bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Influence of Mode Shape on Flutter Stability of a Scaled Composite UHBR Fan
Authors: Goessling Jan , Maroldt Niklas , Stapelfeldt Sina 
Published: August 2024

Abstract
In literature, two common parameters to indicate flutter sensitivity are the reduced frequency and the amount of twist present in the combined first flap mode. A critical parameter is the plunge-to-twist incidence ratio, which is a function of both frequency and twist-to-plunge ratio in the mode shape. However, the limit of this stability criterion for real fan blades is not fully understood yet. This paper investigates the influence of plunge-to-pitch incidence ratio on a 3D transonic test case, the scaled composite UHBR fan of the CA3ViAR project, with the aim to understand the validity of the plunge-to-twist incidence ratio as a flutter parameter for transonic and three-dimensional fan blades. This fan was designed with the unconventional goal to achieve stable operation at the design point but flutter at throttled offdesign conditions. The design was done by varying the CFRP ply material and orientation towards specific reduced frequencies and twist-to-plunge ratios to drive the aerodynamic stability towards the desired behaviour. Here, the aerodynamic damping of a set of 3D mode-shapes based on variations in the composite ply-layup are simulated using TRACE Harmonic Balance for different reduced frequencies. Flutter stability for different reduced frequencies and twist-to-plunge ratio is mapped for several operating points. The results show that the stability boundary only follows lines of constant plunge-to-pitch incidence ratio in some regions of the map but deviates in others. The key deviations are then explained by analysing the aeroacoustic conditions. The study demonstrates that the validity of the plunge-to-twist incidence ratio parameter depends on the flutter mechanism. It is not valid inside the region where the acoustic wave is cut-on upstream but cut-off downstream. To the authors’ knowledge, this is the first time that limits of this stability criterion for fan flutter were explicitly shown and explained.
Numerical Study of Low Engine Order Excitations due to Manufacturing Variability Part 1: Characterization of the Geometric Scatter and its Effect on Forced Response
Authors: Pérez Escobar Óscar , Timón Vicente , Gallardo Juan Manuel 
Published: August 2024

Abstract
The geometric scatter in the surfaces of blades and vanes due to manufacturing variability has an impact on the dynamics (structural mistuning) that has been widely studied, but also on the aerodynamics. This geometric variability changes the fluid field, generating disturbances not directly related to the airfoil count. This work focuses on the aerodynamic forcing generated by this manufacturing variability on the adjacent rows.
In this paper, deviations from the nominal geometry are obtained from a set of scanned parts. The average manufactured geometry is computed through the point-by-point deviations between the scanned parts and the nominal geometry. Then, Principal Component Analysis is applied to the deviations from the average geometry to find a way to describe them in a compact and simple manner. The cold geometries are reconstructed using the mean geometry and the geometric modes; afterwards, a cold-to-hot process is applied to obtain the hot geometry, and finally the resulting aerodynamics are obtained using an in-house CFD solver. The loss of the spatial periodicity of the flow due to the geometric variations generates an aerodynamic forcing with a wave number different from the airfoil count.
The described method is applied to a representative row constituted by packets of vanes, and two forced response cases are generated. In the first one, the average packet geometry is used to analyze the aerodynamic forcing associated to the geometric variation of the airfoils inside the vane packet. The second one is a conceptual study carried out under some simplified assumptions in order to relate the geometric variability to random low engine order disturbances, using the geometric modes obtained from the PCA analysis. In both cases, the induced vibrations on the adjacent rotor row are comparable to the excitation due to the nominal blade-passing.
Influence of Engine Conditions on the Performance Prediction of a Two-Stage Transonic Low Pressure Compressor
Authors: Scheibel Julian Alexander , Stößel Marcel , Kožulović Dragan 
Published: August 2024

Abstract
The derivation of application-driven impact factors on the performance of real engine compressors is an essential prerequisite for the development of efficiency-enhanced modern compressor concepts. This study intends to extend the knowledge of the sensitivity of compressor operation simulation on real-engine design conditions, by investigating the impact of upstream and downstream engine components on the prediction of compressor map characteristics. The investigations are conducted on a two-stage transonic low pressure compressor of an unmixed low bypass ratio turbofan engine. Starting from the basic test case of a compressor operation under non-disturbed and homogeneous boundary conditions, the compressor is systematically subjected to aerodynamic conditions deriving from the compressor positioning downstream of the engine intake and upstream of the bypass splitter. The analysis focuses on both global compressor map characteristics and the causal relations in local aerodynamics, in terms of a radial redistribution of the blade loading, local resistance against flow separation and the role of stage interaction depending on the distinguished engine conditions. A strong sensitivity on the spinner geometry is derived and a less pronounced effect of the downstream throttling condition is analysed.
Lessons Learned From Pandemic-Driven Remote Learning and Sustaining Best Practices in Turbomachinery Laboratory Experiences
Authors: Reeping David , Villalva Rodrigo , Bellur Kishan , Cuppoletti Daniel , Khare Prashant 
Published: August 2024

Abstract
As online educational experiences have become more common for students to engage with while earning an engineering degree, instructors must become more attuned to best practices in digital pedagogies for all courses, including those with heavy laboratory components. Despite potential resistance among faculty to the idea that a laboratory course does not require an in-person experience, pandemic-driven remote learning serves as an intrinsic data point in how, under dire circumstances, laboratory courses could be offered through a digital medium. This paper describes a collaborative autoethnography of four mechanical and aerospace engineering instructors regarding lessons learned while teaching laboratory courses online during the COVID-19 pandemic. To bolster the quality of the research design, an engineering education researcher facilitated the collaborative autoethnography and co-constructed the individual instructor narratives to elicit best practices in online pedagogy for turbomachinery educators.
Schlieren Image Velocimetry and Modal Decomposition Study of Preheated Isothermal Flow From a Generic Multi-Swirl Burner
Authors: Vishnoi Neha , Saurabh Aditya , Kabiraj Lipika 
Published: August 2024

Abstract
This study presents an experimental investigation into the turbulent flow characteristics of an unconfined counter-rotating dual swirl burner under external acoustic excitation. Utilizing Schlieren image velocimetry (SIV), we capture the velocity field of the swirling jets. Mean velocity field analysis reveals the upstream propagation of the central recirculation zone within the burner passages. Through Proper Orthogonal Decomposition (POD) analysis on instantaneous axial velocity fields, coherent structures are identified and the impact of different actuation methods on spatial modes is illustrated. Spatial modes of the unforced (natural) flow show the presence of a single and double helical Precessing vortex core (PVC) modes at St = 0.53. Low-frequency acoustic actuation (St = 0.46) effectively suppresses the PVC mode, while high-frequency (St = 2) actuation stabilizes it. Broadband excitation of the flow field, however, induces the excitation of both single and double helical PVC modes.
Investigation of a Transonic Dense Gas Flow Over an Idealized Blade Vane Configuration
Authors: Hake Leander , aus der Wiesche Stefan , Sundermeier Stephan , Passmann Maximilian , Bienner Aurelien , Gloerfelt Xavier , Cinnella Paola 
Published: August 2024

Abstract
An experimental and numerical study of the flow of the organic vapor Novec 649 and air through an idealized vane was conducted. Due to the profiling of the passage, typical pressure and Mach number distributions for transonic and supersonic flow around an airfoil could be established. The comparable large trailing edge radius enabled the detailed investigation of corresponding flow phenomena. Schlieren pictures and pressure distributions were experimentally obtained and compared with numerical simulations. The trailing edge flow and the transonic and supersonic shock patterns were qualitatively similar to the ones observed in perfect gas flow. However, significant quantitative deviations were observed. The base pressure was lower in dense gas flows characterized by a fundamental derivative Γ &lt; 1, and the corresponding loss contribution was stronger.
Effect of Reynolds Number and Tip Clearance on the Transonic Axial Compressor During Geometric Scaling
Authors: Zhao Wuan , Chen Jiang , Xiang Hang 
Published: August 2024

Abstract
The compressor often needs to adjust geometric dimensions in the process of design and testing to adapt to different use environments and save design costs. However, low Reynolds number conditions can lead to performance degradation in small-scale machines. At the same time, due to the limitations of processing conditions, the relative tip clearance of small machines is relatively large, which also affects the efficiency and stable working range. Therefore, it is necessary to study the impact of Reynolds number and tip clearance changes on the aerodynamic performance in the process of size scaling. This article first uses the similarity law to geometrically scale down the compressor. The calculated numerical results are used as standards to evaluate the published efficiency correction formula. The results show that the correction error can be controlled within 3%, which meets the engineering application standard. Through flow field analysis, it is found that the decrease of Reynolds number will lead to the increase of boundary layer thickness, the weakness of tip leakage vortex, and the aggravation of corner separation. The accumulation of low-energy fluid in the corner is the main reason for the decrease in flow rate under low Reynolds number. Then, the impact of tip clearance changes on aerodynamic performance under different Reynolds numbers is studied. Under different Reynolds numbers, there is a negative linear correlation between efficiency, pressure ratio and clearance, and the influence of Reynolds number variation on the correlation coefficient is inconspicuous. Under low Reynolds number, increasing relative tip clearance to a certain extent can help improve the stable working range.
Effect of Rear Engine Concept Distortion on the Aerodynamic Performance of a Fan Rotor
Authors: Xue Yifan , Deng Hefang , Qiang Xiaoqing 
Published: August 2024

Abstract
The civil aviation industry is facing serious environmental and energy issues, and boundary layer ingestion technology (BLI) is a viable solution. However, how to ensure that the engine can work continuously under the condition of BLI inlet distortion has become the focus of research. In this paper, Unsteady Reynolds-averaged Navier-Stokes (URANS) and RANS simulation methods are used to simulate a full-annular fan, and the aerodynamic performance of NASA rotor 67 under different BLI inlet distortion is studied. The focus of analysis is on swirl distortion, which has been neglected in previous studies. The loss source in non-uniform flow field is studied by using the loss analysis method based on entropy dissipation. Results show that under side-slip conditions, the intensity of swirl distortion on windward side and leeward side is different, and swirl distortion greatly affects swirl angle distribution, which has a significant impact on fan performance. The loss is mainly located near part of the blade tip and part of the wheel hub, which is related to the structure of the BLI inlet distortion. The relative Mach number and shock wave structure change significantly in the tip region, and dramatically in the region directly affected by the distortion. The interaction between shock wave, boundary layer and tip leakage flow can cause a lot of losses. When the total dissipation decreases, the viscous dissipation caused by swirl distortion decreases and the proportion of thermal dissipation increases. The BLI distortion increases the loss mainly through the swirl distortion. In the region with weak swirl distortion, the total pressure distortion still affects the flow in the tip region.
Stability and Robustness Analysis and Optimization for Gain-Scheduled Control of Aero-Engines
Authors: Jiang Jincen , Yang Jiali , Wang Xiting , Yang Xiao , Hu Zhongzhi 
Published: August 2024

Abstract
Gain-scheduled control has found extensive applications for aero-engines, yet the selection of design points for gain-scheduling controllers to ensure stability and robustness throughout the range of scheduling variables remains theoretically unguided. To address this issue, this paper introduces an analysis and optimization method for the stability and robustness of gain-scheduled control, aimed at providing a systematic theoretical framework for design points selection. Initially, the optimization method characterizes the gain-scheduled control system as a polytopic Linear Parameter Varying (LPV) system, wherein the design points of the gain-scheduled control system correspond to the vertices of the polytopic LPV system. Subsequently, the method utilizes Linear Matrix Inequality (LMI) techniques to demonstrate the stability of a polytopic LPV system with a corresponding number of vertices, and by assessing the approximation degree between the polytopic LPV system and the gain-scheduled control system with an identical number of design points, it evaluates and ensures the stability of the latter, thereby establishing the minimal requirements for the number of design points. Upon ensuring system stability, the optimization method further refines the number of design points within the gain-scheduled control system to meet additional robustness and performance considerations. Through a case study on turbofan engine controls, the proposed optimization method has been validated, exhibiting improved system stability and robustness, as well as accurate high-pressure rotor speed tracking performance. This optimization method offers a novel perspective and methodology, assisting engineers in more effectively balancing the interplay between stability, robustness, and the number of design points during the design of gain-scheduled controllers.
Numerical Modelling of a Primary Heat Exchanger in sCO2 Power Cycles for Thermal Energy Storage Systems
Authors: Guille Alexandre , Bangalore Mohankumar Malini , Unger Sebastian , Hampel Uwe 
Published: August 2024

Abstract
Renewable energy sources are the key for long-term decarbonization of energy. However, the intermittent nature of renewables does not always meet the energy demand in the electrical grid. Thus, electrical heated Thermal Energy Storage systems (TES) coupled with sCO2 power cycles are investigated at Helmholtz-Zentrum Dresden-Rossendorf as a possible solution to balance this mismatch. In this study, a Printed Circuit Heat Exchanger (PCHE) is considered as candidate for the 1 MW primary heat exchanger, given the mechanical challenge induced by drastic pressure difference between the hot fluid of the TES and the cold fluid of the power cycle. The present work consists of two parts, one elaborates a 1D model in order to optimize the PCHE regarding the pump power required to compensate the pressure loss. It was found that the hot fluid coming from the TES accounts for 80 % of the total pump power after optimization because of its low density and its high mass flow rate. Furthermore, 3D simulations by Computational Fluid Dynamics (CFD) were done and compared to the results from the 1D model to ensure its validity. It was observed that the results from the 1D model and the CFD simulations are consistent, with a slight potential deviation in the calculation of the pressure profile.
Numerical Investigation of Two-Phase Shock Waves in CO2 Flows Using a Modified Hertz-Knudsen Model
Authors: Petruccelli Giuseppe , Dolatabadi Amir Momeni , Grönman Aki , Turunen-Saaresti Teemu , Guardone Alberto 
Published: August 2024

Abstract
Understanding the complex behavior of two-phase shocks in CO2 flows is essential for a variety of applications, including carbon capture and storage (CCS) and transcritical refrigeration cycles. This study presents a comprehensive numerical investigation of two-phase shock waves using the multispecies User-Defined Real Gas Model in Ansys Fluent. The simulations are performed for de Laval nozzles, exploring the two-phase shock features for three-dimensional (3D), two-dimensional (2D), and two-dimensional axisymmetric geometries. The non-equilibrium condensation, subsequent evaporation and denucleation occurring across the shock are modeled through a set of User-Defined Scalar transport equations implemented within Ansys Fluent. The two-phase CFD simulations are carried out in proximity to the critical point where real gas effects are relevant. The CO2 real gas properties are computed using an in-house Python code and integrated into the solver via User-Defined Functions as external look-up tables. This study provides valuable insights into the physical processes underlying two-phase shocks in CO2 flows and their sensitivity to geometric variations and thermodynamic conditions. The findings contribute to the development and modification of predictive models and optimized designs for systems involving two-phase CO2 flows. The results highlight the influence of geometry configurations and thermodynamic conditions on shock location and intensity, providing comparisons for shock waves occurring in two-phase flows and supercritical single-phase flows.
Understanding Entropy Wave Evolution in High-Pressure Turbines: the Role of Hot Spot Position and Features
Authors: Pinelli Lorenzo , Giannini Giovanni , Marconcini Michele , Pacciani Roberto , Notaristefano Andrea , Gaetani Paolo 
Published: August 2024

Abstract
Mutual interaction of turbomachinery components plays a key role for a comprehensive optimization of the machine. Among these interactions, the aerodynamic coupling between combustor systems and high-pressure turbine (HPT) stages may lead to aerodynamic performance degradation, cooling issues, combustion instability and noise generation. This interaction is mainly caused by steady and pulsating temperature distortions (hot streaks and entropy waves, respectively) generated by combustion systems: such flow non-uniformities are convected downstream in a swirling flow field and interact with HPT stage. New trends of introducing alternative fuels (sustainable aviation fuel, hydrogen, ...) may also require an even more accurate understanding of such interactions. In this context, the paper reports an extensive CFD investigation examining how circumferential and radial injection positions affect the migration and interaction of swirling entropy waves (EWs) with an uncooled aeronautical HPT stage. The numerical method, based on full-annulus URANS analyses, has been already intensively validated against experimental acquisitions in previous works exploring the effect of different EW-vane tangential alignments, swirling flow rotational directions and turbine operating conditions. Results reveal a complex interaction among the EW spots and secondary flows of both stator and rotor. Moreover, a simplified analytical model proposed by the authors for fast prediction of combustor non-uniformities evolution has been applied to all the presented cases to prove its ability to reproduce the main features of EW evolution. The combination of model and CFD results can provide important insights for turbomachinery designers both during the preliminary design and for the final evaluation.
Effects of Secondary Jet Angle Variation on Flow, Flame Structure and Emission in the Reburning Zone Under Axial Fuel Staging Combustion of CH4/NH3/H2 Fuel
Authors: Li Yuze , Li Yuansen , Xiao Yunlai , Jia Yuliang , Zhu Xutong , Ge Bing , Zang Shusheng 
Published: August 2024

Abstract
Axial Fuel Staging (AFS) combustion technology is an advanced low-pollution combustion technology for heavy-duty gas turbines. In order to investigate the impact of jet angle in the reburning zone on flow field, flame structure, and emission in the secondary zone during axial fractional combustion of methane/hydrogen/ammonia fuel, we employed high-frequency PIV and OH-based self-luminescence techniques. Under atmospheric pressure conditions with a momentum flux ratio of 6, we examined the effects of jet angle variations (45°, 90°, and 135°) on axial fractional flow field, reburning flame morphology, and pollutant emission for different fuel types. It is found that when CH4 fuel is used and the jet Angle is 90°, the flame in the reburning zone has three different forms, namely, self-ignition detached flame, transition state flame, and premix continuous combustion plume flame. At this Angle, there is a good mixing effect and the ignition position is controllable, so NOx emission is significantly lower than the other two jet angles; When the jet Angle is 45°, the secondary fuel is mixed with hydrogen, the reburning flame changes from a detached flame to a short continuous flame. The reburning flame during flame form conversion exhibits minimal flame area and chemical residence time, thus reducing NO emissions. When the jet angle is 135°, the methane reburning flame shifts upstream, exhibiting a circular flame shape and an extended high temperature chemical residence time, resulting in reduced CO emissions but increased NO emissions. During the initial stage of ammonium-doped combustion, as the ammonium-doped ratio increases, the jet flame transitions from a continuous flame to a debulk flame.