bluuebunny/crossref_metadata_2025 huggingface dataset:
Design Tools to the Best Coupling of Dry-Friction Solid Underplatform Dampers to Turbine Blades
Authors: Gastaldi Chiara , Gola Muzio M.
Published: November 2019

This work completes the recent authors efforts in the frame of solid dampers optimization, whose goal are to develop systematic design tools to identify the best choice of an underplatform damper (shape, size) matching with a blade (size, modal features) in a turbomachine.

Step 1 was to filter out all those geometries that would lead to undesirable kinematics and contact forces. Step 2 was to identify those ranges of parameters that are better in terms of added stiffness and damping.

The purpose of this third and final step is to complete the picture by exploring how the basic geometrical design parameters of blades interact with the damper parameters and where (i.e., for which parameters combination) a designer may find the best match in view of the vibratory response under resonant excitation. The main focus is on the blades HCF safety. While steps 1 and 2 are based on simple geometrical considerations, this step 3 requires a non-linear coupled dynamic analysis of the system. It is demonstrated how the variation of crucial parameters (e.g. neck thickness, damper geometry, centrifugal force) affects the performance of a real damper coupled to a realistic blade. The method, based on reasonable simplifications, is illustrated and proposed as a tool to make the analysis attractive to designers in the early design stage by guiding their initial choice of an optimal dry friction damper.
A Statistical Characterization of the Effects and Interactions of Small and Large Mistuning on Multistage Bladed Disks
Authors: Kurstak Eric , D’Souza Kiran
Published: November 2019

As turbomachinery systems continue to push the limits of modern technology, the modeling techniques being developed also continue to push modern computational limits. While modeling the pristine system during the design process is important, it is equally important to model behavior of mistuned systems, due to wear or manufacturing processes. This work carries out a statistical analysis on a two-stage system consisting of integrally bladed rotors. Various forms of large geometric mistuning, such as missing mass, bends, and dents, are considered. These forms of large mistuning are based on previously reported damage seen in actual engines that have ingested volcanic ash. This work also aims to investigate the interaction of these large mistuned systems with various levels of small mistuning to further understand this complex interaction. For every case studied, a reduced order model will be constructed that includes the effects of small and large mistuning. Large mistuning will only be applied to a single sector of a single stage. Random patterns of small mistuning will be applied to each case of large mistuning after which a modal analysis and a forced response analysis are run. By observing the energy distribution of each mode for the mistuned system, a qualitative trend can be created between various types and levels of large mistuning and the impact they have on changing the dynamics of the multistage system. The amplification factors from the forced response analyses help in understanding the impact small mistuning has when coupled with large mistuning and when the effects of small mistuning dominate over the large mistuning effects.
Vibration Based Condition Monitoring of Helicopter Gearboxes Based on Cyclostationary Analysis
Authors: Mauricio Alexandre , Zhou Linghao , Mba David , Gryllias Konstantinos
Published: November 2019

The core of a helicopter drivetrain is a complex planetary main gearbox (MGB) which reduces the high input speed generated by the engines in order to provide the appropriate torque to the main rotors and to other auxiliary systems. The gearbox consists of various shafts, planetary gears and bearings and operates under varying conditions under excessive friction, heat and high mechanical forces. The components are vulnerable to fatigue defects and therefore Health and Usage Monitoring Systems (HUMS) have been developed in order to monitor the health condition of the gearbox, focusing towards early, accurate and on time fault detection with limited false alarms and missed detections. The main aim of a HUM System is by health monitoring to enhance the helicopters’ operational reliability, to support the maintenance decision making, and to reduce the overall maintenance costs. The importance and the need for more advanced and accurate HUMS have been emphasized recently by the post-accident analysis of the helicopter LN-OJF, which crashed in Norway in 2016. During the last few decades various methodologies and diagnostic indicators/features have been proposed for the monitoring of rotating machinery operating under steady conditions but still there is no global solution for complex structures. A new tool called IESFOgram has been recently proposed by the authors, based on Cyclostationary Analysis, focusing on the accurate selection of a filtering band, under steady and varying speed conditions. Moreover the Cyclic Spectral Coherence is integrated along the selected frequency band leading to an Improved Envelope Spectrum. In this paper the performance of the tool is tested on a complex planetary gearbox, with several vibration sources. The method is tested, evaluated and compared to state of the art methods on a dataset captured during experimental tests under various operating conditions on a Category A Super Puma SA330 main planetary gearbox, presenting seeded bearing defects of different sizes.
Investigation on Unsteady and Steady Swirling Inflow Effect on Turbocharger Turbine Performance
Authors: Ding Zhanming , Zhuge Weilin , Zhang Yangjun , Chen Yingjie , Liu Chang
Published: November 2019

Turbocharger has experienced a prompt expansion in vehicle industry in recent years, because it enables downsizing of internal combustion engines (ICEs) so as to cutting down CO2 emissions. Turbocharger turbine efficiency is vital for the performance and emission of ICEs. Conventionally, turbines are designed and optimized under steady and uniform inflow conditions, but they are always fed with pulsating and swirling inflow on ICEs. Understanding turbine behaviors under enginelike unsteady swirling inflow conditions is significant to improve turbine on-engine performance.

The purpose of the present study is to examine and compare the unsteady and steady swirling inflow effect on turbocharger turbine performance. The investigation reveals that the turbine suffers substantial efficiency reductions under swirling inflow conditions, no matter under unsteady or steady state, and the efficiency reductions are related with the intensity of inlet swirls. The unsteady and steady swirling inflow leads to reductions in both the absolute and relative flow angles. The swirling inflow results in different effect on turbine performance under unsteady state from steady state. Time lags exist between the unsteady swirling inflow affect the turbine performance. Besides, unsteady swirling inflow effect lead to fluctuations of turbine performance parameters, which discloses a coupled effect of the unsteady and swirling inflow. The unsteady effect and the swirling inflow effect do not simply superpose with each other, but have complicated interactions with each other. Both pulsating and swirling inflow can lead to circumferential flow distortions at rotor inlet by themselves, and when turbine is fed with both pulsatile and swirling inflow together the circumferential flow distortion would be result of their synergetic effect.
Application of Design-for-LCA Methodology to Compare Architectural Alternatives for the Compressor Rotor of an Industrial Gas Turbine
Authors: Musacchio Alessandro , Vicarelli Mattia , Colantoni Simone , Bartocci Pietro , Fantozzi Francesco
Published: November 2019

Nowadays a preliminary assessment on environmental impact of a new product is becoming more and more important. It is useful for a designer to access to a comprehensive methodology that supports configuration assessments taking into account the whole product lifecycle from the beginning of conceptual phase. To develop a competitive product, and particularly a gas turbine, each design trade-off needs to be performed considering not only the typical parameters such as performances, life and costs but also the cradle-to-grave environmental impact.

Scope of the following paper is the application of design-for-Environment methodology to different architectures of GT compressor rotor module. Three design alternatives are analyzed and compared in terms of ELCA considering their design, material selection, manufacturing process and operating life. Specific considerations are proposed as a result of the combination of traditional design practices with environmental assessment.

This study highlighted that number of parts, weight and amount of material removed or scraped that is, in other words, the level of production process optimization, are the key factors to control the environmental impact of a product.
The Role of Turbomachinery Performance in the Optimization of Supercritical Carbon Dioxide Power Systems
Authors: Romei Alessandro , Gaetani Paolo , Giostri Andrea , Persico Giacomo
Published: November 2019

The successful penetration of supercritical carbon dioxide (sCO2) power systems in the energy market largely depends on the achievable turbomachinery performance. The present study illustrates a systematic framework where both the compressor and the turbine are designed via validated (within ±2% pts against experiments) mean-line tools and the related impact on cycle performance estimates is quantitatively and qualitatively assessed. A significant effort is devoted to the analysis of centrifugal compressor performance operating close to the critical point, where sharp thermodynamic property variations may make critical the compression process. The analysis is performed for different compressor sizes and pressure ratios, showing a comparatively small contribution of compressor-intake fluid conditions to the machine efficiency, which may achieve technological competitive values (82 ÷ 85%) for representative full-scale sizes. Two polynomial correlations for both turbomachinery efficiencies are devised as a function of proper similarity parameters accounting for machine sizes and loadings. Such correlations can be easily embedded in power cycle optimizations, which are usually carried out assuming constant-turbomachinery efficiency, thus ignoring the effects of plant size and cycle operating parameters. Efficiency correlations are finally exploited to perform several optimizations of a recompressed sCO2 cycle, by varying multiple cycle parameters (i.e. maximum and minimum temperature, pressure ratio and net power output). The results highlight that the replacement of constant-efficiency assumption with the proposed correlations leads to more accurate performance predictions (i.e. cycle efficiency can differ by more than 4% pts), showing in particular that an optimal pressure ratio exists in the range 2 ÷ 5 for all the investigated configurations.
The Effect of Rated Climb Performance on Low Cycle Fatigue of a Civil Turbojet Engine
Authors: König Jonas , Weißschuh Matthias , von Ende Sven , Staudacher Stephan
Published: November 2019

Low cycle fatigue (LCF) of jet engine disks is a major contributor to the maintenance costs of an engine. The current industry standard for the analysis of LCF is to use representative flight missions to reflect the in-service usage of engines. Based on the engine performance during those missions, the internal stresses and temperatures of life-critical components are calculated. These stresses and temperatures define the cyclic life consumption of a mission and determine the certifiable LCF life of the engine. The engine performance is defined by the power setting schedules of the engine, so-called engine ratings. The effect of the rated climb performance on high pressure turbine disk life is investigated for a generic two-shaft engine operated in a small twin-jet civil aircraft. LCF life is analyzed using a finite element-based cycle counting model. The aircraft climb performance resulting from the changed climb ratings is assessed with an aircraft performance model. It is shown that there are climb ratings which result in reduced LCF life consumption and climb time compared to the reference rating. Employing these ratings on in-service engines increases the certifiable life count and reduces maintenance costs.
Experimental Investigation of a RQL Burner With Jet in Cross Flow Fuel Injection: Characterization of the Reacting Flow Field at Realistic Operating Conditions
Authors: Soworka T. , Behrendt T. , Hassa C. , Heinze J. , Magens E. , Schroll M. , di Mare F. , Ballantyne S. , Gregory J.
Published: November 2019

Future rich-burn/quick-quench/lean-burn (RQL) burners for aero engines face the challenge to further reduce the emission of soot. Alternative ways of fuel injection are therefore in the focus of modern RQL combustion systems. This contribution aims to investigate experimentally the influence of fuel injection on the reacting flow field, with the emphasis on soot production in the primary zone. For the test, a Rolls-Royce prototype burner was used in two different configurations which differ only in the axial location of jet in cross flow fuel injection and thereby provoke different ways of fuel atomization. In the upstream configuration the burner features characteristics of a pre-filming airblast atomizer. Whereas with the fuel tip in downstream position solely Jet-in-Cross-Flow fuel atomisation is expected. The burner was tested at realistic aero engine combustor conditions (p30 = 9.28 bar, T30 = 603 K, AFR = 7.6). Several optical measurement techniques were used to characterise the reacting flow field. Their difficult application in a rich burn environment is described briefly. The structure of the reacting flow field is illustrated by Particle-Image-Velocimetry (PIV). Planar Mie scattering and Planar Laser-Induced Fluorescence (PLIF) are used to characterise the placement of liquid and gaseous fuel respectively. The location and structure of heat release zones are captured in terms of OH* and CO2* chemiluminescence. Finally Laser-Induced-Incandescence (LII) is used to obtain three dimensional soot distributions in the primary zone. On this basis 20% less soot was measured for the upstream configuration at the axial location of maximal soot concentration. This remarkable difference could be attributed to the different placement of liquid fuel and the resulting better mixing.
Computational and Experimental Study of Hot Streak Transport Within the First Stage of a Gas Turbine
Authors: Gaetani Paolo , Persico Giacomo , Pinelli Lorenzo , Marconcini Michele , Pacciani Roberto
Published: November 2019

The paper discusses the migration, the interaction with the blades, and the attenuation of hot streaks generated by combustor burners, during their propagation within the first turbine stage of aero-engines. Experiments and Computational Fluid Dynamic (CFD) simulations were carried out in the framework of the European Project RECORD and on its follow-up. Measurements considering burner-representative temperature perturbations injected upstream of an un-cooled high-pressure gas turbine stage were performed in the high-speed closed-loop test-rig of the Politecnico di Milano (Italy). The hot streaks were injected in streamwise direction at the stage inlet in four different circumferential positions with respect to the stator blade. They feature a 20% over-temperature with respect to the main flow. Detailed temperature measurements as well as unsteady aerodynamic measurements upstream and downstream of the blade rows were performed. Time-accurate CFD simulations of the flow upstream and within the turbine stage were performed with the TRAF code, developed by the University of Florence. Measurements show a relevant attenuation of hot streaks throughout their transport within the stator and the rotor blade rows, highly depending on the injection azimuthal position. The perturbations were observed to lose their spatial coherence, especially in the transport within the rotor, and to undergo severe spanwise migration. Simulations exhibit a good agreement with the experiments on the measurement planes and allow tracking the complex flow phenomena occurring within the blade rows. Finally the aerodynamic and thermal implications of the inlet temperature perturbations are properly highlighted and discussed.
Reducing Secondary Flow Losses in Low-Pressure Turbines With Blade Fences: Part I — Design in an Engine-Like Environment
Authors: Rubechini Filippo , Giovannini Matteo , Arnone Andrea , Simoni Daniele , Bertini Francesco
Published: November 2019

This paper deals with the design of passive control devices for reducing the impact of secondary flows on the aerodynamics of low-pressure turbine (LPT) stages. A novel kind of device is introduced which consists of shelf-like fences to be added to the blade surface. Such a device is intended to hinder the development of secondary flows, thus reducing losses and flow turning deviation with respect to the straight blade.

The first part of this work is devoted to the design of the blade fences, whereas the second part addresses the experimental validation of the device. The blade fences are designed on a LPT stator vane, in an engine-like environment. As secondary flows generated by one blade row produce their major effects on the downstream one, and hence on the stage performance, the assessment is performed on a stator-rotor configuration. Steady calculations are considered for the design, then the optimal geometry is verified via unsteady calculations to include the effects of the actual interaction. The geometry and layout of the blade fences are effectively handled by means of a parametric approach, which enables the fast generation of several configurations. An optimization procedure, based on Artificial Neural Networks (ANNs) is exploited to drive the fences design. The analysis of the relative merit of each solution is carried out using a state-of-the-art CFD approach. Finally, a detailed comparison between the original blade and the one equipped with fences is presented, and the physical mechanisms responsible for the mitigation of secondary flow losses are discussed in detail.
Nonsynchronous Vibration Associated With Transonic Fan Blade Untwist
Authors: Lu Yaozhi , Lad Bharat , Vahdati Mehdi , Stapelfeldt Sina C.
Published: November 2019

Due to manufacturing tolerance and deterioration during operation, fan blades in the aero-engine exhibit geometric variability. This leads to asymmetry in the assembly which will be amplified in the running geometry by centrifugal and aerodynamic loads. This study investigates a phenomenon known as Alternative Passage Divergence (APD), where the blade untwist creates an alternating pattern in passage geometry and stagger angle around the circumference, resulting in two groups of blades. This phenomenon occurs close to, or at, peak efficiency conditions and can significantly reduce overall efficiency. This study focuses on a type of non-integral vibration which occurs during APD. After the formation of alternating tip stagger pattern, APDs unsteady effect can cause the blades from one group to switch to the other, creating a travelling wave pattern around the circumference.It was found from numerical assessment on a randomly mis-staggered assembly that real engines can potentially experience such travelling disturbance and suffer fatigue damage. An idealised case is used to capture the bulk behaviour from the more complex cases in real engines and to decipher the underlying mechanism of this travelling disturbance. The results indicate that the driving force originates from the interaction between passage shock displacement and the passage geometry.
Prediction of Film Thickness of an Aero-Engine Bearing Chamber Using Coupled VOF and Thin Film Model
Authors: Singh Kuldeep , Sharabi Medhat , Ambrose Stephen , Eastwick Carol , Jefferson-Loveday Richard
Published: November 2019

In the present work, a coupled volume-of-fluid (VOF) model with Eulerian thin-film model (ETFM) approach is used to predict the film thickness in an aero-engine bearing chamber. Numerical studies are conducted for a wide range of shaft speeds with lubricant and air flow rates of 100 1/hr and 10 g/s respectively, at a scavenge ratio of 4 on a simplified bearing chamber test rig. Air-flow analysis inside the bearing chamber is also assessed. Primary and secondary airflow predictions are found to be in good agreement with the experimental results. The coupled ETFM+VOF approach is found to be sensitive enough to capture the qualitative trend of oil film formation and distribution over the chamber wall. Oil collection near the sump at a low shaft speed and a rotating oil film at a higher shaft speed are well captured.
Analysis of Composite Blade/Casing Rub Stability Through Delayed Differential Equations
Authors: Xiao Jiaguangyi , Chen Yong , Tian Jie , Ouyang Hua , Wang Anjenq
Published: November 2019

To improve aerodynamic efficiencies, the clearances between blades and casings are becoming smaller and smaller in the aero-engine industry, which might lead to the interactions between these components. These unexpected interactions are known as the so called blade/casing rubs. Abradable materials are implemented on the inner surface of the casings to reduce the potential damages caused by it. However, failures may still arise from blade/casing rubs according to experimental investigations and actual accidents.

In this paper, a reduced-order delayed differential equations are used to simplify the rubbing process between composite blade and casing. It is assumed that the removal of the abradable material in blade/casing rubbing process shares a resemblance with machine tool chatters encountered in machining. The delayed differential equations are established with centrifugal stiffness and the impacts of stacking sequences on the blade damping taking into consideration. Semi-Discretization Method (SDM) is used to study the stabilities of the simplified system, which is verified by Cluster Treatment of Characteristic Roots (CTCR) and direct integrations. The results show that the stacking sequences, rub positions, blade damping and stiffness could have much impact on the relatively dangerous interaction regimes. With the help of this method, one can assist the design processes of the composite blade-casing interface in initial aero-engine structural designs.
Numerical Investigations of Pollutant Emissions From Novel Heavy Duty Gas Turbine Burners Operated With Natural Gas
Authors: Pampaloni Daniele , Nassini Pier Carlo , Andreini Antonio , Facchini Bruno , Cerutti Matteo
Published: November 2019

A numerical investigation of pollutant emissions of a novel dry low-emissions burner for heavy-duty gas turbine applications is presented. The objective of the work is to develop and assess a robust and cost-efficient numerical setup for the prediction of NOx and CO emissions in industrial gas turbines and to investigate the pollutant formation mechanisms, thus supporting the design process of a novel low-emission burner. To this end, a comparison against experimental data, from a recent experimental campaign performed by BHGE in cooperation with University of Florence, has been exploited.

In the first part of this work, a RANS approach on both a simplified geometry and the complete domain is adopted to characterize the global flame behavior and validate the numerical setup. Then, unsteady simulations exploiting the Scale Adaptive Simulation (SAS) approach have been performed to assess the prediction improvements that can be obtained with the unsteady modelling of the flame.

For all simulations, the Flamelet Generated Manifold (FGM) model has been used, allowing the reliable and cost-efficient application of detailed chemistry mechanisms in CFD simulation. However, FGM typically faces issues predicting flame emissions, such as NOx and CO, due to the wide range of time scales involved, from turbulent mixing to pollutant species oxidation. Specific models are typically used to predict NOx emissions, starting from the converged flow field and introducing additional transport equations. Also CO prediction, especially at part-load operating conditions could be an issue for flamelet-based model: in fact, as the load decreases and the extinction limit approaches, a super-equilibrium CO concentration, which cannot be accurately predicted by FGM, appears in the exhaust gases. To overcome this issue, a specific CO burn-out model, following the original idea proposed by Klarmann, has been implemented in ANSYS Fluent. The model allows to decouple the effective CO oxidation term from the one computed by FGM, defining a post-flame zone where the source term of CO is treated following the Arrhenius formulation.

In order to support the design process, an in-depth CFD investigation has been carried out, evaluating the impact of an alternative burner geometrical configuration on stability and emissions and providing detailed information about the main regions and mechanisms of pollutants production. The outcomes support the analysis of experimental results, allowing an in-depth investigation of the complex flow-field and the flame-related quantities, which have not been measured during the tests.
Impact of Wall Temperature in Large Eddy Simulation of Light-Round in an Annular Liquid Fueled Combustor and Assessment of Wall Models
Authors: Puggelli S. , Lancien T. , Prieur K. , Durox D. , Candel S. , Vicquelin R.
Published: November 2019

The process of ignition in aero-engines raises many practical issues that need to be faced during the design process. Recent experiments and simulations have provided detailed insights on ignition in single-injector configurations and on the light-round sequence in annular combustors. It was shown that Large Eddy Simulation (LES) was able to reliably reproduce the physical phenomena involved in the ignition of both perfectly premixed and liquid spray flames. The present study aims at further extending the knowledge on flame propagation during the ignition of annular multiple injector combustors by focusing the attention on the effects of heat losses, which have not been accounted for in numerical calculations before. This problem is examined by developing Large Eddy Simulations of the light-round process with a fixed temperature at the solid boundaries. Calculations are carried out for a laboratory-scale annular system. Results are compared in terms of flame shape and light-round duration with available experiments and with an adiabatic LES serving as a reference. Wall heat losses lead to a significant reduction in the flame propagation velocity as observed experimentally. However, the LES underestimates this effect and leads to a globally shorter light-round. To better understand this discrepancy, the study focuses then on the analysis of the near wall region where the velocity and temperature boundary layers must be carefully described. An a-priori analysis underlines the shortcomings associated to the chosen wall law by considering a more advanced wall model that fully accounts for variable thermophysical properties and for the unsteadiness of the boundary layer.
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

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

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

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

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

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

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

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

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

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.