bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bearing Fault Detection on Wind Turbine Gearbox Vibrations Using Generalized Likelihood Ratio-Based Indicators
Authors: Kestel Kayacan , Peeters Cédric , Antoni Jérôme , Sheng Shawn , Helsen Jan 
Published: October 2022

Abstract
Studies in condition monitoring literature often aim to detect rolling element bearing faults because they have one of the biggest shares among defects in turbo machinery. Accordingly, several prognosis and diagnosis methods have been devised to identify fault signatures from vibration signals. A recently proposed method to capture the rolling element bearing degradation provides the groundwork for new indicator families utilizing the generalized likelihood ratio test. This novel approach exploits the cyclostationarity and the impulsiveness of vibration signals independently in order to estimate the most suitable indicators for a given fault. However, the method has yet to be tested on complex experimental vibration signals such as those of a wind turbine gearbox. In this study, the approach is applied to the National Renewable Energy Laboratory Wind Turbine Gearbox Condition Monitoring Round Robin Study data set for bearing fault detection purposes. The data set is measured on an experimental test rig of a wind turbine gearbox; hence the complexity of the vibration signals is similar to a real case. The outcome demonstrates that the proposed method is capable of distinguishing between healthy and damaged vibration signals measured on a complex wind turbine gearbox.
Real Time Precursor Calculation for the Early Detection of Combustion Instabilities
Authors: Meloni R. , Giannini N. 
Published: October 2022

Abstract
The proper control of the pressure fluctuations inside the gas turbine combustors is becoming a key factor to contain the pollutant emissions and extend their operability limits, as a consequence of the leaner and leaner mixture the engines have to operate with. In this context, the mitigation of the combustion instabilities through active control strategies is nowadays taking more and more benefits from the most advanced data science techniques. The employment of such algorithms has not only the aim to detect an instability and bring the engine to operate in a stable window but, more and more often, to anticipate the rising of a dominant frequency in an early stage of growth, with advantages in terms of extension of the life of the mechanical components and, more importantly, the reduction of the number of startups.
In this context, the present papers presents a Reduced Order Model (ROM) derived from the Dynamic Mode Decomposition (DMD) algorithm that can be applied to analyze the time signals acquired by the pressure probes installed in a generic gas turbine combustor. The most useful information that are retrieved from the signal are the frequency content and the corresponding Growth Rate (GR). The latter parameter can be assumed to act like a precursor of the system instability, enabling the possibility to identify a potential issue well in advance with respect to the traditional approaches. This new method can pave the way to new control strategies, depending on the different kind of instabilities detected. Also these aspects will be addressed along this work, focusing the discussion on both thermo-acoustic instabilities and low-frequency tones associated to the flame extintion. Moreover, additional criteria that could be implemented along a control system based on this new methodology will be provided.
Evaluation of Different Regression Models Tuned With Experimental Turbine Cascade Data
Authors: Dellacasagrande Matteo , Lengani Davide , Paliotta Pietro , Petronio Daniele , Simoni Daniele , Bertini Francesco 
Published: October 2022

Abstract
In the present work linear and non-linear regression functions have been tuned with an extensive database describing the unsteady aerodynamic efficiency of low-pressure-turbine cascades. The learning strategy has been first defined using a dataset published in a previous work concerning the loss coefficient measured in a large-scale cascade for a large variation of the Reynolds number, the reduced frequency, and the flow coefficient. Linear models have been educated accounting for the Occam’s razor parsimony criterion, condensing the effects due to the parameter variation in few predictors. Then, these predictors have been used to generate an extended polynomial-base function, and an ℓ1-norm constrain has been included into the optimization process to promote sparsity. Different non-linear models have been also evaluated, introducing the formulation of Gaussian Processes for regression for different kernel functions. The capabilities of the models here tuned are compared by means of cross-validation global and local criteria. Cross-validated error and leverage distribution have been analyzed. The proper compromise between model accuracy and generalizability is identified as a Pareto front in the space of the cross-validation indicators. In addition, a new variance-based indicator for the identification of the best model among the candidate ones has been introduced and its capability in complementing the cross-validation analysis is here discussed.
The learning strategy has been finally replicated adopting an extremely large database, experimentally acquired in the framework of the extensive collaboration between the University of Genova and AvioAero. For confidentiality, results concerning this database are not shown in terms of response surface, but model performances are discussed in order to strengthen the strategy here adopted, that could be useful also to other research groups adopting their own data.
Theoretical Considerations for Scaling Convection in Overall Effectiveness Experiments
Authors: Bryant Carol E. , Rutledge James L. 
Published: October 2022

Abstract
An increasingly common experimental technique allows measurement of overall effectiveness by matching the Biot number between experimental and engine conditions. The measured overall effectiveness distribution correlates to the expected turbine component temperature distribution. While a good deal of work has been devoted to determining the appropriate flow conditions necessary to scale adiabatic effectiveness, very little attention has been paid to the subtleties beyond matching the Biot number that arise when performing experiments on a conducting model to determine overall effectiveness. Notably, the ratio of the internal and external heat transfer coefficient must be matched. The density ratio and more recently, the specific heat ratio, have been shown to play important roles in scaling adiabatic effectiveness; however, in the present work, we demonstrate the requirements for the coolant and freestream flow conditions required to conduct an appropriately scaled overall effectiveness experiment. Since the viscosity and thermal conductivity of the fluids (in addition to density and specific heat) play significant roles that influence heat transfer coefficient behavior, this gives rise to an additional nondimensional parameter that should, in theory, be matched to properly execute an overall effectiveness experiment.
In this paper, we demonstrate that this new nondimensional parameter will be matched provided that Pr∞, Prc, and Rec are matched in addition to the freestream Reynolds number and the advective capacity ratio. We demonstrate the validity of this requirement through computational fluid dynamics simulations, which are well-suited for this since the over-constrained requirements can be overcome by altering gas properties from the real values. Simulations of an internally cooled wall exposed to a hot freestream were performed with various gases to show the sensitivity of the overall effectiveness to these previously ignored requirements. An additional set of simulations on a film cooled plate reveals additional complexities when coolant mixes with the freestream gas.
Hot-Wire Anemometry in High Subsonic Organic Vapor Flows
Authors: Hake Leander , Sundermeier Stephan , Cakievski Leon , Bäumer Joshua , aus der Wiesche Stefan , Matar Camille , Cinnella Paola , Gloerfelt Xavier 
Published: October 2022

Abstract
The present contribution reports the outcome of an experimental and numerical investigation of the behavior of a constant-temperature hot-wire anemometer in the high subsonic flow up to a Mach number of 0.7 of the organic vapor Novec 649 at pressure and temperature levels of typical organic Rankine cycle (ORC) turbine applications. The experiments were carried out in the calibration section of a closed-loop organic vapor wind tunnel test facility enabling the independent variation of Reynolds numbers, Mach numbers, and total temperature within a certain range. It was found that the calibration and the determination of the sensitivity coefficients can be done in a way as proposed by de Souza and Tavoularis for air. The sensitivity coefficients for velocity and density were essentially equal for higher overheat ratios which support the interpretation of the signals and data reduction for turbulent quantities. Computational fluid dynamics (CFD) provided additional insight into potential real gas effects for hot-wire performance.
Abradable Seal Test Rig for Quantifying Abradable Material Performance During Labyrinth Seal Rubs in Centrifugal Compressors: Design and Test Results
Authors: Katcher Kelsi M. , Revak Thomas , Rimpel Aaron , Ratay Jeffrey , Brun Klaus 
Published: October 2022

Abstract
In centrifugal compressors, the shaft seal clearance is critical to equipment efficiency and performance. Applications employing very small seal clearances must rely on abradable materials in the stator (housing) to prevent damage to rotating components in the case of rubs. An interaction (or rub) between the rotating seal geometry and stationary seal material can occur while traversing critical speeds or during upset conditions or transients outside the normal, designed operating range of the compressor such as thermal transients or excessive vibrations. The standard abradable seal material for compressor applications is mica-filled PTFE, but alternative materials are required in applications with elevated temperatures, elevated pressures, or harsh environments where chemical resistance is necessary. The behavior of these various abradable materials during a rub event is not well understood and needs to be further quantified to allow for proper material selection for each compressor design.
In order to determine suitable alternative materials, a rub simulation test rig was developed to quantify the material wear characteristics and thermal stability of various seal samples. The test rig was designed with a 7.24-inch (184-mm) diameter rotating section with representative labyrinth seal teeth. The rotating shaft was coupled with a variable speed motor capable of operating up to 24,000 rpm, allowing for surface speeds up to 754 ft/s. A 180-degree abradable seal section was mounted concentric to the rotating shaft, which may be forced into the rotating seal teeth by a linear actuator to simulate the rub. The test rig was designed to accommodate various interaction rates, initially considering 0.1 and 1 mil/s (2.54 and 25.4 μm/s) to simulate a rub caused by thermal growth and a rub caused by vibration or bow, respectively. Furthermore, the test rig was equipped with an ambient heater and pressure enclosure to evaluate seal materials at elevated temperatures and with various gas compositions. This paper presents the design and capabilities of the abradable seal test rig as well as the initial rub test results for Fluorosint 500.
Scaling Flat Plate Overall Effectiveness Measurements
Authors: McNamara Luke J. , Fischer Jacob P. , Kernan Marta , Rutledge James L. 
Published: October 2022

Abstract
Low temperature experiments are often performed on models of cooled turbine components in order to predict the temperature of the actual turbine component at engine conditions. Designing the scaled experiment properly takes care beyond simply matching the freestream Reynolds number. For instance, it is well known that for the nondimensional surface temperature distribution, or overall effectiveness, to match that at engine conditions, the Biot number of the experimental model must match that of the engine component. Somewhat less clear is the method by which one must scale the coolant flow rate. Widely used for coolant flow rate parameters to be matched are the mass flux ratio (M), the momentum flux ratio (I), or more recently, the advective capacity ratio (ACR). The selection of coolant flowrate parameter has generally been driven based on the results of adiabatic effectiveness experiments and it remains unclear how well these parameters also allow for matched overall effectiveness, which is highly dependent on internal cooling. In the present work, overall effectiveness distributions were measured on a flat plate with three rows of zero-degree compound angle 7-7-7 shaped holes. The influence of various thermodynamic gas properties were examined using several foreign gases as the coolant while matching coolant flow rate parameters M, I, and ACR. It is shown that the thermal conductivity of the coolant plays an outsized role in the overall effectiveness, but this is not accounted with any of the traditional coolant flowrate parameters. With significant thermal conductivity variations possible between the coolant and freestream gas at both engine and experimental conditions, consideration of this effect is of vital importance to the experimentalist.
A Computational Approach to Aerothermal Analysis of Complex Internal Turbine Cooling Geometries
Authors: Coulton Ben , Murray Alexander V. , Ireland Peter T. 
Published: October 2022

Abstract
Gas turbine inlet temperatures continue to rise with increasing cycle thermal efficiency and specific power output. This has led to turbine inlet temperature far exceeding metal capabilities. The result of this is the need for more advanced cooling systems with increasingly complex manufactured internal features that provide higher convective efficiency more akin to transpiration cooling systems.
This paper begins by assessing a previously developed decoupled method for analysing double-wall cooling systems and identifies potential improvements. A modified method is proposed, termed a “semi-decoupled method”, whereby mainstream flow is not simulated. Instead, the mainstream flow properties are projected onto the external surface of the blade enabling the simulation to focus on the complex internal cooling features, thereby drastically reducing computational resource requirements. The cooling films formed by the effusion holes are calculated based on the outlet conditions from each hole and mapped by a correlation adapted from the literature and superimposed onto the external surface, mid-simulation. The film correlation is adapted to accurately capture experimentally observed trends by accounting for lateral spread as the films move downstream. The new method is used to assess how the geometric parameters of the double-wall system impact the cooling effectiveness of a turbine blade geometry.
Impact of HEFA Fuel Properties on Gaseous Emissions and Smoke Number in a Gas Turbine Engine
Authors: Undavalli Vamsikrishna , Hamilton Jerry , Ubogu Emamode , Ahmed Ihab , Khandelwal Bhupendra 
Published: October 2022

Abstract
The study aims to establish the behavior of hydro processed esters and fatty acids (HEFA), as a type of alternative fuel with a conventional Jet A-1 as a reference fuel using a GTCP85 aircraft auxiliary power unit (APU). The research evaluates the impact of fuel properties on emissions using HEFA (blends in 18 proportions) and Jet A-1. With increasing HEFA proportions in the fuel, it is observed that reduction of gaseous emissions is not absolute. No specific trend of gaseous emissions reduction, in terms of aromatic and hydrogen content, were observed for the 18 blend ratios tested. For 50:50 blend of HEFA and Jet A-1, which meets current American Society for Testing and Materials (ASTM) specifications D7566 as drop-in fuel to D1655, the average reduction of NOX, CO, UHC emissions in PPM are ∼ 40%, 18%, and 28%, respectively. In contrast, no significant difference observed in CO2 emissions as compared with Jet A-1. Furthermore, the smoke number is proportional to the aromatic fuel content, fuel density (at 15°C), and carbon content irrespective of load condition. Conversely, the smoke number tends to be inversely proportional to the hydrogen, Sulphur, iso-paraffinic, and heat content of the fuel. Finally, these findings will contribute to the knowledge of fuel properties on impact engine performance and emissions as the aviation industry moves towards 100% SAFs.
Turbine Vane Passage Cooling Experiments With a Close-Coupled Combustor-Turbine Interface Geometry Part 2: Describing the Coolant Coverage
Authors: Nawathe Kedar P. , Nath Aaditya R. , Kim Yong W. , Simon Terrence W. 
Published: October 2022

Abstract
The first stage gas turbine vane surfaces and endwalls require aggressive cooling. This two-part paper introduces a modified design of the combustor-turbine (C-T) interface, the ‘close-coupled interface,’ that is expected to increase cooling performance of vane passage surfaces. While the first part of the paper describes secondary flows and coolant transport in the passage, this part discusses the effects of the new C-T interface geometry on adiabatic cooling effectiveness of the endwall and vane surfaces. Compared to the traditional C-T interface, the coolant requirement is reduced for the same level of cooling effectiveness on all three surfaces for the new C-T interface design, confirming that it is an improvement over the previous design. The endwall crossflow is reduced by combustor coolant injection with the new interface leading to more pitchwise-uniform cooling of the endwall. For the pressure surface, increasing combustor coolant flowrate directly increases phantom cooling effectiveness and spreading of coolant away from the endwall. With the traditional passage vortex seen in the literature replaced by the impingement vortex of the present design, the suction surface receives less phantom cooling than does the pressure surface. However, cooling performance is still improved over that of the previous C-T interface design.
Impact of Operating Conditions and Axial Casing Grooves on the Evolution of Flow Structure Across Blade Rows in an Axial Compressor
Authors: Saraswat Ayush , Koley Subhra Shankha , Katz Joseph 
Published: October 2022

Abstract
Stereo-PIV measurements in a series of axial planes investigate the impact of operating conditions and semicircular axial casing grooves (ACGs) on the evolution of flow structure across multiple blade rows in an axial compressor. The field of view extends radially from the hub to the tip, and circumferentially over entire blade passages. The flow is examined at two operating conditions, namely pre-stall flow rate and near the best efficiency point (BEP) of the untreated casing. Previous studies in this machine have shown that the ACGs improve the stall margin significantly but reduce the peak efficiency. At pre-stall and with untreated casing, intermittent reverse axial flow near the casing induced by backflow vortices (BFVs), tip leakage vortex (TLV), and the leakage flow extend upstream of the rotor leading edge. Although more probable in front of the blade, this backflow occurs along the entire circumference. Inside the rotor, the tip region blockage is characterized by low axial and high circumferential momentum. This region expands radially inward as the flow evolves axially, extending to half of the span by the time it reaches the rotor trailing edge. In contrast, inward of the region affected by blockage, the axial velocity exceeds the spatially averaged value by well above 60%. This extreme nonuniformity diminishes rapidly as the flow enters the stator, resulting, except for the blade wakes, in a nearly uniform axial velocity distribution at the exit from the stator. Previous measurements focusing on the effect of ACGs on tip flows have established that they entrain portions of the TLV and the backward leakage flow, and the outflow from them causes periodic variations in flow angle near the blade tip leading edge. The current data reveals that the outflow with negative axial and circumferential velocity jetting out from the grooves upstream of the rotor generates axially aligned vortices on both sides of each jet. These vortices act as homogenizers by entraining the faster mid-span flow into the tip region, substantially reducing the axial velocity deficit in the spaces between grooves. Consequently, the blockage in the tip region and flow non-uniformity in the passage are reduced substantially. Indeed, passage-averaged velocity profiles obtained by averaging the data circumferentially highlight that the ACGs modify the flow structure over the entire span, increasing the axial velocity at the tip, and decreasing it near the hub. Near BEP, the blockage is confined to the tip region and differences in flow structure with or without ACGs become more subtle. The flow jetting out of the grooves, and axial vortices are weaker but do not vanish. Furthermore, interactions of the TLV with secondary flows entrained from the grooves into the passage cause circumferential expansion of its signature, which presumably affects the compressor performance adversely.
Investigation of Droplet Shedding in an Aeroengine Bearing Chamber Using Convolutional Neural Networks
Authors: Farbrother Katrina , Cagaeo Paloma Paleo , Johnson Kathy , Ambrose Stephen 
Published: October 2022

Abstract
More efficient aeroengines are needed to reduce the environmental impact of civil aviation. Design changes for increased efficiency mean that higher loads are transmitted through the bearings supporting the rotating shafts. Better bearing chamber design is needed to facilitate these improvements, meaning that higher design capability and therefore, and improved understanding of the two phase flow is required to support modelling of the bearing chamber for future design.
Nottingham University’s Bearing Chamber Rig (BCR) is designed to provide quantitative and qualitative two phase flow data in a simplified, representative bearing chamber geometry. Oil is introduced to the chamber via a rotating cup and static configuration and this paper presents data characterising droplet shedding into the chamber. High-speed imaging data is obtained at the 3 o’clock and 9 o’clock positions. Automated image processing is necessary due to the large quantities of data. A Convolutional Neural Network (CNN) has been developed and is used to detect droplets in the images and convert the data to a numerical format including droplet diameter and speed. The CNN used was trained using images from a different but similar experimental test rig and this paper shows that it can also detect droplets with good accuracy in the BCR.
The experimentally obtained droplet data provides better understanding of the two-phase flow behaviour in the test rig and by extension in an aeroengine bearing chamber. Droplet diameters, normalised against nominal film thickness immediately prior to shedding, are found to be around 1.0 and normalised Sauter Mean Diameters are between 1.1 and 1.6 with diameter not significantly affected by shaft speed or oil flowrate within the ranges investigated. Droplet velocities were found to be between 4% and 13% of the cup rim speed with the numerical value showing little variation over the investigated range. This diameter and velocity distribution information supports future design capability.