Turbulent Flame Propagation in Hydrogen-Air and Methane-Air Mixtures in the Field of Synthetic Turbulence: Direct Numerical Simulation

Round 1

Reviewer 1 Report

Turbulent flame propagation in hydrogen-air and methane-air mixtures in the field of synthetic turbulence: Direct numerical simulation

Valentin Y. Basevich, Andrey A. Belyaev, Fedor S. Frolov, Sergey M. Frolov

 

The manuscript deals with a topic of high scientific interest such as the treatment of turbulence in combustion processes. In particular, the aim of this work is the validation of a 2D model for the characterization of 3D phenomena. This possibility is very interesting for multiple engineering applications, such as piston engines and gas turbines, as well as various industrial burners. In fact, to date, in order to have a faithful reproduction of turbulent combustion processes, a high-fidelity approach with high computational costs must be used. Such an approach could be used to create large lookup tables of turbulent burn rates for different fuels under different thermodynamic and turbulent conditions for the Flame Tracking – Particle (FTP) method. Lookup tables for turbulent burn rate could replace the multiple empirical correlations.

The manuscript is well structured, but it is advisable to diversify the bibliography more, we recommend some examples of recent works dealing with the combustion process as pressure varies (for applications such as gas turbines) and recent models developed to characterize the chemical interaction - turbulence with the effect of flame instabilities. There are many uncited recent works addressing the issues in the article below are two examples, but more literature integration is recommended:

- Subgrid modeling of intrinsic instabilities in premixed flame propagation. PE Lapenna, R Lamioni, F Creta. Proceedings of the Combustion Institute 38 (2), 2001-201. https://doi.org/10.1016/j.proci.2020.06.192

 

- Pressure-induced hydrodynamic instability in premixed methane-air slot flames. R Lamioni, PE Lapenna, L Berger, K Kleinheinz, A Attili, H Pitsch, F Creta. Combustion Science and Technology 192 (11), 1998-2009. 10.1080/00102202.2020.1768081

The mathematical model is clearly explained, and the results are great. The figures are of high quality, it is only advisable to diversify the markers between numerical values and experiments in order to have a clear reading of the results even in black and white. In conclusion, we recommend acceptance of the article following the changes recommended in the introductory section and in the presentation of the graphical results.

Author Response

We are grateful to the reviewer for valuable comments. We have made our best to follow all the comments. All changes in the revised manuscript are marked in yellow.

The manuscript deals with a topic of high scientific interest such as the treatment of turbulence in combustion processes. In particular, the aim of this work is the validation of a 2D model for the characterization of 3D phenomena. This possibility is very interesting for multiple engineering applications, such as piston engines and gas turbines, as well as various industrial burners. In fact, to date, in order to have a faithful reproduction of turbulent combustion processes, a high-fidelity approach with high computational costs must be used. Such an approach could be used to create large lookup tables of turbulent burn rates for different fuels under different thermodynamic and turbulent conditions for the Flame Tracking – Particle (FTP) method. Lookup tables for turbulent burn rate could replace the multiple empirical correlations.

The manuscript is well structured, but it is advisable to diversify the bibliography more, we recommend some examples of recent works dealing with the combustion process as pressure varies (for applications such as gas turbines) and recent models developed to characterize the chemical interaction - turbulence with the effect of flame instabilities. There are many uncited recent works addressing the issues in the article below are two examples, but more literature integration is recommended:

- Subgrid modeling of intrinsic instabilities in premixed flame propagation. PE Lapenna, R Lamioni, F Creta. Proceedings of the Combustion Institute 38 (2), 2001-201. https://doi.org/10.1016/j.proci.2020.06.192

- Pressure-induced hydrodynamic instability in premixed methane-air slot flames. R Lamioni, PE Lapenna, L Berger, K Kleinheinz, A Attili, H Pitsch, F Creta. Combustion Science and Technology 192 (11), 1998-2009. 10.1080/00102202.2020.1768081

The mathematical model is clearly explained, and the results are great. The figures are of high quality, it is only advisable to diversify the markers between numerical values and experiments in order to have a clear reading of the results even in black and white. In conclusion, we recommend acceptance of the article following the changes recommended in the introductory section and in the presentation of the graphical results.

To address these comments, we have added two references indicated by the reviewer to the list of references and changed the markers for numerical values in Figures 4 and 8.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors performed a numerical study on the turbulent flame propagation in hydrogen-air and methane-air mixtures in the field of synthetic turbulence.

Some quantitative results are to be mentioned in the abstract.

The introduction is relatively short and may be extended.

The novelty of the work is to be clearly stated.

The used turbulence model is to be justified.

A figure presenting the 3D studied configuration including the boundary conditions is to be added.

The numerical method is to be detailed.

What is the used numerical method?

What is the convergence criterion?

What is the used time step?

A figure presenting the used mesh is to be added.

A grid sensitivity test is to be performed.

A validation/verification of the numerical model is to be performed.

The authors studied a 3D configuration without presenting any 3D profile.

In figure 3, why the time is limited to 100 us?

What are the values of x and z in figure 9?

The discussion is to be improved by adding physical interpretations.

The paper is to be checked against misprints and grammatical mistakes.

 

Author Response

We are grateful to the reviewer for valuable comments. We have made our best to follow all the comments. All changes in the revised manuscript are marked in green.

The authors performed a numerical study on the turbulent flame propagation in hydrogen-air and methane-air mixtures in the field of synthetic turbulence.

Some quantitative results are to be mentioned in the abstract.

To address this comment, we have added some quantitative information to the abstract.

The introduction is relatively short and may be extended.

To address this comment, we have added two most recent references related to the standard DNS approach.

The novelty of the work is to be clearly stated.

To address this comment, we have added the following sentences at the end of Introduction section: “Thus, we propose and validate a nonempirical technique alternative to the standard DNS of turbulent flame propagation in reacting gas mixtures, which is a distinctive and novel feature of the present work.”

The used turbulence model is to be justified.

Actually, we justify the model by the direct comparison with experimental data in Figures 4 and 8. Nevertheless, to clarify the approach we have added one sentence to Section 2.1: “It is worth emphasizing that the specification of turbulence intensity and spatial turbulence scale is equivalent to the specification of the turbulent energy dissipation and the Kolmogorov scale.”

A figure presenting the 3D studied configuration including the boundary conditions is to be added.

The flow configuration is very simple and described in the text together with boundary conditions in Section 2.2. This is just a rectangular box.

The numerical method is to be detailed.

What is the used numerical method?

To address these comments, we have slightly extended the text in Section 2.2 and added one more reference [33]: “When constructing the implicit scheme, the method of additive decomposition was used [33]. This scheme is first order accurate in time and space and is absolutely stable.”

What is the convergence criterion?

The convergence criterion is 0.001. It is now indicated in Section 2.2.

What is the used time step?

The time step is 1 microsecond. It is indicated in Section 2.2 of the original manuscript.

A figure presenting the used mesh is to be added.

The information on the uniform computational mesh is given in Section 2.2 of the original manuscript.

A grid sensitivity test is to be performed.

To address this comment, we have added a sentence to Section 2.2: “Grid sensitivity tests showed that the simultaneous doubling of the number of computational cells along all three directions while maintaining the dimensions of the computational domain virtually did not affect the value of the turbulent flame propagation velocity.”

A validation/verification of the numerical model is to be performed.

Actually, we have validated the model by the direct comparison with experimental data in Figures 4 and 8.

The authors studied a 3D configuration without presenting any 3D profile.

The 3D profile of the turbulent flame is presented in Figure 1 in the original manuscript.

In figure 3, why the time is limited to 100 us?

As said in the problem statement in Section 2.2, the size of the computational domain along the y-axis is only 5 mm. Thus, during this time interval (100 us) the turbulent flame has already passed half the distance, and its motion is almost stationary in time.

What are the values of x and z in figure 9?

Figures 5, 6 and 9 are plotted for a small patch of turbulent flame with its local normal vector directed along y-axis. The distributions of temperature and molar fractions of species are taken along the normal to the flame. To address this comment, we have added the following sentence to the text: “The temperature profile in the turbulent flame is plotted for a small patch of flame with the local normal vector directed along the y-axis, and the distribution of temperature is taken along the normal to the flame.”

The discussion is to be improved by adding physical interpretations.

To address this comment, we have added the following sentence to the Conclusions section: “Calculations indicate that the “wrinkled flame” model is applicable to fuel-lean and stoichiometric hydrogen – air and methane – air mixtures at turbulence intensities up to 10 m/s.”

The paper is to be checked against misprints and grammatical mistakes.

We asked our native English-speaking colleague to check the text.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript has been implemented in the introductory part, as requested in the review comments. In particular, the part of the state of the art that had gaps has been increased.

 

In this form the manuscript can be accepted for publication.

Reviewer 2 Report

after revision, the paper can be accepted for publication