bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Experimental Investigation of the Dynamic Performance of a Vertical-Application Three-Lobe Bearing
Authors: Khatri Rasish , Childs Dara W. 
Published: September 2014

Dynamic performance test results are provided for a vertical-application three-lobe bearing, geometrically similar to a three-lobe bearing tested by Leader [1] to stabilize a vertical sulfur pump. The bearing has the following specifications: 100° pad arc angle, 0.64 preload, 100% offset, 101.74 mm bore diameter, 0.116 mm radial pad clearance, 76.3 mm axial length, and 100° static load orientation from the leading edge of the loaded pad. The bearing is tested at 2000 rpm, 4400 rpm, 6750 rpm, and 9000 rpm. This bearing is tested in the no-load condition and with low unit loads of 58 kPa and 117 kPa. The dynamic performance of this bearing is evaluated to determine (1) whether a fully (100%) offset three-lobe bearing configuration is more stable than a standard plain journal bearing (0.5 whirl-frequency ratio), and (2) whether a fully offset three-lobe bearing provides a larger direct stiffness than a standard fixed-arc bearing. Hot and cold clearances are measured for this bearing. Dynamic measurements include frequency-independent stiffness and damping coefficients. Bearing stability characteristics are evaluated using the whirl-frequency ratio (WFR). Test results are compared to numerical predictions obtained from a fixed-arc bearing Reynolds equation solver.
Dynamic tests show that the vertical-application three-lobe bearing does not improve stability over conventional fixed-arc bearings. The measured WFRs for the vertical-application bearing are approximately 0.4–0.5 for nearly all test cases. Predicted WFRs are 0.46 at all test points.
The vertical-application bearing dimensionless direct stiffness coefficients were compared to those for a 70% offset three-lobe bearing. Dimensionless direct stiffness coefficients at 0 kPa are larger for the vertical-application bearing by 45–48% in the loaded direction and larger by 15–26% in the unloaded direction. Thus, the vertical-application bearing does impart a larger centering force to the journal relative to the 70% offset bearing, in the no-load condition.
Predictions using both the measured hot clearance and measured cold clearance as inputs to the code are compared to the measured dynamic data. In general, the predicted direct stiffness coefficients using both the hot and cold clearances as inputs were higher than measured direct stiffnesses. The two sets of predicted cross-coupled stiffness coefficients straddle the measured cross-coupled stiffness coefficients. Predicted direct damping coefficients using both solutions were higher than measured values in most cases, but agreement between predictions and measurements improved significantly at high speeds and when applying light loads.
Aerodynamic Analysis and Multi-Objective Optimization Design of a High Pressure Ratio Centrifugal Impeller
Authors: Guo Zhendong , Zhou Zhiming , Song Liming , Li Jun , Feng Zhenping 
Published: September 2014

The design of high pressure ratio impellers is a challenging task. SRV2-O, a typical high pressure ratio centrifugal impeller is selected for the research. A good understanding of flow characteristics in the passage of SRV2-O is obtained by using 3D Reynolds-Averaged Navier-Stokes (RANS) solutions upon numerical validation. It confirms that tip leakage flow and shock wave boundary layer interactions produce the primary energy loss in this transonic impeller.
A 3D multi-objective aerodynamic optimization and data mining method named BMOE is presented and programmed by integrating a self-adaptive multi-objective differential evolution algorithm SMODE, 3D blade parameterization method based on non-uniformed B-Spline, RANS solver technique and self-organization map (SOM) based data mining technique. Using BMOE, multi-objective aerodynamic design optimization and data mining is performed for SRV2-O. 14 Pareto solutions are obtained for maximizing isentropic efficiency and total pressure ratio of the impeller. Three typical Pareto solutions, Design A with the highest efficiency, Design B with the higher efficiency and larger pressure ratio and Design C with the maximum pressure ratio, are analyzed. Detailed analysis indicates that the aerodynamic performance of optimized designs is greatly improved. Furthermore, by SOM-based data mining on optimization results, trade-off relation between objective functions and parameter influence mechanism on impeller aerodynamic performance are visualized and explored.
Nonreflecting Boundary Conditions for Aeroelastic Analysis in Time and Frequency Domain 3D RANS Solvers
Authors: Kersken Hans-Peter , Ashcroft Graham , Frey Christian , Wolfrum Nina , Korte Detlef 
Published: September 2014

This paper describes the implementation of a set of nonreflecting boundary conditions of increasing approximation quality for time-accurate and time-linearized 3D RANS solvers in the time and frequency domain. The implementations are based on the computation of eigenfunctions, either analytically or numerically, of the linearized Euler or Navier-Stokes equations for increasingly complex background flows. This results in a hierarchy of nonreflecting boundary conditions based on 1D characteristics, 2D circumferential mode decomposition, and 3D circumferential and radial mode decomposition, including viscous effects in the latter, for the frequency domain solver. By applying a Fourier transform in time at the boundaries the frequency domain implementations can be employed in the time domain solver as well. The limitations of each approximation are discussed and it is shown that increasing the precision of the boundary treatment the nonreflecting property of the boundary conditions is preserved for more complex flows without incurring an excessive increase in computing time.
Results of a flutter analysis of a low pressure turbine blade obtained by time and frequency domain simulations are validated against each other and against reference results obtained with a 3D Euler frequency domain solver. The comparison of the results for different boundary conditions reveals the importance of using high quality boundary conditions.
Validating the Numerical Prediction of the Aerodynamics of an Axial Compressor
Authors: Wolff Torben , Herbst Florian , Freund Oliver , Liu Le , Seume Joerg R. 
Published: September 2014

Numerical methods have become the basis for the aerodynamic design of turbomachinery in order to reduce the time for development cycles and associated cost. Designing modern axial compressors requires high confidence in the quality of numerical predictions. In terms of the aerodynamics, the loading of the blades as well as the efficiency targets constantly increase. Losses have to be predicted precisely and the impact of three-dimensional secondary flows, separation, and laminar-turbulent transition must be taken into account. In the present paper, the aerodynamic prediction quality of the state-of-the-art turbomachinery design code TRACE is validated against experimental data from a 2.5-stage axial compressor.
The aerodynamic prediction quality is systematically investigated to determine errors and uncertainties regarding the discretization, turbulence and transition models, and importance of considering unsteady effects. Computations are performed for several operating points and the results are validated by means of the compressors integral pressure ratio as well as by means of local pneumatic probe measurements. It is shown that using the empirical γ–ReΘ model improves the prediction quality of the boundary layers and wake flows. Time-resolved computations at the design point of the compressor show that the strength and the losses of a corner separation in both vane rows are reduced to realistic levels when the periodic-unsteady interaction with the upstream wakes is considered. The generally good aerodynamic predictions for both local and integral experimental quantities qualify TRACE for aeroelastic predictions which are planned for the future.
Experimental Analysis of the Unbalance Response of Rigid Rotors Supported on Aerodynamic Foil Bearings
Authors: Balducchi Franck , Arghir Mihai , Gaudillere Sylvain 
Published: September 2014

The paper presents the experimental unbalance response of two slightly different rigid rotors supported by two identical aerodynamic foil bearings. Impulse (Pelton) turbines manufactured directly on the outer surface entrain both rotors at rotation speeds comprised between 50 krpm and 100 krpm. The displacements in the two foil bearings are measured during coast down and are depicted as waterfall plots. They show typical non-linear behavior, i.e. subsynchronous vibrations accompanying the synchronous component. The measurements show clearly that the subsynchronous components bifurcate at typical rotation speeds (mostly rational fractions of the rotation speed). The non-linear behavior of the rigid rotor supported on foil bearings is also underlined by varying the added unbalance: with increasing unbalance the vibration spectrum becomes gradually richer as new subsynchronous vibrations appear.
The experimental results are compared with very simplified theoretical predictions based on the assumption that the air film in the two bearings is infinitely stiff compared to the foil structure. This latter is characterized by a cubic stiffness and a structural damping coefficient. The comparisons show only a rough qualitative agreement and enlighten the actual limits of foil bearings theoretical models.
An Alternative Experimental Method for Establishing Detailed Internal Heat Transfer Coefficient Distributions of Complex Cooling Geometries Using IR Thermography
Authors: Kinell Mats , Utriainen Esa , Jaksch Peter 
Published: September 2014

Experimental methods for obtaining heat transfer coefficients often include building an upscaled, transparent, low conductivity model to which the transient semi-infinite wall method is applied. Hence, each geometry of interest will demand time consuming manufacturing, careful preparation and the heat transfer on the obstacles themselves, e.g. ribs, has to be neglected. This paper introduces an alternative method in which real geometries in an arbitrary material can be used. At the start of the experiment, the test object is at rest with a uniform temperature. By synchronizing internal air flow using a valve with an IR-camera, the thermal response of the outer wall to a sudden change of the inside temperature will be monitored. The temperature variation over time is imported into a conjugate, 1D internal flow and solid 3D FE, transient solver which will calibrate the inner heat transfer coefficient distribution so that the temperatures of the mesh matches the recorded IR-camera temperatures.
The accuracy and reliability of this method will be shown by comparing the results of an impingement cooling case to other published experimental results. A blade or vane trailing edge triple impingement geometry is also investigated. This pose a more complex challenge than the former but which the presented method is still able to handle. This is demonstrated by comparing the evaluated time resolved surface temperatures to the measured ones.
Application of an Advanced Creep-Fatigue Procedure for Flexible Design of Steam Turbine Rotors Based on Fracture Mechanics Methods
Authors: Sheng Shilun , Almstedt Henning 
Published: September 2014

The demand for steam turbine components is driven by high efficiency but also by high plant operational flexibility. Steam turbine rotors are therefore exposed to increased temperatures and increased number of stress cycles. These aspects should be considered for life-time prediction. Fracture mechanics methods are usually applied when crack like defects are detected for new rotors but also for rotor components in service. Based on the findings a decision has to be made with respect to acceptability considering high temperature effects as well as the expected future operating regime.
For defect analysis in the high temperature range, crack initiation and crack propagation under combined creep and fatigue loading need to be taken into account. Based on fracture mechanics methods and long-term testing data, an advanced creep-fatigue procedure for the evaluation of crack initiation and crack growth has been developed within the German Creep Group W14 for creep crack growth behavior. Furthermore, recent studies show that the crack size for creep crack initiation depends on material ductility and creep strain in the ligament.
This paper demonstrates the industrial application of the abovementioned method for steam turbine rotor assessment, which has a focus on crack initiation and crack growth under creep-fatigue conditions. For crack initiation, a simplified approach based on defect size and material ductility is compared to a standard approach — Two-Criteria-Diagram (2CD). For the advanced evaluation concept, the creep crack initiation criterion is combined for analysis with a creep-fatigue crack growth procedure. The benefit of the method especially for ductile material will be highlighted.
Experimental Investigation on Droplet Behaviour in a Transonic Compressor Cascade
Authors: Neupert Niklas , Ober Birger , Joos Franz 
Published: September 2014

In recent years overspray fogging has become a powerful means for power augmentation of industrial gas turbines. Most of the studies concerning this topic focus on the problem from a thermodynamic point of view as summarized by Eisfeld and Joos [1]. Only a few studies, however, were undertaken to investigate the droplet behavior in the flow channel of a compressor. Eisfeld and Joos [2] and Ober [3] revealed qualitative results showing a large variety of two-phase phenomena present.
In this paper results of experimental investigation of a water laden flow through a compressor cascade are presented. A finely dispersed spray was used in the measurements (D10 < 10μm). Results of the droplet behavior in a transonic compressor cascade are shown in terms of shadowgraphy images and images of the blade surface film pattern. The angle of attack, the incoming velocity and the water load were varied to estimate the influence of these parameters on the flow pattern. The qualitative observations of the flow pattern are related to LDA/PDA data of the flow channel and at the outlet of the cascade. The data represents a base for numerical and mean line models of two phase compressor flow concerning droplet-wall interactions as well as flow induced breakup.
Vortex-Induced Vibration and Frequency Lock-In of an Airfoil at High Angles of Attack
Authors: Besem Fanny M. , Kamrass Joshua D. , Thomas Jeffrey P. , Tang Deman , Kielb Robert E. 
Published: September 2014

Vortex-induced vibration is a fluid instability present in many areas, including offshore platforms, wind turbines, and turbomachinery. The vortices due to secondary flows exert an periodic unsteady force on the elastic structure, leading to potentially dangerous vibrations. Under certain circumstances, the shedding frequency can lock into the structure natural frequency and lead to limit cycle oscillations. These high amplitude vibrations can cause material fatigue, and are a common source of structural failure.
This work uses a frequency domain, harmonic balance, CFD code to predict the lock-in of an airfoil at very high angles of attack. The natural shedding frequency is found using a delta phase per iteration method, and the lock-in region is identified by enforcing airfoil motion at different oscillation amplitudes and frequencies. The numerical results are successfully compared to experimental data from wind tunnel testing on a NACA0012 airfoil at deep stall conditions.
Experimentally Verified Study of Regeneration-Induced Forced Response in Axial Turbines
Authors: Aschenbruck Jens , Seume Joerg R. 
Published: September 2014

Geometrical variations occur in highly loaded turbine blades due to operation and regeneration. To determine the influence of such regeneration-induced variances of turbine blades on the aerodynamic excitation, a typical stagger angle variation of overhauled turbine blades is applied to stator vanes of an air turbine. This varied turbine stage is numerically and experimentally investigated.
For the aerodynamic investigation of the vane wake, CFD simulations are conducted. It is shown that the wake is changed due to the stagger angle variation. These results are confirmed by aerodynamic probe measurements in the air turbine.
The vibration amplitude of the downstream rotor blades has been determined by a computational forced response analysis using a uni-directional fluid-structure interaction approach and is experimentally verified here by tip-timing measurements. The results of the simulations and the measurements both show significantly higher amplitudes at certain operating points due to the additional wake excitation. For typical regeneration-induced variations in stagger angle, the vibration amplitude is up to five times higher than in the reference case of uniform upstream stators. Based upon the present results, the influence of these variations and of the vane patterns on the vibration amplitude of the downstream rotor blade can and should be estimated in the regeneration process to minimize the dynamic stresses of the blades.
Effect of Radiative Heat Transfer Factor on the Temperature Distribution of a First Stage Vane
Authors: Yin Hong , Li Mingfei , Chi Zhongran , Ren Jing , Jiang Hongde 
Published: September 2014

As the advanced heavy-duty gas turbine develops, the turbine inlet temperature and pressure have increased quite significantly to achieve better performance. The flow and heat transfer conditions of hot components including combustor and turbine become even more extreme than ever which need corresponding aerodynamic and cooling design development. The issue of combustor-turbine interaction has been proposed as a complicated research topic. Currently the hot streak, turbulence intensity, swirling flow, radiation are the four important factors for combustor-turbine interaction research according to the literature. Especially as the turbine inlet temperature increases, the radiative heat transfer plays a more and more important role.
In this paper, a first stage vane is selected for the conjugate heat transfer simulation including radiative heat transfer since it is almost impossible to identify the radiative effect in experiment. The goal is to examine the effects of radiative heat flux and temperature increment caused by radiation. Several radiative factors including the inlet radiation, gas composition, vane surface emissivity and outlet reflection are investigated. The temperature distribution and heat flux enhancement under different conditions are compared, which can provide reference to the turbine heat transfer design. The general information of radiative effect can be summarized by quantitative analysis.
Results show that the temperature increases obviously when considering the radiation effect as expected. However, these factors show distinct influence on the vane temperature distribution. The inlet radiation has significant impact on the vane leading edge and pressure side. Besides the gas radiation plays quite uniform on the whole vane surface.
Performance Increase of Steam Turbine Condensers by CFD Analysis
Authors: Hecker Simon , Auge Andreas , Ellsel Tobias , Flegler Johan , Musch Christian , Graßmann Arne 
Published: September 2014

An effective measure to increase the performance of turbine power plants is to minimize flow losses in the condenser resulting in a smaller terminal temperature difference (TTD) — the more the TTD of the condenser can be reduced in an optimization process of a given power plant configuration, the more the exhaust pressure will decrease. With an optimized condenser tube bundle design the TTD can be improved.
This study presents the modification of a commercial CFD code to simulate the three-dimensional flow field around and within tube bundles. Additionally the temperature distribution of the cooling water is part of the numerical solution without modeling each individual condenser tube.
To show the accuracy of the CFD code the flow in a large scale power plant condenser is simulated and compared to measurements of local heat transfer coefficients in the bundles. The comparison shows that the presented CFD tool is valid to predict the performance of such condensers.
Based on the results of the study, areas with low cooling performance are identified and suggestions are made for the increase of the overall condenser efficiency.
Dynamic Modeling and Simulation of Gasifier Based on Volume-Resistance Characteristics Method
Authors: Huang Di , Zhang Huisheng , Weng Shilie , Su Ming 
Published: September 2014

Gasifier is one of core parts of Integrated Gasification Combined Cycle, which combines clean coal technology with combined cycle through the gasification of solid coal. The conventional lumped parameters simulation model cannot reflect the distribution characteristics in the gasifier.
In order to obtain a more realistic model which can depict the dynamic response as well as the distribution characteristics, this paper utilizes the volume-resistance modeling technique and modular modeling method for the gasifier modeling. The gasifier will be divided into several compartments. The parameters in each compartment are uniform, while it has distribution characteristics for a whole gasifier. Thus the pressure and temperature distribution in the gasifier will be incorporated into the gasification process.
The gasifier model in this paper can not only be used for the system performance analysis, but also for the control system design and debugging.