bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Study of High-Altitude Relight for an Aviation Gas-Turbine Engine
Authors: Litrico Giuliana , Shrivastava Sourabh , Meeks Ellen , Nakod Pravin , Xu Fang , T. Dhanya , Muthuraj Sivaprakasam 
Published: October 2022

Abstract
The altitude relight capability of an aero-engine is a critical requirement that defines the operational flight envelope of the engine. Regulatory requirements from the Federal Aviation Administration (FAA) and European Union Aviation Safety Agency (EASA) ask to establish the altitude and airspeed envelope for in-flight engine restarting and adherence to engine performance. Further, engine manufacturers are changing combustor designs to meet aggressive goals that limit the emission of nitrogen oxides (NOx). While these design changes help reduce the NOx formation, they can be problematic for restart capabilities at high altitudes. Therefore, the engine design process becomes a complex optimization problem with conflicting goals. Test-rig data can provide insights into the performance; however, using testing to explore the entire design space is challenging, expensive, and sometimes infeasible. In this scenario, high fidelity computational fluid dynamics (CFD) simulations can bridge this gap and are, therefore, widely evaluated by designers and simulation engineers. Such simulations need to resolve flow structures, spray distribution, and ignition processes to predict the high-altitude relight accurately. Moreover, no, or limited parameter adjustments should be required for correctly predicting the relight outcome across different operating conditions.
In this work, numerical simulations are performed to predict an aviation gas-turbine combustor’s relight performance, operating under different conditions, including sea level and 40000 ft operation. The CFD simulations are performed using the unsteady RANS approach for turbulence, solution-adaptive meshing, and finite-rate kinetics for the combustion modeling that tracks the flame propagation during and after the spark event. The results are encouraging and predict accurate behavior of lighting and not lighting operating conditions consistent with the light/no-light outcomes from the experimental tests. The simulation methodology, best practices, and obtained results are discussed in this paper.
Impact of Compressor and Turbine Operating Range Extension on the Performance of an Electric Turbocharger for Fuel Cell Applications
Authors: Lück Sebastian , Schödel Markus , Menze Marco , Göing Jan , Seume Jörg R. , Friedrichs Jens 
Published: October 2022

Abstract
In this study, an electric turbocharger for fuel cell applications is investigated with regards to the extension of both compressor and turbine operating range by means of geometric changes to the turbomachinery components, namely variable nozzle and diffuser vane angles. Therefore, the interaction of the electric turbocharger subsystem with the fuel cell stack is investigated over the full operating range to judge the overall efficiency, system dynamics and stability. Initially, selected options for extending the performance maps of both compressor and turbine are presented and discussed. The numerical methods used for predicting the performance maps are then described. Subsequently, the entire machine is simulated under both steady-state and transient operating conditions using the in-house tool ASTOR (AircraftEngine for Transient Operation Research). Based on the wider operating ranges of compressor and turbine, promising setups are identified and investigated in further detail to select the best choice for the operation of the electric turbocharger. The impact of isolated component modifications is shown initially and substantial improvements of the operating range are shown. The modification of the compressor diffuser leading edge angles in a fixed-geometry diffuser increases the range of covered operating points from 4 to 7 while at the same time improving the compressor surge margin during steady state operation above the required safety margin of 20%. Additionally, the system efficiency can be increased by 0.2%. The application of a positive angle variable nozzle turbine significantly shifts the operating line towards higher mass flows, thus increasing the surge margin especially in the high speed range where the transient effects during deceleration of the machine are the greatest. By applying combined modified compressor with pivoting vanes and and variable nozzle turbine geometry, the operating range can be extended even further. The surge margin can be kept above 20% during the initial critical part of a transient deceleration manoeuvre. Nevertheless, a decrease of 0.5% in overall system efficiency has to be accepted due to the measures.
Part-Load Behaviour and Control Philosophy of a Recuperated Supercritical CO2 Cycle
Authors: Gini Lorenzo , Maccarini Simone , Traverso Alberto , Pesatori Emanuel , Milani Alberto , Bisio Valentina , Valente Roberto , Barberis Stefano , Guedez Rafael 
Published: October 2022

Abstract
High efficiency, flexibility and competitive capital costs make supercritical CO2 (sCO2) systems a promising technology for renewable power generation in a low carbon energy scenario. Recently, innovative supercritical systems have been studied in the literature and proposed by DOE-NETL (STEP project) and a few projects in the EU Horizon 2020 program aiming to demonstrate supercritical CO2 Brayton power plants, promising superior techno-economic features than steam cycles particularly at high temperatures.
The H2020 SOLARSCO2OL project1, which started in 2020, is building the first European MW-scale sCO2 demonstration plant and has been specifically tailored for Concentrating Solar Power (CSP) applications. This paper presents the first off-design analysis of such a demonstrator, which is based on a simply recuperated sCO2 cycle. The part-load analysis ranged from 50% of nominal up to a 105% peak load, discussing the impact on compressor and turbine operating conditions. The whole system dynamic model has been developed in TRANSEO MATLAB® environment. Full operational envelop has been determined considering cycle main constraints, such as maximum turbine inlet temperature and minimum pressure at compressor inlet.
The off-design performance analysis highlights the most relevant relationships among the main part-load regulating parameters, namely mass flow rate, total mass in the loop, and available heat source. The results show specific features of different control approaches, discussing the pros and cons of each solution, considering also its upscale towards commercial applications. In particular, the analysis shows that at 51% of load an efficiency decrease of 20% is expected.
Development of a Large-Scale High-Speed Linear Cascade Rig for Turbine Blade Tip Heat Transfer Study
Authors: Jiang Hongmei , Peng Xu , Xie Wenbo , Lu Shaopeng , Gu Yongmin , Zhang Qiang 
Published: October 2022

Abstract
The high-speed Over-Tip-Leakage (OTL) flow has significant impact on aerodynamic performance of the High-Pressure turbine (HPT) passage and generates high thermal load for the blade tip. Different tip sealing and cooling design strategies are applied to reduce the OTL loss and help turbine survive in high temperature environment. High-speed linear cascade experimental rigs play an important role in understanding the flow physics and evaluating their performance. Multiple blades and passages are often required to maintain a reasonable flow periodicity. To match the engine representative Reynolds number and Mach number, a high-speed multi-passage cascade design inevitably demands more compressed air supply. A very large amount of heating power is also required if the engine condition wall-to-gas temperature ratio needs to be matched. In this study, a simplified two-passage linear cascade rig for high-speed tip heat transfer research was developed. Both the design method and the rig performance are presented. Different from existing design method to match two-dimensional blade loading, this study shows there are other design flexibilities, such as assist blade tip gap, tailboard adjustment and profiling, adjustment, to match the periodic three-dimensional OTL flow structures. The design method was validated by experimental effort. High resolution tip heat transfer coefficient distribution at stationary and rotating conditions (Rotating Mach = 0.35) are reported. The enlarged test model can offer much more improved resolution of optical measurement near the tip region.
Method of the Vaneless Diffuser Rotating Stall Cell Size Assessment Based on the PIV Measurements
Authors: Grapow Filip , Liśkiewicz Grzegorz , Kryłłowicz Władysław 
Published: October 2022

Abstract
This paper presents the universal method of assessing the Vaneless Diffuser Rotating Stall (VDRS) cells’ size with the use of the Particle Image Velocimetry (PIV) technique. Two different cell dimensions’ definitions were introduced: Radial Cell Size (RCS) and Circumferential Cell Size (CCS). The step-by-step instructions for the calculation of both cell sizes are provided. Also, potential issues that readers may encounter while calculating the VDRS cell’s size are presented followed by examples of their solutions. The presented method for cell size assessment is universal and can be used not only with PIV measurements but with any technique allowing flow field reconstruction inside the diffuser or in numerical research. Such an analysis provides information regarding the most crucial zones inside the diffuser for anti-VDRS systems. Based on the results it is possible to increase the efficiency and applicability of the already developed and future VDRS prevention systems. Additionally, this method allows further understanding of the VDRS development by means of the cell growth study. Results of such an analysis may be used to improve compressor design resulting in better performance and wider operation range.
A Numerical Investigation on the Influence of Wall Roughness on the Performance of Volutes of Centrifugal Compressors
Authors: Wolbert D. , Schmitt M. , Koenig S. , Wannek M. , Hartmann J. 
Published: October 2022

Abstract
This paper presents the results of a numerical investigation on the influence of wall roughness on the performance of centrifugal compressor volutes. The main objective of the presented work was to gain further knowledge on the highly three-dimensional flow inside the volute with regard to wall roughness and operating point (surge, best efficiency point and choke). The numerical investigation was carried out with steady state simulations and SST with enabled Reattachment Modification as turbulence model for two centrifugal compressor stages with different outward wound volutes. By means of the equivalent sand-grain roughness ks, the wall roughness was systematically varied and its influence on the volute was evaluated by a thorough performance and flow analysis. The expected drop in efficiency and polytropic head with increasing wall roughness was observed, which was more distinct at choke conditions, mainly due to the increasing skin friction losses at the volute walls. The flow analysis also showed influences of the wall roughness on the secondary vortex flows structures at the smaller volute cross sections near the volute tongue area, with distinct changes compared to the smooth wall case in terms of location and form. An influence of wall roughness on a possible shift of the best efficiency point was not observed.
Transition of a Laminar Separated Boundary Layer Under Varying Adverse Pressure Gradient
Authors: Kumar Ravi , Singh Pradeep , Sarkar S. 
Published: October 2022

Abstract
This paper describes the effects of pressure gradients on the transition of a laminar separation bubble (LSB) formed over the flat plate. The measurements were performed using electronically scanned pressure (ESP) and hot-wire anemometer. The different adverse pressure gradients (APG) are achieved by changing the opening angle (α) of the upper boundary of the domain. The experiments were performed for α = 7°, 9.5° and 11.5° at a Re of 2 × 105 (based on the inlet freestream velocity and plate length) and freestream turbulence intensity (fst) of 1.02%. The onset of separation and transition occurs at x / L = 0.39, 0.449 respectively with reattachment at 0.491 for α = 7°. As APG increases, the separation, transition and reattachment shift upstream with respect to α = 7° leading to the reduction in bubble length. The decrease in the length of LSB is attributed to the earlier transition. Moreover, the growth rate of fluctuations increases with increasing APG. The power spectra of streamwise fluctuations illustrate that the transition occurs via K-H instability for all APG and the predominant shedding frequency increases with increasing pressure gradient. Moreover, the self-similarity of normalized urms profiles in the second half of the bubble show the presence of viscous instability.
Microtomography of Soil and Soot Deposits: Analysis Of Three-Dimensional Structures and Surface Morphology
Authors: Suman Alessio , Vulpio Alessandro , Pinelli Michele , D’Amico Lorenzo 
Published: October 2022

Abstract
The detrimental effects generated by the gas turbine fouling phenomenon are well known. Due to soil and soot particles ingestion, gas turbines experience performance drops related to greater fuel consumption and even lower efficiency. These effects are related to the modification of the shape and surface roughness of relevant surfaces (compressor and turbine blades and vanes, especially) due to the presence of a thin layer generated by micro/nano-sized particle adhesion. Such contaminants are swallowed by the unit and, as a function of the operating conditions, adhere to the surface, causing a sort of dangerous coating to the surface.
In this work, a microtomography analysis of the deposited layer is reported. The deposited layer has been generated using micro-sized soil and soot powders under specific impact conditions and substrate surface roughness similar to those in the cold section of a gas turbine compressor. The microtomography analysis has been carried out using the beamline at the ELETTRA Sincrotrone research center. Thanks to the resolution of the beamline, the detection of the three-dimensional internal structure of the soil and soot layers has revealed that within the layer, the structure is characterized by discontinuities. Soot and soil particles, even characterized by similar diameter distributions and test conditions, generate layer structures that differ by the magnitude, orientation, location of the internal discontinuities, and surface morphology (i.e., roughness). The comprehension of the packing process allows to understand the adhesion process and define general guidelines to predict the fouling phenomenon.
Performance Simulation of Micro Gas Turbines for Hydrogen Application
Authors: Esmaelpour Arias , Nikpey Somehsaraei Homam , Breuhaus Peter 
Published: October 2022

Abstract
The intermittency of renewable energy resources like solar and wind provides unstable outputs and may not comply with the energy demands at all time frames, and the network faces periodic surplus and shortage of energy. Dispatchable energy generation technologies that can be ramped up and down could be combined with intermittent renewables in hybrid systems to match the demand and to address the variability in generation.
Currently, the commonly used dispatchable energy generation technologies are operating with fossil fuels that contribute to CO2 emissions. On the other hand, carbon capture technologies are costly, energy consuming and cannot be applied for small scales. Hence, a dispatchable energy generation technology that can utilize clean and renewable based alternative fuels such as hydrogen to maintain the grid flexibility and stability becomes attractive. In this context, micro gas turbines (MGTs) with high operation flexibility and the ability for operating with various fuels and flue mixtures can potentially represent a lucrative solution for reliable and efficient energy supply, contributing to realize a sustainable future.
Therefore, this study investigates the performance of MGTs in hydrogen application, which is in line with ongoing hydrogen activities at UiS. To this end, this study focuses on the development of a physical model based on an existing Turbec T100 test rig. The modelling is carried out using UniSim software which is a commercial process simulation tool. The model is validated against steady-state experimental data obtained from the test rig operated by natural gas while the dynamic validation of model is a part of future work due to the lack of adequate transitional experimental data. Assuming necessary modifications to the engine, the effects of utilization of mixtures of hydrogen and natural gas from zero hydrogen to 100% hydrogen on the engine performance are analyzed at various operational conditions and compared with the standard natural gas fired engine.
High Accuracy Numerical Investigation of Trailing Edge Noise at Vortex Shedding Critical Angle of Attack
Authors: Zheng Huabin , Chen Jinqiang , Yu Peixiang , Ouyang Hua 
Published: October 2022

Abstract
In this paper, the trailing edge noise generated by a 2D airfoil around the critical angle of attack for vortex shedding is numerically investigated using an in-house code with high accuracy and efficiency. In the present method, a fourth-order upwind compact finite-difference scheme with dispersion relation preserving (DRP) property is applied for the convection terms, and a fourth-order Runge-Kutta scheme is used for temporal discretization. The reflection of sound on the boundary is suppressed with Navier-Stokes characteristics boundary condition (NSCBC). To improve computational efficiency, a novel parallel computing strategy for the high-order compact schemes is employed. Thus, direct numerical simulation (DNS) can be realized for the flows of low Reynolds number (Re), while implicit large eddy simulation (ILES) would be carried for the flows of high Reynolds number. The present numerical method is validated by comparing the lift coefficient, drag coefficient and Strouhal number (St) to the previous publications. Based on the high accuracy and high-fidelity method, the flow field and sound field of a two-dimensional NACA0012 airfoil around critical angle of attack (AoA) at Re = 1000 are simultaneously solved. The results indicate that sound source is dipole centered at the surface of the airfoil at vortex shedding frequency, and is dipole, quadrupole or more complex sources located at the wake close to the trailing edge at higher order frequencies. These findings will help to improve understanding about the generation and propagation mechanisms of trailing edge noises at low Reynolds number.
A Self-Sufficient Oil Cooling Mechanism for Fluid-Film Bearing Applications in Remote Operations
Authors: Gokaltun Seckin , Fabijonas Bruce R. , Krajewski Louis S. , Rodzwic Richard C. 
Published: October 2022

Abstract
The Kingsbury CH Bearing System is a self-contained bearing solution that utilizes a viscosity pump to supply lubrication to individual bearings. The system consists of a CH unit that houses a journal bearing and a double thrust bearing assembly as well as an oil reservoir and internal oil channels and a C unit which houses a second journal bearing. The names ‘CH’ and ‘C’ are historical. An external piping loop connecting the CH and C units lubricates the C journal bearing. Another external piping loop connects the oil reservoir in the CH unit to an external cooling system which cools the hot oil leaving the CH thrust bearings. The system traditionally employs a heat exchanger using cold water provided by a pumping station. Due to the self-contained nature of the CH system as described above, field applications can involve remote locations where utility access could be limited; therefore, it is desirable to avoid the dependence of the cooling system on a reliable water supply. This is especially critical for applications where there is additional difficulty in maintenance of the units due to reduced crew access. In this work, we present a solution for removing the reliance on a water-based cooling system for the CH Bearing System. Instead, the traditional shell-and-tube heat exchanger is replaced with a radiator/fan combination. The fan is mounted to the end of the shaft which extends through the CH housing on the non-drive end of the machine. This mounting method marries the cooling rate with the operating speed of the shaft and ensures that oil is being cooled as long as the shaft is rotating. Experiments with a CH test unit using this new cooling set up show that the required oil temperature in the oil reservoir can be achieved using the air-based system while not adversely affecting pressure drops and flowrates in the lubrication lines.
Modal Identification for Integrally Bladed Rotors Under Traveling Wave Excitation
Authors: Beck Joseph A. , Brown Jeffrey M. , Gillaugh Daniel L. , Kaszynski Alex A. 
Published: October 2022

Abstract
The safety of a fielded Integrally Bladed Rotor (IBR) is often assessed through vibration testing. Responses due to various types of excitation are measured and processed and can be inputs to follow-on analyses, such as mistuning identification. One such excitation technique is the Traveling Wave Excitation (TWE) where all blades are simultaneously excited at phase differences that attempt to replicate naturally occurring mode shapes and certain operating conditions. This test relies on non-contact exciters, e.g. magnets and speakers, that are often not directly measured. As a result, formulating the Frequency Response Function (FRF) is difficult and the extraction of system modal data using FRF fitting techniques in the absence of FRFs is not possible. This paper presents an approach to use measured responses from TWE tests. It is shown that the Fast Fourier Transform (FFT) of the TWE inputs are mostly independent over the prescribed frequency range. Consequently, the output spectral density matrix can be formulated in an Operational Modal Analysis (OMA) sense, where direct measurement of the inputs is not needed. A full spectral density matrix is then formulated from a single measurement on each blade obtained during a single test, thus reducing the number of measurement locations and testing excitation conditions. This matrix is fit by a Polyreference-Least Squares Complex Frequency-domain (P-LSCF) system identification technique tailored for OMA-type measurements. The methodology is tested using simulated TWE data for an IBR model using different damping levels. Comparisons between identified modal data and those used to create the model are made and show the methodology accurately predicts underlying system information even for closely-spaced modes that are common to IBRs. Finally, the method is used on experimental TWE data of an industrial IBR.