bluuebunny/crossref_metadata_2025 huggingface dataset:
The Impact of Hole Depth on the Rotordynamic and Leakage Characteristics of Hole-Pattern-Stator Gas Annular Seals
Authors: Childs Dara W. , Arthur Stephen , Mehta Naitik J.
Published: November 2013

Test results are presented for rotordynamic characteristics of hole-pattern-stator annular gas seals at a 70 bar supply pressures running at 20200 rpm. Leakage results are presented for these conditions and the additional speeds: 10200, 15300 rpm. Hole-depth is the principal test variable of interest. Most published annular test data for these seals have a hole diameter of 3.175mm and a hole depth of 3.302mm. For this work, with the 3.175mm hole diameter, additional results are presented for shallow (1.905 mm) and deep (6.604 mm) hole depths.

Test results show a pronounced dependence of leakage and rotordynamic behavior on hole depth. Test results show much better leakage performance for the shallow-hole-depth seal in both leakage and rotordynamic performance. Compressor manufacturers and users will need to decide whether this observed performance improvement is worth trying in real machines.
Leakage and Rotordynamic Coefficients of Brush Seals With Zero Cold Clearance Used in an Arrangement With Labyrinth Fins
Authors: Gaszner Manuel , Pugachev Alexander O. , Georgakis Christos , Cooper Paul
Published: November 2013

A brush-labyrinth sealing configuration consisting of two labyrinth fins upstream and one brush seal downstream is studied experimentally and theoretically. Two slightly different brush seal designs with zero cold radial clearance are considered. The sealing configurations are tested on the no-whirl and dynamic test rigs to obtain leakage performance and rotordynamic stiffness and damping coefficients. The no-whirl tests allow identification of the local rotordynamic direct and cross-coupled stiffness coefficients for a wide range of operating conditions, while the dynamic test rig is used to obtain both global stiffness and damping coefficients, but for a narrower operating range limited by the capabilities of a magnetic actuator. Modeling of the brush-labyrinth seals is performed using computational fluid dynamics. The experimental global rotordynamic coefficients consist of an aerodynamic component due to the gas flow and a mechanical component due to the contact between the bristle tips and rotor surface. The CFD-based calculations of rotordynamic coefficients provide however only the aerodynamic component. A simple mechanical model is used to estimate the theoretical value of the mechanical stiffness of the bristle pack during the contact. The results obtained for the sealing configurations with zero cold radial clearance brush seals are compared with available data on three-tooth-on-stator labyrinth seals and a brush seal with positive cold radial clearance. Results show that the sealing arrangement with a line-on-line welded brush seal has the best performance overall with the lowest leakage and cross-coupled stiffness. The predictions are generally in agreement with the measurements for leakage and stiffness coefficients. The seal damping capability is noticeably underpredicted.
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.
Real Time Analytical Linearization of Turbofan Engine Model
Authors: Chung Gi-Yun , Prasad J. V. R. , Dhingra Manuj , Meisner Richard
Published: November 2013

This paper presents a methodology for developing a control oriented analytical linear model of a turbofan engine at both equilibrium and non-equilibrium conditions. This scheme provides improved accuracy over the commonly used linearization method based on numerical perturbation. Linear coefficients are obtained by evaluating at current conditions analytical expressions which result from differentiation of simplified nonlinear expressions. Residualization of the fast dynamics states are utilized since the fast dynamics are outside of the primary control bandwidth. Analytical expressions based on the physics of the aerothermodynamic processes of a gas turbine engine facilitate a systematic approach to the analysis and synthesis of model based controllers. In addition, the use of analytical expressions reduces the computational effort, enabling linearization in real time at both equilibrium and non-equilibrium conditions to enable more accurate capture of system dynamics during aggressive transient maneuvers. The methodology is formulated and applied to a separate flow twin spool turbofan engine model in the Numerical Propulsion System Simulation (NPSS) platform. The derived linear model is validated against the full nonlinear engine model.
Feasibility Study of Incorporating Flow Unsteadiness in Control of Secondary Flows in Shrouded Turbines
Authors: Gao Jie , Zheng Qun , Jia Xiaoquan
Published: November 2013

The internal flow in turbomachinery is inherently unsteady, and the endwall losses are major sources of lost efficiency in high-pressure turbine cascades. Therefore, the investigation of the unsteady endwall flow interactions is valuable to improve the performance of high-pressure turbines. Unsteady and steady numerical investigations of endwall flow interactions of 1.5-stage shrouded turbines with straight and bowed vanes are performed using a three-dimensional Navier-Stokes viscous solver. Emphasis is placed on how unsteady stator-rotor interactions affect shrouded turbine endwall secondary flows, on the basis of which the feasibility of incorporating the unsteady endwall flow effects in the control of secondary flows is discussed in detail. Results from this investigation are well presented and discussed in this paper.
An Inverse Heat Transfer Approach to Mitigating Sources of Experimental Error in Transient Heat Transfer Experiments
Authors: Rutledge James L. , McCall Jonathan F.
Published: November 2013

The Inverse Flux Solver for Arbitrary Waveforms (IFSAW) algorithm is a transient, simultaneous solution of time resolved adiabatic effectiveness, η(t), and heat transfer coefficient, h(t). Numerical simulations showed IFSAW maintained its high accuracy despite two experimental sources of error typically found when using a transient heat transfer method. The traditional transient method involves exposing a film cooled wind tunnel model at uniform temperature to a step change in freestream temperature. The experimental design results in nearly one-dimensional heat transfer and allows the surface to be modeled as semi-infinite. Typically, the surface temperature history is correlated to an analytical solution to the governing heat transfer equation (yielding η and h), but the required temperature step change is impossible to achieve in a laboratory. This paper first analyzed the error introduced by imperfect step changes and evaluated an alternative methodology, IFSAW, requiring only an arbitrary change in freestream temperature occurring at any rate. Secondly, severe error in h (found in locations where η is near unity because the surface temperature changes little from the initial temperature) was shown to be mitigated using IFSAW combined with a gradual change in coolant temperature at any point during measurement. With both complications, IFSAW maintains its ability to determine periodic η(t) and h(t) waveforms. In these ways, IFSAW is shown to be superior to the legacy transient method.
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.
Effects of Unsteady Wakes on the Secondary Flows in the Linear T106 Turbine Cascade
Authors: Ciorciari Roberto , Kirik Ilker , Niehuis Reinhard
Published: November 2013

In modern low pressure turbines the efforts to increase aerodynamic blade loading by increasing blade pitch and optimising midspan performance in order to reduce weight and complexity can produce increased losses in the endwall region. Airfoils of high flow turning and high pressure gradients between the blades generate strong secondary flows which impair the global aerodynamic performance of the blades. In addition, the unsteady incoming wakes take influence on transition phenomena on the blade surfaces and the inlet boundary layer, and consequently affect the development and the evolution of the secondary flows. In this paper the T106 cascade is used to identify the effect of unsteady wakes on the development of secondary flows in a turbine cascade. Numerical and experimental results are compared at different flux coefficients and Strouhal numbers, the relative differences and similarities are analysed.
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.
Validation of the ANL Plant Dynamics Code With the SNL S-CO2 Loop Transient Data
Authors: Moisseytsev Anton , Sienicki James J.
Published: November 2013

The ANL Plant Dynamics Code (PDC) is the current state-of-the-art capability for one-dimensional system level transient analysis of supercritical carbon dioxide (S-CO2) Brayton cycle power converters. Earlier validation of code models was carried out with data from testing of individual S-CO2 components such as a small-scale compact diffusion-bonded heat exchanger and compressor tests. The steady-state part of the PDC has been compared with experimental data from the Sandia National Laboratories (SNL) small-scale S-CO2 Brayton cycle demonstration. In this work, predictions of the PDC code are assessed through comparison with SNL S-CO2 loop transient data. Code modifications were needed to properly simulate the actual experimental runs due to the unique features of the small-scale SNL loop. Overall, good agreement with the measured data is predicted by the PDC, although the code predictions could be improved in some cases. Future code improvements for comparisons with future SNL loop data are identified based upon the results.
Unsteady Effects of a Generic Non-Axisymmetric Endwall Contour on the Rotor of a 1½ Stage Low Speed Turbine Test Rig
Authors: Dunn Dwain , Snedden Glen , von Backström Theodor , Mdluli Mthobisi P.
Published: November 2013

Non-axisymmetric endwall contouring has been used as means to improve the characteristics of the flow field exiting a turbine blade row reducing the secondary flows and thus also the secondary losses. The development of non-axisymmetric endwalls has predominantly been done using CFD and detailed measurements in cascades. It has been shown by several researchers that contouring can improve the performance of a gas turbine engine; however the mechanisms that create the improvement are still not fully understood. The current investigation was aimed at unsteady features, if any, and how the unsteady flow field is altered by a non-axisymmetric endwall contour. A previous steady state investigation found that the contouring improved the rotor efficiency of the current rig by 0.4%. The current investigation is an initial experimental investigation into the unsteady nature of the flow in a turbine that has endwdall contours. The unsteady nature of the rotor exit flow field was investigated using an X-film probe to determine if the contouring affected the flow field in ways that the steady measurement technique could not determine. Contour plots, variation in quantities as well as FFT’s were investigated. The unsteady data shows several differences in the flow field of the annular and contoured rotor exit. The velocity range was reduced specifically in the endwall secondary flow region, but the oscillations in the tip leakage flow region were increased. Pitch wise averaged velocity data showed a decrease in the magnitude of the FFT at the blade passing frequency, with the first and second harmonics also being affected. The velocity contours at the rotor exit reveal that the rotor outlet flow field has been made more homogenous (more aligned with the bulk flow) with the addition of the non-axisymmetric endwall contouring.
Modular Turbulence Modelling Applied to an Engine Intake
Authors: Oriji Ugochukwu R. , Tucker Paul G.
Published: November 2013

The one equation Spalart Allamaras (SA) turbulence model in an extended modular form is employed for the prediction of cross wind flow around the lip of a 90 degree sector of an intake with and without surface roughness. The flow features around the lip are complex. There exists a region of high streamline curvature. For this the Richardson number would suggest complete degeneration to laminar flow. Also there are regions of high favourable pressure gradient (FPG) sufficient to laminarize a turbulent boundary layer (BL). This is all terminated by a shock and followed by a laminar separation. Under these severe conditions, the SA model is insensitive to capturing the effects of laminarization and the reenergization of eddy viscosity which promotes the momentum transfer and correct reattachment prior to the fan face. Through distinct modules, the SA model has been modified to account for the effect of laminarization and separation induced transition. The SA modules have been implemented in Rolls-Royce HYDRA Computational Fluid Dynamic (CFD) solver. They have been validated over a number of experimental test cases involving laminarization and also surface roughness. The validated modules are finally applied in unsteady RANS mode to flow around an engine intake and comparisons made with measurements. Encouraging agreement is found and hence advances made towards a more reliable intake design framework.
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.
Measurements and Visualization of Process From Steady State to Stall in an Axial Compressor With Water Ingestion
Authors: Liu Le , Zhang Hongwei , Li Jichao , Yu Chenghai , Lin Feng , Nie Chaoqun
Published: November 2013

In this paper, experiments are performed to measure and demonstrate the whole throttling process from the steady operating state to stall inception with water ingestion in a low speed axial compressor. A transparent casing is used to visualize the water distribution on the casing. Two types of nozzles are used, giving the average droplets diameters of 35 μm and 90 μm, respectively. Six different water mass flow rates are tested, ranging from 0.064% to 2.05% compared to the reference airflow rate. The compressor performance curves change significantly as the ingested water flow rate. Small water flow rates even improve the performance while the middle water flow rates decrease it. For large water flow rates, the pressure rise coefficient drops rapidly and becomes “flat” at low airflow rate but the stall margin is extended much further into the low airflow rate region. To visualize the whole stall evolution process, photos and digital videos are both taken through transparent casing and record the patterns of the water distribution on the casing. Dynamic casing static pressure is also measured at the same time. Due to the centrifugal force acting on the water droplets, the water film on the casing along the tangential direction is observed in photos and videos. The edges of water film can be identified, and the back edge is believed to separate the incoming flow and the tip leakage flow. As the compressor is throttled to smaller flow rates yet still away from the stall limit, this interface moves forwards and becomes fluctuating which can be visualized with bare eyes. The fluctuation becomes more and more violent until the water film suddenly spills out of the leading edge, and thus the stall happens. As the water ingestion rate increases, the film gets wider and thicker, and even exceeds the leading edge before stall inception. Unsteady casing static pressure is also measured. The increased power spectrum density of pressure signals in frequency domain is found and believed to might be related with the water film fluctuation observed on the compressor casing. The phenomena observed in photos and videos provide interesting information of the flow in the compressor and deserve further research.
Modeling and Simulation of Micro-Grid System Coupled With Small Wind Turbine
Authors: Li Saili , Dai Yiping , Li Maoqing , Gao Lin
Published: November 2013

Wind energy has been examined as a clean and economic resource, however, the intermittent and fluctuate feature of which makes it necessary to couple with an energy storage system for compensating the wind energy curtailments. A micro-grid with a compressed air energy storage (CAES) system may help to eliminate the problem resulted from high wind power penetration in the power grid. What is more, it can reduce the network losses. A micro-grid system coupled with small wind turbine presented in this paper. Off-peak power from the wind turbine is used to drive the compressor which serves for the storage vessel. The compressed air supercharges the gas turbine directly when wind energy is not sufficient to guarantee the required load. A dynamic model is built to test the behavior of the system. A statistical model based on stochastic weather data is used to simulate the output of the wind turbine for one day at quarter-hour intervals. An accurate model of CAES includes a compressor, a high pressure vessel and a gas turbine is built in details. A control system is developed to achieve outstanding system’s characteristics like great control performance, stable operation and fast starting. The simulation results show that the CAES can compensate the wind turbine and make the most of wind energy.
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.
Analysis of Nonlinear Vibrations Upon Wear-Induced Loss of Friction Dampers in Tuned and Mistuned Bladed Discs
Authors: Petrov E. P.
Published: November 2013

An effective method has been developed to analyse the progressive loss of friction dampers due to friction-induced wear in tuned and mistuned bladed discs. The method allows the calculation of nonlinear forced response levels and schemes of the damper loss using large-scale finite element bladed disc models and detailed modelling of friction contact interactions at friction contact interfaces by friction contact elements. The progressive damper loss caused by wear is assessed by comparison of energy dissipated by friction forces at all damper friction contact interfaces. The method is applied to a realistic turbine bladed disc and a comprehensive analysis of the forced responses together with the progressive loss of friction tip dampers is performed.
Thrust Vectoring Design Project at Six Universities: Part I — Project Description and Final Designs
Authors: Turner Mark G. , Rumpfkeil Markus P. , VanKuren James T. , Roberts Rory A. , Bons Jeffrey , Smith Tim , Ausserer Joseph K. , Litke Paul
Published: November 2013

An undergraduate student design and build project has been established by the US Air Force, Air Force Research Laboratory as part of an outreach program. During the 2011–2012 academic year, undergraduate students of six universities participated in designing a thrust vectoring system for a small (20 pound-thrust) jet engine. A description of the project parameters and student designs is given in this paper. It proved to be an extremely successful project, and other professors and students can learn from the different approaches taken by the six different teams and the project itself. Industry will also be interested in the depth and breadth of an undergraduate project that is being used to educate their future engineering workforce.
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.
Energy-Based Fatigue Life Prediction for Combined Low Cycle and High Cycle Fatigue
Authors: Holycross Casey M. , Shen M.-H. Herman , Scott-Emuakpor Onome E. , George Tommy J.
Published: November 2013

Gas turbine engine components are subjected to both low and high cycle fatigue as a result of mechanical and vibrational loading. Mechanical loading is generally within the low cycle fatigue regime and attributed to throttle up/throttle down cycles of various flight maneuvers or engine start-up/shut-down cycles over the course of a component’s lifetime. Vibrational loading causes high cycle fatigue of a multiaxial stress state, and is attributed to various forced and free vibration sources manifested as high order bending or torsion modes. Understanding the interaction of these two fatigue regimes is necessary to develop robust design techniques for gas turbine engines and turbomachinery in general. Furthermore, applying a method to accurately predict fatigue performance from a reduced data set can greatly reduce time and material costs. This study investigates commonly used fatigue life prediction models and techniques in their ability to accurately model fatigue lives of Al 6061-T651 cylindrical test specimens subjected to various stress ratios, mean stresses, and high cycle/low cycle interaction. Comparisons between these models are made and modifications are proposed than can account for these complex loading effects where appropriate.
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.
Creep Crack Growth Simulation of Ni-Base Superalloy
Authors: Stewart Calvin M. , Gordon Ali P.
Published: November 2013

The purpose of this study is to develop a numerical approach to simulate the creep cracking of a Ni-base superalloy. The approach is based in continuum damage mechanics (CDM) and uses the classic Kachanov-Rabotnov constitutive equations for creep deformation and damage evolution. Creep damage takes the form of defects such as microcracks, cavities, voids, etc. A numerical crack growth algorithm is developed to predict the onset of crack initiation and the successive growth of cracks via element death in the general purpose finite element software ANSYS. In this paper, the Kachanov-Rabotnov constitutive model is implemented as a user material model in ANSYS and the numerical crack growth algorithm is developed and written in ANSYS parametric design language (APDL) command code. A study of mesh size in relation to initial flaw size and initiation time is performed. A demonstration of the proposed numerical crack growth algorithm is performed and a qualitative analysis conducted. A series of improvements and parametric studies are suggested for future work.
Assessment of Fatigue Reliability of Power Transmission Gearing for Aerospace Propulsion Applications
Authors: Beretta Stefano , Filippini Mauro , Luccarelli Pietro , Motta Andrea , Pasquero Giuseppe
Published: November 2013

The fatigue strength in presence of inclusions is one of the main topics for the fatigue of high strength steels, especially the case hardened ones adopted for power transmission. In this paper we analyze the fatigue strength of carburized gears in presence of inclusions in order to develop the reliability assessment of a power transmission for aerospace propulsion. The high cycle fatigue properties of a high strength carburizing steel have been experimentally determined by conducting bending fatigue tests with specimens with artificial defects and a coherent model for the assessment of fatigue crack growth thresholds by taking into account of the residual stresses due to carburizing has been developed. In parallel, the distribution of non-metallic inclusions has been estimated by carrying out high cycle fatigue tests onto cylindrical smooth specimens and by inspection of mirror polished sections of the material. Eventually, by employing a simplified finite element model of a highly loaded gear wheel, the bending fatigue strength of gear teeth and the reliability of a turbo-propeller power transmission was determined by incorporating the fatigue crack growth thresholds, the measured residual stress profiles and the statistics of extreme non-metallic inclusions into a competing risks model applied to FE discretization.
Under pressure: a contribution to the pathogenesis of acquired ileal atresia
Authors: Houben C H , Lo A W I , Tsui S Y , Chan K W
Published: November 2013

An acquired ileal atresia is a rare occurrence. A 3-week-old neonate is presented, who developed postnatally a type 2 ileal atresia and an ileal stenosis within a pre-existing internal hernia secondary to an adhesion band. The literature reports a total of eight cases (4 females) with acquired ileal atresia in babies ranging in age from 3 weeks to 2 years (median 4 months). Mechanical forces (eg, adhesion band, intussusception and volvulus) onto the intestine are most frequently (75%) implicated as the primary event. The distal ileum is most often affected and a type 3A atresia is identified in six of eight (75%) cases.
Location of Sternal Fractures as a Possible Marker for Associated Injuries
Authors: Scheyerer Max J. , Zimmermann Stefan M. , Bouaicha Samy , Simmen Hans-Peter , Wanner Guido A. , Werner Clément M. L.
Published: November 2013

Introduction. Sternal fractures often occur together with serious and life-threatening additional injuries. This retrospective study was designed to assess concomitant injuries and develop a correlation between fracture location and the severity of injury.Methods.All patients () diagnosed with a fracture of the sternum by means of a CT scan were analysed with respect to accident circumstances, fracture morphology and topography, associated injuries, and outcome.Results. Isolated sternal fractures occurred in 9%. In all other admissions, concomitant injuries were diagnosed: mainly rip fractures (64%), injury to the head (48%), the thoracic spine (38%), lumbar spine (27%), and cervical spine (22%). Predominant fracture location was the manubrium sterni. In these locations, the observed mean ISS was the highest. They were strongly associated with thoracic spine and other chest injuries. Furthermore, the incidence of head injuries was significantly higher. ICU admission was significantly higher in patients with manubrium sterni fractures.Conclusion. Sternal fractures are frequently associated with other injuries. It appears that the fracture location can provide important information regarding concomitant injuries. In particular, in fractures of manubrium sterni, the need for further detailed clinical and radiologic workup is necessary to detect the frequently associated injuries and reduce the increased mortality.
A Biobjective Fuzzy Integer-Nonlinear Programming Approach for Creating an Intelligent Location-Aware Service
Authors: Lin Yu-Cheng , Chen Toly
Published: November 2013

An intelligent location-aware service is created in the present study, in which a timely service is provided to a user without changing the user's pace. To the user, there are two goals to achieve—one is to reach the service location just in time; the other is to get to the destination as soon as possible. To consider the two objectives at the same time and to allow for the uncertainty in the dynamic environment, a biobjective fuzzy integer-nonlinear programming problem is formulated and solved. To illustrate the applicability of the proposed methodology, an experiment has been performed. According to the experimental results, the user's waiting time was reduced by 61% using the proposed methodology.
Reduction of Chern-Simons-Schrödinger Systems in One Space Dimension
Authors: Huh Hyungjin
Published: November 2013

We study Chern-Simons-Schrödinger systems in one space dimension. We show that Chern-Simons-Schrödinger and𝒩=2supersymmetric Chern-Simons-Schrödinger equations can be reduced, under the gauge conditionA1≡0, to equations ofϕ,ψonly which are coupled cubic Schrödinger systems.
Rheumatoid Factors: Clinical Applications
Authors: Ingegnoli Francesca , Castelli Roberto , Gualtierotti Roberta
Published: November 2013

Rheumatoid factors are antibodies directed against the Fc region of immunoglobulin G. First detected in patients with rheumatoid arthritis 70 years ago, they can also be found in patients with other autoimmune and nonautoimmune conditions, as well as in healthy subjects. Rheumatoid factors form part of the workup for the differential diagnosis of arthropathies. In clinical practice, it is recommended to measure anti-cyclic citrullinated peptide antibodies and rheumatoid factors together because anti-cyclic citrullinated peptide antibodies alone are only moderately sensitive, and the combination of the two markers improves diagnostic accuracy, especially in the case of early rheumatoid arthritis. Furthermore, different rheumatoid factor isotypes alone or in combination can be helpful when managing rheumatoid arthritis patients, from the time of diagnosis until deciding on the choice of therapeutic strategy.
Strong Convergence Results for Equilibrium Problems and Fixed Point Problems for Multivalued Mappings
Authors: Vahidi J. , Latif A. , Eslamian M.
Published: November 2013

Using viscosity approximation method, we study strong convergence to a common element of the set of solutions of an equilibrium problem and the set of common fixed points of a finite family of multivalued mappings satisfying the condition (E) in the setting of Hilbert space. Our results improve and extend some recent results in the literature.
Aggressive Pseudomyxoma Peritonei: A Case Report with an Unusual Clinical Presentation
Authors: Touloumis Zisis , Galyfos George , Kavouras Nikolaos , Menis Michalis , Lavant Laurant
Published: November 2013

Introduction. Pseudomyxoma peritonei (PMP) is an uncommon surgical entity. We report a case of aggressive disease with an unusual clinical presentation and we analyze current data on diagnosis and management of PMP.Case Presentation. A 71-year-old male patient presented with intermittent diarrhea and loss of appetite during the last two months, without any other classic symptoms of PMP. The clinical examination was misleading due to patient’s obesity. The radiological evaluation revealed ascites of the abdomen and possible mucocele of the appendix, whereas the laboratory exams showed high values of specific tumour markers. The patient underwent an exploratory laparotomy for definite diagnosis. Biopsies and immunohistochemical examination confirmed the diagnosis of an aggressive and extended peritoneal mucinous carcinomatosis (PMCA). The patient was programmed for adjuvant systematic chemotherapy, which was not completed due to progression of the disease.Conclusions. Progressed PMP can present with unspecific symptoms that mislead diagnosis. Cytoreductive surgery in combination with systematic chemotherapy could be appropriate for aggressive PMCA, even with an unfavourable prognosis.
Blow-Up Phenomena for Porous Medium Equation with Nonlinear Flux on the Boundary
Authors: Hu Yan , Li Jing , Wang Liangwei
Published: November 2013

We investigate the blow-up phenomena for nonnegative solutions of porous medium equation with Neumann boundary conditions. We find that the absorption and the nonlinear flux on the boundary have some competitions in the blow-up phenomena.