Aerodynamic Performance of a Baja SAE Vehicle Using Hybrid RANS-LES Approach

General Assessment
The reviewer would like to first acknowledge the substantial effort invested by the authors. The scope of this work goes well beyond what is typically required for a Baja SAE design exercise, particularly in the use of hybrid RANS–LES modeling, mesh adaptation, vorticity analysis, and 3D post-processing. These efforts demonstrate strong technical ambition and genuine curiosity about advanced CFD methods.
However, while the work is commendable from an educational and exploratory standpoint, the manuscript falls short of the technical, methodological, and validation standards required for archival journal indexing. Importantly, many of these shortcomings are not superficial or editorial in nature, but structural and foundational. As such, the reviewer does not believe that the manuscript is suitable for indexing through major revision alone.
The comments below are offered in a constructive and mentoring spirit, with the hope that the authors may successfully develop this work into a future indexing contribution after addressing the underlying gaps.
Major Technical Concerns
1. Scope and Framing of the Study
Abstract and Introduction, Pages 1 to 3
The abstract (Page 1) positions the study as a high-fidelity aerodynamic investigation using hybrid RANS–LES. While the numerical tools employed are indeed advanced, the scientific scope remains narrow. The manuscript focuses almost exclusively on drag coefficient, with no discussion of side force, lift, or aerodynamic moments.
For a ground vehicle, and especially for a racing or off-road competition vehicle, drag alone is an incomplete descriptor of aerodynamic performance. At minimum, a complete aerodynamic characterization should consider three forces (Cd, Cl, Cs) and three moments (rolling, pitching, yawing). Even if all quantities are not ultimately presented, the absence of discussion or justification for excluding them is a major omission.
Similarly, metrics such as L over D and front-to-rear balance percentage are central to racing vehicle aerodynamics, yet are not meaningfully addressed. This limits both the scientific value and the practical relevance of the results.
2. Absence of Validation and Physical Benchmarking
Section 3, Pages 7–12
A critical limitation of this study is the complete absence of experimental validation, high-fidelity reference data, or benchmark comparison.

• The manuscript presents drag coefficients from RANS and DES simulations at a single velocity of 30 km/h (Section 3.1, Page 7), but provides no comparison to wind tunnel data, coast-down tests, published Baja SAE measurements, or even simplified analytical estimates.
• The claim that DES provides “more accurate” predictions (Abstract; Sections 3.1, 4, and 5) is not substantiated. The manuscript reports only a numerical difference between RANS and DES, not accuracy relative to a reference truth.
• The standard deviation of Cd in DES is interpreted as improved physical realism (Page 7), yet temporal variability alone does not imply improved accuracy.

Without validation, the work remains a numerical comparison study, not a demonstrable advancement in aerodynamic prediction.
3. Questionable Appropriateness of DES for the Problem Scale
Section 2.4, Pages 6–7
The choice and justification of DES for this application is insufficiently supported.

• The vehicle operates at 30 km/h, corresponding to a Reynolds number of approximately 6.7 × 10⁵ (Page 6). This places the flow in a regime where steady or URANS models are often sufficient, especially given the simplified geometry.
• The DES formulation relies on a mesh-dependent transition between RANS and LES regions, yet the manuscript provides no grid sensitivity analysis specific to DES behavior, only a drag-based mesh independence study using RANS (Section 2.2, Page 6).
• The DES mesh adaptation is derived from vortex diameters observed in RANS results (Page 6), which introduces circular reasoning. If RANS does not resolve unsteady structures accurately, it cannot reliably inform LES filter sizing.

As presented, the DES implementation appears methodologically fragile and not robustly justified for this flow regime.
4. Overinterpretation of Flow Visualizations
Sections 3.2–3.5, Pages 7–11
The manuscript places strong interpretive weight on contour plots, streamlines, and Q-criterion visualizations, but these are not supported by quantitative flow metrics.

• Claims regarding vortex shedding, von Kármán-like behavior, and improved wake resolution (Pages 7–9) are made without supporting evidence such as Strouhal number analysis, spectral decomposition, or force coefficient frequency content.
• Streamlines from steady RANS are used to infer vortex topology and persistence (Page 8), which is not physically rigorous for inherently unsteady wake flows.
• Q-criterion plots (Section 3.5, Pages 10–11) are presented qualitatively, without sensitivity to threshold selection or comparison across consistent isovalues.

Overall, the visual analysis is descriptive rather than diagnostic, and conclusions drawn from it exceed what the presented data can support.
5. Insufficient Treatment of Ground and Wheel Effects
Section 2.3, Page 6
All solid boundaries, including the ground and wheels, are modeled as stationary no-slip walls.

• For a ground vehicle application, this modeling choice is known to significantly alter wake structure and drag prediction.
• The manuscript does not discuss the implications of neglecting moving ground and rotating wheels, nor does it attempt a sensitivity study or justify the simplification.
• Given the focus on wake dynamics and drag accuracy, this omission materially affects the credibility of the results.

6. Limited Parametric Scope and Practical Insight
Sections 3–5, Pages 7–12
The study evaluates a single geometry at a single velocity with no parametric variation.

• There is no assessment of ride height, yaw angle, surface modifications, or speed dependence.
• No aerodynamic optimization or design guidance emerges beyond the general statement that DES resolves more structures than RANS.
• As a result, the manuscript does not provide actionable insight for Baja SAE design practice or aerodynamic decision-making.

Presentation and Structure Concerns
While secondary to the technical issues above, the following further limit the manuscript’s readiness:

• The Introduction (Pages 3–4) devotes extensive space to general Baja SAE context but insufficiently narrows the scientific gap being addressed.
• The Methods section intermixes modeling description and justification, making reproducibility difficult.
• Several figures rely on qualitative interpretation without clear scaling rationale or quantitative annotation.

Recommendation
While the reviewer acknowledges the authors’ effort and the educational value of exploring hybrid turbulence models, the manuscript suffers from fundamental methodological and scientific limitations that cannot be resolved through incremental revision.
The absence of validation, the overextension of qualitative visualization, and the insufficient justification for DES usage collectively prevent the work from meeting indexing standards.
Recommendation: Not Approved.