bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Physics of H-Darrieus Turbines Self-Starting Capability: Flapping-Wing Perspective
Authors: Worasinchai Supakit , Ingram Grant L. , Dominy Robert G. 
Published: December 2013

It has been widely reported that Darrieus turbines cannot self-start and that they require external assistance to accelerate to their operating tip speed ratios. However, recent experiments have shown conclusively that H-Darrieus rotors with fixed-pitch blades that employ a symmetrical aerofoil can reliably self-start in steady controlled environments. Previous attempts have also been made to model the starting characteristics but there still exists a significant discrepancy between the experimental data and model prediction, suggesting that our understanding of this starting characteristic remains weak. The investigation and explanation of the starting characteristics is the focus of this paper.
The investigation was made through a careful analysis of aerofoils that undergo Darrieus motion, giving some insights on how the blade experiences different flow conditions and how driving force is developed over the flight path. The analysis reveals that the aerofoil in Darrieus motion is analogous to flapping wing mechanism; the mechanism that fish and birds employ to generate propulsion. The explanation of flow physics and torque development can then be made through a simple pitch-heave concept.
The investigation using this concept together with observations of flapping creatures suggests that the key feature that promotes driving torque generation and the ability to self-start is the unsteadiness associated with the rotor. This unsteadiness is related to chord-to-diameter ratio. This, together with blade aspect ratio, and number of blades, is the reason why H-Darrieus turbines that employ a symmetrical aerofoil can self-start.
Full-Size Rotordynamic Test Rig for Magnetic and Auxiliary Bearing Testing and Initial Results
Authors: De Santiago Oscar , Solórzano Víctor , Díaz Sergio 
Published: December 2013

Recent challenges in turbocompresor design include applications in subsea installations as well as remote operation in unmanned floating platforms. These applications benefit from oil-free operation which solves technical hurdles while being environmentally friendly. The most mature oil-free rotor support technology today is the magnetic bearing which is being used by several manufacturers as their standard solution to these advanced applications. These systems require auxiliary bearings to contain the rotor in case of a power failure to the magnetic bearings or a transient event. In general, there exists the need to develop commercial solutions for auxiliary bearings to extend its life, in particular regarding cumulative damage associated to drop events.
This paper presents the design of a configurable test rig that can accommodate different rotor sizes, up to 1200 mm in bearing span, and 711 mm diameter wheels. The rig can also accommodate bearing sizes up to 229 mm. Rig pedestals can fit different bearing types such as magnetic bearings and/or auxiliary bearings independently, including oil bearings for comparison purposes. Misalignment and support flexibility effects are also possible. A 15.5 kW, variable speed electric motor drives the test rotor up to a speed limit of 10,000 rpm.
Initial experiments on auxiliary bearings are shown for a 5-impeller, 57.8 kg, subcritical compressor rotor without drop events to study the baseline dynamic behavior of roller-element bearings (with inner clearance) on soft supports (o-rings). These experiments are presented to illustrate non-linear vibration regimes present during rotor-stator interaction with a highly unbalanced rotor. Experimental evidence presented can be used to fine-tune current auxiliary bearingmodels to improve rotordynamic predictive codes.
A Comparison of Two Load Transferring Methods in an Unsteady One-Way Fluid-Structure Interaction Analysis
Authors: Drewczynski Marcin , Solinski Marek , Rzadkowski Romuald 
Published: December 2013

A full two-way aeroelasticity coupling analysis of rotating machinery and their main components requires considerable computational analysis and CPU time. This is why the most common methodology for this type of problem is a one-way coupling between fluid and structure. In this case, forces acting on rotor blades that result from a flow are introduced into a structural model of a blade as a local spot load in the centre of gravity or a series of local spot points deployed along the blade length. However, this method does not take into account how the forces change in a chordwise direction (along chord).
An alternative way is to use the method of directly transferring the pressure field as a surface load from the CFD analysis to a structural model of a blade. In this case various interpolation methods are needed to transfer the results from the CFD mesh on to the structural mesh nodes.
In this paper the authors compare how both methods of load transfer affect rotor blade stress and displacement levels during one period of rotation. Calculations were carried out for the first stage compressor blade of an aircraft engine. Ansys 12.1 was used to calculate the entire structure. Unsteady CFD calculations were carried out using Fluent for a 1.5 stage axial compressor model. For the numerical calculations a non-viscous flow was used. The unsteady forces were calculated on 10 control cross-sections of a rotor blade. The transient results obtained from the CFD calculations were transferred onto a structural rotor blade model using APDL language script. For both methods of load transference, transient displacements and transient stresses for the rotor blade were calculated. The harmonic analysis results were compared. Mesh sensivity analysis was also carried out for the structural model.
An Experimental Flow Investigation of Low Pressure Turbine Stages With Various Wet Conditions
Authors: Shibukawa Naoki , Tsukuda Tomohiko , Hashidate Tadayuki , Kawagishi Hiroyuki , Uchida Tatsuro , Goto Koichi 
Published: December 2013

Detail flow characteristics of an actual size low pressure steam turbine stages under real operating conditions were examined in this paper. The main purpose of the experimental work was to obtain the radial distribution of the velocity triangles in the wet flow of the large size turbine, so that a series of tests were carried out with various wet conditions. Some particular changes of the flow pattern were observed at the exit of both the stator and the blade rows which would not predicted by steam turbine design tools.
A kind of flow coefficient was defined and investigated as well as the steam velocities. With an assumption of the steam wetness distribution along the blade span, a tendency of the flow coefficient was appeared which was similar to previous work [7]. The wetness assumption was qualitatively verified by bore-scope observation of the water concentration on the stator surface and the fog condition of the steam path.
Non-Linear Dynamics of Steam Turbine Blades With Shroud: Numerical Analysis and Experiments
Authors: Zucca Stefano , Gola Muzio M. , Piraccini Francesco 
Published: December 2013

The prediction of the aeromechanical behavior of low-pressure blades represents one of the main challenges in the Steam Turbine Industry. The evaluation of forced response and damping is critical for the reliability of new designs and usually requires expensive validation campaigns such as Wheel Box Tests (WBT).
A WBT consists of one or more blade rows assembled on a rotor and spun at the desired rotating speed in a vacuum cell, with synchronous excitation provided by various sources. The WBT provides accurate information about the blade modes frequency, the alternating response level, and allows the evaluation of the mechanical damping.
Given the large effort in terms of costs and time associated to the experimental activity, the possibility to rely on the output of a numerical code either during the first steps of a new design or to investigate the effect of minor changes to a current design would be extremely beneficial to the development of future products.
In order to compute the non-linear forced response of shrouded blades of steam turbines, custom numerical solvers must be developed, since commercial finite element (FE) solvers do not perform this kind of analysis in the frequency domain.
In this paper, the forced response of a blade with shrouds of a low pressure steam turbine is computed and numerical results are compared with the experimental Wheel Box Tests performed at GE Oil & Gas. The calculations require a three-step procedure: in the first step, a non-linear static analysis is performed in ANSYS® in order to compute the actual contact area on the shroud surface and the distribution of static normal loads, then a reduced order model of the blade is generated in ANSYS® taking into account the stiffening effect on the blade of the pre-stress due to the centrifugal force, finally the reduced model is imported in a numerical code and the non-linear forced response of the blade is computed.
The numerical code solves the balance equations of the system in the frequency domain, by means of the Harmonic Balance Method, imposing cyclic symmetry boundary conditions of the system. An interpolation procedure is implemented in order to manage the non-perfectly matching meshes of the shroud contact surfaces, while the tangential and normal contact stiffness is computed with a numerical model based on the contact mechanics principles.
The numerical and the experimental results around some of the critical resonances of the system are compared in order to assess the reliability and accuracy of the numerical tool for its future implementation in the mechanical design practice of the blades.
Performance Analysis of Cogenerative and Trigenerative Plant With Microgas-Turbine
Authors: Brandoni Caterina , Comodi Gabriele , Pelagalli Leonardo , Caresana Flavio 
Published: December 2013

The paper reports on the performance analysis of cogenerative and trigenerative plants based on Micro Gas Turbines. The core of the system is a natural-gas-fuelled Turbec T100 operating on a regenerated open-air cycle.
A code specifically developed by the authors to simulate the micro gas turbine in cogeneration plants, and already checked against experimental data, has been upgraded to simulate the unit’s behavior when facing also a cooling demand (trigenerative case).
For this purpose the model of a water-LiBr single-effect absorption chiller driven by hot water has been used.
The analysis cover all the unit’s application range and represent a start for its economic evaluation.
Decreasing Bladed Disk Response With Dampers on a Few Blades: Part II—Nonlinear and Blade-Blade Dampers Applications
Authors: Murthy Raghavendra , Mignolet Marc P. 
Published: December 2013

This two part paper focuses on the optimum placement of a limited number of dampers, i.e. fewer than the number of blades, on a bladed disk to induce the smallest possible amplitude of blade response with or without involuntary, random mistuning. Intentional mistuning is also considered as an option to reduce the amplitude of blade response and the pattern of two blade types (referred to as A and B blades) is then part of the optimization effort in addition to the location of the dampers on the disk.
This second part of the investigation focuses on the application of the optimization algorithms developed in Part I to nonlinear dampers, more specifically friction dampers, as well as to the consideration of blade-blade dampers, linear or nonlinear (underplatform dampers). Additionally, the optimization of blade-only and blade-blade linear dampers will be extended to include uncertainty/variability in the damper properties that arise during the manufacturing and/or inservice. It is found that the optimum achieved without considering such uncertainty/variability is robust with respect to it.
Improving Tilting-Pad Journal Bearing Predictions: Part II—Comparison of Measured and Predicted Rotor-Pad Transfer Functions for a Rocker-Pivot Tilting-Pad Journal Bearing
Authors: Wilkes Jason C. , Childs Dara W. 
Published: December 2013

As described in Part I [1], most analytical models for TPJBs are based on the assumption that explicit dependence on pad motion can be eliminated by assuming harmonic rotor motion such that the amplitude and phase of pad motions resulting from radial and transverse rotor motions are predicted by rotor-pad transfer functions (TFs). In short, these transfer functions specify the amplitude and phase of pad motion (angular, radial, translational, etc.) in response to an input rotor motion.
Direct measurements of pad motion during test excitation were recorded to produce measured transfer functions between rotor and pad motion, and a comparison between these measurements and predictions is given. Motion probes were added to the loaded pad (having the static load vector directed through its pivot) of a 5-pad TPJB to obtain accurate measurement of pad radial and tangential motion, as well as tilt, yaw, and pitch. Strain gages were attached to the side of the loaded pad to measure static and dynamic bending strains, which were then used to determine static and dynamic changes in pad curvature (pad clearance).
Impact of Secondary Flow on the Accuracy of Simplified Design Methods for Steam Turbine Stages
Authors: Schumann Jan , Harbecke Ulrich , Sahnen Daniel , Polklas Thomas , Jeschke Peter , Schwarz Mark André 
Published: December 2013

The subject of the presented paper is the validation of a design method for HP and IP steam turbine stages. Common design processes have been operating with simplified design methods in order to quickly obtain feasible stage designs. Therefore, inaccuracies due to assumptions in the underlying methods have to be accepted. The focus of this work is to quantify the inaccuracy of a simplified design method compared to 3D Computational Fluid Dynamics (CFD) simulations.
Short computing time is very convenient in preliminary design; therefore, common design methods work with a large degree of simplification. The origin of the presented analysis is a mean line design process, dealing with repeating stage conditions. Two features of the preliminary design are the stage efficiency, based on loss correlations, and the mechanical strength, obtained by using the beam theory. Due to these simplifications, only a few input parameters are necessary to define the primal stage geometry and hence, the optimal design can easily be found. In addition, by using an implemented law to take the radial equilibrium into account, the appropriate twist of the blading can be defined.
However, in comparison to the real radial distribution of flow angles, this method implies inaccuracies, especially in regions of secondary flow. In these regions, twisted blades, developed by using the simplified radial equilibrium, will be exposed to a three-dimensional flow, which is not considered in the design process. The analyzed design cases show that discrepancies at the hub and shroud section do exist, but have minor effects. Even the shroud section, with its thinner leading-edge, is not vulnerable to these unanticipated flow angles.
Energy-Yield-Based Optimization of an H-Darrieus Wind Turbine
Authors: Bianchini Alessandro , Ferrari Lorenzo , Magnani Sandro 
Published: December 2013

Small-size H-Darrieus wind turbines are gaining more popularity in the wind energy market, thanks to some particular benefits (simplicity, reliability and low noise emissions) and to the efforts of industrial manufacturers to propose new exterior solutions coupled with tempting rated-power offers. The actual operating conditions of a rotor over a year can be, however, very different from the nominal one and strictly dependent on the features of the installation site. Based on these considerations, a turbine optimization oriented to maximize the annual energy yield, instead of the maximum power, is thought to represent a more interesting solution.
With this goal in mind, 5400 test cases of H-Darrieus rotors were compared on the basis of their energy-yield capabilities for different annual wind distributions in terms of average speed. To this purpose, the wind distributions were combined with the predicted performance maps of the rotors obtained with a specifically developed numerical code based on a Blade Element Momentum (BEM) approach. The limits related to the wind turbine start-up behavior and to the structural loads (i.e. maximum rotational speed and maximum wind velocity) were also taken into account.
The analysis, developed in terms of dimensionless parameters, highlighted the configurations which ensure the largest annual energy yield for each wind distribution. In addition, the differences between the results of a design process oriented to the maximum power output or to the maximum annual-energy-yield were analyzed; in particular, the comparison showed that a design oriented to the maximum energy-yield is assumed to provide a notable increase in the extracted energy (up to around 20%, with the selected design assumptions) whenever wind distributions with low average wind speeds are considered.
Leakage-Induced Compressor Blade Excitation due to Inter-Segment Gaps
Authors: Bladh Ronnie , Zhuang Qingyuan , Hu Jiasen , Hammar Johan 
Published: December 2013

A comprehensive investigation is presented related to leakage-induced blade excitation from shrouded vane segments found in industrial gas turbine compressors. The focus of the investigation is to explore the excitation mechanism acting on downstream rotor blades that stem from the particularly complex leakage flows around the hub inter-segment gaps.
The aerodynamic forces are here determined using 3D nonlinear time-marching CFD simulations. The employed computational model encompasses the two rear-most stages in an existing industrial gas turbine compressor. The inter-segment gap is implemented in the next-to-last stator, varying from no gap to twice the nominal gap size.
Obtained results indicate that the excitation induced by the inter-segment gap leakage flows is distinctly multi-harmonic and unexpectedly strong. As much as five times the excitation strength of upstream wakes was observed already for the nominal gap. The induced unsteady forces were found to derive from two different sources: (i) a large separation producing local forcing in the hub region; and (ii) circumferentially varying flow speed resulting in distributed forcing over the entire blade.
The findings imply that the excitation induced by inter-segment gap leakage flows can be a significant contributor to blade vibratory responses in the intermediate engine order range, and thereby add to the knowledge base related to blade dynamic integrity.
Performance Analysis of Direct Steam Generation-Central Receiver Systems
Authors: Sanz-Bermejo Javier , Gonzalez-Aguilar José , Romero Manuel 
Published: December 2013

This work presents a comparative study between direct steam generation central receiver solar power plants working at live steam conditions similar to those found in commercial plants. PS10 and PS20 by Abengoa Solar use a single-receiver, producing saturated steam, whereas Sierra SunTower by e-Solar and Ivanpah Solar Electric Generating System (ISEGS) by BrightSource use dual-receiver technology producing superheated steam.
The system analysis includes individual studies for each subsystem: solar field, receiver and Rankine power block; as well as the overall-analysis of a 66.7 MWth plant. PS10 working conditions were analysed with and without intermediate reheat step. It was assumed that Sierra SunTower-configuration has non-reheat turbine and Ivanpah-cycle includes an intermediate reheat step. The reheat process in PS10 configuration was performed using a fraction of live steam coming from the receiver; while for Ivanpah-configuration exhaust steam from high pressure turbine stage was sent back to the superheated steam section of the dual-receiver. These concepts make possible to avoid hybridisation and assure special regimes (such as Spanish feed-in tariff).
The analysis of the heliostat field for dual-receiver concepts reveals that the aiming strategy on the absorbers has not relevant influence on optical performances. However, receiver efficiency decreased from 91.9%, working with saturated steam, to 87.86–84.14% working with superheated steam related to operating temperatures and heat exchange surface area. This study reveals that the improvement achieved in the power block under Ivanpah configuration was able to compensate higher thermal losses at the receiver, increasing net power production by 25.5% compared with saturated steam conditions.
Benefits of Acupuncture for Diabetic Gastroparesis: A Comparative Preliminary Study
Authors: Danielli Miller Netanella , Schiff Elad , Ben-Arye Eran , Singer Joelle , Tsadok Perets Tsachi , Flaut Shlomit , Sahar Nadav , Niv Yaron , Dickman Ram 
Published: December 2013

Objectives The aim of this preliminary study was to compare the effectiveness of domperidone and acupuncture for the management of diabetic gastroparesis. Methods This was a preliminary, prospective non-randomised, unblinded case-crossover study conducted in patients with longstanding, uncontrolled diabetes mellitus and gastroparesis. All patients received domperidone (20 mg four times a day) for 12 weeks, followed by a 2–3 week washout period, and then biweekly acupuncture treatments for 8 weeks. Gastric emptying rate, glucose and glycated haemoglobin (HbA1C) levels were measured at start and end of each treatment period. At each of these timepoints patients completed the Gastroparesis Cardinal Symptom Index (GCSI), the Satisfaction with Life Scale (SWLS), and the Short-Form 36 Health Survey Update (SF-36). Results The trial was curtailed after only eight participants could be recruited in 3 years. The mean age of patients was 57.1±9.9 years, the male:female ratio was 1:7 and mean body mass index (kg/m2) was 25.2±1.2. There was no change in any of the outcome parameters after treatment with domperidone. Acupuncture was associated with a decrease in scores for almost all cardinal symptoms of the GCSI, as well as in increased total score on the SWLS (p=0.002) and the social functioning domain of the SF-36 (p=0.054). Acupuncture did not lead to an improvement in gastric emptying, or glucose control from baseline. Conclusions Acupuncture treatment may lead to symptomatic improvement in patients with diabetic gastroparesis. Within the limitations of this preliminary, non-randomised and unblinded study, it appears that this effect may be due to non-specific mechanisms.