bluuebunny/crossref_metadata_2025 huggingface dataset:
Erosion Testing of Environmental-Barrier-Coated CMC and its Behavior on an Aero-Engine Turbine Vane Under Particle-Laden Hot Gas Stream
Authors: Okita Yoji , Mizokami Yousuke , Hasegawa Jun
Published: November 2019

Ceramic matrix composite (CMC) has better durability at high temperature and lower material density, as compared to nickel-based super-alloys which have been the standard material for hot section components of aero-engines. Among the CMC materials, SiC-SiC CMC is especially promising with its superior mechanical property at higher temperature. It, however, inevitably needs environmental barrier coating (EBC) to protect the substrate against oxidation. The EBC also needs to have other functions and to meet various requirements. One such very critical requirement is the resistance to sand erosion, although the issue hasn’t been investigated well so far.

The primary contribution of this work is to reveal the erosion resistance of the CMC+EBC material with wind tunnel test data of good quality and to demonstrate what erosion behavior the material exhibits in turbine cascade under particle-laden hot gas stream.

In the present work, erosion tests were first carried out in a testing facility with erosion media of 50 microns silica sand. The tests were conducted under flow velocity of 225 m/s and temperature of 1311 K to simulate typical aero-engine conditions and impact angles of 30, 60, and 80deg were investigated. The obtained data showed a typical brittle erosion mode, where the erosion rate had a positive dependence on the impact angles. A typical erosion model, Neilson-Gilchrist model, was applied to correlate the data and the model was shown to have a good agreement with the experimental data once it was properly calibrated.

Then, the numerical computation solving particle-laden flow was carried out to predict three dimensional flow field and particle trajectories across the target turbine cascade. The erosion profile along the airfoil was calculated based on the obtained trajectories and the calibrated erosion model. The trajectories showed that the particles mostly impinged the airfoil pressure surface first and then the rebounded particles attacked the opposite suction surface as well. Accordingly, the predicted erosion profile showed a broad erosion band across the pressure surface and also some slight erosion peak at around the mid-chord of the suction surface.
Surrogate Model Based Optimization for Chevron Foil Thrust Bearing
Authors: Untaroiu Alexandrina , Fu Gen
Published: November 2019

Gas foil thrust bearings have been utilized in high speed lightweight machines for many decades. These bearings are environment-friendly and capable of withstanding extreme conditions. However, there are also some challenges for foil thrust bearings at high speed conditions, such as insufficient heat dissipation and thermal management. The heat generated by viscous shearing continues to raise the temperature inside the gas film and may cause failures. Among all the methods to enhance heat dissipation, a promising passive thermal management method is modifying the top foil’s trailing edge shape. This modification will enhance the air mixing in between the bearing pads.

The aim of this study is to identify the optimal design of the top foil trailing edge shape and provide a guideline for future bearing design. A 3-D computational fluid dynamics (CFD) model for a thrust foil bearing was created using ANSYS-CFX software. The trailing edge of the top foil was modified to a chevron shape. A sensitivity study was conducted to investigate the connection between the top foil trailing edge shape and the thermal conditions in the gas film. The maximum temperature inside the air gas film is selected as the output. The design of experiments (DOE) technique was used to generate the sampling points. A surrogate model was generated based on the output data by using the neural network method. The surrogate model was used together with a genetic multi-objective algorithm to minimize the maximal temperature inside the gas film and maximize the load carrying capacity. The optimal design was then compared with the baseline model. Results suggest the optimized trailing edge shape is capable of reducing the temperature inside the gas film. This optimal design approach can be used for improvements of chevron foil thrust bearing design.
The Effect of Isentropic Exponent on Transonic Turbine Performance
Authors: Baumgärtner David , Otter John J. , Wheeler Andrew P. S.
Published: November 2019

The isentropic exponent is one of the most important properties affecting gas dynamics. Nonetheless, its effect on turbine performance is not well known. The paper discusses a series of experimental and computational studies to determine the effect of isentropic exponent on the flow field within a turbine vane. Experiments are performed using a newly modified transient wind tunnel which enables annular cascade testing with a wide range of working fluids and operating conditions. For the present study tests are undertaken using air, CO2, R134a and argon, giving a range of isentropic exponent from 1.08–1.67. Measurements include detailed wall static pressures which are compared with computational simulations. Our results show that over the range of isentropic exponents tested here, the loss can vary by between 20%–35%, depending on vane exit Mach number. The results are important for future turbines operating with real-gas effects and/or those where high gas temperatures can lead to variations in isentropic exponent.
A Multiphase Computational Framework for Deposit Formation and Growth
Authors: Paul Steven , Tafti Danesh , Yu Kuahai
Published: November 2019

Particle deposits that form in gas turbine engines can change flow dynamics and heat transfer, leading to performance degradation. A computational framework that models the coupled behavior of sand deposits with flow and heat transfer is developed. The coupling is done by using a multiphase framework in which a physics based collision model is used to predict the post-collision state-of-the sand particle. The collision model is sensitized to temperature dependent material properties of sand. Particle deposition is determined by the particle’s softening temperature and the calculated coefficient of restitution of the collision. The multiphase treatment facilitates conduction through the porous deposit and the coupling between the deposit and the fluid field.

The coupled framework is used to model the behavior of sand particles in a laminar impinging jet flow field. The temperature of the jet and the impact surface are varied between 1000 to 1600 K, to observe particle behavior under different temperature conditions. The Reynolds number of the jet is varied between 20 to 100 to vary particle Stokes number between 0.5 to 3.2. The coupled framework was found to increase or decrease capture efficiency, when compared to an uncoupled simulation, by as much as 10% depending on the temperature field. Deposits that formed on the impact surface, using the coupled framework, altered the velocity field by as much as 130% but had a limited effect on the temperature field for the short duration of the simulations.
Assessment of the Theta Projection Model for Interpolating Creep Deformation
Authors: Perez Jimmy , Stewart Calvin M.
Published: November 2019

The objective of this study is to assess the ability of the theta projection constitutive model to fit and predict creep deformation curves of P91 alloy. To accomplish this objective; a systematic method of fitting and prediction is applied. A numerical optimization algorithm is written in the MATLAB programming language. Using the algorithm, the theta projection model is calibrated to creep deformation curves collected from the GENIV nuclear materials database managed by Oak Ridge National Laboratory. The data consists of deformation curves recorded from tests conducted at increasing stresses at 3 different temperatures; 1100, 1157 and 1200°F. The calibrated theta material constants are then fit to simplified interpolation functions of temperature and stress. Predictions are made using the calibrated and interpolated theta constants and the results compared.

It is determined that the theta projection model excels at fitting individual creep deformation curves. The trends of calibrated theta constants when examined across multiple creep deformation curves (at varied stress per isotherm) do not maintain consistent behavior when compared to one another. This inconsistency limits the accuracy of the interpolation functions, resulting in poor predictions of creep deformation using said functions.
Technical and Economic Viability of an EIS 2050 Geared Open Rotor
Authors: Sebastiampillai Joshua , Rolt Andrew , Nalianda Devaiah , Mastropierro Francesco , Sethi Vishal
Published: November 2019

The aviation sector is projected to grow rapidly over the next two decades and beyond. These projections coupled with ever more stringent environmental legislation call for action within the commercial aviation sector to radically reduce greenhouse gas emissions by 2050. It is perceived that by 2050 current state-of the-art direct-drive turbofans will have evolved into geared turbofans and geared open rotor engines for short haul missions. These changes in engine configuration may be attributed to calls from the Advisory Council for Aviation Research and innovation in Europe to dramatically reduce CO2 generation and greenhouse gas emissions by 2050. The geared open rotor architecture is predicted to significantly reduce fuel burn relative to a typical short-range year-2000 aircraft mission, and greatly reduce CO2 emissions per passenger kilometer. Although relative fuel-burn benefits have been estimated in various studies, the economic feasibility of developing the geared open rotor (GOR) engine configuration for potential manufacturers and operators has not been reported.

Therefore, this paper describes methodologies employed to estimate the relative fuel burn benefit of a short-range year 2050 GOR engine-aircraft configuration. In addition, it details the financial feasibility of year-2050 short-range engine and aircraft concepts, for manufacturers and operators alike. An overview of the technical specifications of a potential ‘GOR2050’ engine configuration is provided. This paper further describes methods employed to predict the unit cost of a year-2050 engine and aircraft concept that might be offered by the manufacturers, as well as a revenue model for manufacturers in the 2050-timeframe. In order to capture the supplier–customer relationship between the OEMs and their customers, direct operating cost (DOC) and representative revenue models have been constructed for the operators.

This paper also analyses the effects that potential future fuel price and taxation policies regarding emissions could have on the operational profitability of such an aircraft and engine combination. Based on a representative set of model inputs, an illustrative test-case for a year-2050 short-haul aircraft and engine combination predicts, with a 50% confidence level, that the minimum number of twin-engine aircraft sales needed to ensure the financial feasibility of the program would be 630 units. Furthermore, with a 50% confidence level, a potential operator could expect an internal rate of return over 7%. The impact of different fuel prices and taxation scenarios are quantified in terms of internal rate of return forecasts.
The Impact of Combustor Turbulence on Turbine Loss Mechanisms
Authors: Folk Masha , Miller Robert J. , Coull John D.
Published: November 2019

A blade row which is located downstream of a combustor has an extremely high turbulence intensity at inlet, typically above 10%. The peak turbulent length scale is also high, at around 20% of the chord of the downstream blade row. In a combustor, the turbulence is created by impinging jets in cross flow. This may result in the turbulence being anisotropic in nature. The aim of this paper is to investigate the effect of combustor turbulence on the loss mechanisms which occur in a turbine blade row. The paper has a number of important findings. The combustor turbulence is characterized and is shown to be isotropic in nature. It shows that, when no pressure gradient is present, combustor turbulence increases the loss of a turbulent boundary layer by 22%. The mechanism responsible for this change is shown to be a deep penetration of the turbulence into the boundary layer. It shows that the presence of combustor turbulence increases the profile loss and endwall loss in the turbine cascade studied by 37% and 47%, respectively. The presence of combustor turbulence also introduces a freestream loss resulting in the total loss of the turbine cascade rising by 47%. When these loss mechanisms were applied to the vane alone, of an engine representative high pressure turbine, it was found to result in a 1.3% reduction in stage efficiency.
Multi-Scale Parallelised CFD Modelling Towards Resolving Manufacturable Roughness
Authors: Kapsis Marios , He Li , Li Yan Sheng , Wells Roger , Valero Omar , Krishnababu Senthil , Gupta Gaurav , Kapat Jayanta , Schaenzer Megan
Published: November 2019

Typical turbomachinery aerothermal problems of practical interest are characterised by flow structures of wide-ranging scales, which interact with each other. Such multi-scale interactions can be observed between the flow structures produced by surface roughness and by the bulk flow patterns. Moreover, additive manufacturing may sooner or later open a new chapter in component designs by granting designers the ability to control the surface roughness patterns. As a result, surface finish, which so far has been treated largely as a stochastic trait, can be shifted to a set of design parameters that consist of repetitive, discrete micro-elements on a wall surface (‘manufacturable roughness’).

Considering this prospective capability requirement, the question would arise regarding how surface micro-structures can be incorporated in computational analyses during a design phase in the future. Semi-empirical methods for predicting aerothermal characteristics and the impact of manufacturable roughness could be used to minimise computational cost. However, the lack of element-to-element resolution may lead to erroneous predictions, as the interactions among the roughness micro-elements have been shown to be significant for adequate performance predictions [1].

In this paper a new multi-scale approach based on the novel Block Spectral method is adopted. This method aims to provide efficient resolution of the detailed local flow variation in space and time of the large scale micro-structures. This resolution is provided without resorting to modelling every single ones in detail, as a conventional large scale CFD simulation would demand, but still demonstrating similar time-accurate and time-averaged flow properties. The main emphasis of the present work is to develop a parallelised solver of the method to enable tackling large problems. The work also includes a first of the kind verification and demonstration of the method for wall surfaces with a large number of micro-structured elements.
Flow Characteristics in Aeroengine Bearing Chambers With Shallow Sump
Authors: Chandra Budi , Simmons Kathy
Published: November 2019

In an aeroengine oil is supplied to the bearings for lubrication and cooling. Subsequently, it creates a two phase flow environment in the bearing chamber that may contain droplets, mist, wall film, ligaments, froth or foam and liquid pools. After the oil has served its purpose, it is scavenged out of the chamber and recycled. Effective oil removal is essential as unnecessary working of the oil can lead to excessive heat generation in the chamber, increased risk of seal leakage, and reduced overall efficiency. However the task of oil removal is not trivial as it is entrained in a highly rotating environment induced by the rotating shafts.

Shallow sump variants were investigated using a design of experiments approach. A previous publication discussed the performance of the sump variants using categorization of visualization data relating to the extent of hydraulic uplift in the sump region. Hydraulic uplift was found to be directly related to residence volume in the gravity dominated wall film flow regime. Furthermore, it was found that the flow condition factors such as flow regime and shaft speed are the dominating factors affecting the hydraulic uplift severity. In terms of the geometrical factors, a deeper sump can reduce the hydraulic uplift severity. This reinforces the importance of sump depth, as a deeper sump tends to have lower residence volume but is often not implemented due to space constraint.

This paper presents further results from the experimental study on the shallow sump variants in terms of some important flow characteristics such as upstream flow detachment, upstream flow dry-out, and secondary flow. In addition to the geometrical factors, the flow condition factors such as the flow regime defined by how oil enters the chamber, flow rate, shaft speed, and scavenge ratio were investigated. Upstream flow detachment was observed only for cases where airborne droplets were present and at higher shaft speeds, also known as the windage dominated airborne droplets flow regime. It was noted that the geometrical factors are less important than the flow condition factors for upstream flow detachment as well as upstream flow dry-out and secondary flow.
Gas Path Diagnostics for a Once-Through Steam Generator
Authors: Chen Yu-Zhi , Li Yi-Guang , Newby Mike A.
Published: November 2019

The performance of a once-through steam generator (OTSG) is bound to degrade due to fouling during its operation. The fouling will result in the degradation of the heat transfer between hot gas and water or steam on both sides of the tubes within the OTSG, thereby causing degraded OTSG performance. Such degradation could result in significant economic losses for a power plant where the OTSG plays a key role. Thus, it would be beneficial to develop a diagnostic method to quantify the fouling in an OTSG in order to support the condition monitoring and condition-based maintenance of the plant. In this study, a novel gas path diagnostic method for an OTSG based on Newton-Raphson method was developed to predict the OTSG degradation caused by fouling. The diagnostic method was applied to a model OTSG to test its effectiveness. The impact of measurement noise on the diagnostic accuracy was analyzed and discussed. A comparison between predicted and implanted degradation of a model OTSG demonstrated that the results are promising, and the method is satisfactory. Meanwhile, the diagnostic analysis of an OTSG based on real measurements has further proved that the developed diagnostic method works well and has a great potential to provide useful health information of OTSGs. In theory, the developed diagnostic method has the potential to be applied to different types of OTSGs.
Modeling of Combustor and Turbine Vane Interaction
Authors: Verma Ishan , Zori Laith , Basani Jaydeep , Rida Samir
Published: November 2019

Modern aero-engines are characterized by compact components (fan, compressor, combustor, and turbine). Such proximity creates a complex interaction between the components and poses a modeling challenge due to the difficulties in identifying a clear interface between components since they are usually modeled separately. From a numerical point of view, the simulation of a complex compact aero-engine system requires interaction between these individual components, especially the combustor-turbine interaction. The combustor is characterized by a subsonic chemically reacting and swirling flow while the high-pressure turbine (HPT) stage has flow which is transonic. Furthermore, the simulation of combustor-turbine interactions is more challenging due to aggressive flow conditions such as non-uniform temperature, non-uniform total-pressure, strong swirl, and high turbulence intensity. The simulation of aero-engines, where combustor-turbine interactions are important, requires a methodology that can be used in a real engine framework while ensuring numerical requirements of accuracy and stability. Conventionally, such a simulation is carried out using one of the two approaches: a combined simulation (or joint-simulation) of the combustor and the HPT geometries, or a co-simulation between the combustor and the turbine with the exchange of boundary conditions between these two separate domains.

The primary objective of this paper is to assess the effectiveness of the joint simulation versus the co-simulation and propose a more practical approach for modeling combustor and turbine interactions. First, a detailed grid independence study with hexahedral and polyhedral meshes is performed to select the required polyhedral mesh. Then, an optimal location of the interface between the combustor and the nozzle guide vane (NGV) is identified. Co-simulations are then performed by exchanging information between the combustor and the NGV at the interface, wherein the combustor is solved using LES while the NGV is solved using RANS. The joint combustor-NGV simulations are solved using LES. The effect of the combustor-NGV interaction on the flow field and hot streak migration is analyzed. The results suggest that the joint simulation is computationally efficient and more accurate since both components are modelled together.
Design Considerations for High Pressure Boil-Off Gas (BOG) Centrifugal Compressors With Synchronous Motor Drives in LNG Liquefaction Plants
Authors: Taher Matt , Meher-Homji Cyrus B.
Published: November 2019

The increased size of Liquefied Natural Gas (LNG) plants worldwide has led to an increase in boil-off gas (BOG) flows. The BOG can be either liquefied again to LNG or compressed to higher pressure levels for use as fuel gas. Single shaft multistage centrifugal compressors are used to compress large volume of BOG at high pressures. This paper reviews design considerations for synchronous motor driven BOG centrifugal compressors operating at high discharge pressures. Several design features including compressor selection and sizing, auxiliary system, performance characteristics and testing are reviewed. The use of leading power factor synchronous motors to improve the power factor of the LNG plant is discussed. Capability curves of API 546 synchronous motors for operation in VAR control mode — for maintaining constant reactive power — are explained. The choice between the use of speed control or adjustable guide vanes for BOG compressors is discussed.
A General Study of Counterflow Diffusion Flames for Supercritical CO2 Mixtures
Authors: Manikantachari K. R. V. , Martin Scott , Rahman Ramees K. , Velez Carlos , Vasu Subith
Published: November 2019

A counterflow diffusion flame for supercritical CO2 combustion is investigated at various CO2 dilution levels and pressures by accounting for realgas effects into both thermal and transport properties. The UCF 1.1 24-species mechanism is used to account the chemistry. The nature of important non-premixed combustion characteristics such as Prandtl number, thermal diffusivity, Lewis number, stoichiometric scalar dissipation rate, flame thickness, and Damköhler number are investigated with respect to CO2 dilution and pressure. The result show that, the aforementioned parameters are influenced by both dilution and pressure; the dilution effect is more dominant. Further, result shows that Prandtl number increases with CO2 dilution and at ninety percent CO2 dilution, the difference between the Prandtl number of the inlet jets and the flame is minimal. Also, the common assumption of unity Lewis number in the theory and modeling of non-premixed combustion does not hold reasonable for sCO2 applications due to large difference of Lewis number across the flame and the Lewis number on the flame drop significantly with increase in the CO2 dilution. An interesting relation between Lewis number and CO2 dilution is observed. The Lewis number of species drops by 15% when increasing the CO2 dilution by 30%. Increasing the CO2 dilution increases both the flow and chemical timescales; however chemical timescale increases faster than the flow time scales. The magnitudes of the Damköhler number signifies the need to consider finite rate chemistry for sCO2 applications. Further, the Damköhler numbers at 90% sCO2 dilution are very small, hence laminar flamelet assumptions in turbulent combustion simulations are not physically correct for this application. Also, it is observed that the Damköhler number drops non-linearly with increasing CO2 dilution in the oxidizer stream. This is a very important observation for the operation of sCO2 combustors. Further, the flame thickness is found to increase with CO2 dilution and reduce with pressure.
Development of a 250-kWe Class Supercritical Carbon Dioxide Rankine Cycle Power Generation System and its Core Components
Authors: Seo JeongMin , Choi Won Chul , Lim HyungSoo , Park MooRyong , Kim Dong Ho , Lee KongHoon , Yoon EuiSoo
Published: November 2019

Korea Institute of Machinery & Materials (KIMM) investigated a supercritical carbon dioxide (sCO2) cycle for a heat recovery power generation system for several years. The objective of the study focuses on the development of the technologies and the establishment of the development procedure of turbomachinery, heat exchangers, and auxiliary equipment for the sCO2 power cycle. A motor-driven centrifugal starter pump with an inducer is developed for startup operation. The main pump-drive turbine module adopts magnetic bearings as axial and radial bearings to remove oil lubrication and exhibits a hermetic structure to eliminate leakage problems. The power turbine and a generator are linked via a gearbox in the power turbine-generator module. An oil bearing and floating ring seal with dry gas injection are applied to minimize sCO2 leakage. The recuperator is developed as a printed circuit heat exchanger (PCHE) owing to its high efficiency and compactness.

The integrated test facility is designed as a 250-kWe class sCO2 recuperated Rankine cycle to evaluate the performance of the core modules as opposed to demonstrating the viability of a particular sCO2 cycle. The test facility is proven to successfully operate in startup mode and self-sustaining mode using the starter pump and the main pump-drive turbine module. An overview of the operation of the startup mode and self-sustaining mode is presented.
Numerical Investigation of Ignition Sequence in a Multi-Burner Methane-Air Swirl Combustor Using Flamelet Generated Manifold Combustion Model
Authors: Nakod Pravin , Shrivastava Sourabh , Patwardhan Saurabh , Orsino Stefano , Yadav Rakesh
Published: November 2019

Low emission gas turbine engines, operating under fuel lean conditions, are susceptible to light-around issues. Traditionally, gas turbine manufacturers rely on experimentation and testing to understand the relight characteristics of a combustor. However, since the last decade, numerical simulations are gaining popularity in performance evaluation of the light-around characteristics of the gas turbine combustors. In the present work, assessment of the Flamelet Generated Manifold (FGM) combustion model is carried out to understand its performance for capturing the correct ignition sequence in a linear multi-burner methane-air swirl combustor designed by COmplexe de Recherche Interprof essionnel en Aérothermochimie (CORIA) in the context of Knowledge for Ignition, Acoustics, and Instabilities (KIAI) project. The present work uses linear five, four and two swirled injector configurations for the validation of the simulation results. Non-reacting and reacting Large Eddy Simulations (LES) are performed for three injector arrangements to predict the main flow structure, mixing, flame propagation and ignition sequence. Non-reacting time-averaged flow quantities such as mean axial and radial velocities are data-sampled and compared with the experimental results. The predicted results show a good comparison between simulation and experimental data. Ignition sequence and timing predicted from the reacting LES for all the three configurations studied in this work, also compare well with the experimental data. This numerical investigation confirms that the FGM combustion model used in the LES framework can be successfully employed for the prediction of the relight characteristics of the gas turbine engines.
Impacts of H2 Blending on Capacity and Efficiency on a Gas Transport Network
Authors: Bainier Francis , Kurz Rainer
Published: November 2019

Gas Transport System Operators (TSO1) are considering injecting hydrogen gas in their networks. Blending hydrogen into the existing natural gas pipeline network appears to be a strategy for storing and delivering renewable energy to markets [1], [2],[3].

In comparison to methane, hydrogen gas (dihydrogen or molecular hydrogen) has a higher mass calorific value than methane gas. Because of this property, molecular hydrogen is appreciated for space shuttle engines. A second property is that hydrogen gas has a lower mass density than methane gas. The result of the second property is that the volume calorific value is in favor of methane gas. The list of differences between methane and hydrogen is long. In the relevant range of pressures and temperatures, the Joule-Thomson coefficient has a different sign for hydrogen and methane, and the compressibility factor has the opposite trend when the gas is compressed. The dynamic viscosity is also significantly different, and finally, heat capacity, isentropic exponent, and the thermal conductivity are also different.

What are the impacts of these hydrogen characteristics on the transport capacity and its efficiency in the case of blending in a gas transport network?

The first part of the paper is a review of the differences in characteristics between Hydrogen Gas and a Typical Natural Gas in Europe and their impact on the gas flow performance in a pipeline network equipped with compressors.

The second part of the paper is dedicated to pipe segments. And in the third part, compressor stations are introduced between each pipe segment. At each step, an analysis of a mixed gas from one hundred per cent pure natural gas to one hundred per cent pure hydrogen is done.

The paper provides some results for 10 %, 40 %, and 100 % of hydrogen blending in an international pipeline. The study shows that the energy quantity transported at the same pressure ratio is reduced respectively by 4 %, 14 %, and 15 to 20 %, and energy requirement for compression increases respectively by 7 %, 30 %, and 210 % (i.e. it more than triples). To transport the same quantity of energy in a network, assuming the resizing to the same level of optimizations, the energy requirement increases by 11 %, 52 %, and 280 %. In other words, it takes 4 times the energy to transport a given amount of energy if the gas is pure hydrogen than it takes if the gas is pure natural gas.

The paper does not address the issue of equipment or material, it only compares the influence of hydrogen gas on the network capacity and the transport efficiency. This paper doesn’t take into account the limits of the equipment. All equipment is considered as compatible with any load of hydrogen blending.
Modelling the Unsteady Dynamics of a Turbine Research Facility
Authors: Longley John P.
Published: November 2019

The accuracy with which experimental investigations of turbine performance need to be undertaken require either a semi- or fully-automated control of the operating point as any variation can compromise the reliability of the measurements. Fundamentally, both the mass flow rate through the turbine and the applied brake torque need to be adjusted in real-time so that the required operating point is maintained.

This paper describes the development of a time accurate computational simulation of the unsteady dynamics of a large-scale, low-speed turbine facility when its operating point is determined by a full-authority control system. The motivation for the development of the computational simulation was to be able to safely undertake parametric studies to refine the control system and to investigate the cause of monotonic excursions of the operating point which were observed after a major rebuild.

The monotonic excursions of the turbine operating point could only be reproduced by the computational simulation after an unsteady aerodynamic coupling between the turbine exit flow and the downstream centrifugal fan had been incorporated. Based on this observation a honeycomb was installed upstream of the fan in the turbine facility. This eliminated the monotonic excursions and the fractional noise of the operating point was reduced by 37%. When combined with an earlier refinement of the control system the factional noise was reduced by a factor of three. This enables the number of repeated measurements to be reduced by nine and still obtain the same quality of data.
Mechanical Damage Accumulation in SiCf/SiC CMCs Characterised via In-Situ Computed X-Ray Tomography
Authors: Weston Eleri , Nicholson P. Ian , Pattison Stephen , Bache Martin
Published: November 2019

The use of an in-situ loading stage combined with an X-ray computed tomography (XCT) system is demonstrated for detecting sub-critical damage and ultimate failure mechanisms in a 0/90° continuous fibre reinforced SiCf/SiC ceramic matrix composite. XCT inspection was performed on macroscopic scaled test coupons sampling a significant number of fibre tows, whilst the material was subjected to monotonic tensile load, both static and cyclic in nature. The observation of inherent, post-processing features and the tracking of the resultant damage within the composite were demonstrated, supported by post-test inspections using scanning electron microscopy. Two important fracture modes are illustrated, with the tensile stress axis applied in the 0/90° and ±45° orientations relative to the fibre tows.
A CFD Assessment of Engine Core Zone Casing Heat Transfer
Authors: Sun Zixiang , Hills Nicholas J. , Scott Richard
Published: November 2019

A systematic CFD investigation was conducted to assess the core zone (CZ) casing heat transfer of a large civil aircraft engine. Three key engine operating conditions, maximum takeoff (MTO), cruise (CRZ) and ground idle (GI) were analyzed. Steady flows were assumed. Turbulence was simulated using the realizable k-epsilon model in conjunction with the scalable wall function. Buoyancy effect was taken into account. Radiation was calculated using the discrete ordinate (DO) model. It was shown that the forced convection heat transfer dominates in most of the casing surface in the core zone, and radiation is of second importance in general. However, in some areas where both convection and radiation heat transfer are weak but the latter is relatively greater in magnitude than the former, radiation heat transfer could thus become dominant. In addition, the overall impact of radiation on casing heat transfer increases from MTO to CRZ and GI conditions, as the strength of engine load decreases. The overall effect of buoyancy on casing heat transfer is small, but could be noticeable in some local areas where flow velocity is low. The insight into heat transfer features on the engine core zone casing supported by quantified CFD evidences is the first in the public domain, as far as authors are aware.
Investigation of Cross-Sectional Velocity Field Near the Inducer Plane of a Turbocharger Compressor Using 2D Particle Image Velocimetry
Authors: Banerjee Deb , Dehner Rick , Selamet Ahmet , Miazgowicz Keith , Brewer Todd , Keller Philip , Shutty John , Schwarz Arno
Published: November 2019

Understanding the velocity field at the inlet of an automotive turbocharger is critical in order to suppress the instabilities encountered by the compressor, extend its map and improve the impeller design. In the present study, two-dimensional particle image velocimetry experiments are carried out on a turbocharger compressor without any recirculating channel to investigate the planar flow structures on a cross-sectional plane right in front of the inducer at a rotational speed of 80 krpm. The objective of the study is to investigate the flow field in front of a compressor blade passage and quantify the velocity distributions along the blade span for different mass flow rates ranging from choke (77 g/s) to deep surge (13.6 g/s). It is observed that the flow field does not change substantially from choke to about 55 g/s, where flow reversal is known to start at this speed from earlier measurements. While the tangential velocity is less than 8 m/s, the radial velocity increases along the span to 17–20 m/s near the tip at high flow rates (55–77 g/s). As the mass flow rate is reduced below 55 g/s, the radial component starts decreasing and the tangential velocity increases rapidly. From about 5 m/s at 55 g/s, the tangential velocity at the blade tip exceeds 50 m/s at 50 g/s and reaches a maximum of about 135 m/s near surge. These time-averaged distributions are similar for different angular locations in front of the blade passage and do not exhibit any substantial azimuthal variation.
Computational Study of the Non-Parametric Squeeze Film Damper Bearing Inverse Model Based on Artificial Neural Networks Applied to a Rotor-Casing System Running on Unsupported SFDs
Authors: Torres Cedillo Sergio G. , Al-Ghazal Ghaith Ghanim , Bonello Philip , Cortés Pérez Jacinto , Reyes Solís Alberto
Published: November 2019

Squeeze Film Damper (SFD) bearings play a vital role in attenuating large amplitudes of vibration due to their relatively simple assembly in aero engine designs. The modern aero-engine structures, typically, have at least two nested rotors mounted within a flexible casing via squeeze-film damper (SFD) bearings. There is a growing body of research into identification techniques for bearing models for use in rotor-bearing analysis to improve reliability and/or efficiency of implementation. The authors’ previous work has shown that, for cases where there is no adequate linear connection between the rotor and casing, the identification of the unbalance from externally mounted sensors requires a virtual instrument that can determine the vibration of the rotor relative to the casing, as a substitute for internal instrumentation. The present study is devoted to determining the effectiveness of the inverse SFD model (under different unbalance state conditions), when it is applied to a rotor-casing system, wherein the rotor runs on two unsprung SFD bearings. The validation of the inverse SFD model enables its use in a future study of the identification of unbalance in such complex systems.
Radial Inlet and Exit Design for a 10 MWe sCO2 Axial Turbine
Authors: Cich Stefan D. , Moore J. Jeffrey , Marshall Michael , Hoopes Kevin , Mortzheim Jason , Hofer Douglas
Published: November 2019

An enabling technology for a successful deployment of the sCO2 closed-loop recompression Brayton cycle is the development of a high temperature turbine not currently available in the marketplace. This turbine was developed under DOE funding for the STEP Pilot Plant development and represents a second generation design of the Sunshot turbine (Moore, et al., 2018). The lower thermal mass and increased power density of the sCO2 cycle, as compared to steam-based systems, enables the development of compact, high-efficiency power blocks that can respond quickly to transient environmental changes and frequent start-up/shut-down operations. The power density of the turbine is significantly greater than traditional steam turbines and is rivaled only by liquid rocket engine turbo pumps, such as those used on the Space Shuttle Main Engines. One key area that presents a design challenge is the radial inlet and exit collector to the axial turbine. Due to the high power density and overall small size of the machine, the available space for this inlet, collectors and transition regions is limited. This paper will take a detailed look at the space constraints and also the balance of aero performance and mechanical constraints in designing optimal flow paths that will improve the overall efficiency of the cycle.
Experimental Analysis of a Particle Separator Design With Full-Field 3D Measurements
Authors: Borup Daniel D. , Elkins Christopher J. , Eaton John K.
Published: November 2019

Particle ingestion into turbine engines is a widespread problem that can cause significant degradation in engine service life. One primary damage mechanism is deposition of particulate matter in internal cooling passages. Musgrove et al. proposed a compact particle separator that could be installed between the combustor bypass exit and turbine vane cooling passage inlet. The design had small pressure losses but provided limited particle separation, and its performance has proved difficult to replicate in subsequent experiments. Borup et al. recently developed a Magnetic Resonance Imaging (MRI) based technique for making full-field, 3D measurements of the mean particle concentration distribution in complex flows. A particle separator based on the Musgrove et al. design was fabricated out of plastic using 3D printing. The primary difference from earlier designs was the addition of a drain from the collector, through which 3% of the total flow was extracted. The separator efficiency was measured at two Reynolds numbers, using water as the working fluid and 33-micron titanium microspheres to represent dust particles. Particle Stokes number was shown to play the dominant role in determining efficiency across studies. MRI was used to obtain the 3D particle volume fraction and 3-component velocity fields. The velocity data showed that flow was poorly distributed between the separator louvers, while the collector flow followed the optimal pattern for particle retention. The particle distribution data revealed that strong swirling flow in the collector centrifuged particles towards the outer wall of the collector and into a partitioned region of quiescent flow, where they proceeded to exit the collector via the drain. Future designs could be improved by re-arranging the louvers to produce a more uniform flow distribution, while maintaining the effective collector design.
Parametric Studies on Aerodynamic Performance of Various Types of LP Turbine Airfoils for Aero-Engines Under the Influence Periodic Wakes and Freestream Turbulence
Authors: Funazaki Ken-ichi , Murakami Daichi , Okamura Yasuhiro
Published: November 2019

This study carries out parametric investigations on aerodynamic loss of various types of LP turbine airfoils characterized with different flow deceleration rates (DR) on their suction surfaces under the realistic flow conditions such as wake inflow and freestream turbulence. The Reynolds number examined in this study ranges from 57,000 to 170,000. As for the freestream turbulence, two levels of the turbulence are used, i.e., about 1.2% and 3.5%. Stagnation pressure distributions downstream of each of the airfoil cascades are measured by use of a Pitot tube, while steady-state and unsteady boundary-layers are measured over the rear part of suction surface and pressure side near the trailing edge using a single hot-wire probe. The measured boundary-layer data are used to estimate the cascade loss along with RANS (Reynolds-Averaged Navier-Stokes) simulations by taking advantage of the momentum-theory based Denton’s method. First, relationships between the cascade loss for each flow condition and DR are examined. The estimated loss values are then compared with the measured cascade loss to check the validity of the loss estimation method, which is a derivative of Denton’s method, under the realistic flow conditions.
Numerical Investigation on the Vibration of Steam Turbine Main Inlet Control Valves Considering Fluid Force Effects
Authors: Li Yueyue , Xu Sihua , He Jin , Hu Zhiqiang , Xiao Lei
Published: November 2019

In this paper, a finite element model (FEM) for inlet control valve was built and the structural modal analysis was performed to get the Eigen-frequencies of the valve. The valve plug as well as the stem together with piston rod and spring block were analyzed separately. Some peak frequencies of the main inlet control valves were obtained at the 2% lift case during warm-up stage on a nuclear power plant. The dynamic flow field as well as the steam forces were obtained by computational fluid dynamic (CFD) calculations with DES turbulence model. In order to clarify the cause of the valve vibration, the natural frequencies were compared with the test data to indicate that the frequency of certain rocking modes may coincided with the test results. What’s more, the peak frequencies of the dynamic steam forces from CFD simulations were also compared with the rocking modes of control valve to identify the mechanism that cause the vibration at certain frequencies.
Aerodynamic Comparison Between Circumferential and Wing-Embedded Inlet Distortion for an Ultra-High Bypass Ratio Fan Stage
Authors: Giesecke Daniel , Friedrichs Jens
Published: November 2019

Future aircraft design concepts often show a somewhat wing embedded ultra-high bypass ratio engine. The aircraft concept of the Coordinated Research Centre 880 (CRC880) is a single-aisle configuration with engines partly integrated over the aircraft wing. The aircraft is designed to take off and land on regional airfields with low noise and fuel emissions to address the guidelines set by the ACARE. As a result of the engine installation, the inlet induces a non-axisymmetric boundary layer ingestion into the fan stage.

In experimental setups, inlet distortion has often been seen as a 60-degree circumferential inlet stagnation pressure distortion. However, the fan stage inlet flow of the prescribed engine installation of the CRC880 differs to a great extent from a 60-degree sector. In this paper, an aerodynamic comparison between a realistic inflow situation and a similar 60-degree inlet distortion for the same ultra-high bypass ratio fan stage is given. The realistic inflow situation is a result of the flow moving over the aircraft wing suction side and entering the nacelle. As non-axisymmetric inlet geometry remains the same for both cases, therefore, only the total pressure boundary condition at nacelle inlet was changed between both cases. Hence, full annulus simulations are required. Both inlet distortion cases are equivalent by matching average 60-degree distortion coefficient. This study points out that the method, by using averaged 60-degree segment values, excludes specific inflow characteristics. For the same averaged 60-degree distortion coefficient, the local distortion of the embedded case is up to four times larger at rotor tip compared to the segmental approach. For constant mass flow, fan pressure ratio and isentropic efficiency drop by more than five and eight percent respectively. At peak efficiency operating condition, the decrease is even more significant with more than nine percent in stage efficiency.

For future embedded aircraft engine configurations, the fan designer has to take into account the non-axisymmetric local flow changes. Hence, the 60-degree segment method is not sufficient when investigating experimental boundary layer ingesting fans and therefore, further method developments are necessary.