bluuebunny/crossref_metadata_2025_split huggingface dataset:
Combined Effects of Fluid Inertia and Gas Rarefaction on The Performance of Textured Gas Bearings
Authors: Xu Kefan , Zhang Guanghui , Lu Yiken , Han Jiazhen , Huang Zhongwen , Gong Wenjie 
Published: August 2024

Abstract
Considering the significant discretization effort required to describe texture shapes and possible strong fluid recirculation phenomenon in the deep textured area, this paper attempts to solve the above two hurdles by introducing the multigrid method and inertial correction operation. Furthermore, the first-order slip model and perturbation method were adopted to incorporate gas rarefaction and inertia terms in the compressible Reynolds equation. Moreover, the finite difference method and multigrid algorithm were employed to discretize the pressure governing equations and quickly reduce the iterative residuals of linear systems of equations, respectively. The effects of rotational speed, eccentricity, nominal clearance, state of the lubricated surface, and texture parameters on the static performance of gas bearings were studied. On this basis, the CPU time statistics results show that the computing efficiency of multigrid can be increased by more than 46% compared with the traditional direct solution under the same operating parameters. In addition, it is observed that slip flow and fluid inertia usually reduce the predicted load capacity of gas bearings, and the effect of fluid inertia is stronger than that of the slip flow when the rotational speed is high, the clearance is large, and the dimple texture is deep. The above study supports textured foil journal bearings’ rapid and accurate design in the following engineering practices.
Risk Assessment and Probabilistic Projection of IN706 Gas Turbine Rotor
Authors: Scheibel John , Shi Huawei , Dewey Robert 
Published: August 2024

Abstract
As the limits of starts or hours are approached, a GT owner is presented with several options: replace with a new rotor, swap for a rebuilt rotor, or ship to a shop for disassembly and full inspection. This paper outlines a general two-step procedure which has been used to assess the potential risks of extending the OEM’s interval limits. The approach starts with a failure mode and effects analysis (FMEA). It focuses on and ranks the most relevant durability issues based on a review of the rotor design features, operating history, and maintenance – inspection records. For the F-class, particular attention is focused on the high nickel IN706 turbine discs and spacers, which have been susceptible to both creep and stress-assisted grain boundary oxidation (SAGBO) degradation. The importance of this issue has led to an extensive test program of IN706 specimens, in order to better document and define the material properties, which in turn are used to characterize its resistance to SAGBO and creep. Once the durability issues have been ranked, a probabilistic assessment is performed. The assessment focuses on one or more of the most predominant issues, which pose the highest risk of failure. The probability or chances to achieve a projected interval of hours or starts is calculated, based on historical of GT operating data.
Experimental Evaluation of High Lift, High Work LPT Blades in a Transonic Cascade
Authors: Sauder Ryan R. , Wolff Mitch , Savela Gloria E. , Norris Geoffrey B. , Lethander Andrew T. , Posada Natalia A. , Clark John P. 
Published: August 2024

Abstract
A family of low-pressure turbine stages was recently developed to investigate the limits of achievable work and lift for future engines applicable to unmanned air systems. Subsequently, mid-span sections of a pair of turbine blades from those stages were manufactured for testing in a transonic cascade facility to verify predicted performance at both on- and off-design conditions. Both turbine blades were designed at the meanline level to a work coefficient of 2.80, and the velocity triangles and pitch-to-chord ratios were consistent with incompressible Zweifel coefficients of 1.60 and 1.78. At design conditions, the airfoils provided 123° of flow turning at an exit isentropic Mach number of 0.78. Both inlet- and exit-total pressure traverses were conducted, and the inlet turbulence intensity and length scale were measured at a pair of locations upstream of the instrumented airfoils in the mid-passage. The experimental datasets presented herein include loading variations as well as loss variations versus Reynolds number. It was found that neither airfoil experienced separation at the lowest Reynolds number achievable at design exit Mach number. Accordingly, it was necessary to operate the cascade at reduced total-to-static pressure ratios to observe significant effects of separation on the loading and loss results. The experimental results presented here are compared against design-level predictions using Reynolds Averaged Navier-Stokes (RANS) codes with transition modeling as well as Large Eddy Simulation (LES). The results are encouraging and bode well for the development of future engines that have reduced part-count, weight, and cost while providing acceptable performance lapse at altitude.
Application of an Improved Workflow for the Identification of Flame Dynamics to Swirl Stabilized Wet Combustion
Authors: Désor Marcel , Haeringer Matthias , Hiestermann Marian , Niebler Korbinian , Silva Camilo F. , Polifke Wolfgang 
Published: August 2024

Abstract
The estimation of a flame transfer function (FTF)from time series data generated by large eddy simulation (LES) via system identification (SI) is an established and important element of thermoacoustic analysis. To achieve results with low uncertainties, continuous (non-truncated) time series of adequate length are required. This can be a challenge in the case of turbulent flames, where signal-to-noise ratio may be low. Because LES codes do not scale to an arbitrarily high degree of parallelism, the wall-clock-time required for confident FTF estimation may be excessive. The present paper tackles this challenge by exploiting characteristic features of linear time-invariant systems. Specifically, we explore how the superposition of multiple simulations with the same excitation signal, but varying initial conditions, increases signal-to-noise ratio and leads to more robust identification, i.e. estimates with narrow confidence intervals. In addition, the established SI approach, which relies on broadband excitation, is compared to excitation with approximate Dirac and Heaviside signals, with the advantage of simpler pre- and post-processing.
Results demonstrate that the proposed workflow, which is inherently parallel because it is based on superposition, reduces significantly the wall-clock-time required for robust FTF identification in the case of broadband excitation. This reduction in wall-clock-time requires more simultaneous simulation runs, i.e. more parallel computational resources, but it does not significantly increase the overall computational cost. Furthermore, the new workflow facilitates FTF estimation when exciting with a Heaviside signal.
The proposed method is assessed for the case of a partially premixed, steam enriched (“WET”) swirl burner with significant turbulent noise levels. Steam enrichment is a combustion concept that reduces harmful emissions such as NOx and CO2 while increasing engine efficiency. However, the effect of steam on the flame response, i.e. the FTF, needs to be better understood. To this end, a combustion model that includes an optimized global chemical mechanism for partially premixed wet methane combustion, has been formulated and validated against experimental data.
Evaluation of Subfilter Model Performance for LES of Supercritical Fluids
Authors: Purushotham Dhruv , Oefelein Joseph C. 
Published: August 2024

Abstract
The accuracy of three large-eddy simulations (LES) is assessed using a reference dataset obtained via direct numerical simulation (DNS). All of the LES simulations employ the dynamic Smagorinsky model to close the momentum equation and a dynamic gradient model to close the total energy equation. The LES data are obtained on three grids with resolutions spanning from the wall-resolved LES limit to two successive levels coarser in the spatial and temporal domains. The configuration employed for the study is a three-dimensional spatially evolving turbulent shear layer. The working fluid is pure carbon dioxide. The system is maintained at a supercritical state near the critical point such that the field is dominated by strongly nonlinear thermophysics. This allows the analysis to occur under conditions where the subfilter closures are significantly strained by the thermodynamics. Results explore characteristics of the turbulence from both a modeling and fundamental perspective. First, mixing layer growth rates are quantified. Discrepancies are found between the reference DNS data and the LES data. Energy spectra, turbulent transport coefficients, and Reynolds stress anisotropy results are presented to explore the origins of this mismatch.
A Fretting Wear Test Rig With Time-Varying Normal Force Based on Closed-Loop Controlled Piezoelectric Actuator
Authors: Fan Yu , Wang Jing , Fan Huiru , Sun Yekai , Gao Qian , Liu Jiale , Wu Yaguang 
Published: August 2024

Abstract
Dry friction damping is one of the principal vibration suppression methods for structures in turbomachinery. The friction and fretting wear tests are important ways to study the damping performance and contact parameters evolution of dry friction dampers. The normal force is one of the most important factors affecting friction and wear characteristics. Under service conditions, there are noticeable time-varying components in the normal force due to the coupling of vibration in the normal and tangential directions. It was verified in previous studies that the harmonic components of time-varying normal force had a significant influence on frictional hysteresis behaviors.
In this paper, a fretting wear test rig with accurate time-varying normal force is developed. It can output normal force with stable constant (0–300N) and time-varying (0–50N) components with given amplitude and phase lag in the fretting wear test process. The limit of working frequency is up to 300Hz. The key is to control the output force of the piezo actuator in a closed-loop manner, where the force amplitudes and phase are adjusted by PID controllers in the frequency domain. The control strategy is realized by a DAQ-USB input/output board and the corresponding program of LabVIEW. The conventional “producer-consumer” data flow structure and the array output mode are employed, ensuring the effectiveness of control at high frequencies. The test rig can monitor the wear depth online in real-time through a strain gauge integrated into the piezo actuator. Results show that the time-varying normal force has a significant effect on the wear depth.
Forced Response of Rotating Blisks: Prediction and Correlation to Blade Tip-Timing Measurements
Authors: Zhou Biao , Xie Chengyu , Battiato Giuseppe , Berruti Teresa 
Published: August 2024

Abstract
This paper explores two different blisk dynamic models for resonant vibration prediction of a rotating blisk test piece, i.e. the Model-BDTID and GMM. The former represents a mistuned blisk model with blade mistuning pattern experimentally retrieved by a recently proposed blade mistuning identification method based on blade detuning tests (BDTID). It falls into the scope of the frequency-mistuning modeling approach. The latter refers to a geometrically mistuned model constructed upon high-precision blisk geometry data by leveraging the advanced optical geometry measurement technology. A specifically developed ‘Sector Mode Assembling Reduction Technique’ is exploited for efficient dynamic analyses of the large-sized GMM. Forced response tests are performed in a spinning rig under well-controlled laboratory condition. The Blade Tip-Timing technique is employed to give all-blade vibration measurements of the rotating blisk. Correlation results between the forced response predictions to BTT measurements demonstrate that both the Model-BDTID constructed upon the identified blade mistuning of the blisk at rest and the GMM, can predict the resonant vibration of the rotating blisk with satisfactory accuracy.
Conjugate Heat Transfer Simulation of High-Pressure Cooling Blade Under Rotational Conditions in a Gas Turbine
Authors: Vo Duy-Tan , Jeong Yoonhyeong , Ryu Jaiyoung 
Published: August 2024

Abstract
In a gas turbine, the first-stage blade is the most significant component, operating in an extreme environment with high temperatures, pressure, and rotational speed. Affected by blade row interaction and wake flow from vanes, the rotor flow field exhibits significant unsteady characteristics. These factors can contribute in crack development in turbine blades. In this study, steady and unsteady conjugate heat transfer (CHT) simulations were performed to investigate the heat transfer and aerodynamics of the first stage of the W501F cooling blade. Factors such as internal cooling structure, hot streaks, and rotation were considered. The vane was treated as an empty domain with a film cooling hole inlet on the vane surface. The effects of flow characteristics on the blade’s heat transfer have been discussed in detail. Specifically, the results reveal that the formation of a vortex around the blade strongly affects the distribution of film cooling on the blade. In some cases, the vortex interacts with the wall surface, causing a reduction in film cooling performance on the blade surface. Consequently, overheating occurs in regions such as the leading edge (LE), rim squealer tip, and platform. The maximum temperature at these critical regions could be reached 1380K, close to the blade’s melting temperature. The prediction of the overheating position shows good agreement with a crack position on blade patterns from the power plant company. Furthermore, by understanding the heat transfer characteristics of the blade, we can apply advanced treatments to improve the blade’s cooling performance.
Beyond the Error: Unveiling Uncertainties in Pressure Sensor Measurements
Authors: Saint-Mard Michel , Kozlowski Alexis , Hertay Adrien , Hendrick Patrick 
Published: August 2024

Abstract
In every sensor lies inherent uncertainty. It is crucial to distinguish between error, accuracy, and uncertainty. Error reflects the discrepancy between an exact and measured value, a difference often elusive due to the inaccessibility of the ‘exact’ value. Uncertainty denotes the range of plausible values attributed to a measurement.
For accuracy, understanding the nature of uncertainty and defining the confidence interval is essential. Statistically, broader confidence intervals imply greater uncertainty. For instance, for a normal distribution, 68.3%, 95.4%, and 99.7% confidence intervals are typically represented by σ1, σ2, and σ3, respectively. Many datasheets cite accuracy in terms of average values, with a variation roughly equivalent to σ1.
Calibrating sensors involves many components, including reference pressure sensors and temperature sensors, power supplies, interface cards, and acquisition equipment. Each has its inherent uncertainties which cumulatively influence the tested sensor. It is not known but most of the uncertainty (50% to 80%) is attributed to the test bench used to calibrate/test the sensor. That is what we will show in this paper.
There are several methodologies to evaluate uncertainties.
Primarily, two main methods can be distinguished:
• Type A: This approach focuses on repetitive measurements of a single component. It is thorough and often yields more precise uncertainties specific to that element. However, its detailed nature can be time-consuming.
• Type B: This method leans on datasheets provided by manufacturers. It is faster, but can lead to broader uncertainties, especially if based on generalizations drawn from large component batches. When manufacturer data is lacking or insufficient, resorting to Type A becomes necessary.
Regarding pressure sensors, their operation is defined by a linear equation linking the applied pressure with the output and supply voltage. Using a model to represent this relationship inherently introduces another layer of uncertainty. It is worth noting that no model can perfectly match every data point, hence certain deviations will always exist. The objective is to determine the sensor’s transfer function using the least squares method, which provides a clear understanding of its performance under varying conditions.
Matching Turbulence to a Target Profile in a Flexible Combustor Simulator Design
Authors: Colyer Greg , Li Haidong , Adoua Saturnin Richard , Beard Paul , di Mare Luca 
Published: August 2024

Abstract
We address the generation of tuneable turbulence in a combustor simulator representative of engine conditions. To support a wide range of future engine designs with different properties, including lean burn and novel fuels for low-emissions scenarios, we seek the production, prediction and control of turbulence meeting a variable 2d target specification at the inlet of the high-pressure (HP) turbine nozzle guide vane (NGV), to be achieved simultaneously with other variable target properties including the temperature and velocity profile of the flow.
We discuss appropriate parameters with which to define the turbulence target, including measures of turbulence intensity and length scales. We describe the quantification of the turbulent dynamics as a transport problem for turbulent correlation functions from upstream generation to downstream target plane.
Using a simplified duct model with a programmatically defined mesh, within a production computational fluid dynamics (CFD) solver, we simulate various means of turbulence generation, including combinations of small-scale grids and large-scale obstacles. We find that obstacles collectively possessing geometrical features in both directions perpendicular to the stream are useful, because they can generate wakes in one direction that are large but are then broken up in the other direction, resulting in an intense turbulence field with an intermediate degree of homogeneity.
In these simulations, a k-ω model was employed to parameterize sub-grid turbulence scales, but the overall turbulent kinetic energy density in most of the domain was dominated not by this k but by the unsteady fluctuations at resolved grid and larger scales.
In future work we intend to verify these results by performing large eddy simulations (LES) to resolve smaller scales, using a more detailed and more realistic geometry.
Numerical Stability Analysis of Implicit Solution Methods for Harmonic Balance Equations
Authors: Zhang Yuxuan , Wang Dingxi , Zhang Sen , Zhu Yuze 
Published: August 2024

Abstract
This paper presents an investigation into the numerical stability of various implicit solution methods for an efficient solution of harmonic balance equations for turbomachinery unsteady flows. Those implicit solution methods were proposed to enhance stability and accelerate the convergence of harmonic balance solutions by implicitly integrating the time spectral source term of a harmonic balance equation. They include the block Jacobi method (BJ), the Jacobi iteration method (JI), and their variants, i.e. the modified block Jacobi method (MBJ) and the modified Jacobi iteration method (MJI). These implicit treatments are typically combined with the lower upper symmetric Gauss-Seidel method (LU-SGS) as a preconditioner of a Runge-Kutta scheme. In this study, the von Neumann analysis is applied to evaluate the stability and damping properties of all these methods. The findings reveal that the LU-SGS/BJ and LU-SGS/MJI schemes can allow larger Courant numbers, in the order of hundreds, leading to a significant convergence speedup, while the LU-SGS/MBJ and LU-SGS/JI schemes fail to stabilize the solution, resulting in a Courant number below 10 as the grid-reduced frequency increases. The stabilization effect of the number of Jacobi iterations is also investigated. It is found that the minimum allowable relaxation factor does not change monotonically with the number of Jacobi iterations. Typically 2–4 Jacobi iterations are suggested for the stability and computational efficiency consideration, while any value larger than 4 is not recommended. The stability analysis results are numerically verified by solving the harmonic balance equation system for two cases. One is the inviscid flow over a two-dimensional bump with a pressure disturbance at the outlet. The other is the turbulent flow in a three-dimensional transonic compressor stage.
A Dynamic Thickening Strategy for High-Fidelity CFD Analyses of Multi-Regime Combustion
Authors: Ballotti Andrea , Castellani Simone , Andreini Antonio 
Published: August 2024

Abstract
In this study, a dynamic thickening strategy for DTFLES application to multi-regime combustion is proposed.
The main idea lies in using the numerical solution of an Ordinary Differential Equation (ODE) as a thickening factor. The equation relates the time derivative of the local thickening factor to its production and destruction rates, which are proportional to the gap between the instantaneous value and optimal target values. The smoothness of the thickening factor in time is ensured by the ODE solution, while in space it is achieved through a mathematical function defined in a continuous flame index space.
The equation is numerically integrated with a semi-implicit scheme by making use of the backward Euler formula.
The strategy has been implemented in a commercial Computational Fluid Dynamics (CFD) solver and it has been tested by performing Large Eddy Simulations of the hydrogen/air flame produced by the HYLON injector, which has been individuated as an interesting test case for the proposed dynamic strategy. Turbulence-chemistry interactions are recovered by means of a well-assessed subgrid efficiency model.
Numerical results are compared with the experimental ones obtained at Institut de Mécanique des Fluides de Toulouse (IMFT).
Machine Learning Application to Centrifugal Compressor Design
Authors: Ransom David , Srinivasan Ravichandra 
Published: August 2024

Abstract
The compressor design process starts with a concept that demonstrates key features required to meet the design objectives, and then the design matures through the process to the final manufacture of the engineered product. An important step in this process is the initial conceptual design, often referred to as preliminary machine selection. It’s called a selection since the design solution is a sum of selected, pre-engineered solutions for aerodynamic performance, mechanical integrity, etc.
In this work, the authors present results from a study to leverage all previous industrial compressor builds (already known to be successful designs) to inform a digital library. This library is then used as training data for a ML model capable of presenting the application engineer with a plausible design solution within minutes.