Large Eddy Simulation of the Effect of Hydrogen Ratio on the Flame Stabilization and Blow-Off Dynamics of a Lean CH4/H2/Air Bluff-Body Flame
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe paper reports a numerical work about the Large-eddy simulation (LES) of the hydrogen ratio effect on flame stabilization and blow-off dynamics of lean CH4/H2/air bluff- 3 body flame. The numerical results are also compared with the experimental results.
While the work is interesting, the manuscript suffers the following shortcomings. Thus, I would not recommend its publications
1. Lack of mesh convergence study
Although the numerical results agrees with the experimental results, this does not indicate that the numerical results reached the solution convergence with variation of mesh size.
2. Since LES is adopted in the work, is any wall modelling adopted for the no-slip wall? The wall model can significantly changes the turbulent dissipation. If not used, could the authors please justify not using the wall model?
3. A lot of "Error! Reference source not found" occurs in the manuscript. Could the authors please provide the references?
4. Issues about the figures
- All the figures are too blurred. It is difficult to see the words inside the figures, especially Figure 1. Please make the whole figures easy to look and interpret.
- About Figure 3, it is very difficult to compare the experimental and numerical results as they are in different color scales from the same range. Could the authors use the same color scale?
Comments on the Quality of English Language
The quality of English is good. I can understand the contents easily.
Author Response
see attached
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsSee comments attached
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsNote, for example, some of the expressive errors that compromise the quality and even the readability of the text:
In a quick look I found numerous formatting and/or typing errors, example: "( = 0.2)" on line 366, that is, nothing is equal to 0.2, what is that??; unit of measurement "stuck" to the number, for example Figure 8(a), "0ms", Figure 9 has "J//(s.m3)" the correct thing is to put the "3" elevated.
I have carefully reviewed the manuscript titled "Investigation of Bluff-Body Stabilized CH4/H2/Air Flame through Large Eddy Simulation," and I am pleased to provide a favorable assessment of the work. The study addresses the dynamic behavior of a bluff-body stabilized flame with varying hydrogen ratios, employing Large Eddy Simulation (LES) with the Thickened Flame (TF) model and a 30-species skeletal mechanism in the OpenFOAM open-source code.
The key findings and conclusions presented in the article contribute significantly to the understanding of the combustion characteristics under different conditions. The following points summarize the positive aspects of the study:
Comprehensive Investigation: The study comprehensively investigates four hydrogen ratio conditions (0%, 30%, 60%, and 90%) under both stable conditions and blow-off processes. This thorough examination provides valuable insights into the flame behavior in diverse operational states.
Effect of Hydrogen Ratio on Flame Stability: The results indicate that, under stable conditions, the flame height, inner/outer recirculation zones, and the flame's ability to stabilize in higher strain rate locations are influenced by the hydrogen ratio. The linear increase in the angle between the flame edge and centerline suggests a stronger attachment of the flame to the bluff-body with higher hydrogen blending.
Blow-Off Process Analysis: The identification of a specific precursor event triggering blow-off and the separation of the blow-off process into two stages demonstrate a detailed understanding of the blow-off phenomenon. The study reveals that the duration of both stages decreases with an increase in the hydrogen ratio, highlighting the role of hydrogen blending in the blow-off process.
Enstrophy Analysis: The examination of enstrophy during the blow-off sequence for all cases is a notable contribution. The observed increase in enstrophy, coupled with the decrease in its mean value with hydrogen blending, provides valuable insights into the impact of hydrogen ratio on the flame dynamics.
Enstrophy Budgets Analysis: The detailed analysis of enstrophy budgets, particularly the reduction in vortex stretching source term magnitude with increasing hydrogen ratio, enhances our understanding of the underlying mechanisms. The observed changes in dilatation and baroclinic torque terms close to blow-off further contribute to the comprehensive understanding of the combustion dynamics.
Overall, the manuscript exhibits a high level of rigor in methodology, a thorough analysis of results, and a clear presentation of conclusions. The findings of this study have the potential to significantly contribute to the field of combustion science.
I recommend acceptance of the manuscript for publication, as it makes a meaningful contribution to the existing body of knowledge in the field. I appreciate the author's efforts in conducting this research and presenting the results in a clear and insightful manner.
Author Response
Re of Q1: Thanks for the suggestion. We carefully checked the entire article and fixed the errors in the revision.
Re of Q2: We thank the reviewer’s positive suggestions on the present article. This study investigates the flame structure and dynamics of the bluff-body flame close to blow-off conditions numerically. The results obtained from the numerical simulations show minor differences with experimental data on velocity field and flame structure for all conditions. The presented results reveal that the flame is stabilized in higher strain rate spots more easily in the presence of high hydrogen ratios. Moreover, the flame location moves away from the concentrated vortex area with the hydrogen ratio increasing. The blow-off investigation indicates that the blow-off sequence of premixed bluff-body flame can be separated into two stages. The entire blow-off process becomes shorter with an increase in the hydrogen ratio. The primary reason of global extinction is the reduction of the heat release rate and enstrophy analysis implies that blending hydrogen can reduce the value of enstrophy downstream of flames. The dilatation and baroclinic torque terms decrease close to blow-off and the decline is not significant in high hydrogen ratio conditions. The further researches on this field will be present.
Author Response File: Author Response.pdf
