’ equations for C_D at Re < 1 has been demonstrated and would not have been a novel focus of our study. Therefore, Sharipov’s work is not referenced in our manuscript.