bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhanced Modelling of the Phenomenon of Vortex Shedding From a Low-Speed Axial Flow Rotor Blade Profile
Authors: Daku Gábor , Vad János 
Published: August 2024

Abstract
The paper presents CFD case studies on vortex shedding from an asymmetric RAF-6E airfoil profile being a representative of low-speed axial fan rotor blades, for angles of attack of α = 0.0°...2.7°, and chord-based Reynolds numbers Rec = (0.6...1.0) · 105. The shed vortices were identified on the basis of Lagrangian-averaged vorticity deviation. An organized dataset has been established for a comprehensive overview of the profile vortex shedding (PVS) phenomenon, enabling order-of-magnitude estimation of data and trends related to the size, rotation, circulation, and travelling velocity of the vortices. Literature-based rotationally symmetric aerodynamic models, as well as a simplified description of source term of vortex sound were applied to the shed vortices. On this basis, an enhanced modelling of PVS has been carried out for a straightforward and yet adequate consideration of the concerted aerodynamic and aeroacoustic aspects of PVS. Such modelling can give a contribution to preliminary fan design by taking the effects of PVS into account on blade vibration and fan noise.
Rejuvenation Heat Treatment Development to Extend the Service Life of René N4 Single Crystal Gas Turbine Blades
Authors: Motta Cristina , Mastromatteo Francesco , Gariboldi Elisabetta , Cappuccini Filippo 
Published: August 2024

Abstract
Single crystal superalloys are widely used for gas turbine blades exposed to high stresses, high temperatures in aggressive environments. When these components reach their serviceable limit, they must be replaced by new ones, with an important impact in terms of maintenance costs. Significant savings can be achieved through the application of a rejuvenation heat treatment, able to extend the life of a serviced turbine blade beyond its original design intent and avoid parts scrap.
The success of such a technology for SX-superalloys is related to the effective restoration of the original γ/γ’ microstructure, which is linked to the material mechanical properties, without impairing the original single crystal structure. Indeed, one challenge in designing a rejuvenation heat treatment for single crystal superalloys is the risk of recrystallization, which must be kept under control. This work is focused on the development of a rejuvenation heat treatment for René N4 alloy. Different rejuvenation cycles have been explored through an in-depth material characterization, using samples taken from both new material and real serviced gas turbine blades. Several solutioning heat treatments have been investigated in a window ranging from the theoretical γ’ solvus temperature and the original solutioning temperature used during blades manufacturing.
The assessment of the candidate rejuvenation heat treatments effectiveness is based on the evaluation of microstructure γ/γ’ restoration and the presence of recrystallized grains.
Numerical Method for Investigating Non-Ideal Flow Demonstrated on a Centrifugal Compressor Operating Near the Critical Point of CO2
Authors: Tegethoff Katharina , Borges de Almeida Carolina , Schuster Sebastian , Brillert Dieter 
Published: August 2024

Abstract
This paper focuses on the numerical investigation of the flow of CO2 in the so-called supercritical state (sCO2) through a centrifugal compressor by means of Computational Fluid Dynamics (CFD). The thermodynamic state of the fluid at the inlet of the compressor is characterised by its close vicinity to the critical point and the two-phase region. The low compressibility factors and high gradients of the flow variables marking this state region place high demands on the numerical methods used. First, a high accuracy in the description and evaluation of the thermodynamic state variables must be ensured. For this purpose, the modelling of the fluid as non-ideal is indispensable. Second, the numerical scheme must be robust against oscillations of the changes of state occurring in the course of the iterative solution, otherwise no converged solution can be obtained. This paper aims to contribute to the selection and utilisation of numerical solution methods for sCO2 applications in terms of stability and computing time efficiency. For this purpose, the flow solver TRACE, developed by the German Aerospace Center (DLR), was enabled to compute non-ideal compressible flows. By implementing an adapted Roe scheme, the GIRoe scheme, which is applicable to arbitrary equations of state, a converged solution can be achieved despite high gradients in the flow field and compressibility factors in the order of magnitude of 0.2. The use of state variables stored in the form of tables, which are evaluated based on the Tabular Taylor Series Extrapolation, leads to a reasonable computing time even for industrial applications. The presented methodology thus has the potential to enable the numerical investigation of single-phase turbomachinery flows of arbitrary working media and fluid states in a computationally efficient and numerically stable way.
Effect of Operational Pressure Reduction on Axial Compressor Performance by Means of 3D CFD Modeling at Nominal Operating Speeds
Authors: Galindo José , Navarro Roberto , Pallás Borja , Torres Germán , Lluesma-Rodríguez Federico , Antoranz Antonio 
Published: August 2024

Abstract
The hyperloop system constitutes one of the most promising alternative means of transportation for the next years. Nevertheless, there are still some challenges to face, such as the blockage of the air surrounding the pod inside the tube. To solve that, one proposal consists of including a compressor that helps to relieve the pressure conditions between the pod and the tube. Thus, this work makes, for the first time in this context application, a numerical analysis with CFD tools of the performance of the compressor under low Reynolds conditions by decreasing the pressure of the system until hyperloop operation values. By doing so, it is observed how the compressor performance slightly decreases with the pressure. From this point, the efficiency is severely affected until the point where the compressor is totally lost. The flow analysis supported this idea. Initially, at high Reynolds, the flow behaved completely turbulent, and almost no separation was observed in the boundary layer. Later, some separation started to appear, but the turbulent nature of the boundary layer allowed the reattachment of it. Eventually, it was observed how the laminar conditions of the boundary layer at low Reynolds constitute the main reason for the huge detachments that appear. Other aspects were also explored, such as the interstitial losses at the tip, which seemed to work in the opposite direction, that is, decreasing with the lower pressures, but being globally way less important than the losses generated by the flow detachment.
Therefore, this work suggests that decreasing the pressure could have a big impact on the propulsive system of a hyperloop vehicle, even opening the door to develop an ad hoc turbomachine for its purpose.
Performance Modeling and Analysis of Hydrogen-Fueled Aero-Engines
Authors: Wang Xiting , He Ai , Chen Zhixiong , Jiang Jincen , Liu Yuan , Hu Zhongzhi 
Published: August 2024

Abstract
Amid increasing global demands for carbon neutrality, hydrogen-fueled aero-engines are drawing significant attention due to their zero carbon emissions. To fully harness the advantages of hydrogen-fueled aero-engines, it is essential to design appropriate configurations, including the selection of combustion chambers and the placement of heat exchangers. To investigate this issue, this paper initially surveys ongoing global research programs in hydrogen-fueled aero-engines, summarizing the demands of hydrogen-fueled aircraft and the prevalent configurations of hydrogen aero-engines. Subsequently, to evaluate the merits and limitations of various engine configurations, a specialized simulation platform dedicated to the performance analysis of hydrogen-fueled engines was developed. This platform is equipped with modules specifically designed for hydrogen-fueled aero-engines, including hydrogen fuel, steam injection combustor, and hydrogen fuel heat exchanger modules. These components facilitate the modular assembly of diverse engine configurations, thereby enabling preliminary selection and optimization of engine configurations. Ultimately, employing this platform, the study constructs models of three prevalent hydrogen-fueled aero-engine configurations and undertakes a comparative performance analysis, assessing the relative strengths and weaknesses of each configuration under varied operational conditions, thus providing a robust foundation for future engine configuration design.
Impact of High-Temperature Radiation on the Heat Transfer Characteristics of Film-Cooled Guide Vanes in Gas Turbines
Authors: Wang Meng , You Ruquan , Li Haiwang 
Published: August 2024

Abstract
With the increase in pre-turbine temperatures and the development of cooling technologies, radiation is crucial in vanes’ designs. The present work investigated the radiative transfer of film-cooled guide vanes. Firstly, the impact of radiation on the optically thin and thick thermal boundary layers (TBL) was analyzed using the derived formulas from the microscopic perspective. The findings confirmed that radiation can significantly increase the TBL thickness and the heat transfer rate. When the radiation-convection dimensionless parameter was equivalent to one, the total heat transfer coefficient was approximately 3.76 times higher compared to the case of pure convection. Secondly, the heat loads on the guide vane were numerically solved from the macroscopic perspective, considering the radiation behaviors of the absorbing gases based on the wide band K-distribution model. The findings indicated that the cooling films not only acted as barriers to hot gases but also resulted in convective cooling of the guide vanes in adiabatic conditions. Surrounded by a 1800K environment, radiation can reduce the cooling effectiveness by up to 40%. In addition, the radiation had the most significant impact on the leading edge, and radiation protection at the leading edge is imperative to ensure optimal safety and performance. Subsequently, the measurement procedures for the environmental radiation heat flux on the test plate was first proposed to help quantifying the radiation influence. The conclusions of this work will assist in a clearer understanding of the radiative heat transfer behavior in film-cooled guide vanes.
Influence of Varying Freestream Turbulence on Flow Transition Over Distributed Surface Roughness
Authors: Jain Ishita , Katiyar S. , Sarkar Subrata 
Published: August 2024

Abstract
High-fidelity Large Eddy Simulations (LES) are used to investigate the influence of distributed surface roughness on the spatially developing laminar boundary layer under varying freestream turbulence (FST) levels of 0.07 to 6%. The inlet Reynolds number based on the momentum thickness and freestream velocity is 360. The square-shaped (SQ) riblets that are employed in the present study are homogeneous in the spanwise direction and distributed in a series along the streamwise length. The aspect ratio (s/k) considered here is 3, where k is the riblet height, and s is the longitudinal spacing between the consecutive rows of riblets. The instantaneous flow structures reveal a Λ vortex-induced breakdown for FST levels below 3.2%, attributed to the near wall streamwise vortices arising from embedded recirculation regions between riblets. On the contrary, at a high FST level of 6%, the flow is characterized by low- and high-speed streaks generated via shear sheltering, resulting in the turbulent flow downstream. Moreover, an exponential growth of velocity fluctuations is apparent for a lower FST, which becomes algebraic for a higher FST. The onset and end of transition shift progressively upstream with an increase in FST. Interestingly, the flow features exhibit self-similarity in the turbulent region irrespective of FST levels.
Optimization of Tip Seal Grooves for Aerodynamic and Durability Improvements of Small-Core Turbines
Authors: Wiese Connor J. , Berdanier Reid A. , Thole Karen A. 
Published: August 2024

Abstract
While the clearance gap between the turbine rotor tip and the outer case in a gas turbine engine is necessary for the operation of the machine, the gap is kept as small as possible due to the detrimental effect of the flow over the turbine tip. With the increased investments in ultra-high bypass ratio gas turbines, blade tip clearances are increasing in relative size to the turbine rotor, as engines move towards smaller core sizes. In this work, a constrained topology optimization of a rotor tip seal with discrete axisymmetric grooves was explored computationally using Reynolds-averaged Navier-Stokes simulations. The differential-evolution-based optimization was applied at two tip clearances representing a nominal and small-core-scaled geometry. Furthermore, optimizations were performed at each tip clearance for blade designs with flat and squealer tips.
The multi-objective optimization was designed to simultaneously maximize rotor efficiency and minimize rotor tip heat load. Several tip seal designs were identified for each tip geometry and tip gap that both increased aerodynamic efficiency and reduced the total heat load into the rotor tip. However, some optimal tip seal designs were composed of grooves that were demonstrated to be detrimental in prior work. Furthermore, grooves were more effective at increasing aerodynamic efficiency when applied to flat tipped geometries — increasing the estimated rotor efficiency by up to 0.9 points over the ungrooved seal baseline with flat tipped blades, as opposed to 0.25 points of improvement over the ungrooved case with squealer tipped blades. Finally, for both tip configurations, optimal seal geometries that were obtained from the small-core scaled clearance gap optimizations generally maintained near optimal performance when evaluated at the design tip clearance, while those geometries developed at the design clearance experienced greater sensitivity to clearance gap changes.
Improving the Fatigue Life of an Additively Manufactured Stainless-Steel Specimen Using a Secondary Grinding Process
Authors: Ramachandran Murali Krishnan , Sumaiya Safia Alam , Golvaskar Mandar , Wood Julia , Sluder Isaac , Rakurty Chandra Sekhar , Rangasamy Nithin , Emuakpor Onome Scott , Kannan Manigandan 
Published: August 2024

Abstract
Grinding, an inexpensive and uncomplicated procedure, is commonly employed in most metallic manufacturing facilities to aid in the manufacturing process. With its abundance within industry, this provides an opportunity to use it as a method to also improve material properties such as strength, and fatigue. In addition to improving surface roughness, prolonging fatigue life, and strengthening material, a grinding process combined with a modified cooling method can raise compressive residual stress on metallic material surfaces. This study uses a typical grinding process and the improved grinding process to show imparted residual stress and surface roughness. Residual stress measurement tools were used to measure residual stresses imparted on the material through the thickness. Microstructural analysis via optical, and SEM microscopy was completed for typical and improved grinding methodologies. Mechanical testing through High Cycle Fatigue (HCF) was completed to verify improvement. To establish standards for the optimal mechanical qualities for a given material, this study will compare two distinct cooling techniques.
Spectral Heat Transfer Coefficient for Thermal Design Analysis - Part 2: Leveraging Diabatic Flow Conditioning for Nonlinear Regime
Authors: He Li 
Published: August 2024

Abstract
There are two main issues of interest in the context of Newton’s law of cooling as applied to turbine aerothermal designs. First, in a linear aerothermal regime in which both the conventional wisdom in general and the law of cooling in particular are notionally established, how do we deal with a non-isothermal wall where the surface temperature is nonuniform? Secondly, what can we do if an aerothermal system becomes nonlinear, manifested by qualitatively large changes of the flow field affected by heat transfer?
In Part 1, a new spectral heat transfer coefficient (SHTC) method has been introduced for blade thermal analysis subject to non-isothermal walls in a linear aerothermal regime. It has been demonstrated definitively that the SHTC approach enables more accurate thermal design analyses of a solid temperature field than the conventional method.
Part 2 is devoted to address the issue of nonlinearity when the temperature field actively interacts with the velocity field as in many practical aerothermal problems. It is noted that the conventional method working rests heavily on an adiabatic state. To move away from the adiabatic state, we take advantage of smooth (’differentiable’) heat flux-wall temperature relation afforded by strong solid diffusion. A local linearization can be utilized by decomposing a full thermal variable into a nonlinear base as the reference and a locally linear perturbation. This split enables us to directly compute a nonlinear base as well as to carry out linearized scaling with the SHTC (or HTC for isothermal walls) on top of the selected nonlinear aerothermal base state. The framework method has been implemented with relatively minor changes of the linear SHTC scaling method as presented in Part 1. The results of several computational case studies clearly and consistently support the validity and effectiveness of the present approach and method implementation.
Flow and Heat Transfer in a Ribbed Converging-Diverging U-Duct Under Rotating and Non-Rotating Conditions
Authors: Kim Wanjae , Shih Tom I-. P. , Bryden Kenneth Mark , Dalton Richard P. , Chang Sung Yong , Park Gyu Sang 
Published: August 2024

Abstract
A numerical study based on steady RANS with the SST turbulence model was performed to investigate the flow and heat transfer in a ribbed U-duct with a rectangular cross section that converges linearly in the radially outward direction and diverges linearly in the radially inward direction under rotating and nonrotating conditions. Parameters examined include rotation number (Roi = 0, 0.0219, 0.0336, 0.0731), Reynolds number (Rei = 46,000, 100,000, and 154,000), and the duct’s taper angle (α = 0° and 1.41°) under conditions relevant to gas turbines used for electric power generation. Results obtained show that increasing the taper angle from 0° to 1.41°, which appears negligibly small, significantly increases both the friction coefficient and the Nusselt number whether there is rotation or not. With rotation at Roi = 0.0336 and Rei = 100,000, the maximum increase in the average friction coefficient and Nusselt number was found to be 41.7% and 36.6% respectively. Without rotation at Rei = 46,000, those are 11.5% and 14.7% respectively.
Effects of Combustor Residual Swirl and Hot Spot on Aerothermal Characteristics and Cooling Performance of Gas Turbine Blade
Authors: Sun Tianyi , Li Zhiyu , Li Zhigang , Li Jun , Xu Qingzong , Du Qiang 
Published: August 2024

Abstract
The swirling flow and the hot spot generated in the aeroengine combustor have significant impacts on the downstream turbine components. This paper numerically investigates the influence of the residual swirl clocking position, direction and the hot spot on the aero-thermal characteristics of the turbine stage cascades and the cooling performance of the rotor blades. Computational results show that the hot spot slightly decreases the total pressure loss of the stage cascades. And the negative residual swirl increases the total pressure loss by about 3–5%. The aero-thermal characteristics and the cooling performance of the rotor blade are scarcely influenced by the residual swirl clocking positions. The hot spot decreases the mass flow of the blade tip holes by 2%, compared to the cases with uniform temperature inlet. The negative residual swirl makes the coolants at the pressure surface develop further downstream, reduces the differences in the leading edge holes mass flow at different spanwise positions and brings more intense heat transfer at the tip and better cooling performance at the blade surface. The flow capacity and the working performance of the turbine stage are also almost unaffected by the residual swirl and hot spot. This article presents a numerical method for turbine stage cascades with the residual swirl and the hot spot, analyzes the impact of combustor outflow conditions on turbine stage performance, and provides reference for CFD aided design of turbine aerodynamic and cooling configurations.
Dirt Ingestion Impacts on Cooling Within a Double-Walled Combustor Liner
Authors: McFerran Kyle , Thole Karen A. , Lynch Stephen P. 
Published: August 2024

Abstract
Double-walled liners consisting of impingement and effusion cooling are commonly used to cool gas turbine combustor chambers. Engine ingestion of particulate such as dirt, sand, or ash leads to particulate deposition and blockage of cooling holes in these liners. Prior work on double-walled liners has shown that deposition leads to flow blockage, however, no experimental work has studied the reductions in cooling that result from the deposition. The goal for the present work was to quantify this reduction in cooling by evaluating the heat transfer coefficient on the cold-side of an effusion plate with and without dirt buildup. Heat transfer coefficients were quantified over a range of Reynolds numbers, pressure ratios, plate-to-plate spacings, and dirt injection amounts. The injection of dirt onto the cold-side effusion plate surface resulted in flow blockages and cooling reductions as high as 55%, with these effects differing for pressure ratio and plate-to-plate spacing. Scan data of the dirty effusion plate was used to characterized the deposition thicknesses for the different parameters tested. Overall, the heat transfer when having deposition on the effusion plate affected the cooling much beyond the insulation effect of the dirt layer. These results suggest that the effects of particulate buildup on the cooling flow field are an important driver in double-wall liners.