bluuebunny/crossref_metadata_2025_split huggingface dataset:
Winglets for Improved Aerothermal Performance of High Pressure Turbines
Authors: Coull John D. , Atkins Nick R. , Hodson Howard P. 
Published: November 2013

This paper investigates the design of winglet tips for unshrouded high pressure turbine rotors, considering aerodynamic and thermal performance simultaneously. A novel parameterization method has been developed to alter the tip geometry of a rotor blade. A design survey of un-cooled, flat-tipped winglets is performed using RANS calculations for a single rotor at engine representative operating conditions.
Compared to a plain tip, large efficiency gains can be realized by employing an overhang around the full perimeter of the blade, but the overall heat load rises significantly. By employing an overhang on only the early suction surface, significant efficiency improvements can be obtained without increasing the overall heat transfer to the blade.
The flow physics are explored in detail to explain the results. For a plain tip, the leakage and passage vortices interact to create a three-dimensional impingement onto the blade suction surface, causing high heat transfer. The addition of an overhang on the early suction surface displaces the tip leakage vortex away from the blade, weakening the impingement effect and reducing the heat transfer on the blade. The winglets reduce the aerodynamic losses by unloading the tip section, reducing the leakage flow rate, turning the leakage flow in a more streamwise direction and reducing the interaction between the leakage fluid and endwall flows. Generally these effects are most effective close to the leading edge of the tip, where the leakage flow is subsonic.
An LP Turbine at Extreme Off-Design Operation
Authors: Lipfert Martin , Marx Martin , Rose Martin G. , Staudacher Stephan , Mahle Inga , Freygang Udo , Brettschneider Markus 
Published: November 2013

In a cooperative project between the Institute of Aircraft Propulsion Systems (ILA) and MTU Aero Engines GmbH a two-stage low pressure turbine with integrated 3D airfoil and endwall contouring is tested. The experimental data taken in the altitude test-facility study the effect of high incidence in off-design operation. Steady measurements are covering a wide range of Reynolds numbers between 40,000 and 180,000. The results are compared with steady multistage CFD predictions with a focus on the stator rows. A first unsteady simulation is taken into account as well. The CFD simulations include leakage flow paths with disc cavities modeled. Compared to design operation the extreme off-design high-incidence conditions lead to a different flow-field Reynolds number sensitivity. Airfoil lift data reveals changing incidence with Reynolds number of the second stage. Increased leading edge loading of the second vane indicates a strong cross channel pressure gradient in the second stage leading to larger secondary flow regions and a more three-dimensional flow field.
Global characteristics and area traverse data of the second vane are discussed. The unsteady CFD approach indicates improvement in the numerical prediction of the predominating flow field.
Excitation of Nodal Diameter Mode-Shapes of a Stator Ring of a Turbojet Engine Using a Limited Number of Excitation Sources
Authors: Nyssen Florence , Golinval Jean-Claude , Viguié Régis , Simon Daniel 
Published: November 2013

When considering engine tests, the sensors used to monitor the rotor parts mainly consist in strain gauges whose information is very sensitive to the gauge positioning, especially in high stress gradient regions. Therefore, to reduce the risk of misinterpreting the response given by the gauges, their calibration is required. Because strain gauges are positioned so that specific modes will be monitored, their calibration must be carried out for these modes. For cyclic symmetric structures, their high spectral density imposes the use of dedicated calibration techniques. In the present paper, the concept of modal appropriation is investigated as the first step of the calibration procedure.
This paper aims at presenting the development of an experimental approach enabling the isolation/appropriation of specific nodal diameter modes of a stator stage of an axial compressor using a limited number of excitation sources. A special emphasis has been brought to the minimum number and the optimized location of the excitation sources (shakers) required in laboratory conditions to appropriate specific nodal diameter modes and thereby retrieve the related modal features needed for the gauges calibration and mechanical design.
Full Rotortrain Modelling Approach for Assessment of Dynamic Stresses on Rotor and Blades due to Torsional Disturbances
Authors: Tsypkaykin Igor , Kellerer Rudolf 
Published: November 2013

Torsional rotor vibrations with low frequency always exist during normal operation due to oscillating torques at the generator. For long and flexible gas turbine blades (last stage turbine and first stage compressor), the “blade-rotor” coupled system could come into resonance with the torsion excitation. In order to ensure safe operation, the accurate prediction of eigenfrequencies and dynamic stresses in the blades and rotor is required and can be achieved by modeling the full rotor train with flexible blades.
A direct modeling approach is proposed which includes 3D FE blade models coupled with a rotor/generator FE model. A 1D, 2D or 3D FE mesh can be used for the rotor model. Comparisons of predicted and measured frequencies are presented.
Local Source Based CFD Modeling of Effusion Cooling Holes: Validation and Application to an Actual Combustor Test Case
Authors: Andreini A. , Da Soghe R. , Facchini B. , Mazzei L. , Colantuoni S. , Turrini F. 
Published: November 2013

State-of-the-art liner cooling technology for modern combustion chambers is represented by effusion cooling (or full-coverage film cooling). Effusion is a very efficient cooling strategy typically based on the use of several inclined small diameter cylindrical holes, where liner temperature is controlled by the combined protective effect of coolant film and heat removal through forced convection inside each hole. A CFD-based thermal analysis of such components implies a significant computational cost if the cooling holes are included in the simulations, therefore many efforts have been made to develop lower order approaches aiming at reducing the number of mesh elements. The simplest approach models the set of holes as a uniform coolant injection, but it does not allow an accurate assessment of the interaction between hot gas and coolant. Therefore higher order models have been developed, such as those based on localized mass sources in the region of hole discharge.
The model presented in this paper replaces the effusion hole with a mass sink on the cold side of the plate, a mass source on the hot side, whereas convective cooling within the perforation is accounted for with a heat sink. The innovative aspect of the work is represented by the automatic calculation of the mass flow through each hole, obtained by a run time estimation of isentropic mass flow with probe points, while the discharge coefficients are calculated at run time through an in-house developed correlation. In the same manner the heat sink is calculated from a Nusselt number correlation available in literature for short length holes. The methodology has been applied to experimental test cases of effusion cooling plates and compared to numerical results obtained through a CFD analysis including the cooling holes, showing a very good agreement. A comparison between numerical results and experimental data was performed on an actual combustor as well, in order to prove the feasibility of the procedure.
The Response of High Intensity Turbulence in the Presence of Large Stagnation Regions
Authors: Chowdhury N. , Ames F. E. 
Published: November 2013

Relatively small scale turbulence is known to intensify in the presence of a stagnation region due to the elongation of these eddies by the mean strain field of the approach flow. Experimental evidence also demonstrates that the large scale eddies are blocked as they approach presence of the stagnation surface. Recent heat transfer measurements suggest that very high intensity turbulence or turbulence in the presence of very large scale leading edge regions may not be as strongly influenced by the stagnation region strain field. Understanding the physics of turbulence is critical to the improvement of turbulence models which are used to predict the surface heat load in gas turbine hot sections.
This paper documents the response of high intensity turbulence in the approach flow of two large cylindrical leading edge regions. Measurements of turbulence intensity, scale, spectra, and dissipation have been acquired for five elevated levels of turbulence in the approach flow of two large diameter (0.1016 m and 0.4064 m) leading edge regions. Generally, three influences were observed. Initially, in the presence of the largest cylinder the smaller scale higher intensity turbulence showed increased decay due to longer effective convection times. Secondly, dissipation levels, as estimated from the inertial subrange of the one-dimensional spectra, initially decreased then increased as the strain field intensified in the presence of the stagnation regions. Finally, the measurements indicated that the energy in the low wave number spectra was increasingly blocked in the near wall region of the leading edge.
Experimental Study of Rotating Stall in Vaneless Diffuser of a Centrifugal Compressor
Authors: Ohuchida S. , Kawakubo T. , Tamaki H. 
Published: November 2013

In this study, with a focus on the rotating stall phenomenon in the vaneless diffuser of a centrifugal compressor, 2D-PIV is conducted to better understand the flow structure. Although many studies have reported concerning this problem, most data is obtained through experiments under lower speed conditions, using a simplified model or equipment. Unlike such studies, a ship board turbocharger compressor with a higher impeller rotation speed is selected as an application for the present measurement. In the measurement, an ensemble-averaged phase locking technique is also selected to compensate for the lack of time resolution of the PIV system. Since rotating stall in vaneless diffuser results in a huge amplitude of pressure fluctuation, the trigger signal for the ensemble-averaged measurement was constructed from diffuser wall pressure. The equipment layout for PIV is set to a cross sectional measurement of constant span height in the diffuser passage. PIV is conducted through a sight glass mounted on the diffuser shroud wall, the field of view of which is limited by its size. To obtain the whole flow structure of the diffuser passage, the measurement is repeated for different cyclic phases of the phenomenon.
Five different span heights ranging from diffuser hub to shroud were selected as velocity measurement planes. The result obtained at the mid span indicates a typical pattern of the flow field containing containing low and high-velocity regions mutually in a circumferential direction. Considering other results obtained at different span heights, the whole flow structure is visualized and utilizing this data, both a wall separation pattern and a stall propagation mechanism are considered.
Nonparametric Stochastic Modeling of Structural Uncertainty in Rotordynamics: Unbalance and Balancing Aspects
Authors: Murthy Raghavendra , Tomei Joseph C. , Wang X. Q. , Mignolet Marc P. , El-Shafei Aly 
Published: November 2013

This paper focuses on extending an earlier investigation on the systematic and rational consideration of uncertainty in reduced order models of rotordynamics systems. The current effort concentrates on the consistent introduction of uncertainty in mass properties on the modal mass and gyroscopic matrices as well as on the unbalance force vector. The uncertainty in mass is separated into uncertainty that maintains the rotor symmetry and the one which disrupts it. Both types of uncertainties lead to variations in the system modal matrices but only the latter induces an unbalance. Accordingly, the approach permits the selection of separate levels on the uncertainty on the system properties (e.g. natural frequencies) and on the unbalance.
It was first found that the unbalance response is increased by considering the uncertainty in the rotor modal mass matrices. It was next noted that the approach presented not only permits the analysis of uncertain rotors but it also provides a computational framework for the assessment of various balancing strategies. To demonstrate this unique feature, a numerical experiment was conducted in which a population of rotors were balanced at low speed and their responses were predicted at their first critical speed. These response predictions were carried with the uncertainty in the system modal mass matrices but with or without the balancing weights effects on these matrices. It was found that the balancing at low speed may in fact lead to an increase in both the mean and 95th percentile of the response at critical speed.
On the Benefits of Intentional Mistuning of Friction Dampers to Reduce the Response of Tuned and Mistuned Bladed Disks
Authors: Murthy Raghavendra , Mignolet Marc P. 
Published: November 2013

This paper investigates the potential benefits resulting from using two different types of friction dampers on a bladed disk. In this scenario, every blade or platform is equipped with a damper of either type A or type B with these two types differing by their friction forces. The variations in friction force are assumed here to be induced by similar variations in the damper mass. The benefit of this strategy is measured in comparison with using identical dampers of optimized mass on every blade/platform and is dependent on the pattern of A/B dampers around the disk as well as the damper masses.
It is accordingly desired to optimize both the pattern and the damper masses to obtain the largest benefit. As a discovery effort, this optimization is accomplished here through an exhaustive search for all patterns and on a large grid of values of the two damper masses. Owing to the large computational cost of this effort, only single degree of freedom per blade models are assumed with both blade-blade and blade-ground dampers and only small blade counts are considered (6 and 12).
Three particular situations are considered: disks with tuned blades except for the arrangement of A/B dampers, disks that also exhibit random mistuning of the blade stiffnesses, and, finally, disks exhibiting random mistuning of both blade stiffness and of the friction forces of the dampers. This latter situation is considered to include the variability induced by manufacturing and wear on the friction dampers.
In all cases considered, the benefit of this intentional mistuning of friction dampers is either zero or small, of the order of a few percent, consistently with a single data point reported in the literature.
The Challenges of Uniform Crystal Temperature Sensor (UCTS) Application in Turbomachinery
Authors: Brown Justin , DeVoe Jason , Ginzbursky Lev 
Published: November 2013

The quality of information, which is necessary to help designers further improve turbine engine performance, requires sophisticated analytics working hand-in-hand with well-developed experimental methods. Historically, the test instrumentation used in harsh, real engine conditions was short-lived, invasive, and not very accurate. This was accepted as the practical reality and the data obtained in an engine test cell had been used as little more than a sanity check or a trend indicator during the design process. Today expectations are much higher and the challenge is to develop experimental tools that can deliver the accuracy required to verify analytical predictions, calibrate computer models and to provide ground for critical design decisions in a way which was not possible before.
Successful introduction of UCTS (Uniform Crystal Temperature Sensor) Technology to the leading engine manufacturers demonstrated that it has the potential to overcome the typical issues of testing in a real engine environment. It is robust, non-intrusive and capable of high accuracy temperature measurement. It is based on the mechanism of heat transfer conduction, of which the fundamental theory is rigorous and simple. Our experience has shown that in order for a UCTS-based system to realize its promise, all potential sources of error must be tightly managed. LG Tech-Link identified important factors of influence that could complicate measurement and increase its uncertainty. Among them are variations in the part’s geometry, TBC thickness, boundary conditions, and installation methodology. These have been selected as the focus of this study.
The authors of this paper are using 3D Finite Element Analysis (FEA) methodology to investigate the possible pitfalls in the process of UCTS application that could cause loss of accuracy. It is the authors’ intention to probe the sensitivity of temperature at the location of the sensor to the major technological factors. The findings emphasize the value of collaboration between instrumentation, test and analytical engineers when planning engine tests and interpreting their results. Practicing engineers will be able to use the presented recommendations, methodologies and case studies to ensure the application of UCTS in their projects is accurate, compatible with test objectives and cost effective.
Recommendations of the Sardinian public for the treatment of depression
Authors: Carta Mauro G , Angermeyer Matthias C , Matschinger Herbert , Holzinger Anita , Pintus Elisa , Pintus Mirra , Moro Maria F 
Published: November 2013

Background: Public beliefs about appropriate treatment impact, help-seeking and treatment adherence. Aim: To determine the recommendations of the Sardinian public for the treatment of depression. Methods: In 2012, a population-based survey was conducted by phone in Sardinia ( N = 1,200). In the context of a fully structured interview, respondents were presented with a vignette depicting a case of depression. Subsequently, they were asked about their treatment recommendations. The results are contrasted with findings from a similar survey which had been conducted in Vienna 3 years before. Results: In Sardinia as in Vienna, psychotherapy was the uncontested favorite, while antidepressant medication was recommended by relatively few respondents. In Sardinia, there were also no marked differences between urban and rural areas with regard to these two treatments. However, between Sardinia and Vienna, as well as within Sardinia, great differences were found with regard to autogenic training and ‘alternative’ methods like homeopathic medicines and acupuncture. Conclusion: Cross-cultural comparisons may help better understand treatment preferences of the public. In Sardinia, as in Vienna, there seems to be a need for improving the public’s knowledge about the appropriate treatment of depression.
Effects of 900 MHz electromagnetic field emitted by cellular phones on electrocardiograms of guinea pigs
Authors: Meral I , Tekintangac Y , Demir H 
Published: November 2013

This study was carried out to determine the effects of electromagnetic field (EMF) emitted by cellular phones (CPs) on electrocardiograms (ECGs) of guinea pigs. A total of 30 healthy guinea pigs weighing 500–800 g were used. After 1 week of adaptation period, animals were randomly divided into two groups: control group ( n = 10) and EMF-exposed group ( n = 20). Control guinea pigs were housed in a separate room without exposing them to EMFs of CPs. Animals in second group were exposed to 890–915 MHz EMF (217 Hz of pulse rate, 2 W of maximum peak power and 0.95 wt kg−1 of specific absorption rate) for 12 h day−1 (11 h 45 min stand-by and 15 min speaking mode) for 30 days. ECGs of guinea pigs in both the groups were recorded by a direct writing electrocardiograph at the beginning and 10th, 20th and 30th days of the experiment. All ECGs were standardized at 1 mV = 10 mm and with a chart speed of 50 mm sec−1. Leads I, II, III, lead augmented vector right (aVR), lead augmented vector left (aVL) and lead augmented vector foot (aVF) were recorded. The durations and amplitudes of waves on the trace were measured in lead II. The data were expressed as mean with SEM. It was found that 12 h day−1 EMF exposure for 30 days did not have any significant effects on ECG findings of guinea pigs. However, this issue needed to be further investigated in a variety of perspectives, such as longer duration of exposure to be able to elucidate the effects of mobile phone-induced EMFs on cardiovascular functions.
Theoretical Study on the Selective Fluorescence of PicoGreen: Binding Models and Photophysical Properties
Authors: Okoshi Masaki , Saparpakorn Patchreenart , Takada Yuta , Hannongbua Supa , Nakai Hiromi 
Published: November 2013

Abstract
PicoGreen (PG) is used as a probe to selectively quantitate double-stranded (ds-) DNA because it shows unique fluorescence enhancement when complexed with DNA. By binding to ds- and single-stranded (ss-) DNA, the quantum yields of PG–DNA complexes become remarkably larger than that of a free molecule. In the present theoretical study, the fluorescence enhancement mechanism of PG–DNA complexes was investigated using molecular docking simulations and ab initio quantum chemical methods. The binding energies between PG and ds-DNA were calculated to be larger than those in the case of PG and ss-DNA owing to the existence of an extra π–π stacking interaction. Nonradiative deactivation paths through conical intersections between the ground and the first excited states were obtained for a free PG molecule, while steric repulsions between PG and DNA hindered such deactivation processes in the case of PG–DNA complexes.
Reduction of Graphene Oxide in Solution by Radical Treatment
Authors: Tanaka Hiroshige , Obata Seiji , Saiki Koichiro 
Published: November 2013

Abstract
Reduction of graphene oxide is a promising way for scalable production of graphene. The graphene reduced chemically from graphene oxide, however, retains many defects which were formed in the oxidation process, and thus its crystallinity is rather poor. Here, we report an effective reduction method of graphene oxide by radical treatment in solution. Graphene oxide was reduced more effectively by CH3I or BrC2H4Br than by hydrazine, which is a chemical reagent used for conventional reduction of graphene oxide. This radical reduction would facilitate large-scale production of graphene for various applications.
Ilial crest bone graft transposition as treatment for fracture of the medial femoral trochlear ridge in a dog
Authors: Dimopoulou M. , Lee M. H. , Ostberg S. E. 
Published: November 2013

SummaryThis is a report of a fracture of the medial trochlear ridge of the distal femur occurring as a major complication after surgery for medial patellar luxation. To address the complication, a non-vascularized iliac bone graft was collected and fixated with two positional screws to the trochlea. An external skeletal fixator was placed to prevent motion of the stifle joint during the healing period and to reduce the risk for fragment dislodgment. One year after the graft was placed the dog’s function was satisfactory. This case report indicates that a non-vascularized iliac bone graft provides an alternative for management of fractures of the medial ridge of the distal femur.