## 3 Simulation Setup  
The computational domain consisted of one inlet, one outlet, the pipe, the surface of the bluff body, and the boundary walls. Figure 2 displays the geometry and the structured mesh. The finest grids (i.e., those with a grid size of approximately 0.5 mm) were placed in the flame's front region. The total number of grids for the mesh was about 5 million. For the non-reacting flows, the mesh size was increased to about 700 million in a similar-scale swirl burner, while the results showed no differences. In the experiment, turbulence was generated through two sintered metal plates. In the numerical simulation, a filtered noise inflow generator developed by [PERSON] was used to produce the inlet turbulence [28]. In this method, the parameters of the velocity field were set based on the experimental measurements. For instance, the Reynold stress tensor and length scales, which were the input parameters, were applied based on the calculated values derived from the experimental data. Therefore, the turbulent Reynolds number \(Re\) was computed based on \(u^{\prime}\), which equals 1.4641 m\({}^{2}\)/s\({}^{2}\). The turbulence integral length scale was determined to be approximately 4.323 mm based on the experiments. It should be noted that the turbulence was introduced at 1.4\(d\) (\(d\) represents the top surface diameter of the bluff body) upstream of the combustion chamber. Therefore, the turbulence developed in such a way that the artificially generated turbulent flow was sufficient for capturing the flow features. A non-slip boundary condition was used at the burner and bluff body walls. The temperature of the top surface of the bluff body and side walls in the simulation were selected based on the experimental measurements. Bluff body temperatures of 700 K, 710 K, 730 K, 750 K and mean liner wall temperatures of 800 K, 820 K, 830 K, and 850 K were applied as the temperature boundary conditions for 00H2, 30H2, 60H2, and 90H2, respectively. An adiabatic wall was set for the burner top surface. Wave-transmissive boundary conditions were utilized to reduce the backflow and the effect of pressure wave reflection on combustion. Large eddy simulation (LES) directly solves the turbulence above the filter scale and calculates the small scale with the sub-grid model (SGS). As a result, LES can yield more \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**ID** & \(S_{I}\) **(m/s)** & \(\delta_{I}^{0}\) **(mm)** & **Tad (K)** & \(\Delta_{x}\) **(mm)** & \(\Delta_{x}\)/\(\delta_{I}^{0}\) & **n** & **F** \\ \hline
00H2 & 0.2468 & 0.573 & 1919.71 & 0.5 & 0.872 & 7 & 6 \\
30H2 & 0.2970 & 0.510 & 1927.91 & 0.5 & 0.980 & 7 & 7 \\
60H2 & 0.4112 & 0.429 & 1944.72 & 0.5 & 1.166 & 7 & 8 \\
90H2 & 0.8599 & 0.363 & 2001.72 & 0.5 & 1.377 & 7 & 9 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the characteristic parameters. \(\delta_{I}^{0}\): flame thickness; Tad: adiabatic flame temperature; \(\Delta_{x}\): grid size in the main reaction zone; n: grid number inside the flame front; F: the thickening factor. Figure 2: The computational domain with mesh details (all undefined units: millimeter). detailed simulation results with relatively low computational costs. Therefore, the use of LES coupled with finite rate chemistry is apt for characterizing flames and clarifying the mechanisms of the combustion process. This study adopted the SGS model to describe small-scale vortices. The filtered conservation equations for mass, momentum, total energy, and species were solved using the open-source code, OpenFOAM 2.3.0, as described in Ref. [29]. A thickened flame (TF) model was used to resolve the filtered flame front [30].