bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of an Alternative Approach for Cutting Force Determination in Broaching
Authors: Bergs Thomas , Döbbeler Benjamin , Seelbach Tobias , Seimann Martin , Klocke Fritz
Published: November 2019

Fir tree slots in turbine discs are used as an attachment between the disc and the blades. To a great extend, these slots are manufactured by broaching. Currently, the used cutting tool material is High Speed Steel (HSS). Due to its low high temperature stability, the manufacturing process is limited to low cutting speeds (vc = 2–5 m/min) and presents, therefore, a bottleneck in the turbine manufacturing process. To increase the productivity, cemented carbide can be used as cutting tool material with cutting speeds up to five times higher than those used for HSS. Due to the high safety demands, the broaching process requires extensive process design to ensure a high process reliability. For the tool design, profound knowledge of the mechanical loads is mandatory due to its major effect on the manufactured part. Empirical research to investigate the actual mechanical load is time-consuming and expensive due to high tool costs, especially of cemented carbide broaches, and the high amount of possible tool geometry combinations. In this paper, an alternative approach to determine the cutting forces is presented. Grooving experiments were conducted in order to reproduce the engagement conditions from the broaching process. If the transferability of this approach can be shown, the amount of broaching tools as well as the availability of a broaching machine tool for the design of new broaching tools can be decrease dramatically. This would result in a reduction of tool design time and an increase in productivity for tool manufacturers.
Loss in Axial Compressor Bleed Systems
Authors: Grimshaw S. D. , Brind J. , Pullan G. , Seki R.
Published: November 2019

Loss in axial compressor bleed systems is quantified, and the loss mechanisms identified, in order to determine how efficiency can be improved. For a given bleed air pressure requirement, reducing bleed system loss allows air to be bled from further upstream in the compressor, with benefits for the thermodynamic cycle. A definition of isentropic efficiency which includes bleed flow is used to account for this. Two cases with similar bleed systems are studied: a low-speed, single-stage research compressor and a large industrial gas turbine high-pressure compressor.

A new method for characterising bleed system loss is introduced, using research compressor test results as a demonstration case. A loss coefficient is defined for a control volume including only flow passing through the bleed system. The coefficient takes a measured value of 95% bleed system inlet dynamic head, and is shown to be a weak function of compressor operating point and bleed rate, varying by ±2.2% over all tested conditions. This loss coefficient is the correct non-dimensional metric for quantifying and comparing bleed system performance.

Computations of the research compressor and industrial gas turbine compressor identify the loss mechanisms in the bleed system flow. In both cases, approximately two-thirds of total loss is due to shearing of a high-velocity jet at the rear face of the bleed slot, one quarter is due to mixing in the plenum chamber and the remainder occurs in the off-take duct. Therefore, the main objective of a designer should be to diffuse the flow within the bleed slot. A redesigned bleed slot geometry is presented that achieves this objective and reduces the loss coefficient by 31%.
Effects of Labyrinth Fin Wear on Aerodynamic Performance of Turbine Stages: Part II — Mushrooming Damages
Authors: Dai Xinbo , Yan Xin
Published: November 2019

The main function of labyrinth seal is to control leakage flow in clearance that involves with rotating and stationary parts. Therefore, the effective of clearance gap in labyrinth seal is critical to sealing, heat transfer and vibration characteristics. However, due to the mechanical expansions, vibrations, thermal stress, misalignment of seal components in transient periods of startup, shutdown and hot restart, the stationary and rotating parts of the labyrinth seal are likely to contact each other, causing wear damages in labyrinth fin. Mushrooming damages are often occurred in the rubbing events when labyrinth fin is made of soft material compared with the opposite component. To investigate how mushrooming damage affects the leakage performance of labyrinth seal, many numerical and experimental studies have been carried out in last decades. However, little attention has been paid on the influence of labyrinth fin mushrooming on aerodynamic performance of turbine stages. In this study, using the RANS equations solution methods, the effect of labyrinth fin mushrooming on isentropic efficiency, leakage rates, outlet flow angles, reaction degrees, profile static pressure distributions and flow fields in turbine stages were investigated at three different mushrooming radii and three effective clearances. It shows the leakage rate is increased with increasing the mushroom radius and effective clearance. At the same effective clearance, as the mushrooming radius increases from 0.2mm to 0.4mm, the leakage rate is increased by about 0.19–0.32%, and the overall isentropic efficiency is decreased by 0.78%. At the same mushrooming radius, as the effective clearance increases from 1mm to 1.4mm, the leakage rate is increased by 0.21–0.31%, and the overall isentropic efficiency is decreased by 0.65%. As mushroom radius and effective clearance increase, the secondary flows near hub and shroud are intensified and developed along axial direction, causing pronounced aerodynamic loss in turbine stages.
Predicting the Adiabatic Effectiveness of Effusion Cooling by the Convolution Modeling Method
Authors: Yang Li , Rao Yu
Published: November 2019

Effusion Cooling has a strong potential in protecting hot section components of gas turbines engines such as turbine blades, endwalls and combustor liners. By carefully distributing the cooling holes adaptively to the external thermal load, effusion cooling can dramatically reduce the temperature and thermal stress for the protected components. However, the effectiveness for effusion cooling was not easy to correlate due to the numerous parameters to study and the significant variation from the upstream to the downstream. Conventional equations used in the literature were insufficient to express the complex mechanism for effusion cooling and consequently utilized averaged parameters as variables. This study proposed a convolution method to model the local adiabatic cooling effectiveness for the entire effusion cooled surfaces. The new model treated the cooling hole distribution as an input matrix and applied convolution networks to predict the cooling effectiveness. Compared with conventional correlations, this network based model provided extensive details of the cooling effectiveness distribution while consuming computational time as short as correlations. Training of the proposed model was based on the numerical simulation results of three geometries and the validation was conducted for two additional geometries. Results indicated high accuracy and high robustness of the convolution model. With the aid of this novel model, further designing could adjust hole distribution in a random manner instead of using rows and columns, and generate adaptive effusion cooling based on thermal load.
Experimental Analysis of a Micro Gas Turbine Combustor Optimized for Flexible Operation With Various Gaseous Fuel Compositions
Authors: Bower Hannah E. , Schwärzle Andreas , Grimm Felix , Zornek Timo , Kutne Peter
Published: November 2019

With the push to curb dangerous atmospheric pollutant production, energy generation technologies that reduce green-house gas emissions, while still providing adequate electrical supply are of high importance. With major energy infrastructure already in place, developing enhanced pollutant-reducing combustor systems for micro gas turbines (MGTs), that can utilize low calorific fuels from renewable resources, is a major goal.

The current work focuses on the experimental testing of an optimized two-stage combustor designed to operate with various fuel types, including natural gas and syngas produced via biomass gasification. Atmospheric experimental tests were performed and the results indicate larger flame lift-off heights and slightly higher CO gas emissions levels, while displaying lower NOx gas emissions levels for all thermal loads and air-to-fuel equivalence ratios tested, compared to that of the previous combustor designs. Additionally, steady state CFD simulations were conducted and the results are in general good agreement with the experimental data. Overall, the results indicate high fuel flexibility of the combustor, as well as the ability to comply with the NOx emissions limits for a larger range of operating points, compared to that of the previously tested combustors.
A Reduced Model for Air Foil Journal Bearings for Time-Efficient Run-Up Simulations
Authors: Zeise Pascal , Mahner Marcel , Bauer Marcel , Rieken Markus , Schweizer Bernhard
Published: November 2019

This paper introduces a time-efficient reduced model for gas foil bearings. The foil structure of the considered air foil bearing can be modeled very realistically by a quasistatic nonlinear stiffness/friction hysteresis model; the gas film is assumed to be stiff enough to be neglected for the nonlinear forced response analysis. The main objective is to carry out nonlinear simulations of rotors with foil bearings in time domain. An important feature of the model is to enable fast run-up simulations, while maintaining important physical properties of the bearing. Furthermore, the determination of the model parameters should be simple to enable a fast adaption of new foil bearing geometries into existing rotor models. Finally, it should be possible to implement the bearing model very easily into arbitrary rotordynamic or multibody software tools. The basis of the approach is a two-dimensional hysteresis model, which approximates the nonlinear relationship between the movement of the rotor journal and the corresponding bearing forces. Although the here presented reduced bearing model cannot predict instability effects generated by the air film, the model may capture the nonlinear behavior of the foil bearing accurately. Hence, the nonlinear response of the rotor-bearing system may be predicted very precisely, if the rotor speed is below the threshold speed of instability. The input data for the reduced bearing model are measured or simulated hysteresis curves. The relevant parameters that influence the accuracy and the limits of the numerical model are discussed. Different simulations with very detailed finite element bearing models are presented in order to demonstrate the accuracy of the reduced modeling approach.
Heat Transfer Enhancement for Gas Turbine Blade Leading Edge Cooling Using Curved Double-Wall/Vortex Cooling With Various Disturbing Objects
Authors: Fan Xiaojun , Li Liang , Wang Jiefeng , Wu Fan
Published: November 2019

A new double-wall cooling configuration combined with the vortex cooling is established to study the cooling behavior for the gas turbine blade leading edge. This configuration consists of multiple nozzles, a curved inner cooling passage, a row of bridge holes and a curved outer cooling passage with 4 kinds of disturbing objects (namely smooth wall, pin-fins, dimples and protrusions). Numerical simulations are performed based on the 3D viscous steady Reynolds Averaged Navier-Stokes (RANS) equations and the k-ω turbulence model. The cooling behavior of the Double-wall/vortex cooling configuration is compared with the Double-wall/impingement cooling configuration at the same conditions. Generally, the Double-wall/vortex cooling configuration has a better cooling performance. It is found the Nusselt number of the inner surface for the Double-wall/vortex cooling configuration is 46.7% higher. However, the Double-wall/impingement cooling configuration has a smaller friction coefficient and a total pressure loss. Different disturbing objects have significant influences on the heat transfer performance of the outer surface. The Nusselt number of disturbing objects (pin-fins, dimples and protrusions) is much higher than the smooth wall, and the value is 1.27–2.22 times larger. Configuration with protrusions has the highest globally-averaged Nusselt number. For the heat transfer performance of the inner surface and the total pressure loss coefficient, disturbing objects have no obvious influence. As bridge holes row increases, the overall cooling performance is improved. The globally-averaged Nusselt number of the outer target is enhanced while the total pressure loss is reduced.
Experimental and Numerical Investigation on an Additively Manufactured Gas Turbine Ring Segment With an In-Wall Cooling Scheme
Authors: Wimmer Thomas , Ruehmer Tobias , Mick York , Wang Lieke , Weigand Bernhard
Published: November 2019

An additively manufactured ring segment (AMRS) for the first row of a large gas turbine from Siemens was designed with a novel cooling scheme. The wavy rectangular channels used for in-wall cooling are only viable through Additive Manufacturing (AM). Manufacturing deviations have been tracked using an optical 3D measuring system and were accounted for in the calculation models for thermal analysis. Friction factors of the cooling channels have been investigated experimentally allowing accurate flow prediction. The AMRS was tested in an engine at “Full Speed – Full Load” operating condition. It was instrumented with thermocouples and pressure taps. All crucial engine operating conditions were monitored. The results are compared to a conventional ring segment with similar instrumentation. It was installed next to the AMRS in the wake of the same burner. From a thermal model of the conventional ring segment and the measured temperatures the external boundary conditions are scaled to fit the experimental data. These were applied to the thermal model of the AMRS which was used for performance evaluation of the cooling scheme. This work addresses and quantifies the application of AM on advanced gas turbine cooling schemes. The AMRS underwent a mechanical integrity investigation in a referenced publication.
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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Loop Filling and Start Up With a Closed Loop sCO2 Brayton Cycle
Authors: Cich Stefan D. , Moore J. Jeffrey , Day Towler Meera , Mortzheim Jason , Hofer Douglas
Published: November 2019

Recent testing has been performed on a 1 MWe sCO2 closed loop recuperated cycle under funding from the US DOE Sunshot initiative and industry partners. Some of the goals of this funding included the development of a 1 MWe loop, a 10 MWe turbine, and performance and mechanical testing. One of the key challenges that presented itself was the filling, start-up, and shut down of the entire system. Understanding the loop transient performance is important when having to bring a turbine online, transitioning from peak to partial loading, and also managing routine and emergency shut downs. Due to large changes in density near the critical point for CO2 and its tendency to form dry ice when expanded to atmospheric pressure, managing loop filling and venting is critical in ensuring that components do not get damaged. Specific challenges were centered on protecting the dry gas seals, maintaining proper mass in the loop, and also thermal transients during trips. This paper will take a detailed look at the challenges encountered during start up and shut downs, and also the solutions that were implemented to successful transition between different phases of the testing.
Verification of Combined Main Steam Valve Pressure Distribution and Vibration Characteristics With Downscale Model Test on Air Condition
Authors: Suzuki Fumiyuki , Nishida Shingo , Fukao Shinji , Tsuruta Megumu
Published: November 2019

In order to enhance the efficiency and reduce the manufacturing cost of steam turbine, combined main steam valve consisting of main stop valve and control valve in the same casing has been developed. Combined main steam valve with improved flow path at internal structure will reduce pressure loss. A downscale model test on air condition was conducted to verify pressure distribution characteristics. Experimental result and numerical result obtained by computational fluid dynamics (CFD) showed reasonable agreement in pressure loss and static pressure at each flow point within the design operation range. Main stop valve (SV) and control valve (CV) vibration characteristics tests were performed simultaneously for the stability verification of governing operation from start up to full load. We confirmed that CV aerodynamic added damping ratio was positive under all measured condition of CV stroke and pressure ratio, and self-excited vibration was not generated. We also confirmed that pressure fluctuation acting on main stop valve body was sufficiently small within the operation range. Meanwhile, in the case where pressure ratio or CV stroke deviated from the operation range, pressure fluctuation around main stop valve increased. Based on CFD result and detailed analysis of experimental result, it was found that steam flow along valve seat separates periodically, which revealed the mechanism of increasing pressure fluctuation around main stop valve. By reflecting on these results, the reliability of new combined main steam valve has substantially been enhanced.
Limiting Inlet Conditions for Phase Change Avoidance in Supercritical CO2 Compressors
Authors: Allison Timothy C. , McClung Aaron
Published: November 2019

In many supercritical CO2 cycle implementations, compressor or pump inlet conditions are relatively near the two-phase region. Fluid acceleration near the compressor inlet can result in the potential for condensation or cavitation at the inlet. Despite potential mitigating effects or evidence in the literature, potential two-phase operation is a high-risk condition and may not be recommended for high-reliability system design. This paper presents a summary of the existing literature documenting inlet phase change in sCO2, and presents an analysis of required conditions to avoid phase change as a function of inlet pressure, temperature, and Mach number. Static conditions at the inlet are calculated based on the real gas approach documented in ASME PTC-10, Appendix G. In addition, various total-to-static iteration challenges are discussed and avoided through solution of the inverse problem to convert limiting static conditions at saturation to the full range of limiting total conditions for various Mach numbers up to 1.0. The results show that a threshold total temperature exists above which phase change cannot occur, ranging from 31.1 to 66.95 °C and increasing with Mach number. Lower temperatures below this threshold may also avoid phase change depending on the total pressure. The documented results are useful as a reference for use by cycle designers to impose design limits that minimize risks associated with two-phase flow in the compressor.
Flow Mechanism and Loss Analysis of Tip Leakage Flow With Delayed Detached Eddy Simulation
Authors: Li Hui , Bian Xiutao , Su Xinrong , Yuan Xin
Published: November 2019

The complex leakage flow structure in the tip region of unshrouded rotor is a main source of turbine aerodynamic loss. Due to the complex turbulence characteristics of the tip leakage flow, the widely used Reynolds Averaged Navier-Stokes (RANS) approach may fail to accurately predict the multi-scale turbulent flow and the related loss. In order to effectively improve the turbine efficiency, more insights into the turbulence characteristics and the loss mechanism in the tip leakage flow are required. In this work, a Delayed Detached Eddy Simulation (DDES) study is conducted to simulate the flow inside a high pressure turbine blade, with emphasis on the tip region. DDES results are in good agreement with the experiment and the comparison with RANS results verifies the advantages of DDES in resolving finer flow structures of leakage flow, also in capturing the complex turbulence characteristics. The snapshot Proper Orthogonal Decomposition (POD) method is used to extract the dominant flow features. The flow structures and the distribution of Reynolds stress help to reveal the process of leakage flow and its interaction with the secondary flow. Meanwhile, it is found that the separation vortex (SV) forms from leading edge to trailing edge, and the strong interactions between tip leakage vortex (TLV) and passage secondary vortex (PSV) significantly enhance the turbulence intensity. Based on the DDES results, loss analysis of tip leakage flow is conducted based on entropy generation rates. For the leakage flow related loss, the largest local entropy generation rate occurs at 50 % of axial chord, and the interaction between the leakage vortex and up passage vortex promotes the loss generation. To sum up, the current DDES study about the tip leakage flow provides helpful information about the loss generation mechanism and may guide the design of low-loss blade tip.
Experimental Investigation on Real Under-Platform Dampers: The Impact of Design and Manufacturing
Authors: Gastaldi Chiara , Berruti Teresa M. , Gola Muzio M. , Bessone Andrea
Published: November 2019

The focus of this paper is on underplatform dampers (UDPs), friction damping devices commonly used in turbines for power generation. Given the nonlinear and highly complex nature of dry friction, model validation of bladed disks with UPDs still relies heavily on experimental verification, which is typically performed using the Frequency Response Function. The AERMEC research group has, in the last ten years, promoted an additional experimental/numerical comparison, based on evidence gathered directly at the blade platform/UPD interface to increase the understanding of friction and damper mechanics. A new test rig for the direct experimental investigation of UPDs at frequencies and contact pressures in line with real working condition has been developed. The geometry of the test rig and its technical features are described in detail in the paper.

Different real dampers (real shape and material) are tested. The results analysis includes a complete understanding of the contact states undergone by each damper during a period of vibration and an estimation of its contact parameters. The influence of the damper shape together with the precision of the surface manufacturing and finishing on the damper effectiveness is addressed.
Rotordynamic Stability Evaluation With Constructed Forward Whirl Signals Based on Full Spectrum Technique: Numerical and Experimental Investigation
Authors: Li Qihang , Chu Fulei
Published: November 2019

The rotordynamic stability evaluation by measuring the damping ratio or log-dec of the first forward whirl mode in the shop test is of importance to reduce the risk of instability fault in field. This paper focuses on the signal processing of inverse Fourier transform based on the full spectrum technique to reduce the modal overlap of closely-spaced first order modes (in which the amplitudes of the forward and backward responses are comparable) in the time domain. By using this transform method, forward and backward whirl signals are obtained, and blocking excitations in x or y direction can also achieve the same effectiveness as the forward and backward excitation with the active magnetic bearing (AMB) when there is a significant cross-coupled stiffness (CCS). The envelope of the analytical signal obtained by Hilbert transform is used to analyze the component of the excited vibration and show the effectiveness of weakening the overlap of the closely-spaced twin modes. The result from the numerical investigation indicates that for the rotor-bearing system with a significant CCS, the constructed forward and backward whirl signals are clearly dominated by the respective forward and backward modes with no significant overlap. Besides, experiments are also carried out in a nearly industrial centrifugal compressor test rotor with AMB, which is used as an actuator to apply blocking excitations for rotordynamic stability tests, with result that the unidirectional excitation is enough to estimate the log-dec of the rotor system with a slight CCS. Thus, the traditional circular forward/backward whirl excitation and its associated complicated equipment such as AMB is unnecessary and replaceable, providing a sight to simplify the complicated equipment only by using the signal processing techniques when the rotating machinery has an either slight or significant CCS.