bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Heat Transfer and Coherent Structures of the Tangential Impingement Jets in the Annular Chamber Studied With Extended Proper Orthogonal Decomposition
Authors: Shi Lei , Zhu Xiaocheng , Du Zhaohui 
Published: October 2022

Abstract
The tangential impingement of turbulent circular jets on the cylindrical surface in an annular chamber is numerically investigated based on the SAS-SST model. The main purpose is to understand the role of the coherent structures on the temperature field inside the chamber and the heat transfer coefficient field on the hub surface. Based on the jet diameter and inlet velocity, the jet Reynolds numbers are given as 285000, 332000, and 392000, respectively. The accuracy of the numerical simulation is verified by the experimental data. The spectrum information of the velocity magnitude at the monitor point is obtained by the fast Fourier transform (FFT) method. An improvement of the proper orthogonal decomposition (POD) method is known as the extended POD (EPOD) method, which is mainly suitable for analyzing the correlation between the flow field and the synchronized scalar or vector fields, such as the correlation between the velocity and the heat transfer coefficient fields. In present study, both the POD method and the EPOD method are applied and compared. The POD method allows to visualize the main modes in terms of velocity, temperature, and heat transfer coefficient fluctuations. With the help of the EPOD method, the contribution of velocity fluctuations to temperature fluctuations in the chamber and heat transfer fluctuations on the hub surface are further analyzed. For Rej = 392000, the first two velocity POD modes and the velocity EPOD modes that contribute the most to the temperature fluctuations are very similar, reflecting the same large-scale coherent structures. The first two velocity EPOD modes that contribute the most to the heat transfer coefficient fluctuations have a high proportion of energy in the flow field, corresponding to the deflection motion of the jet.
Correlated Pressure-Velocity Instability in a Transonic High-Pressure Turbine Blade
Authors: Dellacasagrande Matteo , Lengani Davide , Bertolini Ettore , Sanz Wolfgang 
Published: October 2022

Abstract
The present work describes the coupled pressure-velocity instability in the suction side boundary layer of a transonic high-pressure turbine blade. The application case is the VKI LS89 turbine blade MUR237. Modal decomposition techniques such as the Proper Orthogonal Decomposition (POD) and the Dynamic Mode Decomposition (DMD) are applied to data obtained by large eddy simulations (LES) to inspect the existing correlation between pressure fluctuations induced by travelling pressure waves and the velocity disturbances growing into the boundary layer. To this end, POD and DMD were applied to both velocity and pressure fields from the leading edge up to the end of the blade surface. DMD was computed on a 2D slice oriented parallel to the blade surface inside the boundary layer. Data were ordered along the curvilinear abscissas, so that the most spatially amplified waves were obtained. Interestingly, unstable velocity modes were detected in the front blade suction side where pressure waves dominate. The unstable velocity modes computed upstream of the peak suction highlighted the occurrence of elongated streaky structures showing spanwise fluctuations which are typical of their instability. The comparison of pressure and velocity modes highlighted the occurrence of pressure-related fluctuations in the velocity field at the same time instants at which streak instability is observed. The analysis carried out in this work suggests that pressure waves can provoke localized instability of boundary layer streaks, which then break up further downstream causing transition.
Flow Modal Decomposition of a Vertical-Axis Wind Turbine With the Moving Boundaries of Rotating Blades
Authors: Tian Tian , Sun Chong , Zhu Xiaocheng , Du Zhaohui 
Published: October 2022

Abstract
Aiming at analyzing the wake evolution features of a 3-blade vertical axis wind turbine (VAWT), dynamic mode decomposition (DMD) is used to evaluate statistics of the flow field based on unsteady flow field computations. Considering the limitation that DMD can only be applied to problems with stationary boundaries, the technology to deal with the moving boundaries of rotating blades is investigated. First, the flow fields of VAWT are calculated using CFD, and computations are compared with the experimental results to verify the numeral calculations. Then the spectral analysis is performed on the VAWT wake at a tip speed ratio of 2.35, and different frequency characteristics are observed in the near wake, the transition region of the wake, and the far wake, respectively. Next, DMD is employed to investigate the dynamic stall and the wake evolution of the VAWT in the absolute frame and the relative frame, respectively. Details of different possessing methods are presented. Finally, depending on the corresponding frequencies obtained before, the dominant modes are extracted from the CFD results by DMD. The extracted modes corresponding to specific frequencies can capture the coherent structures with different scales, which reflecting the characteristics of the propagation of shedding vortices from blades and the bluff-body oscillation in the wake of the VAWT.
Aeroacoustic Interactions of Blade Skew and Leading Edge Serrations Applied to Low-Pressure Axial Fans
Authors: Biedermann Till M. , Hintzen Nils , Kameier Frank 
Published: October 2022

Abstract
Leading edge serrations are well known for their ability to reduce turbulence-induced noise of single aerofoils while also providing aerodynamic advantages under certain operating conditions. Continuatively, applying leading edge serrations to rotating machinery such as axial fans proved the validity to generally transfer the obtained aeroacoustic benefits of single aerofoils. However, for the rotating applications, besides the discrete and broadband characteristics of the investigated machines, the noise reduction potential highly depends on the point of operation. The current work aims at assessing the aeroacoustic effects of serrated leading edges under the increased geometrical complexity of the fan blades through blade skew, a combination of blade sweep and blade dihedral. Therefore, the question is whether combining two potentially effective noise-reducing treatments through blade skew and leading edge serrations results in leveraging or obstructing effects. By varying the skew angle from 0 deg to 38 deg, four different prototypes of the fan impeller are designed, manufactured and tested experimentally in a test rig according to ISO 5136 and ISO 5801, allowing for simultaneous assessment of the aerodynamic and acoustic performance of the machines. All configurations are tested with original blades of straight leading edges plus five sets of serrations each, parameterised by the serration amplitude and the serrations wavelength. The intensity of the incoming turbulence ranges from 2.6% to 12.1%. The results obtained show the skewed blades to improve both the aerodynamic performance and the noise radiation after exceeding an initial skew angle, complemented by a significant onset of stall. Moreover, no contraindication between blade skew and serrated leading edges is encountered, showing the potential to further extend the noise reduction capabilities by combining effects of blade skew and leading edge treatment.
Experimental and Numerical Characterization of the Self-Excited Dynamics Behavior of a Technically Premixed Burner
Authors: Meloni R. , Gori S. , Riccio G. , Chiarizia N. , Pampaloni D. , Andreini A. 
Published: October 2022

Abstract
In this paper, the numerical findings of a high fidelity CFD model will be compared with the experimental data of a test campaign devoted at characterizing the performance of a technically premixed industrial burner regarding the thermoacoustic instabilities.
The data are retrieved at relevant gas turbine conditions in a test bench where the flame tube can change its length during the test execution allowing its fundamental acoustic frequencies to be modified and, in case, triggered. Mimicking the test configuration, several Large-Eddy Simulations are performed with different lengths of the flame tube in order to verify the ability of the numerical model to reproduce the excited dominant frequency and the corresponding limit cycle amplitude measurements. The numerical model demonstrates the ability to correctly reproduce the frequency triggered during the test and to reach different limit cycle amplitudes along different flame tube lengths in agreement with the tests, as well. However, it is found that the amplitude of the acoustic pressure fluctuation during the limit cycle is generally under-predicted. Despite this, the proposed approach demonstrates to be a robust tool for the characterization of a given design, allowing to dramatically reduce the computational cost of the analysis, at least in the early design phase.
Since the numerical model can correctly reproduce the behavior of the investigated design, a deep post-processing of the solutions is performed to shed light on the physical mechanisms sustaining the thermo-acoustic instability. Among the numerical techniques employed at this purpose, the Phase-Locked Average and the Extended-POD are applied trying to correlate the fluctuations of the different quantities inside the premixed channel of the burner and the primary zone as well.
The Role of Turbine Operating Conditions on Combustor-Turbine Interaction – Part 2: Loading Effects
Authors: Notaristefano Andrea , Gaetani Paolo 
Published: October 2022

Abstract
Aeroengine combustors burn a lean and premixed blend releasing vorticity and temperature perturbations. Interacting with the first turbine stage, these disturbances impact the cascade aerodynamics, add criticality to the blade cooling and are sources of noise. The first of these issues is addressed in this paper, focusing on off-design turbine conditions, as experienced by aero-engines in their duty. This paper, part II of a two-fold contribution, analyses the effect of the stage loading obtained by changing the RPM (three different values) at the same expansion ratio of 1.4, representative of subsonic flow conditions.
Engine-representative disturbances are generated by a combustor simulator able to produce a swirling entropy wave. Two injection positions and four injection patterns are considered. Experimental measurements are carried out through the stage, measuring the injected disturbance and the aerothermal flow field downstream of the stator and the rotor.
Results show that the swirl profile mostly impacts the stage aerodynamics. The different work extraction and the interaction with secondary flow structures change the entropy wave transport, diffusion and decay through the rotor. Furthermore, the increased angle of the incidence caused by the injected disturbance can make the blade stall under the most loaded operating condition.
Metamodelling of Ignition Delay Time for Natural Gas Blends Under Gas Turbine Operating Conditions
Authors: Yousefian Sajjad , Bourque Gilles , Monaghan Rory F. D. 
Published: October 2022

Abstract
Characterisation of autoignition risk is crucial for designing and optimising low-emission combustion systems as there is an increased demand for highly reactive and novel fuel mixtures. Achieving a residence time to prevent autoignition and obtaining an adequate mixing quality is a challenging trade-off for these fuels in lean-premixed combustion systems. The level of complexity increases further due to low-temperature chemical pathways and pressure-dependent reactions that strongly influence ignition delay at engine operating conditions. Detailed chemical kinetic mechanisms with hundreds of species and thousands of reactions are developed and employed to address this complexity and predict ignition delay accurately, especially for heavier hydrocarbons. However, direct implementation of these kinetic mechanisms is computationally prohibitive in high-fidelity CFD approaches such as large eddy simulation (LES) and stochastic simulation tools that require a large number of evaluations. Advanced stochastic methods are essential tools to quantify uncertainties due to the inherent variabilities in ambient, operating conditions and fuel composition on ignition delay time calculation for practical applications. This study introduces and implements a computationally efficient method based on metamodellig to predict ignition delay time over a wide range of operating conditions and fuel compositions for gas turbine combustion systems. A metamodel or surrogate model is an accurate and quick approximation of the original computational model based on a detailed chemical kinetic mechanism. Polynomial chaos expansion (PCE) as an advanced method is employed to build metamodels using a limited set of runs of the original ignition delay time model based on NUIGMech1.0 chemical kinetic mechanism as the most detailed and state-of-the-art chemical kinetic mechanism for natural gas. Developed metamodels for ignition delay time are valid over operating conditions of P = 20–40 bar and T = 700–900 K for natural gas containing C1 to C7 hydrocarbons at stoichiometric condition. These metamodels provide a fast, robust, and considerably accurate framework instead of a detailed chemical kinetic model that facilitates (a) characterising ignition delay time at different operating conditions and fuel compositions, (b) designing and optimising premixers and burners and (c) conducting uncertainty quantification and stochastic modelling studies.
Development of Oil Free Centrifugal Blower As Enabling Technology for Solid Oxide Fuel Cell Anode Gas Recycling
Authors: Wooding Rochelle S. , Lea Hannah G. , Córdova José Luis 
Published: October 2022

Abstract
Broad commercialization of solid oxide fuel cells (SOFCs), requires anode offgas recycle blowers (AORB) that are specifically designed for handling the challenging operating conditions presented by the SOFC process gases. Otherwise, they can be susceptible to frequent maintenance, low reliability, and short life. This work presents details of the development and testing of an oil-free, low cost centrifugal AORB based on compliant foil bearing (CFB) technology for support of a 100 kW solid oxide fuel cell power plant. The advantages of this novel technology are discussed, particularly its long life and maintenance-free operation, which are derived from the use of CFBs. Also included are preliminary techno-economic analysis considerations for cost-effective deployment of the technology.
Design of an Additively Manufactured Recuperator With 800 °C Inlet Temperature for sCO2 Power Cycle Application
Authors: Marshall Michael , Akbari Meysam , Zhao Ji-Cheng , Hoopes Kevin 
Published: October 2022

Abstract
Recuperators with design temperatures at and above 800 °C can further increase the thermal efficiency of supercritical CO2 power cycles by enabling higher turbine exhaust temperatures. Mar-M247 is a well-suited nickel-based superalloy for high temperature service due to its high creep strength that prevents excessive material thickness being required for pressure containment. While not compatible with the diffusion bonding process due to its low ductility, additive manufacturing using a high-speed laser directed energy deposition (DED) process presents a promising solution with the ability to produce non-conventional flow channels for enhanced heat transfer. A design process is presented that includes aerothermal and mechanical evaluation to maximize performance within the constraints of the manufacturing process. The conceptual design stage evaluates the feasibility of numerous heat transfer concepts from a unit cell perspective. A 2-D heat transfer network and pressure drop code allows prediction of flow distribution in each passage and its effect on overall thermal performance. Established literature correlations, along with CFD simulation, inform the prediction of heat transfer coefficients and friction factors for the flowpaths and enhancement features in the heat exchanger core. Sizing codes for the heat exchanger distribute wall thicknesses for pressure containment according to creep life data for Mar-M247. Mechanical evaluation using FEA modeling with the intent of the ASME BPVC Section VIII, Div 2 assesses the operational safety of the design. The capabilities of the laser DED process and the build strategy for minimizing total build time is discussed, along with the results of build trials that evaluate the settings of the powder nozzle and laser and their effect on deposition rate and susceptibility to build defects. Major considerations affecting the core geometry include the overhang angle of passage structures and the alignment of enhancement features for time efficient builds. The presented detailed design features annular finned passages that take advantage of helical flow paths to distribute the flow from separated headers to shared heat transfer surfaces. Performance predictions for the recuperator at a 50 kW scale provide insights on the feasibility of the AM process to produce recuperators on a commercial scale that extend existing operating envelopes.
Novel UAS Propeller Design Part 2: Design Hub and Tip Angle of Attack Sensitivity of UAS Propellers Designed for Minimum Induced Drag
Authors: Van Treuren Kenneth , Wisniewski Charles 
Published: October 2022

Abstract
Increased interest in eVTOL (electronic vertical take-off and landing) vehicles is growing. These vehicles will become urban air taxis and delivery vehicles, reducing the time involved for moving people and goods in the cities. There is also growth in the small Unmanned Aircraft System (sUAS). The propulsion system for both vehicles use an electric motor with propellers. These vehicles need propellers which are more efficient and have reduced noise generation if they are to coexist in either an urban environment or be used on ISR missions.
Previous studies show that a propeller designed for minimum induced drag using a 50% “hub” break with a “tip” break of 90% leading to zero tip thrust loading results in a propeller that is both quieter and more aerodynamically efficient. This design incorporates a constant angle of attack (AOA) from the hub to an r/R of 50% where the section propeller thrust loading then dropped to an AOA with zero lift at an r/R of 90%. AOA sensitivity of both the hub and the tip are studied. Using a hub AOA lower than the value for Cl/Cd max can result in an mechanical power reduction of 6.4% compared to a commercial propeller. A slightly less negative tip AOA than zero lift will also lead to the lowest mechanical power required. However, if a lower sound pressure level is desired, then, for the lower hub angles of attack, a tip angle of attack slightly more negative than zero lift should be used, resulting in up to a 7.8% reduction in SPL. As seen in the data, there exists a tradeoff with between lower aerodynamic power and lower SPL using various combinations of hub and tip angles of attack.
Numerical Investigation at Nominal and Off-Design Operations Of a Supersonic Turbine for Liquid Rocket Engines With Full and Partial Admission Nozzles
Authors: Yamamoto Keita , Ukai Satoshi , Fukasawa Osamu , Fukuda Taro , Negishi Hideyo 
Published: October 2022

Abstract
In recent years, various types of liquid rocket engines have been developed to achieve different types of mission, and modern rocket engines are required to operate at different conditions depending on flight situations such as launch and landing. Thus, rocket engines are required to be more reliable and robust. One of the key components for a rocket engine to enable flexible operating conditions is a turbine since it determines a power of feed-line systems and an efficiency of rocket system itself. To fulfill the requested output of the entire systems, an appropriate design of the turbine, including the selection of full/partial admission configurations, is of crucial importance. On the other hand, the development of supersonic turbines in turbo-pumps remains a challenge due to their complex internal flow structures and systems with high rotational speed. Furthermore, it is necessary to achieve high performance and stable operations under extensive operating range in respect of innovative transport technologies including the development of reusable launch vehicles. However, detailed flow characteristics at off-design conditions of supersonic turbines are yet to be fully understood. Therefore, this paper aims to study internal flow characteristics and performance of a supersonic turbine at different operating points.
The present study first demonstrates the comparisons of 3D RANS simulation results of the selected supersonic turbine (JAXA subscale M-1 turbine) consisting of two stages with full admission nozzles and partial admission nozzles, where the experimental results with the partial admission configuration are available to validate the simulation results. The simulations are conducted with full stages and the entire circumferential configuration at 5 different operating conditions defined by the velocity ratio (the ratio between the turbine rotational velocity and isentropic velocity at the turbine outlet) including the nominal condition. The internal flow structures under off-design operations for both full and partial admission nozzle configurations are investigated to address profound features of the flow field at off-design operations in a supersonic turbine. The analysis is furthermore extended to reveal the mechanisms of the energy loss by comparing the results of the full admission and two different configurations of the partial admission nozzles at different operating conditions. As a result, an empirical method to determine nozzle and ventilation loss curves based on velocity ratio is proposed, and also it is demonstrated that these curves can be applied to predict energy loss of various partial admission configurations at different operating conditions.
Numerical Research on Near Stall Characteristics of a Transonic Axial Compressor Based on Wavelet Analysis
Authors: Xia Kailong , Feng Junda , Zhu Mingmin , Deng Hefang , Qiang Xiaoqing , Teng Jinfang 
Published: October 2022

Abstract
An axial single-stage high-speed test rig was numerically studied in this paper with half-annulus URANS simulations to describe the flow characteristics at the near stall condition. Numerical probes were arranged circumferentially near the casing in each rotor passage from the leading edge to the trailing edge evenly. Wavelet analysis was applied to demonstrate the time-frequency characteristics of the wall pressure signals captured by the probes located at different axial positions. The detailed tip flow fields and wavelet transform results were combined to depict the generation and propagation of the spike type stall inception.
According to the wavelet spectrum, characteristic frequencies correspond to the temporal and spatial features of the rotating stall, such as the fluctuation of the shock wave, self-oscillation and propagation of tip leakage vortex et al. Consequently, the detection of typical spike stall inception can be significantly brought forward through identifying the crucial rotating disturbance and its development for the onset of stall inception. Then, the specific flow fields verified by previous researchers are also discussed to reveal the flow mechanism of stall inception evolution, including the leading edge spillage and the trailing edge backflow. Further investigation showed that the stall inception with smooth casing corresponds to the radial separation vortex caused by the tip leading edge spillage, which continues to develop and propagate in the circumferential direction and finally induces the stall.