# Comparison of Large Eddy Simulation with local species, temperature and velocity measurements in dual swirl confined hydrogen flames

Martin Vilespy, Anthony Teixeira, Zeinab Al Hadi, Sylvain Marragou, Thibault Guiberti, Gaetano Magnotti, Laurent Selle, Thierry Schuller, Thierry Poinsot

► To cite this version:

Martin Vilespy, Anthony Teixeira, Zeinab Al Hadi, Sylvain Marragou, Thibault Guiberti, et al. Comparison of Large Eddy Simulation with local species, temperature and velocity measurements in dual swirl confined hydrogen flames. Combustion and Flame, 2025, 283, pp.114536. 10.1016/j.combustflame.2025.114536. hal-05347258

HAL Id: hal-05347258

https://hal.science/hal-05347258v1

Submitted on 4 Nov 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /></figure>

# Comparison of Large Eddy Simulation with local species, temperature and velocity measurements in dual swirl confined hydrogen flames

Martin Vilespy<sup>a,D</sup>,*, Anthony Teixeira<sup>a</sup>, Zeinab Al Hadi<sup>b,D</sup>, Sylvain Marragou<sup>c</sup>, Thibault Guiberti<sup>b,D</sup>, Gaetano Magnotti<sup>d</sup>, Laurent Selle<sup>a,D</sup>, Thierry Schuller<sup>a,e,D</sup>, Thierry Poinsot<sup>a</sup>

## ARTICLE INFO

### Keywords:

Swirling flames

Conjugate heat transfer

LES

Hydrogen

Raman spectroscopy

## ABSTRACT

Developing new injection systems and combustion chambers for hydrogen is a central topic for the new generation of engines. In this effort, simulations take a central role, but methods developed for conventional hydrocarbons (methane, kerosene) must be revisited for hydrogen. Validation then becomes an essential part and clean, well documented experiments are needed to guaranty that computational fluid dynamics solvers are as predictive and accurate as expected. In this framework, the HYLON case is a swirled hydrogen/air burner used by multiple groups worldwide to validate simulation methods for hydrogen combustion in configurations close to gas turbine burners, with experimental data available through the TNF web site. The present study compares recent Raman spectroscopy and Particle Image Velocimetry measurements and Large Eddy Simulations (LES). The LES results are evaluated against a dataset comprising mean and RMS measurements of H₂, N₂, O₂, H₂O molar fractions, temperature, and velocity fields, offering new insights into flame stabilization mechanisms. The simulations incorporate conjugate heat transfer to predict the combustor wall temperatures and are conducted for two atmospheric-pressure operating conditions, each representing distinct combustion regimes, diffusion and partially premixed.

### Novelty and significance statement

Data on confined hydrogen flames in burner similar as industrial ones are limited. This work aims to fill this gap, by performing multiple and simultaneous diagnostics on the swirled hydrogen-air flame called HYLON. For the first time in such a swirled configuration, mean and RMS fields of temperature, main species and velocities are compared to LES, allowing new insight into the potential and limits of the models as well as the physics of these flames. These experimental results will be made available on TNF, as over 30 research groups worldwide have expressed interest in using them.

## 1. Introduction

Hydrogen is a promising fuel to decarbonize industry, transport and energy production. However, replacing conventional hydrocarbons with hydrogen is a major challenge due to its high reactivity [1]. Using hydrogen may lead to engine failure because of an increased risk of flashback [2,3], increased heat load on the combustor walls, and also high NOₓ emissions [4]. The development of new injection systems and combustion chambers is therefore necessary: for example, to prevent flashback risks, one solution is to use late fuel injection and rapid

mixing technologies [5], with many solutions featuring swirled injectors, already used for the combustion of classical hydrocarbons [6–9]. The one studied here uses a dual swirl injection system to ensure fast mixing [10]. In all cases, the design of these systems relies extensively on Large Eddy Simulations (LES) for complex geometries.

The HYdrogen LOw NOₓ (HYLON) burner uses a separate injection of air and hydrogen to prevent flashback. Both streams are swirled to enhance mixing between air and hydrogen. HYLON has been investigated experimentally under a wide range of operating conditions at

<footnote><sup>a</sup> Univ Toulouse, Toulouse INP, CNRS, IMFT, Toulouse, France</footnote>

<footnote><sup>b</sup> Mechanical Engineering Program, Physical Science and Engineering Division, King Abdullah University of Science and Technology, Saudi Arabia</footnote>

<footnote><sup>c</sup> King Abdullah University of Science and Technology (KAUST), Clean Energy Research Platform (CERP), Thuwal, 23955-6900, Saudi Arabia</footnote>

<footnote><sup>d</sup> INSA Rouen Normandie, CNRS UMR6614-CORIA, Rouen, 76540, France</footnote>

<footnote><sup>e</sup> Institut Universitaire de France (IUF), France</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: martin.vilespy@imft.fr (M. Vilespy).</footnote>
one bar, including preheated air [11] and has demonstrated low NOₓ emissions [10,12], including under high pressure conditions [13]. LES have been performed to study stabilization [14] and NOₓ formation mechanisms [15] for two stabilization modes.

One major issue encountered in LES is the availability of extensive experimental data for comparison and validation [16]. A collaboration between experimental and simulation teams is crucial. This is the purpose of the TNF Workshop [17], especially carried by Dr. Robert Barlow since the first meeting in 1996, which aims to improve the understanding of turbulent combustion by favoring the accessibility of experimental data to validate numerical simulations. Many jet flame configurations have been studied with the objective of providing a complete database for model validations.

The TNF Workshop includes simple jet flames [18–20], piloted flames [18,21,22], bluff-body flames [23] and more recently swirled flames [24,25], in which both hydrocarbons and H₂ flames were studied. All these works have focused on unconfined flames, which facilitates laser diagnostics relevant for flame-turbulence interactions. To analyze these interactions, coupling different diagnostics in simultaneous measurements has shown good results for unconfined configurations, using for instance Raman and Rayleigh spectroscopy and laser-induced fluorescence (LIF) [19,22,26–29], where temperature is extracted from Rayleigh scattering. Recently, all major species (N₂, O₂, H₂, H₂O), OH, mixture fraction and temperature have been measured simultaneously [30] in H₂/N₂/Air turbulent jet flames using only Raman scattering and OH-PLIF.

New experimental data for three distinct confined burners operated with hydrogen have been made available lately in TNF Workshop: the burner from AHEAD project [31] (TU Berlin), the one used in [32] (NTNU) and the HYLON burner developed at IMFT [10]. These burners are closer to real gas turbine engine injectors as they feature confined swirled partially premixed flames. These new additions have broadened the interest in TNF workshop to a bigger part of the combustion community, including industrial groups. The data available on these type of confined flames are often restricted to chemiluminescence images, OH-PLIF, Particle Image Velocimetry (PIV), temperature and pressure measurements (see for example [7,33–36]), which provide limited insight into flame-turbulence interactions. Raman scattering has been applied on confined hydrocarbon flames in a swirled burner [37–40], but there is a gap in the literature of extensive experimental data and numerical simulations comparison of confined hydrogen flames, especially of burners similar to real industrial injectors.

This work compares LES results with 1D-Raman spectroscopy measurements for major species, velocities and temperature in the whole domain and shows how detailed measurements allow much more critical analysis of LES capacities. All computations presented in this work are performed using Conjugate Heat Transfer (CHT) where the flow and the temperature in the solid walls are solved simultaneously.

The paper is organized as follows. Section 2 recalls the burner geometry, the experimental diagnostics and the LES setup. The validation of LES data versus experiments is presented in Section 3.1 for cold flows and in Section 3.2 for reacting cases. CHT results are compared with experimental measurements in Section 3.3. Major species and gas temperature fields are compared between LES and experiments in Section 3.4.

## 2. HYLON set-up

### 2.1. Burner geometry and operating conditions

The HYLON burner uses a co-axial injector in which air and hydrogen are injected separately. Both flows are swirled (clockwise direction from a top point of view) as shown in Fig. 1(a). The present configuration is an evolution of the one studied in [10,14] available on the TNF web site [17]. The flow is swirled with radial-axial and axial vanes for air and hydrogen, respectively [12]. The central cylindrical nozzle

<figure><img src="image_4.png" /><figcaption>**Fig. 1.** (a) HYLON injector, (b) hydrogen internal swirler, (c) air external swirler and (d) computational domain of the HYLON burner with the fluid domain (colored by the volume) and the solid domain shown in red. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

through which hydrogen is injected has an inner diameter $d_i = 6$ mm. It has a geometrically-calculated swirl number $S_l = 0.6$. The external annular duct has inner and outer diameters $d_{ie} = 10$ mm and $d_e = 18$ mm, respectively. It supplies swirled air with a swirl number $S_e = 1.2$ at the exit of the air swirler. The recess of the hydrogen injector with respect to the backplane of the chamber, denoted $z_i$, is equal to 4.3 mm and facilitates mixing upstream the combustion chamber. The injector lip ends with a 45° chamfer that increases the external diameter of the H₂ tube from 10 mm to 13 mm. The chamber has a square cross section of 78 mm width and 145 mm height. Two chamber windows are in quartz for optical diagnostics and two are in stainless steel. The stainless steel windows are perforated with 8 holes each at specific heights to allow for PIV and Raman spectroscopy measurements. A convergent at the outlet allows to contract the square section of the chamber to a round section with a contraction section of 0.51.

Two operating conditions are studied in this work, featuring two distinct stabilization modes: flame A, at 2.5 kW, is anchored to the injector lips, while flame L is lifted above the injector. The operating points are detailed in Table 1. The global equivalence ratio $\Phi_g = 0.42$ is identical for the two operating conditions, and flame L is twice more
<caption>**Table 1**</caption>

Mass flow rates and injection bulk velocities of air and hydrogen (1 bar, 300 K), thermal power and global equivalence ratio of operating points A and L.

<table><thead><tr><th>Flame</th><th>ṁ<sub>air</sub> [g/s]</th><th>ṁ<sub>H₂</sub> [g/s]</th><th>U<sub>b,air</sub> [m/s]</th><th>U<sub>b,H₂</sub> [m/s]</th><th>P<sub>th</sub> [kW]</th><th>Φ<sub>x</sub></th></tr></thead><tbody><tr><td>A</td><td>1.71</td><td>0.021</td><td>11.6</td><td>9.2</td><td>2.5</td><td>0.42</td></tr><tr><td>L</td><td>3.41</td><td>0.042</td><td>23.3</td><td>18.3</td><td>5.0</td><td>0.42</td></tr></tbody></table>

<figure><img src="image_5.png" /><figcaption>**Fig. 2.** Injector CAD (blue contour) validation by comparison with X-ray imaging of the hydrogen air injector in the plane of symmetry. (a) Full injector cut view. (b) Hydrogen injector cut view. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

powerful than flame A. These two stabilization modes have been chosen as they are the most common flames observed in the HYLON burner. The lifted flame is the stabilization mode expected, as it ensures low NOₓ and low thermal load on the burner lips [12]. The attached flame is also chosen as it is likely to occur in certain regimes, notably at high pressure [13].

## 2.2. Injector geometry validation

To ensure that the CAD data used for CFD matches exactly the experimental one, the geometry of the 3D printed injector has been verified by X-ray tomography. The CAD files, originally generated prior to the experiment and verified through X-ray imaging, have been slightly adjusted to precisely match the injector geometry, eliminating any uncertainty regarding the final geometry. The X-ray tomography validations have been carried out on the full 3D volume of the air and hydrogen injection block. An illustration of comparison of the X-ray imaging with the CAD in the plane of symmetry is provided in Fig. 2.

## 2.3. Experimental framework

### 2.3.1. Velocity measurements

Particle Image Velocimetry (PIV) is performed in the axial 'x - z' plane shown in Fig. 1(c), in both non-reactive and reactive conditions.

A dual cavity Nd:YAG laser (BigSkyLaser, CFR200) providing around 180 mJ/pulse/cavity at 532 nm with a pulse duration of 8 ns is used. The laser passes through a Lavision laser sheet generator KL-SO-302, creating a laser sheet of about 1.0 mm thickness. Titanium dioxide (TiO₂) particles of Sauter mean diameter $D_{32} = 200$ nm are used to seed the air and hydrogen streams. Hydrogen and air mass flow rates, along with particle seeding, are controlled by Bronkhorst F-201-AV and F-203-AV mass flow controllers. A 2560 × 2160 pixels dual frame sCMOS camera (LaVision, Imager sCMOS CLHS) equipped with a Nikon AF-S VR Micro-Nikkor 105 mm f/2.8G IF-ED with a bandpass filter centered around 532 nm (± 10 nm) records the Mie-scattered light resulting from the interaction between the laser sheet and the seeded flow.

Each record comprises two single-exposure frames, separated by a time interval *dt*. All PIV measurements were processed with an interrogation window of 16 px and a window overlap of 75%, which limits the spatial resolution to 0.5 mm. Except for the PIV of flame L in reacting conditions, which was performed with a frame time separation of *dt* = 4 µs, all other measurements were conducted with *dt* = 7 µs. The image pairs were processed using the Davis software from Lavision (lavision.de/en/products/davis-software) to infer *x* and *z* velocity vector components in the *y* = 0 vertical plane from statistical cross-correlation analysis [41,42].

During a PIV sequence, reflections caused by particles that contaminate the chamber window in front of the camera require the measurements to be taken as quickly as possible. In this context, each PIV session starts 30 s after ignition, and ends after 30 s. Each session allows approximately 200 images to be taken at a repetition rate of 10 Hz. The windows are subsequently cleaned and the sessions are repeated for the same point until convergence is achieved. At least 1000 instantaneous fields were averaged to ensure convergence of the mean and RMS values. For each point, the PIV provides the mean and RMS velocities in the *x* and *z* directions.

Tests conducted with the laser sheet passing either through the optical windows or through holes drilled in the metal chamber walls showed that the holes had a negligible effect on the measured velocities sufficiently far from the holes within the region where data are presented in this study (see Appendix C in Supplementary Material). Data for velocities are only provided at the same heights as data gathered by 1D-Raman spectroscopy, as explained below.

### 2.3.2. Main species and gas temperature measurements

The Raman spectroscopy system used in this study was first described in Tang et al. [43]. A schematic of the setup is shown in Fig. 3. Three Nd:YAG laser beams are combined and subsequently directed through a triple-leg pulse stretcher, which extends the pulse duration to approximately 500 ns while delivering a total energy output of 0.85 J. The temporally stretched laser pulses are focused into the measurement region using a spherical lens with a focal length of 750 mm. The lasers enter and exit the combustion chamber through one of 8-pairs of 4 mm diameter holes drilled into the sidewalls of the stainless steel chamber. Preliminary studies have shown a negligible effect of holes for cold flow conditions at all heights studied. For reactive conditions, a negligible impact has been observed close the injector outlet for *z* ≤ 12.7 mm, while a limited impact at higher heights was found close to walls for *x* ≥ 20 mm. More details on velocity profiles and OH* intensity signals comparison are given in Appendix C of the Supplementary Material. The collection system is the same used in Tang et al. [43]. A pair of large-aperture (6-inch diameter) achromatic lenses (f#2 and f#4) relays the Raman signal to the entrance of the 2-stages optical shutter. The focused Raman signal passes through an optical chopper, and a stationary slit that reduces the exposure time to 330 µs. The signal is then collimated by a Sigma 135 mm focal length f/1.8 camera lens, and goes through an electro-optical shutter consisting of 2-cross polarizers, and a Pockels cell, that limits the exposure time to ≈ 2 µs centered around the exposure time of the camera. The integration of this electro-optical shutter with the mechanical shutter provides a precise effective
<figure><img src="image_6.png" /><figcaption>Fig. 3. Experimental setup for 1D Raman spectroscopy measurements.</figcaption></figure>

exposure time of approximately 980 ns and yields a contrast ratio of roughly 350 within the central 2 mm probe volume region, effectively eliminating interference from flame chemiluminescence in the hydrogen flames under investigation. A dichroic mirror, separates the Raman signal from the Rayleigh signal and surface scattering, and a bandpass filter (FF01-632/148-50) rejects light outside the wavelength range of interest. The gated Raman signal is then dispersed on volume phase holographic transmission grating with 900 lines/mm from Wasatch Photonics and a Nikon 105 mm prime lens focuses it on a EMCCD camera operated in low-noise mode. The Raman signal is hardware-binned by 12 pixels along the spatial direction, corresponding to a super-pixel resolution of ≈ 102 µm. In the spectral direction the signal is hardware binned in Raman channels to maximize signal-to-noise ratio.

Temperature and major species concentrations are derived from Raman spectroscopy measurements using the hybrid matrix inversion method detailed in Fuest et al. [44]. Measurements conducted in non-reactive air and N₂/H₂ mixtures and a series of premixed H₂/N₂/air flat flames stabilized over a McKenna burner with equivalence ratios ranging from 0.9 to 1.8, provide the needed flatfield correction and calibration coefficients. The temperature dependence is obtained from theoretical spectra presented in Geyer [45]. The measurements are within 60 K of the predicted temperature, and within 0.01 in mole fractions. The standard deviations, indicative of the single shot precision, depend on the signal-to-noise ratio and therefore degrade under flame conditions. In ambient temperature air, standard deviations are limited to 4.6 K for the temperature T, 0.0014 for O₂, and 0.019 for N₂, corresponding to 1.5%, 0.9%, and 0.25% of the mean values, respectively. At stoichiometry, the temperature standard deviation increases to 77 K (4.53% of the mean), and the N₂ and H₂O standard deviations reach 0.011 (1.47% of the mean) and 0.01 (4.55% of the mean), respectively. The standard deviation of the H₂ mole fraction measurements is 0.0023 (2.33% of the mean), and 0.0057 (5.98% of the mean) for the premixed flame at φ = 1.8. Note that the higher standard deviation compared to previously reported Raman measurements is due to the unavailability of Rayleigh scattering.

Gas temperature measurements at the combustion chamber outlet were conducted using a double-bead thermocouple. The double-bead thermocouple is designed for measuring gas temperatures in high-temperature ranges, where standard thermocouple readings are affected by thermal radiation of the hot solid surfaces. It consists of two thermocouples with different bead sizes. Since the radiative heat flux is proportional to the surface area of the thermocouple bead, the radiative contribution to the heat flux can be removed [46]. In this study,

the Reduced Radiation Error method is used to determine the flow temperature from the double-bead thermocouple measurements [47].

### 2.3.3. Wall temperature measurements

A double-wavelength pyrometer is used for wall temperature measurements. The system used is a Fluke Process Instruments E2RL-F2-V-0-0 Endurance Series, which allows temperature measurements from 250 K to 1500 K. The two-color pyrometer measures a luminance ratio and provides the corresponding blackbody temperature through a calibration performed by the manufacturer. An additional calibration was conducted to relate the blackbody temperature to the one of the stainless steel wall. This calibration is performed by measuring the wall temperature using a contact thermocouple screwed at the top of the pillar. The thermocouple temperature is matched by adjusting the emissivity ratio of the pyrometer. The calibration was carried out from 400 to 600 °C and resulted in an emissivity ratio of $s = 1.045 \pm 0.005$. Once calibrated, measurements were performed along the pillar.

## 2.4. Numerical framework

Simulations are conducted with the compressible LES solver AVBP (www.cerfacs.fr/avbp7x/). The computational domain is shown in Fig. 1(c). The fluid domain includes the chamber as well as the air and hydrogen swirlers. The 16 holes in the metal walls, which account for 4% of the outlet section, are not considered in the computational domain for simplicity. The solid domain (in red in Fig. 1(c)) includes the whole chamber as well as the injector.

The lifted flame denoted L is characterized by velocities and a Reynolds number twice higher than the attached flame A, so that a more refined mesh is needed to resolve the boundary layer in the injection ducts and the higher velocity gradients above the injector lips: a cell size of 150 µm is used for flame A while it is 100 µm for flame L. Previous results [14] have shown that this resolution was sufficient for matching the flame shape and experimental velocity fields.

Recent results on hydrogen-air flames show that there can be a strong two-way coupling between flame and flow topology on the one hand and wall temperature on the other hand. For most industrial applications, the wall temperatures are not available so that the most reasonable approach is to solve for Conjugate heat transfer (CHT) between gaseous and solid phases. The LES solver AVBP for the gaseous flow is coupled with a solver dedicated to the resolution of the heat equation in the solid [48,49]. Using CHT has gained interest in the LES community [50–53], but its use remains limited, and many work
still use adiabatic walls or experimental data. As stainless steel 304L and 316L used for the chamber walls have close properties, a unique material for the air and hydrogen swirlers, the chamber (backplane and pillars), the convergent, and the two stainless steel windows is considered with fixed density $ρ = 8000$ kg/m³, conductivity $λ = 16$ W/m/K and $c_p = 512$ J/kg/K. Quartz is considered for the two other windows with a fixed density $ρ = 2200$ kg/m³, conductivity $λ = 2.25$ W/m/K and $c_p = 670$ J/kg/K. At the external walls of the combustion chamber, a natural convection thermal boundary condition is imposed. To take into account thermal radiation, a global heat transfer coefficient is defined as $h_g = h_c + h_r$, with $h_c$ the convection heat transfer coefficient and $h_r$ the radiative heat transfer coefficient. The convective heat transfer coefficient $h_c$ is calculated following [54]. The radiative heat transfer coefficient is defined as:

$$h_r = \frac{\epsilon_m \sigma (T_{wall}^4 - T_{amb}^4)}{T_{wall} - T_{amb}} \quad (1)$$

with the Stefan constant $σ = 5.67 \times 10^{-8}$ W.m⁻².K⁻⁴, $ε_m$ the emissivity of the material and $T_{amb}$ the temperature of the ambient environment, supposed to be at 300 K. The emissivity of the convergent section and the chamber pillars is set to 0.3 according to similar measurements made in [55]. The emissivity of the quartz windows is calculated using the radiative properties of the quartz provided by the manufacturer, following the procedure used in [55,56] and is set to 0.9. For flames A and L, the imposed convective coefficient, corresponding to typical wall temperatures, is $h_g = 30$ W/m²/K on the external side of the quartz windows, 25 W/m²/K on the external side of the convergent section and the pillars, and 10 W/m²/K on the external side of the backplane. The inner and outer wall temperatures are sensitive to the choice of $h_g$ as the thermal resistances in the quartz and metal are small. The investigation of the effect of the wall boundary condition on the flow is left for further studies.

The SIGMA [57] model is used for subgrid-scale viscosity. The skeletal mechanism developed in [58] is used, which includes 15 species and 47 reactions. The Pressure Gradient Scaling (PGS) technique [59] is used to remove the acoustic time step limitation. The maximum Mach number is kept below 0.3 to maintain the low-Mach assumption. As lifted flames feature non-premixed and partially-premixed regimes, the DTFLES model [60] is used. This model thickens premixed flame fronts, allowing for a sufficient resolution of the flame. Combustion regimes are locally identified using the Takeno index [61], defined as the normalized scalar product $H_2$ and $O_2$ mass fraction gradients. A positive value is interpreted as a locally premixed regime, which enables DTFLES, while a negative value is interpreted as a diffusion regime, and no thickening is applied. This strategy has shown to yield successful results for premixed and non-premixed hydrogen flames [14,15,58]. For meshes of 50 to 200 M cells, it is limited to atmospheric, small chambers where the mesh is sufficient to capture the diffusion flamelets where no model is used.

To verify that resolution is sufficient, an instantaneous Flame Resolution Indicator field, defined as $FRI = 1/(\nabla Z \Delta x)$, is shown in Appendix A of Supplementary Material. It measures how many mesh points are used to resolve the local gradient of mixture fraction, or in other words, the diffusion flame thickness. Appendix A shows that $FRI$ is always larger than 5, a value which has been shown to yield reasonable results in strained laminar stagnation point flames [62].

# 3. Results and discussion

## 3.1. Cold flow velocities

Figs. 4 and 5 show time averaged velocity profiles at two heights ($z = 2.7$ mm and $z = 12.7$ mm) in non-reactive conditions for flames A and L respectively. For flame A, peaks of mean and RMS axial radial velocities are well retrieved. For the mean radial velocity, good agreement is found for $x < 0$ mm, but differences are observed for $x > 0$ mm.

<figure><img src="image_7.png" /><figcaption>Fig. 4. Time-averaged velocity profiles for non-reactive conditions at heights (a) $z = 2.7$ mm and (b) $z = 12.7$ mm of flame A. PIV measurements (black symbols) and LES (solid line).</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Fig. 5. Time-averaged velocity profiles for non-reactive conditions at heights (a) $z = 2.7$ mm and (b) $z = 12.7$ mm of flame L. PIV measurements (black symbols) and LES (solid line).</figcaption></figure>

0 mm attributed to asymmetry in experimental results. At $z = 12.7$ mm, the $U_z$ peak is closer to the central line $y = 0$ mm, showing that the width of the Central Recirculation Zone (CRZ) is slightly smaller in the LES. Velocities in the Outer Recirculation Zone (ORZ) are well retrieved. For flame L, similar comments can be made, where good agreement are found globally for mean and RMS velocities, with a slight underestimation of the CRZ width, and an asymmetry of the radial velocity.

## 3.2. Reactive flow velocity and OH fields

Fig. 6 shows the simulated velocity and OH normalized mass fraction fields for both flames A (left) and L (right). The attached flame features two diffusion fronts [14,15]: the external front, called branch I, burns fresh $H_2$ and air, and is attached to the injector lips. The internal front, called branch II, burns fresh $H_2$ and hot vitiated burned gases, and is located in the CRZ. For the lifted flame, the flame shape is different from the one studied in [15]: branch I and branch II are distinguishable on the OH average field, while it was merged in [15]. This flame shape has been observed previously in [11,12]. Velocity fields show that the CRZ and ORZ velocities are higher for flame L.

Fig. 7 shows the experimental line-of-sight (LOS) OH* images (left) and the LOS OH* field from LES (middle) for flames A (top) and
<figure><img src="image_9.png" /><figcaption>**Fig. 6.** Time-averaged velocity and OH fields of flames A (left) and L (right) from LES. Horizontal white lines correspond to locations $z = 2.7, 7.7, 12.7, 22.7$ and $32.7$ mm at which profiles are compared. $Y_{OH}$ is normalized by the maximum of flame A. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>**Fig. 7.** Line of sight experimental (left) and LES (right) time-averaged OH\* fields of flames A (top) and L (bottom). Experimental image is superimposed with isoline 5% of $Y_{OH\*,max}$ (right). $S_{OH\*}$ and $Y_{OH\*}$ are normalized by their maximum value for each flame.</figcaption></figure>

L (bottom). LES OH\* field is reconstructed following the work of Schiavone et al. [63], using the Kathrotia OH\* sub-mechanism [64]. A small asymmetry is found in experiments for both flames. For flame A, the flame is smaller for $x > 0$ mm, while for flame L, branch II is not centered around $x = 0$ mm, which confirms the observations from the velocity profiles in Section 3.1. This asymmetry makes Abel deconvolution less suited for comparison. No asymmetry is observed in LES. For flame A, when comparing branch II (central front) and branch I (lateral front) OH\* intensity, branch II seems to be more reactive in the LES than in the experiments, but only quantitative measurements would confirm this observation. For Flame L, branch II is found to be dissociated from the central front in both experiments and LES, in

<figure><img src="image_11.png" /><figcaption>**Fig. 8.** Time-averaged velocity profiles for reactive conditions at heights (a) $z = 2.7$ mm and (b) $z = 12.7$ mm of flame A. PIV measurements (black symbols) and LES (solid line).</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>**Fig. 9.** Time-averaged velocity profiles for reactive conditions at heights (a) $z = 2.7$ mm and (b) $z = 12.7$ mm of flame L. PIV measurements (black symbols) and LES (solid line).</figcaption></figure>

contrast to the lifted flame studied in [14], where the external front and the central front were merged. Branch I is slightly closer to the backplane ($z = 0$ mm). It is observed that the LES image is sharper than the experimental one. This can be attributed to spurious reflections in the experiments, but also to the shorter integration time in the LES. Therefore, this comparison shows that LES is able to retrieve the lifted flame shapes when flame fronts are merged [14] or dissociated as in this study.

Figs. 8 and 9 show time averaged velocity profiles for flames A and L respectively at heights, $z = 2.7$ mm and $z = 12.7$ mm in reactive conditions. In these experiments, reflections on one side of the quartz windows led to unusable experimental results for $x < 0$ mm. Therefore, only $x > 0$ mm results are plotted. For both flames A and L, mean and RMS $U_z$ are in good agreement. Similarly as in cold flow conditions, discrepancies are found for $U_x$ which are also attributed to asymmetry in experimental results. Flame expansion is well retrieved for flame A, while the CRZ width is slightly under-predicted for flame L. Globally, satisfactory agreements are found for mean and RMS LES velocities for both operating conditions.

### 3.3. Wall and gas temperature prediction

Table 2 presents the time-average outlet, CRZ and ORZ temperatures from LES and experiments for flames A and L. Outlet temperature has been measured using a double-bead thermocouple located at the exit section of the convergent, and the CRZ temperature is deduced from Raman spectroscopy measurements at $z = 22.7$ and $32.7$ mm
<table><caption>**Table 2**
Time averaged gas temperatures obtained in experiments and simulations at the outlet, in the CRZ and the ORZ for flames A and L.</caption><thead><tr><th>Flame</th><th>T<sub>out</sub> [K]</th><th>T<sub>CRZ</sub> [K]</th><th>T<sub>ORZ</sub> [K]</th><th>Wall heat flux [kW]</th></tr></thead><tbody><tr><td>A EXP</td><td>945</td><td>1050</td><td>N/A</td><td>N/A</td></tr><tr><td>A SIMU</td><td>965</td><td>1115</td><td>965</td><td>1.1</td></tr><tr><td>L EXP</td><td>1110</td><td>1300</td><td>N/A</td><td>N/A</td></tr><tr><td>L SIMU</td><td>1085</td><td>1200</td><td>1070</td><td>1.5</td></tr></tbody></table>

<figure><img src="image_13.png" /><figcaption>**Fig. 10.** Left: Time average temperature profile along the pillar of the chamber from AVTP simulation and experiments for flames A and L. Right: The white line indicates the location of the temperature measurements along the pillar and the calibration point (cross).</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>**Fig. 11.** Time average temperature field inside the injector for operating point A (left) and L (right) in the LES.</figcaption></figure>

(available in Appendix B of Supplementary Material). Flame A outlet temperature is slightly higher in LES than in experiments, while it is slightly lower for flame L. Nevertheless, these results are close, and confirm that the CHT strategy works well. The last column of Table 2 indicates the thermal power lost to the walls of the combustor. Since the power of flames A and L are 2.5 and 5.0 kW respectively (Table 1), Table 2 shows that around 44% and 30% of the power is lost through the walls for flames A and L respectively. For a more detailed analysis of CHT, temperature profiles are discussed now.

Fig. 10 shows the temperature profile along one pillar of the chamber for flames A and L. For both LES and experiments, the temperature increases from the back plane at $z = 0$ mm to a maximum near the center of the chamber and then decreases. For flame A, the temperature is well predicted near the back plane, and a maximum difference of 70 K is found around 30 cm from the top of the pillar. For flame L, the temperature at the back plane is underestimated by 50 K, but there is a good agreement for the remainder of the profile. The overall temperature increase from flame A to L is retrieved by LES.

Fig. 11 shows the time averaged temperature of the metal close to the injector lips for both operating conditions A and L. For the attached

flame, the maximum temperature at the lips is 380 K, located at the edge where the flame is stabilized. As expected, the lip temperature for the lifted flame is around 320 K, which is lower than for flame A. Even for the anchored flame, the temperature remains reasonably low, so that the injector can work for long periods of time without any degradation. Moreover, the sidewall of the injector is heated up to 350 K through conduction in the backplane in contact with burnt hot gas. This effect is more pronounced for flame L because of the higher gas temperature in the ORZ as seen in Table 2. However, this temperature is low and should not significantly preheat the incoming air. This effect should be taken into account for operating conditions leading to higher wall temperatures.

### 3.4. Major species comparison

Figs. 12(a) and (b) show mean and RMS profiles for major species molar fractions and temperature obtained in experiments (symbols) and simulations (solid lines) at four different heights (see Fig. 6): $z = 2.7$ mm, 7.7 mm, 12.7 mm and 22.7 mm above the back plane for flame A. For clarity, only RMS values for $T$, $X_H$, and $X_N$ are plotted. The other species are available in Appendix B of the Supplementary Material, as well as profiles of all major species and temperature at $z = 32.7$ mm.

Species and temperature profiles are in good agreement between simulations and experiments, for both mean and RMS values. At $z = 2.7$ mm, the flame, the hydrogen and the air stream locations are well captured, as well as maximum values of temperature and molar fractions. The ORZ region ($x > 10$ mm) is the longest to converge, because of its low velocities. This explains the slight differences in molar fractions observed in the ORZ. Temperatures can be affected by both convergence time and heat losses to the back plane, which calls for additional validation. At $z = 7.7$ mm and 12.7 mm, peaks of temperature allow to locate the two flame fronts in both LES and experiments: branch II is centered around $x = 0$ mm and branch I corresponds to the temperature peak around $x = 10$ mm. A difference in species molar fraction in branch II is found at both heights. In this region, a small shift of the flame position leads to noticeable differences in the species and temperature profiles because of the high gradients in the flame.

Maximum RMS temperature is around 500 K in both LES and experiments, and major species RMS values are also in satisfactory agreement. At $z = 22.7$ mm, branch I and II have similar mean values, but RMS profiles allow to distinguish the two flame fronts. Major species are in satisfactory agreement, as well as RMS values. Profiles at $z = 12.7$ mm and 22.7 mm show that the maximum temperature in branch II varies between 2400 K and 2000 K in the LES, while it changes from 2000 K and 1500 K in the experiments. In the LES, the maximum temperature in branch II is around 2400 K for $11$ mm $\le z \le 13$ mm. This difference is not due to a difference in the flame location and LES seems to overestimate the flame temperature of branch II, while the temperature in branch I is well retrieved for all heights. This can be due to various factors. Flame asymmetry has been observed in experiments, leading to a shorter branch II on the side of comparison. From the maximum flame temperature (at the center of branch II in $x = 0$ mm) to the edge of the branch (connection between branch I and branch II), temperature decreases faster for a short branch than a long branch. Therefore, at a given height, this higher gradient would lead to lower temperature for a short branch than a long branch. As no asymmetry is found in the LES, the asymmetry in experiments might lead to differences in temperature between LES and experiments. On the simulation side, the differences might come from (i) the time to fully establish the temperature field which is very long (minutes in the experiment) compared to the physical time covered by LES (less than 1 s), (ii) wall heat losses underestimated in the LES, or (iii) strain effects incorrectly captured by the LES. Slow movement of the central front around its mean position with a characteristic time of the order of a
<figure><img src="image_15.png" /><figcaption>**Fig. 12.** (a) Mean and (b) RMS Reynolds average profiles from experiments (symbols) and simulation (solid lines) of $X_{O_2}$ (green), $X_{N_2}$ (red), $X_{H_2}$ (blue), $X_{H_2O}$ (magenta) and temperature *T* (black) at *z* = 2.7 to 22.7 mm for flame A. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>**Fig. 13.** (a) Mean and (b) RMS Reynolds average profiles from experiments (symbols) and simulation (solid lines) of $X_{O_2}$ (green), $X_{N_2}$ (red), $X_{H_2}$ (blue), $X_{H_2O}$ (magenta) and temperature *T* (black) at *z* = 2.7 to 22.7 mm for flame L. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

second has been observed experimentally and cannot be reproduced with LES. The convergence time of temperature profiles being very long (minutes in the experiments), the investigation of heat losses and gas radiation impact on the internal flow is left for further studies [48,65]. Chemistry is modeled using a detailed scheme, which is not the weak point of the simulation.

Finally, the flow field can impact the flame through turbulence and strain. Strain reduces the temperature of hydrogen diffusion flames [15, 66,67], so that errors in strain may affect strongly the temperature field. However, it is unlikely that strain underestimation can lead to a difference of 500 K, and a combination of all these factors is most probably responsible for the temperature gap found in branch II.

A similar analysis is proposed for flame L using Fig. 13, where (a) mean and (b) RMS major species and temperature profiles are plotted at the four same heights. Globally, good agreement is also found for this operating condition. At *z* = 2.7 mm, the minimum of temperature at *x* = 0 mm is lower in the LES, showing that branch II is located slightly upstream in the LES compared to experiments. Moreover, mixing between hydrogen and air at *x* = 8 mm is well captured. In the ORZ, burnt gas composition is well retrieved, while temperature is underestimated. Molar fraction and temperature RMS values are in good agreement. At *z* = 7.7, 12.7 and 22.7 mm, branches I and II are not easy to distinguish in the mean profiles, and only one thick front is found. The distinction between branch I and II is seen in RMS profiles, where two peaks are
observed. Branch I (external front) is in good agreement: both location and peak values are well retrieved. Branch II (internal front) is found closer to the center line at $z = 7.7$ and $12.7$ mm in the LES. The merging of RMS peaks is found around $z = 22.7$ mm in both experiments and LES. Compared to flame A, the temperature of the inner branch is similar in experiments and LES.

Overall, results are in satisfactory agreement between LES and experiments for both operating conditions A and L. Mean and RMS major species concentrations are well retrieved for both flames. The main difference between LES and experiments is the overestimation of branch II temperature in flame A. This difference of temperature in this zone, previously shown to be the primary NO formation region, could lead to high discrepancies in future NOₓ studies. Moreover, this modeling strategy, for which no turbulent combustion model is applied to non-premixed flames, is applicable here as resolving these flames is affordable at atmospheric pressure. However, at higher pressure, these diffusion fronts will be under-resolved and will require models for flame turbulence interaction.

## 4. Conclusions

The ability of LES to predict major species and temperature in a H₂-air swirled burner by comparison with Raman spectroscopy and PIV measurements has been demonstrated for a burner operating at atmospheric conditions $p = 1$ bar and ambient temperature injection. Large Eddy Simulations have been performed on the HYLON burner for two operating conditions A and L, corresponding to flames which are attached and lifted from the injector lips, respectively. LES retrieves the stabilization modes and the velocity fields, as in previous works [14,15]. In both operating conditions, good agreement is found for the molar fractions of major species (N₂, O₂, H₂, H₂O) between LES and experiments. Results show that the hydrogen-air diffusion flame (branch I) is well captured. Despite a good agreement on major species molar fractions, temperature is overestimated in branch II by the LES. Further analysis are necessary to identify the origin of these discrepancies. Simulations retrieve RMS values of species molar fractions and temperature for all heights. This modeling strategy has shown good results at these operating conditions, for which all flames fronts can be resolved. However, other strategies would need to be considered when increasing pressure.

This comparison is the first step of future works investigating NOₓ formation as well as flame dynamics. Finally, the experimental database obtained in the present work is a complete and demanding test case for all CFD codes and is available on the TNF web site for other groups.

### CRediT authorship contribution statement

**Martin Vilespy:** Writing – original draft, Investigation, Conceptualization. **Anthony Teixeira:** Writing – review & editing, Investigation. **Zeinab Al Hadi:** Writing – review & editing, Investigation, Conceptualization. **Sylvain Marragou:** Writing – review & editing, Investigation, Conceptualization. **Thibault Guiberti:** Writing – review & editing, Supervision, Conceptualization. **Gaetano Magnotti:** Writing – review & editing, Supervision, Conceptualization. **Laurent Selle:** Writing – review & editing, Supervision, Conceptualization. **Thierry Schuller:** Writing – review & editing, Supervision, Conceptualization. **Thierry Poinson:** Writing – review & editing, Supervision, Conceptualization.

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Acknowledgments

This project has received funding from the ERC H2020 Grant Agreement 832248 (SCIROCCO). It also received funding from the European Research Council (ERC) under the European Union's Horizon Europe research and innovation programme (SELECT-H, grant agreement No. 101097984). HPC resources from GENCI (allocation A0172B10627) is also highly acknowledged. The support of the Competitive Research Grant program (grant number URF/1/5039–01–01) by KAUST, Saudi Arabia is also acknowledged. D. Lattanzi Sanchez is acknowledged for his help in performing the X-ray tomography.

## Appendix A. Supplementary data

Supplementary material related to this article can be found online at https://doi.org/10.1016/j.combustflame.2025.114536.

### References

[1] A.L. Sánchez, F.A. Williams, Recent advances in understanding of flammability characteristics of hydrogen, Prog. Energy Combust. Sci. 41 (2014) 1–55.

[2] F. Halter, C. Chauveau, I. Gökalp, Characterization of the effects of hydrogen addition in premixed methane/air flames, Int. J. Hydrog. Energy 32 (2007) 2585–2592.

[3] H. de Vries, A.V. Mokhov, H.B. Levinsky, The impact of natural gas/hydrogen mixtures on the performance of end-use equipment: Interchangeability analysis for domestic appliances, Appl. Energy 208 (2017) 1007–1019.

[4] M. Skottene, K.E. Rian, A study of NOₓ formation in hydrogen flames, Int. J. Hydrog. Energy 32 (2007) 3572–3585.

[5] H.H. Funke, N. Beckmann, J. Keinz, A. Horikawa, 30 Years of dry-low-NOₓ micromix combustion research for hydrogen-rich fuels - An overview of past and present activities, J. Eng. Gas Turbines Power 143 (2021) 071002.

[6] A. Degeneve, R. Vicquelin, C. Mirat, J. Caudal, T. Schuller, Impact of co and counter-swirl on flow recirculation and liftoff of non-premixed oxy-flames above coaxial injectors, Proc. Combust. Inst. 38 (2021) 5501–5508.

[7] I. Boxx, M. Stöhr, C. Carter, W. Meier, Temporally resolved planar measurements of transient phenomena in a partially premixed swirl flame in a gas turbine model combustor, Combust. Flame 157 (2010) 1510–1525.

[8] M. Leroy, M. Clement, A. Renaud, R. Vicquelin, Stabilization of Low-NOₓ hydrogen flames on a dual-swirl coaxial injector, J. Eng. Gas Turbines Power 145 (2023) 021021.

[9] M. Overbaugh, V. McDonell, B. Williams, P. Buelow, J. Ryon, Design, analysis, and experimental testing of hydrogen lean direct injection nozzles at elevated pressure, ASME Turbo Expo 2024 (2024) GT2024–126814.

[10] S. Marragou, H. Magnes, T. Poinson, L. Selle, T. Schuller, Stabilization regimes and pollutant emissions from a dual fuel CH₄/H₂ and dual swirl low NOₓ burner, Int. J. Hydrog. Energy 47 (2022) 19275–19288.

[11] H. Magnes, S. Marragou, A. Aniello, L. Selle, T. Poinson, T. Schuller, Impact of preheating on flame stabilization and NOₓ emissions from a dual swirl hydrogen injector, J. Eng. Gas Turbines Power 146 (2024) 051004.

[12] H. Magnes, M. Vilespy, L. Selle, T. Poinson, T. Schuller, Interplay between unburned emissions and NOₓ emissions from a dual swirl hydrogen air injector, J. Eng. Gas Turbines Power 147 (2025) 061013.

[13] S. Marragou, D. Mengu, E.-T. Es-sebbar, H. Magnes, T. Schuller, T. Guiberti, Flame stabilization and pollutant emissions from a H₂/air dual swirl coaxial injector at elevated pressure, Int. J. Hydrog. Energy 100 (2025) 163–172.

[14] A. Aniello, D. Laera, S. Marragou, H. Magnes, L. Selle, T. Schuller, T. Poinson, Experimental and numerical investigation of two flame stabilization regimes observed in a dual swirl H₂-air coaxial injector, Combust. Flame 249 (2023) 112595.

[15] M. Vilespy, A. Aniello, D. Laera, T. Poinson, T. Schuller, L. Selle, Analysis of the origin of NOₓ emissions in non premixed dual swirl hydrogen flames, Combust. Flame 273 (2025) 113925.

[16] A.M. Kempf, LES validation from experiments, Flow, Turbul. Combust. 80 (2008) 351–373.

[17] TNF Workshop, https://tnfworkshop.org/.

[18] C. Schneider, A. Dreizler, J. Janicka, E.P. Hassel, Flow field measurements of stable and locally extinguishing hydrocarbon-fuelled jet flames, Combust. Flame 135 (2003) 185–190.

[19] R.S. Barlow, C.D. Carter, Raman/Rayleigh/LIF measurements of nitric oxide formation in turbulent hydrogen jet flames, Combust. Flame 97 (1994) 261–280.

[20] R.S. Barlow, J.H. Frank, A.N. Karpetis, J.Y. Chen, Piloted methane/air jet flames: Transport effects and aspects of scalar structure, Combust. Flame 143 (2005) 433–449.

[21] T.W.J. Peeters, J. Stroomer, J.E.D.E. Vries, D.J.E.M. Roekaerts, C.J. Hoogen- doorn, Comparative experimental and numerical investigation of a piloted turbulent natural-gas diffusion flame, Symp. Combust. 25 (1994) 1241–1248.
[22] P.A. Nooren, M. Versluis, T.H.V.D. Meer, R.S. Barlow, J.H. Frank, Raman-Rayleigh-LIF measurements of temperature and species concentrations in the Delft piloted turbulent jet diffusion flame, Appl. Phys. B 111 (2000) 95–111.

[23] A.R. Masri, R.W. Bilger, Turbulent diffusion flames of hydrocarbon fuels stabilized on a bluff body, Symp. (Int.) Combust. 20 (1985) 319–326.

[24] P.A. Kalt, Y.M. Al-Abdeli, A.R. Masri, R.S. Barlow, Swirling turbulent non-premixed flames of methane: Flow field and compositional structure, Proc. Combust. Inst. 29 (2002) 1913–1919.

[25] C. Schneider, A. Dreizler, J. Janicka, Fluid dynamical analysis of atmospheric reacting and isothermal swirling flows, Flow, Turbul. Combust. 74 (2005) 103–127.

[26] M.C. Drake, R.W. Pitz, M. Lapp, Laser measurements on nonpremixed H2-air flames for assessment of turbulent combustion models, AIAA J. 24 (1984) 905–917.

[27] A.R. Masri, R.W. Dibble, R.S. Barlow, The structure of turbulent nonpremixed flames revealed by Raman-Rayleigh-LIF measurements, Prog. Energy Combust. Sci. 22 (1996) 307–362.

[28] T.M. Wabel, A.M. Steinberg, R.S. Barlow, Multi-scalar measurements of premixed flames in extreme turbulence using Raman/Rayleigh diagnostics, in: AIAA Scitech 2019 Forum, 2019, pp. 1–10.

[29] R.S. Barlow, A.N. Karpetis, J.H. Frank, J.Y. Chen, Scalar profiles and NO formation in laminar opposed-flow partially premixed methane/air flames, Combust. Flame 127 (2001) 2102–2118.

[30] T.F. Guiberti, Y. Krishna, W.R. Boyette, C. Yang, W.L. Roberts, G. Magnotti, Single-shot imaging of major species and OH mole fractions and temperature in non-premixed H₂/N₂ flames at elevated pressure, Proc. Combust. Inst. 38 (2021) 1647–1655.

[31] T.G. Reichel, S. Terhaar, O. Paschereit, Increasing flashback resistance in lean premixed swirl-stabilized hydrogen combustion by axial air injection, J. Eng. Gas Turbines Power 137 (2015) 071503.

[32] J.G. Aguilar, E. Æsøy, J.R. Dawson, The influence of hydrogen on the stability of a perfectly premixed combustor, Combust. Flame 245 (2022) 112323.

[33] R. Mercier, T. Guiberti, A. Chatelier, D. Durox, O. Gicquel, N. Darabiha, T. Schuller, B. Fiorina, Experimental and numerical investigation of the influence of thermal boundary conditions on premixed swirling flame stabilization, Combust. Flame 171 (2016) 42–58.

[34] R. Palulli, S. Dybe, K. Zhang, F. Güthe, P.R. Alemela, C.O. Paschereit, C. Duwig, Characterisation of non-premixed, swirl-stabilised, wet hydrogen/air flame using large eddy simulation, Fuel 350 (2023) 128710.

[35] S. Dillon, R. Mercier, B. Fiorina, Controlling the resolved flame thickness of non-premixed flames in LES with filtered tabulated chemistry, Proc. Combust. Inst. 40 (2024) 105294.

[36] M. Amerighi, A. Andreini, T. Reichel, T. Tanneberger, C.O. Paschereit, LES investigation of a swirl stabilized technically premixed hydrogen flame with FGM and TFM models, Appl. Therm. Eng. 247 (2024) 122944.

[37] O. Keck, W. Meier, W. Stricker, M. Aigner, Establishment of a confined swirling natural gas/air flame as a standard flame: Temperature and species distributions from laser Raman measurements, Combust. Sci. Technol. 174 (2002) 117–151.

[38] W. Meier, I. Boxx, M. Stöhr, C.D. Carter, Laser-based investigations in gas turbine model combustors, Exp. Fluids 49 (2010) 865–882.

[39] W. Meier, C. Dem, C.M. Arndt, Mixing and reaction progress in a confined swirl flame undergoing thermo-acoustic oscillations studied with laser Raman scattering, Exp. Therm. Fluid Sci. 73 (2016) 71–78.

[40] O. Lammel, M. St, P. Kutne, C. Dem, W. Meier, M. Aigner, Experimental analysis of confined jet Flames by laser measurement techniques, J. Eng. Gas Turbines Power 134 (2012) 041506.

[41] M. Raffel, C.E. Willert, F. Scarano, C.J. Kähler, S.T. Wereley, J. Kompenhans, Particle Image Velocimetry, Springer International Publishing, 2018.

[42] B. Wieneke, PIV uncertainty quantification from correlation statistics, Meas. Sci. Technol. 26 (2015) 074002.

[43] H. Tang, D. Ezendeeva, G. Magnotti, Simultaneous measurements of NH₂ and major species and temperature with a novel excitation scheme in ammonia combustion at atmospheric pressure, Combust. Flame 250 (2023) 112639.

[44] F. Fuest, R. Barlow, D. Geyer, F. Seffrin, A. Dreizler, A hybrid method for data evaluation in 1-D Raman spectroscopy, Proc. Combust. Inst. 33 (2011) 815–822.

[45] D. Geyer, 1D-Raman, Rayleigh Experiments in a Turbulent Opposed-Jet (Ph.D. thesis), Technische Universität Darmstadt, Düsseldorf, 2005.

[46] R. Lemaire, S. Menanteau, Assessment of radiation correction methods for bare bead thermocouples in a combustion environment, Int. J. Therm. Sci. 122 (2017) 186–200.

[47] S. Brohez, C. Delvosalle, G. Marlair, A two-thermocouples probe for radiation corrections of measured temperatures in compartment fires, Fire Saf. J. 39 (2004) 399–411.

[48] P. Schmitt, T. Poinsot, B. Schuermans, K.P. Geigle, Large-eddy simulation and experimental study of heat transfer, nitric oxide emissions and combustion instability in a swirled turbulent high-pressure burner, J. Fluid Mech. 570 (2007) 17–46.

[49] F. Duchaine, A. Corpron, L. Pons, V. Moureau, F. Nicoud, T. Poinsot, Development and assessment of a coupled strategy for conjugate heat transfer with Large Eddy Simulation: Application to a cooled turbine blade, Int. J. Heat Fluid Flow 30 (2009) 1129–1141.

[50] S. Jaure, F. Duchaine, G. Staffelbach, L.Y. Gicquel, Massively parallel conjugate heat transfer methods relying on large eddy simulation applied to an aeronautical combustor, Comput. Sci. Discov. 6 (2013) 015008.

[51] K.S. Kedia, C. Safta, J. Ray, H.N. Najm, A.F. Ghoniem, A second-order coupled immersed boundary-SAMR construction for chemically reacting flow over a heat-conducting Cartesian grid-conforming solid, J. Comput. Phys. 272 (2014) 408–428.

[52] K.S. Kedia, A.F. Ghoniem, The response of a harmonically forced premixed flame stabilized on a heat-conducting bluff-body, Proc. Combust. Inst. 35 (2015) 1065–1072.

[53] C. Fureby, Large Eddy Simulation of turbulent reacting flows with conjugate heat transfer and radiative heat transfer, Proc. Combust. Inst. 38 (2021) 3021–3029.

[54] F.P. Incropera, D.P. Dewitt, T.L. Bergman, A.S. Lavine, Fundamentals of Heat and Mass Transfer, sixth ed., 2006.

[55] A. Degenève, P. Jourdaine, C. Mirat, J. Caudal, R. Vicquelin, T. Schuller, Analysis of wall temperature and heat flux distributions in a swirled combustor powered by a methane-air and a CO₂-diluted oxyflame, Fuel 236 (2019) 1540–1547.

[56] P. Rodrigues, O. Gicquel, N. Darabiha, K.P. Geigle, R. Vicquelin, Assessment of external heat transfer modeling of a laboratory-scale combustor: effects of pressure-housing environment and semi-transparent viewing windows, J. Eng. Gas Turbines Power 141 (2019) 1–10.

[57] F. Nicoud, H.B. Toda, O. Cabrit, S. Bose, J. Lee, Using singular values to build a subgrid-scale model for large eddy simulations, Phys. Fluids 23 (2011) 085106.

[58] T. Capurso, D. Laera, E. Riber, B. Cuenot, NOₓ pathways in lean partially premixed swirling H₂-air turbulent flame, Combust. Flame 248 (2023) 112581.

[59] J.D. Ramshaw, P.J. O'Rourke, L.R. Stein, Pressure gradient scaling method for fluid flow with nearly uniform pressure, J. Comput. Phys. 58 (1985) 361–376.

[60] J.P. Legier, T. Poinsot, D. Veynante, Dynamically thickened flame LES model for premixed and non-premixed turbulent combustion, in: Proc. Summer Program, Cent. Turbul. Res., 2000, pp. 157–168.

[61] H. Yamashita, M. Shimada, T. Takeno, A numerical study on flame stability at the transition point of jet diffusion flames, Symp. Combust. 26 (1996) 27–34.

[62] P.A. Baranger, T. Poinsot, On the stabilization mechanisms of a diffusion edge flame in a cross-flow configuration, Proc. Combust. Inst. 40 (1–4) (2024) 105264.

[63] F.G. Schiavone, A. Aniello, E. Riber, T. Schuller, D. Laera, On the adequacy of OH* as heat release marker for hydrogen-air flames, Proc. Combust. Inst. 40 (2024) 105248.

[64] T. Kathrotia, M. Fikri, M. Bozkurt, M. Hartmann, U. Riedel, C. Schulz, Study of the H+O+M reaction forming OH*: Kinetics of OH* chemiluminescence in hydrogen combustion systems, Combust. Flame 157 (2010) 1261–1273.

[65] C. Koren, R. Vicquelin, O. Gicquel, Multiphysics simulation combining Large-Eddy Simulation, wall heat conduction and radiative energy transfer to predict wall temperature induced by a confined premixed swirling flame, Flow, Turbul. Combust. 101 (2018) 77–102.

[66] S.R. Lee, S.S. Park, S.H. Chung, Flame structure and thermal NOₓ formation in hydrogen diffusion flames with reduced kinetic mechanisms, J. Mech. Sci. Technol. 9 (1995) 377–384.

[67] G.J. Røtveit, J.E. Hustad, S.C. Li, F.A. Williams, Effects of diluents on NOₓ formation in hydrogen counterflow flames, Combust. Flame 130 (2002) 48–61.