Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is scientifically sound, with valuable results on mixed-phase icing. However, it requires improvements in reporting clarity (definitions, nomenclature, subscripts), technical rigor (validation, discretization, time-dependence), and practical engineering interpretation (anti-icing context, boundary layer analysis).

• The abstract is descriptive but lacks quantitative results (e.g., % increase in ice growth, thickness values). Adding such findings would enhance clarity and impact.
• In the statement “Dalin Zhang et al. were among the first in China to apply the Eulerian method…”, no reference number is provided. This should be corrected.
• The aspect ratio of crystals is mentioned repeatedly but not defined in physical terms (length-to-width ratio).
• The acronym FENSAP should be spelled out (Finite Element Navier–Stokes Analysis Program).
• Variables such as droplet/ice Reynolds number, Mach number, CL, Cm, and CD are used without proper definitions.
• Numerous symbols and variables (Re, α, LWC, ICC, hf, etc.) are introduced. A nomenclature table is needed for clarity.

• The current notation for droplet drag coefficient (CD) and crystal drag coefficient (Cd) only differs by case. Distinct subscripts would reduce confusion.
• The text states, “five sets of meshes with different densities were used to compute lift forces”. Since Figure 3(b) also shows ice growth, the caption should be revised to “Lift forces and ice growth versus number of elements”.
• The numerical scheme order (first-order, second-order, etc.) is not reported. This is critical for judging numerical accuracy.
• The governing equations include unsteady terms, but no results are shown on the transient evolution of ice thickness or aerodynamic coefficients. Clarify whether steady-state or unsteady simulations were conducted.
• Some validation against NASA CRM-NLF data is shown (CL, CD, Cm vs Alpha and Re). However, explicit validation of icing predictions (ice shape/size) against experimental data is limited. Stronger evidence of agreement is needed.
• While turbulence is modeled with Spalart–Allmaras, boundary layer thicknesses or velocity vector fields around the wing are not presented. These are important diagnostics in icing studies.
• It is not made explicit whether 2D sections or full 3D unsteady computations were performed. This must be clarified, especially since CRM-NLF is inherently a 3D geometry.
• While parametric studies (size, aspect ratio, concentration) are presented, the manuscript could better link results to engineering implications: e.g., thresholds of icing severity, design of anti-icing systems, or operational recommendations.
• Section 5 is titled “Discussion,” but it seems it is a section of conclusions.

Comments on the Quality of English Language

• The English is functional but not polished.
• A thorough language editing (preferably by a professional editor or a fluent technical English speaker) is recommended to:
• Shorten sentences.
• Improve grammar and word choice.
• Ensure consistent technical phrasing.
• Enhance readability for an international audience.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Paper presents a numerical investigation into the complex phenomenon of mixed-phase aircraft icing, a recognized hazard in aviation safety. The topic is of significant interest to the field, and the results suggesting that ice crystals lead to thicker, smoother ice layers are valuable. However, the manuscript in its current form suffers from several major shortcomings that prevent its acceptance.

The main critical point is that study is based on numerical simulations, yet the results are not validated against any experimental data. he authors mention a NASA test of the CRM-NLF model but use it only for clean aerodynamic validation. The ice accretion shapes predicted under mixed-phase conditions are presented as fact without any comparison to wind tunnel data. Without validation, the quantitative claims like increases by 75% are lack scientific rigor.

The complex ice crystal erosion model is introduced but its implementation and impact on the final ice shapes are not discussed or shown. Were erosion effects active in the presented results?

Define all parameters clearly (e.g., aspect ratio, "Ice Growth", Re). Most of them is mentioned but is not defined.

You mentioned « droplet size distribution followed a customized profile [29], as shown in Figure 6.» but figure 6 demonstrated cross-section of the areas of concern for aircraft icing. That confusing.

Quantify "smoothness" (e.g., by analyzing surface contours).

Correct and clarify all figure captions and axes labels. Most figures are of low quality, with unclear small labels. Moreover, some captions are not self-contained, like «ice shape» fig 12.

The core idea of this paper has merit, but in its present form, it does not correspond to the high scientific level of the journal.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors provide a generic description of the Spalart-Allmares turbulence model, highlighting the widespread use in aerospace applications. While the description is factually correct, it does not sufficiently explain why this model was choosen, nor acknowledge its limitations in this specific context (line 144-148). Following should be added: 

1. Justification for the use of the model (i assume that it was choosen due to its computational efficiency and robustness for external aerodynamic flows around aircraft configuration, as the simulations are already computationally intensive due to coupling of flowfield etc. )
2. Comparison to alternative turbulence models - more advanced two-equation models should at least be mentioned as they tend to provide better predictions. 
3. Limitations of this model - current statement omits the fact that icing introduces surface roughness effects, large scale seperation areas where S-A may not perform well without modifications - typically models include turbulence roughness corections when using S-A, but this detail is missing. Without this clarification, the description risks overstating the models accuracy for icing-specific physics. 

In Figure 6, add the profiles of the wing geometry on cross-sections (full ones, without any ice on the wings). 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have addressed most of my earlier comments, which has significantly improved the manuscript.

However, the nomenclature section still needs to be expanded to include all variables and symbols used throughout the manuscript.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have done a good job and taken most of the comments into account. The paper can be accepted for publication.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf