The paper presents a numerical study where a hybrid CFD-Chemical Reactor Network (CRN) approach is used to predict pollutant emissions in a tubular combustor for aero-engine applications. A ...fully-automated clustering of the simulated flow field with the generation of a reactor network representative of the main flow features is exploited. Similar cells are detected and grouped using a two step approach, the first one based only on aerodynamic criteria for turbulent flows followed by a chemical refinement based on mixture fraction. A formulation for turbulent diffusion fluxes is introduced in the reactor code to model species and energy exchanges between reactors. Three different operating conditions are studied for which measured NOx and CO are available. Results highlight the importance of including turbulent diffusion in the network solution. The accurate prediction of pollutant emissions at different load points confirms that CFD-CRN is a valid and flexible approach for preliminary assessment of aero-engine combustor emissions in the design phase.
In the gas turbine framework, the adoption of carbon capture and storage (CCS) systems coupled with strategies to improve the exhaust CO
2
content is a promising technology to abate the carbon ...footprint of such machines. However, any departure of the oxidant from the air can compromise the accuracy of the conventional models to represent the combustion process. In this work, the effect of the CO
2
enrichment of the mixture on an atmospheric premixed swirled flame is investigated by means of large eddy simulation (LES), comparing the numerical predictions with the experimental results. The high-fidelity numerical model features a dedicated global reaction mechanism derived through an in-house optimization procedure presented in this study. The chemical scheme is obtained by optimizing a widely used CH
4
–air two-step mechanism to improve key flame parameters such as the laminar flame speed and thickness and the resistance of the flame to the stretch with moderate CO
2
dilution. The numerical results are analyzed in terms of flame shape, heat losses, and pressure fluctuations, showing a promising agreement with the experimental measurements and demonstrating the capabilities of the numerical model for CO
2
-diluted combustion.
This paper presents a set of numerical analyses carried out on a model combustor equipped with a prefilming airblast injection system using a multi-coupled approach that includes the solution of the ...liquid film over the prefilming surface. The main objective of this study is to perform a systematic investigation of all the relevant aspects involved in the liquid fuel preparation of airblast atomizers, ranging from the interaction between the gas phase and the liquid film to the effect of velocity fluctuations on the dispersion of droplets downstream of the injector exit. Measurements at high pressure and reacting conditions are available for the case considered here, therefore, allowing to perform such investigation at engine-relevant conditions. The solution of the liquid film evolution over the prefilming surface suggests that the interaction between the gas phase and the liquid film is an important aspect to be considered for a reliable simulation of prefilming airblast systems since it has a strong impact on both velocity and fuel temperature at the atomizing edge. The role of primary breakup has been investigated by performing a sensitivity analysis to different theoretical and correlation-based models. Results obtained from this analysis, performed using Reynolds averaged Navier-Stokes simulations, show that the various formulations predict a quite different diameter, affecting the mixing field in the downstream region and therefore pointing out the necessity of more advanced and robust formulations. A comparison between experimental measurements and a scale-adaptive simulation of the combustor, performed using the spray setup determined in the sensitivity analysis, demonstrates the necessity of including in the simulation time-resolved velocity fluctuations to improve the prediction of the dispersion of droplets and therefore give a reliable prediction of fuel location and mixing.
•Numerical investigation of an industrial gas turbine lean premixed burner through a high-fidelity CFD approach.•Validation of the numerical setup through a direct comparison with experimental ...data.•Assessment of the flame shape prediction of two enhanced versions of the FGM and ATF combustion models.•Remarkable accuracy in predicting the flame topology exhibited by both models.•Assessment of both turbulent combustion models in supporting burner design phase.
In the pursuit of decarbonization, the reduction of greenhouse gas emissions from power generation through gas turbine (GT) engines plays a crucial role in the whole industrial sector. As industries strive to transition towards cleaner energy sources, the design and optimization of novel GT burners require a deep comprehension of the complex interaction between fluid dynamics and combustion processes embedded within the system. Computational Fluid Dynamics (CFD) plays a pivotal role in these processes by providing valuable insights into the complex flow patterns, flame topology, and stability limits within the combustor. Concurrently, the burner design phase necessitates a considerable number of simulations to ascertain flame stability limits under various burner designs and operating conditions. Therefore, it is imperative to control computational costs while ensuring a high level of accuracy. The present work is focused on a comprehensive comparative analysis of two widely employed turbulent combustion closure models: the Flamelet Generated Manifold (FGM) and the Artificially Thickened Flame (ATF). Both models utilize extended versions with specific modifications aimed at effectively addressing their respective limitations. The investigation is performed through a Large Eddy Simulation (LES) based CFD analysis within the context of a lean premixed burner designed by Baker Hughes and operated with methane at atmospheric pressure. The primary benchmark for numerical validation will be provided by detailed chemiluminescence images from a test campaign conducted by the University of Florence, thereby yielding valuable insights into flame topology and positioning. Furthermore, potential disparities in the flow field and fuel concentration at the burner exit between the two models will be revealed.
The present work presents a numerical analysis of a low NOx partially premixed burner for heavy duty gas turbine. The first part of the paper is focused on the study of the premixing process inside ...the burner using standard RANS CFD approach. The resulting profiles at different test points have been used to perform reactive simulations of an experimental test rig, where exhaust NOx emissions were measured. A reliable numerical setup was found comparing predicted and measured NOx emissions at different operating conditions and split ratios between main and pilot fuel. The calibrated numerical setup was then employed to explore possible modifications to fuel injection criteria and fuel split, with the aim of minimizing exhaust NOx emissions. This preliminary numerical screening of new fuel injection strategies, allowed defining a set of advanced configurations to be investigated in future experimental tests.
In order to meet the increasingly stringent regulations in terms of pollutant emissions adopted by ICAO-CAEP in last years, a redesign of aero-engine combustors has been required and, today, lean ...combustion technology can be considered as the most effective solution. In this context, common design tools and standard RANS predictive techniques are often not capable of properly characterizing combustors performances. Thus, computational techniques have been rapidly evolving towards an extensive use of Large-Eddy Simulation (LES) or hybrid RANS methods. This paper presents the numerical analysis of an experimental partially premixed flame fed by a dilute spray of acetone1, exploiting a two-phase Eulerian-Lagrangian approach combined with the Flamelet Generated Manifold (FGM) combustion model in the context of LES techniques. All simulations have been performed with thecode Ansys Fluent 15.0.
A comparison both in non-reactive and reactive conditions of the obtained results with experimental data and conventional RANS solution has been realized in order to highlight the LES capabilities to give a new insight into the physics of reactive two-phase flows, particularly on the unsteady evolution of turbulent spray flames involving particles dispersion, evaporation and combustion.
The present study is devoted to verify current capabilities of Large Eddy Simulation (LES) methodology in the modeling of lean premixed flames in the typical turbulent combustion regime of Dry Low NO ...x gas turbine combustors. A relatively simple reactive test case, presenting all main aspects of turbulent combustion interaction and flame stabilization of gas turbine lean premixed combustors, was chosen as an affordable test to evaluate the feasibility of the technique also in more complex test cases. A comparison between LES and RANS modeling approach is performed in order to discuss modeling requirements, possible gains, and computational overloads associated with the former. Such comparison comprehends a sensitivity study to mesh refinement and combustion model characteristic constants, computational costs, and robustness of the approach. In order to expand the overview on different methods simulations were performed with both commercial and open-source codes switching from quasi-2D to fully 3D computations.
The impact on to NOx of three different natural gas compositions, including a hydrogen-enriched fuel blend, is numerically investigated with high-fidelity simulations in the heavy-duty gas turbine ...NOVA LT16® combustor at relevant engine conditions. For describing the NO formation, a novel emission model based on the characteristic NOx-Damköhler number is presented and used to process the LES solution at run time. The numerical predictions are contrasted to the measurements obtained in a dedicated campaign on a full-annular combustor rig, showing a limited discrepancy against the experimental data for any investigated Test Point. The sources contributing to the NO formation are analysed in detail, helping to shed some light on the mechanisms behind the NO formation in the combustor.
•A dedicated NOx model is used based on the local NOx-Damköhler number.•The stretch and heat loss quenching effects are included in the combustion model.•The model reproduces the NOx increase with H2 and C2H6 addition to methane fuel.•The higher flame speed due to the H2 blend compacts the flame near the pilots.•Increasing the pilot split leads to considerably higher NOx emissions with H2.
•The effectiveness of effusion system for liner is influenced by the swirling flows generated by the swirler injectors•A non-reactive single-sector linear combustor has been designed to investigate ...the impact of Swirl number.•Film effectiveness was acquired using fast response pressure sensitive paint (FPSP) technique at 1kHz•The time-resolved analysis allowed to track the impact of swirling flow on the effusion cooling system
Lean burn swirl stabilized combustors represent the key technology to reduce NOx emissions in modern aircraft engines. The high amount of air admitted directly trough the injection system and the higher levels of pressure and temperature requested by the engine cycle make the design of even more efficient cooling systems and the correct estimation of combustor liners heat load a crucial task for the combustor durability. One of the technologies used for the cooling of these components is the effusion cooling, which promotes the formation of a cold layer to protect the liner walls, whose cooling capabilities are described with the adiabatic effectiveness parameter. The effectiveness of these systems is severely influenced by the swirling flows generated by the swirler injectors which promote the mixing between cold and the hot gases of the combustion process. The development of the swirling flow structures inside the combustor chamber and the grade of interaction between swirling flow and the liner walls can be described by the swirl number (SN). In order to investigate the impact of the effects of the SN parameter on the adiabatic film effectiveness, a dedicated non-reactive single-sector linear combustor test rig was designed and equipped with three different axial injectors (SN=0.6−0.8−1.0) and a cylindrical holes effusion plate to simulate the liner cooling system. Film effectiveness was acquired using Fast response Pressure Sensitive Paint (FPSP) technique; the scale of the model and the acquisition frequency of 1 kHz allowed to track the effusion jets and main flow interactions. The collected results show the importance of using an unsteady analysis to perform an in-depth characterization of the mixing phenomena between the main flow and the coolant which are significantly affected by the swilring characteristics.
Summary
The role of dendritic cells (DCs) and macrophages in allogeneic haematopoietic stem cell transplant (HSCT) is critical in determining the extent of graft‐versus‐host response. The goal of ...this study was to analyse slanDCs, a subset of human proinflammatory DCs, in haematopoietic stem cell (HSC) sources, as well as to evaluate their 1‐year kinetics of reconstitution, origin and functional capacities in peripheral blood (PB) and bone marrow (BM) of patients who have undergone HSCT, and their presence in graft‐versus‐host disease (GVHD) tissue specimens. slanDCs were also compared to myeloid (m)DCs, plasmacytoid (p)DCs and monocytes in HSC sources and in patients' PB and BM throughout reconstitution. slanDCs accounted for all HSC sources. In patients' PB and BM, slanDCs were identified from day +21, showing median frequencies comparable to healthy donors, donor origin and kinetics of recovery similar to mDCs, pDCs, and monocytes. Under cyclosporin treatment, slanDCs displayed a normal pattern of maturation, and maintained an efficient chemotactic activity and capacity of releasing tumour necrosis factor (TNF)‐α upon lipopolysaccharide (LPS) stimulation. None the less, they were almost undetectable in GVHD tissue specimens, being present only in intestinal acute GVHD samples. slanDCs reconstitute early, being donor‐derived and functionally competent. The absence of slanDCs from most of the GVHD‐targeted tissue specimens seems to rule out the direct participation of these cells in the majority of the local reactions characterizing GVHD.
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