bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conjugate Heat Transfer Analysis of a Cooled Turbine Blade Using Frozen Rotor Approach
Authors: Ho Kuo-San , Liu Jong , Urwiller Christopher , Konan S. Murthy , Aguilar Bruno 
Published: August 2015

In recent years, conjugate heat transfer (CHT) computational fluid dynamics (CFD) simulation in turbomachinery played an important role in predicting metal temperature. Most of research papers of CHT CFD simulation were emphasized on the mixing plane method. In this paper the ANSYS CFX 14.0 CHT simulation using the frozen rotor approach is employed to predict the blade temperatures. The frozen rotor included five time instances in which the stator-rotor wake influence could be captured.
In this study, the temperature predictions using the frozen rotor approach were compared to the mixing plane predictions and Silicon Carbide (SiC) chip measurements on three different radial spans. The frozen rotor results predicted the minimum and maximum temperatures that bounded the SiC chip data. Compared to the mixing plane predictions, the frozen rotor approach results were similar within 8 K at the mid-span. However, the frozen rotor approach provided more insight information and detailed guidance for model calibration. Finally several future works were suggested to continue striving for high performance gas turbines.
A Comprehensive Through-Flow Solver Method for Modern Turbomachinery Design
Authors: Anderson Mark R. , Bonhaus Daryl L. 
Published: August 2015

Through-flow solvers have historically played a very prominent role in the design and analysis of axial turbomachinery. While three-dimensional, Full Navier-Stokes (FNS) CFD is taking an increasing larger role, quasi-3D through-flow methods are still widely used. Automated optimization techniques that search over a wide design space, involving many possible variables, are particularly suitable for the computationally efficient through-flow solver.
Pressure-based methods derived from CFD solution techniques have gradually replaced older streamline curvature methods, due to their ability to capture flow across a wide range of Mach numbers, particularly the transonic and supersonic regimes. The through-flow approach allows for the solution of the three-dimensional problem with the computational efficiency of a two-dimensional solution. Since the losses are explicitly calculated through empirically based models, the need for detailed grid resolution to capture tiny flow entities (such as wakes and boundary layers) is also greatly reduced. The combined savings can result in computational costs as much as two orders of magnitude lower than full 3D CFD methods.
A state-of-the-art through-flow solver has several features that are crucial in the design process. One of these is the ability to run in both a design and an analysis mode. Also important, is the ability to generate solutions where critical components are solved using 3D FNS, while others are run using a through-flow method. Other desirable features in a through-flow solver are: an advanced equation of state, injection and extraction ability, the handling of arbitrary (non-axial) shapes, and a link to a capable geometry generation engine.
Through-flow solvers represent a unique mix of higher order numerical methods (increasingly CFD-based) coupled with empirically derived models (generally meanline based). The combination of these two methods in one solver creates a particularly challenging programming problem. This paper details the techniques required to effectively generate through-flow solutions. Special attention is given to an improved off-design loss model for compressors, as well as a transonic loss model needed for high-speed compressor and turbine flows. Validation with recognized test data along with corresponding 3D FNS CFD results are presented.
Reduction of Gas Turbine Exhaust Temperature Limit due to HRSG Limitations by Change on Control Curve to Optimize Plant Operation and Performance
Authors: Mendoza Eduardo , Lin TsungPo , Jiang Xiaomo 
Published: August 2015

Most of the GE gas turbine fleet operates with exhaust temperature control characterized by various forms of Temperature Control Curves (TCC). The TCC which all have specific isothermal limits (maximum exhaust gas temperature) assigned. The isothermal limit is defined mainly by the materials used in the exhaust area including the exhaust frame, exhaust diffuser, struts. The isothermal limit is set to protect the turbine exhaust section from damage by excessive temperature. Although the isothermal limit is typically driven by turbine exhaust temperature limitation, there is a growing demand for isothermal limit adjustment due to HRSG operation limitation, e.g., HP steam attemperation, and also due to emission issues at part load operation.
The content of this paper presents a systematic approach for adjusting the isothermal limit to enhance the plant performance while still satisfying limitations in HRSG and DLN combustor operability. This exercise is a multi-disciplinary optimization process and it requires iterative communications among different disciplinary engineering teams. The methodology was applied to the case of 107FA Combined Cycle isothermal limit reduction for part load operation.
Prediction of Thermoacoustic Oscillations With a Linearised Euler Methodology
Authors: Quaglia C. F. , Cant R. S. 
Published: August 2015

Combustion instabilities in the aviation, aerospace and power generation industries have been a matter of concern for engineers since the 1950s, but with the increase in computer processing speed and the development of CFD it is now possible to attempt to predict frequencies and stability of a combustion system by numerical means, or by combining numerical, analytical and experimental approaches.
Currently available analytical methods for the prediction of the frequency and stability of thermoacoustic oscillations make use of one-dimensional models where the frequency of oscillation is assumed to be low enough that only plane waves propagate in the burner, with higher order modes decaying quickly. While accurate and well-suited for longitudinal oscillations, these methods are unable to predict the frequency of instabilities where the unsteady heat release couples with the higher frequency transverse acoustic modes. Therefore a method is needed for applications where high frequency transverse oscillations are important.
A method in which the linearised Euler equations are employed to calculate the propagation of acoustic waves is then suitable for solving this thermoacoustic problem. When a flame model that appropriately represents the frequency-dependent dynamics of the flame front is included, this method can predict the frequency of the oscillation resulting from the coupling between acoustics and combustion in an arbitrarily complex geometry.
In this paper, a linearised Euler solver called INSTANT is introduced and validated against a well known theoretical model for the calculation of thermoacoustic oscillations in a one dimensional cylindrical duct with rigid walls and a radially uniform mean flow. The frequencies of oscillation and the modeshapes for this stable configuration match the theoretical ones well.
An example calculation of transverse acoustic resonant mode is then presented. The ability of the code to predict the production of an entropy mode as a result of the interaction between an acoustic wave and a heat source region and its ability to predict frequencies of oscillation and modeshapes in a one dimensional configuration give confidence it can serve as a predictive tool for high frequency, transverse thermoacoustic oscillations in the more complex geometries of practical combustion systems once a suitable model for the frequency dependent flame response is included. The development of such a flame model is left for future work.
Preliminary Design Assessments of Pusher Geared Counter-Rotating Open Rotors: Part II — Impact of Low Pressure System Design on Mission Fuel Burn, Certification Noise and Emissions
Authors: Bellocq Pablo , Garmendia Inaki , Sethi Vishal 
Published: August 2015

In this 2-part publication, the impact of the main low pressure system parameters of a counter rotating Geared Open Rotor (GOR) on mission fuel burn, certification noise and emissions is presented for a 160 PAX medium haul class aircraft.
Due to their high propulsive efficiency, GORs have the potential to significantly reduce fuel consumption and emissions relative to conventional high bypass ratio turbofans. However, this novel engine architecture presents many design and operational challenges both at engine and aircraft level.
The assessment of the impact of the main low pressure preliminary design parameters of GORs on mission fuel burn, certification noise and emissions is necessary at preliminary design stages in order to identify optimum design regions. These assessments may also aid the development process when compromises need to be performed as a consequence of design, operational or regulatory constraints.
Part I of this two-part publication describes the main low pressure (LP) system design choices for a GOR as well as the preliminary design philosophy and simulation framework developed for the assessments. Part II presents the assessment studies. A fixed reference aircraft and mission were used to evaluate the different GOR engine designs. The results are presented in the form of 1-D or 2-D plots in which one or two design parameters are varied at the same time. The changes in mission fuel burn, certification noise and emissions are expressed as differences relative to a baseline design, due to the fact that preliminary design tools were used for the assessments. The main conclusions of the study are:
• Increasing spacing between the propellers (from 0.65 to 1.3m) reduces noise significantly (∼6 EPNdB for each certification point) with a relatively small fuel burn penalty (∼0.3–0.5%)
• Relative to unclipped designs, 20% clipped CRPs reduce flyover noise by at least 2.5 EPNdB and approach noise by at least 4.5 EPNdB. The corresponding fuel burn penalty is ∼2%.
• Sideline and flyover noise can be reduced by increasing the diameter of the CRP and appropriately controlling CRP rotational speeds. Approach noise can be reduced by either reducing the diameters or the rotational speeds of the propellers.
• Regardless of clipping, reducing the rotational speed of the rear propeller relative to the forward propeller reduces noise and, to a certain limit, also mission fuel burn. Further reductions in rotational speed would have an adverse effect on fuel burn.
• For given rotational speeds of the propellers, the torque ratio of the gearbox is fixed within ±3%.
Computation and Monitoring of the Deviations of Gas Turbine Unmeasured Parameters
Authors: Zarate Luis Angel Miro , Loboda Igor 
Published: August 2015

One of the principle purposes of gas turbine diagnostics is the estimation and monitoring of important unmeasured quantities such as engine thrust, shaft power, and engine component efficiencies. There are simple methods that allow computing the unmeasured parameters using measured variables and gas turbine thermodynamics. However, these parameters are not good diagnostic indices because they strongly depend on engine operating conditions but in a less degree are influenced by engine degradation and faults.
In the case of measured gas path variables, deviations between measurements and an engine steady state baseline were found to be good indicators of engine health. In this paper, the deviation computation and monitoring are extended to the unmeasured parameters. To verify this idea, the deviations of compressor and turbine efficiencies as well as a high pressure turbine inlet temperature are examined. Deviation computations were performed at steady states for both baseline and faulty engine conditions using a nonlinear thermodynamic model and real data. These computational experiments validate the utility of the deviations of unmeasured variables for gas turbine monitoring and diagnostics.
The thermodynamic model is used in this paper only to generate data, and the proposed algorithm for computing the deviations of unmeasured parameter can be considered to be a data-driven technique. This is why the algorithm is not affected by inaccuracies of a physics-based model, is not exigent to computer resources, and can be used in on-line monitoring systems.
A LCF Life Assessment Method for Steam Turbine Long Blade Based on Elastoplastic Analysis and Local Strain Approach
Authors: Yu Deqi , He Aping , Yang Hong , Yang Jiandao , Cheng Kai , Zhou Daiwei , Wang Gongyi , Gu Luyin 
Published: August 2015

Cyclic loads applied to a structure can develop local cyclic plasticity deformation, lead to fatigue damage and fracture at the high-stress regions, which can be assessed through a local strain approach. Each cycle of start-operation-stop steam turbine, making the low cycle fatigue (LCF) load of long blade, results in damage to the long blade, and the fatigue fracture occurs when the damage accumulated to its critical value. To evaluate the fatigue life, the experimental data illustrating the cyclic behavior of a material under simple loading condition must be gathered, and also a suitable local stress-strain range calculation approach needs to be chosen to represent the accurate material behavior under loadings. With the consideration of the difference between the specimen and actual blade, the influential factors, such as mean stress, geometry effect, blade surface quality, and water erosion, on the fatigue life should be investigated when using the cyclic fatigue data of specimen to predict fatigue life of actual blade.
In this study, a new local stress-strain range approach is introduced based on elastoplastic finite element analysis and Neuber rule. And also a modified strain-life fatigue model is used by considering leading causes of fatigue and also the cumulative damage rule is set up to predict the LCF life of the steam turbine long blade. It is found that the assessment method proposed in this study is capable of predicting the LCF life of steam turbine long blade.
Stabilizing Hydrodynamic Bearing Oil Whip With μ-Synthesis Control of an Active Magnetic Bearing
Authors: Pesch Alexander H. , Sawicki Jerzy T. 
Published: August 2015

Oil whip is a self-excited vibration in a hydrodynamic bearing which occurs when the rotation speed is above approximately twice the first natural frequency. Because of this, the oil whip phenomenon limits the operational speed of a rotor system on hydrodynamic bearings. Below the oil whip threshold, the related phenomenon of oil whirl can cause large vibrations at frequencies below half the rotation speed.
A method is presented for stabilizing oil whip and oil whirl in a hydrodynamic bearing with an active magnetic bearing (AMB). The AMB controller is designed with μ-synthesis model-based robust control utilizing the Bently-Muszynska fluid film bearing model, which predicts the unstable phenomena. Therefore, the resulting AMB controller stabilizes the natural instability in the hydrodynamic bearing. Rotor speed is taken into account by use of a parametric uncertainty such that the method is robust to changes in running speed.
The proposed method is demonstrated on an experimental hydrodynamic bearing test rig. Details of the test rig and implementation of the AMB controller design are presented. Waterfall plots for the controlled and uncontrolled system are presented which demonstrate the improved stability limit.
Influence of Design Parameters on the Performance of a Multistage Centrifugal Compressor for Supercritical Carbon Dioxide Applications
Authors: Monge B. , Sánchez D. , Savill M. , Pilidis P. , Sánchez T. 
Published: August 2015

The development of the supercritical Carbon Dioxide power cycle has relied on parallel tracks along which theoretical and experimental works have successfully complemented each other in the last few years. Following this approach, intensive work on the development of critical components has enabled the demonstration of the technology in small-scale test loops. The next step in the roadmap is scaling-up the technology in order to bridge the gap to commercialisation. To this aim, not only is it necessary to demonstrate that the cycle works, but it is also mandatory to rise component (and system) efficiencies to levels comparable with competing technologies. In this process, assessing the impact of the main design parameters on the efficiency of turbomachinery is deemed crucial.
The present work is a follow-up to others presented by the authors in previous years where preliminary analysis on centrifugal compressor design combining tools of different levels of fidelity were used. Nevertheless, whilst these presented guidelines to design the main compressor successfully, this new piece of research presents how the design space of the unit is affected by the characteristics of the working fluid. A review of past research is first presented to evidence that the design space is largely influenced by the particular behaviour of the working fluid close to the critical point. Then, design maps are presented for different operating conditions (cycle heat balance), showing that their shapes change substantially depending on compressor inlet pressure and temperature. Also, a comparison of these maps confirms that the design regions enabling high efficiency can be substantially reduced depending on the inlet/outlet thermodynamic states. Finally, conclusions are drawn regarding optimal intervals for the main design parameters involved in the process.
Development and Assessment of Combustion Models for Gas Turbine and Aero-Engine Applications
Authors: Anker Jan E. , Wunsch Dirk , Romagnosi Luigi , Claramunt Kilian , Hirsch Charles 
Published: August 2015

The classical flamelet method, the new Flamelet Generated Manifolds method (FGM), and the hybrid BML/flamelet approach are assessed in the context of the Reynolds-averaged Navier-Stokes (RANS) equations on a large range of configurations for both gaseous and spray flames. The conceptual differences, advantages, and shortcomings of the models are discussed in detail both from a theoretical and a practical point of view.
In order to assess the models under gas turbine like conditions, the reactive flow in TU Darmstadt’s Generic Gas Turbine (GGT), DLR Stuttgart’s PRECCINSTA burner, and a premixed industrial combustor are computed. The computational results are compared to available measurement data and are used to discuss the strengths and the weaknesses of each of the aforementioned combustion models.
In the current study it is shown that the hybrid BML/flamelet method globally performs well, but that it can be difficult to obtain a burning solution with this method, especially when the combustion process is operated close to the flammability limits. While the flamelet method is very robust, it is outperformed by the FGM method even for purely non-premixed configurations. It is demonstrated that the FGM approach can be used for the whole range of combustion modes, from non-premixed over to premixed combustion processes. Since the model did not lead to any difficulties with attaining a burning solution, and is computationally as efficient as the flamelet approach, the authors recommend the usage of this model over the other models investigated.
Evaluation of an empirical monitor output estimation in carbon ion radiotherapy
Authors: Matsumura Akihiko , Yusa Ken , Kanai Tatsuaki , Mizota Manabu , Ohno Tatsuya , Nakano Takashi 
Published: August 2015

Purpose:A conventional broad beam method is applied to carbon ion radiotherapy at Gunma University Heavy Ion Medical Center. According to this method, accelerated carbon ions are scattered by various beam line devices to form 3D dose distribution. The physical dose per monitor unit (d/MU) at the isocenter, therefore, depends on beam line parameters and should be calibrated by a measurement in clinical practice. This study aims to develop a calculation algorithm for d/MU using beam line parameters.Methods:Two major factors, the range shifter dependence and the field aperture effect, are measured via PinPoint chamber in a water phantom, which is an identical setup as that used for monitor calibration in clinical practice. An empirical monitor calibration method based on measurement results is developed using a simple algorithm utilizing a linear function and a double Gaussian pencil beam distribution to express the range shifter dependence and the field aperture effect.Results:The range shifter dependence and the field aperture effect are evaluated to have errors of 0.2% and 0.5%, respectively. The proposed method has successfully estimated d/MU with a difference of less than 1% with respect to the measurement results. Taking the measurement deviation of about 0.3% into account, this result is sufficiently accurate for clinical applications.Conclusions:An empirical procedure to estimate d/MU with a simple algorithm is established in this research. This procedure allows them to use the beam time for more treatments, quality assurances, and other research endeavors.
Compressed sensing for longitudinal MRI: An adaptive‐weighted approach
Authors: Weizman Lior , Eldar Yonina C. , Ben Bashat Dafna 
Published: August 2015

Purpose:Repeated brain MRI scans are performed in many clinical scenarios, such as follow up of patients with tumors and therapy response assessment. In this paper, the authors show an approach to utilize former scans of the patient for the acceleration of repeated MRI scans.Methods:The proposed approach utilizes the possible similarity of the repeated scans in longitudinal MRI studies. Since similarity is not guaranteed, sampling and reconstruction are adjusted during acquisition to match the actual similarity between the scans. The baseline MR scan is utilized both in the sampling stage, via adaptive sampling, and in the reconstruction stage, with weighted reconstruction. In adaptive sampling, k‐space sampling locations are optimized during acquisition. Weighted reconstruction uses the locations of the nonzero coefficients in the sparse domains as a prior in the recovery process. The approach was tested on 2D and 3D MRI scans of patients with brain tumors.Results:The longitudinal adaptive compressed sensing MRI (LACS‐MRI) scheme provides reconstruction quality which outperforms other CS‐based approaches for rapid MRI. Examples are shown on patients with brain tumors and demonstrate improved spatial resolution. Compared with data sampled at the Nyquist rate, LACS‐MRI exhibits signal‐to‐error ratio (SER) of 24.8 dB with undersampling factor of 16.6 in 3D MRI.Conclusions:The authors presented an adaptive method for image reconstruction utilizing similarity of scans in longitudinal MRI studies, where possible. The proposed approach can significantly reduce scanning time in many applications that consist of disease follow‐up and monitoring of longitudinal changes in brain MRI.
Postural Steadiness and Ankle Force Variability in Peripheral Neuropathy
Authors: Paxton Roger J. , Feldman-Kothe Caitlin , Trabert Megan K. , Hitchcock Leah N. , Reiser Raoul F. , Tracy Brian L. 
Published: August 2015

Introduction:The purpose was to determine the effect of peripheral neuropathy (PN) on motor output variability for ankle muscles of older adults, and the relation between ankle motor variability and postural stability in PN patients.Methods:Older adults with (O-PN) and without PN (O), and young adults (Y) underwent assessment of standing postural stability and ankle muscle force steadiness.Results:O-PN displayed impaired ankle muscle force control and postural stability compared with O and Y groups. For O-PN, the amplitude of plantarflexor force fluctuations was moderately correlated with postural stability under no-vision conditions (r = .54, p = .01).Discussion:The correlation of variations in ankle force with postural stability in PN suggests a contribution of ankle muscle dyscontrol to the postural instability that impacts physical function for older adults with PN.