bluuebunny/crossref_metadata_2025_split huggingface dataset:
Off-Design Modelling and Operational Optimization of Trans-Critical Carbon Dioxide Heat Pumps
Authors: Gabrielli Paolo , Singh Siddhant , Sansavini Giovanni , Sanz Garcia Luis , Jacquemoud Emmanuel , Jenny Philipp 
Published: October 2022

Abstract
Industrial heat pumps, and specifically those using carbon dioxide (CO2) as a refrigerant, can play a key role in the de-carbonization of the heating and cooling sector, due to their low global warming potential, toxicity and flammability. However, challenges arise when dealing with the modeling and optimization of CO2 heat pumps under different operating conditions. We address this challenge by presenting a modeling and optimization tool to predict and optimize the operation of heat pumps in off-design conditions. The tool improves on the current state-of-the-art in several ways. First, it describes a novel thermodynamic cycle, which features higher performance than conventional heat pumps. Also, it is based on a mathematical model that describes accurately the behavior of CO2 across a wide range of thermodynamic conditions, especially near its critical region, and takes into account effects of motor-cooling, leakages and performance limits. Furthermore, it maximizes the coefficient of performance (COP) of the heat pump via an accurate and computationally-efficient optimization problem. The capabilities of the model are illustrated by looking at different typical heat pump applications based on real-world projects within the heating and cooling sector. Different case studies are considered, showing how the heat pump is optimally operated during the year to maximize its COP while meeting the varying boundary conditions.
Experiment Study of Pilot Stage Swirler Outlet Angles and Swirl Number on Flame Structures and Flow Field in a Stratified Swirl Combustor
Authors: Zhang Liang , Xue Xin , Yang Qian , Wang Huiru , Li Jibao 
Published: October 2022

Abstract
The stratified swirl combustor is generally used in an advanced aero-engine, in order to achieve a low emission and wide stabilization at the same time. The complex interactions between the pilot stage and main stage can determine the flame structure, flow field, further affecting the emission formation and stabilization. The present study investigates the interaction between pilot flame and flow field of a stratified swirl combustor, by varying the outlet angles and swirl numbers of the pilot stage swirler. Flame structures and flow fields are obtained while only the pilot stage working. The flame structures are represented by the OH* chemiluminescence (OH-CL) image with Abel deconvolution, non-reacting and reacting flow fields are measured by Particle Image Velocimetry (PIV). The results show that heat release from the pilot flame causes rapid expansion of the pilot gas which may significantly change flow field distribution. Two types of flame structures and flow fields are formed with different outlet angles and swirl numbers of pilot stage. The correspondence between the flame structure and flow field is obtained. For large outlet angle or high swirl number, a M-shape flame combining with a typical stratified swirl flow field and converged pilot and main flow jet are observed, including a large main recirculation zone (MRZ), a lip recirculation zone (LRZ), and a corner recirculation zone (CRZ). For small outlet angle and low swirl number, the flame structure presents a lifted inverted U-shape flame, pilot and main stage jet are separated, there are a small pilot recirculation zone (PRZ), a main recirculation zone (MRZ) and a corner recirculation zone (CRZ) in the combustor. The MRZ is broken into two parts by the accelerated of pilot flow, the LRZ is merged into the MRZ.
Characterization of Flame Behavior and Blowout Limits at Different Air Preheating Temperatures in Plasma Assisted Stabilized Combustor
Authors: De Giorgi Maria Grazia , Mehdi Ghazanfar , Bonuso Sara , Shamma Mohamed , Harth Stefan , Trimis Dimosthenis , Zarzalis Nikolaos 
Published: October 2022

Abstract
This study investigates the flame characterization near to lean blowout (LBO) limits at different pre-heating temperatures in lifted swirl methane-air plasma discharge stabilized flame. The combustor was equipped with a needle-ring type plasma actuator driven by a sinusoidal generator at 20 kHz directly coupled with methane-air premixed flame close to the injector exit. The needle electrode connected with high voltage (HV) and the nozzle acted as a grounded electrode. The electrical characterizations of combustion characteristics and LBO measurements have been carried out at different plasma power, air preheating temperatures, and air mass flow rates. Flame shape and intensity in the flame area have been analyzed based on the images acquired by using a high-resolution camera. Acoustic measurements were performed using high sensitivity microphone. Furthermore, post-processing of the microphone data involved the application of Fast Fourier Transform (FFT) and the wavelet decomposition to identify and characterize any periodic phenomena present in the system. It has been perceived that when the plasma is on, LBO limits were extended significantly. The maximum reduction of equivalence ratio at LBO was noticed in terms of percentage (79.4%) at 40% voltage amplitude, T = 373 K, and ma = 6 m3/h. Proper orthogonal decomposition was implemented on the high-speed chemiluminescence images and the frequency analysis of the time coefficients of the modes of the POD permits the identification of the dominant frequency ranges in the different operating conditions. The results were in good agreement with the findings of the FFT and Wavelet analysis on the microphone measured signals.
Rotordynamic Force Coefficient Prediction of an Unshrouded Radial Inflow Expander and Labyrinth Seal Using Transient Computational Fluid Dynamic Analysis
Authors: Kulhanek Chris D. , Delgado Hector A. , Marshall Michael P. , Moore J. Jeffrey , Lillard Joseph , Kim Yunbae 
Published: October 2022

Abstract
The current study uses a transient computational fluid dynamic (CFD) analysis to predict the rotordynamic force coefficients for an unshrouded radial inflow expander and labyrinth wheel seal in a high pressure natural gas turboexpander. Direct and cross-coupled terms are predicted for both the stiffness and damping for the expander wheel and labyrinth seal, including the aerodynamic cross-coupling forces or cross-coupled stiffness coefficients that impact rotordynamic stability. A static eccentric method was applied where a transient simulation where the rotor portion is displaced with a known static eccentricity and the resulting forces allow for the calculation of direct stiffness and cross-coupled stiffness. In addition, a whirling method using transient simulations at various whirling frequencies is applied to solve for the full set of rotordynamic coefficients, including direct and cross-coupled stiffness and damping terms through curve fitting a KCM model for both the expander wheel and labyrinth seal. Wheel force coefficients are presented for several operating conditions, including low, nominal, and high flow regimes. In addition, a parametric study is performed, including hypothetical cases to evaluate sensitivity of wheel tip clearance, rotational speed, gas density on the expander cross-coupled stiffness. The predicted wheel cross-coupled stiffness shows a very strong dependence on the wheel tip clearance compared to the other parameters studied.
To Drill or Not to Drill? - Creep of an Oxide-Oxide Composite With Diamond-Drilled Discharge Holes at Elevated Temperature
Authors: Harkins Megan , Ruggles-Wrenn Marina 
Published: October 2022

Abstract
Ceramic matrix composites (CMCs) are leading contenders for use in aircraft engines. Yet even with their high-temperature capabilities, many CMC components will need cooling. External or film cooling technique of a component requires rows of small holes through the component surface. Effects of multiple small holes on tensile stress-strain and tensile creep resistance of an oxide fiber-oxide matrix composite comprising Nextel™720 alumina-mullite fibers and a porous alumina matrix were evaluated at 1200°C. Gauge section of each test specimen included seventeen (17) 0.5-mm diameter holes. The holes were precision drilled using diamond coated drill bits. The presence of diamond-drilled (DD) holes noticeably degraded tensile strength and modulus. Specimens with DD discharge holes were creep tested in air and steam at 1200°C. Applied creep stress varied from 40 to 130 MPa. Endurance of 100 h at creep stress without failure was defined as creep run-out. The existence of diamond drilled holes lowered creep resistance of the CMC as evidenced by higher steady-state creep strain rates and lessened creep lives. An earlier study at the Air Force Institute of Technology considered the effects of small holes drilled using a CO2 laser on the tensile properties and tensile creep resistance of this material system. Geometry of test specimens and test conditions were the same as in the present effort. The earlier study found that the existence of rows of small laser drilled (LD) holes also considerably lowered the creep resistance of the Nextel™720/alumina CMC. In both cases the reduction in tensile strength and creep resistance are due to damage caused to composite microstructure by fabrication of the holes, i. e. drilling. However, different hole drilling techniques result in different microstructure degradation mechanisms. Changes to the CMC microstructure triggered by these two drilling techniques and implications for mechanical performance and durability are discussed.
Effect of Deflection Angle on Flow and Heat Transfer in a Rotating U-Channel
Authors: Li Honglin , Li Lei , Tang Zhonghao , Zhang Zhenyuan , Yuan Tianyu 
Published: October 2022

Abstract
In this work, the effect of spanwise deflection of a rotating smooth U-channel on flow and heat transfer characteristics is investigated through numerical simulation. Seven deflected U-channel with different angles are adopted, including α = 90°, 60°, 30°, 0°, −30°, −60°, −90°, and three rotation numbers vary from 0 to 0.29. Using verified numerical method, the flow pattern, detailed and overall heat transfer characteristics and flow friction factor are analyzed. Results show that the deflection angle will enhance the heat transfer in turning section and outlet passage, which can be attributed to the enhancement of flow impact and more complex vortex structure. The deflection of U-channel would generate a Coriolis force at turning section and thus interact with the centrifugal force to change the vortices, which makes the U-channel with negative deflection angle has higher heat transfer enhancement and larger movement of peak Nu number. Compared with positive deflection angle, the negative deflection angle has higher thermal performance and the maximum emerges at α = −30° since the U-channel can generate larger heat transfer enhancement with smaller flow loss increase. Besides, the rotation will enhance the local and overall thermal performance of the U-channel, and the effect of deflection angle on the thermal performance of U-channel keep the same at different rotations numbers.
Transition Model Extension for Roughness Effects
Authors: Kožulović Dragan , Juchmann Nemo , Führing Alexander , Bode Christoph 
Published: October 2022

Abstract
Depending on the manufacturing process and the operating conditions, airfoil surface may show many different roughness characteristics, together with a significant influence at the boundary layer development. In this paper, only the influence at the laminar-turbulent transition is considered and modeled by an extension of the γ-ReΘ transition model of Langtry and Menter. Essentially, an additional transport equation for a roughness amplification scalar is used to modify the transition onset and development, as already presented by Dassler et al. in 2012. In the meantime, the calibrated functional relationship for Argr has been released for the publication for the first time in this paper. In addition, the model performance will be demonstrated and discussed on test cases with increasing complexity, including turbomachinery cascades and rigs.
As an input to the model, the equivalent sand-grain roughness is required. In this way, the versatile roughness characteristics of the investigated surface are reduced to only one parameter. The model has been implemented into the CFD software package TRACE of DLR Institute of Propulsion Technology. Only steady flow test cases have been investigated and validated. The transition intermittency is coupled to the two-equation turbulence model of Wilcox. In this model, the roughness influence at the fully turbulent boundary layers is also captured by the variation of the boundary condition for the specific turbulence dissipation rate ω.
Refinement of a High Cycle Fatigue Decision-Gate Assessment for Additively Repaired Blades
Authors: Scott-Emuakpor Onome , Runyon Brian , Gillaugh Daniel , Smith Lucas , Johnson Philip 
Published: October 2022

Abstract
A recently developed high cycle fatigue (HCF) Acceptance Criteria demonstrates effectiveness in assessing the viability of two laser directed energy deposition (DED) repair processes on Titanium 6Al-4V (Ti 6Al-4V) fan blades. The assessment of these repairs requires a keen understanding of the average HCF behavior and the associated empirical data distribution. Specifically, detailed observations of the HCF regression behavior, stress amplitude dataset distribution, porosity size and distribution, and crack nucleation and propagation life are necessary. The amalgamation of these observations leads to information that quantifiably compares predicted fatigue life and data reliability of repaired blades to baseline blades within a percentage margin of acceptability. Despite a demonstration of the effectiveness of the HCF Acceptance Criteria, additional factors need to be considered to include available material or component information and nondestructive evaluation (NDE) conditional acceptance. This study explores the rigidity of the HCF Acceptance Criteria by applying it to Laser DED repaired turbine engine fan blades. The results help define a prior rule (entrance statement) that identifies expected results based on manufacturing/microstructure information as well as a second-tier rule incorporating NDE for a more refined HCF Acceptance criteria.
Design and Testing of a 275 Bar 700 Degree Celsius Expander for an Integrally Geared Supercritical CO2 Compander
Authors: Wilkes Jason , Robinson Kyle , Wygant Karl , Pelton Rob , Bygrave Jonathan 
Published: October 2022

Abstract
An integrally-geared (IG) compressor-expander (compander) for use in a nominal 10 MW-scale concentrated solar power (CSP) supercritical carbon dioxide (sCO2) plant application was designed, manufactured, and tested. The integrally-geared compander (IGC) developed for this application comprises multiple pinion shafts interacting through a single bull gear to create a compact package and utilize a low-cost, low-speed driver.
The present work will detail the design of the high-pressure high-temperature expander casing on an integrally geared frame, and illustrate how the project successfully mitigated the risk of fatigue and creep while allowing for rapid thermal transients in the design. Furthermore, test data from the test campaign will be presented supporting the analysis. Test results also show temperature profiles during operation exceeding 720° Celsius.
Printability and Overall Cooling Performance of Additively Manufactured Holes With Inlet and Exit Rounding
Authors: Veley Emma M. , Thole Karen A. , Furgeson Michael T. , Bogard David G. 
Published: October 2022

Abstract
To improve cooling effectiveness of gas turbine hardware, various film cooling hole shapes have previously been researched. Unique design modifications have recently been made possible through the design freedom allotted by additive manufacturing. As one example, creating a rounded inlet for a film-cooling hole can mitigate separation at the inlet. This study explores various geometric features by exploiting the uses of additive manufacturing for shaped film cooling holes at engine scale. Both printability and cooling performance were evaluated.
Resulting from this study, additively manufactured holes with hole inlet and exit rounding were printed with some variations from the design intent. The largest deviations from the design intent occurred from dross roughness features located on the leeward side of the hole inlet. The measured overall effectiveness indicated that an as-built inlet fillet decreased in-hole convection as well as decreased jet mixing compared to the as-built sharp inlet. Including an exit fillet, which prevented an overbuilt diffuser exit, was also found to decrease jet mixing. A particular insight gained from this study is the importance of the convective cooling within the hole to the overall cooling performance. In-hole roughness, which is a result of additive manufacturing, increased convective cooling within the holes but also increased jet mixing as the coolant exited the hole. The increased jet mixing caused low overall effectiveness downstream of injection.
Tip Flow Control in Optimized Large Gas Turbine Compressor Blading
Authors: Hummel Katja , Streit Anton , Peitsch Dieter 
Published: October 2022

Abstract
In transonic axial compressors of gas turbines, casing treatments (CTs) have the capability to improve the stability and delay stall. A full comprehension of the stall mechanism is essential to design a beneficial CT. Tip stall is a prerequisite. Most CT investigations and publications investigate flight propulsion applications. There is a need for detailed investigations in stationary large gas turbines concerning stability optimization. Typically, the tip gaps in the front stages are — relative to the blade span — by one magnitude smaller than for aero engines. This is due to the large absolute dimensions.
The goal of the present study is to increase the operating range towards stall without losing efficiency at design point conditions. Axisymmetric active and passive CT types are investigated.
The model is based on an optimized tip critical rotor design, which matches the boundary conditions of a large gas turbine. Most other investigations from the last decades are conducted for known airfoil shapes that were not automatically optimized for their operating conditions. A tip flow control was developed to improve the stability limits. The numerical investigations are carried out on a single rotor optimization using RANS simulations.
The study investigates in depth the ability of axisymmetric grooves with and without mass injection to postpone stall. It is shown why passive circumferential grooves do not improve the stability for the specific blade geometry. It is essential to quantify the influence of the axisymmetric types of CT onto the rotor tip flow especially for near stall conditions. Of particular interest is how the circumferential grooves perform when used in combination with mass injection. The results show that for this aerodynamically optimized rotor, a mass injection is needed to energize the tip leakage and therefore reduce the blockage. Passive circumferential grooves do not increase the stability. The injection of 1% stall mass flow rises the stall margin by 15% only with little losses.
Shrinkage Prediction Using Machine Learning for Additively Manufactured Ceramic and Metallic Components for Gas Turbine Applications
Authors: Warren Peter , Raju Nandhini , Krsmanovic Milos , Ebrahimi Hossein , Kapat Jayanta , Subramanian Ramesh , Ghosh Ranajay 
Published: October 2022

Abstract
Additive manufacturing of metallic and ceramic components can provide several benefits for gas turbines. This technology can help to decrease time and cost required for prototyping of both operational components and assistive tooling equipment. There are currently many methodologies for metallic and ceramic material printing, and these processes typically involve a sintering phase during the manufacturing procedure. The amount of shrinkage that occurs is dependent upon the sintering oven conditions, the printed material, and the geometry of the printed component. These factors can be broken down into many subfactors leading to an equation that is too complex and with too many variables to be solved in an analytical matter. Additive manufacturing can provide the ability to rapidly manufacture geometrically specific components for turbomachinery operations. To increase the accuracy of the geometric dimensions of the final product, the sintering shrinkage must be accurately predicted. Machine learning can assist by using data-driven approaches to ensure accurate prediction of shrinkage. This ultimately will increase the dimensional accuracy of the printed components. If there is an accurate shrinkage prediction formula that accounts for the material type, sintering oven conditions, and geometric specifications, the components can be scaled up in CAD (computer aided design) software prior to 3D printing and entering the sintering oven. This predictive capability will allow the end user to create dimensionally accurate parts at a rate that has not yet been possible. In this work, a machine learning approach is developed for the prediction of shrinkage during sintering of additive manufactured components. This paper uses a combination of experimental data and artificially generated data to create a framework for implementing linear regression tools to predict sintering trajectories. An accurate knowledge of the sintering trajectory for a given material can allow for more user control over the final properties and geometrical accuracy of a given component.
Wake Structure in Yawed Approaching Flows for an Axial-Flow Wind Turbine
Authors: Ahmadi Mohammad H. B. , Yang Zhiyin 
Published: October 2022

Abstract
Effects of yawed wind turbines on the wake structure are not fully understood. To obtain a better understanding, numerical studies of a small-scale three-bladed horizontal axis wind turbine at TSR = 6.7 with yaw angles of zero, 15°, 30° and 45° have been carried out to investigate the wake characteristics of the turbine in the near- and farwake. A hybrid approach coupling Large Eddy Simulation (LES) with Actuator Line Modelling (ALM) has been employed in the present study. The predicted results confirm the previous finding that the turbine wake is asymmetric under yawed approaching flows and the wake is inclined to the direction where the rotor is yawed. The present work further demonstrates that at high yaw angles the main wake may be divided into two smaller parallel wakes further downstream that are not symmetric suggesting a dependency on the turbine rotation direction. This study quantitatively explains how the non-uniform variations of radial velocity components at the turbine plane caused by the yawed flows result in the wake deflection and intersection of hub and blade tip vortices further downstream which leads to the wake splitting at high yaw angles.