bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identification of Dynamic Coefficients of a Five-Pad Tilting Pad Journal Bearing up to Highest Surface Speeds
Authors: Zemella Philipp , Hagemann Thomas , Pfau Bastian , Schwarze Hubert 
Published: January 2021

Abstract
Tilting-pad journal bearings are widely used in turbomachinery industry due to their positive dynamic properties at high rotor speeds. However, the exact description of this dynamic behavior is still part of current research. This paper presents measurement results for a five-pad tilting-pad journal bearing in load between pivot configuration. The bearing is characterized by a nominal diameter of 100 mm, a length of 90 mm, and a pivot offset of 0.6. Investigations include results for surface speeds between 25 and 120 m/s and specific bearing loads ranging from 0.0 to 3.0 MPa.
Results of theoretical predictions are commonly derived from perturbation of stationary operation under static load. Therefore, experimental results for stationary operation including pad deflection under static load are presented first to characterize the investigated bearing. Measured results indicate considerable non-laminar flow in the upper region of the investigated range of rotor speeds. Second, dynamic excitation test are performed with excitation frequencies up to 400 Hz to evaluate dynamic coefficients of a stiffness (K) and damping (C) KC-model, and additionally, a KCM-model using additional virtual mass (M) coefficients. KCM-coefficients are obtained by fitting frequency dependent KC-characteristics to the KCM-model structure using least square approach. The wide range of rotating and excitation frequencies leads to subsynchronous as well as supersynchronous vibrations. Excitation forces are applied with multi-sinus and single-sinus characteristics. The latter one allows evaluation of KC-coefficients at the particular frequency ratio in the time domain. Here, frequency and time domain evaluation algorithms for dynamic coefficients are used in order to assess their special properties and quality. The impact of surface speed, bearing load, and oil flow rate on measured and predicted KCM-coefficients is investigated. Measured and predicted results can be well fitted to a KCM-model and show a significant influence of the ratio between fluid film and pivot support stiffness on the speed dependent characteristic of bearing stiffness coefficients. However, the impact of this ratio on damping coefficients is considerably lower. Further investigations on the impact of oil flow rates indicate that a significant decrease of direct damping coefficients exists below a certain level of starvation. Above this limit, direct damping coefficients are nearly independent of oil flow rate. Results are analyzed in detail and demands on improvements for predictions are derived.
Spectral Analysis of an Aeronautical Lean Direct Injection Burner Through Large Eddy Simulation
Authors: Carreres M. , García-Cuevas L. M. , García-Tíscar J. , Belmar-Gil M. 
Published: January 2021

Abstract
During the last decades, many efforts have been invested by the scientific community in minimising exhaust emissions from aeronautical gas turbine engines. In this context, many advanced ultra-low NOx combustion concepts, such as the Lean Direct Injection treated in the present study, are being developed to abide by future regulations. Numerical simulations of these devices are usually computationally expensive since they imply a multi-scale problem. In this work, a non-reactive Large Eddy Simulation of a gaseous-fuelled, radial-swirled Lean-Direct Injection (LDI) combustor has been carried out through the OpenFOAM Computational Fluid Dynamics (CFD) code by solving the complete inlet flow path through the swirl vanes and the combustor. The geometry considered is the gaseous configuration of the CORIA LDI combustor, for which detailed measurements are available. Macroscopical analysis of the main turbulent features related to the swirling flow and the generated Central Recirculation Zone (CRZ) are well established in the literature. Nevertheless, a more in-depth characterization is still required in this area of active research since theory and experimental data are not yet able to predict which unstable mode dominates the flow. This work aims at using Large Eddy Simulation for a complete characterisation of the unsteady flow structures generated within the combustion chamber of a gaseous methane injection immersed in a strong non-reactive swirling flow field. To do so, a spectral analysis of the flow field is performed to identify the frequency, intensity and instabilities associated to the phenomena occurring at the swirler outlet region. A coherent structure known as Precessing Vortex Core (PVC) is identified both at the inner and the outer shear layers, resulting in a periodic disturbance of the pressure and velocity fields. The pressure and velocity fluctuations predicted by the CFD code are used to compute the spectral signatures through the Sound Pressure Level (SPL) amplitude at multiple locations. This allows investigating both the complex behaviour of the PVC and its associated acoustic phenomena. The acoustic characteristics computed by the numerical model are first validated qualitatively by comparing the spectrum with available experimental data. In this way, the use of dimensionless numbers to characterise the most energetic structures is coherent with the experimental observations and the characteristics of the PVC. Then, the numerical identification of the main acoustic modes in the chamber through Dynamic Mode Decomposition (DMD) allows overcoming the Fast Fourier Transform (FFT) shortcomings and better understanding the propagation of the hydrodynamic instability perturbations. This investigation on the main non-reacting swirling flow structures inside the combustor provides a suitable background for further studies on combustion instability mechanisms.
Data-Driven Identification of Nonlinear Flame Models
Authors: Ghani Abdulla , Boxx Isaac , Noren Carrie 
Published: January 2021

Abstract
This paper presents a data-driven identification framework with the objective to retrieve a flame model from the nonlinear limit cycle. The motivation is to identify a flame model for configurations, which do not allow the determination of the flame dynamics: that is commonly for industrial applications where (i) optical access for non-intrusive measurements of velocity and heat release fluctuations are not feasible and (ii) unstable combustion is monitored via multiple pressure recordings.
To demonstrate the usefulness of the method, we chose three test cases: (i) a classical Rijke tube; (ii) an experiment of a laminar flame (EM2C case) (iii) and a high-pressure, turbulent premixed flame (DLR case). The procedure is as follows: First, acoustic network models for the three cases are generated for which the in-house software taX is employed. Next, the acoustic network models are embedded in an optimization framework with the objective to identify flame parameters that match the experimental limit cycle data: based on the instability frequency and pressure amplitudes, we formulate physical constraints and an objective function in order to identify the flame model parameters gain nopt and time delay τopt in the nonlinear regime. We demonstrate for the three cases that the identified flame parameters reproduce the unstable combustion processes and highlight the usefulness of the method for control purposes.
Effects of Casing Relative Motion on Aerodynamic Performance With Modified Designs of Winglet and Squealer Tip
Authors: Garg Anmol , Singh Rawat Sachin , Prasad B. V. S. S. S. 
Published: January 2021

Abstract
For unshrouded high pressure turbines, the design of rotor blade tips is a dynamic multi-purpose process. The model should have least aerodynamic and heat transfer losses caused by the flow through the tip gap and the blade. Recent studies show that by the modification of the blade tip, there is some improvement in efficiency and reduced tip gap flow. These include mainly parametric study of cavity tip and winglet tip modifications. Previous studies confirm the benefit of overhang in reducing tip leakage loss and heat transfer by changing the location of the tip leakage vortex away from the blade. But, to the best of authors’ knowledge none of the study reports the effect of casing relative motion on modified winglet and squealer tip. In the present study, novel modified tip blade geometry is introduced named as Top Squealer with Bottom Winglet (TSBW). Tip gap physics and loss generation has been investigated on three other different designs of squealer and winglet geometries and compared with the novel design. These designs are named as Flat Winglet, Cavity Squealer, Top Squealer with Bottom Winglet (new design) and Top Winglet with Bottom Squealer (TWBS). The flat tip rotor blade is considered as the base case for comparison. Three-dimensional computational study using ANSYS CFX 18.2 has been performed in order to examine the effect of casing relative motion on various designs of winglet and squealer tip. Structured mesh is created using ANSYS ICEM 18.2. At the downstream of trailing edge, distinct regions of momentum deficits named as the tip leakage vortex (LV), tip passage vortex (TPV), wakes and hub passage vortex (HPV) has been observed. Wakes formed due to the interaction of scraping vortex (SV), Tip passage vortex (TPV) and the leakage vortex. It has been found that Cavity Squealer and Top Squealer with Bottom Winglet (TSBW)gave the lowest total pressure loss coefficient and lowest tip leakage flow rate. But in casing relative motion case, cavity squealer with bottom wingletout runs the cavity squealer aerodynamic performance. This is due to the enlarged cavity at the tip. The incoming pass over flow got blocked because of enhanced interaction of LV and Scraping vortex (SV) in the tip cavity. As a result, tip leakage losses and tip leakage mass flow rate decreased.
Long Duration Uniform Crystal Temperature Sensor Application in Industrial Gas Turbine for Cooling Design Validation
Authors: Vogel Gregory , Thomas Anastasia , Ginzbursky Edward , Torkaman Alex 
Published: January 2021

Abstract
This paper describes an in-situ validation of advanced cooling designs for turbine airfoils using high accuracy Uniform Crystal Temperature Sensors (UCTS). This was achieved by running a rainbow test of UCTS instrumented parts with different cooling designs in an industrial gas turbine in commercial operation for a period exceeding 6 months. Test results provided valuable information on the cooling performance benefits of the improved design, as well as on different thermal barrier coatings tested as part of the rainbow configuration. This paper presents the comparison between empirical and analytical results.
The real engine environment presented obvious challenges to the validation effort, which assumes high accuracy experimental data from a well-controlled test as the basis for comparison. To get as close as possible to this high standard, sources of variation and uncertainties were identified and accounted for in the preparation of the test campaign. This paper describes these in some detail, providing a useful model to practicing engineers.
Survival and timeliness of the results were also a concern. Expert installation and removal of the micro-sized crystal sensors was a key contributing factor to the sensor survival. Automated, quality controlled post processing, which correlated changes in the crystal structure and the time history of testing with temperature, enabled accurate reporting of the maximum temperature experienced during the full length of the test for each crystal.
The results show excellent agreement between the UCTS reported temperature and the Conjugate Heat Transfer (CHT) model predictions. Hence the experimental results validated the advanced cooling design configuration. Additionally, this case study demonstrates that UCTS is a well suited non-intrusive, accurate and practical technique applicable for long duration in-situ temperature measurements of turbine components in the conditions most representative of the engine.
Entropy Generation and Efficiency of a Transonic Rotor With Water Injection: A Numerical Study
Authors: Zawadzki Natan , Szymanski Artur , Block Novelo David Alejandro , Igie Uyioghosa 
Published: January 2021

Abstract
The application of compressor water injection in aeroengines is of renewed interest in the civil aviation industry. Water due to its unprecedented heat capacity has the potential to cool the engine air through evaporation and thus reduce the NOx emissions formed in a combustion process. It is well known that the evaporative cooling increases thermodynamic cycle efficiency and thus improves the fuel economy. A relatively unexplored area, however, is the entropy generation due to water phase change as well as the balance between the corresponding entropy yield and the savings from the cooling of the core compressor flow. Hence, little consensus in the literature exists on the ultimate effect of water injection on compressor efficiency. In this study, a numerical analysis of water injection on an axial transonic rotor was carried out. The compressor model was tested at near-peak efficiency conditions with and without water injection. The flow was analysed using the Eulerian-Lagrangian approach with two-way coupling and the k-ω Shear Stress Transport turbulence model with Reattachment Modification. A universal, second thermodynamic law approach to quantify the entropy generation is proposed and used to evaluate the compressor flow. Results show that evaporation can facilitate the compression process and does not impair the compressor efficiency if applied at favourable conditions. The entropy generation in droplet-laden flow scales according to the gains from cooling effect and losses due to the evaporation and increased friction in the fluid. Some of the discrepancies in the public domain could be addressed, showing that the observed improvement in compressor efficiency is highly sensitive to the entropy flux measurement location. Most benefits from water injection were observed at the rotor tip proving the case for part-span injection from an entropy balance perspective.
Static Performance of a Hydrostatic Thrust Foil Bearing for Large Scale Oil-Free Turbomachines
Authors: LaTray Nguyen , Kim Daejong , Song Myongsok 
Published: January 2021

Abstract
This work presents a novel design of a hydrostatic thrust foil bearing (HSTFB) with an outer diameter of 154mm along with simulation and test results up to specific load capacity of 223kPa (32.3psi). The HSTFB incorporates a high pressure air/gas injection to the thrust foil bearing with a uniform clearance. This bearing has high load capacity, low power loss, and no friction/wear during startup and shutdown. In addition, the HSTFB allows for bidirectional operation. The paper also presents an advanced simulation model which adopts the exact locations of a tangentially arranged bumps to a cylindrical two-dimensional plate model of the top foil. This method predicts top foil deflection with better accuracy than the traditional independent elastic foundation model which distributes the bump locations over the nodal points in the cylindrical coordinates, and with less computational resource than the finite element method applied to the entire bump/top foils. The presented HSTFB, was designed for Organic Rankine Cycle (ORC) generators, but its performance was predicted and measured using air in this paper. The bearing static performance is compared analytically against the rigid counterpart, and presented at different supply pressures, speeds, and minimum film thicknesses. Experimental verification is conducted at 10, 15 and 20krpm. The measured load capacity and frictional loss agree well with the prediction. The measured film thickness also agrees with the prediction after the structural deflection of the thrust runner disc is compensated. Overall, the novel HSTFB demonstrates an excellent static performance and shows good potential for adoption to the intended ORC generators and other large oil-free turbomachines.
Analytical Formulation of the Performance of the Allam Power Cycle
Authors: Haseli Yousef 
Published: January 2021

Abstract
Thermal power plants operating on fossil fuels emit a considerable amount of polluting gases including carbon dioxide and nitrogen oxides. Several technologies have been developed or under development to avoid the emissions of, mainly, CO2 that are formed as a result of air-fuel combustion. While post-combustion capture methods are viable solutions for reduction of CO2 in the existing power plants, implementation of the concept of oxyfuel combustion in future power cycles appears to be a promising technique for clean power generation from fossil fuels. A novel power cycle that employs oxyfuel combustion method has been developed by NET Power. Known as the Allam cycle, it includes a turbine, an air separation unit (ASU), a combustor, a recuperator, a water separator, CO2 compression with intercooling and CO2 pump. (Over 90% of the supercritical CO2 flow is recycled back to the cycle as the working fluid, and the rest is extracted for further processing and storage. The present paper introduces a simplified thermodynamic analysis of the Allam power cycle. Analytical expressions are derived for the net power output, optimum turbine inlet temperature (TIT), and the molar flowrate of the recycled CO2 flow. The study aims to provide a theoretical framework to help understand the functional relationships between the various operating parameters of the cycle. The optimum TIT predicted by the presented expression is 1473 K which is fairly close to that reported by the cycle developers.
Design of a Compact Magnetically Levitated Blower for Space Applications
Authors: Hawkins Larry , Filatov Alexei , Khatri Rasish , DellaCorte Chris , Howard S. Adam 
Published: January 2021

Abstract
NASA is leading the design and development of a next-generation CO2 removal system, the Four Bed Carbon Dioxide Scrubber (4BCO2), and intends to use the International Space Station (ISS) as its testbed. A key component of the system is the blower that provides the airflow through the CO2 sorbent beds. To improve performance and reliability, magnetic levitation (magnetic bearings) will be used in lieu of more conventional bearings (e.g. ball bearings or air bearings) to improve resistance to contaminants and enable extensibility with regards to blower speed, pressure rise and mass flow rate. The blower will pull air from the ISS through an adsorbing desiccant bed and push it through a CO2 sorbent bed and desorbing desiccant bed. The 4BCO2 blower features an overhung permanent magnet motor, a centrally located five-axis, active magnetic bearing system, backup bearings, and an overhung centrifugal impeller in a very compact package. Magnetic bearings are a natural choice for this application due to low power consumption, low transmitted vibration and oil free operation. This paper describes the design considerations and design selections for the blower system with a focus on the magnetic bearings. Magnetic FEA of the actuator/sensor system, rotordynamics/controls analysis, and backup bearing drop simulations are discussed in detail. It is expected that the successful implementation of magnetic bearings for this space application will encourage the more widespread adoption in other space applications (e.g., fluid pumps, reaction wheels) that challenge conventional bearing technologies.
Aerodynamic Performance Investigation of Turbine in the Event of One Blade Primary Fracture Failure
Authors: Zhang Shenghui , Ding Shuiting , Qiu Tian 
Published: January 2021

Abstract
One of major safety requirements from current airworthiness regulations is that the probability of hazardous engine effects should not occur exceed 10−7 per engine flight hour even in the event of component failure. Service experience of aeroengines indicates that turbine blade fracture is a common fault whose probability is far more than 10−7 per engine flight hour. It is obvious that overall engine system will be affected by blade failure. So, aerodynamic performance investigation in the event of one blade fracture failure has been assessed in the current study. With ANSYS-CFX, numerical model of GE-E3 (Energy Efficient Engine) high pressure turbine was established according to literature data. By comparing surface Mach number distribution at mid-span of vane in the first stage obtained numerically and experimentally, the most efficient turbulence model, i.e., the SST k-ω model, was identified. Based on the model, the 3-dimensional flow simulations under two configurations, full wheel geometry GE-E3 high pressure turbine without and with one blade fracture failure have been achieved. The following conclusions were drawn from 3-dimensional simulations: firstly, as for GE-E3 high pressure turbine, the effect of single turbine blade failure on turbine characteristics is slight; secondly, with blade loading coefficient as a criterion which is used for judging whether blade is affected, five blades which are significantly affected can be identified, and the surface pressure distributions of these five affected blades alter to varying degrees, accord-ingly, these film outflow static pressure characteristics alter as well; thirdly, after turbine blade fails, airflow accelerates violently along the suction side of downstream blade closest to failed blade and separates, however, air flow can not expand efficiently along the pressure side of upstream blade nearest to failed blade.
Experimental Investigation of Tip Design Effects on the Unsteady Aerodynamics and Heat Transfer of a High Speed Turbine
Authors: Cernat Bogdan , Lavagnoli Sergio 
Published: January 2021

Abstract
While modern engine manufacturers devote significant efforts to the development of reliable and efficient machines, the introduction of novel, optimized components in the hot gas path represents a risky opportunity. Accurate experimental and numerical data are critical to assess the impact of new technologies on the harsh engine environment. The present study addresses the impact of a selection of high-performance rotor blade tips on the aerodynamic and heat flux field of a high pressure turbine (HPT) stage. A combined numerical and experimental approach is employed to characterize the interaction of the tip leakage flow with the rotor secondary flows and the casing heat transfer mechanisms for each individual tip geometry. The turbine stage is tested at engine-scaled conditions in the rotating turbine facility of the von Karman Institute. For the present study, the turbine rotor is operated in rainbow configuration to allow the simultaneous testing of multiple blade tip geometries. RANS simulations are employed to predict the aerodynamic and thermal field of the individual profiles using test-calibrated boundary conditions. Isothermal steady computations are performed at different wall temperatures to compute the adiabatic wall temperature and heat transfer convective coefficient. Low-order models are used to represent the over-tip thermal field and the driving heat transfer mechanisms. The time-resolved outlet flow is characterized using a vortex tracking technique and high frequency aerodynamic measurements to identify the rotor secondary flow structures.