bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Analytical-Empirical Approach to Model Liquid Fuel Combustion Dynamics
Authors: Magina Nicholas , Han Fei , Samarasinghe Janith , Venkatesan Krishna 
Published: October 2022

Abstract
Combustion dynamics is one of the most important factors to be understood and navigated in the design of modern gas turbine combustors. For liquid-fueled combustors this becomes especially challenging given the complexity of additional physics involved, which includes fuel atomization and transport, mixing, reactive kinetics, and acoustics. In this paper an analytical approach to model combustion dynamics is described for an industrially relevant liquid fuel nozzle. For determining the flame fluctuating heat release response to inflow perturbations, an analytical liquid-fuel model was leveraged, developed as an extension and augmentation of traditional diffusion flame models. The acoustic response of the combustor was calculated using 3D finite-element models, including acoustic damping effects of key geometric features. These individual responses were then utilized in a time-domain Green’s function based approach to calculate the response, including growth and saturation, of pressure oscillations. To gain modeling approach confidence and enhanced accuracy, some model parameters impacted by real effects were calibrated manually to achieve better general agreement with the breadth of experimental and computational data available. This included measured flame transfer functions and dynamics metrics, both frequencies and amplitudes, and computed mode shapes and flame shapes. The calibrated modeling approach was then applied to two different combustors, a single-cup and full-annular configurations. It was found that the results agreed well with test data, especially trend-wise, across a modest range of operating conditions. However, at conditions which extended too far beyond the bounds of the data used for model calibration, model inaccuracies became evident. Lastly, sources of model inaccuracies and areas for improvement were discussed.
Extending Highly Loaded Axial Fan Operability Range Through Novel Blade Design
Authors: Lopez Diego I. , Ghisu Tiziano , Kipouros Timoleon , Shahpar Shahrokh , Wilson Mark 
Published: October 2022

Abstract
The tip clearance size has historically been considered to be the main factor affecting stability range in axial fan and compressors. This paper reveals that the stall characteristics are defined by the axial momentum flux of the tip leakage flow and that tip clearance is primarily a strong driver for this metric. A bespoke methodology for carefully tailoing the axial momentum via three-dimensional design is presented, which enables a higher degree of control over the stability range for cases where the tip clearance responds to other considerations and cannot be defined for this purpose. The effect of the axial momentum on efficiency is also addressed and the trade-off between operability range and design point performance derived. The results show that that the conditions for optimal stability differ from those for optimal efficiency and that control over the axial momentum enables tuning the design for a desired exchange. Numerical simulations have been employed to drive the analysis through a high-fidelity computational model whose behavior is supported by rich set of experimental data. Contrary to current belief, results further indicate that an accurate characterization of stall, including onset mechanism, can be achieved through steady-state simulations, minimising the need for expensive time-accurate computations during the design phase.
Assessment of Computational Fluid Dynamic Modeling of Multi-Jet Impingement Cooling and Validation With the Experiments
Authors: Tabassum Sadiya , Hilfer Michael , Brakmann Robin G. , Morsbach Christian , Willert Christian , Matha Marcel , Schroll Michael 
Published: October 2022

Abstract
The current study involves numerical and experimental investigations of circular in-line jets impinging on a heated flat plate. The generic configuration is characterized by 9 jets, each with a diameter of D = 0.0152 m. The jets are influenced by a self-generating crossflow and are positioned at a nozzle-to-plate distance (H/D) of 5 and a jet pitch (p/D) of 5. The steady Reynolds-Averaged Navier-Stokes (RANS) simulations are performed for turbulent jet Reynolds numbers with the DLR in-house CFD code TRACE. The Menter k-ω SST model is applied for turbulence modeling and the turbulent scalar fluxes are modeled based on the Reynolds analogy for a constant turbulent Prandtl number. To gain a closer insight into the impingement jet physics, high-resolution near-wall velocity and thermal fields are obtained through Large Eddy Simulations (LES) and measurements from the Particle Image Velocimetry (PIV). Focus is laid on the comparison of RANS results with the LES data and the experimental data. The results exhibit a qualitative similarity between the simulations and the experiments. Furthermore, correlations of the Nusselt number from the literature are used to validate the simulation results.
Automatized Experimental Combustor Development Using Adaptive Surrogate Model-Based Optimization
Authors: Reumschüssel Johann Moritz , zur Nedden Philipp Maximilian , von Saldern Jakob G. R. , Reichel Thoralf G. , Ćosić Bernhard , Paschereit Christian Oliver 
Published: October 2022

Abstract
Lean premixed combustion is the state of the art technology to achieve ultra low NOx emissions in stationary gas turbines. However, lean premixed flames are susceptible to thermoacoustic instabilities, lean blowout and flashback. The design of such a combustion system is thus always related to the balancing between the levels of emissions and flame stability. Data-driven optimization methods and the adaptation of models through artificial intelligence have experienced a surge in development in the past years. The goal of this study is to show the potential of these methods for gas turbine burner development. A special pilot burner that features 61 different positions of fuel injection, manufactured by means of selective laser melting is used to modify the gas mixture close to the flame anchoring position. Each of the injector lines is equipped with an individual valve, such that the distribution of fuel-air mixture can be modified variously. Installed into an industrial MGT6000 swirl combustor, a data-driven optimization method is used to find an optimal subset of injection locations by automated experiments. The method uses a surrogate model that is based on Gaussian Processes Regression. It is adopted for experimental optimization, keeping measurement efforts to a minimum. The optimizer controls the fuel valves and uses live measurements to find a distribution that generates minimal NOx emissions, while ensuring flame stability. The solutions found by the optimization scheme are analyzed and advantages and limitations of the approach are discussed.
Parametric Studies and Simulations of a Hydrogen Micromix Combustor
Authors: French Ainslie , Mingione Giuseppe , Schettino Antonio , Roncioni Pietro , Vitagliano Pier Luigi , Minervino Mauro 
Published: October 2022

Abstract
The use of hydrogen as an alternative fuel in the combustion chamber of an aircraft turbine engine would offer a practical solution to reducing levels of emissions which contribute to atmospheric pollution. In recent years various designs of the basic system component of such an engine have been proposed being described as the hydrogen micromix combustor. This technology requires the design and development of a safe mechanism for hydrogen combustion which avoids auto-ignition and flashback and permits the initial balance and mixing of a hydrogen-air mixture to produce thrust from the combustion of hundreds of miniature low temperature diffusion flames which produce extremely low levels of NOx.
In this paper a potential geometry and typical operating conditions of such a micromix combustor has been selected for a critical examination of the numerical modelling with particular attention to the levels of NOx predicted. In particular the level of grid independence of the NOx modelling is assessed as well as the variations in NOx levels generated in the march towards steady state solutions for various numerical methods.
Additionally, a series of parametric studies associated with modifications of the basic micromix combustor design are explored to verify both the consistency in the numerical methods adopted as well as assessing the impact of such modifications on the overall micromix combustor performance.
Operating Characteristics of a Flameless Combustor Obtained By Experiments Informed Modelling
Authors: Sampat Rishikesh , Goselink Niek , Schrijer Ferry , Gangoli Rao Arvind 
Published: October 2022

Abstract
Flameless Combustion is an interesting low NOx combustion technology for gas turbine engines. In order to design systems for stringent performance standards, it is important to understand emission formation in this regime. To this end, the characteristics of a combustor capable of operating in the Flameless regime are studied. Particle Image Velocimetry and thermocouple measurements were performed to obtain the velocity field and gas temperatures respectively, in the combustor under reacting conditions. Results from experiments were used to generate an “informed” chemical reactor network (CRN) model from which, temperature and species distributions were obtained. As such, this paper presents measured data and a methodology to combine it with CRN modelling to obtain gas composition and temperature. The temperature, NOx, CO and O2 mole fractions obtained at three different operating conditions shall be validated with gas composition measurements in the future.
Methodology for the Pitch Controller Wind Prediction System in Small Wind Turbines
Authors: Lara-Mendoza Oscar , Jáuregui-Correa Juan Carlos , Chavero-Navarrete Ernesto , García-Martínez José R. 
Published: October 2022

Abstract
Nowadays, it is necessary to generate electrical energy using renewable natural resources even when the wind is limited. Small wind turbines are required to operate even with turbulence due to operation height. In this research, a fuzzy logic controller for the angular position of the blades in a wind turbine is proposed. The pitch system regulates the rotational speed of the generator to keep it at a nominal value. The mechanics of a blade pitch system usually act slower than an electrical control signal, which causes problems when the blades need fast positioning. The need for a quick blade positioning response arises when wind gusts occur. Wind gusts are undesirable in all regions of wind turbine operation, making efficient pitch control a problem. This work develops the experimental platform on a small wind turbine located in Mexico at the Autonomous University of Queretaro (UAQ). The wind speed conditions in a non-steady-state regime are presented at the experimental site. A weather station meters ahead of the wind turbine anticipates the position of the rotor blade before being impacted. Results of this methodology prove that the rotor blades reach in advance the ideal position to receive air gusts. This methodology will contribute to the efficient and safe utilization of wind turbines with turbulent wind speeds.
System-Level Assessment of a Partially Distributed Hybrid Electric Propulsion System
Authors: Sahoo Smruti , Kavvalos Mavroudis D. , Diamantidou Dimitra Eirini , Kyprianidis Konstantinos G. 
Published: October 2022

Abstract
Hybrid electric propulsion system based aircraft designs are paving the path towards a future greener aviation sector and thus, have been the major focus of the aeronautical community. The fuel efficiency improvements of such propulsion system configurations are realized at the aircraft level. In order to assess such benefits, a radical shift in the sub-system modeling requirements and an integrated conceptual aircraft design environment is necessary. This work highlights performance model development work pertaining to different hybrid electric propulsion system components and development of a design platform which facilitates tighter integration of different novel propulsion system disciplines at aircraft level. Furthermore, a serial/parallel partially distributed hybrid electric propulsion system is chosen as the candidate configuration to assess the potential benefits and associated trade-offs by conducting multidisciplinary design space exploration studies. It is established that the distributed hybrid electric configurations pose the potential for aircraft structural weight reduction benefits. The study further illustrates the impacts from onboard charging during the low thrust requirement segments, quantitatively. It is highlighted that the amount of off-take power extraction for onboard charging of the battery is limited due to engine operability and higher specific fuel consumption issues. Though provisioning of onboard charging lowers the potential for block fuel savings, improvement in battery specific energy can make it more promising, which is also dependent on the hybridization power level. It is established that distributed propulsion system configurations particularly benefit from a high aspect ratio wing structure, which manifests for high hybridization power levels. A high voltage level transmission system with more efficient electrical components, enhances opportunities for achieving block fuel saving benefits.
Numerical Investigation of Potential Flow Induced Vibrations of Steam Turbine Last Stage Rotor at Low Load Operation - Part 2: Rotating Instabilities Detection
Authors: Diurno Tommaso , Andreini Antonio , Facchini Bruno , Maceli Nicola , Arcengeli Lorenzo 
Published: October 2022

Abstract
Steam turbines play an important role in global power generation since they are widely used, as thermal engines, in fossil-fueled, nuclear, and concentrated solar power plants. Therefore, recent trends in steam turbine design practices are closely related to the development of the energy market, which is especially focused on expansion of fast renewable energy. As a direct consequence, due to intrinsic variability of the green-energy resources, the steam turbines address the need to increase their flexibility to ensure the stable functioning of the power grid. Greater flexibility is linked to even increasing Low Volume Flow (LVF) operating conditions which could trigger dangerous non-synchronous aerodynamic excitations of the last stage bucket (LSB). In order to discover the source of such excitations, an extensive numerical study, presented in a two-part publication, has been carried out to investigate two different mechanisms potentially accountable for flow induced vibrations. In part one, the focus is on the flutter stability, while the present part deals with the detection of rotating instability phenomena that might arise in the last stage during LVF conditions. Such aerodynamic instabilities are investigated using CFD simulations by performing 3D, Unsteady Reynolds Averaged Navier Stokes (URANS) of the low pressure, last turbine stage coupled with an axial exhaust hood, with structural struts. The full annulus mesh of both the last stage and diffuser is considered with the transient stator-rotor interface to properly account for unsteady interaction effects.
The influence of the operating conditions on the fluid dynamic behavior is assessed by considering six different operating conditions, starting from the design condition and gradually decreasing the mass flow rate. The presence of rotating instabilities is demonstrated by monitoring the fluid dynamic variables during the simulation and by using advanced post-processing techniques, such as Proper Orthogonal Decomposition (POD).
Effects of Freestream Turbulence on Air-Mist Film Cooling: Two-Phase Flow Simulations
Authors: Dwivedi Anjali , Sarkar S. 
Published: October 2022

Abstract
Air-mist film cooling is a potential technique to protect the surface of turbine vanes operating at high temperatures for improved thermal efficiency. The variation in the performance of air-mist film coolant is evaluated here for a wide range of freestream turbulence (0.2 to 10%) like the operating condition of the gas turbine. The investigated domain consists of a flat plate with a series of discrete holes of 35° streamwise orientation and connected to a common delivery plenum chamber via a pipe of diameter D = 12.7mm. A two-phase mist consisting of finely dispersed water droplets of 10.0μm in an airstream at a mist concentration of 3.0% is introduced as a secondary flow. The blowing ratio and density ratio are 0.5 and 1.2, respectively, where the Reynolds number based on the diameter of the hole is 1.0 × 104. The Reynolds Averaged Navier Stokes equation in the Eulerian-Lagrangian frame is used to simulate the two-phase flow by ANSYS Fluent 15.0 with the k-ε realizable model. The simulation resolves the mean thermal-flow field and dynamics of droplets. The injected droplets in the crossflow behave like a small heat sink as they evaporate while advecting downstream and are expected to provide improved protection of the heated surface. High turbulence intensity enhances the mixing of droplets with the crossflow, thereby improving the spanwise diffusion of droplets. Reduction of the strength of the counter-rotating vortex pair is also evident. The area-averaged film cooling effectiveness increases by 21.5%, with an increase of turbulence intensity from 0.2 to 10%. However, the increase in aerodynamic losses is almost as high as 39%.
Research on Acoustic Resonance Characteristics of Flat Plate Cascades Based on Acoustic Analogy
Authors: Zhao Feng Tong , Cui Bo , Yang Mingsui , Sha Yun Dong 
Published: October 2022

Abstract
The model of flow around the flat plate cascades is a fundamental study for the flow-induced acoustic resonance phenomenon. Parker first conducted an experimental study on the acoustic issue with the vibration of the built-in plate in the rectangular pipe. It was found that the plate vibration amplitudes and the sound pressure level inside the pipe grow rapidly when the plate vortex frequency, the acoustic mode frequency and the natural frequency of the blade are the same, which is a new resonance mechanism. In this paper, a rectangular pipe built-in flat plate model is established on the basis of the Parker experimental model. A method combined the large eddy simulation used to process the flow field and the Lighthill acoustic analog used to capture the acoustic characteristics of the acoustic calculation model is proposed. The obtained sound pressure spectrum curves are highly consistent with the experimental data of Parker, which verifies the applicability and accuracy of the large eddy simulation and Lighthill acoustic analog calculation methods. The acoustic resonance problem of flat plate cascades is investigated using this method. The sound pressure spectrum curve at different flow velocities are obtained. The sudden jump of the sound pressure level when the acoustic resonance, the relationship between the characteristic frequency and the shedding vortex, and the anti-phase shedding mode of the shedding vortex at the trailing edge of the plate had been captured by taking the above methods for the flat plate cascades research. The flat plate cascades model established in this paper shows well the law of the plate shedding vortex motion and the sound pressure distribution characteristics under different incoming flow speeds. This paper may provides a model research method for the blade fracture problem caused by acoustic resonance of the aero-engine compressor.
Analytical Modeling of the Injector Response to High Frequency Modes in a Tubular Multi-Jet-Combustor
Authors: Rosenkranz Jan-Andre , Sattelmayer Thomas 
Published: October 2022

Abstract
Gas turbine combustors with multi-jet burners have been shown to provide better fuel flexibility compared to large swirl burners and can meet current low emissions standards at increasing turbine inlet temperatures. In case thermoacoustic combustion instabilities occur, the resonant feedback loop of the thermoacoustic mode in the chamber leads to injector coupling, which has not yet been investigated in same depth as in rocket engines in the past. The higher order mode inside the combustor initiates longitudinal modes in the upstream injector tubes leading to flame surface and location modulations as potential drivers of instability. Furthermore, fuel injection in the mixing tubes generate equivalence ratio fluctuations, which have an additional influence on flame dynamics. As these effects deteriorate emissions, flashback safety and lead to increased wear or even severe damage of the combustor, proper calculation of the acoustic injector response is an important aspect of combustor stability modelling. The paper at hand aims for an analytical model to describe the injector response to higher order modes as an alternative to the existing approaches, which are largely based on numerical computations. For this purpose, lumped parameter models are used to calculate the wave scattering at the injector tube-chamber interface. It is shown that the Rankine-Hugoniot conditions at the area jump can be applied to high frequency acoustics in a similar manner as to low frequency acoustics. Numerical simulations in COMSOL are used to verify the model for the first and second transversal and the first radial mode.
Experimental Verification of a Practical Engineering Design Method for Mixed-Flow Compressor Stages
Authors: Zhang Chenqing , Zhao Chenxi , Tang Yonghong , Xi Guang 
Published: October 2022

Abstract
The mixed-flow compressor has high efficiency and pressurization ability even at an extremely high flow rate. However, so far the design principle of the mixed-flow compressor has not well been established. In this paper, a novel and practical design method of mixed flow impellers is developed, in which the meridional construction needs few control parameters, and easily applied to engineering product design.
In order to verify the developed method, a mixed-flow impeller with flow rate coefficient of 0.2374 is designed and manufactured for the experimental study. The experimental results show that the peak efficiency of the compressor at the machine Mach number of 0.6 and 0.8 reach 85.17% and 85.20%, respectively, which are competitively well-performed at large flow coefficient in the published literature. The comparison between experimental and numerical results verifies the feasibility and effectiveness of this proposed method and also provides some valuable guidance for the choice of the exit inclination angle of the mixed-flow impellers.