bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stability Analysis of an Ammonia-Based Emulsion With Additives for Lean Combustion
Authors: Di Gloria Pasquale , Strafella Luciano , De Giorgi Maria Grazia , Ciccarella Giuseppe , Castelluzzo Gregorio , Baldassarre Francesca , Ficarella Antonio 
Published: September 2023

Abstract
In recent years, considerable progress has been made in exploring new fuel additives to reduce emissions and improve combustion performance compared to conventional fuels. Reducing total nitrogen oxide (NOx) emissions can be achieved by reducing the flame temperature using a fuel emulsified with water and/or using ammonia-based nano-additives such as urea. For the preparation of emulsified fuel, it is desirable to achieve greater stability of the emulsified fuel with a minimum cost of chemicals and energy, so that it can be used for a longer period. The stability of an emulsion is influenced by the water-fuel ratio and the amount of surfactant. In the present work, the influence of dispersed urea nanoparticles, water, and surfactant (Span 85/Tween 80) on the combustion performance and emission characteristics of aviation fuel has been investigated. The experimental campaign was carried out in a 300-kW swirled turbine combustor. It consists of a cylindrical combustion chamber with three optical windows, equipped with pressure sensors, thermocouples, and an exhaust gas analyzer. The experimental campaign was conducted with the same air/fuel ratio (Φ) to facilitate the comparison of different emulsions. The focus is on the stability of the emulsion with the use of surfactants. Chemiluminescence imaging was performed to characterize the effects of the additive on flame emissions. A spectrometer was also used to verify the presence of particulate matter under different fuel conditions. Finally, NOx, CO, CO2, and O2 emissions were measured.
Part I: Validation and Verification of CFD Analysis for NASA SDT Transonic Fan Stage Test Rig
Authors: Robles Vega Gregorio , Lee Daryl Y. , Ni Michael , Ni Ron-Ho 
Published: September 2023

Abstract
In this paper, the NASA SDT (Source Diagnostic Test) was used for CFD code validation as it provides experimental data that includes an operating map of the turbomachinery rig and 2D radial profiles at multiple operating points. The configuration with the baseline OGV geometry is analyzed using steady RANS simulations with the mixing plane approximation at the rotor/stator interface and Wilcox K-w 98 two equation turbulence model.
An operating map consisting of seven speedlines and an operating line, 126 points in total, was generated and compared against experimental data. Since only the 100% speed fan geometry was available, it was used for all speeds. The CFD model showed good agreement with 1D mean performance data at design speed. The pressure rise and efficiencies across the bypass stage were predicted within 0.5%. Off-design predicted performance captured the bulk pressure rise and efficiency. Comparisons of radial profiles showed good agreement to data at the fan exit. The CFD model adequately predicted the shape and magnitude as compared to data.
The validation and verification of the NASA SDT fan and baseline OGV configuration provides a foundation for a multipart effort aimed at understanding the impact of airframe installation effects on turbomachinery performance.
A Probabilistic Approach to Turbine Uncertainty
Authors: Bhatnagar Lakshya , Paniagua Guillermo , Clemens Eugene , Bloxham Matthew 
Published: September 2023

Abstract
Efficiency is an essential metric for assessing turbine performance. Modern turbines rely heavily on numerical computational fluid dynamic (CFD) tools for design improvement. With more compact turbines leading to lower aspect ratio airfoils, the influence of secondary flows is significant on performance. Secondary flows and detached flows, in general, remain a challenge for commercial CFD solvers; hence, there is a need for high-fidelity experimental data to tune these solvers used by turbine designers. Efficiency measurements in engine-representative test rigs are challenging for multiple reasons; an inherent problem to any experiment is to remove the effects specific to the turbine rig. This problem is compounded by the narrow uncertainty band required to detect the incremental improvements achieved by turbine designers. Efficiency measurements carried out in engine-representative turbine rigs have traditionally relied upon assumptions such as constant gas properties and neglecting heat loss.
This research presents an uncertainty framework that combines inputs from experiments and computational tools. This methodology allows quantifying uncertainty for high-fidelity efficiency data in engine-representative turbine facilities. This manuscript presents probabilistic sampling techniques to allow for uncertainty propagation. The effect of rig-specific effects, such as heat transfer and gas properties, on efficiency is demonstrated. Sources of uncertainty are identified, and a framework is presented which divides the sources into bias and stochastic. The framework allows the combination of experimental and numerical uncertainty. Gaussian Regression models are developed to obtain speed-lines for the turbine map using the uncertainty of the measured efficiency.
Purge-Mainstream Interactions in a Turbine Stage With Rotor Endwall Contouring
Authors: Mesny Alex W. , Pountney Oliver J. , Scobie James A. , Li Yan Sheng , Sangan Carl M. 
Published: September 2023

Abstract
Purge flows are prevalent in modern gas turbine design allowing for increased turbine entry temperatures. The purge flow passes through a rim seal and interacts with the mainstream flow, modifying the blade secondary flow structures and reducing stage efficiency. These structures may be controlled using End Wall Contouring (EWC), though experimental demonstration of their benefit is seldom reported in the literature. The optically accessible turbine at the University of Bath was designed to directly measure and visualize the flow field within the blade passage for a rotor with EWC.
The single-stage turbine enables phase-locked flow field measurements with volumetric Particle Image Velocimetry (PIV). Purge flow was supplied to investigate a range of operating conditions in which the secondary flow structures were modified. The modular turbine rotor allowed for expedient change of a bladed ring, or bling, featuring non-axisymmetric EWC.
The identified secondary flow structures were the Pressure-Side leg of the Horse Shoe Vortex (PS-HSV) and an Egress Vortex (EV) of concurrent rotational direction. An increase in purge flow rate monotonically shifted the EV toward the suction-side (SS) of the adjacent blade. The migration of the PS-HSV towards the SS caused the two aforementioned vortices to merge.
The EWC rotor design included a Leading-Edge (LE) feature to alter the PS-HSV, and a trough to guide the EV low spanwise in the passage and maintain displacement from the adjacent suction side. The EWC rotor was found to be effective at altering the formation and positioning of the secondary flow structures at a range of purge flow conditions.
Experimental and Numerical Study of Purge Flow Effects in an HP Turbine Stage
Authors: Payne Daniel , Kanjirakkad Vasudevan 
Published: September 2023

Abstract
To improve the efficiency of gas turbines, it is essential that designers understand the interaction between primary and secondary air systems in critical regions of the engine. One of the most important regions is the rotor-stator cavity of the first stage high pressure turbine, where the high temperatures could cause a catastrophic failure if the supply of secondary air is too low or the cavity is not effectively sealed. This paper presents experimental results and analysis of data from the Rim Seal (RiSe) rig at the University of Sussex. This is a single stage engine representative axial turbine facility and allows for measurements to be made of the interaction between the main annulus flow and the coolant flow within the rotor stator cavities. Experiments are completed at a set operating point of the turbine, at an Axial Reynolds number of 7 × 105 and a fixed Pressure Ratio of 2.5, whilst the purge flow is varied from 0.05% to 1% of the main annulus flow. Numerical simulations are completed using a Reynolds Averaged Navier-Stokes (RANS) solver for a periodic sector of the test section. The simulations conducted include those with the cavity domain alone and those where both the cavity and the main annulus domains are combined. This allows for comparisons to be made of the different physical mechanisms associated with the interaction between the main annulus and cavity flows. In this paper we will present comparisons between the experimental measurements and numerical simulations for a range of purge flow rates and simulation setups. Analysis of the simulations along with that of the experimental data will explain the various aero-thermal mechanisms involved in the cavity regions.
Resolving Issues and Failures of Diaphragms in Turbines
Authors: Gowreesan Vamadevan , Greaves Wayne , Grebinnyk Kyrylo 
Published: September 2023

Abstract
Diaphragms are used in steam turbines to regulate the flow of the steam to the rotating blades. The regulation or the change of flow direction is to increase the efficiency of the turbine. Though diaphragms are non-rotating parts, they may experience elevated temperature and they may also be subjected to high stress and or cyclic stresses during service. As a result, they may develop failures and other issues due to long term service. The vanes of the diaphragms may develop cracks and the diaphragms may develop dishing which is generally a result of creep deformation resulting from long term service at elevated temperature.
This paper discusses different types of diaphragms and their fabrication methods first. The fabrication of the diaphragm involves casting or machining of vanes. Then these vanes or vane segments are welded to the inner and outer rings to make the rigid diaphragms.
Then some of the common failures and issues these diaphragms see in their service will be discussed. These will be illustrated with some recent field examples. This will be followed by some approaches to mitigate the risk of these failures and issues.
On the Aeroacoustic Properties of a Prandtl-Fan
Authors: Czwielong Felix , Benz Julian , Ocker Christof , Renz Andreas , Sedlmajer Michael , Merkel Markus , Becker Stefan 
Published: September 2023

Abstract
Axial fans are used in many machines and equipment in close proximity to people. Therefore, acoustic optimization of the fans is essential to protect the well-being of people and to ensure a quiet environment. The sound emission of fans is determined, among other factors, by the selected load distribution of the blades and the resulting angles of attack and chord lengths. A bell-shaped load distribution developed by Prandtl in 1933 was applied to a benchmark fan and investigated aeroacoustically. A total of three axial fans were numerically simulated for flow and acoustics at the design point. One of these fans is an international benchmark fan, the second is a fan with the same isoenergetic load distribution but a different chord length, and the third fan has the Prandtl load distribution and the same modified chord length. Based on the simulations performed, it was shown that a larger chord length leads to an improvement in the aerodynamic and acoustic properties of the axial fan with isoenergetic load distribution. This is due to the reduced blade tip overflow and the associated reduced pressure fluctuations at the blade surface. The bell-shaped load distribution increases the efficiency of the fan, but also increases the total sound emission by 1.5 dB compared to the axial fan with constant chord length and isoenergetic load distribution. This is due to the increased interaction between the blades, as the blade tip vortex hits the following blade leading edge more frontally. This increase occurs despite a reduction in the strength of the blade tip vortex. Compared to the benchmark fan, the changes in chord length and Prandtl’s load distribution resulted in a sound reduction of 3.9 dB and an increase in efficiency of 4%. It was shown that the modifications can be used for future aeroacoustic optimization of axial fans.
Fast Prediction of Combustor Stability Limits in Humidified Micro Gas Turbines Using Hybrid 0D/1D Model
Authors: Pappa Alessio , Bricteux Laurent , De Paepe Ward 
Published: September 2023

Abstract
Cycle humidification is considered as an interesting route to enhance the micro Gas Turbine (mGT) operational flexibility, ensuring a place for mGTs in future small-scale decentralized power production. Indeed, humidifying the mGT cycle when there is no heat demand increases the electrical efficiency of the cycle, and thus the operational flexibility of the unit. However, the rather small operating range of the mGT combustor under these diluted conditions remains the main limitation, restricting the humidification rate, and thus the potential cycle improvement. Therefore, a complete characterization of the combustor performances for a range of operating conditions in combination with an increasing water-to-air ratio allows quantifying the operability limit of the engine under these unconventional diluted conditions. To improve the mGT cycle further, the limits to reach stable, complete, and low emissions combustion are assessed using a hybrid 0D/1D model of the combustor of typical mGT, namely the Turbec T100 mGT, for different humidification pathways (steam or water injection, saturation tower, ...). This model combines 0D Chemical Reactor Networks with 1D unstretched laminar flame calculations. The results of this computationally fast and flexible model are experimentally validated for both dry and wet cycle operation. For moderate water fractions, the simulation results show that complete combustion with low CO emissions, but at reduced temperature, could be achieved at a constant equivalence ratio compared to the dry reference case. At increased water fraction, stable and complete combustion at similar CO emission levels could still be achieved by increasing the equivalence ratio, compensating for the reduced temperature in the combustion chamber. Finally, at high water fractions, the results show unacceptably high CO levels, as a result of incomplete combustion due to the too-low temperature or too-low flame speed. With these simulations, we were able to assess the influence of humidified conditions on the combustion stability as well as to determine the operating limit helping so future cycle improvements.
Integrated Design of a Variable Cycle Engine and Aircraft Thermal Management System
Authors: Clark Robert A. , Tai Jimmy , Mavris Dimitri 
Published: September 2023

Abstract
The integrated design of a variable cycle engine (VCE) and an aircraft thermal management system (TMS) is investigated. The integrated system is designed using the multiple design point (MDP) approach in order to achieve required performance metrics at points other than the cycle design condition. The VCE architecture under investigation is a three-stream design where the third-stream is split off after the fan, exhausting through a separate third-stream nozzle. The primary air stream passes through a low-pressure compressor before splitting into an inner bypass stream and a core stream. The inner bypass and core streams mix aft of the low-pressure turbine and exhaust through a core nozzle. The variable cycle engine utilizes multiple variable geometry components: variable compressor inlet guide vanes (IGVs), a variable area bypass injector (VABI) at the inner bypass / core stream mixing plane, and variable throats in the two exhaust nozzles. The TMS architecture modeled is an open-loop air cycle system (ACS) that uses air bled from the high-pressure compressor as the working medium. The bleed air passes through heat exchangers (located in the engine third stream) before and after passing through a supercharging compressor, and is then expanded through two turbines to reach the low temperatures required to absorb heat from the aircraft cooling system. The effect of integrating the TMS into the engine design loop is investigated. In addition, a comparison is made to prior studies, where the same TMS architecture was connected to a low-bypass ratio turbofan engine, with the heat exchangers placed in either a ram-air stream or the engine bypass stream. The comparison shows that the variable cycle engine is able to improve heat dissipation capability versus a ram-air cooled system, while eliminating the airframe integration impact that comes with a separate ram-air stream. Lastly, the impact of modulating the variable geometry features on overall cooling capability is investigated. Results are presented for individual operating points as well as at the aircraft mission level.
A Machine Learning Approach for the Prediction of Time-Averaged Unsteady Flows in Turbomachinery
Authors: Blechschmidt Dominik , Mimic Dajan 
Published: September 2023

Abstract
Recent advances in deep learning have led to its increased application in the field of fluid dynamics. By using a data-driven approach instead of a more conventional numerical approach, it is possible to reduce the computational cost of fluid simulations significantly. Especially unsteady computational fluid dynamics (CFD) are known to require a considerable amount of time and resources. Hence, it is common practice in turbomachinery to model the flow as steady by averaging the flow between the rotor and stator in a so-called mixing plane. While this approach is numerically efficient, the full interactions between the rotor and the stator can no longer be predicted accurately due to the averaged upstream flow field. Contrary to this, the time-average of an actual unsteady flow does not contain such a modeling error while still resulting in a flow field that is decoupled from its temporal fluctuations. In this work, we introduce a graph neural network (GNN), which predicts the time-averaged flow field of a rotor stage in an axial compressor based on its steady solution. Because GNNs are able to operate directly on the high-fidelity CFD mesh, we are able to retain the spatial resolution necessary to depict more complex flow behaviour. Consequently, the fidelity of our predictions can compete with conventional high-accuracy flow simulations. Our model is capable of predicting the velocity, pressure, density, and temperature field of a single rotor stage from a 4½-stage axial compressor test case and shows significant improvements compared to the steady state solution, while also being substantially faster than conventional unsteady CFD simulations.
Multi-Objective Numerical Optimization of Radial Turbines
Authors: Fuhrer Christopher , Kovachev Nikola , Vogt Damian M. , Mahalingam Ganesh Raja , Mann Stuart 
Published: September 2023

Abstract
The growing demand of high flexibility and wide operating ranges of radial turbines in turbocharger applications necessitates new methods in the turbomachinery design process. Often, design criteria such as high performance at certain operating conditions or low inertia contradict the requirement for high durability. This paper demonstrates a newly developed optimization approach for radial turbines that allows to optimize for several design objectives. The presented approach is based on a parametric model of the turbine wheel geometry.
On the one hand, the model is designed to capture the most important geometry and design features, and on the other hand, it is flexible for use on various machines. A surrogate model-based genetic algorithm is used to optimize the geometries with respect to several objectives, including efficiency, durability (HCF), Low-Cycle Fatigue (LCF), inertia and mass. Certain operating points or criteria can be particularly emphasized and specified constraints throughout the process allow for customized optimization. The simulations underlying the optimization are state-of-the-art CFD and FE analyses, involving the respective components.
The newly developed and fully automated approach includes tasks of different disciplines. In the end, a selection of several promising geometries is examined more intimately to finally find a most suitable geometry for the given application. For the current study, this geometry has been manufactured and tested on a hot-gas-test facility to successfully validate the design process.
Effect of Centrifugal Force of Gas Film on the Load Capacity of Thrust Gas Bearing
Authors: Kim Daejong 
Published: September 2023

Abstract
A modified Reynolds Equation including centrifugal force of gas film was derived, and it was used to study the effect of gas film centrifugal force and associated streamline on the load capacity of both rigid and foil thrust bearings operating in hydrodynamic and hybrid modes. The thrust bearings have 6 pads with an outer diameter of 82 mm and an inner diameter of 47 mm with typical aper-flat geometry. The setup for the simulations is a single-acting air thrust bearing operating at various ambient pressures and isothermal temperature. Air was chosen for the gas film for the investigations, but the modified Reynolds Equation can handle any general gas films through non-dimensional parameter governing the centrifugal force. The simulations were performed with varying ambient pressure from 1 to 9 bar. The simulation results at different ambient pressures and temperatures are presented in forms of pressure profiles, streamlines, and bearing’s load capacity. The bearings’ load capacity becomes worse when the centrifugal force is considered at very low temperature, and the reduction of the load capacity grows more noticeable with the increase of the ambient pressure and the decrease of the ambient temperature. However, at higher temperature where centrifugal force is not large enough to create large leakage, the centrifugal force helps to redistribute the streamline to favorable way to increase the load capacity.
Aerodynamic Parametrization of Last Stage Steam Turbine Blades
Authors: Schippling Stefan , Fuhrer Christopher , Vogt Damian M. 
Published: September 2023

Abstract
The present paper introduces a novel method to parametrize blade profiles of last stage steam turbines with aerodynamic data. This offers the possibility to specifically influence the flow in order to reduce thermodynamic relaxation losses without changing the desired expansion and redirection of the flow from the ini-tal blade profile. The idea is that the flow channel between two adjacent blades can be regarded as a bent nozzle and the nozzle contour is calculated using aerodynamic data. This nozzle is bent over an ideal streamline, which represents the desired flow redirection, and completed with leading and trailing edges to form a blade profile. In the presented parametrization, the expansion rate is used as variable to adapt the blade profile, as it has a direct influence on condensation and thus thermodynamic relaxation losses. In addition to the distribution of the expansion rate and static pressure along the streamline, the coordinates of the streamline, the total pressure and total enthalpy at the inlet of the profile as well as the distance of the throat are necessary to describe the blade geometry. The new aerodynamic parametrization is capable of accurately representing a Laval-nozzle and a stator cascade. With adapting expansion rates, wetness losses are reduced by 3.5 % for the nozzle and by 2 % for the blade profile.