bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Pad and Liner Material Properties on the Static Load Performance of a Tilting Pad Thrust Bearing
Authors: Koosha Rasool , San Andrés Luis 
Published: November 2019

Abstract
Tilting Pad Thrust Bearings (TPTBs) control rotor axial placement in rotating machinery and their main advantages include low drag power loss, simple installation, and low-cost maintenance. The paper details a novel thermo-elasto-hydrodynamic (TEHD) analysis predictive tool for TPTBs that considers a 3D thermal energy transport equation in the fluid film, coupled with heat conduction equations in the pads, and a generalized Reynolds equation with cross-film viscosity variation. The predicted pressure field and temperature rise are employed in a finite element structural model to produce 3D elastic deformation fields in the bearing pads. Solutions of the governing equations delivers the operating film thickness, required flow rate, shear drag power loss, and the pad and lubricant temperature rises as a function of an applied load and shaft speed. To verify the model, predictions of pad sub-surface temperature are benchmarked against published test data for a centrally pivoted eight-pad TPTB with 267 mm in outer diameter operating at 4–13 krpm (maximum surface speed = 175 m/s) and under a specific load ranging from 0.69 to 3.44 MPa. The current TEHD temperature predictions match well the test data with a maximum difference of 4°C and 11°C (< 10%) at laminar and turbulent flow conditions, receptively.
Next, the TEHD predictive tool is used to study the influence of both pad and liner material properties on the performance of a TPTB. The analysis takes a whole steel pad (without a liner or babbitt), a steel pad with a 2 mm thick babbitt layer (common usage), a steel pad with a 2 mm thick hard-polymer (polyether ether ketone, e.g PEEK®) liner, and a pad entirely made of hard-polymer material, whose elastic modulus is just 12.5 GPa, only 6% that of steel. The bare steel pad reveals the poorest performance among all the pads as it produces the smallest fluid film thickness and consumes the largest drag power loss. For laminar flow operations (Reynolds number Re < 580), the babbitted-steel pad operates with the thickest fluid film and the lowest film temperature rise. For turbulent flow conditions Re > 800, the solid hard-polymer pad, however, shows a 23% thicker film than that in the babbitted pad and produces up to 25% lesser drag power loss. In general, the solid hard-polymer TPTB is found to be a good fit for operation at a turbulent flow condition as it shows a lower drag power loss and a larger film thickness, however, its demand for a too large supply flow rate is significant. Predictions for steel pads with various hard-polymer liner and babbitt thicknesses demonstrate that using a hard-polymer liner, instead of white metal, isolates the pad from the fluid film and results in an up to 30°C (50%) lower temperature rise in the pads than that for a babbitted-steel pad. For operations under a heavy specific load (> 3.0 MPa), however, a thick hard-polymer liner extensively deforms and results in a small film thickness.
Controlling Leakage Flows Over a Rotor Blade Tip Using Air-Curtain Injection: Part I — Aero-Thermal Performance of Rotor Tips
Authors: Yang Xing , Zhao Qiang , Liu Zhao , Feng Zhenping , Simon Terrence W. 
Published: November 2019

Abstract
The rotor casing of gas turbine engines is generally cooled with cooling air from compressors and then the cooling air is discharged into the passage flow of the rotor. In this paper, a novel design both for the blade tip leakage flow control and for the rotor casing and tip cooling is proposed. Cooling air is injected through a pair of inclined rows of discrete holes positioned between 30% and 50% axial chord downstream of the blade leading edge in the casing. The casing injection forms as air-curtain within the blade tip gap, and inhibits the development of the tip leakage flows and provides secondary-order cooling for the rotor tip. Air injection from the rotor casing onto flat and recessed blade tips is investigated using numerical simulations that is validated by extensive aerodynamic and heat transfer experimental data. Flow and film cooling over the blade tip and turbine overall aerodynamic performance are examined in detail for two casing injection rates. Comparisons between flat tip without casing injection (baseline) case and the casing injection cases show that the air-curtain injection significantly alters the flow structures near the casing by modifying the development and migration of the tip leakage flow. The air-curtain injection over the flat and recessed tips both generates turbine stage overall aerodynamic efficiency improvement due to the sealing effects of the casing injection, but the efficiency gain depends on the competing results between the sealing effects and the “over-blown” effects of the air-curtain injection. Applying a recess to the blade tip is generally detrimental to the efficiency improvement by the air-curtain injection. In addition to efficiency improvement, secondary-order cooling effects from the casing injection are found to provide considerable thermal protection for the blade tips. However, increasing injection rate reduces the film cooling performance over the rotor tip surfaces. The recessed tip could present better film cooling effectiveness than the flat tip in the presence of the air-curtain.
Controlling Leakage Flows Over a Rotor Blade Tip Using Air-Curtain Injection: Part II — Rotor Casing Film Cooling
Authors: Zhao Qiang , Yang Xing , Liu Zhao , Feng Zhenping , Simon Terrence W. 
Published: November 2019

Abstract
In modern gas turbine engines, the rotor casing region experiences high thermal loads due to complex flow structures and aerothermal effects. Thus, casing cooling is one of essential measures to ensure turbine service lifetime and performance. However, studies on heat transfer and cooling over the rotor casing with tip leakage flows are limited in the open literature during the past decades. The present work aims at controlling leakage flows over the blade tip and decreasing heat loads on the rotor casing. A novel approach proposed in a companion paper (GT2019-90232) is adopted in this paper as Part II by introducing an air-curtain injection from the rotor casing through a pair of inclined rows of discrete holes positioned in the range of 30% and 50% axial chord downstream of the blade leading edge in the casing. This air-curtain injection approach is applied to flat and recessed tips with and without tip injection to evaluate its sealing capability on tip leakage flows and film cooling effectiveness on the casing for two injection ratios of 0.7% and 1.0%. In this paper, Reynolds-averaged Navier-Stokes (RANS) simulations with Shear Stress Transport (SST) k-ω turbulence model and γ-Reθ transition model, which are validated with relevant experimental data, are performed to investigate tip leakage flows and film cooling effectiveness on the casing in a single-stage, high-pressure gas turbine engine. Results show that casing injection can reduce tip leakage mass flow effectively by changing the development and migration of tip leakage mass flows, especially when the recessed tip is applied. Adding tip injection would further reduces the tip leakage. The casing injection also provides an excellent cooling effect on the casing across rotor middle chord through trailing edge regions. In the presence of the recessed tip, coolant spreads out well on the rotor tip and the casing surfaces, resulting in better film cooling effectiveness on the casing over rotor tip leading edge. In addition, the tip injection could provide an extra cooling effect in some other regions of the casing.
Impact of Damper Placement on the Stability Margin of an Annular Combustor Test Rig
Authors: Betz Michael , Zahn Max , Hirsch Christoph , Sattelmayer Thomas 
Published: November 2019

Abstract
In the presented study a lab scale lean-premixed annular combustor comprising different axial and azimuthal patterns of dampers as well as several symmetrical and unsymmetrical damper placement patterns is investigated in five steps:
In the first step the number of the dampers is increased considering only optimal distributions obtained from literature. As a result a nearly linear increase of damping with the number of dampers is observed.
Second, other damper patterns are examined, which perform worse than the ideal distributions. It can be seen that a mode split can lead to differing damping rates of the two decomposed modes. In the worst case one of the modes isn’t damped any stronger than in the baseline measurement without any dampers.
A number of selected representative circumferential damper patterns is investigated at two axial locations. It is generally observed that the axial position has an influence on damper performance as the upstream configurations with dampers in the flame region perform better than the downstream configurations.
Using an optimum configuration with four dampers equally distributed around the circumference the increase of the window of operation of the annular combustor test rig in terms of equivalence ratio and thermal power is demonstrated.
The azimuthal distribution of the dynamic pressure amplitude of the annular combustor test rig is determined and compared with the local damping rate. A correlation can be found which reveals that already very moderate damping rates lead to very low dynamic pressure amplitudes.
Impact of Combustion Chamber Dynamics on the Temperature Distribution in a Resonator
Authors: Betz Michael , Zahn Max , Hirsch Christoph , Sattelmayer Thomas 
Published: November 2019

Abstract
The results of an experimental study on the influence of the purge air mass flow and the acoustic pressure in an annular combustor test rig on the temperature distribution in resonators with perforated plates at the exit are provided in the paper. The amplitude of the acoustic pressure in the combustor is found to have a high impact on the mean temperature and thus on the performance of the resonators, which originates primarily from the temperature sensitivity of the effective eigenfrequency.
In the experiments the temperature in the cavity of one of the resonators is spatially and temporally resolved at 13 locations. The dependence of the mean temperature change on the combustor amplitudes and the purge air mass flow is measured quantitatively. In addition, the axial temperature gradient of the resonator is resolved. The mean temperature changes up to 8% depending on the level of siren forcing. Using acoustic pressure data from the cavity, the velocity of the hot gas jets periodically entering the resonator is calculated.
If high amplitudes occur in the combustor and there is no adequate purge air flow in the resonators then hot gas ingestion into the cavity of the resonator occurs, leading to detuning of the resonator and the breakdown of its performance. Once hot gas ingestion occurs, the resonator quickly heats up within a few seconds as the generation of the mixture of hot gas and purge air requires only a low number of cycles. This leads to a thermal runaway of the frequency range of the resonator with high damping. When the combustor returns to quiet operation, a cooling phase with two different time constants is observed.
Modeling and Quantification of Acoustic Damping Induced by Vortex Shedding in Non-Compact Thermoacoustic Systems
Authors: Hofmeister Thomas , Hummel Tobias , Schuermans Bruno , Sattelmayer Thomas 
Published: November 2019

Abstract
This paper presents a methodology to compute acoustic damping rates of transversal, high-frequency modes induced by vortex-shedding. The acoustic damping rate presents one key quantity for the assessment of the linear thermoacoustic stability of gas turbine combustors. State of the art network models — as employed to calculate damping rates in low-frequency, longitudinal systems — cannot fulfill this task due to the acoustic non-compactness encountered in the high-frequency regime. Furthermore, it is yet unclear, whether direct eigensolutions of the Linearized Euler Equations (LEE), which capture the mechanism of vortex shedding, yield correct damping rate results constituted by the implicit presence of acoustic as well as hydrodynamic contributions in these solutions. The methodology’s applicability to technically relevant systems is demonstrated by a validation test case using a lab-scale, swirl-stabilized combustion system.
High Resolution Measurements of Heat Transfer, Near-Wall Intermittency, and Reynolds-Stresses Along a Flat Plate Boundary Layer Undergoing Bypass Transition
Authors: Albiez Holger , Gramespacher Christoph , Stripf Matthias , Bauer Hans-Jörg 
Published: November 2019

Abstract
A new experimental dataset focusing on the influence of high free-stream turbulence and large pressure gradients on boundary layer transition is presented. The experiments are conducted in a new wind tunnel equipped with a flat plate test section and a new kind of turbulence generator which allows for a continuous variation of turbulence intensity. The flat plate features an elliptic nose and is mounted midway between contoured top and bottom walls. Two different wall contours can be implemented to create pressure distributions on the flat plate that are typical for the pressure and suction side of high pressure turbine cascades. A large variation of Reynolds number from 3.0 · 105 to 7.5 · 105 and inlet turbulence intensity between 1.1 % and 8 % is realized, resulting in more than 100 test cases. Measurements comprise highly resolved heat transfer, near-wall intermittency and free-stream Reynolds stress distributions. Near-wall intermittency is measured using a traversable hotfilm sensor embedded in a steel-belt that is running around the flat plate while free-stream Reynolds stresses are measured simultaneously at the same position with a revolvable X-wire probe. Additionally, turbulent length scales are analyzed using the X-wire signal along the flat plate. Results show that heat transfer and near wall intermittency distributions are in good agreement and that heat transfer at high turbulence levels increases prior to the formation of first turbulence spots. Transition onset is found to be influenced by the turbulence Reynolds number, i.e. turbulent length scales. At constant inlet turbulence intensity, transition onset moves upstream, when the turbulent Reynolds number is decreased.
Investigation on the Degree of Reaction in Twin Scroll Radial Turbines at Different Operating Conditions for Turbocharging Applications
Authors: Cravero Carlo , De Domenico Davide , Ottonello Andrea 
Published: November 2019

Abstract
Frequently in turbocharging radial turbine studies, some assumptions have to be done in order to make 1D matching calculations as easy as possible and to develop simulation approaches that can be useful for different purposes, like axial thrust prediction. One of these assumptions concerns the degree of reaction, which is often considered constant and equal to the value 0.5. In standard radial turbines design the velocity triangles are set by the target to keep a mean degree of reaction of 50%, in order to obtain low rotor losses and to minimize the exit swirl to get lower losses in the exhaust diffuser. From the experience gained on radial turbines operating in a wide range of conditions, it is evident that: the degree of reaction presents large variations along a given isospeed (especially at low rotational speed) and the mean value is far from 0.5 (particularly true in high performance applications). In the present work a method for the representation of the degree of reaction for radial turbine is suggested. The approach has been developed onto a twin scroll radial turbine for turbocharging, considering a large dataset of operating conditions (at both equal and partial admission). The discussion and the method suggested are based on a rich database from experimental data and numerical simulations developed by the authors on the 3D configuration of the turbines under investigation.
Pressure-Sensitive Paint Measurements in Narrow Clearances: A Feasibility Study
Authors: Zimmermann Anna-L. , Graiff Mattia , Nguyen Tran Q. Tue , Guemmer Volker 
Published: November 2019

Abstract
Pressure distribution in the bearing clearance of aerostatic bearings has received great attention since it has fundamental influence on the performance of the bearing. Thus, it is important to seek for accurate and global pressure distribution measurements. Pressure-sensitive paint (PSP) therefore qualifies as a promising measuring technique. It is of non-invasive nature, and hence eliminates many of the otherwise unavoidable drawbacks of conventional pressure taps. This paper introduces a conceptual test configuration aiming for employing PSP as measuring technique in narrow clearances. It is a pilot study including hardware modifications as well as considerations of an appropriate choice of paint, imaging equipment and calibration method. The effect of the coat surface quality is discussed, and a scaling methodology is proposed to transfer the high pressure conditions from machine to test rig conditions, so that PSP measurements are possible.
Unsteady Analysis of Adiabatic Film Cooling Effectiveness Behind a Row of Circular Holes Fed by Internal Crossflow
Authors: Qenawy Mohamed , Zhou Wenwu , Chen Han , Shao Hongyi , Peng Di , Liu Yingzheng 
Published: November 2019

Abstract
The adiabatic film cooling effectiveness behind a single row of circular holes fed by internal crossflow was measured by fast-response pressure-sensitive paint technique. During the experiment, the coolant flow was discharged from the coolant holes via either plenum or crossflow channel. The test model has a row of circular holes with 3D spacing, 6.5D entry length, and 35° inclination angle. Two blowing ratios (M = 0.40 and 0.80) were tested with a density ratio of 0.97. A numerical steady-state RANS simulation, using SST k-ω and Realizable k-ε turbulence models, was conducted to understand the internal crossflow behaviors. The unsteadiness caused by the flow structures (counter-rotating vortex pair (CRVP) and horseshoe vortex) was quantified by the root mean square and the cross-correlations. In addition, the proper orthogonal decomposition was used to identify the large-scale unsteady coherent structures and their contributions. The fluctuations of the crossflow feed were asymmetric, which were significantly weaker compared with the plenum case. The CRVP, as the most significant coherent structures, were demonstrated to play the main role in the unsteadiness of the crossflow feed.
Wet Gas Compressor Modeling and Performance Scaling
Authors: Bakken Martin , Bjørge Tor , Bakken Lars E. , Lakshmanan Ajay , Arulselvan Suriya 
Published: November 2019

Abstract
Today, a few subsea compressor systems are already operating while several new installations are expected within the next years. This creates a need for dynamic simulation tools to ensure proper system design and to facilitate production. The well-known process simulator Hysys Dynamics has been extended to include wet gas compressors, which includes the possibility for the user to input multiple performance curves based on the inlet gas/liquid content.
The current paper analyzes the accuracy of the compressor performance procedure within the simulation model when operating with multiple wet performance curves. The findings have been validated against both air/water and hydrocarbon performance data. Further, the affinity laws have extensively been used by the industry and within process simulation tools for performance scaling. Experimental data from the wet gas compressor test facility at the Norwegian University of Science and Technology (NTNU) have been used to validate the applicability of the affinity laws in wet gas flow. The test facility is an open loop configuration consisting of a single shrouded centrifugal impeller, a vaneless diffuser and a circular volute.
The test reveals that the compressor performance procedure within the model provides accurate results in both air/water and hydrocarbon flow. Further, for the given application the affinity laws yield a satisfactory estimation in wet gas flow.
Diagnostics of Fatigue Crack in the Shaft Using Spectral Kurtosis
Authors: Rathna Prasad Sagi , Sekhar A. S. 
Published: November 2019

Abstract
Rotating machinery components like shafts subjected to continuous fluctuating loads are prone to fatigue cracks. Fatigue cracks are severe threat to the integrity of rotating machinery. Therefore it is indispensable for early diagnostics of fatigue cracks in shaft to avoid catastrophic failures. From the literature, it is evident that the spectral kurtosis (SK) and fast kurtogram were used to detect the faults in bearings and gears. The present study illustrates the use of SK and fast kurtogram for early fatigue crack detection in the shaft using vibration data. To perform this study, experiments are conducted on a rotor test rig which is designed and developed according to the function specification proposed by ASTM E468-11 standard. Fatigue crack is developed, on three shaft specimens, each seeded with the same circumferential V-Notch configuration, by continuous application of stochastic loads on the shaft using electrodynamic shaker in addition to the unbalance forces that arise in normal operating conditions. Vibration data is acquired from various locations of the rotor, using different sensors like miniature accelerometers, laser vibrometer and wireless telemetry strain gauge, till the shaft specimen develops fatigue crack. The analysis results show that the combination of SK and fast kurtogram is an effective signal processing technique for detecting the fatigue crack in the shaft.
Advanced Control System for Grid-Connected SOFC Hybrid Plants: Experimental Verification in Cyber-Physical Mode
Authors: Ferrari Mario L. , Rossi Iacopo , Sorce Alessandro , Massardo Aristide F. 
Published: November 2019

Abstract
This paper presents a Model Predictive Controller (MPC) operating an SOFC Gas Turbine hybrid plant at end-of-life performance condition. Its performance was assessed with experimental tests showing a comparison with a Proportional Integral Derivative (PID) control system. The hybrid system operates in grid-connected mode, i.e. at variable speed condition of the turbine. The control system faces a multivariable constrained problem, as it must operate the plant into safety conditions while pursuing its objectives. The goal is to test whether a linearized controller design for normal operating condition is able to govern a system which is affected by strong performance degradation. The control performance was demonstrated in a cyber-physical emulator test rig designed for experimental analyses on such hybrid systems. This laboratory facility is based on the coupling of a 100 kW recuperated microturbine with a fuel cell emulation system based on vessels for both anodic and cathodic sides. The components not physically present in the rig were studied with a real-time model running in parallel with the plant. Model output values were used as set-point data for obtaining in the rig (in real-time mode) the effect of the fuel cell system.
The result comparison of the MPC tool against a PID control system was carried out considering several plant properties and the related constraints. Both systems succeeded in managing the plant, still the MPC performed better in terms of smoothing temperature gradient and peaks.