bluuebunny/crossref_metadata_2025 huggingface dataset:
Towards High Productive Roughing of Profiled Grooves in Nickel Based Alloys
Authors: Klocke F. , Doebbeler B. , Seimann M. , Binder M.
Published: September 2016

Facing a high demand for aircraft engines over the next decades in combination with new challenging materials, aircraft engine manufacturers are striving for new manufacturing processes. The manufacturing of profiled grooves for the mounting of the turbine blades on the disc is a bottle neck process today due to the exclusive use of High Speed Steel (HSS) tools in broaching. Because of the limited hot hardness of HSS, the applied cutting speeds are low compared to other conventional machining processes, i.e. 2–5 m/min. Furthermore, the broaching process has some more drawbacks regarding flexibility, capital commitment for machinery and tools as well as costs. Nevertheless, broaching offers outstanding properties regarding surface finish, manufacturing accuracy and is still a productive process due to the many cutting edges applied. There are some alternative process chains which are not yet in industrial use, which are able to substitute and/or complement the HSS-broaching process.

In this paper, results are presented on two different roughing strategies for the manufacturing of profiled grooves in Nickel Based Alloys Allvac718plus and Inconel718. On the one hand, rough broaching with cemented carbide tools using indexable inserts was investigated at different cutting speeds, which are up to five times higher than the applied cutting speeds in industrial applications with HSS-tools. Two different carbide grades were investigated varying the cobalt content and the grain size. Cemented carbide is not state of the art in broaching Nickel Based Alloys due to its low fracture toughness. Different cutting edge inclination angles were applied and their effect on cutting forces, wear and tool chipping tendency were analyzed. On the other hand, rough side milling with ceramic cutting tools was investigated. Ceramic cutting tools excel in high hot hardness and thus can be used at very high cutting speeds i.e. up to 1000 m/min in Nickel Based Alloys. However, being very brittle and sensitive to alternating loads and thermal shock, machining processes with ceramic tools require extensive process design. In side milling experiments, Whisker reinforced as well as SiAlON and Oxide ceramic were investigated. In a first step, a window for machining parameters was identified. Then, tool life tests were conducted varying the feed at a fixed cutting speed of 1000 m/min. Subsequent to the experiments, the rim zone of the roughed grooves was investigated depending on the wear state of the used tools. The condition of the rim zone is a major criterion for the assessment of the adequacy of the roughing processes, because it can affect the subsequent finishing process. In further work, the interdependencies between the investigated roughing processes and finishing will be addressed.
Impact of Bearing Clearance on Measured Stiffness and Damping Coefficients and Thermal Performance of a High-Stiffness Generation 3 Foil Journal Bearing
Authors: Wilkes Jason C. , Wade Jonathan , Rimpel Aaron , Moore Jeff , Swanson Erik , Grieco Joseph , Brady Jerry
Published: September 2016

High speed foil bearings are currently used in increasingly demanding, high performance applications. The application under consideration is a 120 krpm natural gas turboexpander-compressor, which requires 38 mm (1.5 in.) foil journal bearings with high stiffness and load capacity to help enhance rotordynamic stability. This paper describes the development of the foil bearing for this application and includes measured stiffness and damping coefficients recorded on a high-speed dynamic bearing test rig. The dynamic test data were taken for several different foil bearing configurations with varying spring-element foil thicknesses, number of spring-element foils, and bearing shim thickness. All three parameters have a direct impact on bearing clearance. The influence of these different parameters on measured stiffness and damping coefficients and thermal performance of the bearings are presented and discussed.
Theoretical Study of Top Foil Sagging Effect on the Performance of Air Thrust Foil Bearing
Authors: Xu Fangcheng , Kim Daejong , Zamanian Yazdi Behzad
Published: September 2016

Air thrust foil bearings are used in small turbomachinery to support axial load. Typically, thrust bearings are designed with certain amount of taper from the leading edge until flat land area with uniform clearance. Therefore, the bearing performance is affected by many factors such as taper ratio, taper height, configuration of structural support, top foil thickness, etc. The most popular form of structural support is a corrugated array of bumps in either circumferential or radial direction, and many thrust foil bearings are manufactured with the bump foils in the land area only. Because the taper region does not have the bump foils and hydrodynamic pressure begins to build from the taper region, certain amount of top foil sagging in the taper area is inevitable. This paper studies the effect of the top foil sagging in the taper region on the static performance of the thrust foil bearings. The top foil is modeled as a 2D plate, and finite element method is used to predict the sagging effect of the top foil and coupled with finite difference method to solve Reynolds equation. Hydrodynamic pressure, top foil deflection, minimum film thickness, and power loss with different top foil thicknesses are calculated. Simulations show that under the identical external load, thin top foil allows very large sagging in the taper area resulting in abrupt change of film thickness around the beginning of land area accompanied by larger peak pressure and power loss and smaller minimum film thickness compared to the case of thicker top foils. Further studies with various top foil thicknesses and full bump supports in the taper region give insight to the design principle of thrust foil bearings with various sizes.
Electrical Resistance and Acoustic Emission During Fatigue Testing of Pristine and High Velocity Impact SiC/SiC Composites at Room and Elevated Temperature
Authors: Han Zipeng , Morscher Gregory N. , Maillet Emmanuel , Kannan Manigandan , Choi Sung R. , Abdi Frank
Published: September 2016

Electrical resistance (ER) is a relatively new approach for real-time monitoring and evaluating damage in SiC/SiC composites for a variety of loading conditions. In this study, ER of woven silicon carbide fiber-reinforced silicon carbide composite systems in their pristine and impacted state were measured under cyclic loading conditions at room and high temperature (1200C). In addition, modal acoustic emission (AE) was also monitored, which can reveal the occasion of matrix cracks and fiber. ER measurement and AE technique are shown in this study to be useful methods to monitor damage and indicate the failure under cyclic loading. Based on the slope of the ER evolution, an initial attempt has been made to develop a method allowing a critical damage phase to be identified. While the physical meaning of the critical point is not yet clear, it has the potential to allow the failure to be indicated at its early stage.
Performance of Supercritical CO2 Dry Gas Seals Near the Critical Point
Authors: Zakariya Mohd Fairuz , Jahn Ingo H. J.
Published: September 2016

The Queensland Geothermal Energy Centre of Excellence is investigating the use of supercritical CO2 closed loop Brayton cycles in the Concentrated Solar Thermal power cycle plant. One of the important components in the turbomachinery within the plant are seals. As the cycle is closed loop and operating at high pressures, dry gas seals have been recommended for future use in these systems. One of the main challenges of using supercritical CO2 dry gas seals is that operating conditions are near the critical point. In the supercritical region in the vicinity of the critical point (304 K, 7.4 MPa), CO2 behaves as a real-gas, exhibiting large and abrupt non-linear changes in fluid and transport properties and high densities. To correctly predict the seal operation and performance, the interaction between this real gas and the seal rotor (primary ring) and the seal stator (mating ring) need to analysed and investigated in detail, as they can lead to significant changes in flow and seal performance. Results from this paper show that increased centrifugal effects caused by higher gas densities can reduce the pressure in the sealing dam region. This adversely affects the loading capacity of the dry gas seal. However, it also benefits seal performances by reducing the leakage rate. The current work presents an investigation of the supercritical CO2 dry gas seals operating close to the critical point with an inlet pressure and temperature of 8.5Mpa and 370K respectively and a speed of 30000 RPM. Results highlighting the effects of the groove length or dam to groove ratio on the performance of the dry gas seal are presented. The seal is simulated using Computational Fluid Dynamics to study the flow behaviour of the supercitical CO2 in the dry gas seal. Supercritical CO2 fluid properties are based on the fluid database REFPROP. The numerical model was validated with previous work and good agreement was demonstrated.
Comparative Analysis of Stress Relaxation and Creep in a Single-Crystal Superalloy
Authors: Leidermark Daniel , Moverare Johan
Published: September 2016

The creep response of the single-crystal nickel-base superalloy MD2 has been investigated in this study. A set of constant load creep experiments was performed loaded in the nominal [001], [011] and [111] crystal orientations. A crystal plasticity - creep relaxation model, based on thermomechanical fatigue stress relaxation tests, was benchmarked to simulate the creep behaviour. The responses from the model were then compared to the results obtained during the creep tests. From the comparison it could observed that a trend for the [001] crystal orientation is present. A relative creep response between the simulations and experiments could be observed for the different stress levels. At high and increasing stress levels the relative relation is increasing. Under a certain stress level the relative relation is instead increasing for decreasing stress levels. This relative relation arises from the stress relaxation evaluation process, in which the creep parameters are defined, presumably due to the high stress relaxation that is present in the initial time frame. No trend was seen for the [011] and [111] crystal orientations. A discrepancy between the simulations and experiments was still obtained, also related to the high stress relaxation of the initial time frame.
Support Vibration Diagnostics and Limits in Gas Turbines
Authors: Bielecki Marcin , Costagliola Salvatore , Gebalski Piotr
Published: September 2016

The paper deliberates vibration limits for non-rotating parts in application to industrial gas turbines. As a rule such limits follow ISO 10816-4 or API616, although in field operation it is not well known relationship between these limits and failure modes. In many situations, the reliability function is not well-defined, and more comprehensive methods of determining the harmful effects of support vibrations are desirable.

In the first part, the undertaken approach and the results are illustrated based on the field and theoretical experience of the authors about the failure modes related to alarm level of vibrations. Here several failure modes and diagnostics observations are illustrated with the examples of real-life data. In the second part, a statistical approach based on correlation of support vs. shaft vibrations (velocity / displacement) is demonstrated in order to assess the risk of the bearing rub. The test data for few gas turbine models produced by General Electric Oil & Gas are statistically evaluated and allow to draw an experimentally based transfer function between vibrations recorded by non-contact and seismic probes. Then the vibration limit with objectives like bearing rub is scrutinized with aid of probabilistic tools. In the third part, the attention is given to a few examples of the support vibrations — among other gas turbine with rotors supported on flexible pedestals and baseplate. Here there is determined a transfer coefficient between baseplate and bearing vibrations for specific foundation configurations. Based on the test data screening as well as analysis and case studies thereof, the conclusions about more specific vibration limits in relation to the failure modes are drawn.
Statistical Evaluation of the Performance Impact of Manufacturing Variations for Steam Turbines
Authors: Xiong Juntao , Yang Jing , McBean Ivan , Havakechian Said , Liu Feng
Published: September 2016

A fast method is presented for evaluating the impact of blade manufacturing variations on the aerodynamic performance of turbomachines. The method consists of two parts. Firstly, an adjoint method is developed to evaluate the aerodynamic sensitivities for multistage turbomachines. This sensitivity information may then be used to perform fast direct Monte Carlo simulations to obtain the statistical distribution of the variations of aerodynamic performances resulting from any given set of manufacturing variations. Secondly, a method is developed to construct reduced-order models for the three-dimensional blades manufacturing variations using the Principal Component Analysis (PCA) method. Monte-Carlo simulations with the adjoint sensitivities can then be applied to the full and individual modes of the blade manufacturing deviations. The proposed method is applied to the last two stages of a low-pressure steam turbine. A total of 29 sets of measured manufacturing deviations of the last-stage rotor blades are used to construct a reduced-order model of the manufacturing variations. The manufacturing variation reduced-order model helps identify origins of the manufacturing deviations connected to the machining processes of the blades. Relations of the statistics of the aerodynamic performance variations such as mean, standard deviation, etc. to the different modes of manufacturing deviations are studied and analyzed.
The Application of Ceramic Matrix Composite to Low Pressure Turbine Blade
Authors: Watanabe Fumiaki , Nakamura Takeshi , Shinohara Ken-ichi
Published: September 2016

The structural reliability of composite parts for aircraft is established through the “building block” approach, which is a series of tests that are conducted using specimens of various levels of complexity. In this approach, the failure modes and criteria are validated step by step with tests and analysis at coupon, element, sub-component, and component levels.

IHI is developing ceramic matrix composite (CMC) components for aircraft engines to realize performance improvement and weight reduction. We conducted the concept design of CMC low pressure turbine (LPT) blade with the building block approach. In this paper, we present the processes and results of the design, which was supported by a series of tests.

Typical low pressure turbine blade has dovetail, airfoil and tip shroud. Each element has different function and characteristic shape. In order to select the configuration of CMC LPT blade, we conducted screening tests for each element. The function of dovetail is to sustain the connection with blade and disk against centrifugal force. The failure modes and strength of dovetail elements were examined by static load tests and cyclic load tests. The configuration of airfoil was selected by modal tests. The function of tip shroud is forming gas passage and reducing the leakage flow, therefore this portion needs to sustain the shape against the centrifugal force and the rubbing force. The feasibility of tip shroud was verified by spin tests and rubbing tests. The initial CMC LPT blades were designed as combination of the selected elements by these screening tests. Prototype parts were made and tested to check the manufacturability and the structural feasibility. The static strength to the centrifugal force was examined by spin test. The durability to vibration was examined by HCF test.
Non-Uniform Array Impingement on a Curved Surface
Authors: Harrington John , Hossain Jahed , Garrett Christian , Wang Wenping , Kapat Jay , Thorpe Steven , Maurer Michael
Published: September 2016

Experiments to investigate the effect of varying jet hole diameter and jet spacing on heat transfer from jet array impingement on a curved target surface are reported. The jet plate configurations studied have varying hole diameters and geometric spacing for spatial tuning of the heat transfer behaviour. The configuration also includes a straight section downstream of the curved section, where the effect on heat transfer and pressure loss is also investigated. For all configurations, spent air is drawn out in a single direction which is tangential to the target plate curvature. First row jet Reynolds numbers ranging from 50,000 to 160,000 are reported. The jet plate holes are sharp-edged. A steady-state measurement technique utilizing temperature sensitive paint (TSP) was used on the target surface to obtain heat transfer coefficients. Pressure taps placed on the sidewall and jet plate of the channel were used to evaluate the flow distribution in the impingement channel. Alongside the experimental work, CFD simulations were performed utilizing the v2-f eddy viscosity turbulence model to understand better the relationship between the flow field and the heat transfer on the target surface. The results from this study are compared against past results for uniform array impingement on flat surfaces.
Evaluation of Measurement Uncertainties for Pneumatic Multi-Hole Probes Using a Monte Carlo Method
Authors: Hölle Magnus , Bartsch Christian , Jeschke Peter
Published: September 2016

The subject of this paper is a statistical method for the accurate evaluation of the uncertainties for pneumatic multi-hole probe measurements. The method can be applied to different types of evaluation algorithms and is suitable for steady flowfield measurements in compressible flows. The evaluation of uncertainties is performed by a Monte Carlo method (MCM), which is based on the statistical law of large numbers. Each input quantity, including calibration and measurement quantities, is randomly varied on the basis of its corresponding probability density function (PDF) and propagated through the deterministic parameter evaluation algorithm. Other than linear Taylor series based uncertainty evaluation methods, MCM features several advantages. On the one hand, MCM does not suffer from lower-order expansion errors and can therefore reproduce nonlinearity effects. On the other hand, different types of PDFs can be assumed for the input quantities and the corresponding coverage intervals can be calculated for any coverage probability.

To demonstrate the uncertainty evaluation, a calibration and subsequent measurements in the wake of an airfoil with a 5-hole probe are performed. MCM is applied to different parameter evaluation algorithms. It is found that the MCM approach presented cannot be applied to polynomial curve fits, if the differences between the calibration data and the polynomial curve fits are of the same order of magnitude compared to the calibration uncertainty.

Since this method has not yet been used for the evaluation of measurement uncertainties for pneumatic multi-hole probes, the aim of the paper is to present a highly accurate and easy-to-implement uncertainty evaluation method.
Parametric Experimental and Numerical Study of LP Diffuser and Exhaust Hoods
Authors: Taylor Derek , Singh Gurnam , Hemsley Phil , Claridge Martin
Published: September 2016

The design of an effective diffuser for a given last stage blade of an LP turbine is known to be highly dependent on the size and shape of the exhaust hood in which it is located. For retrofit steam turbines in particular, where a new last stage blade and diffuser are fitted into an existing exhaust hood, the shapes and sizes of the exhaust box have been seen to vary significantly from one contract to the next. An experimental parametric study of diffuser lips and exhaust hood configurations has been run on a model test turbine rig at GE Power to investigate the impact of various geometric parameters on the performance of the diffusers. Improved testing and post-processing methodologies means the diffuser performance has been obtained for a greater number of geometric configurations than was previously typically possible. The results of these experiments are compared with numerical calculations and confirm the accuracy of the standard in-house diffuser design tools. Key geometric parameters are identified from the test data and used to generate improved diffuser design guidelines.
Response of a Squeeze Film Damper-Elastic Structure System to Multiple and Consecutive Impact Loads
Authors: San Andrés Luis , Jeung Sung-Hwa
Published: September 2016

Squeeze Film Dampers (SFDs) are common in aircraft gas turbine engines, customized to provide a desired level of damping while also ensuring structural isolation. This paper presents measurements obtained in a test rig composed of a massive cartridge, an elastic structure, and an open ends SFD with length L=25.4 mm, diameter D=127 mm, and radial clearance c=0.267 mm. ISO VG 2 oil at room temperature lubricates the thin film. The measurements quantify the system transient response to sudden loads for motions departing from various static eccentricity displacements, es/c=0 to 0.6. The batch of tests include recording the system response to (a) one single impact, (b) two (and three) impacts with an elapsed time of 30 ms in between, and (c) two or more consecutive impacts, without any delay, each with a load magnitude at 50% of the preceding impact. The load actions intend to reproduce, for example, a hard landing on an uneven surface or plunging motions from sudden contacts in a machine tool. The test system transient responses due to one or more impacts, each 30 ms apart, show the peak amplitude of motion (ZMAX) is proportional to the magnitude of applied load (FMAX). The identified system damping ratio (ξ) is proportional to the peak dynamic displacement as a linear system would show. Predictions of transient response from a physical SFD model accounting for fluid inertia correlate best with the experimental results as they produce greatly reduced peak dynamic motions when compared to predictions from a purely viscous SFD model. For the responses due to consecutive impacts, one after the other with no delay, the system motion does not decay immediately but builds to produce larger motion amplitudes than in the earlier cases. Eventually, as expected, after several oscillations the system comes to rest. For an identical damper having a smaller clearance cs=0.213 mm (0.8c), its damping ratio (ξs) is ∼1.3 to ∼1.7 times greater than the damping ratio for the damper with a larger film clearance (ξ). Hence, the experimentally derived (ξs/ξ) scales with (c/cs)2. The finding demonstrates the importance of manufacturing precisely the components in a damper to produce an accurate clearance.
Experimental and Numerical Investigation on Leakage Characteristic of Stepped Labyrinth Seal
Authors: Zhang Li , Zhu Hui-ren , Liu Cun-liang , Tong Fei
Published: September 2016

Labyrinth seals represent an important flow element in the secondary air system of aero engines. The influence of seal clearance and teeth parameters on the leakage characteristic of a real size stepped labyrinth seal was experimentally and numerically analyzed in a stationary state. Two kinds of labyrinth seals were studied in this investigation that are generally used in gas turbines, namely downward stepped labyrinth and upward stepped labyrinth. The differences of seal flow leakage mechanisms between the two types of the labyrinth were investigated. In order to eliminate the scaling effects on leakage losses in labyrinth seals, the experimental labyrinth seal model took the size of the real one in an aero engine. The experiments covered a range of pressure ratio from 1.1 to 3.5.

The experimental and numerical results show that in the range of the studied parameters the main teeth parameters affecting leakage coefficient are seal clearance, tooth tip thickness, tooth number and tooth front inclination. The influence of tooth height, pith and rear inclination angle on leakage coefficient of downward stepped labyrinth seal can almost be neglected in this research. And when the step height is more than twice the width of seal clearance, its effect on seal performance can be ignored. An empirical formula express of leakage coefficient with pressure ratio, seal clearance and teeth parameters of downward stepped labyrinth seal was organized which fits the experimental data with a maximal deviation of 8%. With similar pressure ratios and seal clearances, the downward stepped labyrinth seal displays lower leakage rates and provides the best sealing efficiency.
Effect of Reynolds Number, Hole Patterns, Target Plate Thickness on Cooling Performance of an Impinging Jet Array: Part II — Conjugate Heat Transfer Results and Optimization
Authors: Li Weihong , Li Xueying , Ren Jing , Jiang Hongde , Yang Li
Published: September 2016

This study comprehensively illustrates the effect of Reynolds number, hole spacing, jet-to-target distance and target plate thickness on the conjugate heat transfer performance of an impinging jet array. Test model is constructed with a relatively high conductivity material so that the Biot number of the models match engine condition. Highly resolved temperature distributions on the target plate are obtained utilizing steady liquid crystal over a range of Reynolds numbers varying between 5,000 and 27,5000. Effect of streamwise and spanwise jet-to-jet spacing (X/D, Y/D: 4–8), jet-to-target plate distance (Z/D: 0.75–3) and target plate thickness (t/D: 0.75–2.75) are employed composing a test matrix of 108 different geometries. Measured data are utilized as boundary conditions to conduct finite element simulation. Local and averaged non-dimensional temperature and averaged temperature uniformity of target plate “hot side” are obtained. Optimum hole spacing arrangements, impingement distance and target plate thickness are pointed out to minimize hot side temperature, the amount of cooling air and maximize the temperature uniformity. Also included are 2D predictions with different convective boundary conditions, i.e. row-averaged and local heat transfer coefficients, to estimate the accuracy of temperature prediction in comparison with the conjugate results.
Numerical Investigation on Flow and Heat Transfer Characteristics of Steam and Mist/Steam in Internal Cooling Channels With Different Rib Angles
Authors: Zeng Junxiong , Gao Tieyu , Li Jun , Zhu Jiangnan , Fei Jiyou
Published: September 2016

In order to further increase the gas turbine efficiency by increasing the turbine inlet temperature, an advanced cooling technology needs to be developed. Recently, mist /steam (air) cooling is considered as a promising technology to effectively cool the hot components such as gas turbine vanes and blades. A series of experimental investigations and numerical simulations conducted in the past proved the feasibility and superiority of mist cooling technology in elevated gas turbine working condition. The aim of this study is to numerically analyze the secondary flow structure and the influence of secondary flow distribution on heat transfer in steam and mist/steam cooling channels with different rib angles by using vortex core interaction. In addition, the heat transfer characteristics of steam and mist/steam in gas turbine cooling channels with rib angles of 30°, 45°, 60°, 90°, duct aspect ratio 2:1, Reynolds number ranging from 10000 to 60000 and mist ratio increasing from 2% to 8% are also investigated.

The commercial software ANSYS CFX 14.5 is used to solve the 3-D steady Reynolds-averaged Navier–Stokes equations with a SST turbulent model. The numerical results of Nusselt number (Nu) distribution along the centerline of each channel with steam-only are validated with the experimental values. Numerical results indicate that the predicted results are in good agreement with the experimental data. The distribution and strength of longitudinal secondary flows in 30°, 45°, 60° ribbed channels and transverse secondary flows in 90° ribbed channel have a great influence on the distribution of Nusselt number. The averaged Nu in 30°, 45°, 60° ribbed channels is higher than that in 90° ribbed channel due to longitudinal secondary flow having a better heat transfer performance than transverse secondary flow. The decrease of averaged Nu between two neighbored ribs along inclined ribs is mainly induced by the decreased strength of longitudinal secondary flow along the same direction in 30°, 45°, 60°ribbed channels. The averaged Nu of mist/steam with 5% mist injection in the four channels increases by 97.98%–151.9% compared with steam at Re=60000. Furthermore, the averaged Nu increases by about 11.08% to 213.6% compared with steam, when the mist ratio increases from 2% to 8%. The 60°ribbed channel achieves the best heat transfer performance in mist/steam cooling channels.
Strategic Blade Shape Optimization for Aerodynamic Performance Improvement of Wind Turbines
Authors: Kim Youjin , Al-Abadi Ali , Delgado Antonio
Published: September 2016

This study introduces strategic methods for improving the aerodynamic performance of wind turbines. It was completed by combining different optimization methods for each part of the wind turbine rotor. The chord length and pitch angle are optimized by a torque-matched method (TMASO), whereas the airfoil shape is optimized by the genetic algorithm (GA). The TMASO is implemented to produce an improved design of a reference turbine (NREL UAE Phase V). The GA is operated to generate a novel airfoil design that is evaluated by automatic interfacing for the highest gliding ratio (GR). The adopted method produces an optimized wind turbine with an 11% increase of power coefficient (Cp) with 30% less of the corresponding tip speed ratio (TSR). Furthermore, the optimized wind turbine shows reduced tip loss effect.
Feasibility of a Direct Coupled Turbine-Compressor Power Block for S-CO2 Brayton Cycles
Authors: Dhar Eshan , Srivatsa Shreyas , Kumar Pramod
Published: September 2016

This paper explores the feasibility of a direct coupled turbo-compressor power block for a simple recuperated S-CO2 Brayton cycle. The turbine inlet temperature is fixed at 600°C and the maximum working pressure is restricted to 300 bar due to material constraints to enable use of conventional steel alloys. Analysis is performed for a single stage radial flow turbine and a centrifugal compressor configuration. Mean-line flow is individually analyzed for the turbine and compressor to generate contour maps of optimum operating speeds for a range of power levels at various isentropic efficiencies. While performing the mean-line analysis real gas properties and friction coefficients of S-CO2 have been considered. The mean-line flow code is coupled with thermodynamic model of the simple recuperated S-CO2 Brayton cycle for generating a range of optimum operating conditions where direct coupled power blocks can be used.
Influence of Shroud Seal Dimensions on Aerodynamic Performance of Steam Turbine Stages: Part I — Honeycomb Seal
Authors: Yan Xin , Chen Xiuxiu , He Kun
Published: September 2016

Effect of leakage flow in honeycomb shroud seals on the aerodynamic performance of steam turbine stages in the high-pressure cylinder was numerically investigated by using the commercial CFD (Computational Fluid Dynamics) software ANSYS CFX11.0. The geometrical parameters of the honeycomb shroud seal, including the sealing clearance, cell depth and cell diameter, were selected as the research objectives to compute the aerodynamic performance of turbine stages at a wide range of dimensions. The numerical results show that the leakage rate in the shroud honeycomb seal is almost linearly increased with increase of sealing clearance. Correspondingly, the total-total isentropic efficiency of turbine stages decreases as well. As the cell depth increases, the total-total isentropic efficiency of the turbine stages is firstly increased and then almost kept constant, and the leakage rate in the honeycomb shroud seal is firstly decreased and then almost kept constant as well. For different honeycomb cell diameters, the leakage rate and stage efficiency are mainly determined by the flow structures in the honeycomb cells and seal outlet region. The present studies also show that, as the cell diameter increases, the total-total isentropic efficiency increases whereas the leakage rate decreases. Among the studied geometrical parameters (i.e. sealing clearance, cell depth and cell diameter), the variation of sealing clearance has a pronounced influence on the mixing loss in the main flow paths, but the variation of cell diameter has less effect on the aerodynamic performance of the turbine stages than that of sealing clearance. If the cell depth is not very small, the variation of cell-depth has a minor effect on the aerodynamic performance in the turbine stages.
Influence of Shroud Seal Dimensions on Aerodynamic Performance of Steam Turbine Stages: Part II — Hole-Pattern Seal
Authors: Yan Xin , Chen Xiuxiu , He Kun
Published: September 2016

The hole-pattern seal is usually used as a replacement of honeycomb seal due to their similarities in geometry and performance (leakage and rotordynamic). Compared with the honeycomb seal, the hole-pattern seal is easier to be manufactured and installed thus it is welcomed by the manufactures. However, most current literatures about the hole-pattern seal mainly addressed the rotordynamic characteristic of the shaft seal. Almost no research attempts to give an insight into the aerodynamic performance of the hole-pattern seal applied in turbine stages. Therefore, the main objective of the present paper is to investigate how the hole-pattern seal geometries, i.e. sealing clearance, hole-diameter and hole-depth, affect the aerodynamic performance of the steam turbine stages. With the commercial CFD (Computational Fluid Dynamics) software ANSYS CFX11.0, the leakage rates and aerodynamic efficiencies for the two stages with hole-pattern shroud seals were obtained and compared with those configured with honeycomb shroud seals at a range of seal dimensions. The results show that the leakage rate from the hole-pattern shroud seal is a bit higher than that from the honeycomb shroud seal at the same geometrical parameters (i.e. sealing clearance, hole/cell-diameter and hole/cell-depth). However, for these two configurations, the aerodynamic efficiencies are very close at the small sealing clearance cases. Big differences are shown at the large sealing clearance cases due to the difference in hole-area ratio. For the turbine stages with various hole-diameters and hole-depths, the aerodynamic performance of the turbine stages with honeycomb/hole-pattern seals are mainly affected by the flow patterns at the seal outlet if the sealing clearance is fixed. The sealing clearance has little effect on the flow pattern in the cells/holes, but it has a significant effect on the flow fields in the seal outlet chamber, thus affects the secondary flow development in the downstream flow paths.
Experimental Investigation of Convergent and Convergent-Divergent Micro Swirling Flame Behavior and Stabilization
Authors: Zhang Xintong , Lin Yuzhen , Xue Xin , Zhang Liang , Zhang Chi
Published: September 2016

With the miniaturization of mechanical and electrical systems, the demands for small-scale power resources with high energy density have promoted studies on small-scale combustors as well as methods to achieve stable small-scale combustion. In the present paper, a micro swirl injector for a small-scale combustor was designed to study the shape and stability of swirl flame in a 4 mm diameter quartz tube experimentally. The influences of fuel equivalence ratio, axial average velocity in the tube, and structure of the swirler exit were investigated under atmospheric pressure and ambient temperature. The fuel equivalence ratio was in the range of 0.5 to 3.0 and axial average velocity varied from 0.2 to 6 m/s. Methane was used as fuel. Results show that when the axial average velocity increases to a certain value and is kept constant, the methane flame abruptly changes from a swirl flame outside the tube into a stable spindle flame located at the exit of the swirl injector inside the tube within certain limits of equivalence ratio. The equivalence ratio ranges that the shape transition can happen extends with the increase of axial average velocity to certain limits, which is approximately 0.7–1.1 for methane. While under low axial velocity conditions, the spindle flame cannot be formed by the changing of equivalence ratio under a certain velocity, it can be formed and stabilized in a wide equivalence ratio range by slowly decreasing the axial velocity of a high-velocity spindle flame under a constant equivalence ratio of the premixed mixture. A flare at the exit of the swirl injector has little influence on stability limits while it makes the spindle flame to shift down and anchor nearer to the swirler exit. Flame shapes under the structure are characterized, and a brief explanation is given based on the vortex bursting mechanism and the match between local gas velocity and flame propagation velocity.
Micro Gas Turbine Firing Ammonia
Authors: Iki Norihiko , Kurata Osamu , Matsunuma Takayuki , Inoue Takahiro , Tsujimura Taku , Furutani Hirohide , Kobayashi Hideaki , Hayakawa Akihiro , Arakawa Yoshiyuki , Ichikawa Akinori
Published: September 2016

A demonstration test with the aim to show the potential of ammonia-fired power plant is planned using a micro gas turbine. 50kW class turbine system firing kerosene is selected as a base model. A standard combustor is replaced by a prototype combustor which enables a bi fuel supply of kerosene and ammonia gas. Diffusion combustion is employed in the prototype combustor due to its flame stability. Demonstration test firing ammonia gas was achieved using a new facility of large amount of ammonia supply. The gas turbine started firing kerosene and increased its electric power output. After achievement of stable power output, ammonia gas was started to be supplied and its flow rate increased gradually.

41.8kW power output was achieved by firing ammonia gas only. Ammonia gas supply increases NOx in the exhaust gas dramatically. However post-combustion clean-up of the exhaust gas via Selective Catalytic Reduction can reduce NOx successfully.
Thermal Field Measurements for a Shaped Hole at Low and High Freestream Turbulence Intensity
Authors: Schroeder Robert P. , Thole Karen A.
Published: September 2016

Shaped holes are increasingly selected for airfoil cooling in gas turbines due to their superior performance over that of cylindrical holes, especially at high blowing ratios. The performance of shaped holes is regarded to be result of the diffused outlet which slows and laterally-spreads coolant, causing coolant to remain close to the wall. However, few thermal field measurements exist to verify this behavior at high blowing ratio or to evaluate how high freestream turbulence alters the coolant distribution in jets from shaped holes. The present study reports measured thermal fields, along with measured flowfields, for a shaped hole at blowing ratios up to 3 at both low and high freestream turbulence intensities of 0.5% and 13.2%. Thermal fields at low freestream turbulence intensity showed that the coolant jet was initially attached, but far downstream of the hole the jet lifted away from the surface due to the counter-rotating vortex pair. Elevated freestream turbulence intensity was found to cause strong dilution of the coolant jet and also increased dispersion, almost exclusively in the lateral as opposed to the vertical direction. Dominance of lateral dispersion was due to the influence of the wall on freestream eddies, as indicated from changes in turbulent shear stress between the low and high freestream turbulence cases.
Natural Cooling Affecting the Restart of Micro Gas Turbine
Authors: Tisarev Andrei , Falaleev Sergey , Koch Christian , Nagorski Matthias , Staudacher Stephan
Published: September 2016

The research into natural cooling of a shutdown gas turbine engine is necessary to understand the factors reducing the engine components life by restart. The additional unbalance, bearing overheating and clearance changes are phenomena, which can appear during cooldown and engine restart. In this work, experimental and numerical research for a micro GTE cooldown were conducted.

Numerical conjugate flow & heat-transfer model of the whole engine was created for these purposes. The calculated temperature distribution at an operating point was used as a starting point of the cooldown time. Cooldown calculation included two phases: run-down and natural cooling. The numerical investigation was supported by experimental measurements, which were obtained using a micro gas turbine test rig.

From the results obtained it can be concluded that the allowed time before the restart must generally be based on individual factors such as bearings temperature, the displacement of turbine wheels centers of gravity etc. These factors attain their peak values at different time points after the engine shutdown.
Method to Determine Initial Estimates for the Air Handling System Layout of IC Engines Based on Turbomachinery Design Rules
Authors: Rodriguez Erdmenger Rodrigo , Clancy Cathal , Vadvadgi Aneesh , Lavertu Thomas
Published: September 2016

During the initial layout of a new air-handling system for internal combustion engines, the systems engineers need to make significant assumptions based on experience regarding the compressor performance, operating range, the turbine performance and volute and ducting losses. Typically, the initial sizing occurs before the selection of the turbocharger layout and before actual turbocharger maps are available. On the other hand the system information is key to be able to customize and match the compressor and the turbine performance to meet the specific engine requirements which may be significantly different depending on the engine type application. The current paper proposes a simple method to leverage basic turbomachinery design rules, correlations and databases to provide guidance to the system engineers on the expected performance of the air handling components. Additionally the current paper discusses the trade-offs that could be made on turbocharger performance by the adequate selection of the turbine and compressor couple that addresses the specific engine application needs.
A Preliminary Study of the Blade Erosion for a Wind Turbine Operating in a Dusty Environment
Authors: Hossam El-Din Ahmed , Diab Aya
Published: September 2016

The process of surface erosion due to particle collision has been the focus of a number of investigations with regards to gas turbine engines, aircraft, reentry missiles, pipelines carrying coal slurry, etc. Recently, increased interest in wind energy by countries in the Saharan regions of the Middle East and North Africa (MENA) brings about some concern about leading edge erosion of wind turbines operating under such dusty conditions. Leading edge erosion can have a detrimental impact on the extracted energy as it changes the blade surface roughness causing premature/unpredictable separation. Though erosion may not be easily avoided; it may be mitigated via using airfoil families characterized by low roughness sensitivity. In this paper, a model of an airfoil erosion subjected to sand blasting is developed using the discrete phase modeling capability in ANSYS-FLUENT along with the DNV erosion model. The effect of various flow parameters, such as angle of attack, and particle size, on the extent of erosion is investigated for a number of airfoil designs. The developed model is used as a predictive tool to assess the power deterioration of eroded wind blades.
The Exergy Optimization Analysis of 700°C HUSC Steam Turbine Using a Echelon Cycle System
Authors: Yi Xiaolan , Fan Shiwang , Li Haitao , Yang Jiandao , Chen Tao , Yang Hong
Published: September 2016

700°C HUSC technology is considered as the next generation of more efficiently coal-fired power generation technology, the heat rate of which can be reduced by more than 8% on the basis of current ultra-supercritical units. That means there is a huge energy saving benefits. With the main steam / reheat steam temperature increasing from 600°C / 620 °C to 700°C/ 720°C, the temperature of extraction steam increases dramatically, especially the first extraction stage after reheater, the temperature of which will increase to 630 ∼ 650 °C. That means a substantial increase in the cost of the initial investment because of the nickel-based material being used in extraction pipe and heaters. With EC system, the extraction steam temperature is reduced sharply because the high temperature extraction steam is moved from the main turbine to a small parallel extraction turbine and the steam source of the small extraction turbine is from the cold reheater. So the highest extraction steam temperature will not exceed 500 °C, and the high temperature risk of heat recovery system will be eliminated completely.

In this paper, exergy theory is introduced to analyze the cycle efficiency of the new thermodynamic system and the conventional one. In order to obtain a better 700 °C high ultra-supercritical thermodynamic system solution, GA method is used to optimize the regenerative system parameters to lower the overall heat consumption. The exergy theory is also used to analyze the reason why optimal solution can bring economic benefits. Finally, the feasibility of the entire system project will be analyzed.
Evaluation of Torsion Axis Positon on Turbine Blade Flutter by Direct Measurement Experiment: Rig Design and Numerical Simulation
Authors: Tani Naoki , Aotsuka Mizuho , Kazawa Junichi
Published: September 2016

Flutter has been a very important and severe problem for gas turbines, and its importance is increasing since a modern jet engine has very thin blades to reduce weight. There have been a lot of researches on its mechanism and evaluation technique[1][2][3], however, almost all of these researches are done by CFD, forced excitation and post evaluation of engine test. Among these activities, it became clear that torsion axis plays an important role to suppress flutter onset, however, there are few data on direct measurement during flutter on an influence of torsion axis. In the present study, two blade cascades which has different torsion axis were prepared and evaluate flutter can truly suppressed or not. Test rig was designed not to disturb circumferential disturbance which is generated by flutter at the test cascade, and pressure fluctuation transduces are introduced to measure pressure field during flutter vibration. The first test campaign will be held February 2016, and the experimental data will be compared with design and CFD results. The data will help clarifying the present design criteria can be truly applied to actual flutter onset and suppression. The present paper reports rig and blade design, and these evaluations by CFD simulations.