bluuebunny/crossref_metadata_2025_split huggingface dataset:
Creep and Fatigue of Single Crystal and Directionally Solidified Nickel-Base Blades via a Unified Approach Based on Hill48 Potential Function: Part 2 — Low Cycle Fatigue
Authors: Ramaglia Alessandro D. , Villari Paolo 
Published: November 2013

In the first part of this work the modeling of the anisotropic plastic and creep response of Single Crystal (SX) and Directionally Solidified (DS) nickel-base blades was discussed.
In this second part, the set of tools based on the Hill’s potential function is extended by showing how Hill like operators can be used to describe basic anisotropic features of the low cycle fatigue of SX and DS nickel-base superalloys. To this end a new Hill operator is introduced in order to set empirical life correlations and straightforward calibration procedures were set. The work is accompanied by applications on real heavy duty gas turbine components.
Prediction of High-Frequency Blade Vibration Amplitudes in a Radial Inflow Turbine With Nozzle Guide Vanes
Authors: Schwitzke Martin , Schulz Achmed , Bauer Hans-Jörg 
Published: November 2013

Impeller blades in radial inflow turbines are not only exposed to high thermal loads and centrifugal forces. Additional dynamic stresses occur by the aerodynamic excitation of a variety of blade and disc modes and can lead to damages by fatigue. This is a critical consideration for engines with nozzle guide vanes in particular, where excitation is caused by the interaction between guide vanes and rotor blades. This leads to high excitation frequencies, which are within the range of eigenfrequencies of the stiff impeller.
Previous experimental analyses provide vibration amplitude data for resonances in a radial inflow turbine equipped with three nozzle rings with varying vane numbers.
The experimental data is used for validation of numerical investigations. The numerical work presented involves the simulation of the transient flow field of the entire turbine as a first step. Aerodynamic excitation forces on the blades are derived from the results for various resonance conditions. The influence of the operating condition and the vane number is pointed out. Higher speed and lower vane number increase the amplitudes of the blade force. In a second step, the transient and spatially resolved pressure distribution is used as a boundary condition in an FE model. The damping ratio is an essential parameter in order to calculate the forced response of the structure, and it is determined from the experimental data. The damping behavior is characterized and compared to ratios derived from additional experimental studies using laser vibrometry at the non-rotating turbine wheel under ambient conditions. A disparity in the damping ratios is recovered, depending on the eigenmodes and the boundary conditions. The forced response of the structure is computed using the individual damping ratios for four resonance conditions. Harmonic analyses are conducted, applying the pressure forces from CFD. The calculated amplitudes are validated with data from strain gauge measurements under operating condition. The prediction of the vibration amplitudes shows acceptable agreement to the test data with a tendency towards lower values.
Measurement and Prediction of the Static Operating Conditions of a Large Turbine Tilting-Pad Bearing Under High Circumferential Speeds and Heavy Loads
Authors: Hagemann Thomas , Kukla Sebastian , Schwarze Hubert 
Published: November 2013

The identification results for the static performance characteristics of a large tilting-pad bearing in load between pad configuration are presented for specific bearing loads between 1.0 and 2.5 MPa and for circumferential speeds up to 79 m/s. The bearing is lubricated by spray-bars and can be described by the following specifications: Five pads, 0.23 nominal preload, 60% offset, 56° pad arc angle, 500 mm inner diameter, 350 mm pad length and 1.28 per mille relative bearing clearance. The axial oil flow is reduced by a fixed seal on both bearing edges which has a nominal radial clearance of 1 mm. The film pressure and the gap width are determined in the whole area of the sliding surface by an axial shift of the shaft. The bearing temperatures are measured by means of 100 thermocouples located 5 mm behind the sliding surface. The experimental results indicate that significant pad deformation occurs in circumferential and in axial direction. Also the effective supply temperatures are much higher than the nominal ones. According to the lubricant flow the sensor temperatures close to the spray-bars at the sliding surface rise about 20 K for 7 l/s and 40 K for 3.5 l/s at 3000 rpm. The temperatures are nearly constant between all pads and depend only on speed and not on load.
The theoretical analyses of the bearing performance was accomplished with the bearing calculation software COMBROS. This code models the transition between laminar and turbulent flow and solves an extended Reynolds equation, the three dimensional energy equation of the film and the heat conduction equations of the shaft and the pads considering various boundary conditions due to the judgment of the user. Concerning the minimum film thickness, the maximum temperature on the sliding surface and the maximum film pressure only poor agreement was reached if the influence of the axial pad deformation was neglected. In advanced analyses a co-simulation between COMBROS and a structural mechanics software shows that an improvement of the prediction was achieved. The comparison of the measurement data and the advanced simulation shows very good agreement for the characteristic bearing parameters as well as for the local distributions of film pressure, temperature and film thickness in the whole operating range of the bearing. Further, the applied inlet mixing model for the lubricant supply process proves to be very suitable.
Numerical Investigation of the Origin of Losses in the Rotor Hub Region of a Multistage Axial Compressor
Authors: Herve Simon , Reutter Oliver , Wieler Mark , Nicke Eberhard 
Published: November 2013

Endwall losses and secondary air flow are considered to be responsible for a significant part of the flow losses in compressors. Their reduction can be achieved by 3D blade design and non-axisymmetric endwalls. In order to evaluate the potential of both effects, an analysis of secondary air flow and the origin of losses is realized. This paper presents multiple numerical simulations to determine the predominant phenomena at the origin of losses in the hub region of the last rotor of the Rig 250, a 4-stage compressor with cantilevered stators and rotor tip clearances.
In a first study (I), an inviscid endwall condition at the hub of rotor 4 has been investigated. This condition strongly reduces the secondary air flow from the pressure side to the suction side and shows a significant reduction of the losses in the hub region. But the typical loss distribution over the blade height with a local maximum between 5 and 15 % of the blade height is not changed. Through this study the losses generated by the endwall boundary layer and the resulting secondary air flow are evaluated. Moreover, the potential for endwall contouring and 3D blading in the hub region is estimated, which can be used in future design studies.
In the second study (II), ideal radial distributions of the velocity and of the inflow angles at the inlet of the rotor 4 are set. The results show the dependencies between the inflow condition and the loss production in the blade passage near the endwall.
These studies sets the theoretical maximal potential for improvement techniques, like endwall contouring or the modification of the upstream stator.
Aerodynamic Optimization of the Radial Inflow Turbine for a 100kW-Class Micro Gas Turbine Based on Metamodel-Semi-Assisted Method
Authors: Shao Shuai , Deng Qinghua , Feng Zhenping 
Published: November 2013

In this paper, an aerodynamic optimization of the radial inflow turbine for a 100kW-class micro gas turbine is conducted based on the metamodel-semi-assisted idea. The idea is applied by first using the metamodel as a rapid exploration tool and then switching to the accurate optimization without metamodel for further exploration of the design space [1]. The non-dominated sorting genetic algorithm (NSGA-II) is used to drive the optimization process and the BP neural network is used to construct the metamodel.
The optimization of this radial inflow turbine is divided into two parts, the stator optimization and the rotor optimization. The stator optimization is based on the accurate optimization strategy. The minimum total pressure loss of the stator and the maximum isentropic total-to-static efficiency of the stage are considered as the objective functions with constant mass flow rate as a constraint. The rotor optimization is conducted through the metamodel-semi-assisted idea. The maximum power output and isentropic total-to-static efficiency of the stage are considered as objective functions while keeping the mass flow rate to be constant.
The accurate optimization system is demonstrated to be effective for the stator optimization, and the total pressure loss is reduced by 11.6% while the mass flow rate variation is less than 1%.
The rotor optimization is conducted based on the metamodel-semi-assisted optimization and the results confirm the effectiveness of this new idea. The output power of the rotor increased by 1.5%, the isentropic total-to-static efficiency of the stage increased by 1.19% and the mass flow variation is less than 1%.
Object-Oriented Open-Source CFD for Turbomachinery Applications: A Review and Recent Advances
Authors: Casartelli Ernesto , Mangani Luca 
Published: November 2013

CFD is nowadays an indispensable tool for the design and analysis of high performance turbomachinery. In the community, the commercial codes play a major role, offering specific features, especially in pre- and postprocessing, but also in the solver technology, suited to ease the approach to CFD for the development engineers. Nevertheless, in the last ten years many institutions, both in academia and in industry, have seriously started to look at alternatives in order to have more flexibility in the implementation of specific models and more freedom in the large-scale usage of CFD, like for example in automated optimization-processes and L-DES computations. Among the different possibilities, the open-source toolbox OpenFOAM® has been used in the turbomachinery community over a broad spectrum of applications, showing how well-suited it is for customization and how reliable the results can become, when the implemented solver-technology is upgraded to state-of-the-art models.
In the present publication a review of the community and some of the author’s development-activities are presented. About the latter, selected applications are presented, from transonic internal flow to turbine cooling and conjugate heat transfer, showing how specific customizations can allow to achieve industrially relevant results. Details on recent advances like the implementation of a fully-implicit mixing-plane interface and of a transition model show how competitive this environment can be. Moreover an outlook of ongoing future developments of the solver technology, such as a pressure-based coupled solver, is also given.
The Dynamics of Prestall Process in an Axial Low-Speed Compressor With Single Circumferential Casing Groove
Authors: Du Juan , Liu Le , Nan Xi , Lin Feng , Chen Jingyi , Nie Chaoqun 
Published: November 2013

The fact that the location of single circumferential casing groove can have a large impact on the stall margin of axial compressors has been actively investigated in recent years. However, it remains a tough challenge to numerically predict the groove performance and clarify its underlying mechanism on the difference of stall margin improvement (SMI) for different groove locations. In this paper, a single rotor, which had been proven to be a tip sensitive rotor with spike type stall inception, is tested and numerically simulated with an unsteady Reynolds averaged Navier-Stokes (URANS) solver. The test results show that the rear grooves perform better than the front grooves in this rotor. A multi-passage numerical scheme is used to capture the prestall process involving the unsteady cross-passage flow interaction. Although the calculation did not fully capture the measured trend of stall margin improvement, the numerical result did show that the front groove, which is the closest to the leading edge, generates the worst stall margin extension, and the rear groove, which is located right behind the front groove, gives the best stall margin improvement.
The prestall dynamics for smooth casing and the two typical grooves are chosen for a comparative study to clarify the underlying mechanism. Three different prestall processes are found. For smooth casing, a rotating disturbance evolves into spike after the interface between tip leakage flow (TLF) and incoming main flow (MF) spills in front of the leading edge. For the front groove, the interface is prevented by the groove to move forward during the throttling process. A modal wave is captured before stall. When the rear groove is applied, the interface location as a function of flow coefficient behaves much similar to the case of smooth casing. However, there is no any rotating disturbance, neither the modes nor the spike, with this groove. The flow is symmetric until all the passages break down at the same time.
Experimental and Numerical Investigation of Losses in Centrifugal Compressor Components
Authors: Doustmohammadi Ali Asghar , HajilouyBenisi Ali , Mojaddam Mohammad 
Published: November 2013

In this research an analytical model for performance prediction of centrifugal compressors is developed. The loss mechanisms are investigated in impeller, diffuser and volute separately for wide operating rotational speeds of the compressor. The contributions of compressor components in total entropy generation are further studied using different experimental correlations and methods. The results are verified using experimental test results, carried out at Sharif University of technology Turbocharger laboratory which has been designed to derive performance curves of turbocharger compressors. The test rig is equipped to measure static and stagnation pressures at inlet and outlet of each component to determine the total pressure drop of each one. The model results show good agreement with experimental results.
The results show the losses which are related to the impeller are higher than stationary component losses at design and off design operating conditions and the incidence loss is the main source of entropy generation in off design conditions. Also the diffuser losses increase with increasing mass flow rate while volute losses decrease.
Evaluation of Foil Bearing Performance and Nonlinear Rotordynamics of 120kW Oil-Free Gas Turbine Generator
Authors: Kim Daejong , Lee An Sung , Choi Bum Seog 
Published: November 2013

This paper presents design approach of air foil bearings (AFBs) for 120kWe gas turbine generator, which is a single spool configuration with gas generator turbine and alternator rotor connected by a diaphragm coupling. Total four radial AFBs support the two rotors, and one set of double acting thrust foil bearing is located inside the gas generator turbine.
The rotor configuration results in eight degree of freedom (DOF) rotordynamic motions, which are two cylindrical modes and two conical modes from the two rotors.
Stiffness of bump foils of candidate AFB was estimated from measured structural stiffness of the bearing, and implemented to computational model for linear stiffness and damping coefficients of the bearing and frequency-domain modal impedances for cylindrical and conical modes. Stiffness of the diaphragm coupling was evaluated using finite element analysis and implemented to non-linear rotordynamic analyses of entire engine. Analyses show conical mode of turbine rotor is the main source of instability of entire engine when AFB clearance is not selected properly. Optimum AFB clearance is suggested from frequency domain modal analyses and nonlinear transient analyses.
Eulerian-Lagrangian Numerical Simulation of Wet Steam Flow Through Multi-Stage Steam Turbine
Authors: Sasao Yasuhiro , Miyake Satoshi , Okazaki Kenji , Yamamoto Satoru , Ooyama Hiroharu 
Published: November 2013

In this paper, we present an inclusive tracking algorithm for water droplets in a wet steam flow through a multi-stage steam turbine. This algorism is based on the Eulerian-Lagrangian coupled solver. The solver continuously computes water droplet growth, kinematic non-equilibrium between vapor and droplets, capture and kinetics of droplets on turbine blades, departure of large droplets from the trailing edge of blades, acceleration and atomization of large droplets, and recollisions between blades and droplets.
Our Eulerian-Lagrangian coupled solver is used to predict wetness in unsteady three-dimensional (3D) wet steam flows through three-stage stator rotor cascade channels in a low pressure (LP) steam turbine model which is developed by Mitsubishi Heavy Industries (MHI). Droplet groups tracked by the discrete droplet model (DDM) are placed in the computational domain according to the predicted wetness. Interference from the gas phase on the droplets is considered, to track their kinetic and behavior, until they reach the outlet of the computational domain.
The aim of this research is to investigate those multi-physics phenomena that trigger all forms of loss in steam turbines. In addition, this method will also be applied to multi-physics problems such as erosion in future work. This paper is presented as a first step in the research. Overviews of model of current coupling solver and several test calculations are presented.
Review of the von Karman Institute Compression Tube Facility for Turbine Research
Authors: Paniagua G. , Sieverding C. H. , Arts T. 
Published: November 2013

Advances in turbine-based engine efficiency and reliability are achieved through better knowledge of the mechanical interaction with the flow. The life-limiting component of a modern gas turbine engine is the high-pressure (HP) turbine stage due to the arduous environment. For the same reason, real gas turbine engine operation prevents fundamental research. Various types of experimental approaches have been developed to study the flow and in particular the heat transfer, cooling, materials, aero-elastic issues and forced response in turbines. Over the last 30 years short duration facilities have dominated the research in the study of turbine heat transfer and cooling.
Two decades after the development of the von Karman Institute compression tube facility (built in the 90s), one could reconsider the design choices in view of the modern technology in compression, heating, control and electronics. The present paper provides first the history of the development and then how the wind tunnel is operated. Additionally the paper disseminates the experience and best practices in specifically designed measurement techniques to both experimentalists and experts in data processing. The final section overviews the turbine research capabilities, providing details on the required upgrades to the test section.
The effects of gantry tilt on breast dose and image noise in cardiac CT
Authors: Hoppe Michael E. , Gandhi Diksha , Stevens Grant M. , Foley W. Dennis , Schmidt Taly Gilat 
Published: November 2013

Purpose:This study investigated the effects of tilted‐gantry acquisition on image noise and glandular breast dose in females during cardiac computed tomography (CT) scans. Reducing the dose to glandular breast tissue is important due to its high radiosensitivity and limited diagnostic significance in cardiac CT scans.Methods:Tilted‐gantry acquisition was investigated through computer simulations and experimental measurements. Upon IRB approval, eight voxelized phantoms were constructed from previously acquired cardiac CT datasets. Monte Carlo simulations quantified the dose deposited in glandular breast tissue over a range of tilt angles. The effects of tilted‐gantry acquisition on breast dose were measured on a clinical CT scanner (CT750HD, GE Healthcare) using an anthropomorphic phantom with MOSFET dosimeters in the breast regions. In both simulations and experiments, scans were performed at gantry tilt angles of 0°–30°, in 5° increments. The percent change in breast dose was calculated relative to the nontilted scan for all tilt angles. The percent change in noise standard deviation due to gantry tilt was calculated in all reconstructed simulated and experimental images.Results:Tilting the gantry reduced the breast dose in all simulated and experimental phantoms, with generally greater dose reduction at increased gantry tilts. For example, at 30° gantry tilt, the dosimeters located in the superior, middle, and inferior breast regions measured dose reductions of 74%, 61%, and 9%, respectively. The simulations estimated 0%–30% total breast dose reduction across the eight phantoms and range of tilt angles. However, tilted‐gantry acquisition also increased the noise standard deviation in the simulated phantoms by 2%–50% due to increased pathlength through the iodine‐filled heart. The experimental phantom, which did not contain iodine in the blood, demonstrated decreased breast dose and decreased noise at all gantry tilt angles.Conclusions:Tilting the gantry reduced the dose to the breast, while also increasing noise standard deviation. Overall, the noise increase outweighed the dose reduction for the eight voxelized phantoms, suggesting that tilted gantry acquisition may not be beneficial for reducing breast dose while maintaining image quality.
Patient‐specific quantification of respiratory motion‐induced dose uncertainty for step‐and‐shoot IMRT of lung cancer
Authors: Li Heng , Park Peter , Liu Wei , Matney Jason , Liao Zhongxing , Balter Peter , Li Yupeng , Zhang Xiaodong , Li Xiaoqiang , Zhu X. Ronald 
Published: November 2013

Purpose:The objective of this study was to quantify respiratory motion‐induced dose uncertainty at the planning stage for step‐and‐shoot intensity‐modulated radiation therapy (IMRT) using an analytical technique.Methods:Ten patients with stage II/III lung cancer who had undergone a planning four‐dimensional (4D) computed tomographic scan and step‐and‐shoot IMRT planning were selected with a mix of motion and tumor size for this retrospective study. A step‐and‐shoot IMRT plan was generated for each patient. The maximum and minimum doses with respiratory motion were calculated for each plan, and the mean deviation from the 4D dose was calculated, taking delivery time, fractionation, and patient breathing cycle into consideration.Results:For all patients evaluated in this study, the mean deviation from the 4D dose in the planning target volume (PTV) was <2.5%, with a standard deviation <1.2%, and maximum point dose variation from the 4D dose was <6.2% in the PTV assuming delivery dose rate of 200 MU/min and patient breathing cycle of 8 s. The motion‐induced dose uncertainty is a function of motion, fractionation, MU (plan modulation), dose rate, and patient breathing cycle.Conclusions:Respiratory motion‐induced dose uncertainty varies from patient to patient. Therefore, it is important to evaluate the dose uncertainty on a patient‐specific basis, which could be useful for plan evaluation and treatment strategy determination for selected patients.