bluuebunny/crossref_metadata_2025_split huggingface dataset:
Heat Transfer and Flow Field Characteristics of Variable Aspect Ratio, Serpentine Passages
Authors: Wang Hanlin , Klein Denali , Wright Lesley M. 
Published: August 2024

Abstract
This study investigates the effect of acceleration and deceleration in the turn region of a two-pass, serpentine channel. Channel aspect ratios of 2:1 and 4:1 are considered in three combinations to investigate the effect of acceleration and deceleration through the turn region in a smooth, two-pass channel. The length of the inlet section enables the flow entering the first pass to approach fully developed. For each aspect ratio combination, the experiments include nominal Reynolds numbers ranging from 15,000 to 45,000 in the first passage. The Reynolds numbers in the second pass range approximately from 9,000 to 75,000. A transient thermochromic liquid crystal technique is used to measure the detailed surface heat transfer coefficient distributions, and the flow field characteristics are measured by tomographic PIV. Enhanced heat transfer from the impinging flow on the side wall and downstream in the second pass is observed for all cases. On the basis of the first pass Nusselt number ratio, the accelerating case provides the best overall heat transfer enhancement. However, on the basis of the second pass Nusselt number ratio, the decelerating case is a promising arrangement. If the Reynolds number is controlled, the constant cross-section case has the highest Nusselt number and heat transfer coefficient in the turn, and if the mass flow is controlled, the accelerating case exhibits the lowest overall average Nusselt numbers and heat transfer coefficients. The flow field results suggest the secondary flow induced by the turn is weakened when the flow accelerates after the turn for the accelerating channel. The opposite is observed for the decelerating channel. The strength of the counter-rotating vortex pair, turbulence level, and local heat transfer enhancements are closely correlated in a serpentine channel.
Meanline Design and Aerodynamic 3D RANS Investigations of a Multistage Helium Axial Compressor
Authors: Prabhakar Arvind 
Published: August 2024

Abstract
A mean line aerodynamic design and analysis of a multistage helium gas axial flow compressor is presented for a High-Temperature Gas Reactor (HTGR) application. The multistage axial flow compressor design geometry from mean line design is based on a free vortex design method and targeted for achieving high loading, high polytropic efficiency, and is further tuned and investigated for optimum performance by performing three-dimensional Reynolds Averaged Navier Stokes (3D RANS) CFD studies. Performance of the axial compressor and key design quantities are compared with similar previous designs to highlight robustness of the presented design methodology. The design studies also discuss the impact of selecting optimum parameters like thickness to chord length of rotor blades in spanwise direction from hub of the blades to shroud of the blades. Key loss-causing phenomena are identified through 3D RANS CFD analysis, with the intent to improve the final design.
Further, The presented designs are verified by 3D RANS CFD analysis for achieving high aerodynamic polytropic efficiency, targeted design pressure ratio while maintaining high blade loading, and negligible flow separation at the design point. Such a design can also reduce the number of stages for typical HTGR applications, thereby lowering the overall weight of the large multistage axial flow compressor.
Effect of Rotation on 45-Degree Broken V-Ribs in a 2 Pass Square Channel
Authors: Thirumalai Madhusudan Pallikaranai , Ekkad Srinath V. 
Published: August 2024

Abstract
The demand for elevated turbine inlet temperatures in gas turbine airfoils requires the innovation of advanced internal cooling designs to enhance turbine durability and performance. The internal cooling passages in gas turbine blades typically feature ribs that are designed to induce turbulent mixing consequently increasing heat transfer. As the turbine blades rotate, the Coriolis and Buoyancy forces affect the fluid flowing through these channels, thereby causing a non-uniformity in heat transfer distribution between the pressure side and suction side of the turbine blade internal cooling channels. Prior studies have explored various geometries of ribs under stationary and rotating conditions. The present study investigates the heat transfer characteristics of a two-pass channel (AR = 1) featuring 60 degree broken-V ribs which has not been studied in detail under rotation. The rib-height to hydraulic diameter ratio is 0.125 and rib-pitch to height ratio of 16. The heat transfer coefficient was measured using transient liquid crystal thermography technique and detailed Nusselt numbers have been reported. The experiments were carried out for varying Reynolds number (35000, 45000 & 60000) to cover a typical range of operating conditions found in air-breathing engines.
A Study on Average Eigenvalue Sensitivity for the Improvement of Rotordynamic Stability of Integrally Geared Centrifugal Compressors
Authors: Luo Zhusan , Schwarz Carl L. 
Published: August 2024

Abstract
This paper presents a study on the average eigenvalue sensitivity to design variables of an integrally geared centrifugal compressor pinion-bearing system and its application to the improvement of the rotordynamic stability. The average eigenvalue sensitivity is the approximation of the eigenvalue sensitivity, i.e., the central difference of eigenvalue is substituted for the partial derivative of eigenvalue with respect to a design variable. Hence, the average sensitivity coefficients can be calculated using a rotordynamic analysis program integrated with a bearing analysis program. The results are presented in a new frequency versus logarithmic decrement diagram, which is designed for multiple analysis cases.
The average eigenvalue sensitivity to the mass properties of an impeller can not only predict how much an eigenvalue of interest varies with the mass properties, but also indicate where the impeller should be modified. The average eigenvalue sensitivity to a bearing design variable strongly depends upon pad length, bearing load and pivot offset. The sensitivity study tells what design variables should be changed for satisfactory rotordynamic stability and bearing performance. The effects of main shaft dimensions on the average eigenvalue sensitivity are examined to select and tune certain dimensions for the rotordynamic stability. This numerical method has been implemented to improve the rotordynamic stability of two compressor pinions.
High Speed Rotating HPT Blade Thermal Imaging of a Full Scale Cooled 1+1/2 Stage Turbine in a Short Duration Transient Test Facility
Authors: Anthony Richard J. , Vanasse Neil , McClaren Scott 
Published: August 2024

Abstract
This paper presents results from original development of a long wavelength infrared (LWIR) high pressure turbine (HPT) blade thermal imaging system on a Full Scale Cooled 1+1/2 Stage Rotating Turbine in the Air Force Research Laboratory Turbine Research Facility (TRF) at WPAFB, OH. The TRF is a short duration transient turbine blowdown rig capable of matching relevant non-dimensional parameters such as Reynolds Number, Prandtl Number, corrected speed, along with cooling pressure ratios. A LWIR HPT blade thermal imaging camera and custom optical probe are carefully designed and installed to capture transient surface temperatures across a 46-blade rotor arranged in a rainbow wheel of cooled and uncooled airfoils. Over ten transient rotating turbine tests were run acquiring rotating HPT blade images from four different rotor blade views at full RPM. Lessons are shared regarding signal-to-noise challenges of fast transient rotor IR measurements. Together, data from these views show different transient thermal gradients across cooled and uncooled airfoils, revealing insight into cooling flow circumferential platform leakage, and film cooling variations under varying backflow margin. Transient thermal images are also captured showing the effects of momentary hot gas ingestion and film cooling recovery. Furthermore, this paper demonstrates the ability to locate individual subsurface blocked cooling hole passages that do not appear in borescope inspection. This experiment is the first to show such behavior on a full-scale rotor at full RPM in the TRF.
Practical Application of ARMA Model Method for Blade Tip Timing
Authors: Chai Pengfei , Wang Shang , Meng Yiming , Chen Yong , Tian Jie , Ouyang Hua 
Published: August 2024

Abstract
Blade tip timing (BTT) is a non-contact measurement technology for rotating blade vibration. However, BTT often has nonuniform undersampling. Building a response mode is an efficient method for BTT signal analysis. The autoregressive moving-average (ARMA) model is famous for modelling a linear stationary time series in discrete time. We modified the classical Yule-Walker equation-based ARMA solving method to adapt to BTT measurement. The ARMA model method is applied in compressor field tests. The tests are conducted in stable states with different rotational speeds. The ARMA models with different order and probe arrangements are performed on the measured data. The results show that the identified natural frequency is credible and has close results for most ARMA models. The identified natural frequency increased as the rotational speed increased, which confirmed the rationality of the results. The results of different probe arrangements indicated that at least four probes are recommended in our test.
An Active Turbulence Grid for Turbomachinery Flow Experiments
Authors: Bertelli Federico , Okada Mizuki , Lavagnoli Sergio , Hillewaert Koen 
Published: August 2024

Abstract
Quantifying and predicting free-stream turbulence effects on the aerodynamic performance of turbomachinery flows continue to be of primary interest to advance the physical understanding and the modeling of the loss mechanisms. This work is motivated by the need to expose turbine flows to a wide class of inlet turbulence fields, characterized by the peculiarity of setting the turbulence intensity levels and yet tuning the turbulence scales independently. This paper describes the development and the experimental characterization of an active turbulence generator concept that provides the authority for enabling future experimental measurements in turbine cascade rigs. The study has been conducted in an auxiliary low-speed test bench with a small cross-sectional area, testing at low Mach numbers (∼ 0.05) and ambient conditions. Pressure, hot-wire anemometry and particle image velocimetry (PIV) measurements are presented. The results indicate that the active turbulence generator is capable of generating a wide range of homogeneous and isotropic free-stream turbulence. Values from low to high turbulence levels (1.5–13%) with minimum pressure losses and a low degree of non-uniformity (&lt; 5%) have been obtained with the ability to independently control the integral length scale within the range of 6–25 mm.
Multi-Disciplinary Optimization of Gyroid Topologies for a Cold Plate Heat Exchanger Design
Authors: Daifalla Elhusseiny , Shahpar Shahrokh , Tristanto Indi , Carta Mario 
Published: August 2024

Abstract
The strive to reduce the environmental impact of aviation has led to electrification and increasing demand for powerful onboard power electronic systems. These high-performance electrical components are bound to produce significant amounts of low-quality heat waste that, if not dissipated properly, will lead to malfunctioning and even permanent damage. For this reason, high performance heat exchangers represent a key enabler for future advances in aircraft systems electrification and are vital to meet net zero goals and reduce the aviation’s carbon footprint. For a given volume of the exchanger, the heat flow rate can be increased by adopting more sophisticated fluid domains. However, excessive geometrical complexity will lead to an increase in pressure losses, often resulting in inhomogeneous temperature distributions. In this paper, a novel optimization procedure is employed to maximize the efficiency of a high-performance heat exchanger, while minimizing overall pressure loss and temperature gradients. The optimization is performed with full-3D high-fidelity computational flow simulations. The geometry of the fluid domain is constituted by triply periodic minimal surfaces, with a parametrization based on thickness and aspect ratios, done by using the nTopology suite. To assess the performance gain, the topology-optimized design is compared against the datum case and a conventional serpentine design.
Numerical Simulation and Experimental Study of a Full-Scale Mild Combustion Chamber
Authors: Xiong Yan , Ben Yali , Yang Ningjing , Liu Zhigang , Zhang Zhedian , Shao Weiwei , Xu Xiang 
Published: August 2024

Abstract
Over the past four decades, gas turbine combustion has been dedicated to achieving low emissions, resulting in numerous advancements in combustion technologies. MILD combustion, a relatively promising new technology with unique characteristics, has garnered extensive research and attention in the last twenty years. However, applying MILD combustion to gas turbines remains a significant challenge due to limited space and high heat release rates per unit. Currently, most MILD combustion experiments are conducted on a laboratory scale. To address this issue, we conducted full-scale MILD combustion experiments under pressure test conditions in this study. NOx data were obtained at different outlet temperatures (1473 K–1773 K) under experimental conditions of 1.5 bar pressure and air inlet temperature at about 423K and 510K. These results were compared with previous lab-scale research data. The findings indicate that while the NOx emission data for full-scale experiments increased relative to lab-scale studies, it still remained below 10 ppm@15%O2 during operating conditions, demonstrating the low NOx emission potential of MILD combustion. This outcome can be attributed primarily to the adiabatic state of the full-scale combustion chamber’s process and relatively poor mixing effects between fuel and air as well as flue gas and unburned reactants due to size enlargement. These findings have significant implications for designing full-scale MILD combustion chambers in gas turbine engines.
Methanol-Fired Allam Cycle: Combining Oxy-Fuel Power Cycles With Synthetic E-Fuels
Authors: Manente Giovanni , Rahim Ahtasham , Ficarella Antonio 
Published: August 2024

Abstract
Direct-fired supercritical CO2 cycles combine oxy-combustion with supercritical CO2 to achieve high thermal efficiencies in power plants with carbon capture. The Allam cycle is a transcritical CO2 oxy-fuel cycle, named after its inventor. It achieves the highest thermal efficiencies compared to other oxy-fuel cycles, with a relatively simple configuration. Currently, most of the research and the commercial development of this cycle focuses on the use of natural gas or coal-derived syngas as a fuel, and oxygen obtained in cryogenic air separation units. Only recently, a few studies have investigated the integration of water electrolysis units that provide the oxygen for combustion. Instead, it appears that currently there are not studies about the use of biofuels or e-fuels in the Allam cycle. However, their use would allow to achieve net negative CO2 emissions and, possibly, to mitigate the issues of CO2 storage. This paper proposes and analyzes for the first time a methanol-fired Allam cycle. Methanol is produced from CO2 hydrogenation using hydrogen from an electrolyzer (e-methanol). Oxygen for methanol combustion is produced in the electrolysis unit. The methanol oxy-combustion generates a stream of flue gases composed uniquely by water vapour and CO2, being supercritical CO2 used as a combustion diluent. After turbine expansion and recuperation the water vapour is condensed and used as feed to the electrolyzer. Instead, the CO2 is partially recycled to the compressor and partially used for methanol production. The aim of the study is to evaluate the performance of the integrated system, and possibly its improvement by identifying any synergy between the Allam cycle and the methanol synthesis. Distinctive features of turbine expansion deriving from the use of methanol as a fuel are highlighted. The results show the optimum operating conditions of the overall system and the energetic and environmental performance, also in comparison with the natural gas fired Allam cycle.
RANS Prediction of Low-Pressure Turbine Tip Shroud Flows
Authors: Uncu Fatih , François Benjamin , Buffaz Nicolas , Le Guyader Sébastien 
Published: August 2024

Abstract
In low-pressure turbines, an attached tip shroud is often used to mitigate rotor tip leakage. The interaction between tip shroud’s bypass flow and the primary flow leads to mixing losses and amplifies vortex structures, which contribute to aerodynamic losses. Accurately predicting these losses remains a challenge with RANS approaches, especially for engine manufacturers aiming to design an efficient tip shroud geometry that ensures proper sealing while minimizing losses. This study aims to evaluate the capability of RANS simulations in tracking loss evolution with changes in tip shroud geometry. To do so, the present work assesses a second order Reynolds Stress Model (RSM), as well as an eddy-viscosity model, in a two stage low-pressure turbine with attached tip shrouds. Two different geometries (axisymmetric and non-axisymmetric) of the off-channel components have been simulated and their performance have been compared to relevant experimental measurements to understand the loss sources. The RANS simulations capture the correct trend in the isentropic efficiency: the non-axisymmetric tip shroud increases entropy production, resulting in poorer aerodynamic performance. The RSM simulations align better with the measurements and predict secondary structures that differ from those predicted by the linear model.
Rotordynamics of a Single-Stage Brush Seal in Isolation: The Effects of Variable Stiffness and Back Plate Geometry
Authors: Bird Joshua , Keogh Patrick S. , Sangan Carl M. , Bowsher Aaron A. , Crudgington Peter F. , Scobie James A. 
Published: August 2024

Abstract
Brush seals control leakage around rotating components from areas of high to low pressure inside turbomachinery. They are known to contribute to the overall stability of gas turbines, therefore their dynamic behaviour is of particular importance to engine designers. Despite this, limited research exists in the literature on the rotordynamic behaviour of brush seals. This paper aims to experimentally characterise the leakage and rotor-dynamic performance of two seals with different bristle diameters tested with both conventional and pressure-relieved back plates with a slight interference. A dynamic test facility was utilised to study the dynamic characteristics of an isolated seal with changes in excitation frequency, rotational speed and pressure drop.
Seal leakage increased with bristle diameter and with the use of the pressure-relieved back plate but reduced with increasing rotational speed for all tests. The direct dynamic coefficients were shown to increase with pressure difference. The back plate geometry influenced the change in stiffness coefficient with rotational speed. The larger bristle diameter resulted in a stiffer seal, however, the damping coefficient reduced with the reduction in packing density. The insight provided by these results will help inform engine manufacturers on the suitability of implementing brush seals in future gas turbine designs.
Integrated Performance Assessment and Decarbonising Potential for Aircraft Retrofitted With Sustainable Aviation Fuels
Authors: Rompokos Pavlos , Sasi Sarath , Mourouzidis Christos , Roumeliotis Ioannis , Pachidis Vassilios , Akure Michelle , Swindell Hannah 
Published: August 2024

Abstract
The aviation industry is transitioning towards sustainable fuels from conventional fossil-based jet fuels to make air travel sustainable and environment-friendly. Hydrogen, Ammonia, and Methane are all potential long-term solutions since their implementation relies heavily on the redesign of existing aircraft configurations. Sustainable aviation fuels (SAF) on the other hand, due to their similar physico-chemical characteristics with conventional fossil-based jet fuels, are an effective drop-in solution for both short and long term. This solution enables next, current, and older generation aircraft to reduce their carbon footprint.
This paper focuses on the retrofit application of SAF for an older-generation trainer jet aircraft for defence applications and aims to demonstrate the performance, economic and environmental impact of using the alternative fuels. A baseline high-manoeuvre mission profile with Jet A-1 is established, upon which all the SAF variants are compared. Reductions in fuel weight, in-flight CO2 as well as NOx emissions of up to 2–3% were observed, which are mostly attributed to the properties of the alternative fuels. Contrary to the fuel weight savings, higher operational costs are expected due to the higher SAF costs. At engine level, the fuel burn reduction enables a slight decrease in turbine entry temperatures. Finally, when switching to SAF, there exists shortcomings in terms of maximum operational range, mainly attributable to its lower density and consequently, lower energy stored in the fuel tanks.
Gas Turbine Design Point Definition Using Economics, Environmental and Optimization Aspects
Authors: Henrique De Paiva Pinheiro Carlos , Bringhenti Cleverson , Takachi Tomita Jesuíno , Jefferds Dos Santos Silva Franco , Roma Alexandre , Lopes Salgado Mayara 
Published: August 2024

Abstract
This work aims to provide a methodology for defining the design point for industrial gas turbine considering the economic, environmental, and engine performance aspects. The definition of the design point is a key step in the development project of a gas turbine since this definition involves the analysis of several operational points to verify if the desired performance can be obtained. Thus, to extend the methodology presented in the literature developed for micro-turbines to consider industrial gas turbines a computer program was developed in MATLAB®. This program is capable of performing thermodynamic calculations for design point definition and of performing single- and multi-objective thermoeconomic and thermodynamic optimizations using genetic algorithms. For the optimization process, total cost minimization, yield maximization, and gas turbine-specific work maximization were chosen as objective functions. The decision variables chosen were compressor pressure ratio, compressor polytropic efficiency, turbine polytropic efficiency, and maximum cycle temperature. For the calculation of economic aspects, fixed costs (equipment, installations, land acquisition cost, etc.) and variable costs (fuel, emissions, and operation and maintenance costs) were considered. The emission cost of NOx, CO, and UHC was considered for the environmental cost calculations. The thermodynamic calculations were based on enthalpy and entropy. The developed computer program was validated by simulating a commercial gas turbine and comparing the results obtained, also using a commercial program, GASTURB®. The presented optimization process shows results for a single objective, two objectives, and three objectives, where the results show a comparison between different design points obtained. The software developed will be of great assistance in the learning of engineering students.