bluuebunny/crossref_metadata_2025_split huggingface dataset:
Large Eddy Simulations of Wind Turbine Flows
Authors: Dabas Jérôme , Gicquel Laurent , Odier Nicolas , Duchaine Florent 
Published: October 2022

Abstract
The development of the wind energy sector has to come with an increase in wind turbine and wind farm efficiency. This increase can be achieved through the use of CFD tools that allow to accurately predict, at a reasonable cost, the efficiency of new wind turbine designs, wind farm layouts and control strategies. In this context, high order CFD tools such as the ones based on the LES approach are required to develop and calibrate lower order models that can be used for industry purposes. The aim of the present study is to assess the ability of CERFACS’ LES solver developed for turbo-machinery applications — AVBP — to perform high fidelity simulations of wind turbine flows.
To this end, a wall-modelled approach was chosen to describe the boundary layer on the blades. In addition, A static mesh adaptation method was developed to optimise the mesh size while accurately resolving the turbine wake. Finally, a Pressure Gradient Scaling method [1] was applied to artificially relax the compressible flow CFL condition to a low-mach one and increase the time step.
The aforementioned framework was assessed on reduced wind turbine configurations developed and experimentally investigated by NTNU. Although the Reynolds number of these configurations is one to two orders of magnitude inferior to real wind turbine one, the controlled boundary conditions and the available experimental data make these configurations particularly interesting for code validation. Two configurations have been simulated.
The results show the ability of the numerical approach to capture the transition between near and far wake and the interaction between inflow turbulence and the wake. The comparison with experimental measurements shows that simulations accurately predict the velocity deficit and recover the right amount of turbulent kinetic energy at the beginning of the far wake. As a conclusion, the framework developed in this study is adapted to reduced turbine computation yet it has to be further validated on real scale wind turbines.
Impact of Operating Conditions on Rotor/Stator Interaction of a High-Pressure Ratio Centrifugal Compressor
Authors: Lottini Fabrizio , Agnolucci Andrea , Pinelli Lorenzo , Pacciani Roberto , Toni Lorenzo , Guglielmo Alberto , Grimaldi Angelo 
Published: October 2022

Abstract
The current design trend of centrifugal compressors is aimed at obtaining compact machines with high pressure ratios and performance. This leads to high circumferential speeds and lighter components, thus increasing static stresses and dynamic forcing due to rotor/stator interactions. Therefore, the aerome-chanical characterization of these machines is a fundamental step of the design chain. This paper presents an in-depth aerome-chanical study of a high-pressure ratio centrifugal compressor using CFD. Firstly, the computational setup is validated against the experimental data; then, the same numerical setup is used to characterize the aeromechanical interactions between the impeller and the upstream and downstream static components. The URANS simulations are carried out at three different operating points (near stall, design, near choke), and the unsteady flow field is time and space decomposed showing higher forcing functions at near stall and near choke conditions with respect to the design point, as confirmed by the experimental acquisitions. The presented results highlight the importance of extending the aeromechanical evaluations to different operating points in order to avoid unexpected vibration responses when operating at off-design conditions. Finally, by virtue of an acoustic post-processing techniques, the unsteady pressure coupling in the inter-row region is analyzed to discern the main sources of the overall unsteady interaction.
Stabilization of Low-NOx Hydrogen Flames on a Dual-Swirl Coaxial Injector
Authors: Leroy Maxime , Mirat Clément , Renaud Antoine , Vicquelin Ronan 
Published: October 2022

Abstract
Hydrogen-fuelled carbon-free energy is a growing prospect for the future of several industries, among them the aeronautical and energy generation sectors. However, the transition to hydrogen comes with several challenges: flame stabilization due to the unique combustion properties of hydrogen compared to conventional fuels and control of nitrogen oxides (NOx) production due to the higher combustion temperature. In addition, the high flammability of hydrogen poses an increased risk of flashback in premixed configurations commonly used to generate low-NOx flames. As a consequence, research into strategies for low-NOx hydrogen combustion is developing, and several technologies are being considered for industrial use. Among these technologies, we consider here a dual swirl coaxial injector operated in non-premixed conditions. This setup enables the stabilization of multiple types of flame structures that are parametrically investigated for their NOx emissions. The flame structure is observed using OH* chemiluminescence images collected using an intensified CCD camera equipped with a band-pass filter. Exhaust gas species mole fractions of NO, NO2 and O2 are measured using NDIR gas detectors and a paramagnetic sensor. This investigation reveals that stabilization of hydrogen-air flames on the double swirl injector is possible and that varying the flow parameters induces changes in structure that affect NOx emissions, independently of swirl level, residence time and temperature that also play a role. The study is carried out at atmospheric pressure.
Flow Visualization Study From a Flat Plate With Multiple Impinging Jets for Different Cross-Flow Schemes
Authors: Dhanasegaran Radheesh , Pugazhendhi Ssheshan 
Published: October 2022

Abstract
A flow visualization study has been carried out computationally on a flat plate with a 5 × 5 array of impinging jets for different cross-flow schemes. The k-ω SST turbulence model is used for carrying out the RANS simulations. The parameters investigated are (i) cross-flow schemes (minimum, medium & maximum), (ii) jet-to-plate spacing (H/D = 1, 2, 3 & 5) and (iii) turbulent jet Reynolds numbers (15000, 25000 & 35000). The topology and three-dimensional separation phenomena are used to explain the flow and heat transfer characteristics. The skin friction lines on the interaction surface are explained with the help of nodal points of attachment and separation, saddle point, separation, and attachment lines. It is observed that the skin friction lines change their pattern with H/D and cross-flow. Peaks in the heat transfer are observed corresponding to the impingement point and wall jet interaction points. At lower H/D values, the effect of cross-flow is more prominent. However, these effects are marginal for higher H/D values. For lower H/D, the localized heat transfer rates are high but the uniformity in heat flux is obtained with an increase in H/D. In maximum and medium cross-flow cases, the heat transfer pattern changes with the distance from the center of the plate. It is found that the flow structure on the surface is independent of the jet Reynolds number.
Dynamic Seal Test Rig: O-Ring Leakage and Sliding Friction Measurements
Authors: Kerr Thomas , Nielson Jordan 
Published: October 2022

Abstract
Sliding seals play a critical role in the dynamic sealing of a wide-variety of machinery applications. There are many type of sliding seals, such as segmented carbon ring, O-ring, or bellows; and are used as sealing elements in hydraulic rod and piston seals, as well as secondary sealing elements in mechanical and dry-gas seals. Motion between the dynamic and static parts of the machine is most often lubricated by the process fluid, and therefore has leakage. This paper presents a new test rig capable of measuring leakage and friction force of annular sliding seals for a range of sealing pressures (0–24.8 MPa), temperatures (20–700 C), gasses, and motion. The rig is capable of large linear motions and high frequency dynamic motion. The large linear motion replicates piston movement or shaft thermal growth and the dynamic excitation matches the typical vibration response from a spinning shaft. Currently, there is little available information in the literature on the leakage performance of dynamic O-rings at high pressures, especially for gas sealing. The paper presents experimental results from two different material, 150 mm diameter, O-rings at sealing pressures up to 70 bar (1,000 psi) in CO2. The rings were tested for large ranges of motion, up to 4 mm. Two different durometer FKM O-rings (70 and 90) were compared to a 70 durometer BUNA O-ring. The softer rings exhibited superior leakage performance, and similar friction forces. The BUNA O-ring performed slightly better at sealing (10–20%) then the similar hardness Viton ring.
Tip Vortex Effects on Air-Cooled Condenser Axial Flow Fan Performance
Authors: Pretorius Johannes P. , Van Der Spuy Sybrand J. , Strümpfer Martin 
Published: October 2022

Abstract
Air-cooled Condensers (ACCs) are often used as main cooling system in modern power generation applications. These systems employ a multitude of large diameter axial flow fans, which draw power and reduce the net power produced by the power station. The improvement of fan operational efficiencies could therefore have a considerable positive influence to reduce these parasitic loads. This study aims to reduce the effect of blade tip vortices in order to improve fan performance. This is achieved through the addition of endplates at the blade tips. Previous work only drew preliminary conclusions, due to constraints in testing at a representative large tip clearance and the necessity to test at reduced speeds to avoid contact between the tip appendages and the fan casing. Through the introduction of a new fan hub design, experimental investigations are repeated on the same ACC scale fan to evaluate the effect of two tip endplate designs on fan performance. Results from testing confirm previous preliminary findings — increased fan static pressure rise and fan static efficiency are found when incorporating blade tip endplates, compared to the unmodified fan.
The Development of Turboexpander-Generators for Gas Pressure Letdown Part 3: Design Validation
Authors: Najeeb Ovais Ahmed Bin , Khatri Rasish , Zheng Liping , Liu Jeremy 
Published: October 2022

Abstract
This paper is a follow-up to GT2021-60125 (“Design and Analysis”) and GT2021-60317 (“Economic Analysis”), which collectively covered the design, analysis, and economics of innovative Turboexpander Generators (TEG) used in pressure letdown (PLD) applications. This paper describes the testing data of a family of TEGs, 280 kW and 125 kW, for natural gas pressure letdown applications. The TEGs are supported by active magnetic bearings (AMB). Machine design for the two TEGs is very similar for ease of manufacturing and control system design, with wheel design being the primary difference. A comprehensive controls analysis and AMB closed-loop dynamics study were presented earlier. This paper compares predicted and measured transfer functions along with the pre and post brush seals installation data. Drop testing results on the touchdown bearing are shown along with the full-speed touch-down events. Active front-end variable speed drive (VSD) design is presented along with the power generation results. Finally, measured force vs deflection data is presented for a tolerance ring, used as the resilient element for the touchdown bearings.
FELTMETAL™ Abradable Turbine Seal Materials: Structure and Property Responses to Blade Rub and Oxidation
Authors: Motyka Elaine , Schricker Robert , Ceiler Kelly 
Published: October 2022

Abstract
Abradable seals are a common technology employed to improve turbine engine performance by reducing the gap between blades and the casing in compressor and turbine stages. Because operating conditions and material requirements vary significantly as a function of turbine stage and turbine design, many abradable compositions have been developed. Generally, all abradable seal materials employ voids or pores in the microstructure as a designed-defect to mitigate thermal and kinetic energy from blade rub. Some also have added non-metallic phases to provide other means of maintaining a seal that is sacrificial to the blade tip.
This paper describes the microstructures of specific fiber metal abradable materials known as FELTMETAL™, as well as the distinctly different abradable microstructures of honeycomb material and thermal spray coating. The effect of the porosity and metallic surface area in each type of microstructure on seal abradability and seal oxidation is discussed. In addition, the effect of oxidation by aging at elevated temperatures on strength, ductility, and abradability for several FELTMETAL™ materials is also discussed.
It is proposed that the pore structure aids in mitigating blade contact energy primarily by internal deformation of the metal matrix surfaces and that abradability is improved by formation of protective metal oxide films that reduce ductility without significant loss of strength.
Numerical Investigation of the Effect of Trailing Edge Thickness of Simulated CMC Blades on Loss Profiles
Authors: Miki Kenji , Ameri Ali 
Published: October 2022

Abstract
Ceramic Matrix Composite (CMC) is an enabling material allowing higher turbine inlet temperatures and possibly resulting in better thermal efficiency of gas turbine engines. This is because CMC layers with environmental barrier coating (EBC) have significantly higher thermal limits (∼1755K) compared with the more conventional alloyed metallic blades. CMCs possess a complex fabrication process resulting in different geometrical characteristics than metallic blades (e.g., larger trailing edge thickness, large leading-edge curvature, etc.). It is therefore desirable to assess the aerodynamic performance of the CMC blades using experimental and numerical simulations. To investigate, three different CMC blades with varying trailing edge thicknesses were numerically simulated. Both Large Eddy simulation (LES) with the dynamic subgrid closure as well a recently implemented Reynolds-averaged Navier-Stokes (RANS) coupled with an intermittency function-based transition model were utilized. Two sets of experimental test points with different Reynolds numbers at a given high-free stream turbulence range (Tu = ∼10–13%) were considered. The LES was previously validated by comparing with experimental data. The RANS transition model was validated against the experimental data of the Stripf’s for a turbine blade. The predicted pressure loading profiles, total loss distributions, and integrated loss of the three different CMC blades were computed and comparisons against the experimental data are presented herein. The mixing and boundary layer loss was evaluated by both the RANS and LES and was found that the mixing loss forms a larger proportion of the overall loss as the trailing edge thickness increases.
Shape Optimization of the Laidback Fan-Shaped Film Cooling Hole on Pressure Surface of Turbine Guide Vane
Authors: Jiang Yan , Tao Zhi , Li Haiwang , Zhou Zhiyu 
Published: October 2022

Abstract
The present study employed computational fluid dynamics (CFD) to explore the effect of the shape parameters of fan-shaped holes on film cooling effectiveness, and the optimum values and variation laws of each shape parameter to maximize the averaged film cooling effectiveness were presented. Meanwhile, experimental verification was used in the optimum holes and reference cylindrical holes.
Among the shape parameters of a laidback fan-shaped film hole, the injection angle, the hole diameter and the hole length were fixed as 30 degrees, 0.5 millimeter and 2 millimeters, respectively, and the three shape parameters, the forward expansion angle, the lateral expansion angle, and the shaped-length ratio, were selected as design variables by the Box-Behnken Design (BBD) method. And RSM (Response Surface Methodology) was used to obtain the optimized values of each parameter. Results show that the film cooling effectiveness of the optimized hole (15-20-0.25) was higher than that of the reference cylindrical holes by 336%. The factors influence analysis showed the film cooling effectiveness increased as the forward expansion angle increased, and increased and then decreased with the lateral expansion angle and the shaped-length ratio. The points of the change in trends were when the lateral expansion angle was almost equal to 15 degrees and the shaped-length ratio was nearly 0.475, respectively. Moreover, there was the oscillation of the film cooling effectiveness distribution, possibly due to the asymmetric and irregular distribution of velocity w of the injected coolant along the downstream direction, when the holes outlet area was excessive. In general, the variation laws were not monotonous; therefore, all shape parameters should be considered simultaneously to achieve shape optimization of the laidback fan-shaped film cooling hole on pressure surface of turbine guide vane.
Calculating Cooled Turbine Efficiency With Weighted Cooling Flow Distributions
Authors: Berdanier Reid A. 
Published: October 2022

Abstract
The ability to accurately characterize the thermal efficiency of turbine stages with cooled components is essential to advance turbine technologies. There are many methods for calculating aerodynamic efficiency of turbomachinery components, with most encompassing either single point or simple integrated values at the inlet and exit locations. For cooled turbine stages, there is an added complexity of how to incorporate cooling flow streams. Although these techniques may include multiple cooling flows, a fully-mixed assumption is often invoked without directly accounting for distributions of cooling flow in the annulus. However, the distribution of cooling flows in turbine stages may vary significantly depending on the location and nature of injection. This study addresses how calculated efficiency may vary depending upon how cooling flows are injected and the manner in which these cooling flows are accounted. The analyses utilize experimentally measured cooling flow concentration profiles to motivate a new approach for calculating cooled turbine efficiency with weighted cooling flow distributions. Validation data for a one-stage high-pressure turbine geometry from the Energy Efficient Engine (E3) program are assessed to determine the range of influence for cooling flow distributions. Results show that cooling flows injected at similar axial positions can have unequal influences on integrated stage efficiency based on known distributions of cooling flow and other properties at the turbine stage exit plane. In some cases, deviations approaching half a point of efficiency can be observed relative to traditional equations, and the magnitude of influence is shown to increase as stage total pressure ratio decreases.
The Inter-Bristle Pressure Field in a Large-Scale Brush Seal
Authors: Bowen Joshua P. , Jenkins Matthew R. , Bowsher Aaron A. , Crudgington Peter F. , Sangan Carl M. , Scobie James A. 
Published: October 2022

Abstract
Brush seals promise improvements to the widely used labyrinth seal in regulating turbomachinery leakages. Enhanced resistance to the flow is provided by a static ring of densely packed fine wire bristles that are angled in the direction of rotation and flex to accommodate rotor excursions. A large-scale brush seal was constructed to study the leakage characteristics in direct relation to the pressure field within and surrounding the bristle pack for multiple clearance conditions, therefore developing the understanding of brush seal fluid dynamic behaviour.
The governing parameter controlling leakage behaviour transitioned from pressure ratio for a large clearance, to pressure load for a line-on-line configuration. In all cases, leakage flow converged to an asymptotic value once maximum levels of bristle blow-down and pack compaction were attained. For both clearance configurations, this occurred at a pressure ratio corresponding to that at which axial distributions of pressure converged; equivalent behaviour was noted for the line-on-line configuration with pressure drop. Comparatively small changes were experienced in leakage behaviour and to the inter-bristle pressure field with increasing pressure drop for the line-online brush seal. This indicated that brush seal performance is more influenced by changes in bristle blow-down than bristle pack compaction.
Creep Analysis and Microstructural Evaluation of a Novel Additively Manufactured Nickel-Base Superalloy (ABD®-900AM)
Authors: Bridges Alex , Shingledecker John , Clark John , Crudden David 
Published: October 2022

Abstract
Nickel-base superalloys containing 30 to 50% gamma prime (γ′) volume fraction are typically used in hot section components (e.g. guide vanes or blades) for power generating gas turbines, and suitable time dependent properties are required for long-term elevated temperature operation. Additive manufacturing (AM) has recently been used to develop complex hot-section parts utilizing innovative designs with enhanced cooling features which improve efficiencies by reducing cooling air consumption.
To further explore the opportunity to improve time-dependent AM superalloys, this paper focuses on a fundamental creep study and characterization of a novel nickel-base superalloy (ABD®-900AM) that was manufactured using a laser-based powder bed fusion AM process. The material was subjected to a sub-solvus solution anneal and multi-step aging heat-treatment to produce a bi-modal distribution with ∼35% volume fraction of gamma prime without post-processing hot isostatic pressing (HIP). Microstructural characterization was carried out for the as-built and fully heat-treated structures, and a creep-rupture test program was conducted to study the resultant creep properties. Activation energies and stress exponents in addition to rupture strength and deformation resistance, were compared to traditionally cast IN939 and IN738 materials. After testing, specimens were evaluated using a variety of microscopy tools to determine location and features associated with creep damage.
The optimized chemistry for ABD®-900AM was printed crack free and fully dense in contrast to studies on similar alloys where significant process development and post-build heat-treatments were required. High-temperature mechanical properties in the heat-treated material showed some decrease in creep strength when compared to traditional casting. This strength and rupture life debit was dependent on build orientation, but a considerable increase in creep ductility was observed due to differences in the microstructure when compared with similar AM alloys. Analysis of creep data showed differences in creep mechanisms compared to traditional cast alloys. The relationship between microstructure and creep mechanisms is discussed, and ongoing work to further improve rupture strength through heat-treatment optimization will be highlighted.