bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multi-Disciplinary Tool Coupling for the Determination of Turbofan Transients During Preliminary Design
Authors: Vieweg M. , Wolters F. , Reitenbach S. , Hollmann C. , Becker R.-G. 
Published: November 2019

Abstract
Over the past decades of preliminary aero-engine design a great effort has been invested in increasing steady-state efficiency to reduce missions fuel burn and thus CO2 emissions. Whilst pushing the performance cycle further to its limits previously minor deemed processes such as the transient behavior become more important because engines stability must still be granted for. It is therefore beneficial to integrate transient performance early into the overall aero-engine design tool chain to be able to predict the dynamic behavior from the beginning.
This paper presents a methodology to couple predesign and transient performance simulation in order to get a more holistic picture of aero-engines early in the design process. This procedure entails extensive amount of data transfer throughout multi-disciplinary tools with different fidelity levels. This task is tackled using DLRs virtual engine platform GTlab (Gas Turbine Laboratory), which provides a geometric data model with abstract description of predesign components and standardized interfaces for data exchange. In order to demonstrate the proposed methodology a performance model of a turbofan similar to the V2500 aero-engine is used. For that purpose, a performance cycle is established providing boundary conditions for the preliminary aerodynamic engine design. The designed components provide necessary input data for the subsequent transient certification maneuver Eventually, parametric studies are conducted to show the impact of design variations on transient data such as the minimum surge margin and minimum tip clearance as well as on preliminary engine design.
Automatic Numerical Analyses and Optimization of Operating Maps Applied to a Radial Compressor
Authors: Wagner Markus , Einzinger Johannes , Velde Oliver , Lampert Ralf 
Published: November 2019

Abstract
This paper contributes to the field of radial compressor design by proposing an adaptive, automated workflow incorporating the analysis of the compressor performance for a multitude of operation points by means of the respective operating maps. Most state-of-the-art approaches do not consider that the operating map limits are not conserved while changing geometric parameters which constraints these analyses to a rather small design space. In contrast, the presented methodology considers the varying operating map limits in regards to the corresponding mass flow and with that expands the possible input parameter range.
The presented workflow integrates different software solutions, starting with the automated generation of the compressor geometry based on a parametric CAD model. For each geometry a mesh is generated that is used for all subsequent CFD simulations which finally result in the operating map. For every speed line, the choke point is identified by an adaptive CFD computation (based on the principle of similarity). By using the calculated choke mass flow, supplementary CFD simulations obtain additional operating points on the current speed line by a stepwise reduction of the mass flow.
However, the identification of the surge line is not within the scope of the presented approach. Therefore, the range covered by the map is determined by the mass flow at the maximum efficiency and the mass flow at the choke line.
The developed framework is applied to optimize the operating map of a radial compressor. A successful optimization shows that the optimized design has an enlarged choke mass flow for lower compressor speed while the pressure ratio and polytropic efficiency are comparable. At the same time, this design has a comparable choke mass flow and efficiency for higher compressor speed, but an improved maximal pressure ratio. The obtained results from the optimization show that the methodology is applicable to a wide parameter range. By adaptively calculating the operating map limits, the approach is not restricted to a small design space.
Investigating Ethanol-Gasoline Spray Characteristics Using an Interferometric Drop Sizing Technique
Authors: Davies Hywel , Talibi Midhat , Hyde Martin , Balachandran Ramanarayanan 
Published: November 2019

Abstract
To reduce reliance on fossil fuels there has been a global push to minimise fuel consumption, and incorporate the use of bio-derived fuels. In practical combustion systems that use liquid fuels, observing the spray behaviour of these biofuels is key in understanding fuel performance; in particular, droplet size distribution is known to have a strong influence on the fuel energy release and pollutant formation processes. This paper is aimed at the use of the TSI Global Sizing Velocimetry (GSV) interferometric technique as a method to gain detailed understanding of droplet number and size distribution, with a particular focus on ethanol-gasoline fuel blends.
The imaging system for the GSV technique consisted of a Nd:YAG laser and a 4 MP (million pixel) camera, and the spray was generated using a generic automotive port fuel injector. The results showed that the GSV technique was able to effectively measure droplet concentration and diameters for all the fuel blends tested in this study. Ethanol was observed to have larger droplet diameters (both D10 and D32) as compared to fossil gasoline, with droplet diameters generally increasing as the proportion of ethanol in the gasoline was increased. The droplet concentration reduced with increasing radial distance from the spray centreline, but no appreciable change was observed with axial displacement from the nozzle tip. Degradation in the image quality was observed for fuel blends with less than 40% ethanol content. The GSV drop sizing measurements were validated using a mono-disperse droplet generator, and an excellent agreement (within 2%) was observed.
Modeling Effusion Cooling and Conjugate Heat Transfer Using Local Source Method
Authors: Gottiparthi Kalyana C. , Cao Changmin , Sankaran Vaidyanathan 
Published: November 2019

Abstract
Aerodynamic cooling of hot components/surfaces such as those encountered in gas turbine engines is needed to avoid premature failure of parts due to thermo-mechanical stresses. An effective way of achieving this cooling is through the exchange of heat via effusion/film cooling holes on the hot surfaces. The gases absorb heat as they flow through the cooling holes and also by forming a protective layer of relatively cool gases near the hot surface. Modeling these processes allow for durable design of components and computational simulations offer a complementary way to design new parts or enable performance assessment of the existing parts at new operating conditions. However, in order to perform numerical simulations of heat transfer through effusion holes, the heat conduction through the solid liner and the convection from the gas phase must be coupled considering all the relevant length and time scales. The time scale separation between the solid and the gas phase makes this prohibitively expensive for large scale computations. In applications involving hundreds of effusion holes, resolving the geometry of each effusion hole along with the primary flow (with typically larger length scales) is very challenging. In the current work, we overcome the difficulties associated with the resolution of cooling holes by employing a local source method (Andreini et al, J. Eng. Gas Turb. Power, 2014) to model the heat transfer to the walls. This method is assessed in a canonical configuration based on experiments performed by Gustafsson (Gustaffson, Ph.D. Thesis, 2001).
Large Eddy Simulations (LES) coupled with conjugate heat transfer (CHT) models are used in this study. Simulations that resolve the flow passages explicitly using mesh both in the fluid and the solid domains, were used to validate the fidelity of grid resolution, turbulence models and other simulation parameters in predicting velocity fields and wall temperature data. Although, resolving all the effusions passages provides the most accurate results, it is not practical in real applications. Hence, a local source model is employed to model the heat transfer that happens in the cooling-hole passages. In this method, the effusion passage is not resolved (using a mesh) and the mass transfer across the cooling hole passage is prescribed as an injection-extraction boundary condition. The heat transfer at the fluid-solid interface of the cooling-hole passage is also modeled based on Nusselt number correlations available in the literature. This modeling procedure enables simulations with flexible mesh topologies that can be generated at a relatively low cost in comparison to the fully resolved mesh configurations. The local source method is assessed and validated using the available experimental data. The results show that the meshes which resolve the penetration depth in the solid and which conform at the solid-gas interface provide better prediction of the wall temperatures.
Multiphysics Numerical Investigation of an Aeronautical Lean Burn Combustor
Authors: Bertini D. , Mazzei L. , Andreini A. , Facchini B. 
Published: November 2019

Abstract
The importance of the combustion chamber has been underestimated for years by aeroengine manufacturers that focused their research efforts mainly on other components, such as compressor and turbine, to improve the engine performance. Nevertheless, stricter requirements on pollutant emissions have contributed to increase the interest on combustor development and, nowadays, new design concepts are widely investigated. To meet the goals of ACARE FlightPath 2050 and future ICAO-CAEP standards one of the most promising results is provided by the Lean Burn technology. As this combustion mode is based on a lean Primary Zone, the air devoted to liner cooling is restricted and advanced cooling systems must be exploited to obtain higher overall effectiveness. The pushing trends of Turbine Inlet Temperature and Overall Pressure Ratio in modern aeroengine are not supported enough by the development of materials, thus making the research branch of liner cooling increasingly relevant.
In this context, Computational Fluid Dynamics is able to predict the flow field and the complex interactions between the involved phenomena, supporting the design of modern Lean Burn combustors in all stages of the process. RANS approaches provide a solution of the problem with low computational cost, but can lack in accuracy when the flow unsteadiness dominates the fluid dynamics and the strong interactions, as in aeroengine combustors. Even if steady simulations can be easily employed in the preliminary design, their inaccuracy can be detrimental for an optimized combustor design and Scale-Resolving methods should be preferred, at least, in the final stages. Unfortunately, having to deal with a multiphysics problem as Conjugate Heat Transfer (CHT) in presence of radiation, these simulations can become computationally expensive and some numerical treatments are required to handle the wide range of time and space scales in an unsteady framework.
In the present work the metal temperature distribution is investigated from a numerical perspective on a full annular aeronautical lean burn combustor operated at real conditions. For this purpose, the U-THERM3D multiphysics tool was developed in ANSYS Fluent and applied on the test case. The results are compared against RANS and experimental data to assess the tool capability to handle the CHT problem in the context of scale-resolving simulations.
Transient Modeling of 10 MW Supercritical CO2 Brayton Power Cycles Using Numerical Propulsion System Simulation (NPSS)
Authors: Tang Ching-Jen , McClung Aaron , Hofer Douglas , Huang Megan 
Published: November 2019

Abstract
Four different control methods for ramping down the power output from a Supercritical Carbon Dioxide (sCO2) simple cycle were studied to support the development of 10 MWe Pilot Plant Test Facility, funded by the US Department of Energy. These detailed transient models are written using NPSS (Numerical Propulsion System Simulation). The main components of the NPSS models include a compressor, turbine, High-Temperature Recuperative heat exchanger (HTR), cooler, heater, pipes, and valves. In the transient models, the thermal mass and CO2 fluid volume for each main component are based on representative data or proven design practices for the corresponding component. The steady-state performance of each main component has been validated with representative data while the transient performance of the HTR has been validated with published experimental data. The models have been used to study the methods to ramp down the power output. The methods include extracting the CO2 from the inventory, reducing the opening of turbine inlet throttle valve, and increasing the temperature of the cooling water entering the cooler. These methods, along with a hybrid method of combining the first two methods, were evaluated for the rate of turndown in the power output, operability of the compressor, and cycle efficiency. The preliminary results suggest that inventory extraction is the most efficient but has a slow turndown rate while turbine throttle control is less efficient but results in a faster turndown rate. In addition, the inventory extraction reduces the margin of the compressor choke line but the turbine throttle control increases the margin of the choke line.
Time-Resolved Flow Field Analysis of Effusion Cooling System With Representative Swirling Main Flow
Authors: Lenzi T. , Palanti L. , Picchi A. , Bacci T. , Mazzei L. , Andreini A. , Facchini B. , Vitale I. 
Published: November 2019

Abstract
Film cooling jets behaviour in a combustor chamber is deeply affected by swirling flow interactions and unsteadiness; on the other hand, the jets behaviour has a direct impact on different phenomena such as cooling capabilities and ignition. For these reasons, an in-depth characterization of the film-cooling flows in the presence of a swirling mainflow, demands dedicated time-resolved analyses. The experimental setup consists of a non-reactive single-sector linear combustor simulator installed in an open loop wind tunnel. It is equipped with a swirler and a multiperforated plate to simulate the effusion cooling system of the liner. The rig is scaled with respect to the engine configuration, to increase spatial resolution and to reduce the characteristic frequencies of the unsteady phenomena. Time-Resolved Particle Image Velocimetry (TRPIV) was exploited for the investigation testing different values of liner pressure drop. In addition, numerical investigations were carried out to gain a deeper insight of the behaviour highlighted by the experiments and to assess the capability of CFD in predicting the flow physics. In this work, the Stress-Blended Eddy Simulation (SBES) approach implemented in ANSYS Fluent was adopted.
Oscillations of the jets and intermittent interactions of the mainstream with the wall of the liner and hence with the film development have been investigated in detail. The results demonstrate how an unsteady analysis of the flow structures that characterize the jets, the turbulent mixing of coolant flows and the interaction between mainstream and cooling jets is strictly necessary to have a complete knowledge of the behaviour of the coolant which in turn affects combustor operability and life-time.
Performance Assessment of an Integrated Parallel Hybrid-Electric Propulsion System Aircraft
Authors: Sahoo Smruti , Zhao Xin , Kyprianidis Konstantinos G. , Kalfas Anestis 
Published: November 2019

Abstract
Hybrid-electric propulsion system promises avenues for a greener aviation sector. Ground research work was performed in the past for the feasibility assessment, at the system level, for such novel concepts and the results showed were promising. Such designs, however, possess unique challenges from an operational point of view, and for sizing of the sub-system components; necessitating further design space exploration for associating with an optimal operational strategy. In light of the above, the paper aims at presenting an operational analysis and performance assessment study, for a conceptualised parallel hybrid design of an advanced geared turbofan engine, based on 2035 timeframe technology level. It is identified that the hybrid power operation of the engine is constrained with respect to the requirement of maintaining an adequate surge margin for the low pressure side components; however, a core re-optimised engine design with consideration of electrical power add-in for the design condition, relieves such limit. Therefore such a design, makes it suitable for implementation of higher degree of hybridisation. Furthermore, performance assessment is made both at engine and engine-aircraft integrated level for both scenarios of hybrid operation and the benefits are established relative to the baseline engine. The performance at engine level engine specific fuel consumption (SFC), thrust specific power consumption (TSPC), and overall efficiency, shows improvement in both hybridised scenarios. Improvement in SFC is achieved due to supply of the electrical power, whereas, the boost in TSPC, and overall efficiency is attributed to the use of higher efficiency electrical drive system. Furthermore, it is observed that while the hybridised scenario performs better at engine level, the core re-optimised design exhibits a better saving for block fuel/energy consumption, due to the considerable weight savings in the core components.
Surface Curvature Effects on Film Cooling Performance for Shaped Holes on a Model Turbine Blade
Authors: Moore Jacob D. , Yoon Christopher , Bogard David G. 
Published: November 2019

Abstract
Surface curvature has been shown to have significant effects on the film cooling performance of round holes, but the literature includes few studies of its effects on shaped holes despite their prevalence in gas turbines. Experiments were performed using two rows of holes placed on the suction side of a scaled-up turbine blade in a low-Mach-number linear cascade wind tunnel with low freestream turbulence. The rows were placed in regions of high and low convex surface curvature, respectively. Geometries and flow conditions for the rows were matched to those from previous flat plate studies. Comparison of the adiabatic effectiveness results from the high curvature and flat plate rows revealed the same trends as those in the literature using round holes — with increased performance for the high curvature row at lower blowing ratios and the opposite at higher ones. The low curvature row had similar performance to the flat plate row at lower blowing ratios, suggesting the mild convex curvature had little beneficial effect. At higher blowing ratios, the low curvature row had inferior performance, which was attributed to the local freestream adverse pressure gradient that generated additional turbulence, promoting jet-to-mainstream mixing and decreasing performance.
A Biogas Fuelled Micro Gas Turbine: Energetic Performance and Environmental Impact Analysis
Authors: Chiariello Fabio , Reale Fabrizio , Calabria Raffaela , Massoli Patrizio 
Published: November 2019

Abstract
The use of biogas in micro gas turbines (MGTs) generally requires invasive structural modifications to fuel compression units, control valves and combustor. Costs associated with the modifications significantly reduce the benefits of a rational and sustainable exploitation of energy resources of lower value as the biogas.
In order to overcome this aspect, in a recent paper the authors proposed a dual fuel approach, identifying a structurally non-invasive and cost-effective technical solution to increase the CO2 concentration in the fuel and to extend the operation domain of the MGT when low calorific value fuels are used. In that study, it has been evaluated, implemented and tested an innovative management strategy of fuel feeding and combustion. Experimental preliminary tests validated the idea of a new supply strategy for exceeding the current limits of biogas exploitation as MGT fuel.
With this approach the MGT operating domain has been extended, increasing more than twice the CO2 concentration limit than experimentally validated limit available in literature.
In this study the authors present a more extensive investigation concerning the energetic performance and the environmental impact of a 100 kWe MGT Turbec T100 when fuelled with a mixture of natural gas and carbon dioxide (synthesis biogas) in the dual fuel approach, by varying CO2 concentration in the fuel at part load condition.
The data acquired by an extensive experimental campaign, in terms of thermodynamic parameters and gaseous exhaust emissions, are presented and compared with the results of numerical simulations.
A 3D CFD analysis of the combustion process is also presented. Initial and boundary conditions of the numerical approach were obtained from a previous validated 0D thermodynamic matching model.
The synergistic activity between numerical modeling and experimental work allows to analyze and explain the overall behavior of the micro gas turbine in the dual fuel mode with biogas fuel.
The study shows that the micro gas turbine can stably operate in a dual fuel mode until the CO2 content rises above 25%.
Effects of Swirl on the Stabilization of Non-Premixed Oxygen Enriched Flames Above Coaxial Injectors
Authors: Degeneve A. , Mirat C. , Caudal J. , Vicquelin R. , Schuller T. 
Published: November 2019

Abstract
An experimental study is carried out to analyze effects of swirl on the structure and stabilization of methane non-premixed oxygen-enriched flames above a co-axial injector in which the two streams are eventually swirled. The mean position of the flame and the liftoff height above the injector lips are investigated with OH* chemiluminescence images. The oxygen enrichement, the momentum flux ratio between the two co-flows, the swirl level inside the central jet and the swirl level in the annular jet are varied over a large range of operating conditions. It is found that, in the absence of swirl in the central stream, the flame is always attached to the lips of the internal injection tube. As the inner swirl level increases, the flame front located at the lips of the internal injection tube disappears. When the annular swirl level is high enough to create a central recirculating bubble, the flame detaches from the nozzle rim and remains lifted at a finite distance above the injector. Increasing the oxygen concentration shifts this transition to smaller momentum flux ratios and smaller annular swirl levels. The lift-off distance can be finely tuned and depends on the inner and outer swirl levels, and on the momentum flux ratio between the two coaxial streams. It is shown that this feature neither depends on the confinement of the injector nor on the thermal stress exerted by the hot burnt gases on the injector back plane. About 1000 configurations were investigated that could be classified into only four distinct stabilization modes, in which the flame structure was shown to follow a similar pathway when the momentum flux ratio between the two streams, the swirl level in the central and external streams and the quarl angle of the annular stream are varied. It is finally shown how these limits are altered when the oxygen concentration in the annular oxidizer stream is varied from air to oxygen-enriched operation.