bluuebunny/crossref_metadata_2025 huggingface dataset:
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

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

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

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

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

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

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

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

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.
High-Fidelity Investigation of Vortex Shedding From a Highly-Loaded Turbine Blade
Authors: Gloerfelt Xavier , Cinnella Paola
Published: August 2024

High-fidelity numerical simulations based on wall-resolved large-eddy simulations (LES) are used to investigate the vortex shedding dynamics in a linear turbine cascade. The profile geometry is the well-documented LS59 highly-loaded rotor blade. The simulation campaign covered several outlet Mach numbers (subsonic and transonic) and several experimental configurations to shed light on the relations between vortex shedding frequency, the laminar or turbulent states of boundary layers and the resulting cascade losses. A first major result concerned experiments for transonic outlet Mach number. LES without inlet turbulence and without tripping the suction side boundary layer are unable to match the experimental flow field. In the untripped case, the recirculation bubble is shorter leading to a vortex shedding Strouhal number of 0.17, whereas in simulations with trip wire or inlet turbulence the bubble was longer, with a Strouhal of 0.24. A second finding is that the inlet turbulence intensity is able to drive the switching between two regimes for subsonic outlet Mach numbers: a so-called ‘detached vortex shedding’ (long bubble, St ∼0.24) or a ‘transonic vortex shedding’ (short bubble, St ∼0.19). The appearance of shock waves and very coherent rolls in the wake for the ‘transonic’ regime can lead to a doubling of the cascade losses due to the drastic pressure drop near the trailing edge. Such a change in the flow regime, due solely to an increase in freestream turbulence, has not been reported before.
Aerodynamic Shape Optimization of a Stator
Authors: Dehpanah Payam , Doolittle C. J. , Fuetterer Carsten , Brenner Mattia
Published: August 2024

In this paper, a numerical study conducted on a compressor stator is presented. The results are compared with existing literature and experimental data. For this purpose, a grid refinement study for the baseline geometry at the design condition with an unstructured mesh family is performed. The total pressure loss coefficient and the exit flow angle are compared against the experimental data. Moreover, the corner separation on the suction side is compared against the experimental data. Subsequently, a multi-objective optimization is performed on the baseline geometry to improve two objectives: flow deviation angle and total pressure loss coefficient at the stator exit. For the CAD-based optimization, a parametric model with 55 design variables is built in the parametric design platform CAESES. This parametric model is fitted to the baseline geometry to start the optimization process. The Flow360 compressible flow solver is employed for the steady RANS analysis, utilizing the Spalart-Allmaras turbulence model. The surrogate-assisted multi-objective genetic algorithm (MOGA) is employed for the optimization. Non-uniform profile boundary conditions, obtained from experimental tests, are applied at the inlet. The results for the baseline simulation at the design condition demonstrate strong agreement with both experimental and numerical findings. In the optimal Pareto front solutions, both objectives exhibit improvement. The optimal solution is compared with previously published results in literature.
Reversionary Control Modes for the Mitigation of Failures in a Partially Turboelectric Aircraft Propulsion System
Authors: Simon Donald L. , Chicatelli Amy K. , Bianco Santino J. , Horning Marcus A. , Saus Joseph R.
Published: August 2024

In support of emission and fuel burn reduction goals, the aviation industry is actively pursuing the advancement of electrified aircraft propulsion (EAP) technology. This includes turboelectric and hybrid electric propulsion designs that combine gas turbine engine and electrical system hardware. Such architectures exhibit a high degree of coupling between subsystems. This drives the need for system-level control strategies to ensure the safe, coordinated, and efficient operation of all subsystems. The design and certification of any aircraft propulsion system requires that all potential subsystem failures are identified, and the hazards posed by these failures are appropriately mitigated. This requirement is particularly challenging for EAP systems due to their integrated nature. One approach to assist in EAP failure mitigation is the inclusion of automated reconfiguration capabilities within the propulsion control system. Such control modes, referred to as reversionary control modes, are designed to automatically detect failures and activate backup control modes upon failure detection. This paper covers the design and evaluation of reversionary control mode logic developed for a partially turboelectric propulsion concept. Test results from a real-time hardware-in-the-loop evaluation of the concept are also presented and discussed. The results show that the developed reversionary control logic can successfully detect and mitigate subsystem failures in a representative environment that includes actual electrical system hardware.
Natural Gas Overhung Pipeline Compressor Rotordynamic Design, Test Validation, and Consideration of Morton Effect
Authors: Li Wei , Braman Christopher , Hatori Hiroki , Thorat Manish , Pettinato Brian
Published: August 2024

This study examines a natural gas pipeline compressor design and its potential for “Morton effect” instability. The compressor is designed to utilize a rotor with two tandem stages arranged in an overhung configuration. An overhung rotor design allows for increased compressor efficiency by lowering the inlet losses in the compressor, eliminating a balance piston, and minimizing leakage by having only one dry gas seal. Comprehensive rotordynamic analysis was performed on the rotor-bearing system accompanied by an iterative design optimization. The rotordynamic unbalance response and stability characteristics were good and met the API requirements. Another important aspect “Morton effect” for overhung rotor was also carefully examined because the rotor design has large overhung weight, long overhung length and high bearing surface speed making it subject to a high Morton effect (ME) risk. Bearing optimization, for example, using offset pivot tilting pad bearing and adjusting bearing clearance was performed to minimize the ME risk through the ME analysis. Eventually a test rotor was built to experimentally validate the rotordynamic performance of the worst cases rotor-bearing design, which had minimum clearance at the bearings. The rotor was operated up through its trip speed. Testing was performed to validate that the rotor design is rotordynamically sound and there is no ME within the operating speed range of the rotor.

An attempt was then made to induce ME by altering the bearing configuration from the intended design to one where ME would be more likely. Larger amounts of unbalance were applied. Some additional amplitude and phase change was observed; however, this did not become the classic ME instability.
Understanding EBC Lifetimes and Performance for Industrial Gas Turbines
Authors: Ridley Mackenzie J. , Lance Michael J. , Aguirre Trevor G. , Kane Kenneth A. , Pint Bruce A.
Published: August 2024

Hydrogen or hydrogen blend fuels are expected to replace natural gas in land-based industrial gas turbines (IGTs) to support a greener power economy. Silicon carbide (SiC) base ceramic matrix composites (CMCs) are considered for replacement of Ni-based superalloys to facilitate future efficiency improvements. SiC CMCs require environmental barrier coatings (EBCs) to mitigate volatilization from high-temperature steam, thus making the EBC lifetime critical information for identifying CMC component lifetimes. The goal of this project is to determine the maximum bond coating temperature underneath the EBC for achieving an IGT component lifetime goal of 25,000 h, which is far greater than current CMC component lifetime requirements for aero-turbine applications. To provide data for the lifetime model, laboratory testing used plasma-sprayed rare-earth silicate EBCs on monolithic SiC substrates with an intermediate Si bond coating. Specimens exposed to 1-h thermal cycles in flowing air-steam environments and reaction kinetics were assessed from 700°-1350°C by measuring the thickness of the thermally grown silica scales. The silica growth and phase transformation appear critical in predicting EBC lifetime and several strategies have been explored to reduce the oxide growth rate and improve EBC durability at elevated temperatures. Advanced characterization using Raman spectroscopy has helped clarify this system.
Experimental Investigation on the Effect of Inlet Temperature on Thermoacoustic Oscillation in a Centrally-Staged Combustor
Authors: Ma Jinglong , Han Xiao , Yang Zhipeng , Hui Xin
Published: August 2024

Self-excited thermoacoustic oscillations frequently manifest in lean premixed prevaporized (LPP) centrally-staged combustors, impacting the dynamic characteristics of flames and potentially causing damage to combustor components. Due to the susceptibility of thermoacoustic oscillations to passive control factors, this study explores the influences of the combustor inlet air temperature on these oscillations. The two investigated schemes in this study exhibit thermoacoustic oscillations at 400 K, and as the inlet temperature increases, the overall oscillation amplitude of the system decreases, reaching approximately 50 Pa at 600 K. A noteworthy observation is that at 450 K, the oscillation amplitude of the counter-swirl (CNS) scheme exceeds that observed at 400 K. Furthermore, the shapes and CH* chemiluminescence intensities of the flame are determined through time-averaged and Abel-inverted transform methods, allowing for the characterization of the dynamic features of the flame. By combining insights from the local Rayleigh map, it is found that the driving thermoacoustic oscillation occurs at the inner/out shear layer and the region where the main and pilot flames intersect. A stronger thermoacoustic oscillation in a region indicates a more pronounced coupling between pressure and heat release fluctuations. Hence, exploring the mechanism through which the inlet temperature influences thermoacoustic oscillations is beneficial for the design and optimization of the combustor.
Mechanical Properties of the Support Structure With Recoverable Stiffness
Authors: Sun He , Zhang Dayi , Zhang Qicheng , Yang Cheng
Published: August 2024

The Fan Blade-Off event can have a significant impact on the rotor, and fuse structures are commonly employed to absorb the resulting energy. However, fused structures often lead to excessive loads on other bearings. In this paper, we propose a support structure with recoverable stiffness, integrating a chiral structure using shape memory alloy and a folding squirrel cage. The mechanical properties of chiral unit-cells with various configurations are analyzed. An analytical model of the support structure is established to examine mechanical properties, and the findings are validated through experiments. The support structure can effectively absorb impact energy through the phase transition of materials. The support stiffness rapidly decreases, reaching negative stiffness, and can be restored through heating. Experimental results indicate that the support stiffness aligns with the analytical model, with a stiffness reduction ratio of up to 61.81%. The support stiffness can be fully restored, and the loss factor of the support structure is 0.32. The proposed support structure proves to be effective in absorbing impact energy and achieving stiffness recovery. This, in turn, reduces rotor amplitude and enhances rotor working stability. It stands as a secure and efficient support structure capable of handling impact loads.
Comprehensive Understanding of TGO Morphology Effect on the Thermal Barrier Coatings Failure Under Free Edges
Authors: Qiao Da , Zeng Wu
Published: August 2024

The growth stresses induced by the thermally grown oxide (TGO) will be amplified at the free-edge site, making the free-edge site a weak part of the thermal barrier coatings (TBCs). In this study, the TBCs failure behavior is investigated based on different TGO morphologies under free edges. The thermo-mechanical model is established by creating straight lines and simplified sinusoidal curves, respectively. Dynamic TGO growth is realized by the secondary development of the subroutine. The cohesive element is inserted at the TC/TGO interface to simulate the delamination. The stress evolution near different TGO morphologies under the influence of the free edge are examined. In addition, the interfacial cracking behavior near the free edge is also explored. The results show that the appearance of the free edge will deteriorate the stress condition in the nearby area, change the preferred cracking area, and induce the earlier failure behavior. The straight line morphology has the most “friendly” stress distribution. The sinusoidal curves have peaks and valleys, and different areas of the TGO shape are different under the influence of the free edge, but all of them have the effect of stress “convergence”. These results can provide significant guidance to develop the next-generation advanced TBCs.
Revisiting Dimensionless Parameters Quantifying Film Cooling
Authors: Lee Chien-Shing , Shih Tom I-. P. , Straub Douglas , Weber Justin
Published: August 2024

Effectiveness of film cooling (η) has been characterized by the density (DRh) and blowing (BRh) ratios. In this study, a dimensional analysis and a computational study, based on steady RANS with and without conjugate heat transfer, were performed to identify and examine parameters needed to quantify η, where film cooling is crossflow fed instead of plenum fed. The test problem studied is film cooling of a flat plate, where the cooling air, issuing through 30-degree inclined circular holes, is fed from a cooling channel with a flow direction that is perpendicular to the direction of the hot-gas flow. For this test problem, dimensional analysis shows an additional blowing ratio is needed, denoted as BRc, to quantify η, and BRc is the ratio of the mass flux through the film-cooling hole to the mass flux in the cooling channel upstream of the film-cooling hole. CFD results obtained by varying the mass-flow rate in the cooling channel, while keeping the DRh and BRh constant (DRh = 1.9 and BRh = 0.75 or 1.0), show reducing the mass-flow rate in the cooling channel by one half, which doubles BRc (from 2.6 to 5.2) to slightly affect the discharge coefficient (< 5%) but up to 25% on overall cooling effectiveness and up to 85% on laterally-averaged adiabatic effectiveness. Results are presented that show the flow mechanisms induced by BRc. This computational study was validated by comparing with experimental data generated at the National Energy Technology Laboratory.
A Wide-Bandwidth and High-Resolution Identification Method for the Dynamic Characteristics of Annular Gas Seals Using Hilbert Transform
Authors: Wang Tianhao , Li Zhigang , Li Jun
Published: August 2024

Efficient and accurate parameter identification methods are urgently needed to develop high-performance sealing devices. Although the existing prediction methods have been widely validated, researchers are still grappling with the trade-off between frequency resolution and computational cost. This paper proposed a Hilbert-transform-based time-frequency analysis method to identify the dynamic characteristics of annular gas seals. The frequency-sweep whirling orbit model (FSM) was adopted as the excitation signal of rotor whirling motion. The transient flow field within the seal clearance was numerically simulated by the computational fluid dynamic (CFD) solution combined with the mesh deformation technique. The empirical amplitude-modulated (AM) and frequency-modulated (FM) decomposition and the direct quadrature method were utilized to approximate the analytic signals of the monitored response forces. High-resolution and frequency-dependent dynamic coefficients were determined by the Hilbert transform (HT) of the linear response-force/rotor-motion model. To validate the present method and determine the frequency-sweep mode, the dynamic coefficients of three typical annular gas seals, including a labyrinth seal (LABY), a fully-partitioned pocket damper seal (FPDS), and a hole-pattern seal (HPS), were evaluated by the linear and quadratic frequency-sweep modes, respectively. The results indicate that the dynamic coefficients obtained by the quadratic FSM are all in good agreement with the experimental data, and have almost the same accuracy as the well-known multi-frequency whirling orbit model (MFM). Combined with the proposed adaptive timestep scheme, the present method can obtain the high-frequency-resolution dynamic coefficients of annular gas seals with a 48.6% reduction in the computational time compared to the MFM. Furthermore, the application of the present method in wide-bandwidth cases was also illustrated.
An Aero Engine Disk Sizing and Weight Estimation Approach With Improved Temperature Profiles
Authors: Zaimis Ioannis , Carpentari Elias , Begiebing Tim , Gümmer Volker
Published: August 2024

During the predesign phase of an aero engine, interdisciplinary parametric studies are crucial for identifying an optimum engine. As innovative engine concepts emerge, it is essential to study trends aiming to minimize climate impact and one of its key contributors, fuel burn. The comparatively heavy disks, subjected to high thermal and mechanical loads, are central to this analysis due to their high impact on the overall module mass. This paper proposes an approach to achieve a first lightweight mechanical design of disks in the predesign phase.

Based on a performance and aerodynamic baseline, the design space and physical boundary conditions are set. Firstly, an initial mass optimized disk is derived using simplified temperature profiles and stress calculations under the Mechanical Design Point conditions. Subsequently, all the module disks are considered and an estimation for each bore temperature is achieved through a novel loop over the entire module and all available operating points. By evaluating the temperature and stress profiles across various operating conditions, the low cycle fatigue life of each disk can be studied. As part of a highly modular engine predesign framework, this method allows for zooming capabilities of single disk calculations by prescribing individual boundary conditions. The proposed approach already yields an initial assessment of the rotors within a short runtime, facilitating simple iterations with the succeeding design phases due to method and tool commonalities. While the primary focus of the current work is on compressor design, the principles presented are adaptable and expandable to turbine disk applications as well.
Experimental Investigation and System Simulation Analysis for the Aerodynamic Performance of a Two-Stage Axial Compressor With Inlet Dynamic Distortion
Authors: He Rong , Wang Tong , Liu Yongwen
Published: August 2024

The performance and reliability of a compressor can be adversely affected by its inlet conditions. In this paper, the effect of planar wave on a two-stage axial compressor is investigated experimentally with aperiodic inlet dynamic distortions generated by the insertion and extraction of a plate at the compressor inlet. The transient pressure is measured by the high-response static pressure sensors at different axial and circumferential positions in the flow path. It is found that the inlet distortion is attenuated greatly by the IGV cascade, and then behaves as a planar wave at the inlet of the first stage. At the near-stall operating point, the axial compressor gets through the unstable condition with a hysteresis loop in the performance map by the inlet planar pressure ramp. The hysteresis loop, including asymmetric stall development and recovery processes, is discussed. The sudden pressure increase is found at the beginning of the loop and it could be used as a pre-cursor of stall inception. The inertia of the flow in the loop is discussed with the so-called lag parameter. The inertial effect is more evident in the stall development process than in the recovery process. It is believed that the experimental method with the distortion generation way could be applied widely in the study of the unstable operation characteristics of axial compressors.
The Development of Turbulence Quantities in Different Intermediate Turbine Duct Configurations
Authors: Hafizovic Asim , Krajnc Nicolas , Merli Filippo , Staggl Marian , Mangini Francesco , Sterzinger Patrick Zeno , Marn Andreas , Göttlich Emil
Published: August 2024

The experimental investigation examined the influence of high turbulence intensity, large scales, and turbulence anisotropy on turbulence decay within the intermediate turbine duct (ITD). The paper focuses on two different test configurations of the intermediate turbine duct, which is an annular s-shaped channel used in turbofan engines to guide the flow from the high-pressure turbine (HPT) at a smaller radius to the low-pressure turbine (LPT) at a higher radius. Two state-of-the-art intermediate turbine duct concepts are in focus. The most common duct is the turbine center frame (TCF), featuring non-turning struts. The exit-to-inlet area ratio of the TCF is higher than one, leading to a flow deceleration through the duct.—On the other hand, the turbine vane frame (TVF), also known as integrated concept, can be considered as a direct evolution of the diffusive duct. The integrated concept involves integrating the function of the LP turbine’s first vane row into the duct by introducing turning struts and splitters. However, the turning struts and splitters cause an acceleration in the tangential flow direction while deceleration in the meridional direction occurs. The overall Mach number increases from the inlet to the exit within the component.

The present study obtained hot-wire anemometry measurements using a triaxial and a single hot-film probe. The experiments were conducted in a two-stage, two-spool transonic turbine test rig at the Institute of Thermal Turbomachinery and Machine Dynamics at Graz University of Technology, which includes relevant purge and turbine rotor tip leakage flows. The two test setups include the same (HPT) stage, different intermediate turbine ducts, and a low-pressure vane or blade row, respectively. Several methodologies were used to process the data and to obtain the autocorrelation function, integral length scale, and turbulence kinetic energy dissipation rate.

The turbulence quantities at the inlet to the ducts show the same characteristics in both configurations. The acquired measurement data illustrates different turbulent mixing within the intermediate turbine duct. Moreover, the high turbulence quantities at the exit of the TCF duct dominated the shroud region. In contrast, the flow field at the TVF exit is dominated by TVF secondary flow and vane wakes. These results acquired under engine realistic rig flow conditions enable a deeper understanding of the relationship between loss and turbulence quantities for different intermediate turbine duct configurations.
Cavity Impact on the Base Flow Unsteadiness for a High-Speed Exhaust System
Authors: Tsentis Spyros , Goulos Ioannis , Prince Simon , Pachidis Vassilios , Zmijanovic Vladeta
Published: August 2024

Future propulsion systems will be essential to enable sustainable high-speed flight and routine space access. Such concepts usually employ base-embedded, convergent-divergent nozzles and cavity regions to facilitate their mission, thus altering the flow dynamics at the base notably in comparison to contemporary launch vehicles. This paper presents a numerical investigation on the impact of a cavity region on the base flow unsteadiness for a sub-scale, high-speed exhaust system at over-expanded mode. The fully-installed model in the test section of a wind tunnel is employed to facilitate an ongoing experimental campaign. The Delayed Detached Eddy Simulation turbulence modeling approach is utilized to investigate the flow at the base. The configuration featuring the cavity is directly compared to a baseline apparatus, where the cavity has been removed, thus allowing for the impact of the cavity to be identified. Results show that the cavity region can reduce the base pressure fluctuations up to 20% and acts in a damping-like manner for the base flow unsteadiness. The total energy of the pressure fluctuations spectrum at the base can be reduced by as much as 38% compared to the baseline configuration. However, the impact of the cavity on the time-averaged pressure distribution at the base is negligible. Finally, the cavity is found to have a notable effect on the nozzle side loads, which are are reduced by an order of magnitude compared to the baseline case, and behave in an axisymmetric manner. This indicates that the cavity could act as a passive flow control mechanism for side loads reduction.
Fan Non-Synchronous Forced Vibration Under Crosswind
Authors: Chennuru Venkata Y. T. , Corral García Roque , Rodríguez-Blanco Salvador , Vahdati Mehdi , Zhao Fanzhou
Published: August 2024

In this paper, a new aeroelastic phenomena for fans, referred to as Non-Synchronous Forced Vibration (NSFV), is presented. This type of aeroelastic instability can occur at high crosswind conditions when the flow at the intake lip separates and the disturbances caused by flow separation become unsteady. The results show that in presence of unsteady separation in the intake, the fan can experience non-synchronous frequency excitations, which can result in resonant response in modes that are not identified by the Campbell diagram. The findings are corroborated by aeroa-coustic theories. To the best knowledge of authors this is the first time that fan forced response due to unsteady distortion is studied and the findings can unlock some of unexplained and unexpected vibrations experienced by engines.
Effect of Leading Edge Erosion on the Tip Leakage Flow in a Compressor Cascade
Authors: Stein Thomas , Leitner Markus W. , Staudacher Stephan
Published: August 2024

The interaction between tip leakage flow and passage flow in axial compressor blade rows creates complex flow mechanisms that impair flow stability. Caused by erosion of the compressor blades, these flow mechanisms become time dependent. Especially the compressor tip regions experience erosion-related surface loss owing to the particle-laden flow inside the engine. The corresponding reduction in chord length varies in height and leads to varying shapes of eroded compressor blades. It is likely that these impact the engine’s operability. The optical accessibility of flow structures in water was exploited by analyzing four blade tip geometries at different angles of incidence in a linear compressor cascade. The impact of these geometries on the tip flow structures is analyzed by observing the movement of inked fluid elements in space and time. Particle Tracking Velocimetry (PTV) is used to obtain 3D trajectories of both stable and unstable flows. Whilst the non-eroded blade geometry shows stable vortex formation, a notable change in the flow characteristics is observed for particular erosion patterns. In these cases, the tip leakage flow exhibits unsteadiness, featuring fluctuations and unstable flow phenomena. A large blockage of the flow passage occurs due to a vortex breakdown.
Redistribution of Purged Cavity Air Inside a Turbine Exit Vane Frame due to the Interaction With the Main Airflow
Authors: Schien Malte , Lopez Pablo , Bratusek Lukas , Heitmeir Franz , Marn Andreas
Published: August 2024

As a consequence of enhanced pressure ratios and combustion exit temperatures for higher jet engine efficiencies, the exit temperature of the Low Pressure Turbine (LPT) increases, too. To prevent hot gas from entering the rim seal cavity between the LPT’s last stage rotor and the Turbine Exit Vane Frame (TEVF), purge air is needed.

The present work investigates the spatial redistribution of purged cavity air inside an annular Turbine Exit Vane cascade due to its interaction with the main airflow. For this purpose, experimental investigations have been conducted using aerodynamic 5-hole pressure probes and the CO2 trace gas technique. Furthermore, numeric results yield better insights into the flow’s characteristics.

Three operating conditions are investigated, representing the aircraft’s states: take-off, maximum climb, and cruise.

It is shown that the interaction between the purge fluid and main airflow is mainly dominated by the ingress upstream of the vane’s leading edge and the egress at locations of lower static pressure. Inside the vane passage, the cross-flow pressure gradient mainly determines the cavity fluid’s pathway.

At off-design conditions, purge fluid does not contribute significantly to the cascade’s total pressure loss.
Ignition of Aged Lubricants in a Shock Tube
Authors: Abulail Matthew , Juárez Raquel , Petersen Eric L.
Published: August 2024

Lubricants experience harsh conditions which result in degradation of the oil. To imitate similar conditions, Mobil DTE 732, a common gas turbine lubricating oil, was subjected to high temperatures for an extended period of time, until thermal degradation occurred, indicated through the creation of coke. Samples were taken throughout this process, with the sample that was tested having been exposed for 78 hours. Utilizing an endwall injector system, the samples were ignited behind reflected shock waves in the High-Pressure Shock Tube at Texas A&M University. The injector system utilizes the incident wave to increase the temperature of the lubricant past its vaporization temperature, thereby vaporizing the fuel prior to the arrival of the reflected shock. Using this system, the base Mobil DTE 732 and the 78-hour sample produced from the coking test were tested at 1.06 to 1.58 atm and between 1171 and 1373 K. The ignition delay times of the samples were recorded utilizing pressure rise and hydroxyl chemiluminescence located in the sidewall of the shock tube. Upon the analysis of the results, there were negligible changes in the ignition behavior of the fuel, based on ignition delay time. However, changes in the combustion behavior were experienced, such as an absence of two-stage ignition and lower viscosity for the post-coke sample.
Experimental Studies on Lean Blowout Limits for a Hydrogen-Enriched Methane-Fueled Trapped Vortex Combustor
Authors: Verma Nikhil , Ravikrishna R. V.
Published: August 2024

In light of stringent emission regulations and environmental considerations, hydrogen is being considered a viable alternative to replace hydrocarbon fuels. However, hydrogen combustion poses challenges regarding NOx emissions, combustion instability, flashback, and blowout limits. The present study aims to investigate the lean blowout of TVC using methane-hydrogen blends with varied hydrogen concentrations. Furthermore, the flame dynamics near lean blowout in the TVC is achieved by reducing the equivalence ratio and studied in detail using high-speed OH*-chemiluminescence (5 kHz), emissions, and temperature measurements. A trapped vortex combustor is considered for the present study because of its numerous advantages: reduced emissions, improved flame stabilization, increased combustion efficiency, exceptional high-altitude re-ignition capabilities, and operating in lean burn or RQL combustion modes. The lean blowout limit is achieved by reducing the equivalence ratio in the cavity inlet until the blowout event occurs, while the equivalence ratio in the main flow is set to zero. The findings reveal significant changes inflame structure as the lean blowout limit is approached. At higher equivalence ratios, the heat release zone is observed to be distributed within the cavity. However, near the lean blowout limit, the heat release zone is confined to the cavity jet shear layer, which is observed to stabilize near the aft wall of the cavity. As the percentage of hydrogen increases, a significant decrease in the lean blowout limit is observed, accompanied by lower hydrocarbon and CO emissions. Thus, the present study demonstrated a broadening of the operating range of the trapped vortex combustor with lower emissions when hydrogen concentration increases.
Non-Parametric Surrogate Model (NPSM) for High-Dimensional Aerodynamics Optimization
Authors: Cao Jiajun , Xu Liping
Published: August 2024

An non-parametric surrogate model for high-dimensional aerodynamic optimization is introduced in this paper. It directly builds a mapping relationship between surface meshes of objects and the two-dimensional (2D) distributions of flow variables. NPSM utilizes Graph Neural Networks (GNNs) to extract performance-sensitive geometric features from surface meshes according to the feedback of prediction errors. With this geometric information, NPSM can predict 2D distribution of flow variables with Convolutional Neural Networks (CNNs) rather than only several scalar performance metrics. This process reduces the uncertainties caused by manual parameterization of high-dimensional geometries, such as fuselage, wings and blades in turbomachinery. The mapping relationship established by NPSM enables the Non-Parametric Sensitivity Analysis (NPSA) via Automatic Differentiation (AD), which can derive sensitivity of each mesh vertex rather than sensitivity of geometric parameters. This sensitivity information makes NPSM explainable, and provides more information for redistribution of geometry control points. To safeguard the robustness of optimization, a design classifier is designed to utilize the latent space built by NPSM to identify predictable designs. In this paper, two cases are used to demonstrate NPSM. The symmetric bumps case is used to demonstrate the methodology and functionalities of NPSM. The capability of processing high-dimensional geometries is demonstrated with the low-pressure (LP) steam turbine rotor.