bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Pivot Stiffness on the Dynamic Force Coefficients of Tilting Pad Journal Bearings
Authors: San Andrés Luis , Tao Yujiao
Published: November 2013

Recent comprehensive experimental data showcasing the force coefficients of commercial size tilting pad journal bearings has brought to rest the long standing issue on the adequacy of the [K,C,M] physical model to represent frequency independent bearing force coefficients, in particular viscous damping. Most experimental works test TPJBs with large preloads, operating over a large wide range of rotor speeds, and with null to beyond normal specific loads. Predictions from apparently simple fluid film bearing models stand poor against the test data which invariably signals to theory missing pivot and pad flexibility effects, and most importantly, ignoring significant differences in bearing and pad clearances due to actual operation, poor installation and test procedures, or simply errors in manufacturing and assembly. Presently, a conventional thermo hydrodynamic bulk flow model for prediction of the pressure and temperature fields in TPJBs is detailed. The model accounts for various pivot stiffness types, all load dependent and best when known empirically, and allows for dissimilar pad and bearing clearances. The algorithm, reliable even for very soft pad-pivots, predicts frequency reduced bearing impedance coefficients and, over a certain frequency range, delivers the bearing stiffness, damping and virtual mass force coefficients. Good correlation of predictions against a number of experimental results available in the literature bridges the gap between a theoretical model and the applications. Predicted pad reaction loads reveal large pivot deflections, in particular for a bearing with large preloaded pads, with significant differences in pivot stiffness as a function of specific load and operating speed. The question on how pivot stiffness acts to increase (or decrease) the bearing force coefficients, in particular the dynamic stiffness vs. frequency, remains since the various experimental data show contradictory results. A predictive study with one of the test bearings varies its pivot stiffness from 10% of the fluid film stiffness to an almost rigid one, 100 times larger. With certainty, bearings with nearly rigid pivot stiffness show frequency independent force coefficients. However, for a range of pad pivot stiffness, 1/10 to ten times the fluid film stiffness, TPJB impedances vary dramatically with frequency, in particular as the excitation frequency grows above synchronous speed. The bearing virtual mass coefficients become negative, thus stiffening the bearing for most excitation frequencies.
Extreme Temperature Coatings for Future Gas Turbine Engines
Authors: Alvin M. A. , Gleeson B. , Klotz K. , McMordie B. , Warnes B. , Zhu D.
Published: November 2013

The National Energy Technology Laboratory-Regional University Alliance (NETL-RUA) has been developing extreme temperature coating systems that consist of a diffusion barrier coating (DBC), a low-cost wet slurry bond coat, a commercial yttria stabilized zirconia (YSZ) thermal barrier coating (TBC), and an extreme temperature external coating that are deposited along the surface of nickel-based superalloys and single crystal metal substrates. Thermal cyclic testing of these multi-layer coatings was conducted in steam-containing environments at temperatures ranging between 1100–1550°C. This paper discusses the response of these materials during bench-scale testing, and their potential use in advanced H- and J-class land-based gas turbine engines.
Study of Wash Fluid Cleaning Effectiveness on Industrial Gas Turbine Compressor Foulants
Authors: Roupa Agbadede , Pilidis Pericles , Allison Isaiah , Lambart Paul
Published: November 2013

Online compressor washing is an advanced method of mitigating the effects of fouling as well as to increase the interval between offline washes. The major concern with online compressor washing has been its cleaning effectiveness, since it is carried out when the engine is running at full or near full speed. Hence, injecting wash fluid into the compressor to achieve an efficient cleaning is a challenge. This work investigates the most appropriate wash fluid for cleaning a particular type of foulant. Contaminants found on the surface of the compressor blades are of different composition; if the correct wash fluid is not selected, efficient cleaning cannot be achieved. In this study, wash fluids are applied to different compositions of foulants in a wind tunnel compressor cascade to ascertain their effectiveness in removing foulants. The research demonstrates that aqueous surfactant wash fluid is more effective for removing foulants composed of crude oil and carborundum particles.
Contactless Shaft Torque Detection for Wide Range Performance Measurement of Exhaust Gas Turbocharger Turbines
Authors: Lüddecke Bernhardt , Filsinger Dietmar , Ehrhard Jan , Steinacher Bastian , Seene Christian , Bargende Michael
Published: November 2013

Turbochargers develop away from an auxiliary component — being “off the shelve” — towards an integrated component of the internal combustion engine. Hence, increased attention is paid to the accuracy of the measured turbine and compressor maps. Especially turbine efficiency measurement under engine-relevant operating conditions (pulsed flow) is recently receiving increased attention in the respective research community. Despite various turbine map extrapolation methods, sufficient accuracy of the input test data is indispensable. Accurate experimental data are necessary to achieve high quality extrapolation results, enabling a wide range and precise prediction of turbine behavior under unsteady flow conditions, determined by intermittent operation of the internal combustion engine.

The present work describes the first application of a contactless shaft torque measurement technique — based on magnetostriction — to a small automotive turbocharger. The contactless torque measuring system is presented in detail and sensor principle as well as sensor calibration are illustrated. A sensitivity study regarding sensor position influences onto sensor signal proves the robustness and very good repeatability of the system. In the second part of the paper, steady state experimental results from operation on a conventional hot gas test stand over a wide map range are presented. These results are validated against full turbine stage (adiabatic as well as diabatic) CFD results as well as against “cold” efficiency measurements, based on measured inlet and outlet temperatures. The influence and relevance of bearing friction for such measurements is underlined and the improvements on this matter — achieved by direct torque measurement — are demonstrated.
Investigation on Aeroacoustics and Aerodynamics of the Stator Lean Effect for Rotor-Stator Interaction
Authors: Liu Hai-jian , Ouyang Hua , Wu Ya-dong , Tian Jie , Du Zhao-hui
Published: November 2013

The rotor-stator interaction in a 1.5 stage compressor with different lean angle of downstream stator blades was investigated by aeroacoustic and numerical study. The aeroacoustic performance with narrow spectra, the sound pressure level distribution and the unsteady loading of the compressor were tested and analyzed. The RMS pressure, the axial thrust and torque of the downstream stator blade distribution revealed the unsteady characteristic of rotor-stator interaction at different downstream stator blade lean angle. The positive lean stator had better noise constraint than the negative lean stator. However, the RMS pressure and the unsteady force increased with the increase of the lean angle when the stator had positive lean angle. The time-spatial contours of the axial velocity demonstrated the effect of time delay for the rotor wake intersection with the leading edge of the stator blade. And the phase lag distribution of the wake presented the detail distribution of the wake phase along the span. The downstream stator blade lean was effective to obtain a significant reduction for the unsteady force and get large phase lag for the rotor’s wake of rotor-stator interaction. Leaned positive blade had better benefits than negative for the noise reduction and the phase lag of the wake.
Investigation of Influence of Two-Stage Turbocharging System on Engine Performance Using a Pre-Design Model
Authors: Chen Jinke , Zhuge Weilin , Zheng Xinqian , Zhang Yangjun
Published: November 2013

As the result of increasingly strict emission regulations and demand of fuel reduction, current light and medium duty engines are being highly boosted with complex two-stage turbocharging systems. The purpose of this work is to investigate the influence of two-stage turbocharging system parameters on the engine performance and the optimization of these parameters.

An analytical pre-design model of the series two-stage turbocharging system for an internal combustion engine was developed, which builds the relationship between total pressure ratio, total expansion ratio and other two-stage turbocharging system parameters. Considering total expansion ratio as a function of expansion ratio between HP and LP turbine, minimum total expansion ratio can be determined using this model. The ratio of total pressure ratio to total expansion ratio, engine brake thermal efficiency and total heat exchange of coolers are considered as the parameters for engine performance evaluation. Influence of two-stage turbocharging system parameters, such as efficiency of compressors and turbines, cooling water temperature, cooler efficiency, pressure loss of coolers, EGR rate and bypass gas rate of wastegate, etc., on engine performance was analyzed respectively.

Results show that the performance of a two-stage turbocharging engine is impacted mainly by LP turbocharger efficiency, intercooler performance and air filter performance.
Study on the Controlling of Flow Separation Zone Near Unshrouded Impeller Exit for Centrifugal Compressors
Authors: Xi Guang , Li Xuechen , Gong Wuqi
Published: November 2013

A large-size centrifugal compressor test rig with an unshrouded impeller was established to investigate the flow field characteristics of the stage. However, the author’s previous researches indicated that there was a separation zone near the exit of the unshrouded centrifugal impeller, which was undesirable to assess the performance of the impeller and vaned diffuser respectively. In order to control the separation zone, the impeller was redesigned. Four kinds of available strategies, such as changing the loading distribution of the impeller blades, altering the meridian contour of the impeller, adjusting the design flow rate and the rotation speed of the stage and shrinking the casing at the entrance of the vaned diffuser were tried. It was demonstrated that by means of decreasing the shroud-side blade loading, increasing the nominal design flow rate and shrinking the shroudside casing of the diffuser, the separation zone near the impeller exit could be effectively suppressed to an acceptable extent.
Characterization of Flow Through Porous Metals
Authors: Hargather Michael J. , Thole Karen A.
Published: November 2013

Porous metals have long been considered as an ideal material in which to manufacture turbine components given the inherent large convective surface area. One consideration, however, in using porous metals is the increase in pressure drop that accompanies these materials. To characterize increases in pressure drop for porous materials, flow measurements were made on numerous porous metal coupons. The porosity of the coupons investigated had a range of four in terms of density. A technique for determining the effective internal flow area from pressure drop measurements was developed to provide an effective diameter. The pressure drop measurements were compared to an ideal isentropic compressible-flow nozzle and to a smooth, straight-walled tube. The comparisons show that the porous channels have a similar, but much larger pressure drop than the smooth walls. The experiments performed demonstrated that these porous geometries can be scaled to provide generalized pressure drop characteristics for all geometries.
Experimental Validation of Methods Providing Boundary Conditions to Simulate the Evaporation Process of Water Injected Into High Speed Air Flow
Authors: Nagabhushan P. S. , Rossetti A. , Barabas B. , Schnitzler J. P. , Kefalas A. , Benra F. K. , Dohmen H. J.
Published: November 2013

Water injection into a high speed air flow has been recently investigated by many scientists and is still an important field of research in gas turbine technology. To study the behavior of droplets in gas turbines, expensive experimental tests and their validation with analytical and Computational Fluid Dynamics (CFD) models are necessary.

The Euler-Lagrange approach can be used to tackle these problems due to their capability in tracking particles along the domain, relative ease in formulating and applying them to the current industrial problems in terms of acceptable computational cost. However, providing spray boundary conditions using Euler-Lagrange approach is quite challenging because the spray pattern depends upon various parameters like spray angle, velocity, diameter distribution etc. In this paper, to obtain these parameters, two different approaches are described. The first approach depends on an analytical model for velocity and spray angle injection conditions and the second approach depends on an Euler free surface simulation. For diameter distribution, Rosin Rammler distribution function and experimental data are used. When combined together these lead to four particle injection conditions. The results achieved from all the four cases are compared with the experimental data of water droplet evaporation in a high speed air flow obtained from a hot air test rig operating at conditions of real gas turbines.
The Use of Probabilistic Methods in Determining Turbine Disc Cyclic Life Uncertainty
Authors: Williams David T. , Smout Peter , Bianchi Matteo , Joinson Martin B.
Published: November 2013

Gas turbine discs are classified as Critical Parts since, in the event of their primary failure, high energy debris can be released potentially resulting in hazardous consequences to the aircraft. Critical Parts are monitored during the life cycle of a gas turbine engine to ensure that integrity is established and maintained. The predicted safe cyclic life for an engine disc must be calculated as part of this monitoring process. For calculating the life of a turbine disc, a thorough understanding of material properties, operating conditions, metal temperatures and the resultant stress field is required. These inputs are obtained variously by component or whole engine testing or by predictive methods. These methods evolve over time, and materials may need to be changed, so for legacy engine designs, it’s important that the monitoring process recognises this and reacts appropriately. This paper describes the application of probabilistic methods to determine the uncertainty of turbine disc cyclic life for a two shaft low by-pass ratio gas turbine engine designed originally in the 1950s but predicted to be in service to beyond 2030. For the subject gas turbine the original material used to manufacture the turbine discs was declared technically and commercially obsolete. A new material was selected, requiring a new cyclic life to be determined. Rather than run an engine test to measure temperatures of the new discs, an analytical approach was adopted involving air system and thermal modelling and robust design techniques. These included Monte-Carlo analyses and the linking of thermal modelling and cyclic lifing codes using optimisation tools. It is shown how a probabilistic approach to air system and thermal modelling has enabled: (i) a quantitative judgment on the value of an air system survey (ii) the uncertainty of thermal predictions and the resultant variation in life to be quantified. These methods and results have then been used to release a safe cyclic life of a turbine disc for operation in an aircraft without the use of a dedicated thermocouple test.
Low-Flow-Coefficient Centrifugal Compressor Design for Supercritical CO2
Authors: Lettieri C. , Baltadjiev N. , Casey M. , Spakovszky Z.
Published: November 2013

This paper presents a design strategy for very low flow coefficient multi-stage compressors operating with supercritical CO2 for Carbon Capture and Sequestration (CCS) and Enhanced Oil Recovery (EOR). At flow coefficients less than 0.01 the stage efficiency is much reduced due to dissipation in the gas-path and more prominent leakage and windage losses. Instead of using a vaneless diffuser as is standard design practice in such applications, the current design employs a vaned diffuser to decrease the meridional velocity and to widen the gas path. The aim is to achieve a step change in performance.

The impeller exit width is increased in a systematic parameter study to explore the limitations of this design strategy and to define the upper limit in efficiency gain. The design strategy is applied to a full-scale re-injection compressor currently in service. Three-dimensional, steady, supercritical CO2 CFD simulations of the full stage with leakage flows are carried out with the NIST real gas model. The design study suggests that a non-dimensional impeller exit width parameter b2* = (b2/R)ϕ of 6 yields a 3.5 point increase in adiabatic efficiency relative to that of a conventional compressor design with vaneless diffuser. Furthermore, it is shown that in such stages the vaned diffuser limits the overall stability and that the onset of rotating stall is likely caused by vortex shedding near the diffuser leading edge. The inverse of the non-dimensional impeller exit width parameter b2* can be interpreted as the Rossby number. The investigation shows that, for very low flow coefficient designs, the Coriolis accelerations dominate the relative flow accelerations, which leads to inverted swirl angle distributions at impeller exit. Combined with the two-orders-of-magnitude higher Reynolds number for supercritical CO2, the leading edge vortex shedding occurs at lower flow coefficients than in air suggesting an improved stall margin.
Flow Fields in an Axial Flow Compressor During Four-Quadrant Operation
Authors: Gill Andrew , von Backström Theodor W. , Harms Thomas M. , Dunn Dwain
Published: November 2013

It has been shown in previous investigations that when all combinations of both positive and negative direction of rotation and flow direction are allowed in operating a multistage axial flow compressor, the operating point may be in any of the four quadrants of the pressure rise versus flow characteristic. The present paper is the first discussion of the flow field of all possible modes of operation of an axial flow compressor. During the present study interstage time dependent hot film velocity measurements and five hole pneumatic probe measurements were combined with steady and time dependent CFD solutions to investigate the flow fields in the three-stage axial compressor. Results are presented in terms of mean-line velocity triangles, mean stream surface plots, mid-span radial velocity contours right through the compressor, rotor-downstream radial distributions of axial and tangential velocity, stator-downstream axial velocity contours and mid-span entropy contours through the compressor. Main flow features are pointed out and discussed. The study was instigated in an effort to understand possible accident scenarios in a three-shaft closed cycle nuclear powered helium gas turbine.
Decentralized Engine Control System Simulator
Authors: McArthur John , Boehm Travis , Hegwood Bobbie , Watts Oran
Published: November 2013

LibertyWorks™ (Rolls-Royce North American Technologies Inc.) is developing an integrated environment for design, development, testing, and integration of current and future decentralized gas turbine engine control systems. This paper serves as a mid-project status update to solicit recommendations from industry and academia on what might be done to make it better, and to give the community a preview. Identified as the Decentralized Engine Control System Simulator (DECSS), this system has the capabilities to support flexible, decentralized control system architectures containing both simulated and physical hardware-in-the-loop control components. Neither the DECSS nor the project developing the DECSS will make a selection of a preferred control system architecture/design method, nor a preferred communication architecture/protocol, but instead will provide a flexible environment for future users to rapidly evaluate potential solutions in a real-time environment with hardware in the loop. This paper describes the DECSS functions, capabilities, organization and how it will be used as a NASA asset for future engine control system development.
Deposition With Hot Streaks in an Uncooled Turbine Vane Passage
Authors: Casaday B. , Prenter R. , Bonilla C. , Lawrence M. , Clum C. , Ameri A. , Bons J. P.
Published: November 2013

The effect of hot streaks on deposition in a high pressure turbine vane passage was studied both experimentally and computationally. Modifications to Ohio State’s Turbine Reaction Flow Rig allowed for the creation of simulated hot streaks in a four-vane annular cascade operating at temperatures up to 1093°C. Total temperature surveys were made at the inlet plane of the vane passage, showing the variation caused by cold dilution jets. Deposition was generated by introducing sub-bituminous ash particles with a median diameter of 11.6 μm far upstream of the vane passage. Results indicate a strong correlation between surface deposits and the hot streak trajectory. A computational model was developed in Fluent to simulate both the flow and deposition. The flow solution was first obtained without particulates, and individual ash particles were subsequently introduced and tracked using a Lagrangian tracking model. The critical viscosity model was used to determine particle sticking upon impact with vane surfaces. Computational simulations confirm the migration of the hot streak and locations susceptible to enhanced deposition. Results show that the deposition model is overly sensitive to temperature and can severely overpredict deposition. Model constants can be tuned to better match experimental results, but must be calibrated for each application.
Influence of Blade Profile on Secondary Flow in Ultra-Highly Loaded Turbine Cascades at Off-Design Incidence
Authors: Tsujita Hoshio
Published: November 2013

An increase of aerodynamic loading of turbine blade leads to the reductions of the numbers of blade and stage. As a result, the size and the weight of gas turbines could be reduced. However, the secondary flow becomes much stronger because of the steeper pressure gradient across the cascade passage, and consequently deteriorates the turbine efficiency. Therefore, it is very important to minimize the loss generation increased by the increase of loading. In the present study, the influences of blade profile on the secondary flow structure in a linear ultra-highly loaded turbine cascade (UHLTC) at off-design incidence were investigated in detail by using a numerical method.

The computations were performed for the flow in three types of UHLTC at zero and off-design incidences. The present three types of turbine blade are same in the inlet and the outlet metal angles but different in the length of the blade suction surface. The verification of the computed results was performed by comparing with the experimental oil flow visualizations and the measured static pressure on the blade surface. The decrease of the length of blade suction surface increased both the profile loss and the secondary loss according to the increase of incidence angle in the positive range. The positive incidence not only strengthened the horseshoe and the passage vortices but also induced a new vortex along the blade suction surface on the end-wall. The incidence angle at which the newly formed vortex appeared was influenced by the blade profile. Moreover, the newly formed vortex affected the strength of the pressure side leg of horseshoe vortex.
On the Effect of Pad Clearance and Preload Manufacturing Tolerances on Tilting Pad Bearings Rotordynamic Coefficients
Authors: Gomez Jose L. , Pineda Saira , Diaz Sergio E.
Published: November 2013

Tilting pad bearings (TPB) are commonly used in high-speed and high-power turbomachines, due to its contributions in avoiding rotor instabilities. Studies related to the estimation of dynamic coefficients have been carried out considering a uniform value of the geometric parameters (clearance, pre-load) for all bearing pads. These assumptions give a reasonable agreement on the direct coefficients prediction while, recently, some discrepancies have been found on the cross-coupled coefficients. In this work, a numerical study is devised to analyze the influence of the pre-load and clearance variations from pad to pad, due to manufacturing tolerances, on the dynamic coefficients prediction. The numerical code for the estimation of the dynamic coefficients uses the finite element method to integrate the Reynolds’s equation through a perturbation approach. Variations on the pre-load and clearance for each bearing’s pad were performed, producing plots quantifying the sensitivity of the tilting pad bearing cross coupled coefficients to manufacturing tolerances.
Development of a Turning Mid Turbine Frame With Embedded Design: Part II — Unsteady Measurements
Authors: Spataro Rosario , Göttlich Emil , Lengani Davide , Faustmann Christian , Heitmeir Franz
Published: November 2013

The paper, which is constituted by two parts, presents a new setup for the two-stage two-spool facility located at the Institute for Thermal Turbomachinery and Machine Dynamics (ITTM) of Graz University of Technology. The rig was designed in order to reproduce the flow behavior of a transonic turbine followed by a counter rotating low pressure stage like those in high bypass aero-engines. The meridional flow path of the machine is characterized by a diffusing S-shaped duct between the two rotors. The role of wide chord vanes placed into the mid turbine frame is to lead the flow towards the LP rotor with appropriate swirl.

Experimental and numerical investigations performed on this setup over the last years showed that the wide chord struts induce large wakes and extended secondary flows at LP inlet flow. Moreover, large deterministic fluctuations of pressure, which may cause noise and blade vibrations, were observed downstream of the LP rotor. In order to minimize secondary vortices and to damp the unsteady interactions, the mid turbine frame was redesigned to locate two zero-lifting splitters into the vane passage.

While in the first part paper the design process of the splitters and the time-averaged flow field were presented, in this second part the measurements performed by means of a fast response probe will support the explanation of the time-resolved field. The discussion will focus on the comparison between the baseline case (without splitters) and the embedded design.
Development of a Continuous Coupling of Steam Turbine Blades by Contact of Shrouds
Authors: Hlous Jan , Kubin Zdenek , Kellner Josef , Misek Tomas , Prchlik Lubos
Published: November 2013

As modern blade designs are breaking historical technical barriers to blade loading levels, adding extra damping is needed to improve blade resistance against excitation. For this purpose, various ways of blade coupling are used. One of most commonly used method is to design a special shroud geometry that makes it touch the adjacent shroud through an interface. These contacting surfaces are assembled with a preload providing a normal acting force. Performing FEM analyses is required to study the influence of manufacturing tolerances and assembly procedure on contact conditions.

In recent years, a new coupling design has been developed in Skoda Power. This work describes the analytical approach selected for simulation of bladed disk assembly procedures regarding blade-to-blade and blade-to-disk contact conditions and consequent stress distribution. First, the common method of assembly that is used for similar blades with free-standing design was studied with an unsatisfactory coupling condition results. Consequently, a new assembly method was developed to improve the disadvantages of the common method. Experimental measurements were performed to verify the credibility of computational analyses for both methods and confirmed their results.

The contact conditions were studied both in state after assembly and during operation, and based on the findings, dynamic properties were predicted. A full scale bladed disk was manufactured for experimental tests to investigate dynamic behaviour. Based on the results of the test, it was possible to choose the most convenient FEM model that can be used for blade tuning during blade design procedure. Additionally, vibration damping was evaluated for several mode shapes and as a whole the measurement confirmed benefits of the coupling design.
Design for Six Sigma: The First 15 Years
Authors: Gardner Martha , Wiggs Gene
Published: November 2013

The original MAIC version of Six Sigma was launched at GE in 1995. Within a couple of years after launch it was recognized that the Engineering Design community needed methods and tools that focused on achieving performance goals, reliability, and producibility, while meeting cost targets and reducing cycle time. Design for Six Sigma was born out of this need and has evolved into a company-wide approach integrated into many engineering design processes. The initiative has continued to grow over the last 15 years. This paper is an update to a paper the authors published in 2007. Many new learnings from the subsequent 5 years are being integrated into the prior version of the paper by the authors (Ref. 1).
Comparison of BLISS 2000 and CO in Turbine Blade MDO for Aircraft Engine
Authors: Yang Junjie , Chen Jingyang , Yan Jiachao
Published: November 2013

In this paper, the two methods of CO and BLISS 2000 are compared by using a classical numerical example firstly. The results show that the BLISS 2000 performs better in both computational accuracy and efficiency, because the scale of the optimization problem, such as the number of variables and constraints, in the BLISS 2000 is less than that in the CO. Moreover, the BLISS 2000 optimizes directly the system objectives while the CO focuses on decreasing the discrepancy between the coupled variables in different fields.

The two methods are then applied to an aerodynamics-thermal-structure coupled design problem for the turbine blades of an aircraft engine. Based on the results of sensitivity analysis, the number of design variables is reduced from 34 to 12. To eliminate the impact of the surrogate models on the different MDO algorithms as much as possible, the same initial Kriging surrogate models are not refreshed during the MDO procedures. Without the high fidelity simulation such as CFD and FEM analysis in the MDO processes, the BLISS 2000 method shows the more powerful capability of the convergence than that of the CO method, as shown in the numerical example. The optimization steps of the system level for BLISS 2000 are approximate 1/5 of those for CO, and the iteration number of step in the sub-system level with BLISS 2000 is only about 1/8 of that with CO.

Based on the weight sum of two objectives, the BLISS 2000 shows more robust than the CO because both weight reduction and aerodynamic efficiency are improved in the BLISS 2000 but only the blade weight reduction is gained in the CO. For other multi-objective optimization approaches, however, it still needs to be demonstrated through more studies.
A Wireless Vibration Control Technique for Gas Turbine Blades Using Piezoelectric Plates and Contactless Energy Transfer
Authors: Botta Fabio , Marx Nigel , Schwingshackl Christoph , Cerri Giovanni , Dini Daniele
Published: November 2013

Gas turbine blade vibrations can give rise to catastrophic failures, and cause a reduction of the blades’ life due to fatigue-related phenomena. Damping is often required to improve performance of bladed disks. Recently, the adoption of piezoelectric elements has received considerable attention by many researchers for potential applicability in different areas of mechanical, aerospace, aeronautical and civil engineering. Furthermore, studies of blades’ vibration-control via piezoelectric plates are beginning to appear. In previous contributions, the authors have proposed a model to control multimode beam vibrations using piezoelectric elements. Analytical results have been validated through comparison with the results of a multi-physics finite elements package (COMSOL), as well as with data available in the literature. Experimental investigations carried out by the authors using a cantilever beam support the proposed theory. The model defines the optimal position of the plates to damp the multimode vibrations. Different loading scenarios where different modes were excited with different percentages were considered [1]. This model has also been extended to a rotating beam, and a finite elements code has been used to obtain the optimal position of the piezo-plates at different rotating speeds ([4]). In this paper the authors report the first results of the experimental investigations performed using a rotating beam. An experimental apparatus has been designed and constructed, including a new wireless power transfer system to eliminate issues associated with the use of slip rings. A Matlab program has been developed to control the system and interpret the data. Also, a laser pointing system has been used to measure the vibrations of a single blade and, thus, the effectiveness of the system. The preliminary results obtained using the newly developed test rig are discussed after presenting the experimental setup and the acquisition system designed and implemented by the authors.
Experimental Identification of Force Coefficients of Large Hybrid Air Foil Bearings
Authors: Wang Yu Ping , Kim Daejong
Published: November 2013

Foil bearing technology using air or gas as a lubricant has been around since the mid 60’s, and it made significant progress in its reliability, performance, and applications. Even if significant progress has been made to the technology, their commercial applications to relatively large machines with journal shaft diameter bigger than 100mm was not reported. This paper presents dynamic characteristics of hybrid (hydrodynamic + hydrostatic) air foil bearing (HAFB) with diameter of 101.6mm and length of 82.6mm. The test rig configuration in this work is a floating HAFB on a rotating shaft driven by electric motor, and the HAFB is under external load.

HAFB stiffness coefficients were measured using both 1) time-domain quasi-static load-deflection curves, and 2) frequency-domain impulse responses, and HAFB damping coefficients were measured using only impulse responses. The HAFB direct stiffness coefficients measured from both methods are close to each other in the range of 4∼7 MN/m depending on speed, load, and supply pressure, but frequency domain method shows larger scatter in the identified coefficients. HAFB coefficients simulated with linear perturbation method using a bump stiffness matched to the load-deflection characteristics at 18,000rpm show reasonably good agreements with experimentally measured values.
Using Unsteady Analysis to Improve the Steady State CFD Assessment of Minimum Flow in a Radial Compressor Stage
Authors: Vezier Clementine , Dollinger Michael , Sorokes James M. , Pacheco Jorge E.
Published: November 2013

This paper presents a Computational Fluid Dynamics (CFD) study performed to assess the prediction of the minimum stable volume flow for a high Mach number, high head, and high volume flow compressor stage. CFD was run on a “pie slice” or sector stage model in steady-state condition and on a full 360° stage model under both steady and unsteady state conditions. The predictions of the minimum stable flow were compared to experimental data. Results showed the CFD performed on the “pie slice” stage model over-predicted the minimum stable flow by 9% compared to the test results, while the transient CFD predicted the minimum stable flow within 5.8%. Flow field comparisons of the impeller between unsteady and steady state CFD revealed that the steady state CFD accurately predicted the flow phenomena until the onset of surge. However, the unsteady flow features could not propagate through the diffuser because of the limitations of the impeller-diffuser interface modeling in the steady state analysis.
Hydrodynamic Analysis of Hydrostatic Bearings With Runner Misalignment and Pad Damage
Authors: Dimond Timothy , Barnes David
Published: November 2013

Hydrostatic bearings are used in applications where surface speeds are low, or viscosities are insufficient to develop significant load capacity due to shear flow. They are also used in jacking applications for initial liftoff of rotors under low or no rotation conditions, especially for heavy rotors where significant babbitt damage would otherwise occur. Traditional hydrostatic bearing analyses assume isothermal lubricating flows. Analytical solutions also assume that the pressure in the pocket of the hydrostatic bearing is constant. This assumption is only approximately correct for low and zero operating speeds. Analytical solutions also assume that the runner and pad surfaces are parallel. The analytical solutions are not capable of capturing damage or misalignment effects. This paper describes a hydrodynamic analysis of a hydrostatic thrust bearing. The solution is based on a finite element solution to the generalized Reynolds equation. The finite element solution is applied in both the pocket and pad regions of the hydrostatic bearings. The analysis includes a flow loop balance that considers the effects of pressure losses in the lubricant supply piping, allowing for modeling of saturation effects in bearing load capacity. The flow loop balance for the lubrication supply is coupled with the bearing solution. This allows for pad loads to vary as a function of circumferential position in thrust bearings. The analysis was applied to the operation of a hydrostatic thrust bearing system for the HUSIR radio telescope at the Massachusetts Institute of Technology. Simplified models of pad damage and runner misalignment were considered in the analysis. The minimum film thickness and pressure profile was calculated. Runner misalignment reduced minimum film thickness by up to 80% when compared to a parallel runner under identical loading conditions. Runner damage equivalent to twice the nominal film thickness reduced the minimum film thickness by approximately 10%.
Performance Characteristics of Metal Mesh Foil Bearings: Predictions vs. Measurements
Authors: San Andrés Luis , Chirathadam Thomas Abraham
Published: November 2013

Proven low-cost gas bearing technologies are sought to enable more compact rotating machinery products with extended maintenance intervals. The paper presents an analysis for predicting the static and dynamic forced performance characteristics of metal mesh foil bearings (MMFBs) which comprise of a top foil supported on a layer of metal mesh of certain compactness. The analysis couples a finite element model of the top foil and underspring support with the gas film Reynolds equation. Comparison of predictions against laboratory measurements with two bearings aims to validate the analysis. The predicted drag friction factor in one bearing (L = D = 28.00 mm) during full film operation is just f ∼ 0.03 at ∼ 50 krpm, agreeing well with measurements at increasing applied loads. The predictions further elucidate the effect of the applied load and rotor speed on the bearing minimum film thickness, journal eccentricity and attitude angle. For a second bearing (L = 38.0 mm, D = 36.5 mm), predicted bearing force coefficients show magnitudes comparable with the measurements, with less than 20% difference, in the 250–350 Hz excitation frequency range. While the predicted direct stiffness coefficients are rather constant, the experimental force coefficients increase with frequency (max. 400 Hz), due mainly to the increasing amplitudes of dynamic force applied to excite the bearing with a set amplitude of motion. The analysis under predicts the direct damping coefficients at high frequencies (>300 Hz). The cross-coupled stiffness and damping coefficients are typically lower (< 40%) than the direct ones. The bearings operated stable at all speeds without any sub synchronous whirl. The reasonable agreement of the predictions with the available test data promote the better design and further development of MMFB supported rotating machinery.
Leakage and Rotordynamics Numerical Study of Circular Grooved and Rectangular Grooved Labyrinth Seals
Authors: Marsis Emanuel , Morrison Gerald
Published: November 2013

Labyrinth seals are used in many turbomachines to reduce the leakage from high to low pressure zones. In this paper, a new labyrinth seal design with a circular groove is presented. A 2D CFD simulation was used to model the leakage and optimize the tooth thickness of the new design and compare it to the traditional labyrinth seals with a rectangular groove. The rotordynamics coefficients for the new circular groove design as well as the traditional rectangular groove design were computed using 3D CFD simulations. The results show that the new proposed design provides less leakage than the traditional rectangular groove design. Moreover the new design provides more direct damping when compared to the traditional rectangular labyrinth seal.
The Development of an Air Injection System for the Forced Response Testing of Axial Compressors
Authors: Wegman E. , Snedden G. , van der Spuy S. J. , Holzinger F. , Schiffer H. P. , Mårtensson H. , Őstlund J.
Published: November 2013

A phase-controllable air injection exciter system was developed to enable measurement of the forced response properties of a transonic axial compressor blisk. The project was performed as part of the FP7 European framework programme project FUTURE. The eventual aim of this project is to improve existing turbomachinery blade flutter prediction methods.

The development and manufacturing of the exciter system was performed by the Council for Scientific and Industrial Research (CSIR) in Pretoria, South Africa. The exciter system consists of 15 air injectors, each with its own servo motor and controller. The injectors consist of a small rotating disc with a specific number of holes equispaced around the periphery, rotating within a pressurised volume. When the holes are rotated, using a servo motor, past an exit tube an air pulse is generated that is injected upstream of the compressor. The controllers enable adjustment of the relative phase angle between the exciters and in this way a pattern that resembles different nodal diameters can be excited on the rotor blisk.

Once the construction of the system was completed, it was transferred to Stellenbosch University, South Africa for sub-scale testing on a low speed compressor. The purpose of the sub-scale tests was to commission and verify the operation of the exciter system. The tests started with simple in-phase tests and then worked towards more complex test parameters that included frequency sweeps through the natural frequency of the compressor blades. The tests showed that it is possible to generate a blade response of different nodal diameters using the exciters. The blade response was also found to vary depending on the number of rotor holes, air supply pressure and sweep rate used for the exciters.

Following completion of the sub-scale tests, the completed system was transferred to the transonic compressor test facility of the Technical University Darmstädt (TUD) where both free flutter and forced response experiments were performed on a purpose-designed blisk in the transonic compressor test rig. The experimental campaign was successfully completed with the forced response experiments showing that the air injection system could be used to measure the response characteristics of the blisk.
Seismic demand of moderately ductile reinforced concrete shear walls subjected to high-frequency ground motions
Authors: Luu Hieu , Léger Pierre , Tremblay Robert
Published: November 2013

A parametric study was performed to examine the seismic behaviour of moderately ductile (MD) reinforced concrete shear walls designed according to Canadian code provisions, including National Building Code of Canada (NBCC) 2010 and Canadian Standards Association (CSA) 23.3-04, when subjected to typical high-frequency eastern North America earthquakes. The numerical models were experimentally validated based on large specimens shaking table test results. The results obtained following the code response spectrum procedure were compared with the results from inelastic response history analyses to investigate the effect of higher modes on seismic force demands. The results indicate that current code provisions for MD shear walls need to be modified. A new base shear factor and shear force design envelop are proposed to evaluate the seismic shear force demand more realistically. This study also recommends that the current CSA 23.3-04 requirements for ductile shear walls for bending moments could be applied to constrain the location of inelastic flexural deformations at the base of MD shear walls.
GM-CSF Exhibits Anti-Inflammatory Activity on Endothelial Cells Derived from Chronic Venous Disease Patients
Authors: Tisato Veronica , Secchiero Paola , Rimondi Erika , Gianesini Sergio , Menegatti Erica , Casciano Fabio , Zamboni Paolo , Zauli Giorgio
Published: November 2013

Twenty patients affected by chronic venous disease (CVD) in tertiary venous network and/or saphenous vein were analyzed before surgical ablation by echo-color-doppler for the hemodynamic parameters reflux time (RT) and resistance index (RI), a negative and a positive prognostic factor, respectively. RT and RI were next correlated with relevantin vitroparameters of venous endothelial cells (VEC) obtained from surgical specimens, such as cell migration in response to serum gradient, proliferation index, intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 expression, as well as cytokines release. Of interest, ICAM-1 expression in patient-derived VEC cultures correlated positively with RT and negatively with RI. Moreover, RT showed a positive correlation with the baseline osteoprotegerin (OPG) expression by VEC and an inverse correlation with VEC proliferation index. On the other hand, RI correlated positively with TNF-related apoptosis inducing ligand (TRAIL) expression. Among the cytokines released by VEC, GM-CSF showed a positive correlation with VEC proliferation and TRAIL expression and a negative correlation with OPG, ICAM-1 and VCAM-1 expression. Sincein vitrorecombinant GM-CSF induced VEC proliferation and counteracted the induction of ICAM-1, VCAM-1 and OPG upon exposure to TNF-α, our data suggest an anti-inflammatory activity of GM-CSF on venous endothelial cells.
The Method of Coupled Fixed Points and Coupled Quasisolutions When Working with ODE’s with Arguments of Bounded Variation
Authors: Figueroa Rubén
Published: November 2013

The aim of this paper is to show the use of the coupled quasisolutions method as a useful technique when dealing with ordinary differential equations with functional arguments of bounded variation. We will do this by looking for solutions for a first-order ordinary differential equation with an advanced argument of bounded variation. The main trick is to use the Jordan decomposition of this argument in a nondecreasing part and a nonincreasing one. As a necessary step, we will also talk about coupled fixed points of multivalued operators.