bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanical Characterization of Bi-Layer EBC Coatings Under Tension and Bending Using Acoustic Emission and Digital Image Correlation
Authors: P. Panakarajupally Ragav , Morscher Gregory N. , Shi Jun 
Published: September 2023

Abstract
Fracture characteristics of bi-layer environmental barrier coatings (EBC) deposited on a woven ceramic matrix composite (CMC) substrate using air plasma spray (APS) processes were investigated under uniaxial tension and bend tests at room temperature. Health monitoring techniques such as acoustic emission (AE) and digital image correlation (DIC) were employed to better understand the cracking behavior of the coating and its progression. Post-test microscopy was performed to correlate the coating cracks with DIC and AE location. The results indicate that multiple transverse cracks first occurred in the coating, followed by substrate transverse cracks and additional coating cracks. DIC analysis was able to highlight the formation and location of these cracks. The fracture strength of the coating was estimated assuming the composite beam theory.
Experimental Characterization of Flow Structure and Reynolds Stresses Covering an Entire Rotor Passage of an Axial Compressor
Authors: Saraswat Ayush , Koley Subhra Shankha , Evans Simon , Joly Michael , Katz Joseph 
Published: September 2023

Abstract
This experimental study characterizes the mean flow structure, distribution of Reynolds stresses, and the mechanisms affecting turbulence production in the entire rotor passage of an axial compressor. The stereo-PIV (Particle Image Velocimetry) measurements are performed in the JHU refractive index matched facility and cover an entire rotor passage of a 1.5 stage axial compressor. The rotor blades have an aspect ratio of 0.73 and a measured tip gap of 2.8% of the blade span. The primary focus is on pre-stall flow rate, but trends and distributions are compared to those obtained at a higher flow rate. While many flow features exist at both flow rates, they differ in size, magnitude, and location. The tip leakage vortex (TLV) roll up, breakdown, migration, and double leakage occur earlier, and the associated blockage covers a larger area and has a lower axial and higher circumferential velocity at pre-stall. Furthermore, instantaneous velocity samples and cavitation images at pre-stall showcase transient extreme events involving a backward leakage flow extending upstream of the rotor, spillage of the leakage flow and backflow vortices from one passage to the next around the leading edge (LE), and intermittent boundary layer separation on the blade suction side near the trailing edge. All of these intermittent phenomena affect the distribution of turbulence, including an extension of elevated turbulent kinetic energy (TKE) upstream of the rotor LE plane. The turbulence is particularly high around the TLV, at the interface between the backward leakage flow and the forward passage flow upstream of the TLV, and along the boundary of the blockage area radially inward of the TLV. Vortex breakdown expands the elevated turbulence area substantially. As a general observation, the turbulence is highly anisotropic and inhomogeneous. The spatial distribution and the evolution of the normal Reynolds stresses vary greatly with operating condition and among components. In most regions, the associated trends can be explained by examining the corresponding production rate terms. Finally, a comparison of the TKE and normal Reynolds stress distributions downstream of the rotor as well as the production rates across two compressors show striking similarities, demonstrating that the same flow features play dominant roles in both machines.
Effect of the Blowing Ratio on the Interaction Between a Flame and an Air-Cooled Combustor Wall
Authors: Blaise Antoine , Petit Sylvain , Grisch Frédéric , Xavier Pradip 
Published: September 2023

Abstract
Innovative low-carbon aero-engines rely on ultra-compact and high energy density combustors, increasing the thermal loads of the walls. This study aims at experimentally enhancing the understanding of the interrelated physical processes between a flame, a wall and a cooling technology. The test rig operates at atmospheric pressure and generates a methane/air turbulent flame interacting with a wall that is air-cooled by means of a splash cooling plate device. Optical diagnostics are simultaneously implemented, including reactive particle image velocimetry (PIV) to assess the flow field, planar laser induced fluorescence on the OH radical (OH-PLIF) to study the flame structure, and laser induced phosphorescence to measure the wall temperature in contact with the reactive flow. Results show that the mean flame location is shifted away from the wall as the blowing ratio is increased. The wall temperature reveals that to enhance cooling efficiency, blowing ratio and flame location must not be considered without each other. Eventually, a classical flame-wall interaction process is retrieved when the blowing ratio is small, whereas flame strain, originating from the aerodynamic shear layer, pilots the flame dynamics for large blowing ratios.
Rapid Algorithmic Blade Design Applying Machine Learning From Shape Optimization to Satisfy Multidisciplinary Constraints
Authors: Dasadhikari Kingshuk , Kuwamura Yoshihiro 
Published: September 2023

Abstract
This paper presents a new, rapid, flexible approach for turbine blade section design combining algorithmic and inverse techniques to enable automatic generation of blade sections guaranteed to conform to multidisciplinary requirements, with the aim of accelerating turbomachinery design iterations.
The approach links a base algorithm to parametrize and generate blade section geometry conforming to structural and manufacturability constraints such as section area, trailing edge radius, and exit wedge angle with a 2D CFD solver to calculate surface isentropic Mach number profile for aerodynamic performance evaluation. To achieve blade sections with smooth surface and lenticular Mach number profile concave up on the pressure-side and concave down on the suction-side, the base algorithm is tuned by a surrogate inverse model trained by machine learning from pre-generated tuning data obtained by case-by-case shape optimization for a range of design conditions. A weighted objective function is applied to quantify both geometric and aerodynamic quality of blade sections for the optimization.
Shape optimization improves output section quality by 54–87% compared to the untuned algorithm. Aerodynamically, suction-side flow separation is eliminated in the optimized sections, giving 70% less pressure loss compared to the untuned algorithm for the best cases. Across all conditions spanning the examined design space, the surrogate model successfully captures most of this improvement, yielding blade sections of similar quality to explicit optimization sufficient to meet the geometric and aerodynamic requirements for design. Furthermore, section quality is preserved even if imposed structural and manufacturability constraints are perturbed within typical margins, guaranteeing blade sections that are always viable for practical use. Blade sections from the surrogate-tuned algorithm are output within minutes, eliminating time-intensiveness of existing manual or case-by-case design approaches.
The Role of Turbulence Transport in Mechanical Energy Budgets
Authors: Przytarski Pawel J. , Lengani Davide , Simoni Daniele , Wheeler Andrew P. S. 
Published: September 2023

Abstract
In this paper we study the role of turbulence transport on loss prediction using high fidelity scale-resolving simulations. For this purpose we use eight high-fidelity simulation datasets and compute flux of entropy and stagnation pressure transport equation budgets for all the cases. We find that under certain unsteady inflow conditions the stagnation pressure coefficient is not a reliable loss metric even at low Mach number conditions. This is due to the turbulence transport terms. The impact of these terms, typically assumed to be negligible, made stagnation pressure loss coefficient under-predict loss from 0% to over 40% when compared to entropy loss coefficient for cases considered here. This effect was most pronounced for the cases with highly unsteady inflow conditions and at low Reynolds numbers.
Experimental Study on Total Pressure Distortion Characteristics of a High Bypass Ratio Turbofan Engine
Authors: Li Huihui , Teng Jinfang , Luo Guangqi , Zheng Shangnan , Lv Chongyang , Qiu Chao 
Published: September 2023

Abstract
Relative to the surge and stall compliance governed by civil aviation airworthiness regulation of FAR/CCAR33.65, the engine needs to have adequate stability margin throughout its operating envelope. That requires engine compression components to have sufficient surge margin. Inlet distortion is one of the main factors affecting compression components’ surge margin and engine operability. According to the civil aero engine operation scenario, the most likely cause for total pressure distortion formed by the uneven flow field at the exit of the inlet is crosswind condition. In order to quantify the inlet distortion characteristics and understand the distortion attenuation for each compression component of a high bypass ratio turbofan engine, whole engine inlet distortion test was conducted. Three distortion conditions were simulated by different grids, and the distortion characteristics in terms of distortion index was measured by total pressure rake in the test. The test results showed that for high bypass ratio turbofan engine, the inlet distortion is mainly distributed in the area of outer 60% height of fan blade and does not enter the engine inner flowpath. However initial distortion exists in the clean inlet condition at the outlet of both the outer and inner flowpath since the engine structure is not completely circumferentially symmetric. After passing through the flowpath, the degree of distortion will be reduced. At a maximum IDCmax = 6.5% in the inlet, it is reduced to no more than 1% at both outlets of outer flowpath and booster (excluding the initial distortion due to the initial inhomogeneity). The smaller inlet distortion will produce smaller instability effect to the downstream components. At the higher speed/mass flow condition, the amount of distortion attenuation through the flowpath is larger.
Analysis of Different Emission Metrics for Power Generation Machinery in Flexible Co-Generation Energy Systems
Authors: Goßrau Christian , Petersen Nils Hendrik , Wirsum Manfred 
Published: September 2023

Abstract
There are many different metrics used for characterizing the emission behavior of power generation units, making it difficult to compare different technologies, fuels, and cycle layouts comprehensively. The present study analyses and evaluates different metrics for emission quantification (e.g., relative, absolute, or performance-based values). Mixtures of conventional fuels (natural gas, represented by methane) and alternative, carbonneutral fuels (hydrogen and ammonia) are compared. Different cycle adaptations of power generation systems (exhaust gas re-circulation, water and steam injection) are addressed. Both NOx and CO2 emissions are investigated using a gas turbine model and a chemical reactor network for a state-of-the-art industrial gas turbine. The results show that by using common metrics (i.e., ppmvdr) the emission behavior is significantly and moderately exaggerated for H2 and NH3, respectively. Performance-based metrics, however, are found to be most suitable for emission quantification across different fuels and cycle layouts: for example, if a standard gas turbine NOx emission limit of 15 ppmvdr is applied, lower NOx are found for fuel substitution with H2 than with NH3. Additionally, introducing the equivalent NOx emission limit of 150 mg/kWhel for gas turbines (considering full load efficiency of 39 %) as a regulative limit enlarges the suitable hydrogen addition rate from 47 vol.% up to 60 vol.% H2 from an emission perspective.
Computational Analysis of a Savonius Wind Rotor Using Bio-Inspired Corrugated Blades
Authors: Rathod Umang H. , Kulkarni Vinayak , Saha Ujjwal K. 
Published: September 2023

Abstract
For harvesting wind energy, especially at low-velocity regions, Savonius vertical-axis wind rotors are usually preferred. Among other variants of the vertical-axis wind rotors, the Savonius rotor has become an attractive candidate as a small-scale stand-alone system due to its direction independency, ease of fabrication and the absence of yaw-mechanism. The present paper attempts to study the effect of corrugated blades on the performance of a conventional Savonius rotor. The corrugation is a bio-inspired concept derived from the dragonfly wings. As reported in literature, the corrugation applied in the chord-wise direction of the airfoil improves the lift characteristics. This lift improvement is caused by the trapped vortices inside the corrugation that promotes a low-pressure region over the leading edge and suction surface of the airfoil. This concept of corrugation and its effect has been applied to the blades of a conventional Savonius wind rotor to improve its torque characteristics. In this paper, a rotor with corrugated semicircular blade profiles is studied by two-dimensional (2D) transient numerical simulation in ANSYS FLUENT using shear stress transport (SST) k-ω turbulence model. The simulations are conducted in the range of 5 m/s to 7 m/s to suit the lower wind velocities of the Savonius rotor. The torque and power coefficients of the corrugated semicircular-bladed rotor are calculated at the rotating conditions. Further, the pressure and local torque distributions over the corrugated blade surfaces are obtained and analyzed to understand the torque mechanism of the rotor with corrugated blade profiles. In order to have a direct comparison, the study has also been carried out for semicircular-bladed rotor without corrugation.
A Full Three-Dimensional Transient Fluid-Structure Interaction Model for the Dynamic Characteristics Predictions of Bump-Type Gas Foil Journal Bearings
Authors: Li Zhuocong , Li Zhigang , Li Jun 
Published: September 2023

Abstract
Oil-lubricated bearings are used in most present-day rotating machinery due to their high load capacity. This bearing, however, requires a complicated lubrication system which significantly increases the operating cost of the equipment. Moreover, the problem of the heat generation of lubricated oil after a long time of operation cannot be ignored, especially in high-speed turbomachinery. As for oil-free turbomachinery, the gas-lubricated bearing is regarded as a revolutionary technology to support the rotor. Bump-type gas foil bearing (bump-type GFB) is one of the most widely used gas-lubricated bearings, due to its high speed, low wear, no pollution, high temperature and pressure resistance and other excellent properties. As one of the critical components in the rotor system of a rotating machinery, bump-type GFBs can provide not only the static load capacity but also the dynamic gas film response forces, significantly affecting the dynamic stability performance of the rotor system. Therefore, an accurate and efficient dynamic characteristics prediction method for bump-type GFBs is crucial for the industrial safe operation of the rotating machinery system. This paper focuses on the assessment and validation of a novel numerical method for the dynamic coefficients prediction of bump-type gas foil journal bearings (bump-type GFJBs).
To predict the dynamic characteristics of bump-type GFJBs, in this paper, a novel full three-dimensional (3D) transient fluid-structure coupled numerical method was proposed, based on the finite element analysis (FEA) and the computational fluid dynamics (CFD). In order to improve computational efficiency and conform more to the bearing actual situations, a multiple-frequency elliptical-orbit rotor whirling model for arbitrary eccentric positions was proposed to define the rotor whirling motion, based on the mesh deformation techniques. The present full 3D transient CFD/FEA method was validated by the published experimental data of the dynamic stiffness and damping coefficients of a bump-type GFJB. The influences of the disturbance frequency and foil deformation on the dynamic characteristics of bump-type GFJBs were also presented and discussed.
The results indicate that the dynamic characteristics predicted by the present method has reasonable accuracy compared to the experimental results. The dynamic performance of the bearing is influenced by both the gas film and the foil structure. The foil structure adjusts the thickness and pressure distribution of the gas film through the foil deformation to change the dynamic performance of the bump-type GFJBs. The bump-type GFJB has a positive energy dissipation factor so that the rotor-bearing system supported by bump-type GFJBs has the ability to comeback and remain stable.
Dynamic Response and Suppression Method of High-Speed Rotors Under the Rotary Inertial Moment
Authors: Liu Cong , Wang Dong , Wang Yongfeng , Chen Xueqi , Yang Zhefu , Hong Jie 
Published: September 2023

Abstract
Current studies on rotor dynamic response mainly focus on the unbalance forces caused by mass eccentricity, while little attention is paid to the rotary inertial moments caused by the skew angle of the principal axis of inertia. Especially for the rotors operating at high rotational speeds, the influence of rotary inertial moments on rotor response could not be ignored. Therefore, it is necessary to study the influence of rotary inertial moments on the rotor response and provide corresponding response suppression methods. This paper established a dynamic model based on the key structural characteristics of aero-engine high-pressure rotors. The excitations from mass eccentricity and skew of the principal axis of inertia are both considered. Numerical analysis was performed, which shows that the dynamic response excited by the unbalance force remains at a low level after passing the critical speed, however, the response excited by the rotary inertial moment increases continuously with the rotational speed, because of the self-centering of the principal axis of inertia at the high speed. Experiments are conducted on a test rig, results show that the decrease of local angular stiffness around the disk could reduce the influence of rotary inertial moments, eventually suppressing the dynamic response at high rotational speed.
Extension of the MULTALL Open Source Throughflow Code for the Improved Endwall Loss Simulation
Authors: Bilgiç Mustafa , Baran Özgür Uğraş , Aksel Mehmet Halûk 
Published: September 2023

Abstract
Accurate loss modeling is critical for throughflow calculations to capture correct streamtube geometry and the accurate spanwise distribution of flow properties during quasi three-dimensional design of a turbomachinery blade. In this study, the modification of Cf (friction factor)-based loss computation in MULTALL throughflow code and its difference from classical empirical loss-based throughflow solvers are studied. The original form of the MULTALL applies a constant friction factor on all wetted surfaces to account for the losses in the throughflow analysis. However, in a typical turbomachinery blade passage regardless of being compressor or turbine passage, the entropy generation near the endwall regions cannot be handled by imposing constant Cf on the wetted surface due to the complex endwall flow structure. To improve the loss prediction capability of MULTALL, the friction factor near the endwall regions is modified. Therefore, all these complex flow structures can be resolved. In other words, the Cf distributions are recalculated near the endwall regions such that the secondary and tip clearance losses can be represented accurately. Furthermore, an empirical-based loss prediction capability is also brought to the MULTALL via distributed loss model approach. The entropy gradient required for the calculating of friction force on blade surfaces is calculated from empirical loss models. Then, the calculated friction force is included in the solution via the source term. Both methods are validated with the experimental results of a single stage transonic compressor. The modified Cf model shows better agreement with the experimental data near endwalls as compared to results of empirical based model and the original form of MULTALL solver.
Time-Averaged Aerodynamics of a High-Speed Low-Pressure Turbine Cascade With Cavity Purge Flow and Unsteady Wakes
Authors: Lopes Gustavo , Simonassi Loris , Lavagnoli Sergio 
Published: September 2023

Abstract
The time-averaged aerodynamics of a high-speed low-pressure turbine (LPT) cascade were investigated under the impact of unsteady wakes and purge flows. The tests were performed at an outlet Mach (M) and Reynolds numbers (Re) of 0.90 and 70k, respectively. Unsteady wakes were simulated by means of a spoked-wheel type wake generator (WG) and a reduced frequency of 0.95 was achieved. The development of a purge flow system to operate at low pressure levels is presented alongside guidelines for the operation of the circuit. The new purge system was commissioned in terms of its long-term stability and flow uniformity at the cascade inlet. The impact of varying purge flows from a cavity versus a flat endwall was assessed by means of static pressure measurements on the blade pressure side (PS) and suction side (SS) and traverses performed downstream with a miniaturized multi-hole probe. Differences in the secondary flow structures resultant from injecting purge flow into the flowfield are observed, namely the intensification of the trailing shed vortex (TSV) and passage vortex (PV) that is also displaced away from the endwall. An increase of the endwall losses occurs as the flat endwall was replaced with a cavity geometry and the cavity purge flow rate increases.
Multi-Objective Experimental Combustor Development Using Surrogate Model-Based Optimization
Authors: Reumschüssel Johann Moritz , von Saldern Jakob G. R. , Ćosić Bernhard , Paschereit Christian Oliver 
Published: September 2023

Abstract
The majority of premixed industrial gas turbine combustion systems features two or more separately controlled fuel lines. Every additional fuel line improves the operational flexibility but increases the complexity of the system. When designing such a system, the goals are low emission of various pollutants and avoiding lean blow out or extinction. Typically, these limitations become critical under different load conditions of the machines. Therefore, it is particularly challenging to develop combustors for stable and clean combustion over a wide operating range. In this study, we adopt the machine learning method Gaussian process regression for application to burner development, aiming to improve the process, which is often driven by a trial-and-error approach. To do so, a special pilot unit is installed into a full-scale industrial swirl combustor. The pilot features 61 positions of fuel injection, each of which is equipped with an individual valve, allowing to modify the fuel-air mixture close to the flame root in various degrees. In fully automatized atmospheric tests, we use the pilot system to train two surrogate models for different design objectives of the combustor, relevant for full load and part load operation, respectively. Once trained, the models allow for prediction for any possible injection scheme. In combination they can be used to identify pilot injector configurations with an improved operation range in terms of low NOx emissions and part load stability. The adopted multi-model approach enables combustor design specifically for high operational flexibility of gas turbines, but can also be extended to other similar industrial development processes.