bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of Detailed and Reduced Chemical Kinetic Models for Ammonia Combustion Under Gas Turbine Operating Conditions
Authors: Rahman Ramees K. , Pierro Michael , Winquist Mark , Subbaraman Ganesan , Sun Wenting , Steele Robert , Vega John , Vasu Subith S. 
Published: August 2024

Abstract
The power generation sector has been recently moving towards decarbonization and there is an increased interest in replacing conventional fossil fuels with fuels that produce reduced/zero carbon emissions. One such fuel is ammonia (NH3). However, ammonia is hard to ignite, has a low flame speed, and produces a significantly large amount of nitrogen oxide (NOx) emissions. Hence, using 100% ammonia as fuel in gas turbines requires significant modifications and the development of novel combustors. Blending hydrogen with ammonia, however, helps in having better control over the combustion properties. For example, a 70%/30% mixture of NH3/H2 mixture has a flame speed comparable to natural gas. Before utilizing hydrogen-blended ammonia in an actual gas turbine combustor, thorough simulation studies are required to evaluate its performance, possible hazards, and emissions. The literature lacks well-validated chemical kinetic models for the combustion of hydrogen-blended ammonia for undiluted mixtures at gas turbine-relevant conditions (∼20 bar). Most models available in the literature have been developed for ammonia extremely diluted in diluents such as argon or nitrogen. Hence, in this work, we develop a detailed chemical kinetic model for hydrogen blended ammonia combustion and validate it with a wide range of experimental data for both dilute and undiluted mixtures relevant to gas turbine operating conditions. We outline the strengths and weaknesses of the current mechanism to aid future users of our chemical kinetic mechanism. The detailed chemical kinetic mechanism was reduced to a smaller version (32 species mechanism) without significant loss in accuracy using the direct relation graph with error propagation (DRGEP) and full species sensitivity analysis. The resultant mechanism can predict a wide range of experimental results with the least cumulative error and will be a valuable tool in CFD simulations that will enable the development of gas turbines for zero-carbon power generation.
Development of Transonic Centrifugal Compressor With an Inducer Casing Bleed System
Authors: Erdem Erinc , Sepetci Kutmaral Gulsevim , Cay Seyfullah , Alican Ozan , Yazgan Bora , Arslan Ahmet 
Published: August 2024

Abstract
A transonic centrifugal compressor (MU2 &gt; 1.5) is developed with an inducer bleed system. The configuration is comprised of an axial intake, an impeller and a vaned diffuser that are suited for high efficiency applications. Rig test data is based on performance rakes, wall static pressure taps distributed along static parts, dynamic pressure measurements at critical locations, etc. acquired at various rotational speeds. Impeller and diffuser performance are deduced and the inlet recirculation is observed upstream of the impeller from the test. Numerical method is validated against test data and different turbulence models are also tried. Inducer bleed system widens the flow range and improves stall margin, efficiency (by more than 5%) at low rotational speeds by correcting the incidence at the impeller inlet. On the other hand at design speed operations, choke margin is enhanced by the drawing air from the inducer port into the impeller. The benefit of the inducer bleed system is clearly shown in the results from the stall margin, efficiency and flow range standpoints. Impeller stall is entirely averted and vaned diffuser stall is observed in all occasions, in terms of choking, vaned diffuser is responsible for the entire range of operation.
Comparison of Geothermal Power Systems in Texas
Authors: Pryor Owen , Replogle Cole , Roddy Reese 
Published: August 2024

Abstract
The state of Texas has the highest renewable energy production in the United States with 31% of their total power generation from wind and solar resources. This study explores the ability to utilize geothermal energy as an underutilized resource in the state. Different cycle architectures and fluids have been compared given the specific geological conditions in the state. The cycle architectures include a supercritical carbon dioxide (sCO2) thermosiphon, a natural-convection-driven system utilizing the temperature gradient between the geological reservoir and the surface level power generation system, and water-brine binary simple cycle for both sCO2 and ORC systems. Four different fluids were assessed for the different architectures: sCO2, R134a, R-600a, and R-601a. The cycles were compared through the total power output for the cycles, the cooling duty required, the thermal efficiency and the exergetic efficiency for geothermal reservoir source temperatures between 100–200°C. The pressures and the flow rates were varied to maximize the variables of interest. The results show that all the architectures are viable for power production, but the sCO2 thermosiphon is least attractive due to the low flow rate achieved from natural convection alone. The ORC systems performed the best for low temperature reservoirs while the directly heated sCO2 system performed the best for the higher temperature reservoirs.
On the Predicted Effects of Recess Depth and Orifice Diameter on Pneumatic Hammer Instability in Hydrostatic Journal Bearings Using Compressible Fluid and Comparisons With Test Data
Authors: Jung Hyunsung , Kim Kyuman , Ryu Keun 
Published: August 2024

Abstract
Hydrostatic journal bearings (HJBs), employed in highspeed turbomachinery under extreme operating conditions, offer enhanced reliability, durability, load-carrying capacity, and stiffness, even when lubricated with low-viscosity fluids. A significant challenge with these bearings, particularly when deep recesses are involved and compressible fluids are used, is the occurrence of pneumatic hammer instability. This phenomenon poses a substantial risk, potentially leading to catastrophic system failures. The focus of this research is to quantify the influence of orifice diameter and recess depth on pneumatic hammer instability in HJBs. The study employs a predictive model, prioritizing the understanding and mitigation of this instability. Key to this research is the examination of volume and pressure ratios, particularly the recess volume to fluid film volume ratio and the recess pressure to supply pressure ratio. These ratios are fundamentally influenced by the orifice diameter and recess depth, which in turn significantly affect the HJBs’ characteristics and susceptibility to pneumatic hammer instability. The current study reveals that both the load-carrying capacity and flow rate of the bearings increase progressively with the recess pressure ratio. Meanwhile, the bearing stiffness peaks at a specific orifice diameter and recess depth, typically where the recess pressure ratio is around 0.6. Under these conditions, the bearings demonstrate maximum stiffness with minimized risk of instability. This research also proposes a framework for selecting design parameters in HJBs, aiming to maximize stiffness while averting pneumatic hammer instability. The effectiveness of these design strategies is validated through experimental data from two test bearings, each with different recess depths and orifice diameters. This work contributes significantly to the field by offering strategies for optimizing HJBs. It provides a balance between achieving high performance and mitigating the risks associated with pneumatic hammer instability. By careful selection of orifice diameter and recess depth, it is possible to attain maximum bearing performance, effectively circumventing the challenges posed by pneumatic hammer instability.
The NexGen Burner: Analysis of Turbulent Fuel-Air Mixing
Authors: Kamin Manu , Bravo Luis , Khare Prashant 
Published: August 2024

Abstract
Improving aircraft survivability in case of a fire is the key to improving safety. To achieve this goal, the Federal Aviation Administration (FAA) requires fire certification to determine the survivability of aircraft components in case of a fire. Any test environment used for certification must meet the temperature and heat flux requirements defined by federal regulations. To this end, the FAA is developing the NexGen burner in an attempt to standardize fire tests. In support of this effort, this paper describes a comprehensive computational investigation to identify the interactions between high-temperature air and (vaporizing) Jet A and its subsequent mixing with air in the NexGen burner. This is a sister paper to our previous article [1], where we discussed the dynamics of spray and swirling air under room temperature conditions. The burner consists of a draft tube, a stator that introduces swirl to the incoming air, a turbulator downstream of the stator to intensify turbulence, and a burner cone where Jet A fuel, injected through a Delavan type W nozzle at 2.5 Gph under room temperature conditions, vaporizes and subsequently burns. Air enters the burner at a velocity of 3.5 m/s at a temperature of 600 K; these conditions correspond to a Reynolds number of 26,872. The liquid jet is injected as a semi-hollow cone characterized by a sauter mean diameter of 38.0 microns. The gas phase is described in an Eulerian frame using a compressible large eddy simulation framework, and the discrete phase is modeled in the Lagrangian frame to simulate droplet kinematics, heating, and vaporization. Observations indicate that maximum vaporization occurs in the conical zone created by the semi-hollow spray cone. However, the vaporized fuel extends outward as a result of the expansion of the swirling core. A detailed turbulence budget analysis is conducted to discern energy transfers and interactions within the turbulent flow field. Turbulence production is observed to lead primarily to the generation of axial Reynolds normal stress Rxx. Furthermore, the correlation between pressure and strain rate plays an important role in coupling the axial Reynolds stress Rxx with the normal components Rrr and Rθθ, leading to a transfer of turbulent kinetic energy from the axial component to the azimuthal and radial components.
Design and Integration of a Microtube Precooler Into an Aircraft Engine Waste Heat Recovery and Fuel Systems
Authors: Bury Claire-Phonie , Vesely Ladislav , Kapat Jayanta , Shi Mingxuan , Stoia Michael 
Published: August 2024

Abstract
In the context of advancing aviation technology towards greater efficiency and reduced environmental impact, the design of a Microtube Precooler Heat Exchanger integrated with a Waste Heat Recovery System (WHRS) for a Jet Engine fuel system has emerged. The primary objective is to harness energy from the WHRS to preheat, NH3, ammonia before undergoing a cracking process, where it is decomposed into its constituent elements — nitrogen and hydrogen. The WHRS precooler design meets requirements for prolonged cruise operation, which ensures its robustness and viability across diverse operational regimes. The inlet parameters for the supercritical carbon dioxide (sCO2) side are derived from the results of a modified simple Brayton cycle analysis at the specified steady state operating condition. Concurrently, the demands of the ammonia side at this condition dictate the corresponding boundary conditions for effective heat transfer. The successful design and integration of this component is crucial because it enhances the overall efficiency of the jet engine and consequently reduces the carbon footprint.
Forecasting High Cycle and Very High Cycle Fatigue Through Enhanced Strain-Energy Based Fatigue Life Prediction
Authors: Celli Dino , Sheridan Luke , George Tommy , Warner Justin , Smith Lucas 
Published: August 2024

Abstract
This study applies a novel strain-energy based fatigue life prediction method to low cycle fatigue (LCF) data of conventionally wrought and additive manufactured (AM) Inconel 718 round dog-bones, specifically focusing on cycles to failure less than 105. The objective is to forecast high cycle fatigue (HCF, 106–107) and very high cycle fatigue (VHCF &gt; 107), aiming to approximate stress versus cycles to failure (SN) behavior and the inherent variability in the fatigue life of the material system. This tool is motivated by the need to characterize an expanding and diverse array of materials produced by additive manufacturing methods, process modifications, and optimizations, which can significantly impact fatigue life and overall structural reliability. The fatigue life prediction method achieves this by generating a fatigue life distribution as a function of stress level. Bayesian statistical inference and stochastic sampling techniques are employed iteratively for each test data point, incorporating stress, cycles to failure, and total strain-energy dissipated leading to fatigue failure. Experimental LCF fatigue data are acquired using a standard axial servo-hydraulic load frame equipped with an axial extensometer for strain and strain-energy data collection. HCF and VHCF data is generated utilizing an ultrasonic fatigue test frame capable of cycling at 20kHz. The fatigue data obtained from both servo-hydraulic and ultrasonic fatigue testing are presented and compared. The energy-based fatigue life prediction framework, utilizing only LCF data, is deployed to forecast HCF and VHCF fatigue behavior for both conventionally wrought and AM Inconel 718 fatigue. The HCF and VHCF data generated are then used to validate the forecasts generated from the novel energy-based fatigue life prediction method. Comparisons are made against Random Fatigue Limit curve estimations to assess the effectiveness and accuracy of the proposed methodology.
Commissioning and Operation of an Inventory Management System
Authors: Warren Joshua , Khawly George 
Published: August 2024

Abstract
The DOE STEP 10 MWe Pilot Scale sCO2 Power Plant encompasses several pieces of turbomachinery that utilize dry gas seals to contain the process fluid. The system also has a large piping loop and multiple heat exchangers making it a large volume to fill with CO2. The plant requires an inventory management system (IMS) in order to supply the dry gas seal systems, fill the process volume, and allow for the system to change load while operating. The size of this system is important to have the ability to support the operation of the plant. In order to allow the plant to change load quickly, the pressure of the IMS needs to stay between the low pressure of the compressor suction and the high pressure of the compressor discharge. This allows the natural pressure differential to drive flow in and out of the IMS as the plant changes load. The major factor in changing load is the mass flow through the system. With CO2 near the critical point, the temperature of the tanks will be an important part of the design selection of the IMS volume required. In order to supply the dry gas seal systems when the machinery is stopped, there also needs to be a system to increase the pressure and drive flow to the dry gas seals. This paper will discuss the commissioning and operation of the IMS system in the STEP power plant.
Sweeping Jet Film Cooling Over the Suction Surface of HP Turbine NGV With Forward and Reversed Hole Configurations
Authors: Sharma Hitesh , Mistry Chetankumar S. , Roy Arnab 
Published: August 2024

Abstract
Film cooling is essential for the proper functioning and desired operation of modern gas turbine engines. In this study, numerical investigations were performed to study the effects of forward and reversed hole configurations on the performance of sweeping jet film cooling. A comparison of film cooling performance is presented for sweeping jet and straight jet over a flat plate with both forward and reversed configurations. Operating parameters were maintained for matching the real engine conditions with freestream Reynolds number of 1 × 106 and favorable pressure gradient of HP turbine NGV suction surface imposed on the flat plate. The blowing ratio (M) was varied in the range of 0.35 to 2.0, at a density ratio (DR) of 1.8 with an injection angle of 30° for both the steady and sweeping jet for each configuration. The results indicated that the sweeping jet with a reversed configuration provides the highest coolant coverage and the straight jet with a forward configuration provides the highest cooling effectiveness out of all the configurations. The averaged adiabatic film cooling effectiveness reduces with the blowing ratio for all the configurations except for the straight jet in the forward configuration. Sweeping jet and reversed configuration both are prone to higher diffusion of coolant stream as compared to straight jet and forward configuration comparatively. Instantaneous CRVP (contra-rotating vortex pairs) is detected in sweeping jet with a reversed hole configuration at a higher blowing ratio (M = 2.0).
Numerical Investigation on Mechanism and Modeling of Tip Leakage Flow Loss in Partially Shrouded Axial Flow Fans
Authors: Qin Jinkong , Hu Xiaowen , Wang Mingyi , Fan Hongzhou , Wang Zhiheng , Xi Guang 
Published: August 2024

Abstract
The Partially Shrouded Axial-Flow Fan (PSAFF), extensively used in air conditioning and various industrial settings, exhibits a unique design wherein the shroud encompasses only a portion of the blade tips. However, there is a research gap in comprehending the tip leakage flow (TLF) behavior and developing more accurate loss models for PSAFF. The study addresses the gap by conducting numerical simulations on several structures with isolated fixed blades that replicate PSAFF’s blade tip design, and performing numerical simulations over diverse attack angles, shrouded ratios, and tip clearance heights, the paper elucidates how PSAFF’s structural intricacies significantly influence TLF’s flow pattern. The results underscore that the distinctive flow configuration profoundly affects TLF’s genesis and progression. Furthermore, pronounced disparities exist in the intensity and distribution of TLF loss in PSAFF compared to conventional fans. The straightforward application of prevailing axial compressor blade tip leakage flow loss models to the PSAFF leads to considerable prediction discrepancies. To remedy this, the study introduces tailored structural factors peculiar to PSAFF, in conjunction with traditional semi-empirical models. The new model effectively forecasts the total pressure loss coefficient and its fluctuation across different attack angle, marking a substantial progress in precisely predicting TLF loss in PSAFF and surmounting the constraints of current models.
Blade Excitation Alleviation of a Nozzleless Radial Turbine by Casing Treatment Based on Reduced Order Model
Authors: Yang Mingyang , Lu Zhaokai , Sato Wataru , Kuwata Teppei 
Published: August 2024

Abstract
High cycle fatigue (HCF) is the most common form of blade failure in nozzleless radial turbines. Current studies relating to blade vibration reduction focus on redesign of blade and volute geometries. These methods have the drawbacks of time consuming, performance sacrifice and lack of generalizability. This paper investigates a novel flow control method for blade vibration reduction without sacrificing the aerodynamic performance based on a reduced order model. Firstly, the mechanism of the blade excitation is studied by the numerical method validated by experimental measurement. It is confirmed that the blade excitation is triggered by different mechanism between low- and high-pressure ratios. An equivalent excitation pressure is proposed to quantitatively evaluate vibration behaviors of the turbine blade. Based on the mechanism, a reduced order model is developed to predict the equivalent excitation pressure at high pressure ratio when the excitation is triggered mainly be the disturbance of potential flow field. The method of casing treatment is proposed inspired by the reduced order model and then optimized to attenuate the blade vibration. The experiment is carried out for the validation of the method and results show that the displacement of the vibration is reduce by 48% by this new method.
An Analytical Study on the Effect of Non-Uniform Vane Spacing on Forced Response Reduction in a Mistuned Blisk Rotor in a Multistage Axial Compressor
Authors: Leng Yujun , Dodda Jhansi R. , Key Nicole L. 
Published: August 2024

Abstract
Stators with non-uniform vane spacing (NUVS) have been sought as an effective way to reduce the rotor forced response at certain resonance crossing of concern. A comprehensive experimental study has been conducted in Purdue 3-stage axial research compressor to evaluate the effectiveness of NUVS stator on reducing the forced response of the downstream rotor using strain gage measurement. The experimental results showed that the classical estimation method failed to predict the reduction factor correctly, mainly due to the lack of consideration for the damping and mistuning effects.
To better understand the experimental results, and to provide an efficient and more accurate analysis tool for the rotor forced response under NUVS stator excitation, a detailed analytical study was conducted in this paper. The blade forced response was solved using an efficient, steady-state linearized approach. A single blade analysis was done first to study the effect of damping. The case studies show that higher damping causes more overlap of the blade forced response from adjacent engine order (EO) excitations and, thus, increases the total normalized blade response under NUVS stator excitation. A mistuned blisk aeroelastic model was introduced next, with the mistuning effect modelled using Fundamental Mistuning Model (FMM). Both structural coupling and aerodynamic coupling effects can be included in the aeroelastic model. Similar to the experimental results, the mistuned blisk case study shows a large blade-to-blade variation in the blade forced response under both symmetric and asymmetric NUVS stator excitation, even at a low, non-intentional mistuning level. A statistical study with 100 randomly generated mistuned blisks shows that the forced response reduction effect of a specific NUVS design could vary significantly with a small change of the mistuning pattern, which suggests that mistuning has to be carefully considered in the design, evaluation, and optimization of a NUVS stator.