bluuebunny/crossref_metadata_2025 huggingface dataset:
Disintegration of Oil Films Emerging From Radial Holes in a Rotating Cylinder
Authors: Glahn A. , Blair M. F. , Allard K. L. , Busam S. , Schäfer O. , Wittig S.
Published: July 2014

A fundamental study has been performed to examine the disintegration of oil films emerging from radial holes in a rotating hollow cylinder. The configuration investigated is an abstraction of one of the droplet generation sources in an aero-engine bearing compartment; similar configurations may also occur inside gearboxes. The paper aims to contribute to both the determination of directly applicable droplet characteristics and the establishment of a data-base that can be used for the development of droplet generation models. Similar to a prior paper on droplet generation processes at the rim of a rotating disk (Glahn et al, 2000), the near-term objectives of the study are (i) to determine droplet sizes under relevant aero-engine bearing compartment operating conditions, and (ii) to measure individual droplet diameter/velocity relationships. The long-term objective is to incorporate this information into advanced CFD-based design tools. Therefore, special emphasis has been directed towards a correlation of test results that enables determination of boundary conditions for a two-phase (oil droplets/air) simulation of lubrication system components. Based on the results of the present paper, droplet flow boundary conditions in terms of mean diameter, standard deviation of the diameter distribution, starting velocity, and flow angle are available for oil droplets generated by disintegration of oil films emerging from rotating radial holes and rotating disks.
A Unique Approach for Thermo-Economic Optimization of an Intercooled, Reheat and Recuperated Gas Turbine for Cogeneration Applications
Authors: Bhargava R. , Peretto A.
Published: July 2014

In the present paper, a comprehensive methodology for the thermo-economic performance optimization of an intercooled reheat (ICRH) gas turbine with recuperation for cogenerative applications has been presented covering a wide range of power-to-heat ratio values achievable. To show relative changes in the thermo-economic performance for the recuperated ICRH gas turbine cycle, results for ICRH, recuperated Brayton and simple Brayton cycles are also included in the paper. For the three load cases investigated, the recuperated ICRH gas turbine cycle provides the highest values of electric efficiency and Energy Saving Index for the cogenerative systems requiring low thermal loads (high power-to-heat ratio) compared to the other cycles.

Also, this study showed, in general, that the recuperated ICRH cycle permits wider power-to-heat ratio range compared to the other cycles and for different load cases examined, a beneficial thermodynamic characteristic for the cogeneration applications. Furthermore, this study clearly shows that implementation of the recuperated ICRH cycle in a cogeneration system will permit to design a gas turbine which has the high specific work capacity and high electric efficiency at low value of the overall cycle pressure ratio compared to the other cycles studied.

Economic performance of the investigated gas turbine cycles have been found dependent on the power-to-heat ratio value and the selected cost structure (fuel cost, electric sale price, steam sale price etc.), the results for a selected cost structure in the study are discussed in this paper.
Predicted Effects of Shunt Injection on the Rotordynamics of Gas Labyrinth Seals
Authors: Kim Namhyo , Park Sung-Young , Rhode David L.
Published: July 2014

A recent CFD-perturbation model for turbomachinery seal rotordynamics was extended for labyrinth shunt injection with an arbitrarily high pressure gas. A large number of measured cases with labyrinth injection pressure at approximately 13.8 bars (200 psi) were computed and compared with measurements. The drastically reduced (negative) cross-coupled stiffness, which is the primary advantage from the use of shunt injection in gas labyrinth seal applications, was well predicted. The agreement with measurements for k, C, and Ceff was within about 40 percent, 60 percent and 10 percent, respectively. In addition, it was found that moving the injection toward the high pressure end of the seal gives k, C and Ceff values that are rotordynamically only slightly more stabilizing. Further, the radial distributions of the flow perturbation quantities give support to the two-control volume approach for developing bulk-flow models for labyrinth seal rotordynamics.
Estimation of Distributed Unbalance of Rotors
Authors: Yang Tachung , Lin Chunyi
Published: July 2014

Mass unbalance commonly causes vibration of rotor-bearing systems. Lumped mass modeling of unbalance was adapted in most previous research. The lumped unbalance assumption is adequate for thin disks or impellers, but not for thick disks or shafts. Lee et al. (1993) proposed that the unbalance of shafts should be continuously distributed. Balancing methods based on discrete unbalance models may not be very appropriate for rotors with distributed unbalance. A better alternative is to identify the distributed unbalance of shafts before balancing.

In this study, the eccentricity distribution of the shaft is assumed in piecewise polynomials. A finite element model for the distributed unbalance is provided. Singular value decomposition is used to identify the eccentricity curves of the rotor. Numerical validation of this method is presented and examples are given to show the effectiveness of the identification method.
A Multi-Point Measurement Technique for the Enhancement of Force Measurement With Active Magnetic Bearings
Authors: Marshall Jeremy T. , Kasarda Mary E. F. , Imlach Joe
Published: July 2014

Active magnetic bearings (AMBs) have the unique capability to act concurrently as support bearings and load cells for measuring shaft forces. Current state-of-the-art methods for force measurement rely on models with limited accuracy due to effects which are difficult to characterize such as fringing, leakage, and variations in material properties. In addition, these effects may be a function of actual air gaps which are difficult to determine in a dynamic operating environment. This paper discusses a new force measurement methodology that inherently accounts for these types of effects and other system uncertainties by utilizing multiple sets of current pairs in opposing actuators, in conjunction with a calculation algorithm, to accurately determine the force applied by the AMB. This new multi-point methodology allows for the determination of bearing forces from information on basic actuator geometry and control currents only, with no knowledge of actual operating air gaps required. The inherent nature of the methodology accounts for model uncertainties such as fringing, leakage, and other system unknowns. Initial static experimental test results are presented demonstrating 3% error in measuring the nominal determined bearing load, and a variation in calculated forces of less than 5% in most cases (8% in one case) when the location of the rotor within the bearing stator is modified. For the analogous conventional single-point measurements, the results show 15% error and 23% variation.
Study of Stator Structure Modeling for Rotor Dynamic Analysis
Authors: Shinozaki Masaharu , Funatogawa Osamu , Kobayashi Masao
Published: July 2014

When applying the rotor dynamic analysis model to the design of the lightweight and flexible stator structure of aero-engines, it is indispensable to consider stator-structure dynamics. In order to simulate stator-structure dynamics, entire engine system are modeled by several layers including stator structures in the Transfer Matrix Method. Additionally, in the context of an accurate analysis of stator-structure dynamics, the Transfer Matrix Method has been found to be very useful when using Direct Matrix to calculate stiffness and mass matrix data with the aid of the finite element method. A stator-structure model is evaluated by measuring engine vibration data under normal imbalance conditions. Then selecting 25 quantitative parameters that characterize engine vibration, these parameters are optimized to minimize the difference between the calculated response and the measured vibration data. Optimization results show the influence of these parameters upon engine vibration characteristics. These investigations are effective in helping to improve engine stator-structure modeling techniques.
Multi-Blade Row Interactions in a Transonic Axial Compressor: Part II — Rotor Wake Forcing Function and Stator Unsteady Aerodynamic Response
Authors: Sanders A. J. , Fleeter S.
Published: July 2014

The unsteady aerodynamic flow field of the downstream stator in an advanced design 1&1/2 stage axial-flow compressor is experimentally investigated at both subsonic and transonic compressor operating conditions. The stator response at the subsonic rotor speed is mainly due to changes in the airfoil circulation distribution resulting from the incidence fluctuations generated by the passing of the rotor wakes. This is not the case for the transonic rotor speed in which phenomena associated with the intra-stator transport of the chopped rotor wake segments through the vane passage dominate the stator unsteady aerodynamic response characteristics. Rotor-IGV and rotor-stator interactions also generate static pressure fluctuations that act as an additional unsteady aerodynamic forcing function to the downstream stator. The spatial periodicity of these acoustic interactions is over the entire annulus of the machine due the unequal number of blades and vanes in the compressor, with the amplitude of the acoustic excitation to the downstream stator varying from vane-to-vane around the compressor annulus.
Reduced Order Modeling Techniques for Dynamic Analysis of Mistuned Multi-Stage Turbomachinery Rotors
Authors: Bladh Ronnie , Castanier Matthew P. , Pierre Christophe
Published: July 2014

Recent findings indicate that structural interstage (stage-to-stage) coupling in multi-stage rotors can have a critical impact on bladed disk dynamics by altering significantly the flexibility of the disk. This affects local eigenfrequency veering characteristics, and thus a design’s sensitivity to mistuning. In response to these findings, two reduced order modeling techniques are presented that accurately capture structural interstage coupling effects, while keeping model sizes at practical levels. Both free and forced responses of an example two-stage rotor are examined using novel component-mode-based reduced order modeling techniques for mistuned multi-stage assemblies. Both techniques employ an intermediate multi-stage model constructed by component mode synthesis (CMS), which is further reduced by either: (a) partial secondary modal analyses on constraint-mode partitions; or (b) a full-scale secondary modal analysis on the entire multi-stage CMS model. The introduced techniques are evaluated using finite element results as a benchmark. The proposed reduced order modeling techniques are shown to facilitate accurate multi-stage modeling and analyses with or without blade mistuning, using only computationally inexpensive modal data from a cyclic disk sector and a single blade per stage. It is concluded that the most promising and practically feasible approach may be a combination of approaches (a) and (b), in which secondary modal analyses and truncations are first carried out on disk-blade constraint-mode partitions, followed by a tertiary modal analysis on the resulting multi-stage model. In conclusion, by alleviating the restriction to single-stage analyses, the presented multi-stage modeling techniques will enable engineers to analyze the dynamics of mistuned turbomachinery rotor assemblies with greater confidence.
Stress Redistribution for Increased Creep Life in the GE MS6001 B Second Stage Blade
Authors: DiCristoforo Paul E. , Elledge Mark
Published: July 2014

When a hot end blade for a gas turbine is designed, several failure criteria must be considered to insure reliability. The criteria include (but are not limited to) creep rupture, low cycle fatigue, high cycle fatigue and creep deflection. This paper will focus on the second stage turbine blade for the GE MS6001 industrial gas turbine. BP Amoco has experienced failure of this blade due to excessive creep deflection.

Creep deflection rate is a function of stress level and metal temperature. A typical approach to reducing creep deflection is to reduce the bulk temperature in the blade. In this paper a design is reviewed that has had the stress redistributed, so that the high temperature regions of the airfoil are at a lower stress level, thereby reducing the creep rate to an acceptable level.
Prediction of Bird Impact Pressures and Damage Using MSC/DYTRAN
Authors: Moffat T. J. , Cleghorn W. L.
Published: July 2014

Finite element modeling of bird impacts has been developed and calibrated using the 3-D impact analysis code MSC/DYTRAN. These modeling efforts have shown that the Arbitrary Lagrange Euler (ALE) formulation within MSC/DYTRAN is capable of capturing the physics of the bird impact problem, producing impact pressures and damage similar to that of a real bird.

This work is divided into two areas. First, a review of the literature was carried out to identify the physical processes, pressures and damage associated with real bird impacts. Second, finite element modeling of two simple bird impacts cases were carried out using MSC/DYTRAN. A comparison of the finite element predictions with the experimental data showed excellent agreement, and demonstrated the robustness of the ALE formulation.
Damage Assessment of Creep Tested and Thermally Aged Udimet 520 Using Acousto-Ultrasonics
Authors: Gyekenyesi Andrew L. , Kautz Harold E. , Cao Wei
Published: July 2014

Due to elevated temperatures and excessive stresses, turbine components may experience creep behavior. As a result, it is desirable to monitor and assess the current condition of such components. This study employed the Acousto-Ultrasonics (AU) method in an effort to monitor the state of the material at various percentages of used up creep life in the nickel base alloy, Udimet 520. A stepped specimen (i.e., varying cross sectional area) was employed which allowed for a post mortem nondestructive evaluation (NDE) analysis of the various levels of used up life. The overall objectives here were two fold: First, a user friendly, graphical interface AU system was developed, and second the new AU system was applied as a NDE tool to assess distributed damage resulting from creep. The experimental results demonstrated that the AU method shows promise as an NDE tool capable of detecting material changes as a function of used up creep life. Furthermore, the changes in the AU parameters were mainly attributed to the case of combined load and elevated temperature (i.e., creep) and not simply because of a timed exposure at elevated temperature (i.e., heat treatment or thermal aging).
Analysis of 8 Centrifugal Compressor Impellers Using Two Different CFD Methods: Part I — Code Validation
Authors: Oh JongSik , Ro SooHyuk
Published: July 2014

Two different CFD methods, a time marching method and a pressure correction(or based) method, are developed and applied to centrifugal compressor impellers to investigate their validity of applications. 8 impellers are selected for analysis, among which 7 impellers are open to the public, ranging from low to high level of pressure ratio. In all cases, the time marching method gives a satisfactory solution, but the pressure correction method does not. Up to about 18% less level of total-to-total pressure ratio is predicted by the pressure correction method as the level of the impeller pressure ratio increases up to about 10. The drop of total pressure ratio is caused by the underestimation of static pressure rise which seems to be attributed to inappropriate linearization and discretization of the pressure/density coupling terms in the pressure correction equation.
Non-Intrusive Temperature Measurements in a Transonic Axial Compressor Using Spontaneous Rotational Raman Spectroscopy
Authors: Berreby Roger , Le Guével Alain , Grisch Frédéric
Published: July 2014

Spontaneous rotational Raman spectroscopy was used to measure static temperature in a transonic axial compressor. This laser technique has the general advantages of such techniques, i.e. possibility of performing in-situ measurements with high spatial resolution and temporal resolution, and non-intrusiveness. The experimental investigations were performed just downstream the rotor for the design mass flow rate. The results are obtained from Raman scattering of air by using a high repetition rate pulsed Nd:YAG laser and a spectrally and spatially resolving detector system that consists of a triple spectrograph and a CCD camera. Raman Spectra presented here are integrated over 20 s. Profiles of temperature at various locations relative to the casing are presented and the measured temperatures are compared with theoretical values. Of great importance for the results is the accuracy of the technique, and a sensitivity analysis is performed to test the temperature on uncertainties in experimental parameters. It was shown that the absolute accuracy of temperature could be as low as ± 1 K in the 300 - 400 K operating range of interest.
Probing Into the Connotation of Sweep Aerodynamics of Transonic Fans and Compressors
Authors: Xing X. Q. , Zhou S. , Zhao X. L.
Published: July 2014

Theory researches, numerical analyses and experiment studies of sweep aerodynamics in turbo-machinery had rapidly developed during the 1990s. Taking a low-aspect-ratio, high-loaded axial flow transonic rotor as the baseline, this paper attempts to probe the connotation of sweep aerodynamics of transonic fans and compressors. The definition of sweep angle was discussed. Flow field, key factors that affect structures of flow fields, linkage between leading edges as well as flow field structures in swept rotors were presented. In order to find out the optimum sweep leading edge curve under prescribed conditions, a numerical optimization program that can be added into design processes was developed.
Aerodynamic-Aeroacoustic Performance of Parametric Effects for Skewed-Swept Rotor
Authors: Cai Na , Xu Jianzhong
Published: July 2014

An experimental investigation and an engineering calculation of aerodynamic-aeroacoustic performance in axial-flow fans (or propellers) with skewed-swept rotors and radial rotors were carried out. It is shown that the calculated results agree with the experimental data. The approach for parametric effects on aerodynamic-aeroacoustic performance was investigated. The approach involves skew-sweep direction and angle, four kinds of stacking line for cascade. Results are presented that the performance with forward skewed (or swept) blades is better than that of backward skewed (or swept) blades. The selected forward-skew angle of 11.2 deg and forward-sweep angle of 23.7 deg are obtained. The line-arc combination stacking line of cascade has the best performance within the four kinds of stacking lines. In addition, the spanwise position of maximum pressure rise tends gradually to the hub with the skewed-swept angle increase on a constant pressure rise. Therefore, with appropriate blade design, significant noise reduction and efficiency increase are possible while maintaining similar geometric and aerodynamic parameter excepting skewed-swept angle.
Use of an Extractive Laser Probe for Time-Resolved Mixture Fraction Measurements in a 9 ATM Gas Turbine Fuel Injector
Authors: Girard James W. , Dibble Robert W. , Arellano Leonel O. , Smith Kenneth O.
Published: July 2014

This paper describes the use of a high velocity extractive sampling probe in a gas turbine fuel injector operating at 9 atm. This instrument has the ability to measure the temporal and spatial fluctuations of the mixture fraction. Knowledge of the fuel-air mixing characteristics is necessary to further decrease levels of pollutant emissions such as nitrogen oxides (NOx), and to sustain stable combustion. The extractive probe resolves temporal fluctuations due to the high flow rate through the sampling probe. The residence time of the sample gas in the sampling probe is sufficiently short so that axial diffusion on the relevant time scale can be ignored. Measurements were taken at two operating points: one at a stable low-emissions condition, and one at a condition where pressure oscillations in the combustor were high. At the second operating point, it was found that the frequencies of the pressure oscillations coincided with the frequencies of fluctuation in air-fuel ratio resolved by the probe.
3D LES Modeling of Combustion Dynamics in Lean Premixed Combustors
Authors: Cannon Steven M. , Adumitroaie Virgil , Smith Clifford E.
Published: July 2014

A lean premixed fuel injector/combustor typical of industrial gas turbine combustors has been analyzed using 3D Large Eddy Simulation (LES) methods. The objective of the study was to evaluate the 3D LES modeling approach for predicting combustion dynamics and compare it with simpler unsteady Reynolds Averaged Navier Stokes (RANS) methods using 2D and 3D analyses. Large amplitude pressure oscillations were observed experimentally at the modeled operating conditions, and previous 2D axisymmetric unsteady RANS analysis has shown reasonable, but not perfect, engineering agreement with pressure measurements. Although the pressure amplitude was accurately predicted, the frequency was substantially in error. This study sought to see if 3D modeling would improve the agreement.

2D axisymmetric and full 3D calculations were performed with a state-of-the-art, unstructured-grid, parallel (domain decomposition) CFD code. For the unsteady RANS calculations, the RNG k-ε turbulence model was employed, while for the LES calculation the Smagorinsky subgrid turbulence model was employed. Surprisingly, the 2D unsteady RANS, 3D unsteady RANS, and 3D LES calculations gave nearly identical pressure oscillation predictions, and all calculations had the oscillation frequency around 280 Hertz. This work has shown that smaller turbulent structures captured with 3D LES have very little effect on capturing combustion instability driven primarily by a fuel time-lag.
Using CFD for Time-Delay Modeling of Premix Flames
Authors: Flohr Peter , Paschereit Christian Oliver , van Roon Bart , Schuermans Bruno
Published: July 2014

This paper presents a refined model of the transfer function of a premix burner, compares the model with experiments, and discusses how the model can be used to map stability characteristics of a combustion system. The model is based on the assumption that acoustic velocity fluctuations cause modulations of fuel concentration at the fuel injector which, after a time delay, result in fluctuating heat release rates at the flame. Here, the time delay is modeled as a multitude of single time delays. The distribution of these time delays can be found either from model fitting to experimental data, or can be obtained directly from numerical simulations of the burner. The effect of distributed time delays is caused by axially distributed fuel injectors, turbulent diffusion, and a non-planar flame shape. As a consequence, heat release fluctuations at higher frequencies cancel, an effect which is also observed experimentally. It is found that the model is generally in good agreement with experiments. It is also demonstrated that the model can be used to map the burner stability charactistics for various operating conditions, e.g. for variations in power and flame temperature. A stability analysis is performed by incorporating the flame model into a combustor network model.
Development of a Variable Fuel Placement Airblast Atomiser
Authors: Morgan Leigh C. , Wheatley Alan J. , Brundish Kevin D.
Published: July 2014

This paper presents the progress made on the development of a dual spray, direct injection airblast fuel nozzle capable of variable fuel placement. It is anticipated that by varying the fuel placement within the confines of a combustion chamber it will be possible to control localised flame ‘Fuel Air Ratio’ and thus extend both stability and emissions performance in respect of engine power range. The extension of combustion stability is particularly desirable to high pressure, temperature and turndown ratio aero engines where the ratio between maximum and flight idle fuel flows is extreme.

Atomiser aerodynamics have been developed that produce two different airflow re-circulating regions within the combustor. A concentric fuel filmer feeds each of these regions. By staging the fuel into each flame re-circulation zone the variation of local ‘Fuel Air Ratio’ can be more accurately controlled.

A combination of bench testing and CFD has been used to analyse and manipulate airflow distribution between swirlers to form the two distinct flame regions. The work is ultimately concerned with the rationalisation of airflow distribution and fuel placement to best fit the operational envelope of the engine.

The variable placement fuel injector features three or more air swirlers (inner swirler, middle swirler and dome swirler) and two ‘airblast’ fuel filmers (pilot and main).

The paper describes the progress made with a number of fuel injector configurations.
Pre-Integrated Non-Equilibrium Combustion-Response Mapping for Gas-Turbine Emissions
Authors: Korakianitis T. , Dyer R. , Subramanian N.
Published: July 2014

In gas-turbine combustion the gas-dynamic and chemical-energy-release mechanisms have comparable time scales, so that equilibrium chemistry is inadequate for predicting species formation (emissions). In current practice either equilibrium chemical reactions are coupled with experimentally derived empirical equations, or time-consuming computations are used. Coupling non-equilibrium chemistry, fluid-dynamic, and initial- and boundary-condition equations results in large sets of numerically stiff equations; and their time integration demands enormous computational resources. The response modeling approach has been used successfully for large reaction sets. This paper makes two new contributions. First it shows how pre-integration of the heat-release maps eliminates the stiffness of the equations. This is a new modification to the response mapping approach, and it performs satisfactorily for non-diffusion systems. Second the theoretical framework is further extended to predict species formation in cases with diffusion, which is applicable to gas-turbine combustion systems and others. The methodology to implement this approach to reacting systems, and to gas turbine combustion, is presented. The benefits over other reaction-mapping techniques are discussed.
Turbulent Spots in Strong Adverse Pressure Gradients: Part 2 — Spot Propagation and Spreading Rates
Authors: D’Ovidio A. , Harkins J. A. , Gostelow J. P.
Published: July 2014

The study of turbulent spots in strong adverse pressure gradients is of current interest in turbomachinery research. The aim of this investigation is to use information gathered from boundary layer transition and laminar separation, in wind tunnel tests on flat plates, to predict the equivalent phenomena occurring on turbomachinery blade surfaces.

In Part 1 turbulent spot behavior was documented for two Reynolds numbers, corresponding to a laminar separation bubble (LSB) and an incipient separation condition (IS). In Part 2 further results are reported characterizing typical spot propagation and spreading rates and serving to validate or modify existing correlations for predicting transition length.
Economic Feasibility Study of Micro Gas Turbine Cogeneration Systems by an Optimization Approach
Authors: Gamou Satoshi , Joko Katsuhiro , Yokoyama Ryohei , Ito Koichi
Published: July 2014

Economic characteristic of micro gas turbine cogeneration systems for commercial and public purposes is evaluated rationally by an optimization method. The number of multiple kinds of micro gas turbine cogeneration units, capacities of other pieces of equipment and utility maximum contract demands are determined so as to minimize the annual total cost in consideration of operational strategies for energy demand requirements. Numerical studies are carried out on systems installed in hotels or office buildings. Through the studies, the following are clarified: (a) the relationships between the number of the installed micro gas turbine cogeneration units and the maximum electricity demands of hotels and office buildings, and (b) the economic effects of the micro gas turbine cogeneration units.
Optimizing Deformation Path for Stress Relaxation Tests on Superalloys at High Temperatures
Authors: Sinha Nirmal K. , Kearsey Rick
Published: July 2014

Stress relaxation results are highly sensitive to test conditions at elevated temperatures. The tests require precise control of environmental conditions and test methods. An experimental technique has been developed for conducting isothermal closed-loop controlled, constant strain, tensile stress relaxation tests at low strains (lower than 0.003) imposed in about one second. It is based on optimizing the initial strain, initial loading path and subsequent control of strain during the hold time. The methodology developed and the technical details used in conducting the stress relaxation tests, for temperatures up to 1000°C, are presented by using a nickel-base superalloy (IN-738LC) as a test material. The approach discussed has been found to be suitable for evaluating the microstructure - flow properties relationship of superalloys, corresponding to as-heat-treated initial microstructure, and could be applicable to any metals, alloys and ceramics at elevated temperatures. The method is being assessed as a means of evaluating the weldability of nickel-base superalloys.
Friction Damping of Interlocked Vane Segments: Experimental Results
Authors: Berruti T. , Filippi S. , Gola M. M. , Salvano S.
Published: July 2014

Experimental methods and results of the stator bladed segment of an aircraft engine are presented. Investigation concern the energy dissipation due to friction between contact surfaces of adjacent segments. The influence of the force normal to the contact surface (due to interference between adjacent segments) on friction damping is shown. Moreover the experiments show the nature of friction at contact surfaces. The parameters of a contact model to be used in a numerical analysis have been identified from the experiments.
A Solution Strategy Based on Segmented Domain Decomposition Multigrid for Turbomachinery Flows
Authors: Celestina M. L. , Adamczyk J. J. , Rubin S. G.
Published: July 2014

A Segmented Domain Decomposition Multigrid (SDDMG) procedure was developed for viscous flow problems as they apply to turbomachinery flows. The procedure divides the computational domain into a coarse mesh comprised of uniformly spaced cells. To resolve smaller length scales such as the viscous layer near a surface, segments of the coarse mesh are subdivided into a finer mesh. This is repeated until adequate resolution of the smallest relevant length scale is obtained. Multigrid is used to communicate information between the different grid levels [1]. To test the procedure, simulation results will be presented for a compressor and turbine cascade. These simulations are intended to show the ability of the present method to generate grid independent solutions. Comparisons with data will also be presented. These comparisons will further demonstrate the usefulness of the present work for they allow an estimate of the accuracy of the flow modeling equations independent of error attributed to numerical discretization.
Pressure and Suction Surfaces Redesign for High Lift Low Pressure Turbines
Authors: González P. , Ulizar I. , Vázquez R. , Hodson H. P.
Published: July 2014

Nowadays there is a big effort toward improving the low pressure turbine efficiency even to the extent of penalising other relevant design parameters. LP turbine efficiency influences SFC more than other modules in the engine. Most of the research has been oriented to reduce profile losses, modifying the suction surface, the pressure surface or the three-dimensional regions of the flow. To date, the pressure surface has received very little attention.

The dependence of the profile losses on the behaviour of both pressure and suction surfaces has been investigated for the case of a high lift design that is representative of a modern civil engine LP turbine. The experimental work described in this paper consists on two different sets of experiments: the first one concluded an improved pressure surface definition and the second set was oriented to achieve further improvement in losses modifying the profile suction surface. Three profiles were designed and tested over a range of conditions. The first profile is a thin-solid design. This profile has a large pressure side separation bubble extending from near the leading edge to mid-chord. The second profile is a hollow design with the same suction surface as the first one but avoiding pressure surface separation. The third one is also a hollow design with the same pressure surface as the second profile but more aft loaded suction surface. The study is part of a wider on-going research programme covering the effects of the different design parameters on losses.

The paper describes the experiments conducted in a low-speed linear cascade facility. It gathers together steady and unsteady loss measurements by wake traverse and surface pressure distributions for all the profiles. It is shown that thick profiles generate only around 90% of the losses of a thin-solid profile with the same suction surface. The results support the idea of an optimum axial position for the peak Mach number. Caution is recommended as profile aft loading would not be a completely secure method for reducing losses.
Development of a Crack Growth Prediction System for First Stage Nozzle of Gas Turbine
Authors: Fujii Tomoharu , Takahashi Takeshi
Published: July 2014

A system was developed for predicting the length of cracks generated in the first-stage nozzles of 1100 °C class gas turbines. The system consists of three programs, namely, crack input, crack display, and crack predicting programs, and a database containing data on 210,000 cracks generated in first-stage nozzles gathered from existing maintenance records maintained at three major power plants in Japan. The crack database also contains numerous crack data collected during inspections, operating hours and number of starts of gas turbine up to the time of inspection. The distinctive features of the system are 1) the crack data can be input as an image over the drawing of first-stage nozzles with a mouse, 2) by accumulating crack data, the sections in which most cracks occur in the first-stage nozzles can be clarified, 3) the correlation of crack length to operating time and number of starts can be analyzed simply, and 4) the length of cracks growing in any direction of any section of first-stage nozzles can be predicted.

Crack data collected from three power plants were analyzed. It was found that the cracks that were comparatively long and grew in proportion to an increase in operating time and number of starts were only 11 crack patterns as compared to the entire first-stage nozzles. The length of these 11 crack patterns was predicted for new first-stage nozzles and compared with the measured values obtained from inspection. As a result, it was verified that the crack length could be predicted.
Performance Measurement of the Second Stage of a Transonic Turbine
Authors: Seyr A. , Kulhanek G. , Neumayer F. , Rossi E. , Sanz W.
Published: July 2014

In November 1999 the turbine test facility at the Institute for Thermal Turbomachinery and Machine Dynamics was completed. This test stand is a cold flow transonic test turbine facility, which is a unique combination of a 2.3 MW axial test turbine and a directly-coupled compressor that generates about the half of the compressed air needed to drive the turbine. To cover the losses, additional air is provided by an electrically-driven compressor station. A 600 kW suction blower driven by a helicopter gas turbine is used to decrease the exhaust pressure, thus increasing the expansion ratio up to 4.5 (see Erhard and Gehrer “Design and Construction of a Transonic Test-Turbine Facility”, ASME Paper 2000-GT-480).

Since then, flow measurements with two different transonic turbine stages have been carried out.

This paper will focus on the description of the measurement system, data analysis and the newest test results that have been obtained on a turbine stage developed by Nuovo Pignone. This stage has been configured to be representative of advanced designs for medium/small land based gas turbines and is characterized by high pressure ratios and strongly transonic effects. The characteristic feature of this stage is the convergent- divergent flow channel. Basic data of this turbine stage to obtain flow similarity are: 2.2 MW shaft power at 11500 rpm, pressure ratio 4.5, mass flow 22 kg/s. The paper will contain appropriately plotted results of dimensionless stage characteristic curves over a broad range of operation points.
Acoustic Control of Thermoacoustic Instabilities Using Experimental Model-Based Controllers
Authors: Allgood Daniel , Campos-Delgado Daniel U. , Acharya Sumanta , Zhou Kemin
Published: July 2014

This paper presents an implementation of active control of thermoacoustic instabilities for a swirl- stabilized spray combustor. Loudspeakers located upstream of the burner were used as control actuators in the closed-loop system. Experimental models of the combustor dynamics were developed using a non-parametric identification method. Several controllers were obtained based on optimal control strategies. These controllers were simulated and tested in the experimental setup showing good agreement. Phase-delay control was used as a baseline method to compare the performance of these different controllers. The advantages of the model-based controllers over the baseline strategy are clearly presented.
A Reevaluation of the Holzwarth Gas Turbine Cycle for Use in Small Power Plants
Authors: Venturini Osvaldo José , Varella Sebastião
Published: July 2014

The purpose of this work is to analyze a gas turbine working under a cycle similar to the one proposed, by the Dr. Holtzwarth, at the beginning of the last century, showing its potentiality, mainly when applied to small power turbines. The method for analysis is based in the quasi-steady thermodynamic equilibrium principle, where the effects of the pressure and temperature variation, due to the intermittent combustion, are considered. Conclusions are presented considering the increase of the thermal efficiency and the available specific work, resulting from the constant volume combustion, when compared with those of a turbine operating under constant pressure combustion (Brayton Cycle). These results are obtained using actual curves of operation for the compressor and the turbine and, as well as, the “matching” of them.
Microturbine Cycle Options
Authors: Rodgers C.
Published: July 2014

The deregulation of electric power and growing emphasis placed on distributed power generation, is establishing the need for a compact thermal energy system capable of providing the total energy needs for a small business. Natural gas fueled microturbines with ultra low emissions can fulfill this need.

The results of a study comparing the thermodynamic performances of various cycle options for microturbines in the 50 Kwe range are presented. It was determined that with current state of art component peak performance levels, and metallic materials, a thermal efficiency of 30% was attainable for the recuperated open cycle single shaft microturbine.

The challenge to success of the microturbine may not be curtailed by gas turbine component or cycle technology, insomuch as the achievement of low emissions and low cost component manufacturing techniques.

If in the future heat engines are to be regulated on net global warming potential, semi-closed cycle gas microturbines with high exhaust flow recirculation may politically penetrate the marketplace.
A CFD Method for Axial Thrust Load Prediction of Centrifugal Compressors
Authors: Han Zhen-Xue , Cizmas Paul G. A.
Published: July 2014

This paper presents the development of a numerical algorithm for the computation of axial thrust load on a centrifugal compressor. An unstructured flow solver has been developed for the computation of a hybrid, structured and unstructured grid. The computational domain of the impeller has been discretized using a structured mesh, while the computational domain on the back side of the wheel has been discretized using an unstructured mesh. The two grids are merged and a median dual-mesh is generated. The Navier-Stokes equations are discretized using a finite volume method. Roe’s flux-difference scheme is used for inviscid fluxes and directional derivatives along edges are used for viscous fluxes. The gradients at the mesh vertices are calculated using the Least-squares method. An explicit scheme is used for time integration. Convergence is accelerated using a local time-step and implicit residual smoothing. The results of the numerical simulation include the axial thrust load of the centrifugal compressor. In addition, details of the leakage flow are presented.
Development and Evaluation of a High Resolution Turbine Pyrometer System
Authors: Eggert Torsten , Schenk Bjoern , Pucher Helmut
Published: July 2014

Optical pyrometers provide many advantages over intrusive measuring techniques in determining the spatial and time varying temperature distribution of fast rotating components in gas turbines. This paper describes the development and evaluation of a versatile high resolution pyrometer system and its application to radial turbine rotor temperature mapping as has been done in a R&D project at the Technical University Berlin under funding from Siemens Power Generation (KWU). The development goal was a pyrometer system with a temporal resolution of 1μs, a minimum field of view of 1 mm, and a measurement range from 600 to 1500°C. A prototype of the pyrometer system has been built and tested at the small gas turbine test facility of the Technical University Berlin. The system yielded excellent results with respect to measurement uncertainty, resolution, and reliability. Finally, measurement results obtained with the new system on a radial turbine rotor and on a heavy duty industrial gas turbine are compared with measurements conducted with a commercially available turbine pyrometer system.
Physical Inactivity and Associated Factors Among Women From a Municipality in Southern Brazil
Authors: Marcellino Cristiano , Henn Ruth Liane , Anselmo Olinto Maria Teresa , Bressan Ana Weigert , Vieira Paniz Vera Maria , Pattussi Marcos Pascoal
Published: July 2014

Background:

Physical inactivity is one of the most important modifiable risk factors that is raising the global burden of chronic diseases.

Methods:

This is a cross-sectional, population-based study of 790 women aged 20 years or older living in the urban area of a municipality in Southern Brazil. The level of physical activity was measured using the International Physical Activity Questionnaire, short form. Inactivity was defined as fewer than 150 min/wk−1 spent in moderate or vigorous physical activities. Prevalence ratios were calculated by robust Poisson regression.

Results:

The prevalence of physical inactivity was 48.7% (95% CI, 43.3%–54.1%). After adjusting for confounders, we found a linear trend for increasing prevalence of physical inactivity with increasing body mass index (P = .008). Women who were married or in a domestic partnership were 29% less physically active than single women (P = .044). A borderline association was detected between the presence of minor psychiatric disorders (MPD) and physical inactivity (P = .058).

Conclusions:

There was a high prevalence of inactivity. Obese women, those married or in domestic partnerships and those with MPD were more likely to lead an inactive lifestyle. These results suggest that strategies are required for breaking down barriers to physical activity in this demographic group.
The Association of Adolescent Fatness and Fitness With Risk Factors for Adult Metabolic Syndrome: A 22-Year Follow-up Study
Authors: Jekal Yoonsuk , Kim YoonMyung , Yun Ji Eun , Kim Eun Sung , Naruse Masayo , Park Ji Hye , Lee Dong Hoon , Hong Seung-youn , Jee Sun Ha , Jeon Justin Y.
Published: July 2014

Background:

Few studies have been conducted to explore the associations of fatness and fitness during adolescence with risk factors of metabolic syndrome (MetS) during adulthood, particularly in Asians.

Methods:

Adolescent anthropometric and fitness data were collected during the participants’ high school years (N = 15,896) and their corresponding health examination data from adulthood were taken from the National Health Insurance Corporation (NHIC) in Korea. A total of 1,006 participants (6.3%) were analyzed in the study.

Results:

The odds ratios (ORs) for being overweight (BMI ≥ 25 kg/m2) during adulthood was 11.87 (95% CI: 4.19–33.59) in men and 8.44 (95% CI: 1.78–40.02) in women, respectively, in the fattest group vs. the leanest group during adolescence. Participants with low fitness levels during adolescence were more likely to be overweight and have abnormal MetS risk factors in adulthood vs. those with high fitness levels. Joint exposure analyses of fatness and fitness showed that male participants who were more fat and unfit during adolescence had 4.11 (95% CI: 1.19–14.14) and 3.04 (95% CI: 1.17–11.12) times higher risk of having abnormal glucose and MetS risks during adulthood, respectively.

Conclusions:

Fatness and fitness levels during adolescence appear to be significantly associated with the MetS risk factors and prevalence in adulthood in Koreans.
Developing Interventions for Children’s Exercise (DICE): A Pilot Evaluation of School-Based Exercise Interventions for Primary School Children Aged 7 to 8 Years
Authors: Hind Karen , Torgerson David , McKenna Jim , Ashby Rebecca , Daly-Smith Andy , Truscott John , MacKay Heather , Jennings Andrew
Published: July 2014

Background:

Developing Interventions for Children’s Exercise (DICE) is an initiative aimed at determining effective schoolbased exercise programs. To assess feasibility, we conducted a pilot study of exercise sessions which varied in duration and frequency.

Methods:

Exercise interventions were delivered to Year 3 pupils (age 7–8 years; n = 73) in primary schools within Yorkshire, UK. Evaluations were conducted using focus group sessions, questionnaires and observations.

Results:

The study revealed positive aspects of all interventions, including favorable effects on children’s concentration during lessons and identified the value of incorporation of the DICE concept into curriculum lessons. Children appeared enthused and reported well-being and enjoyment. Areas requiring attention were the need for appropriate timetabling of sessions and ensuring the availability of space.

Conclusion:

The concept and sessions were well-accepted by teachers who confirmed their full support of any future implementation There appears to be potential for the encouragement and empowerment of teachers to support physical activity and healthy school environments, and to take an interest in the health of their pupils. Ultimately, these findings should assist in the design of successful exercise interventions in the school setting.