bluuebunny/crossref_metadata_2025_split huggingface dataset:
Linking MRO to Prognosis Based Health Management Through Physics-of-Failures Understanding
Authors: Patnaik Prakash , Wu Xijia 
Published: August 2018

Traditional engine maintenance, repair and overhaul (MRO) are geared toward fixed schedules. However, with online condition monitoring, assessments and prognosis, it is required that MRO be adaptive to the life consumption with respect to the actual usage of the engine to realize the benefit of prognosis. Shifting to this new paradigm, there are several challenges:
1. How exactly the life is consumed in components under complex usage profiles that may involve a combination of low and high cycle fatigue, thermomechanical fatigue and creep, for regular usage (aside from incidents)?
2. What are the physical failure mechanism(s) in components under the above conditions, the understanding of which may help to select the most appropriate detection, repair and replacement (including material insertion) strategy, for life renewal/extension and cost reduction?
3. Understanding the limitations of repairs for the particular failure mechanism.
To overcome these challenges, one needs physics-based material failure models that can reflect the true failure mechanisms on the component level under actual (complex) usage profiles. Conventional, empirical test-data correlations for isolated conditions fall short of this requirement because pure fatigue and pure creep are not experienced by real components in service. In addition, to ensure the repaired component’s structural integrity, the material database would have to be comprehensive enough to cover the effect of intrinsic repair defects and microstructures that are not present in the original component material. While models and data are integral parts of digital twins, it is proposed that physics-based models are needed to cover the entire application domain continuously. This paper will introduce a physics-based method of life consumption evaluation and discussion through past experience in line with the development of Digital Twin concepts for sustainment.
On the Choice of Turbine Type for a Twin-Turbine Heavy-Duty Turbocharger Concept
Authors: Anton Nicholas , Genrup Magnus , Fredriksson Carl , Larsson Per-Inge , Christiansen-Erlandsson Anders 
Published: August 2018

In this study, a fundamental approach to the choice of turbocharger turbine for a pulse-charged heavy-duty diesel engine is presented. A standard six-cylinder engine build with a production exhaust manifold and a Twin-scroll turbocharger is used as a baseline case.
The engine exhaust configuration is redesigned and evaluated in engine simulations for a pulse-charged concept consisting of a parallel twin-turbine layout. This concept will allow for pulse separation with minimized exhaust pulse interference and low exhaust manifold volume.
This turbocharger concept is uncommon, as most previous studies have considered two stage systems, various multiple entry turbine stages etc. Even more rare is the fundamental aspect regarding the choice of turbine type as most manufacturers tend to focus on radial turbines, which by far dominate the turbochargers of automotive and heavy-duty applications. By characterizing the turbine operation with regards to turbine parameters for optimum performance found in literature a better understanding of the limitations of turbine types can be achieved.
A compact and low volume exhaust manifold design is constructed for the turbocharger concept and the reference radial turbine map is scaled in engine simulations to a pre-set AFR-target at a low engine RPM.
By obtaining crank-angle-resolved data from engine simulations, key turbine parameters are studied with regard to the engine exhaust pulse-train. At the energetic exhaust pressure pulse peak, the reference radial turbine is seen to operate with suboptimum values of Blade-Speed-Ratio, Stage Loading and Flow Coefficient.
The study concludes that in order to achieve high turbine efficiency for this pulse-charged turbocharger concept, a turbine with efficiency optimum towards low Blade-Speed Ratios, high Stage Loading and high Flow Coefficient is required. An axial turbine of low degree of reaction-design could be viable in this respect.
Large Eddy Simulation of Boundary Layer Transition Mechanisms in a Gas-Turbine Compressor Cascade
Authors: Scillitoe Ashley D. , Tucker Paul G. , Adami Paolo 
Published: August 2018

Large Eddy Simulation (LES) is used to explore the boundary layer transition mechanisms in two rectilinear compressor cascades. To reduce numerical dissipation, a novel locally adaptive smoothing scheme is added to an unstructured finite-volume solver. The performance of a number of Sub-Grid Scale (SGS) models is explored.
With the first cascade, numerical results at two different freestream turbulence intensities (Ti’s), 3.25% and 10%, are compared. At both Ti’s, time-averaged skin-friction and pressure coefficient distributions agree well with previous Direct Numerical Simulations (DNS). At Ti = 3.25%, separation induced transition occurs on the suction surface, whilst it is bypassed on the pressure surface. The pressure surface transition is dominated by modes originating from the convection of Tollmien-Schlichting waves by Klebanoff streaks. However, they do not resembled a classical bypass transition. Instead, they display characteristics of the “overlap” and “inner” transition modes observed in the previous DNS. At Ti = 10%, classical bypass transition occurs, with Klebanoff streaks incepting turbulent spots.
With the second cascade, the influence of unsteady wakes on transition is examined. Wake-amplified Klebanoff streaks were found to instigate turbulent spots, which periodically shorten the suction surface separation bubble. The celerity line corresponding to 70% of the free-stream velocity, which is associated with the convection speed of the amplified Klebanoff streaks, was found to be important.
Steady CFD Simulation of a High Pressure Turbine Rotor With Hub and Shroud Purge Flow
Authors: Sanz Wolfgang , Zerobin Stefan , Egger Manfred , Bader Pascal , Pieringer Paul , Göttlich Emil , Heitmeir Franz 
Published: August 2018

Purge air is injected at the hub and shroud of axial turbines in order to avoid hot gas entering the gaps between stationary and rotating blade rows. The purge flows considerably interact with the main flow and influence the secondary flow like the tip leakage vortex. Therefore, at Graz University of Technology the flow in a product-representative one-and-a-half stage test turbine under the influence of purge flows was investigated. Four individual purge mass flows differing in flow rate, pressure, and temperature were injected through hub and tip cavities before and after the unshrouded high-pressure turbine rotor.
In order to get more insight into the cavity flows and the flow evolution in the rotor this configuration is studied with a steady CFD simulation with and without purge flows. It was found that the secondary flow and especially the tip leakage vortex is significantly influenced by the purge flow which varies in circumferential direction. The differences between purge and zero-purge flow conditions are discussed with the help of radial distributions and contour plots of stream-wise vorticity. Streamlines allow to follow the path of the purge flows in the rotor and show the radial displacement of the secondary flow vortices. Wall streamlines describe the changes in the boundary layer flow and their effect on the vorticity after the trailing edge.
Conjugate Heat Transfer Methodology for Thermal Design and Verification of Gas Turbine Cooled Components
Authors: Winchler Lorenzo , Andreini Antonio , Facchini Bruno , Andrei Luca , Bonini Alessio , Innocenti Luca 
Published: August 2018

Gas turbine design has been characterized over the years by a continuous increase of the maximum cycle temperature, justified by a corresponding increase of cycle efficiency and power output. In such way turbine components heat load management has become a compulsory activity and then, a reliable procedure to evaluate the blades and vanes metal temperatures, is, nowadays, a crucial aspect for a safe components design.
In the framework of the design and validation process of HPT (High Pressure Turbine) cooled components of the BHGE NovaLT™ 16 gas turbine, a decoupled methodology for conjugate heat transfer prediction has been applied and validated against measurement data. The procedure consists of a conjugate heat transfer analysis in which the internal cooling system (for both airfoils and platforms) is modeled by an in-house one-dimensional thermo-fluid network solver, the external heat loads and pressure distribution are evaluated through 3D CFD analysis and the heat conduction in the solid is carried out through a 3D FEM solution. Film cooling effect has been treated by means of a dedicated CFD analysis, implementing a source term approach.
Predicted metal temperatures are finally compared with measurements from an extensive test campaign of the engine, in order to validate the presented procedure.
Uncertainty Quantification Analysis of Back Facing Steps Film Cooling Configurations
Authors: Sakai Eiji , Bai Meng , Ahlfeld Richard , Montomoli Francesco 
Published: August 2018

This paper compares two back step film-cooling configurations under an uncertainty quantification framework. An important limit of such configurations is their reliability under geometrical variations, which is taken into account in this study.
For the back step configurations, a straight and a curved step is used. Detached eddy simulations with k-ω turbulence model are performed using OpenFOAM ver. 4.0. The Reynolds number is based on the main stream velocity and film cooling hole diameter, d, and is Re = 15,300. The investigated step heights are 0.5d and 0.75d, and the blowing ratios, BR, are 0.5 and 1.0. The straight and the curved steps are found to enhance lateral spreading of coolant flow, resulting in higher film cooling effectiveness compared to the baseline case without the step at comparatively higher BR conditions. The curved step shows better performance than the straight one in particular from BR = 1.0 upwards with the step height of 0.5d.
At lower BR with lower H/d, and at higher BR with higher H/d, deterministic simulations are not able to identify the best performer. However when the performance of the two configurations is evaluated considering the stochastic variation of step height and the cooling condition, the benefit of the curved step becomes clear. In particular, the curved step shows better mean performance and has a higher probability to achieve a better performance than the other one. The uncertainty in the film cooling effectiveness caused by the uncertainty of the step height and the BR is investigated using Sparse Approximation of Moment-Based Arbitrary polynomial chaos (SAMBA).
Development of Blade Tip Repair for SGT-700 Turbine Blade Stage 1, With Oxidation Resistant Weld Alloy
Authors: Barhanko Dikran A. , Åberg Niclas R. , Andersson Olov H. 
Published: August 2018

The SGT-700 gas turbine currently rated at 33 MW (simple cycle) and with an efficiency of ∼ 37% has been in service since 2002. In order to reduce life cycle cost, a repair process with an acceptable repair yield needed to be developed for turbine blade stage 1. The stage 1 blade is made from the polycrystalline cast alloy IN792, and the blade is coated with PtAl or MCrAlY+TBC depending on engine model. The blade is internally air cooled. After the row 1 vane, the stage 1 blade is forced to withstand the highest temperatures. The combination of high temperatures, and thermomechanical fatigue loading results in blade tip degradation, which leads to a loss of thermal efficiency. The blade tip repair process described in this document is one step in a continuous repair development plan for the SGT-700. To ensure quality in each reparation, the blade tip repair described here was developed using Siemens’ Product Development Process (PDP).
The development of the repair procedure include:
• Coating removal
• Pre- and post-weld heat treatment
• Machining of oxidized areas
• Hot box welding with manual GTAW
• Grinding to final air foil shape
• Re-opening of the cooling holes with EDM
• EDM to restore the squealer tip
• Recoating and air flow check
This technical paper describes the repair process developed together with a sub-supplier. The project resulted in a successful repair process for the component as well as repaired blades with higher blade tip oxidation resistance compared with the original design.
Numerical Investigation of Spray Development in a Micro Gas Turbine LPP Combustor With Airblast Atomizer
Authors: Annunziata Gianluca , Cameretti Maria Cristina , De Robbio Roberta , Tuccillo Raffaele 
Published: August 2018

The purpose of the paper is the investigation of the combustion development in a Lean Premixed Prevaporized (LPP) combustor supplied with liquid fuels of a Micro Gas Turbine. The injection system is equipped by an airblast atomizer with three air inlets.
In such a study the analysis is performed by a CFD tool that can simulate the injection conditions, by isolating and studying some specific phenomena. A 3-D fluid dynamic code (the FLUENT® flow solver) has been used to simulate the spray pattern in the chamber fuelled by kerosene fuel. Preliminarily, the numerical simulation refers to cold flow conditions, in order to validate the estimation of the fundamental spray parameters, such as the spray angle and Sauter Mean Diameter of the droplets; in a second step, the calculations employ boundary conditions close to those occurring in the actual combustor operation, in order to predict the fuel vapour distribution throughout the premixing chamber. In particular, the fuel is injected under the typical conditions that occur in the injection system of a gas turbine LPP combustor and in all cases examined, the boundary information is introduced in terms of air and fuel mass flow rates and of inlet characteristics of the air flow entering the revalorizing chamber, in order to estimate the fuel vapour formation and its distribution.
In a third phase the combustion phenomenon is simulated and the NO emissions calculated. Finally, the best solution obtained is also tested by using a bio-fuel to compare the combustion performance and NO amount.
Acoustic Properties of Perforated Liners With Perpendicular Arrangements of Narrow Slots
Authors: Jetté François-Xavier , Shanian Ali , Schaenzer Megan , Pham Minh Quan , Bourgeois Geneviève , Farhangi Mehran , Sanchez Fabian , Innes Matt 
Published: August 2018

Cooling holes in combustion liners are typically circular, as are the holes used for acoustic damping of combustor instabilities. This hole geometry is chosen for several reasons, which include manufacturability, stress concentration considerations, and because the behavior of round holes is well understood. However, developments in both manufacturing techniques and modeling methods now allow other hole geometries to be considered, such as perpendicular arrangements of narrow slots carefully shaped to prevent high stress concentrations (patent pending). The latter have been demonstrated to provide more efficient cooling and lower stress compared to round holes. However, the acoustic properties of such arrangements are not straightforward to model yet since it is not known how some important factors are affected by this geometry change.
In order to study the acoustic behavior of such arrangements of holes, a series of tests were conducted in an impedance tube (in reflection) for various slot shapes, width and spacing, with a backing cavity and purge flow (controlled via pressure drop). Some baseline measurements for circular holes were also obtained in an attempt to quantify any difference resulting from the change in hole shape.
The results have shown that at any pressure drop, the maximum absorption coefficient for narrow perpendicular slots and round holes is nearly equal when the hole area corrected by the discharge coefficient (i.e. the effective area) is also nearly the same, and that narrow perpendicular slots give more broadband absorption on the high frequency side of the absorption peak for a given cavity. It is suggested that since the maximum absorption between round holes and narrow perpendicular slots are nearly equal at an equivalent effective area, the resistance (real part of impedance) of the holes depends on the maximum flow velocity through the hole rather than the average velocity, for the particular combinations of hole dimension and sample plate thickness tested. It is also suggested that the greater broadband absorption at high frequencies for the narrow slots could be due to the fact that their high length to width ratio would result in a characteristic dimension dominated by their small width (similar to the airfoil thickness being the representative dimension of the size of the wake for an airfoil) hence a lower Strouhal number.
Improved Smith Chart for Axial Compressor Design
Authors: Anderson Mark R. 
Published: August 2018

Preliminary design of a turbomachinery stage usually begins with target flow states, represented by a velocity triangle. Guidance for these target velocities comes from a variety of sources, which include some physics-based rules but, more often than not, have a significant empirical basis.
The best-known guidelines for axial designs are the so-called “Smith Charts”. This approach was documented in detail by Smith [1] and quickly became a preferred approach for initial design of axial turbines stages. The method was based on a significant set of test data for various turbine designs, corrected for complicating factors, such as various clearance gaps and so on. Similar, but less well-documented methods, have been developed for axial compressor design. Despite the widespread use of the Smith chart method, these approaches have a very limited substantiation and no clear pedigree. Most attempts to develop Smith-like charts for compressor design guidance are based on fairly simplified models that carry significant unknowns, particularly at high loading.
This paper details the development of new Smith charts for axial compressor designs, by making extensive use of optimization techniques. Profile designs are optimized for a range of target flow coefficients and work coefficients. The result is a performance map, representing the maximum possible performance for a given set of coefficient values. The analysis was limited to 2D profile design (quasi-3D analysis) and a reaction of 50%, the theoretical ideal reaction rate for 2D flow.
Using the newly developed maps of maximum performance potential, the accuracy of various modeling methods is examined, along with their ability to determine the optimum design condition. Improvements to profile loss methods, based on the new data, are suggested.
Conceptual Aerodynamic Design of a Tail-Cone Thruster System Under Axi-Symmetric Inlet Distortion
Authors: Lee B. J. , Liou May-Fun , Liou Meng-Sing 
Published: August 2018

This paper presents a conceptual design of a tail-cone thruster system which is operating under an axisymmetric inlet distortion. An effort to realize the targeted fuel burn saving that was proposed in NASA’s STARC_ABL aircraft design is made through a CFD based design approach. This method employs three iterative steps to exploit the CFD tools until the design requirements are met: a quasi-2D through-flow model to design the fan/EGV, a 3-D RANS simulation of the single blade row to account for the inlet/fan and the EGV/nozzle interaction, and a 3-D RANS simulation of the airframe with a propulsor installed – propulsion airframe integration (PAI). The design requirements which include the thrust, and shaft power of the propulsor are matched throughout the evaluations coming from two CFD domains, i.e., the turbo-machinery and the PAI. During the switch between these different computational domains, the inlet and exit profiles are matched via the correction factors of the body-force model.
The present tail-cone thruster (TCT) aerodynamic design leverages a low-pressure ratio fan (FPR = 1.2∼1.25) of which the camber-line angles are predicted by a quasi-2D through-flow model. The quasi-2D model is derived to analyze the radially distorted flow resulting from the ingested boundary layer at the inlet. It also estimates the appropriate velocity vectors of the metal angles of the fan and EGV which is subjected to different types of vortex at the fan exit.
The baseline geometry is revisited and its internal flow-path and exhaust cone are redesigned to illustrate the strong correlation among the components of the propulsor in the PAI domain. The peak efficiency point of the fan/EGV with respect to the blade counts, a.k.a. solidity, and rotational speed is chosen for the cruise condition via parametric studies. The corresponding performance maps are presented. The resulting performance metrics of the new conceptual design of the BLI propulsor are analyzed and compared with these of the baseline in the PAI aspect. Finally, ideas of the CFD based design of a BLI propulsor are discussed based on the observations drawn from the numerical results.
Using Turbulence Intensity and Reynolds Number to Predict Flow Separation on a Highly Loaded, Low-Pressure Gas Turbine Blade at Low Reynolds Numbers
Authors: Van Treuren Kenneth , Pharris Tyler , Hirst Olivia 
Published: August 2018

The low-pressure turbine has become more important in the last few decades because of the increased emphasis on higher overall pressure and bypass ratios. The desire is to increase blade loading to reduce blade counts and stages in the low-pressure turbine of a gas turbine engine. Increased turbine inlet temperatures for newer cycles results in higher temperatures in the low-pressure turbine, especially the latter stages, where cooling technologies are not used. These higher temperatures lead to higher work from the turbine and this, combined with the high loadings, can lead to flow separation. Separation is more likely in engines operating at high altitudes and reduced throttle setting.
At the high Reynolds numbers found at takeoff, the flow over a low-pressure turbine blade tends to stay attached. At lower blade Reynolds numbers (25,000 to 200,000), found during cruise at high altitudes, the flow on the suction surface of the low-pressure turbine blades is inclined to separate. This paper is a study on the flow characteristics of the L1A turbine blade at three low Reynolds numbers (60,000, 108,000, and 165,000) and 15 turbulence intensities (1.89% to 19.87%) in a steady flow cascade wind tunnel. With this data, it is possible to examine the impact of Reynolds number and turbulence intensity on the location of the initiation of flow separation, the flow separation zone, and the reattachment location. Quantifying the change in separated flow as a result of varying Reynolds numbers and turbulence intensities will help to characterize the low momentum flow environments in which the low-pressure turbine must operate and how this might impact the operation of the engine. Based on the data presented, it is possible to predict the location and size of the separation as a function of both the Reynolds number and upstream freestream turbulence intensity (FSTI). Being able to predict this flow behavior can lead to more effective blade designs using either passive or active flow control to reduce or eliminate flow separation.