Combustion Flow Field Research Articles

Droplet group combustion model improvement for sodium spray fire pre-combustion analysis

Sodium spray fire could happen in sodium-cooled fast reactor, which will cause the rapid rise of temperature and pressure in the vessel. In this paper, based on the droplet pre-combustion model, droplet motion model, multi-node spray fire combustion model and flow field model, a one-dimensional sodium fire combustion analysis code NAFCALX is developed. Its original droplet group combustion model and other inadequacies are improved, coupling the change of droplet with the movement of droplet during droplet combustion. The improved model is used to simulate the ABCOVE and KAERI sodium spray fire experiments. The predicted temperature and pressure peaks and the trend of temperature changing with time were in good agreement with the experimental values, which is much better than that from the original model. Through the comparison and analysis of the calculation results, the accuracy of the improved model is verified.

Rapid online tomograph in non-uniform complex combustion fields based on laser absorption spectroscopy

Laser absorption spectroscopy tomography is widely applied to measure the two-dimensional distribution information in complex combustion flow fields. Rapid and accurate estimation of the integrated absorption area (IA) is the key to achieving accurate online reconstruction. In this paper, a novel method is introduced with the wavelength modulation spectroscopy (WMS) for obtaining the IA, which is applied in the reconstruction of temperature and species concentrations distributions of non-uniform complex combustion flames. With this method, the traditional time-consuming line-shape fitting process is no longer required, and the IA is obtained through simple algebraic operations instead. This method has been validated via numerical simulations and field experiments on afterburner flames. The experimental results show that the measurement accuracy is comparable to that achieved with the conventional WMS with line-shape fitting (WMS-F), however the computational efficiency is improved significantly by at least two orders of magnitude, demonstrating its potential for real industrial applications, where often rapid reconstructions are desirable or required.

Large-Eddy Simulations of Unsteady Reaction Flow Characteristics Using Four Geometrical Combustor Models

Combustion instability constitutes the primary loss source of combustion chambers, gas turbines, and aero engines, and it affects combustion performance or results in a sudden local oscillation. Therefore, this study investigated the factors affecting flame fluctuation on unsteady combustion flow fields through large-eddy simulations. The effects of primary and secondary holes in a triple swirler staged combustor on flame propagation and pressure fluctuation in a combustion field were studied. Moreover, the energy oscillations and dominant frequencies in the combustion field were obtained using the power spectral density technique. The results revealed a variation in the vortex structure and Kelvin–Helmholtz instability in the combustion field, along with a variation in the pressure pulsation during flame propagation under the influence of the primary and secondary hole structures. Additionally, the spatial distributions of pressure oscillation and heat release rate amplitude were obtained, revealing that the foregoing increased owing to the primary and secondary holes in the combustion field, reaching a peak in the shear layer and vortex structure regions.

Experimental study on flow field characteristics of TBCC multibypass combustor

The turbine-based combined cycle (TBCC) engine, as a hypersonic air-breathing propulsion system, involves the transition between multiple bypasses during flight. During the transition process, the flow field of the combustor is affected. In this paper, the flow field of a TBCC multibypass combustor with typical structures is investigated experimentally. The effect of the combined structure on the mixing performance, total pressure loss and flow field distribution downstream of the TBCC multibypass combustor is investigated by changing the inlet aerodynamic parameters and structural parameters of the combustor. The results show that the diffusion ratio increased from 1.0 to 1.4, the thermal mixing efficiency decreased by 24.7%, and the total pressure recovery coefficient increased by 1.86%. Meanwhile, the recirculation zone is wider, and the velocity distribution behind the stabilizer is more uniform. The thermal mixing efficiency increases by 55.8% with the increase in the down inclination (35°∼45°) of the lobe mixer. The mixing characteristic of the triple-bypass combustor is greater than that of the double-bypass combustor. There is an obvious “phase difference” of the vortex shedding in the double-bypass combustor at different spanwise sections, while it does not exist in the triple-bypass combustor. The turbulence disturbance degree in the recirculation zone behind the stabilizer in the triple-bypass combustor is slightly higher than that in the double-bypass combustor, but the velocity distribution is more uniform. The increase in inlet Mach number increases the flow losses and decreases the mixing performance. However, the thermal mixing efficiency is positively impacted with respect to the inlet temperature. In addition, the turbulent kinetic energy of the shear layer behind the stabilizer is large, while it is relatively small in the recirculation zone. There is not only spanwise vortices but also radial vortices behind the stabilizer.

Study of recirculating water-based and carbon-based working fluids on the combustion flow field and the cycle performances of semi-closed CO2-capturing Brayton-derived cycles

• A performance analysis was performed in CO 2 and H 2 O recycling cycles. • A CFD combustion study was performed in H 2 O and CO 2 representative conditions. • An economic analysis was performed in CO 2 and H 2 O recycling cycles. • CO 2 fluids give better cycle performances and H 2 O better combustion temperature fields. The transition into new power technologies that utilize fossil fuels with near zero emissions to the ambient is an urgent need to mitigate the worldwide environmental problems. In this study, detailed analyses of carbon-based and water-based oxy-combustion power cycles are introduced. The applied methodologies to perform these analyses comprise CFD analysis of reacting flows for dual recuperative cycle (DRC) and reheated cycle (RHC). The employed CFD methodologies used the non-simplified Navier-Stokes formulation of reacting flows to avoid the use of extra models or assumptions. It was found that recycling carbon-based fluids would allow better overall performances of the resulting cycles. Recycling water-based fluids, however, would provide some interesting features regarding the temperature field in the combustion chamber. Hence, it would avoid in a better way the possibility of facing overheating caused by oxy-combustion, as well as provide some valuable aerodynamic features for the turbines. When analyzing the obtained combustion flow field, CO 2 and H 2 O working fluids create a more important temperature abatement in the flame surrounding areas and trail than Air. When comparing CO 2 and H 2 O working fluids between them, the H 2 O working fluid initially showed a slightly bigger high-temperature zone than the CO 2 working fluid. Despite this fact, and after those initial zones, the H 2 O working fluid showed a more important temperature abatement than the CO 2 working fluid, except for the transversal tip of the flame trail, where temperatures are in a safe range for superalloys. When considering the temperature on the fluid domain symmetry axis and at the outlet, for the 30 atm case (30.4 bar), it was found that the CO 2 fluid presented a temperature equal to 86.9% of the Air one in the same location and pressure, whereas the H 2 O fluid presented an 82% of the Air one. In addition, thermoeconomic analyses were conducted for the DRC and RHC that are working at high pressure of less than 42 bar and operating temperatures of 1100 K to 1450 K to ensure feasible design for the cycle components. Furthermore, it is found that a maximum efficiency of 47.50% is obtained by the carbon-based RHC under wet-cooling conditions and a minimum cycle efficiency of 33.54% is obtained by the water-based DRC under dry-cooling conditions. From an economic point of view, the average LCOE of the present carbon-based and water-based cycles is 4.17 ¢/kWh, which is 28% lower than the average LCOE of the supercritical carbon-based and integrated gas-turbine-based cycles. Moreover, the LCOE of the carbon-based RHC is minimum (3.92 ¢/kWh) at minimum cycle temperature (T min ) of 305 K (wet cooling) and identical to the water-based RHC (4.00 ¢/kWh) at T min of 323 K (dry-cooling).

超音速流における気流境界層吸込みが流れ場および保炎性能へ与える影響

The changes in the flow field and combustion behavior of a scramjet combustor with a cavity flameholder under boundary layer bleeding condition were investigated by direct imaging, PIV measurement and numerical calculations, at the mainstream conditions of Mach number of 2.5 with total temperature of 580--760K and total pressure of 0.6MPa. Hydrogen gas was used as fuel, and the ignition was forced by precombustion gas injection. From PIV measurement and numerical calculations, it was found that the boundary layer bleeding decreased the static pressure, the density and the static temperature of the mainstream and increased the maximum velocity and the velocity of the boundary layer. Direct imaging of the combustion experiments and numerical calculations showed that the boundary layer bleeding increased the momentum flux of the mainstream and changed the interaction between the precombustion gas jet and the mainstreams, which in turn changed the static temperature and the local equivalence ratio distribution inside the cavity flameholder, resulting in a change in the combustion behavior more favorable to flameholding. It was concluded that the increase in momentum of the mainstream could improve the flameholding performance.

Investigation of Combustion Structure and Flame Stabilization in an Axisymmetric Scramjet

The combustion characteristics and flame stabilization mechanisms in an axisymmetric scramjet with a high-enthalpy inflow are investigated numerically in this paper. To consider the strong compressibility induced by the high Mach number, a pressure-related flamelet/progress variable model is proposed, examined, and applied, which can efficiently relate the database to the local pressure and thus more accurately consider the effect of pressure changes on chemical reaction rates. On this basis, the cold flow and combustion flowfields are analyzed; it is found that the mixing process is mainly dominated by a large-scale flow structure, and the prominent shock waves further enhance the mixing and combustion intensity. The whole combustion process exhibits multiscale characteristics in time and space, and the intermediate’s oxidation process determines the subsequent generation of end products and the primary heat release. The diffusion combustion and the scramjet mode dominate the main reactive zone: most of which satisfies the basic assumption of flamelet. The upstream recirculation zone acts as a hot reactive tank, which is a self-sustaining ignition source to shorten the ignition delay time and maintain flame stability.

Lift-off region temperature field and planar flow field of a twin-nozzle reacting jet in hot crossflow

Secondary fuel injection affects the combustion organization and flame dynamic in axial fuel staging gas turbines. Here, we experimentally investigate a front-fuel rear-air twin-nozzle configuration in which the fuel and air can be independently injected to stabilize a lifted flame front, control the jet trajectory and tune the combustion mode in a very flexible way. A high repetition two-line formaldehyde planar laser induced fluorescence thermometry technique is used to measure the lift-off preheat zone temperature field of the flame with different amount of secondary air injection. The combustion flow field and the flame front dynamics are investigated using particle image velocimetry and CH* chemiluminescence. When the air to fuel ratio increases from 0 to 3, the preheat zone temperature, which is affected by the local equivalence ratio and injection air cooling, increases from 1300 K to 1600 K and then slightly declines. The lift-off region temperature and flow field dynamics are related to the variation of lift-off height, heat release rate and stability of the reacting jet in hot crossflow.

Impact of passive fuel injections techniques in the flow field of the scramjet combustor

• The introduction of passive injection techniques in a parallel cavities scramjet combustor influences the internal flow filed charateristics. • The effect of fuel injection location on the internal flow field charaterictics is also investigated. • Out of all the configuration , the scrmajet combustor showef optimum performance when the fuel is injected through the wall only. The development of scramjet technology has paved the path of possibilities for researchers to develop light-weighted space missions in the years to come. Many countries around the globe have already tested successful scramjet engines. The researchers are making continuous efforts to improve the combustor design by improvising turbulence inserts and flame holders in the combustor. One such improvisation is the introduction of strut into the parallel-cavities combustor. The research paper uses computational fluid dynamics to investigate the effect of internal flow field variables on a strut and cavity-based scramjet combustor. The current work presents a comparative study by analyzing two different scramjet combustor configurations namely case A and Case B to understand the effect of presence of strut in the cavity combustor. The velocity and static pressure profiles are analyzed at different streamwise locations. At x = 70 mm, the velocity values are reduced to lower magnitude for case B as compared to case A and the static pressure values towards downstream detoriates with reduction in intensity of shock waves. It is seen that the magnitude of velocity values and pressure values increases with increase is Mach number. The high-pressure values are observed for M-2.75. A performance assessment of the combustor is carried out for both the configurations, maximum combustion and mixing performance is obtained for M-2.52 for case B as compared to Case A. The paper further analyses three different fuel injection locations namely fuel injection strut only, fuel injection through the wall only and fuel injection through both strut+wall recognized as the case I, II, and III respectively. From various flow-field parameters analysis, it is seen that the production of eddies and vortices in the combustor region indicates proper mixing which is observed for case I. On studying the mass fraction concentration of H 2 0 species for all the cases it is observed that the H 2 0 species is increasing in the lateral direction which indicates that the combustion efficiency is incrementing in the same direction. The maximum combustion and mixing efficiency is observed for case I than the other two cases.

Noise suppression method for hydroxyl tagging velocimetry based on generative adversarial networks

Hydroxyl tagging velocimetry (HTV) technology is crucial in the velocimetry diagnosis of combustion flow fields. However, obtaining accurate HTV information in practical engineering applications is difficult because of complex flow fields and background noise interference. Therefore, for noise suppression, we proposed a generative adversarial network method for targeted network training based on the analysis of HTV image noise characteristics in a complex flow field and the construction of a high-confidence noise description model. The proposed method can effectively suppress noise in HTV experimental data, improve the signal-to-noise ratio of HTV images, and improve the accuracy of HTV measurement.

Optimized CT-TDLAS reconstruction performance evaluation of least squares with the polynomial-fitting method

Computed tomography-tunable diode laser absorption spectroscopy (CT-TDLAS) has been widely used in the diagnosis of the combustion flow field. Several optimized CT reconstruction algorithms such as iteration methods, transformation methods, and nonlinear least squares were applied. Considering the industrial application background, the performances of algebraic iteration reconstruction with the simultaneous algebra reconstruction technique (SART), Tikhonov regularization, and least squares with the polynomial fitting method were discussed in this study. For the mentioned algorithm, identical simulated reconstruction parameters that contained 32-path laser structures, assumed temperature distribution, and absorption databases were adopted to evaluate the reconstruction performance including accuracy, efficiency, and measurement of environment applicability. In this study, different CT reconstruction algorithms were also used to calculate the temperature distribution of the Bunsen burner flame. The different reconstruction results were compared with thermocouple detection data. With the theoretically simulated and experimental analysis, the least squares with the polynomial fitting technique has advantages in reconstruction accuracy, calculation efficiency, and laser path applicability for the measurement condition. It will be helpful in enhancing CT-TDLAS technique development.

Numerical Investigation on Hybrid Rocket Motors with Star-Segmented Rotation Grain

A novel fuel grain configuration comprising two star-segmented grains is proposed. The effect of the rotation, mid-chamber length, and segmented position on the fuel regression rate and the combustion efficiency in hybrid rocket motors with star-segmented grains is investigated in this paper. To this end, 90% hydrogen peroxide (H2O2) and hydroxyl-terminated polybutadiene (HTPB) are selected as the propellant combination in this research. Three-dimensional numerical simulations of the star-segmented grain configuration are conducted. A firing test of a lab-scale hybrid rocket motor was conducted to verify the accuracy of the numerical model, and the errors between simulation data and experimental results are no more than 4.5%. The case without segmented grain configuration is regarded as the base case. The simulation results demonstrate that the combustion flow field structure of the motor could be ameliorated by the segmented rotation grain configuration. Compared with the base case, the rotation of aft-section grain has little effect on the regression rate in the fore-section grain, while the average regression rate in aft-section grain increases, with a maximum increase of 25.04%. The combustion efficiency of the motor with the segmented rotation grain configuration is higher than the base case. Compared with the base case, the combustion efficiency of segmented rotation grain case with mid-chamber length 40 mm and segmented position of 1/2 is raised by 4.06%. The average fuel regression rate and the combustion efficiency of hybrid rocket motors with segmented rotation grains are higher than those in the base case during the entire period of operation, and the combustion efficiency is increased by 1.40–4.21% during the motor operation. The research findings of this paper can provide valuable guidance for the performance improvement of hybrid rocket motors with star grain.

Understanding the role of flow dynamics in thermoacoustic combustion instability

Thermoacoustic combustion instability is one of the most challenging operational issues in several high-performance, low-emissions combustion technologies, including gas turbines, aircraft engines, rockets, and industrial boilers. Driven by the coupling between combustor acoustics and flame heat release rate fluctuations, thermoacoustic combustion instability can lead to reduced operability, increased emissions, and, in the most extreme cases, catastrophic failure of combustor components. The feedback loop between acoustics and combustion is often facilitated by fluid mechanic oscillations, referred to as “velocity coupling,” whereby acoustic oscillations drive flow fluctuations, which in turn create fluctuations in the flame. The character of these fluid mechanic oscillations is highly dependent on the structure of the flow field and the receptivity of the flow to external excitation. Combustor flow fields use features like fluid recirculation and shear to enhance flame holding and reduce emissions, but these are also the same features that can make the flow receptive to acoustic excitation or even drive self-excited oscillations. In this paper, we discuss the basics of thermoacoustic instability with a focus on the role of hydrodynamic oscillations in typical combustor flows. To facilitate this discussion, we explore the hydrodynamic instability characteristics of several key combustor unit flows (wakes, swirling jets, etc.) and show how the hydrodynamic stability of a flow is an important consideration in determining a combustor’s propensity for thermoacoustic oscillations. Several examples of coupling between hydrodynamics and thermoacoustics are discussed to illustrate this important link. The paper concludes by discussing the potential for designing flow fields that are thermoacoustic instability resistant, either through a reduction in the receptivity of the flow or through nonlinear coupling mechanisms by which self-excited flow instabilities can suppress velocity-coupled combustion oscillations.

A method for optimizing reaction progress variable and its application

This paper presents a practical method for optimizing reaction progress variables for FPV models, and the potential of this method is demonstrated in the application of a scramjet model combustor simulation. Reaction progress variable is commonly employed in flamelet-based models as a reaction tracker, while it is normally given with less verifications. Focusing on the global reaction process, this optimization method is proposed with respect to the constraint of monotonicity and the target of the heat release rate, using a hybrid PSO/GA algorithm to quickly give the weighting factors. Consequently, the optimized progress variable together with another three progress variable expressions are utilized and compared in the simulations of a supersonic combustor with vaporized RP-3 injection upstream of dual parallel cavities. Noting that, a pressure-related FPV model is presented and adopted here to consider the effect of pressure pulsations in the combustion flow field. It is shown that the progress variables appear to be specifically coupled with the heat release process and the extent of reaction proceeding, thus affecting the temperature, pressure, and components. Significant improvements brought by the optimized progress variable over the conventional expressions are presented, and it is noteworthy that this method is also applicable to the original FPV model.

One-dimensional equivalence ratio measurements by femtosecond laser filament-triggered discharge plasma spectroscopy

Equivalence ratio measurements are of great importance for combustion systems. In this paper, femtosecond laser filament-triggered discharge plasma spectroscopy is proposed for one-dimensional equivalence ratio measurements of combustion flow fields. The optical emission spectra of femtosecond laser filament-triggered discharge plasma in methane-air premixed laminar flames were measured. The spectral intensity ratios of different species show a linear correlation with the equivalence ratio. It can be demonstrated that femtosecond laser filament-triggered discharge plasma spectroscopy can be used for equivalence ratio measurements. We investigated the effect of the temperature of the methane-air mixture on the equivalence ratio measurements. We further analyzed the one-dimensional spatial intensity distributions of the plasma spectral lines. The results demonstrated the capability of femtosecond laser filament-triggered discharge plasma spectroscopy for one-dimensional equivalence ratio measurements. Finally, femtosecond laser filament-triggered discharge plasma spectroscopy was applied to a methane diffusion flame and measured the one-dimensional equivalence ratios of the diffusion flame at different heights. Femtosecond laser filament-triggered discharge plasma spectroscopy offers a new method for one-dimensional equivalence ratio measurements of combustion flow fields.

Experimental and numerical investigations on the condensed combustion products of Mg-based solid fuels

The exploration of condensed combustion products (CCPs) is essential to reveal the ignition, combustion, and infrared radiation mechanisms of Mg-based (Magnesium/polytetrafluoroethylene/Viton) solid fuels that have been considerably employed in the field of aerospace. Systematic experiments and numerical simulations are performed with the physicochemical properties (including morphology, element distribution, phase composition and particle size distribution) and flow field distribution characteristics of CCPs, respectively. The effects of formulation and pressure on the combustion behaviors of pyrotechnic compositions are thoroughly investigated based on thermal analysis measurements, laser ignition, optical diagnosis and CCPs collection. The results demonstrated that the major solid products for all cases are MgF2 agglomerates and MgO smoke oxide particles (SOPs). Increasing the Mg content in the formulation is simultaneously beneficial for the reduction of large agglomerates and SOPs. As the pressure is decreased from 0.1 MPa to 0.02 MPa, the volume weighted mean diameter of CCPs increases significantly due to the decrease in burning rate. The numerical model established in this paper better approximates the realistic combustion process by coupling the heterogeneous condensation reactions, and is adopted to predict the distribution of CCPs in the combustion flow field under different experimental conditions. Numerical results reveal that the MgF2 is mainly distributed in the anaerobic combustion core zone immediately above the burning surface, while MgO is located in the peripheral aerobic combustion diffusion zone. The negative pressure environment has more profound influence on the oxidation reaction of Mg than fluorination reaction. The scientific findings are expected to facilitate the development of more complete combustion and infrared radiation models, while theoretically providing in-depth guidance for the increasing military and civilian application of Mg-based solid fuels.

Three-dimensional rapid visualization of flame temperature field via compression and noise reduction of light field imaging

Light field (LF) imaging, as an emerging temperature measurement technique, can simultaneously capture the intensity and direction information of radiation in the combustion flow field and has recently attracted extensive attention. However, the dense sampling of the LF introduces a large amount of redundant information and makes the plenoptic data susceptible to noise pollution, which can significantly affect the performance of 3D temperature field reconstruction. To address this problem, a novel approach, i.e., light field compression and noise reduction (LFCNR), is proposed to extract the main features of the projection matrix and separate the noise-related and signal-related subspaces of the plenoptic data, thus improving the reconstruction accuracy and efficiency. The performance of the proposed LFCNR method and the effect of the hyper-parameters on reconstructed quality are investigated thoroughly. It has been observed that the proposed LFCNR-based method for 3D temperature tomography imaging has higher accuracy, more efficiency, and better anti-noise ability compared to the well-established method. LFCNR can improve the reconstructed temperature accuracy by approximately 20%, and the calculation time is shortened to 10%. Priori smoothing is introduced into the optimization objective to constrain the fluctuation of the retrieval temperature, called LFCNR-PS, which can further improve the reconstructed accuracy of axisymmetric and non-axisymmetric fields about 1.79% and 1.23%. Furthermore, experiments of the LFCNR-based method are carried out to reconstruct the 3D temperature field of ethylene diffusion flames. The reconstructed temperature slices demonstrate that the flame topology can be clearly and rapidly identified at different depths. The efficiency and robustness of the proposed method can be applied to the harsh environment, which will be beneficial to the reliable operation of thermal equipment, the study of turbulent chemical reaction mechanisms, fuel utilization, and the optimization design of the engine combustion chamber.

Influence of jet-to-crossflow pressure ratio and combustor width on performance of a hydrogen fueled scramjet

In the development of hypersonic propulsion systems, efficient mixing of gaseous jets in supersonic cross-stream has been facing formidable challenges for over a decade. This paper presents a numerical analysis of a non-reacting scramjet (Supersonic Combustion Ramjet) combustor flow field by solving the two-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations coupled with the Menter SST k-ω model. The focus of this study is to investigate the effects of jet-to-crossflow pressure ratio and combustor width on various performance parameters such as mixing efficiency, total pressure recovery, and mass-flux-weighted Mach number. Accordingly, gaseous jets of hydrogen are injected from two opposite walls on finite parallel streams of air with rearward-facing step configurations. The jet-to-crossflow pressure ratio is varied as 4.5, 9.0, 13.5, and 18.0 while the combustor widths of 40, 50, and 60 mm are considered for the present investigation. Particular emphasis is placed on the utilization of internal shock waves to enhance the combustor performance in lieu of the conventional methods of using shock generators. The insight physics of fuel-air mixing under the influence of internal shocks is also explained. The results reveal that proper shock utilization can improve the overall performance and reduce the overall dimension of the combustion chamber. For the jet-to-crossflow pressure ratio of 4.5, around 10% higher mixing efficiency and 15% greater total pressure recovery are achieved without choking the internal flow when the combustor width is reduced from 60 to 40 mm.

Super-resolution reconstruction of flow field of hydrogen-fueled scramjet under self-ignition conditions

This paper reports experiments on a hydrogen-fueled scramjet performed at different equivalence ratios in a ground pulse combustion wind tunnel with a Mach-2.5 incoming flow. In the non-chemical reaction flow before the fuel was ignited, the flow field was oscillatory, and from the pressure monitor, the oscillation period was 0.07 s and the oscillation amplitude was 0.035 MPa. Schlieren and flame self-luminescence images of the combustor flow were obtained synchronously, and the flow-field structure was stable with the flame concentrated in the shear layer. Deep learning was used to subject the low-resolution combustion flow field to super-resolution analysis to reconstruct a high-resolution flow field. To improve the spatial resolution of the flow field during self-ignition of the hydrogen-fueled scramjet and study the flow mechanism and coupling rule of turbulent fluctuations in the ignition process, a multipath asymmetric residual network (MARN) is proposed based on a single-path super-resolution convolutional neural network (SRCNN) and a residual network model (ResNet_16). The experimental results show that compared with SRCNN and ResNet_16, MARN has the best precision and performance regarding the super-resolution flow field in the self-ignition of hydrogen fuel in terms of the mean peak signal-to-noise ratio, mean structural similarity, and average correlation coefficient as well as being the least complicated. The proposed method offers the possibility of developing lightweight super-resolution models for the flow fields in supersonic combustors; it shows enormous potential for revealing the physical flow of the fuel and air mixture, and it offers accurate forecasts of self-ignition times.

Evaluation of flamelet/progress variable model for the applications in supersonic combustion using hybrid RANS/LES approach

The Flamelet/Progress Variables (FPV) model coupled with large eddy simulation (LES) has been performed to appraise its applicability and performance for supersonic hydrogen combustion, based on the simulations of strut based scramjet and cavity based combustors. For the two typical schemes involved in the present work, the validation of the numerical solver compiled by in-house code is realized by the comparisons with the experimental measurements including temperature, velocity, and wall pressure. The methods for calculating mixture fraction variance in the framework of LES are also investigated and examined in both cases. It can be observed that the diffusion combustion mode is in the dominant state for the whole reactive zone in both cases, where the FPV model is physically compatible. Through the comparisons of the scale similarity method and the transport equation method for calculating mixture fraction variance, the importance of calculating this sub-grid turbulent scalar flux is emphasized. The results show that the mixture fraction variance calculated by the scale similarity model is locally high, but its diffusion is insufficient, which makes the local temperature of the combustion flow field overpredicted and concentrated. On the contrary, the transport equation of the mixture fraction variance can overcome this problem and improve the combustion prediction accuracy, thus, it is more recommended if the computing resources are guaranteed. Qualitatively, the Flamelet/Progress Variables (FPV) model with the large eddy simulation approach can accurately capture the structure and characteristics of the supersonic combustion flow field.