bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Investigations of Flows and Heat Transfer in Turbine Disc Cavities
Authors: Beaux Jean-Hugues , Girardeau Julian , Khelladi Sofiane , Deligant Michael , Perilhon Christelle 
Published: September 2023

Abstract
In gas turbines, the stator wells play a key role in the efficiency of the turbomachine. The research for performance gains requires a good understanding and an accurate modelling of the flows and heat transfers occurring in these areas. Indeed, engineers try to maintain sustainable temperatures of the turbine components while minimizing the amount of cooling required to do so. Within the framework of the European program MAGPI WP1, a two-stage axial turbine test rig provided an experimental database used to validate the CFD models.
The aim of the current study is to set up a numerical methodology using the CFD solver ANSYS Fluent to accurately predict the conjugate heat transfer in the stator well area. The validation of the methodology relies on thorough comparison of the results with the MAGPI WP1 experimental temperature / pressure measurements. A geometry with axial cooling injection through lock plate slot was chosen. A RANS 3D sectorized CFD model of the turbine with conjugate heat transfer was used. It includes main gas path, cavities with labyrinths, discs rotor, the casing and the Nozzle Guide Vanes (NGV). Mixing planes are placed between the static and rotating frames. Different influences (mesh, turbulence model, thermal boundary conditions, radial labyrinths clearances) were studied and compared with experimental data.
As a baseline, the first calculations were performed with a cooling flow rate chosen so that hot gas ingresses from the main stream into the stator well cavity. Good agreements between predicted and measured temperatures / pressures were observed, especially in the vicinity of the stator well. Discrepancies were spotted at the first rotor hub endwall and at the upstream wheelspace and will be discussed. Finally, a configuration with a different cooling flow rate was conducted where cooling air egresses from the disc rim cavity to the main gas path.
Numerical Investigation of a Thermally Perfect Gas Model for a Centrifugal Compressor Design With Water Vapor as Working Medium
Authors: Kajasa Bojan , Nicke Eberhard , Kügeler Edmund 
Published: September 2023

Abstract
Due to the use of fossil energy sources in the industry sector for which process heat is needed, the footprint on the global climate has increased significantly. The Implementation of High-Temperature Heat-Pumps (HTHP) into industry processes can make a significant contribution to reducing the consumption of fossil energy and thus to reduce the CO2 emissions. In order to realize a high Coefficient of Performance (COP) using natural refrigerants/working medium the application of Rankine thermodynamic cycle is favored. The operation of turbomachinery with a reasonable efficiency within HTHP provides high COPs and the design of the centrifugal compressor geometry considering superheated water vapor as working medium is required. Since a calorically perfect gas model is predominantly used in Computational Fluid Dynamics (CFD) for example for air as working medium with a heat capacity independent from pressure and temperature. Deviations in the evaluated performance can occur when this model is used for designing the centrifugal compressor geometry with superheated water vapor, where the heat capacity coefficients (Cv and Cp) are highly dependent on the temperature. For the numerical investigation of superheated water vapor within the CFD the influence of a thermally perfect gas model is compared to a calorically perfect ideal gas model. The influence on the operating range with respect to the design point is studied and the compressor map trend is investigated. The results of the thermally perfect gas model in the design process on the performance parameters like pressure ratio and efficiency are discussed.
Development of Near-Wall Treatment to Improve Flame Flashback Prediction for Hydrogen Flames
Authors: Choi Minjun , Gu Inyeong , Shin Youngjun , Cho Eun-Seong , Hwang Jeongjae , Kim Min Kuk , Shin Dong-Hyuk 
Published: September 2023

Abstract
Numerical investigations on prediction of flashback of a lean premixed hydrogen flame in an industrial gas turbine combustor were conducted. Three combustion models were tested for prediction capabilities: (i) the flamelet-generated manifold-finite rate (FGM-FR) model, (ii) the flamelet-generated manifold-turbulent flame speed (FGM-ST) model, and (iii) the eddy dissipation concept (EDC) model. Without an additional wall damping model, the three models are unable to predict the flame flashback limit correctly. A wall damping model was applied to modify the reaction rate near the wall. With certain values of the wall damping coefficient, the FGM-FR and FGM-ST models successfully predict the flame flashback limit.
Robust Tip Gap Measurements: A Universal In-Situ Dynamic Calibration & Demonstration in a Two-Stage High-Speed Turbine
Authors: Castillo Sauca Antonio , Paniagua Perez Guillermo 
Published: September 2023

Abstract
Tip clearance monitoring is essential for the active health monitoring of turbomachinery and their development towards more efficient systems. Proper sensor calibration is paramount to this purpose, frequently being a time-consuming process. This paper introduces a novel in-situ dynamic calibration routine for high-frequency capacitance sensor measurements for tip clearance. The method predicts the calibration curve based on a single clearance measurement, the evolution of the acquired signal through various operational conditions, and the dimensional features of the multi-rim squealer-tip passing blades. The experimental data was obtained at 2MHz in a state-of-the-art two-stage high-speed turbine operated by the Purdue Experimental Turbine Aerothermal Lab. A description of the empirical setup is provided, emphasizing the capacitance probes, the conditioning and acquisition systems, the metrology instruments used, and other ancillary instrumentation relevant to the calibration procedure. The prior filtering and data identification from the raw signal is detailed. The step-by-step development of the algorithm is presented, including justification of the curves imposed by the method. The resulting calibrations are provided, achieving accuracies of a few microns. The results are compared against previously used calibration techniques, emphasizing the potential advantages of the presented routine. Finally, the time-resolved tip clearance is analyzed against high-frequency aerothermal data within the gap region, identifying relationships between the tip gap, unsteady pressure, and heat flux on the shroud.
Numerical Analysis of Reversible Radial-Flow Turbomachinery for Energy Storage Applications
Authors: Parisi Simone , Haglind Fredrik 
Published: September 2023

Abstract
Decarbonization of energy systems is expected to require significant amounts of energy storage. Among the different technologies studied, thermo-mechanical storage is being considered for long duration storage due to its low cost and limited usage of critical materials. Based on the experience of pumped hydro plants, significant cost savings can be achieved if a single stage reversible compressor-turbine is used for both the charging and discharging of the storage. Due to the modest (&lt; 4.5) pressure ratio involved, low temperature adiabatic compressed air energy storage and pumped thermal energy storage are considered as candidate applications for reversible turbomachinery.
This paper presents a numerical analysis of an existing high efficiency centrifugal compressor operating both as a compressor and a turbine using mean-line analysis and steady-state simulations with Reynolds-Averaged Navier-Stokes equations in ANSYS CFX. After validation against experimental data in compressor operating mode, the turbine mode was tested by changing only the inlet and outlet boundary conditions and reversing the direction of rotation. Subsequently, a new stage was designed using conventional procedures developed for compressors and evaluated using computational fluid dynamics simulations.
The results indicate that for an up-scaled version of the existing compressor it is possible to reach total-to-total polytropic efficiencies exceeding 86.7% as a compressor and 92.1% as a turbine, which is comparable with the efficiencies of dedicated machines. The new design reaches a polytropic efficiency of 89.4% as compressor and 90.4% as turbine. In both cases the numbers obtained do not include a volute or diffuser cone. Furthermore, the results indicate that there is a compromise between the optimal design for the compressor and turbine mode.
Real-Time Parameter Inference of Nonlinear Bluff-Body-Stabilized Flame Models Using Bayesian Neural Network Ensembles
Authors: Croci Maximilian L. , Sengupta Ushnish , Ekici Ekrem , Juniper Matthew P. 
Published: September 2023

Abstract
We assimilate the parameters of a low order physics-based model of a bluff-body-stabilized premixed flame by observing OH PLIF and PIV images of a 1.1 MW flame. The model is a five parameter level set (G-equation) solver with a prescribed velocity field. A Bayesian ensemble of neural networks (BayNNE) is trained on numerical simulations of the model at 2400 different parameter combinations. Once trained, the BayNNE observes the experimental data and outputs the expected values and uncertainties of the parameters of the model that best fits the experimental data. Using this model, we extrapolate the heat release rate field in physical space beyond the observed window in the experiments, and in parameter space to smaller perturbation amplitudes. We then convert the periodic heat release rate field into a distributed n-τ model, which we enter into a thermoacoustic Helmholtz solver. We find that the thermoacoustic eigenvalue drift is small but measurable, is stabilizing, and does not vary significantly during the experimental run or with the velocity amplitude. This is primarily because the time delay field τ, which is determined by the convection speed, is similar for all cases. This is consistent with the experimental images, which exhibit intermittent bouts of thermoacoustic oscillations that die away. Although this paper’s conclusions for thermoacoustic behaviour are unsurprising, the method it describes is a potentially cheap way to combine sparse experimental measurements with copious low order simulations.
Convergence of Dynamic Mode Decomposition As an Assessment Criteria for Completion of Internal, Unsteady Flow Simulations
Authors: George Amelia , Defoe Jeff 
Published: September 2023

Abstract
The length of simulation time for unsteady computational fluid dynamics (CFD) is often based on intuition or best practices, as there is no established convergence criteria to guarantee the computations have generated enough flow to resolve all spatio-temporal content. Thus, these simulations are often run longer than necessary, but this increases the run time and computational resources required. This is often the case for unsteady CFD for turbomachines. This paper introduces an algorithm, based on dynamic mode decomposition (DMD), that can determine when continuing an unsteady CFD computation no longer yields additional spatio-temporal information. The algorithm is shown to correctly determine the modal content for an analytical dataset with a start-up transient with 44% less data than by only using data from after the start-up transient. The algorithm is then applied to 2D CFD of a fully turbulent flow over a cylinder with periodic boundaries, where the amount of flow time required is just sufficient for the size of fluctuations in cylinder lift coefficient to stop growing. The algorithm is also applied to a 2D periodic flow over a rotor airfoil, with an empty stationary duct downstream. The algorithm determines the point at which the statio-temporal content of the flow stops changing meaningfully greatly in advance of using conventional methods.
Quantification of Mixing Quality Effects on Flashback Limits for H2-Rich Fuel Gases
Authors: Kim Taesung , Doll Ulrich , Faldella Filippo , Jansohn Peter 
Published: September 2023

Abstract
One of the main challenges arising from hydrogen-rich fuel mixtures is to prevent flame flashback. In typical gas turbines the fuel is commonly injected through holes in the axial swirler vanes to achieve a high mixing quality. However, this injection method is not perfect and can cause non-homogeneous mixing regions, so that locally rich fuel clusters can significantly increase flashback propensity. This work aims to establish a link between the local mixing quality of fuel and air and flashback limits obtained experimentally under elevated pressure conditions. The non-reacting experiments have been conducted at an atmospheric mock-up test rig and acetone-PLIF has quantified the local fuel concentration. Zones of high equivalence ratio are evident close to the center body wall. The near-wall equivalence ratio fields reveals that the critical probability of the local equivalence ratio being greater than the one for perfect premixing is between 20% and 35% for all hydrogen concentrations at the flashback limits observed. A probability of 35% is selected as a critical threshold to derive a correlation between the local and the global equivalence ratio in technical premixing. Even though the correlation is specific to the investigated burner configuration, the presented methodology offers valuable insights into the impact of the local mixing quality on flashback propensity, which can improve flashback prediction models formulated for perfect premixing conditions.
Evaluating the Effect of Liquid Water and Steam on Jet Flame Physics
Authors: Schihl John , Skiba Aaron W. , Carter Campbell D. , Gandomkar Amirreza , Whitcomb Jack , Allison Patton M. 
Published: September 2023

Abstract
The present research effort focuses on determining the effect of steam and liquid water addition on flame structure in preheated, premixed, piloted methane-air jet flames. The turbulent Reynolds Number (ReT) varied between 760 and 4,200, and two equivalence ratios (0.9 and 1.1) were considered. Planar laser-induced fluorescence (PLIF) imaging of OH radicals was performed via excitation of transitions in its A-X (0,0) band (near 311 nm). Flame surface density (FSD) and average progress variable maps (c−) were derived from those images, which facilitated analysis of the turbulent flame-surface area ratio, brush thickness, and turbulent flame speeds. It was found that steam had a large impact on flame surface statistics, whereas liquid water with similar mass fractions had little-to-no effect. In cases with varying steam loading but the same ReT, FSD along the mean reaction variable contours did not appear to be affected, and minimal changes in flame structure were observed. A weak correlation between brush thickness and steam flow rate was observed, whereas liquid water addition had no impact on brush thickness. In addition to the experimental aspect of this study, computations were performed using CHEMKIN to investigate the effect of steam loading on freely propagating premixed methane-air flames. Laminar flame speed decreased with increasing steam and argon concentration, with results suggesting the leading order impact of steam dilution is to act as a heatsink due to its large specific heat constant.
Adaptation of Aeroengine Micromixing Injectors for Lean Direct Injection of Hydrogen and Hydrogen/Natural Gas Blends
Authors: Gomez Escudero Iker , Tran Britney , Overbaugh Malcolm , McDonell Vincent , Williams Brandon , Buelow Philip , Ryon Jason , DeBeni Ottavio 
Published: September 2023

Abstract
A set of novel fuel injectors has been developed and manufactured for systematic evaluation of the combustion performance of hydrogen and hydrogen/natural gas mixtures. The test hardware is derived from lean direct injection concepts developed for low emissions aeroengines. Computational Fluid Dynamics (CFD) was used to design the test hardware using target flows associated with a Solar Turbines industrial engine. A statistically designed test plan was adopted to study the effect of air split, air swirl, and fuel swirl on the combustion performance. A Box-Behnken three level design was used to facilitate the development of response surfaces of performance as a function of the design factors considered. This resulted in a total of 13 test configurations. Three additional configurations were also developed to allow validation of response surface correlations. Atmospheric combustion testing was carried out for a range of preheats, injector pressure drops, and fuel type. Prior to the combustion tests, air flow testing was performed on each injector to quantify the effective areas of the fuel and air circuits. The air effective area was consistent within 2.5% for the 16 test parts. The fuel side effective areas varied by about 12%. Considering the parts were all additively manufactured, the variation was considered reasonable. Next, an atmospheric combustion testing was performed to study the lean blowoff characteristics and flame stability, and it was determined that the air splits and air swirl were more statistically significant than the fuel swirl. While all configurations were stable, the configurations with lower air swirl had increased stability. Lower air pressure drop across the injector and increased preheat temperatures increased the stability range, and also allowed increased hydrogen content. Finally, the mid-point injector design was further studied with atmospheric combustion including emission sampling and imaging, and a set of these results are included herein. This expanded effort defined a baseline which allows the comparison of the full matrix of injectors that is going to be studied in subsequent efforts, to characterize the performance of each individual injector design at atmospheric conditions.
Accelerated Structural Assessment for Risk Reduction of an AM Cruciform Rotor
Authors: Scott-Emuakpor Onome , Warner Justin , Celli Dino , George Tommy 
Published: September 2023

Abstract
Minimal material information is used to accelerate the structural assessment of an additive manufacturing (AM) fabricated stainless steel 316L cruciform rotor in a spin rig environment. The primary purpose of the spin test is to demonstrate the vibration suppression and damage tolerance capability of the Inherent Damping via AM Processes (i-DAMP™) technology. Therefore, the rotor is expected to experience induced vibration fatigue as well as centrifugal load stresses, which make the rotor susceptible to Burst and High Cycle Fatigue (HCF) failures. All the material data necessary to determine limits for Burst and HCF are acquired from 12 coupon specimens built during the same Laser Powder Bed Fusion (LPBF) print operation as the rotor. Using tensile strength, fatigue, and computed tomography scan data from both coupon specimens and the rotor, this study establishes a safe approach using minimal data to set the structural limits of a critical AM component operating in an extreme environment.
Numerical Simulation of an Organic-Rankine-Cycle Nozzle Cascade Using a Tabulated Real-Gas Thermodynamics Model for Siloxane MDM
Authors: Haake Alexander , Wittek Matthäus , Müller Hagen 
Published: September 2023

Abstract
Power generation based on the Organic Rankine Cycle has become a viable option for exploiting the large potential of thermal energy currently emitted into the environment as waste heat in many industrial processes. For this reason, reliable and efficient numerical methods are needed to improve current designs and increase their efficiency. In this work, a pressure-based CFD solver is used to perform Reynolds-averaged Navier-Stokes simulations that extract the real-gas thermodynamic properties from look-up tables. The tables are generated using a recent multi-parameter equation of state based on the Helmholtz residual energy. The method is applied to simulate two configurations using the working fluid octamethyldisiloxane (MDM). As a first step, the numerical method is validated for a converging-diverging nozzle flow under non-ideal operating conditions. The simulation results agree well with available measurements for pressure and Mach number on the centerline. The method is then used to simulate a linear blade cascade operating in the non-ideal supersonic regime. The results are analyzed in terms of properties along the blade surface and the expansion-shock system starting at the trailing edge. Good agreement with other simulation results is obtained. A runtime analysis shows that tabulating thermodynamic properties significantly reduces the numerical effort. In summary, these results demonstrate the suitability of this approach for simulating non-ideal compressible fluid flow applications.
Integration of a Gas Model Into CFD Analysis for the Simulation of Turbine Exhaust Flows With High Steam Loads
Authors: El-Soueidan Mahmoud , Schmelcher Marc , Görtz Alexander , Häßy Jannik , Bröcker Marius 
Published: September 2023

Abstract
The Water-Enhanced Turbofan (WET) is a promising future propulsion concept to reduce aero engine emissions. In the WET-engine, a heat exchanger uses turbine exhaust heat in order to generate superheated steam out of liquid water. For evaporator design, CFD simulations are necessary since correlation-based predictions have a high uncertainty during preliminary design. A common way of modeling steam loaded flows is the integration of gas models into CFD analysis. However, to the author’s knowledge, there is no gas model published that accounts for the exact gas composition of turbine exhaust flows with high steam loads and is commonly used by low- and high-fidelity methods. Therefore, a gas model predicting the thermodynamic behavior of the turbine exhaust flow considering high steam loads is presented and integrated into an existing CFD solver. The approach is able to incorporate the implemented gas model into the CFD simulation by two methods: runtime and offline. The offline method has a computational advantage in iteration time compared to the runtime integration. As demonstration case, a single two dimensional cylinder is considered. A variation of the steam loading of the flow shows a significant effect on local properties and therefore on local and average heat transfer. Increasing the steam loading up to 40% results in an increase of the average Nusselt number of 17%.