bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Investigation of Reheat Hydrogen Flames in the Sequential-Combustion Stage of a Heavy-Duty Gas Turbine
Authors: Gruber Andrea , Meyer Ole H. H. , Heggset Tarjei , Wood Birute , Ciani Andrea 
Published: August 2024

Abstract
Recent theoretical studies and experimental evidence suggest that turbulent burning-rate augmentation, flame instabilities and NOx emissions, notoriously characterizing fuel-lean hydrogen premixed combustion, are significantly mitigated at reheat combustion conditions. This is due to the favorable effects of high reactants temperature in reducing the strength of thermo-diffusive instabilities that occur in hydrogen premixed combustion with augmented severity for increasing pressure and flame temperature. In this context, Ansaldo’s Constant Pressure Sequential Combustion (CPSC) system appears as an attractive approach to enable hydrogen firing of gas turbines that target high flame temperatures to retain high cycle efficiency. The present numerical modelling effort represents the first attempt to perform high-resolution Large-Eddy Simulation (LES), featuring detailed chemical kinetics and a fully compressible representation of the reactive flow, of hydrogen reheat combustion in a full-scale industrial combustor geometry with realistic geometrical features. Building upon earlier numerical modelling efforts that were limited to generic and geometrically simplified configurations with idealized reactants mixing conditions (GT2022-83218) [1], the ability of the turbulent combustion model to predict injection of the hydrogen fuel, mixing with the vitiated oxidizer stream and spontaneous ignition of the reactants mixture at the expected stabilization location is verified. Low and high flame-temperature conditions for 100% hydrogen-firing of the engine are simulated confirming that the numerical results are in accordance with the expected flame stabilization behavior observed in test-rig experiments. Furthermore, an analysis of the hydrogen premixed flame structure at reheat combustion conditions is provided highlighting the differences observed at various locations within the combustion chamber.
Frequency Topology Optimization of Fan Blade Considering Stress Stiffening and Spin Softening
Authors: Xu Shenli , Wang Mingzhou , Mu Lizhong , Zhou Yan 
Published: August 2024

Abstract
Fan blades are prone to failures due to dynamic loads and their optimal design ensures the stability of aircraft engines. Compared with the shape and parameter optimization, topology optimization design has a larger design space and frequency adjustment range. However, fan blades are limited by performance requirements such as aerodynamics and load-bearing, and are often designed as hollow structures with fixed main path of load transfer. The existing fan blade design methods impose strict requirements on the construction of frequency topology optimization design space.
This paper constructs a frequency topology optimization method of fan blades that considers both stress stiffening and spin softening. The effect of element pseudo density on stress stiffness matrix and spin softening matrix is taken into consideration. A local structural topology optimization method based on the initial path of load transfer is proposed, and a casting constraint method was used to achieve small amplitude frequency control without changing the blade basic structure through erosion and dilation. This paper also constructs the topology optimization formulations of the fundamental frequency maximization, the frequency gap maximization and frequency avoidance constraint. A simple plate example and a hollow fan blade example are used to verify the effectiveness of the optimization method.
Experimental Investigation of Stall Mechanism and Warning Method in a Two-Stage Transonic Fan Under Inlet Distortion With Axial Slot Casing Treatment
Authors: Fan Zhonggang , Du Juan , Liu Yang , Ba Dun , Zhang Min , Ji Guofeng 
Published: August 2024

Abstract
The stall warning method has been employed to predict the level of disturbances in active control systems. Significant advancements have been made by identifying the pre-stall disturbances. Regardless of the propagation, disturbances almost initiate simultaneously at a specific circumferential location under uniform inflow. When the compressor suffers from inlet distortion, the disturbances might disappear in the undistorted region. The differences between the distorted and undistorted regions pose challenges to developing an accurate and robust warning method. Revealing the characteristics of pre-stall disturbances under the distorted inflow is a key to realizing engineering applications. For this purpose, the stalling process and stall warning method was conducted in a two-stage transonic fan. Work on this project has concluded that the pre-stall disturbances initially arise in the region where the rotor exits the distorted region, diminish in the process of circumferential propagation, and ultimately disappear in the position where the rotor enters the distorted region. Due to the impact of circumferential secondary flow, the incidence is largest and the fluctuation of the tip leakage flow is strongest in the position where the rotor exits the distorted region. Consequently, the reduction in warning parameters can be first detected. In the pursuit of an effective stall warning system under inlet distortion, a novel warning index associated with the characteristic frequency band is proposed. This index, coupled with a variable threshold, enables stall warning at any circumferential position with only one transducer. The efficacy of this method is further validated under axial slot casing treatment boundary.
Impact of Steady-State and Mixing Plane Assumptions: An Application to an Industrial Two-Stage High-Pressure Turbine
Authors: Mazzei Lorenzo , Casini Niccolò , Da Soghe Riccardo , Michelassi Vittorio , Ciani Alessandro , Jurek Tomasz , Andrei Luca 
Published: August 2024

Abstract
The continuous temperature and pressure increase to target thermodynamic efficiency and power density in modern gas turbines (GT) stretches the design space and calls for high-pressure turbines (HPT) designed with very accurate design tools. Cooling, both internal and external, is necessary as the evolving fluid temperature is beyond the material’s capability. Therefore, the HPT design process is growingly assisted by computational fluid dynamics (CFD) that due to computers and numerical methods improved efficiency and accuracy respectively allows running CFD during design iterations. The design evolves from the conceptual phase, usually completed with the help of simple correlations and proprietary technology curves, not covered here, and proceeds with the preliminary and detailed phases where aero, thermal, mechanical, and geometrical details are progressively defined. It is paramount that design choices made in the preliminary phase are refined in the detailed phase without requiring excessive rework.
This paper concentrates on the CFD approach typically used in a detailed design phase, where the flow path and airfoils defined in a preliminary phase are completed with the geometrical and operational details of disk cavities and their purge, shrouds or squealer tips, seals, cooling and all the details that completely define the HPT. The paper describes the challenges of incorporating all the geometrical details and compares two approaches: steady-state with mixing plane and unsteady with a specific technique to reduce the computational effort compared to the full-wheel simulation (Time Transformation method). The differences in terms of aerodynamics and adiabatic wall temperatures are highlighted and assessed in the perspective of the computational effort associated with the different modelling approaches. The analysis reveals that unsteady effects and cavity purge flows and cavity geometry may have an important effect on the predictions of the thermal load in specific areas of the hot gas path.
Numerical Study of Flow and Combustion Dynamics in a Hydrogen-Air Rotating Detonation Combustor-Stator Integrated System
Authors: Pal Pinaki , Braun James , Wang Yiqing , Athmanathan Venkat , Paniagua Guillermo , Meyer Terrence R. 
Published: August 2024

Abstract
In the present work, a first-of-its-kind 3D large-eddy simulation (LES) study is conducted to numerically investigate the combustion dynamics as well as aero-thermal phenomena in a full-scale non-premixed hydrogen-air rotating detonation engine (RDE) (with a diverging-shaped lower-end wall), when integrated with nozzle guide vanes (NGV) acting as the turbine stator. The wall-modeled LES framework incorporates hydrogen-air detailed chemical kinetics and adaptive mesh refinement (AMR). A comparative analysis is carried out for two operating conditions with different fuel/air mass flow rates but global equivalence ratio of unity, and considering RDE configurations without and with stator. The LES model is validated against available experimental data for the low mass flux condition with respect to detonation wave speed/height, wave dynamics, and axial static pressure distribution. Numerical results indicate significant deflagrative combustion occurring in the fill region near the inner wall due to the formation of recirculation zones in the injection near-field driven by the backward facing step. The leading detonation wave is found to be trailed by an azimuthal reflected-shock combustion (ARSC) wave, consistent with experimental observations, which consumes unburned vitiated reactants that leak through the main detonation wave. The main detonation wave characteristics, such as detonation wave speed/height, and combustion efficiency do not change appreciably with the presence of NGV. A novel combustion diagnostic technique based on chemical explosive mode analysis (CEMA) is employed to quantify the fraction of heat release occurring in the detonative mode versus deflagrative mode for the simulated conditions. The exit flow is found to be nearly fully subsonic and supersonic for the low and high mass flux conditions, respectively. Further analysis of the exit flow profiles shows that the presence of the NGV renders the flow more axial and significantly impacts the exit Mach number and total pressure, while the total temperature shows negligible change. In addition, the low mass flux operating point, despite exhibiting more deflagrative losses within the combustor, yields overall lower pressure drop from plenum to exhaust, which is mainly attributed to lower pressure drop across the injectors. Lastly, the RDE-NGV configuration exhibits higher total pressure loss compared to RDE without stator across both the mass flux conditions. This study extends the state-of-the-art in numerical modeling of pressure gain combustion systems by demonstrating high-fidelity 3D reacting LES of a full-scale RDE-NGV systems for practical insights pertaining to RDE-turbine integration for power generation.
Acoustic Modes in an Open Box Cavity With Variable Depth Using Two Distinct Wind Tunnels
Authors: Hammer Steffen , Twaddle James , Fridh Jens , Paniagua Guillermo 
Published: August 2024

Abstract
Cavity resonances in ducts is a classical problem that has involved researchers from very different fields over time. More recently the aerospace community became engaged again due to resonances found within the flow path of aero-engines, for example in bleed cavities in the low pressure compressor section. These resonances can lead to problems with the structural integrity of upstream components, and thus warrant investigation.
This study expands the previous data set of an open box cavity with variable depth (D) and a rectangular opening with length (L), effectively testing L/D = [4, 2, ½] ratios. This parameter was indicated by Rossiter to be a strong predictive parameter in frequency generation.
The paper compares the results of the same cavity geometry within two wind tunnels of different dimensions and operational setups. The intention of the study is to isolate the Rossiter modes from any other geometric modes that are due to the wind tunnel’s test section geometry. This isolation allows the modification of the model of Rossiter and the cavity depth model of East in order to improve the predictive capability over a larger range of Mach numbers and for deeper cavities.
One wind tunnel has an open loop continuous flow operation where the Mach number is set by changing the outlet static pressure. The second wind tunnel has a blow-down operation where both Mach and Reynolds numbers can be set independently by pulling a downstream vacuum and setting the upstream total pressure. The experiments were performed for an operating range from low subsonic to transonic Mach numbers. The analysis focuses on modifying the constants in both the Rossiter model and the cavity depth model proposed by East along with investigating the phenomenon of mode switching for Rossiter modes.
The analyses show a good repeatability of the data set between the two wind tunnels displaying strong resonances at similar operating points. The new proposed constants for the Rossiter model when using an L/D = 2 are γ = 0.15, κ = 0.58. For the deeper cavity with L/D = 0.5 the constants proposed are γ = 0.15, κ = 0.9. The modification of the cavity depth model by East to better predict the mode above Mach 0.3 is proposed by adjusting the constant B = 2.5 and leaving A = 0.65. An independence from Reynolds number of the acoustic frequency generation is demonstrated within the operating range. A mode-switching behavior is identified with the shallowest and deepest cavity showing multiple mode transitions within the operating range and a near constant Rossiter mode 1 for L/D = 2.
Combustion Computational Fluid Dynamics Simulations of a Range of Experimental Lean Hydrogen/Natural Gas Blend Flames
Authors: Gauthier Pierre , Zghal Malika , Durocher Antoine , Vena Patrizio , Fan Luming , Francolini Benjamin , Bergthorson Jeffrey M. , Yun Sean 
Published: August 2024

Abstract
Hydrogen micromix combustion is a promising technology to reduce the environmental impact of both aero and land-based gas turbines by delivering carbon-free, and potentially ultra-low-NOx, combustion with a greatly reduced risk of autoignition or flashback.
A preliminary investigation of such novel injector geometries, that are capable of stabilizing premixed, partially premixed, and diffusion flames, using fuel mixtures ranging from pure methane to pure hydrogen, was performed in an Atmospheric Combustion Rig at the National Research Council Canada (NRC). High quality experimental data was collected using Particle Image Velocimetry (PIV) and both OH and acetone planar laser-induced fluorescence (PLIF). Combustion Computational Fluid Dynamics (CCFD) Methods and Tools were developed and validated against these experimental results, for multiple flame shapes, and combustion modes, resulting from fuel lean mixtures of H2/CH4 ranging from 70%/30% to 90%/10% blends, by volume.
Within the current study, Large Eddy Simulations (LES) of a single injector, as well as an array of 5 injectors were investigated. A Flamelet Generated Manifold (FGM), Kinetic Rate, tabulated chemistry approach, using 1D Freely Propagating Flamelets, is used as the combustion model. LES-FGM simulations of the entire experimental injector and test section assembly were performed. Meshing and numerical methodologies were developed, resulting in good agreement for the flame shapes and positions; as well as for the measured thermoacoustic pressure fluctuation amplitude changes, over the range of simulated operating conditions. Further work is underway in applying and assessing the validity of this LES-FGM methodology for flames, with injection systems using micromix technology, at more typical engine conditions, where higher pressures and temperatures are found.
Flow Disturbance by Intrusive Instrumentation: Part 1 – Protrusions on the Pressure Side of HP Compressor Vanes
Authors: Jung Daniel , Schäflein Lukas , Jeschke Peter , Wunderer Roland 
Published: August 2024

Abstract
In this study, we quantify the aerodynamic impact of spanwise pressure tubes located on the pressure side of a high-pressure compressor stator vane. We conducted experiments in a linear cascade wind tunnel (Mach number ∼0.5, Reynolds number 790,000) by modeling the pressure tubes as simplified protrusions with varying dimensions. Testing eight configurations with protrusion heights of 33% and 66% of the maximum vane thickness and a protrusion width ranging from 8% to 24% of the chord length reveals that narrow, as well as high, protrusions increase the total pressure loss the most. Therefore, the narrowest and highest protrusion configuration increases the loss by a factor of 4.7 compared to a vane without a protrusion, while the widest and flattest protrusion increases the loss by a factor of 1.2. Oil flow visualization and CFD simulations reveal that narrow and high protrusions lead to separation-induced losses. The study offers insights for test engineers who are responsible for designing compressor vane instrumentation to minimize additional total pressure loss.
A Large Eddy Simulation Study on Hydrogen Microjets in Hot Vitiated Crossflow
Authors: Broumand Mohsen , Yun Sean , Hong Zekai 
Published: August 2024

Abstract
In the present paper, the results of a large eddy simulation (LES) study on hydrogen microjets (dj ∼ 0.5 mm) injected into a hot (1600 K) vitiated crossflow at different angles — namely, normal (90°) and inclined jet (30°), are presented. The goal is to explore the effects of injection angle on coherent turbulent structure formations, flame-vortex interactions, and wall heat flux contributions. The LES identifies the presence of the horseshoe vortex, the shear layer vortices (SLV), and the counter-rotating vortex pair (CVP), along with the shedding of spanwise-symmetry hairpin vortices in both the normal and inclined jets. The structures in the latter, however, appear more convoluted. In the near field, the SLV-induced flow is found to play a key role in the mixing and flame propagation in the windward side of the jet that is stabilized through the autoignition process along the front edge of both the normal and inclined jets close to their exits. The flame-shear layer offset phenomenon is also noticed on the windward side of the jets. In the far field, the CVP is found to be the dominating mechanism in the entrainment of the hot vitiated crossflow by the reacting jet and large-scale mixing. Its induced counter rotating flow field give rises to the flame propagation and the heat and species transfer from the windward to the leeward side of the jet near the injection wall. In the wake region, the combustion and its byproducts persist in closer proximity to the jet exit of the normal case because of the presence of a much stronger recirculation zone behind the jet. Accordingly, higher wall heat fluxes are obtained in this region for the normal jet. The mean wall heat flux values of both the normal and inclined jets decrease and approach each other with moving away from the jet exit in the streamwise direction. The findings indicate that the CVP-induced flow drastically increases heat transfer to the near wall region, resulting in a spanwise-symmetry heat flux profile with double peaks in downstream. The results of the present LES study are compared to the experimental data available in the literature by considering instantaneous hydroxide (OH) fields and mean wall heat fluxes.
Investigation of Ammonia/Hydrogen Mixtures and Pilot-Split Strategies in a Laboratory-Scale Radial Swirl Combustor
Authors: Rizza Raad , Talibi Midhat , Cosway Benjamin , Kenny Lucas , Beita Jadeed , Ducci Andrea , Sadasivuni Suresh , Balachandran Ramanarayanan 
Published: August 2024

Abstract
The transition to a decarbonised energy future relies on identifying the most suitable alternative fuels that can meet the needs of various energy sectors. While both ammonia and hydrogen are zero-carbon energy vectors, their physical properties and burning characteristics sit on either side of that of natural gas. Hence, mixtures of ammonia and hydrogen are being increasingly looked at as having the potential to fuel current energy systems without requiring significant combustor redesign. However, the combustion characteristics and operation limits for different ammonia/hydrogen mixtures still need to be evaluated. For GT applications in particular, the effect of ammonia/hydrogen mixture composition and operating condition on flame behaviour and stability is not well understood.
The current work was carried out in a laboratory scale, radial swirl-stabilised turbulent combustor. A systematic study of two ammonia/hydrogen blend ratios (70:30 and 80:20 by volume) and a range of equivalence ratios were tested for different pilot-split ratios, to understand the effect on flame shape, stability and dynamics. Time-resolved pressure and integrated heat release fluctuations were measured to evaluate combustor dynamics, and NH2* chemiluminescence flame images were captured to understand spatial differences in flame structure. When comparing blend ratios, differences were observed inflame macro-structures and combustor dynamics, which could be largely attributed to the considerable difference in the laminar flame speeds of the blends. The addition of pilot generally improved the stability and lean operation for both blend ratios.
Characterization of a Premixed Gas Turbine Injector for Light-Duty and Low Emissions Applications
Authors: Carusotto Salvatore , Salvadori Simone , Cavalli Alberto , Casto Elisabetta , Cardile Francesco , Misul Daniela Anna 
Published: August 2024

Abstract
Recent trends in gas turbine combustor design aim at lowering pollutant emissions through the usage of lean premixed solutions that allow for controlling the fuel mixture and the temperature field. Modern injector-combustor systems guarantee low levels of NOx emissions thanks to the employment of premixed and swirl-stabilized flames. Such kind of solution must be designed also considering the possible use of hydrogen as fuel, thus abating emissions further. Unfortunately, this type of technology is significantly more susceptible to flashback and instability when switching to hydrogen blends. For that reason, it becomes necessary to correctly characterize the injection system before considering any possible redesign at the industrial level. In this research, a premixed injector for light-duty applications, with a relatively limited net power of around 5MW, is investigated through experimental and numerical analysis. In the experimental campaign, consisting of a series of flow tests in quiescent air, the mass flow rate associated with different expansion ratios is evaluated in terms of the equivalent area of a calibrated orifice. The obtained data are used to construct and validate the numerical fluid-dynamic models. First, the 1D model is developed with AxSTREAM® NET by fitting the available experimental data through calibrated losses in an equivalent geometrical setup and is used to obtain quick and reliable information on the mass flow rates and pressure levels at different points of the gas circuit. Second, a set of 3D CFD simulations is performed with the ANSYS® FLUENT® solver to achieve a higher level of detail in terms of fluid-dynamic characterization. In that case, the injector domain is split into two parts, the pilot and the main and the two components are analyzed by varying the expansion ratio in quiescent air to validate to numerical approach by matching pressure levels and mass flow rates. Moreover, due to the complex geometry of the main part, the main fuel circuit is divided further into two components to reduce the computational cost, then the characterization is based on an iterative procedure. The grid dependence ensures that no effect of the spatial filter is present, whereas the validation against experimental data with a maximum error of around 5% for the pilot geometry allows for obtaining fundamental preliminary information for the creation of reacting simulations setup or to proceed with the redesign of part of the injection system using additive manufacturing techniques to reduce component cost.