bluuebunny/crossref_metadata_2025_split huggingface dataset:
Correlating and Updating Finite Element Models of Different Fidelity Using an Energy-Based Approach
Authors: Hardenberg Alexander , Kühhorn Arnold , Fanter Maren 
Published: January 2021

Abstract
Building finite element models of complex structures requires the engineer to make various simplifying assumptions. While there exists no unique way of modeling, the resulting model depends to a level on experience and engineering judgment. The inherent model uncertainties can be subdivided into three categories: idealization errors, discretization errors and parameter errors. Understanding the effect of different modeling assumptions and minimizing these uncertainties is key for creating efficient and physical meaningful finite element models. In this paper the effects of different modeling assumptions are analyzed by comparing finite element models of an aero engine turbine casing. Various models of different fidelity are created reaching from simple shell element representations neglecting geometric features like bosses, fixings and holes, to higher fidelity mixed dimensional models using coupled shell and three-dimensional elements. To quantify their impact on the stiffness and mass properties, the different models are correlated with a high-fidelity three-dimensional finite element model using numerical modal data. A novel method is proposed based on the strain and kinetic energy distribution to assess the effect of different modeling assumptions on the model structure. This is done by splitting the discretized model into multiple sections of interest and calculating the deviation of energies within the related splits. The derived strain and kinetic energy deviations are then used in addition to other correlation criteria like the modal assurance criteria or the relative difference in eigenfrequencies to analyze the impact of the different modeling assumptions. Having quantified the differences, the difficulties of error localization using modal data are discussed in the context of the correlation results. Finally, the effectiveness of the derived deviation values are demonstrated by updating a finite element model of an aero engine turbine casing in the presence of structural simplifications using an evolutionary optimization algorithm and comparing the model updating strategy to the standard sensitivity-based updating approach. If the resulting updated model is used to predict structural modifications or untested loading conditions, the updated parameters might lose their physical meaning when altering regions of the model not in error. Therefore, it is important to examine the physical significance of the updated parameters. It is shown, how the energy-based model updating can help to address this problem. All in all, the proposed energy-based approach can be used to compare various modeling strategies in order to build efficient finite element models as well as assist in the choice of parameters for subsequent model updating to validate the numerical model against test data.
The Impact of Various Modelling Decisions on Flow Field Predictions in a Centrifugal Compressor
Authors: Gooding William J. , Meier Matthew A. , Key Nicole L. 
Published: January 2021

Abstract
Computational tools have become increasingly important in design and research applications in recent years due to increasing computational resources. In most cases, model geometry and flow-physics are simplified to reduce the complexity of the computational model. While this was necessary historically, modern computational tools are capable of including realistic features such as fillets, surface roughness, and heat transfer.
This work presents extensive and systematic numerical results from a simulation of a centrifugal compressor stage for an aero-engine application. Numerical results are compared to detailed experimental data to investigate the effect of various modelling decisions, including turbulence models, on the predicted aerodynamics developing through the diffuser passage. Roughness and the inclusion of fillets significantly impact the flow development, especially with the SST turbulence model.
This approach leads to the conclusion that the BSL-EARSM model is best able to predict the experimentally determined diffuser flow profiles and overall performance trends with the inclusion of the previously mentioned model features. Additionally, the misleading conclusions can be reached if modelling decisions are based on merely matching overall performance values. Finally, frozen rotor simulations are used to roughly approximate the impact of unsteadiness on the flow field. The results show a significant impact and also that the inclusion of approximate unsteady effects tends to further improve the predictive capability of the computational models that were considered.
Infrared Temperature Measurements of the Blade Tip for a Turbine Operating at Corrected Engine Conditions
Authors: Christensen Louis , Celestina Richard , Sperling Spencer , Mathison Randall , Aksoy Hakan , Liu Jong 
Published: January 2021

Abstract
A high-speed infrared camera is used to measure the temperature of blade tips in a cooled high-pressure turbine operating at corrected engine conditions in The Ohio State University short duration Turbine Test Facility. These experiments create a challenging problem for infrared imaging since the rotor turns at over 13,000 rpm with tip speeds on the order of 300 m/s, and the surface temperature of the airfoils is on the order of 350 K. This means that the camera needs to capture a low intensity signal in a very short time period. This paper will review the design and operation of a measurement procedure to accomplish this difficult task along with the post-processing steps necessary to extract useful data. Raw infrared images are processed by deblurring the images using a non-blind Wiener filter and mapping the two-dimensional data onto the three-dimensional blade.
This paper also describes experiments covering a range of cooling flow rates and main flow temperatures. In addition, several tests with no main flow and only cooling flow were performed at lower speeds to reduce motion blur and enable the separation of internal and external heat transfer information. Results show that the infrared data is consistent and can provide quantitative comparisons of cooling performance even at the high rotation speed. This paper presents the lessons learned for high-speed infrared measurement along with representative data to illustrate the repeatability and capability of the measurement scheme as well as suggested improvements to guide further development.
3D Multi-Solver Coupled Simulation of Combustor-Turbine Interaction in an Aero-Engine
Authors: Zhang Yufang , Lei Kai 
Published: January 2021

Abstract
Generally, combustor and turbine components of aeroengine are designed in a relatively isolated manner and simplified boundary conditions from experiment or numerical simulation are commonly used at the interface. However, the hot gas at combustor exit is characterized by high non-uniformity of temperature, pressure, and flow distribution which may significantly affect turbine performances and reliability. Moreover, the presence of high-pressure turbine guide vanes also affects combustor flow field. The coupled simulation of combustor and turbine can describe the interaction between them more accurately.
Combustor and turbine components are generally simulated with different flow solvers since they are working at different Mach number range with different flow and physical characteristics. In this work, a 3D multi-solver coupled simulation system is developed where multiple flow solvers are coupled by using two different coupling approaches. In the first approach, a 2D interface is used to connect the computational domains of combustor and turbine, the data extracted from combustor exit (including total pressure, total temperature, velocity profile and turbulent quantities) is sent to turbine guide vane inlet and the static pressure profile at combustor exit is defined by turbine. In the second approach, the computational domains have a 3D overlap region where virtual body forces are added in combustor simulation in order to enforce the 3D velocity, temperature and turbulence profiles which is provided by the turbine simulation. Moreover, data from combustor simulation is also extracted and interpolated onto the turbine inlet and vice versa in the second approach.
The validation from a swirling jet case shows that the coupling system works well and the second approach provides more accurate results. Then a coupled simulation of aeroengine combustor and turbine are performed. Isolated simulation is also done for comparison. Results of these simulations are compared. It can be seen that the non-uniformity of temperature and flow distribution at combustor exit and hot streaks transport are successfully captured by the coupled simulation. The features have an important influence on the temperature distribution of turbine. Besides, the influence of turbine guide vanes on combustor flow field is mainly at the region close to combustor exit. The multi-solver coupled simulation system could be useful for designer to fully consider the interaction between combustor and turbine and gain more precise engine performance and improved turbine cooling design.
Study on the Influence of Inlet Asymmetry on Aerodynamic Noise of Cooling Fan
Authors: Tian Jie , Sun Zonghan , Chai Pengfei , Ouyang Hua 
Published: January 2021

Abstract
Experimental and numerical studies on the aerodynamic noise characteristics of a variable-speed axial fan commonly used for electronic device heat dissipation were conducted. First, the far-field noise spectrum of the fan was measured using a microphone array on the contour plane of the fan axis. The spectral analysis indicated that the discrete single-tone noise energy ratio was high, which indicates that it was the dominant aerodynamic noise. Afterwards, the double-uniform sampling point mode correction technique, which is based on the circumferential acoustic mode measurement method, was used to obtain the modal distribution on the inlet and outlet sides of the cooling fan. The influence of inlet unevenness on the cooling fan was identified. The traditional Tyler-Sofrin rotor-stator interaction formula was modified to account for the non-axisymmetric shape of the fan inlet bellmouth. The validity of the modified formula was verified by measuring the circumferential acoustic modes of three cooling fans with different rotor and strut counts. Furthermore, a CFD numerical study was conducted using Fluent to understand the influence of uneven inlet flow. The results showed that uneven inlet flow significantly affects the size and distribution of unsteady pulses on the rotor blades, which cause regular, periodic changes as the rotor blades rotate. Interactions between rotor blades and inlet unevenness were observed via the POD method as well. The discussion of the circumferential modes from aerodynamic noise of an axial flow cooling fan can act as a reference for further cooling fan noise reduction measures.
Large Eddy Simulation of Periodic Wake Impact on Boundary Layer Transition Mechanisms on a Highly Loaded Low-Pressure Turbine Blade
Authors: Winhart Benjamin , Sinkwitz Martin , Schramm Andreas , Post Pascal , di Mare Francesca 
Published: January 2021

Abstract
In the proposed paper the transient interaction between periodic incoming wakes and the laminar separation bubble located on the rear suction surface of a typical, highly loaded LPT blade is investigated by means of highly resolved large-eddy simulations. An annular, large scale, 1.5-stage LPT test-rig, equipped with a modified T106 turbine blading and an upstream rotating vortex generator is considered and the numerical predictions are compared against hot film array measurements. In order to accurately assess both baseline transition and wake impact, simulations were conducted with unperturbed and periodically perturbed inflow conditions. Main mechanisms of transition and wake-boundary layer interaction are investigated utilizing a frequency-time domain analysis. Finally visualizations of the main flow structures and shear layer instabilities are provided utilizing the q-criterion as well as the finite-time Lyapunov exponent.
Steady State Modeling of Unsteady Wake Induced Transition Effects in a Multistage Low Pressure Turbine
Authors: Führing Alexander , Kožulović Dragan , Bode Christoph , Franke Matthias 
Published: January 2021

Abstract
As low pressure turbine blade rows can operate at fairly low Reynolds numbers, long laminar boundary layers and transitional separation bubbles are not unusual in conventional blade design. Upstream wakes interact with the boundary layer in multistage low pressure turbine applications in a way that can alter the engine performance. In order to provide quick turnaround times, industrial applications mainly involve steady state computations which do not accurately model the unsteady wake effects. In this study, a low-pressure turbine cascade with periodic unsteady inflow as well as a two-stage low pressure turbine are computed at various Reynolds numbers using unsteady and steady RANS methods in the flow solver TRACE by DLR and MTU Aero Engines AG. A quasi-unsteady wake model working together with the γ – ReΘt model by Langtry and Menter is applied to the steady state simulation in another step in order to improve the prediction accuracy of low cost simulations utilizing mixing plane interfaces. The steady state results with and without wake model are compared to the time-resolved reference solution and the computation time is evaluated in order to show that the additional model is able to improve steady state mixing plane simulation results without sacrificing the low computational effort provided by the status quo.
Uncertainty Evaluation on Multi-Hole Aerodynamic Pressure Probes
Authors: Notaristefano Andrea , Gaetani Paolo , Dossena Vincenzo , Fusetti Alberto 
Published: January 2021

Abstract
In the frame of a continuous improvement of the performance and accuracy in the experimental testing of turbomachines, the uncertainty analysis on measurements instrumentation and techniques is of paramount importance. For this reason, since the beginning of the experimental activities at the Laboratory of Fluid Machines (LFM) located at Politecnico di Milano (Italy), this issue has been addressed and different methodologies have been applied.
This paper proposes a comparison of the results collected applying two methods for the measurement uncertainty quantification to two different aerodynamic pressure probes: sensor calibration, aerodynamic calibration and probe application are considered. The first uncertainty evaluation method is the so called “Uncertainty Propagation” method (UPM); the second is based on the “Monte Carlo” method (MCM).
Two miniaturized pressure probes have been selected for this investigation: a pneumatic 5-hole probe and a spherical fast response aerodynamic pressure probe (sFRAPP), the latter applied as a virtual 4-hole probe. Since the sFRAPP is equipped with two miniaturized pressure transducers installed inside the probe head, a specific calibration procedure and a dedicated uncertainty analysis are required.
Criteria for the Stability Limit Prediction of High Speed Centrifugal Compressors With Vaneless Diffuser: Part II — The Development of Prediction Criteria
Authors: Cravero Carlo , Marsano Davide 
Published: January 2021

Abstract
The challenge to be able to predict the stability limit in high speed centrifugal compressor is particularly strategic in an initial design phase. Furthermore, to be able to predict the limit massflow rate through the use of simplified numerical models (which does not require excessive computational resources) is very important. In the literature there are several methods to predict the chocking condition, while there is a lack as regards the surge condition. The authors have already presented a criterion to predict the surge line valid for centrifugal compressors with vaned diffuser. Instead those with vaneless diffuser have a very different behavior. For this reason, in the first paper an in-depth fluid dynamic analysis has been carried out, in order to identify the main phenomena linked to the trigger of instability in this type of compressors. This analysis has allowed understanding that the rotational speed is a discriminating factor in the phenomenology. In this second part, using the previous information, different criteria to predict the limit massflow rate for centrifugal compressors with vaneless diffuser are described. All the criteria are based on different simplified CFD approaches that can be routinely used during the design phase.
Effect of a Vortex Distortion on the Operability of an Ultra High Bypass Ratio Fan
Authors: Awes Amaury , Brosse Alexandre , Dufour Guillaume , Carbonneau Xavier , Godard Benjamin 
Published: January 2021

Abstract
Inlet distortion can significantly impact turbofan operability. In the present contribution, the focus is on vortex ingestion, which is a type of distortion that has received less attention in the literature for high-bypass-ratio fans of civil engines than inlet separation or boundary layer ingestion. Due to the unsteady and non-axisymmetric nature of the inflow, full annulus computations are performed, using an unsteady RANS approach with a sliding mesh interface between the rotor and the stator. The goal is to provide a detailed analysis and understanding of the mechanisms responsible for operability loss when a vortex is ingested by the fan. To that end, a simplified model of vortex is derived from previous simulations in crosswind conditions including the presence of the ground plane. The study test case is a turbofan demonstrator representative of modern turbofans. Simulations are run with and without vortex at several operating points until rotating stall is observed. The global results show that the vortex ingestion induces a stall margin loss of up to 8%. Modal analysis indicates a stall pattern with 10 cells rotating at somewhere between 52 and 67% of the shaft speed. A comparison of the two configurations shows that the stall inception mechanism is similar with and without distortion. In particular, examining the incidence at the fan blade, a similar critical angle is observed for the two configurations, which is leveraged to establish a stall criterion valid for vortex ingestion cases.
A Machine-Learning Approach to Assess Aircraft Engine System Performance
Authors: Tong Michael T. 
Published: January 2021

Abstract
Machine learning and big data have become the most disruptive technologies for organizations to improve workplace efficiency and productivity. This work explored the application of machine learning-based predictive analytics that would enable aircraft engine designers to estimate engine system performance quickly during the conceptual design stage. Supervised machine-learning algorithm was employed to study patterns in an open-source database of one-hundred-eighty-three production and research turbofan engines, and built predictive analytics for use in predicting system performance of new turbofan designs. Specifically, the author developed deep-learning analytics to predict turbofan system weight, using turbofan design parameters as the input. The predictive analytics were trained and deployed in Keras, an open-source neural networks API (application program interface) written in Python, with TensorFlow (an open-source Google machine learning library) serving as the backend engine. The current engine-weight prediction results, together with those for the TSFC (thrust specific fuel consumption) and core-size predictions that were studied previously by the author, show that machine learning-based predictive analytics can be an effective, time-saving tool for assessing aircraft engine system performance (TSFC, weight, and core size) during the conceptual design stage. It would enable expeditious identification of the best engine design amongst several candidates.
Analysis of Thermoacoustic Modes in Can-Annular Combustors Using Effective Bloch-Type Boundary Conditions
Authors: von Saldern Jakob G. R. , Orchini Alessandro , Moeck Jonas P. 
Published: January 2021

Abstract
Heavy-duty gas turbines are commonly designed with canannular combustors, in which all flames are physically separated. Acoustically, however, the cans communicate via the upstream located compressor plenum, or at the downstream gaps found at the transition to the turbine inlet. In the present study, a coupling condition that is based on a Rayleigh conductivity and acoustic flux conservation is derived. It enables acoustic communication between adjacent cans, in which one-dimensional acoustic waves propagate. In addition, because can-annular systems commonly feature a discrete rotational symmetry, the acoustic field can be expressed as a Bloch-periodic wave in the azimuthal direction. We demonstrate how the coupling conditions resulting in a combustion system with N cans can be expressed as an effective impedance for a single can. By means of this Bloch-type boundary condition, the thermoacoustics of a can-annular system can be analyzed considering only one can, thus reducing the size of the problem by a factor of N. Using this method, we investigate in frequency domain the effect of the coupling strength of a generic can-annular combustor consisting of 12 identical cans, which are connected at the downstream end. We describe generic features of can-annular systems that can be efficiently addressed with this framework and derive results on the frequency response of the cans at various Bloch numbers in the low-frequency and high-frequency limits. Furthermore, the formation of eigenvalue clusters with eigenvalues of close frequency and growth rate, but very different mode shapes is discussed.
Critical Location Identification for Multi-Mechanistic Damage Modes Using Damage Interaction Charts
Authors: Scaletta Brent , Green Richard 
Published: January 2021

Abstract
Damage in gas turbine engines can accumulate from multiple damage mechanisms including creep, fatigue, and oxidation. Each damage mechanism is influenced by various parameters which typically occur during different portions of engine operation. For instance, fatigue is influenced by large stress/strain ranges that occur during startup and shutdown transient conditions while creep is affected by sustained stress and temperature at dwell conditions. In some cases, the maximum damage location for one mechanism could experience negligible contribution in damage from any other mechanism, but in most cases, there is some degree of influence from two or three mechanisms. In those instances, damage will accumulate at various rates during separate portions of operation under different damage mechanisms. Since some applications require engines to dwell for long periods of time while other applications favor more frequent cycling, every engine will accumulate damage differently at each location. Therefore, it is difficult to estimate which location is critical to durability, rendering it necessary to capture all possible critical locations so that damage can be estimated for each application.
This paper suggests a method by which to visualize and select critical locations based on all possible customer use scenarios. Once critical locations are identified, a Reduced Order Model (ROM) can be generated for each point of interest and damage can be estimated and monitored using data collection. Damage mechanisms can be combined if micromechanistic affects are additive, the material response compounds, or the material properties evolve with time. Examples of each case are demonstrated. In addition, the visual representation of damage interaction allows for uncertainty to be visualized and implemented to rank location criticality.