bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Collaborative Framework for Design and Validation of Next-Generation Transonic Low-Pressure Turbines
Authors: Cernat Bogdan , Halby Alexandre , Lavagnoli Sergio , Rubechini Filippo , Guidolotti Stefano , Hanifi Ardeshir , Mihaescu Mihai , Lengani Davide , Bertini Francesco 
Published: August 2024

Abstract
This paper presents the design of a transonic low-pressure turbine (LPT) for the next-generation fighter air-breathing engines. The study focuses on the design of a cascade profile representative of an LPT Nozzle Guide Vane (NGV), that follows conventional literature guidelines for transonic turbine airfoils. The paper reports on the numerical and experimental methods that will be employed for a detailed understanding of the flow physics for this baseline solution.
The experimental setup includes a high-speed linear cascade that can be operated at a wide range of inlet turbulence levels (Tu = 5%–8%) and outlet Mach numbers (M = 0.8–1.2). The test section inlet is equipped for hot-wire anemometry measurements, while a purposely designed multi-hole probe is traversed to measure the aerodynamic flow quantities at the cascade outlet. The central passage airfoils feature arrays of pneumatic pressure taps to evaluate the blade loading and hot films to study the status of the boundary layer. Optical sidewalls enable full-field Schlieren and Background-Oriented Schlieren imagery to study cascade shock patterns and unsteady shock-boundary layer interactions. The test section is designed with provision for time-resolved stereo-PIV measurements to cross-validate the cascade velocity field and quantify the turbulence statistics and transport mechanisms through the transonic LPT passage.
A detailed planning for high-fidelity flow simulations (LES and DNS) is presented in the second part of the paper. State-of-the-art computational methodologies will be employed along with advanced post-processing techniques including mode decomposition to enhance the understanding of the flow physics, assess the limitations of traditional numerical methods and complement the experimental findings.
Integration of Cooling Holes Into a Turbine Vane Made Using Additive Manufacturing
Authors: Gailey Nicholas L. , Barringer Michael D. , Berdanier Reid A. , Thole Karen A. 
Published: August 2024

Abstract
Additive manufacturing (AM) has emerged as a method to prototype novel designs for turbine airfoil cooling with complex internal and film cooling geometries. Creating engine scale features with AM comes with challenges that impact flow and heat transfer, which consequently affect the overall performance of the component. While AM has proven to be faster and more cost effective than traditional casting methods, the scalability of AM requires further investigation. The purpose of this study was to integrate various film-cooling hole geometries identified through large-scale models and true-scale simple coupons into a true-scale turbine vane to assess overall cooling effectiveness. The National Experimental Turbine (NExT) vane was additively manufactured with a singular cooling passage feeding two rows of film-cooling holes: a row of baseline 7-7-7 holes; and a row of holes containing both parametrically optimized 15-15-1 holes and modified adjoint optimized cross flow (X-AOpt) holes. The internal passage was designed to have a section with ribs and a section without ribs to assess how internal features impact the cooling holes’ performance. The vane was tested in the Steady Thermal Aero Research Turbine (START) rig over a range of film cooling blowing ratios. A combination of computed tomography (CT) scanning and non-contact infrared (IR) thermal imaging measurements were used to evaluate how as-built geometries impacted the overall cooling effectiveness on the NExT vane for each hole group. The 15-15-1 film cooling holes with no internal ribs was shown to be the most effective in lowering surface temperatures relative to the other cooling hole configurations. Also, the 15-15-1 holes with no internal ribs to affect the cooling flow entrance to the hole was the least affected by blowing ratio changes. The 7-7-7 hole was found to have a negative impact on the vane because the downstream surface was warmed by a separating internal channel wall.
Aeroelastic Influence of Blade-Shaft Coupling in a 1 1/2-Stage Axial Compressor
Authors: Maroldt Niklas , Seume Joerg R. 
Published: August 2024

Abstract
During the design process of turbomachinery, it is often not possible to use aerodynamically optimal designs due to aeroelastic constraints. The design choices are limited by possible structural failure, which can be caused by high vibration amplitudes, for example due to self-excited vibrations (flutter) or forced response. In particular, the modal damping has an important impact on these phenomena. In the absence of frictional contacts, damping is mainly created by aerodynamics. In this paper, the influence of additional damping created by the rotor bearing on the total damping and on forced vibrations will be investigated. This influence becomes relevant when blade vibrations with nodal diameters 1 and −1 couple with the shaft vibrations. The coupling is caused by a structural dynamic interaction of these two components. To investigate the blade-shaft coupling, a simulation process is set up to best represent the physical effects during operation. This simulation process is essentially based on a full structural dynamic model of the blisk-shaft assembly and a harmonic balance CFD model to account for the aeroelastic effects. In addition, mistuning identification is performed based on an experimental modal analysis at standstill. All results are incorporated into a structural reduced order model that calculates the vibrational behavior of the blading. These results are compared to damping determined during operation using an acoustic excitation system and measured forced frequency responses. The numerical results agree well with the experimental results, i.e. within the measurement uncertainty, both with respect to the damping and the mistuned frequency responses. Furthermore, the blade-shaft coupling results in significant changes of the eigen-frequencies and damping. As a consequence, damping increases by up to twelve times when taking the coupling into account. This reduces amplitudes by a factor of nine for the mistuned blade responses. Consequently, higher structural safety factors can be achieved by taking the blade-shaft coupling into account so that the remaining potentials in the aerodynamic design could be better exploited.
Mitigation of Laminar Separation Bubble Through Leading-Edge Modification of an Aerofoil With Herringbone Riblets
Authors: Kumar Ravi , Singh Pradeep , Sarkar Subrata 
Published: August 2024

Abstract
The present study describes the potential of a passive technique involving the leading-edge modification using herringbone riblets with a triangular cross-section in mitigating the leading-edge separation at various angles of attack (α). Pressure and instantaneous flow measurements by hotwire were performed over a semicircular leading-edge aerofoil for α — 0°, 3° and 5° with and without leading-edge modification. The Reynolds number (Re), based on the chord length and the inlet freestream velocity, was 1.6 × 105, where freestream turbulence (fst) being 1.2%. A laminar separation bubble is witnessed on the hydrodynamically smooth leading-edge aerofoil at all α where the transition is governed by inviscid instability. Leading-edge modification with herringbone riblets induced higher turbulence in proximity to the wall, resulting in an earlier transition of the shear layer and a reduction in bubble length by 36–20% for α = 0–5° along with a change in the transition mechanism. In brief, herringbone riblets show promising results in reducing the leading-edge separation.
Economic Modeling of Renewable Integration and the Application of Energy Storage to the ERCOT Energy Grid
Authors: Karg Bulnes Fernando , Hofer Douglas , Smith Natalie R. , Schmitt Joshua , Pryor Owen , Khawly George , McClung Aaron 
Published: August 2024

Abstract
As the energy sector transitions to lower carbon emission solutions, there is a need to better understand the limitations and impacts of increased renewable energy generation sources on the grid. This study investigates the potential for energy storage technology across Texas using historical data of renewable energy sources. The Texas electric grid currently relies mostly on wind and natural gas to meet its load, with both seasonal and daily variations due to the availability of renewables. The Texas electric grid data for 2022, published by ERCOT, showed a yearly consumption of over 428,000 GWh, out of which 36% is covered with natural gas, 25% with wind, 6% with solar, 17% with coal, and the rest using other electric sources. This study focuses on a techno-economic evaluation of behind-the-meter commercial microgrids to evaluate the impacts of energy cost and renewable penetration on the Texas energy landscape by increasing the levels of solar photovoltaic and wind generation along with energy storage and decreasing the state’s reliability on fossil fuels (coal and gas). The results are assessed from the perspective of a large commercial user with a dedicated behind-the-meter microgrid used to minimize or replace purchased grid power across eight different regions. To complete the analysis, an in-house tool will be used to assess the techno-economics for different levels of renewable energy generation and decarbonized generation with various energy storage sizes with a specific energy cost and load in the distinct load zones across the Texas grid. Conclusions are drawn for optimal renewable penetration at this scale with the addition of the proper amount of storage.
Dry Gas Seal Condition Monitoring With Embedded Acoustic Emissions Sensors
Authors: Palmer Christopher , Fritz Colleen , Kotar Chris 
Published: August 2024

Abstract
Dry gas seals (DGS) are commonly used in turbomachinery applications when handling gases. These applications include centrifugal compressors, expanders, and turbines. Historically, DGS have been monitored via leakage and pressure measurements taken outside of the compressor. In recent years, researchers and DGS manufacturers have developed monitoring systems with sensors embedded in the seal. These systems allow seal designers, equipment manufacturers, and machinery operators to monitor the condition of the seal during operation via direct seal measurements as opposed to the traditional downstream or upstream measurements.
Acoustic Emission (AE) sensors measure high frequency elastic waves. Embedding these sensors into a DGS offers an exciting possibility to measure elastic waves propagating through the DGS metalwork.
This paper will show how measuring acoustic vibrations on a test rig and on field installations provides the opportunity to monitor the health of a DGS.
Investigation on Flow Field Characteristic in a Double-Wall Configuration Using MRV and CFD
Authors: Duan Jingtian , Zhang Ke , Wang Zirui , Chen Ruoyu , Yang Yibo , Lei Jiang , Wu Junmei 
Published: August 2024

Abstract
The three dimensional full flow field distribution of a double-wall cooling structure including impingement jets, pin fins and film effusion holes is measured by magnetic resonance velocimetry (MRV). The flow field in the same geometry is simulated numerically using commercial code as well. Flow field results from MRV are used to validate the reliability of different turbulent models. MRV resolves the complex three dimensional flow field inside and outside the double-walled sandwich. The affecting regions of impingement jets on the target wall, as well as the interaction between the film jet and mainstream boundary layer is discussed. Flow establishment, shear layer and jet deflection regions of impingement jet inside double-wall structure are identified using measured flow field. Possible cooling mechanism in the double-wall structure is discussed based on the resolved full-field three dimensional flow.
Effect of Frequency Characteristics and Swirl Brakes on Fluid Destabilization Force Acting on Compressor Closed Impeller Leakage Path
Authors: Iwasaki Makoto , Nishida Shingo , Yamashita Shuichi , Oda Takashi 
Published: August 2024

Abstract
In turbomachinery, the trend toward higher performance, smaller size, and higher speed has led to a decrease in the rigidity of the rotor system and an increase in the pressure and flow velocity, which in turn has increased the fluid destabilization force and increased the risk of vibration problems. The fluid destabilization forces generated at the front shroud and labyrinth seal components have been studied for many years. However, there are few measured data on the frequency characteristics of the fluid destabilization force in a system-level test combining a front shroud and a labyrinth seal. In this paper, dynamic characteristic tests were conducted using air as the working fluid in a closed impeller single-stage test rig.
In the closed impeller single-stage dynamic characteristic test, the rotor was excited with a hydraulic shaker while the 381mm diameter impeller was rotating at a maximum of 11,000 rpm. From the measurement results, it was confirmed that pressure fluctuations of the same order of magnitude as those of a labyrinth seal were generated in the front shroud. Since the front shroud has a larger pressure receiving area than the labyrinth seal, it was confirmed that the front shroud has a very large effect on the fluid destabilization force in the closed impeller leakage path.
As a device to reduce the fluid destabilization force in the closed impeller leakage path, this paper proposes the installation of the swirl brakes on the front shroud instead of at the labyrinth seal inlet. To validate the effectiveness of the swirl brakes, dynamic tests were conducted without and with the swirl brakes. Comparative test results showed that the swirl brakes can significantly reduce the fluid destabilization force.
Transient CFD analysis was conducted as a method for predicting the fluid destabilization force, and the prediction accuracy of the CFD analysis method was confirmed by comparing the CFD analysis results with the measured fluid destabilization force. Furthermore, by visualizing a portion of the leakage path with glass, the surface distribution of pressure fluctuations acting on the closed impeller leakage path was measured using Pressure-Sensitive Paint (PSP). The visualization test results also confirmed that significant pressure fluctuations were generated not only at the labyrinth seal but also at the front shroud, thus confirming the validity of the CFD analysis method.
Reduction of the Excitation of Volute on Turbine Rotor by a Groove Treatment
Authors: Wang Yv , Chen Hua 
Published: August 2024

Abstract
Nozzleless volutes are often used to provide required flow conditions to downstream radial and mixed flow turbine rotors. These flow conditions are generally not circumferentially uniform, with a sharp change around volute tongues. Due to this non uniformness, rotors blades will experience an aerodynamic force excitation in rotor rotating frequency. This excitation could cause high cycle fatigue (HCF) of rotor blades if the natural frequencies of rotor blades coincide with those of its harmonics. To avoid this HCF, turbine rotors are designed typically with their natural frequencies several times above the highest rotating frequency of rotors, but this increases rotor weight and reduces rotor efficiency.
Various efforts have been made to reduce the excitation force created by nozzleless volutes. Here we propose a simple method by adding in turbine housing a small groove located near rotor leading edge (LE) shroud. The idea is that when a rotor blade rotates passing through the groove, blade loading around LE will reduce suddenly, creating an excitation to the blade, and by circumferentially positioning the groove correctly, the excitations from volute and the groove will partially cancel each other. A hypothesis to allow easy prediction of the best positions of the groove is also put forward.
The idea was applied to an industrial turbocharger turbine for heavy truck application to reduce the 3rd order excitation generated by its turbine volute. The nozzleless volute was well designed so that the 4th order excitation is no longer an issue. The Campbell diagram was first used to obtain the rotor speed of resonance, and unsteady computational fluid dynamics (CFD) then applied to obtain the excitation force on rotor blades both with and without the groove. The resultant alternative vibratory stress of blades was obtained by a harmonic response method and results were compared. They show more than 55% reduction of the maximum vibratory stress, while turbine mass flow is reduced by 0.89% and efficiency by 0.45% points.
Influence of the Tip Winglet Structure Modeling on Leakage Flow at a High-Load Compressor Stage
Authors: Zhong Jingjun , Zhao Ao , Hu Yi , Wu Wanyang 
Published: August 2024

Abstract
Tip winglet technology is an effective method for increasing the stable operating range of compressors. This paper examines six types of pressure-side tip winglets with varying circumferential widths and chord lengths, to assess their influence on the stability expansion ability and flow structure of the compressor stage. The effectiveness of stability expansion via tip winglets is enhanced with increased tip winglet width. Specifically, when the tip winglet width reaches twice that of the rotor blade tip width, the stable operating margin improvement can attain 11.43%. Moreover, when the tip winglet width is 1.5 times the rotor blade tip width, the full-chord tip winglet yields the most significant stability expansion effect, surpassing that of partial-chord length tip winglets.
Tip winglets mitigate the leakage mass flow rate by balancing the mismatch in flow velocity components, exacerbating leakage flow deterioration. Concurrently, the degree of leakage vortex fragmentation is weakened, controlling the accumulation of low-energy fluid within the passage. Furthermore, tip winglets prevent the concentration of low-energy fluid in the radial region, effectively enhancing the flow structure and stability of the compressor. When designing the tip winglet structure, it is crucial to maximize the stable operating margin of the compressor stage without compromising efficiency. To this end, extending the blade into the passage from the 90% chord to the rotor trailing edge should be avoided.
Spatial Temperature Measurements in a Swirl-Stabilized Hydrogen-Air Diffusion Flame at Elevated Pressure Using Laser-Induced Grating Spectroscopy
Authors: Chaib Oussama , Weller Lee , Giles Anthony , Morris Steve , Williams Benjamin A. O. , Hochgreb Simone 
Published: August 2024

Abstract
Laser-induced grating spectroscopy (LIGS) is applied, for the first time, to a swirling non-premixed hydrogen-air flame in a high-pressure combustion facility. A portable LIGS unit is used to probe 35 different axial and radial locations in the flame and a new conditioned processing approach based on laminar flame simulation is introduced to infer temperatures from instantaneous LIGS spectra. Thermal and electrostrictive frequencies are used to produce a spatial map of temperatures in the combustor. Temperatures up to 2,500 K are measured in this work, which constitute the highest temperatures ever measured using LIGS. Challenges associated with the deployment of the technique in turbulent stratified hydrogen flames are discussed, as are potential measures to overcome them, including the use of data-driven clustering techniques.
Roughness Effects on Dense-Gas Turbine Flow: Comparison of Experiments and Simulations
Authors: Gloerfelt Xavier , Hake Leander , Bienner Aurélien , Matar Camille , Cinnella Paola , aus der Wiesche Stefan 
Published: August 2024

Abstract
This paper presents a combined numerical and experimental study of the high-subsonic organic vapor flow in a linear turbine cascade. The profile geometry is the well-documented LS59 highly-loaded rotor blade and the working fluid is Novec649, a dense gas used in organic Rankine cycles. Large-eddy simulations are carried out with and without the roughness introduced by the additive manufacturing process. The results for the rough blade are in fair agreement with experiments, while the smooth surface induces a change in the vortex shedding regime. A detached shedding, characterized by a long recirculation downstream of the trailing edge and a base-pressure plateau, is obtained in the experiments and by discretizing the roughness in the simulation. By contrast, a transonic vortex shedding is established when the surface is smooth: intense vortices roll up immediately after the trailing edge, yielding a short bubble and a lattice of shock waves. A strong pressure drop is observed at the trailing edge, resulting in high profile losses. In both cases, the boundary layer is turbulent ahead of the separation but its thickness is significantly greater in the rough configuration, which may be the reason for the change of regime.
Numerical Surface Roughness Influence on the Aerodamping of an Axial Transonic Compressor at Nominal Speed and Part-Speed
Authors: Tavera Guerrero Carlos , Gutierrez Salas Mauricio , Glodic Nenad , Deshpande Srikanth 
Published: August 2024

Abstract
In a turbomachine, with time, wear and depositions modify the surface from smooth to rougher characteristics. These effects are also prevalent in emerging manufacturing technologies such as additive manufacturing (AM). Surface roughness characterization is based on a correlation between a physical length scale or surface statistic moments, and a non-physical equivalent sand-grain roughness (ks). Depending on the flow characteristics and ks, three wall regimes can be considered: hydraulically smooth, transitional or fully rough. In compressors, an increase in surface roughness translates into a reduction in efficiency and pressure ratio. While steady-state roughness effects over airfoils and stage performance are well documented, its consequences over the aerodynamic damping are not. This paper aims to investigate numerically the effect of surface roughness on the aero-damping for the three wall regimes. The test geometry is the first stage of an open-source transonic axial compressor. Operating points considered are peak efficiency and near-stall conditions at nominal speed (N100) and part-speed (N70). The presented numerical simulations are obtained using the commercial software Ansys CFX with SST as the turbulence model with a reattachment modification. At near-stall part-speed, there are non-physical separation regions that are mesh independent but assumed to come from the numerical roughness implementation. Amplitude fluctuations in the aerodynamic damping per unit area, ζ*, are driven by the tip gap presence as well as normal shocks at N100 whereas the presence of separated flow regions appear to have a negligible effect at N70. The phase between the pressure and blade motion appears to remain almost constant regardless of the wall regimes, implying that only the amplitude distribution drives the aerodynamic damping stability. This numerical observation is aimed to be experimentally tested at the transonic linear cascade at KTH Royal Institute of Technology.