bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Simulation of a Radial Turbine at Off-Design Conditions in Presence of Choked Flow
Authors: Tiseira Andrés , García-Cuevas Luis Miguel , Inhestern Lukas Benjamin , Echavarría Juan David 
Published: January 2021

Abstract
In the application of turbocharging and organic Rankine cycles (ORCs) the radial turbine can operate at high pressure ratio leading to the presence of choking inside the turbine. Information in this map region is needed to estimate the overall machine performance and to achieve an optimum matching of engine-turbocharger or an integration into ORCs. As a preliminar study before doing experimental tests in a turbocharger gas stand and before starting modeling activities, 3D CFD simulations were run for this paper. The occurrence of choking in the stator passage, in the vaneless space and in the rotor passage is categorized and analyzed under different operating conditions and VGT openings. The appearance of the shock wave depends strongly of the stator vane position and pressure ratio. In the analyzed turbocharger VGT turbine no choking has been identified in the throat of the stator vanes. In technically relevant closed VGT position choking was identified in the vaneless space. Whereas at open vane position the shock wave appears at the rotor throat and the Mach number can increase from the blade tip to the hub or from the hub to the tip depending on the rotational speed. Furthermore, tip leakage flow plays an important role, being responsible of subsonic regions in the rotor outlet although a big percentage of the section is choked.
Design and CFD Simulation of a Micro Gas Turbine Combustor Fuelled With Low LHV Producer Gas
Authors: Nicolosi Francesco F. , Renzi Massimiliano 
Published: January 2021

Abstract
In this paper, the authors analyze the feasibility of fuelling a small-scale 3.2 kWe MGT, manufactured by the Dutch company MTT, with a low LHV fuel produced via a gasification process. In particular, a CFD analysis on the combustor of the MGT is carried out in order to assess the behaviour of the component when it is fuelled with a traditional fuel (natural gas) and with a producer gas coming from a gasification process. The operating conditions of the combustor, used as boundary conditions for the simulations, are obtained by analyzing the characteristic performance curves of the turbo-machines used in the MGT. The simulation of the combustion process with methane has been validated using the temperature output from experimental tests and the NOX emissions. A RANS simulation using the Non-Adiabatic Non-Premixed Combustion Model Approach has been adopted. NOX formation has been simulated by the adoption of the extended Zel’dovich mechanism. Both nominal and part load simulations have been performed. This simplified modelling strategy allows to assess the main issues and figures of the combustion process with a reasonable computational effort. The CFD simulations showed that the combustion with a low LHV fuel are feasible but some modifications of the present configuration of the combustor are required, with specific attention to the fuel injection system. Results showed that, with Natural Gas, the average temperature of the exhaust mass flow is 1297 K, the level of CO and NOX referred to the 15% of O2 are respectively less than 1 ppm and 30.365 ppm, respectively. With S the original design of the injector proved to be non-adequate for a proper air and fuel mixing; therefore, a modified design has been proposed with an increased injection section. In the novel design for syngas, a better temperature distribution and lower emissions have been found: an average temperature of the flue gas at the combustor discharge of 1249 K is obtained, and the level of CO and NOX are both less than 1 ppm. The lower operating temperature is determined by the higher fuel flow rate and, in particular, by the high share of inert gases in the fuel. Additional simulations have been run at part load operation to assess the viability of the proposed design also in off-design conditions.
Detailed Velocity and Heat Transfer Measurements in an Advanced Gas Turbine Vane Insert Using MRV and IR Thermometry
Authors: Benson Michael J. , Bindon David , Cooper Mattias , Davidson F. Todd , Duhaime Benjamin , Helmer David , Woodings Robert , Van Poppel Bret P. , Elkins Christopher J. , Clark John P. 
Published: January 2021

Abstract
This work reports the results of paired experiments for a complex internal cooling flow within a gas turbine vane using Magnetic Resonance Velocimetry (MRV) and steady-state Infrared (IR) thermometry. A scaled model of the leading edge insert for a gas turbine vane with multi-pass impingement was designed, built using stereolithography (SLA) fabrication methods, and tested using MRV techniques to collect a three-dimensional, three-component velocity field data set for a fully turbulent test case. Stagnation and recirculation zones were identified and assessed in terms of impact on potential cooling performance. A paired experiment employed an IR camera to measure the temperature profile data of a thin, heated stainless steel impingement surface modeling the inside turbine blade wall cooled by the impingement from the vane cooling insert, providing complementary data sets. The temperature data allow for the calculation of wall heat transfer characteristics, including the Nusselt number distribution for cooling performance analysis to inform design and validate computational models. Quantitative and qualitative comparisons of the paired results show that the flow velocity and cooling performance are highly coupled. Module-to-module variation in the surface Nusselt number distributions are evident, attributable to the complex interaction between transverse and impinging flows within the apparatus. Finally, a comparison with internal heat transfer correlations is conducted using the data from Florschuetz [1]. Measurement uncertainty was assessed and estimated to be approximately +7% for velocity and ranging from +3% to +10% for Nusselt number.
Auto-Ignition of Gas Turbine Lubricating Oils in a Shock Tube Using Spray Injection
Authors: Cooper Sean P. , Browne Zachary K. , Alturaifi Sulaiman A. , Mathieu Olivier , Petersen Eric L. 
Published: January 2021

Abstract
In choosing the lubricating oil for a gas turbine system, properties such as viscosity, viscosity index, corrosion prevention, and thermal stability are chosen to optimize turbine longevity and efficiency. Another property that needs to be considered is the lubricant’s reactivity, as the lubricant’s ability to resist combustion during turbine operation is highly desirable. In evaluating a method to define reactivity, the extremely low vapor pressure of these lubricants makes conventional vaporization by heating impractical due to the high temperatures and fuel cracking as well as issues with preferential vaporization. To this end, a new experiment was designed and tested to evaluate the reactivity of lubricating oils using an existing shock-tube facility at Texas A&M University equipped with an automotive fuel injector. This experiment disperses a pre-measured amount of lubricant into a region of high-temperature air to study auto-ignition. To ensure proper dispersal, a laser extinction diagnostic was used to measure the lubricant particles behind the reflected shock as they are dispersed and vaporized. An OH* chemiluminescence diagnostic measuring light emitted during combustion at around 306 nm was used to determine ignition delay time. Pressure was also measured at the sidewall and endwall positions for test repeatability and exothermicity of the experiments. The methods were validated by conducting experiments with ethanol and comparing the results to previous heated shock-tube experiments conducted in the same facility. Using this method, various 32-, 36-, and 46-weight lubricants identified as widely used in the gas turbine industry were tested. Experiments were conducted in post-reflected shock conditions around 1370K (2006 °F) and 1.2 atm, where ignition delay time, peak OH* emission and time-to-peak values were recorded and compared. Ignition was observed for all but one of the lubricants at these conditions, and mild to strong ignition was observed for the other lubricants with varying ignition delay times.
Damage Detection of Composite Materials Using Data Fusion With Deep Neural Networks
Authors: Dabetwar Shweta , Ekwaro-Osire Stephen , Dias João Paulo 
Published: January 2021

Abstract
Composite materials have enormous applications in various fields. Thus, it is important to have an efficient damage detection method to avoid catastrophic failures. Due to the existence of multiple damage modes and the availability of data in different formats, it is important to employ efficient techniques to consider all the types of damage. Deep neural networks were seen to exhibit the ability to address similar complex problems. The research question in this work is ‘Can data fusion improve damage classification using the convolutional neural network?’ The specific aims developed were to 1) assess the performance of image encoding algorithms, 2) classify the damage using data from separate experimental coupons, and 3) classify the damage using mixed data from multiple experimental coupons. Two different experimental measurements were taken from NASA Ames Prognostic Repository for Carbon Fiber Reinforced polymer. To use data fusion, the piezoelectric signals were converted into images using Gramian Angular Field (GAF) and Markov Transition Field. Using data fusion techniques, the input dataset was created for a convolutional neural network with three hidden layers to determine the damage states. The accuracies of all the image encoding algorithms were compared. The analysis showed that data fusion provided better results as it contained more information on the damages modes that occur in composite materials. Additionally, GAF was shown to perform the best. Thus, the combination of data fusion and deep neural network techniques provides an efficient method for damage detection of composite materials.
Experimental Study on the Effect of Clocking on the Propagation of Inflow Pressure Distortions in a Low Pressure Turbine Stage
Authors: Simonassi L. , Zenz M. , Bruckner P. , Pramstrahler S. , Heitmeir F. , Marn A. 
Published: January 2021

Abstract
The design of modern aero engines enhances the interaction between components and facilitates the propagation of circumferential distortions of total pressure and temperature. As a consequence, the inlet conditions of a real turbine have significant spatial non-uniformities, which have direct consequences on both its aerodynamic and vibration characteristics.
This work presents the results of an experimental study on the effects of different inlet total pressure distortion-stator clocking positions on the propagation of total pressure inflow disturbances through a low pressure turbine stage, with a particular focus on both the aerodynamic and aeroelastic performance. Measurements at a stable engine relevant operating condition and during transient operation were carried out in a one and a half stage subsonic turbine test facility at the Institute of Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. A localised total pressure distortion was generated upstream of the stage in three different azimuthal positions relative to the stator vanes. The locations were chosen in order to align the distortion directly with a vane leading edge, suction side and pressure side. Additionally, a setup with clean inflow was used as reference. Steady and unsteady aerodynamic measurements were taken downstream of the investigated stage by means of a five-hole-probe (5HP) and a fast response aerodynamic pressure probe (FRAPP) respectively. Strain gauges applied on different blades were used in combination with a telemetry system to acquire the rotor vibration data.
The aerodynamic interactions between the stator and rotor rows and the circumferential perturbation were studied through the identification of the main structures constituting the flow field. This showed that the steady and unsteady alterations created by the distortion in the flow field lead to modifications of the rotor vibration characteristics. Moreover, the importance of the impact that the pressure distortion azimuthal position has on the LPT stage aerodynamics and vibrations was highlighted.
Experimental Assessment of a Sliding-Blade Inside-Out Ceramic Turbine
Authors: Thibault D. , Dubois P. K. , Picard B. , Landry-Blais A. , Plante J.-S. , Picard M. 
Published: January 2021

Abstract
In order to reach 40% efficiency, sub-MW turbines must operate in a recuperated gas Brayton cycle at a turbine inlet temperature (TIT) above 1300°C. Current sub-MW turbines have material-related operating temperature limits. Still to this day, there is no cost-effective rotor design which operates at such high temperatures. This paper introduces a novel, sliding-blade, inside-out ceramic turbine (ICT) wheel configuration, which could enable high-efficiency sub-MW recuperated engines to be achieved with cheap monolithic ceramic blades.
The inside-out configuration uses a rotating structural hoop, or shroud, to convert centrifugal forces into compressive blade loading. The sliding-blade architecture uses a hub with angled planes on which ceramic blades slide up and down, allowing to match the radial expansion of the structural shroud. This configuration generates low stress values in both ceramic and metallic components and can achieve high tip speeds.
A prototype is designed and its reliability is calculated using CARES software. The result is a design which has a single blade probability of failure (Pf) of 0.1% for 1000 h of steady operation. Analyses also demonstrate that reliability is greatly dependent on friction at ceramic-to-metal interfaces. Low friction could lead to acceptable reliability levels for engine applications. The prototype was successfully tested in a laboratory turbine environment at a tip speed of 350 m/s and a TIT of 1100 °C without any damage.
These achievements demonstrate the robustness of the sliding-blade ICT configuration. Further research and development will focus on increasing tip speed and TIT to higher values.
FEM Considerations to Simulate Interlocked Bladed Disks With Lagrange Multipliers
Authors: Córdoba Oscar 
Published: January 2021

Abstract
A few structural simulation issues with constrained Finite Elements using Lagrange multipliers are described. The main difficulties associated to interlocked bladed disks are:
1. Contacts. The structural state must be calculated by the FEM solver accounting the centrifugal, thermal and pressure loads. The interlock surfaces may slide, some area will be in contact and some others will be separated. This is a nonlinear condition that needs solver iterations.
2. Interference. The blade surfaces susceptible to contact are not necessarily periodic. In many cases pretwist is needed during assembly to couple the blades. The solution for surfaces in contact require a cyclic symmetry boundary condition. Different issues related to coordinates systems will be discussed.
3. Overconstraint. The model mesh nodes may accommodate more than one boundary condition. Interlock nodes are affected for both conditions, possibility of contact and cyclic symmetry.
The use of Lagrange multipliers may cope with these problems. This is a well-known method although some FEM methodology peculiarities will be derived from scratch, either in the static and modal simulations. Pros and cons of this approach will be discussed related to classical solutions to the aforementioned problems. Every algorithm described has been already implemented in a FEM code than runs with successful results.
Low Rank Education of Cascade Loss Sensitivity to Unsteady Parameters by Proper Orthogonal Decomposition
Authors: Lengani D. , Simoni D. , Yepmo V. , Ubaldi M. , Zunino P. , Bertini F. 
Published: January 2021

Abstract
In the present work, Proper Orthogonal Decomposition (POD) has been applied to a large dataset describing the profile losses of Low Pressure Turbine (LPT) cascades, thus allowing: i) the identification of the most influencing parameters that affect the loss generation; ii) the identification of the minimum number of requested conditions useful to educate a model with a reduced number of data.
The dataset is constituted by the total pressure loss coefficient distributions in the pitchwise direction. The experiments have been conducted varying the flow Reynolds number, the reduced frequency and the flow coefficient. Two cascades are considered: the first for tuning the procedure and identifying the number of really requested tests, and the second for the verification of the proposed model. They are characterized by the same axial chord but different pitch-to-chord ratio and different flow angles, hence two Zweifel numbers.
The POD mode distributions indicate the spatial region where losses occur, the POD eigenvectors provide how such losses vary for the different design conditions and the POD eigenvalues provide the rank of the approximation. Since the POD space shows an optimal basis describing the overall process with a low rank representation (LRR), a smooth kernel is educated by means of Least-Squares method (LSM) on the POD eigenvectors. Particularly, only a subset of data (equal to the rank of the problem) has been used to generate the POD modes and related coefficients. Thanks to the LRR of the problem in the POD space, predictors are low order polynomials of the independent variables (Re, f+ and ϕ). It will be shown that the smooth kernel adequately estimates the loss distribution in points that do not participate to the education. Additionally, keeping the same steps for the education of the kernel on another cascade, loss distribution and magnitude are still well captured. Thus, analysis show that the rank of the problem is much lower than the tested conditions, and consequently a reduced number of tests are really necessary. This could be useful to reduce the number of hi-fidelity simulations or detailed experiments in the future, thus further contributing to optimize LPT blades.
Periodic Unsteadiness of Tip Clearance Vortex in an Axial Compressor Rotor
Authors: Yang Fan , Wu Yanhui , Zhang Ziyun , Wang Zhenyang 
Published: January 2021

Abstract
A series of unsteady simulations, supported by experimental data, are used to characterize the periodic unsteadiness of the tip clearance vortex in an axial compressor rotor. The numerical probes detect significant periodic fluctuations in the blade tip region at near stall conditions. A reduced frequency at different condition is limited to a small range although there exist a large difference on the natural frequency. Physical explanations of the periodic fluctuations are made in terms of vortex-core identification, contour, etc. The nature of the periodic unsteadiness in the tip region is the periodic bubble-type breakdown of the tip leakage vortex induced by the broken vortex core generated by the previous breakdown. The life cycle of the broken vortex core can be summarized as three processes, generation, propagation and inducing breakdown of tip leakage vortex. The broken vortex core arrives at mid-chord of the adjacent blade, resulting in change of momentum in the tip clearance and pressure in the leading edge of the adjacent blade. The flow in this blade tip region is similarly affected by another adjacent blade. The tip leakage vortex core is bent, then the breakdown of tip clearance happens and a new broken vortex core appears accompanied by a back flow region.
Linear MPC Operating Far From Design Condition: Assessment Derived From Experiments
Authors: Rossi Iacopo , Ferrari Mario Luigi , Traverso Alberto 
Published: January 2021

Abstract
Model Predictive Control (MPC) is a well-known control architecture that has encountered an enormous variety of applications since the very beginning until current days. The pros and cons of such control technique are very well known and both of them rely on the embedded model, which is used to determine the control trajectory. Still, the discrepancy between embedded model and real operative conditions can affect the control response due to uncertainties in measurement chain, noise and so on. Still, it is hardly available in literature what would happen in case the plant is operating far from the design condition of the model. This is of particular interest once a linear MPC is governing a non-linear process where the linearization of the target plant must be processed to tune the MPC itself. This paper analyses experimental results from a fuel cell gas turbine hybrid system, namely SOFC/GT emulator test rig, where a linearized MPC was adopted to control stack inlet temperature. The test rig is constituted by a modified Turbec T100 micro gas turbine where a volume of 4 m3 is interposed between compressor and turbine. This emulates the impact of the SOFC on the GT. The system is connected in real-time mode to a model, which runs in parallel and reads what is going on the plant side and simulates the behavior of the associated SOFC stack. The MPC controller governs the plant according to the stack inlet temperature computed by the model in real-time mode. This MPC must be considered as a supervisor of the system, as the gas turbine was still equipped with its original control system. The plant was subject to an on-purpose strong degradation -operated via a constant venting of air from compressor to ambient. This operation strongly influenced the performance of the system, which were no longer able to operate at a level of temperature and power for which the controller was designed for. Still, a ramping down in power and back up was performed and the MPC showed performance which were in agreement with the design performance. Such surprisingly good result is explained with the complexity of the embedded model, which was derived from a completely physical model of the target system and constituted by more than 200 states.
Influence of Pre-Swirl, Rotor Speed and Blade Count on Aeroelastic Coupling Mechanisms During Stall Inception of a Transonic Compressor
Authors: Franke Daniel , Jüngst Maximilian , Möller Daniel , Schiffer Heinz-Peter , Giersch Thomas 
Published: January 2021

Abstract
The aeroelastic effects during stall inception in modern axial compressors have been a research focus for decades and yet are not fully understood. Experimental investigations, conducted at the 1.5-stage transonic compressor test rig at TU Darmstadt, using extensive unsteady aerodynamic and structural instrumentation, show global trends and influencing parameters on non-synchronous vibration and associated unsteady aerodynamics.
During stall inception, aerodynamic disturbances occur and vary in count, size, cell speed and trajectory. The interaction with non-synchronous blade vibration results in changing stability mechanisms, indicating influences of pre-swirl, rotor speed and blade count on the traveling aerodynamic wave as well as the coupling with the structural wave. Supplementary numerical simulations of the test setup extend the available set of aerodynamic and aeromechanical data, and support the experimental findings.
The study reveals the convective nature of NSV, influenced by the propagation speed of aerodynamic pre-stall disturbances, depending on rotor speed and pre-swirl, as well as its interaction with blade vibration, based on specific phase synchronization conditions and rotor blade count.