bluuebunny/crossref_metadata_2025 huggingface dataset:
A Parametric Impact Study of the Geometry, Air System and Thermal Boundary Conditions on the Life of a Two-Stage High Pressure Turbine
Authors: Weiss Thomas , Rey Villazón Jose Maria , Kühhorn Arnold
Published: December 2013

High Pressure Turbine Discs of Aero Engines are classified as Critical Parts. Critical Parts are those whose failure is classified as likely to have hazardous or even catastrophic effects (e.g. damage to or loss of aircraft structure, injury/loss of the crew/passengers) and therefore require special control in order to achieve an acceptably low probability of individual failure. Even though special care is taken during the design and manufacturing process of these parts, there are still tolerances within their manufacturing route and during operation. Historically, Aero Engine parts were designed and laid out not to fail by using large safety factors to allow for scatter in different parameters. With the advent of high power computing, the time to conduct detailed thermo-mechanical assessments has drastically reduced and is therefore now open for Probabilistic Analytical Methods to determine the influence of parameter scatter on life and integrity.

This paper presents a parametric study of a typical two stage High Pressure Turbine (HPT) disc arrangement with a micro-turbine system, which feeds cooling air into the interstage cavity [1]. A series of automated studies were performed to determine the relevance of parameters, assess their sensitivity and evaluate their combined impact on the targets of the disc design process. The automated workflow couples a chain of programs that perform geometry manipulation, Finite-Element Thermo-Mechanical analysis simulation and life prediction. This process was used to assess parameter variations in the air system, thermal boundary conditions and the geometry of several turbine disc features. The resulting outputs of this study are the percentile impacts and correlations of each parameter on the life expectancy of the turbine discs. This provides a qualitative understanding of the relevance of each parameter when approaching the design of turbine discs.
Influence of Shroud Cavity Jet and Steam Admission Through a Circumferential Slot on the Flow Field in a Steam Turbine
Authors: Engelmann David , Kalkkuhl Tobias J. , Polklas Thomas , Mailach Ronald
Published: December 2013

Steam turbines for industrial application are often constructed according to modular design concepts. This allows interchangeable combinations of modules including steam admission and extraction. Prior to field tests the flow in a typical stage configuration of such a steam turbine is predicted numerically. Focus of the current work is the axial gap between high pressure and intermediate pressure part containing a circumferential slot. Mass flow used for axial thrust balancing re-enters the blade channel through this slot. Another exceptional feature appears at the high pressure vane carrier: For manufacturing reasons the last rotor shroud next to and upstream of the gap is not fully enclosed by the vane carrier. This results in a turbulent jet at the exit of the rotor shroud cavity mixing with both the blade channel flow as well as the incoming flow from the slot.

A commercial 3D RANS CFD-solver (ANSYS CFX 12) is used to predict the mixing of the different flow partitions within the stage gap. Therefore, the last stage of the high pressure part, the gap with the slot and the first stage of the intermediate pressure part are modeled and solved numerically. The amount of flow through the circumferential slot is varied to discern the influences of the specific flow partitions. Additionally, a modification of the vane carrier helps to analyze radial distribution of incoming flow for the downstream vane row as well as scoring global loss characteristics. As the simulation results indicate, flow parameters up- and downstream and also fluctuations crossing the gap are affected by flow through the slot. Furthermore, the computed flow field shows locations appropriate for a traversing probe system to be used in the test facility.
Fatigue and Crack Growth in 7050-T7451 Aluminum Alloy Under Constant- and Variable-Amplitude Loading
Authors: Newman James C. , Shaw Justin W. , Annigeri Balkrishna S. , Ziegler Brett M.
Published: December 2013

The 7050 aluminum alloy is used in many aerospace structural applications. Previous studies have identified that fatigue cracks develop very rough crack-surface profiles, which cause very high crack-closure levels due to a combination of plasticity, roughness and debris. Previously, tests were conducted on compact, C(T), specimens to generate crack-growth data from threshold to near fracture over a wide range in stress ratios (R). New threshold testing methods, based on compression precracking, were used to generate the data in the near-threshold regime. The plasticity-induced crack-closure model, FASTRAN, was used to correlate the data over a wide range in stress ratios and crack-growth rates from threshold to near fracture. To account for the very high crack-closure levels, a very low constraint factor, like plane-stress conditions, had to be used in the model. In addition, the crack-opening loads were measured during these tests using a local strain-gage method to generate another ΔKeff-rate curve. These two curves differed only in the near-threshold regime.

Herein, fatigue-crack-growth tests were conducted on C(T) specimens under spike overloads and simulated aircraft spectrum loading. Also, fatigue tests were conducted on single-edge-notch bend, SEN(B), specimens over a wide range in loading conditions (constant amplitude and three aircraft spectra). All specimens were machined from a single forged block of 7050-T7451. However, no residual stresses were measured in both the SEN(B) and C(T) specimens. Two European standard spectra were used, but modified to have only tension-tension loading. The purpose of this paper was to evaluate the two different effective stress-intensity factor curves for making crack-growth and fatigue-life predictions. Small-crack theory was used to make fatigue-life predictions using inclusion-particle sizes from the literature. Fatigue predictions on the SEN(B) specimens agreed fairly well (± 30%) using a 12-micrometer semi-circular initial flaw located at the semicircular-edge notch under all loading conditions, except the model was unconservative (factor of 3) on one of the severe aircraft spectra (Mini-TWIST+, Level 1). For the C(T) specimens subjected to single-spike overloads, the life-prediction code produced much more retardation than observed in the tests. However, the predicted crack-length-against-cycles under the Mini-Falstaff+ spectrum were only about 15% longer than the tests. The discrepancy under the single-spike overloads and the severe aircraft spectra was suspected to be caused by the low constraint factor and/or crack paths meandering around overload plastic zones. Ideally, a roughness-induced crack-closure model, in addition to the plasticity model, would be needed to obtain more reasonable results.
Ceramic Micro Channel Recuperator Fabrication Methods for Small Gas Turbine Engines
Authors: Kelly Matthew M. , Pan Ming-Jen , Atre Sundar , Rancourt Gregory , Heyes Andrew , Vick Michael J.
Published: December 2013

Recuperators can greatly improve the fuel efficiency of gas turbine engines, but they are normally heavy, bulky, expensive, and susceptible to high temperature creep, oxidation, and thermal stresses. One way to alleviate these problems is to make them from ceramic materials rather than metal alloys. However, fabricating these complex structures is a challenge. The technique investigated in this study was to laser-cut thin sheets of tapecast material into complex patterns, laminate them together into stacks, and sinter at high temperature. The layers were laminated together by applying heat, pressure, chemical solvents, and varying combinations of the three. This paper presents the results of all fabrication tests, describes the method used to successfully laminate and sinter one 33-layer stack, and summarizes other possible fabrication techniques for future investigation that would facilitate lamination the process.
On Blade Damping Technology Using Passive Piezoelectric Dampers
Authors: Schwarzendahl Sebastian M. , Szwedowicz Jaroslaw , Neubauer Marcus , Panning Lars , Wallaschek Jörg
Published: December 2013

This paper deals with a new damping concept for turbine blade vibrations utilizing piezoelectric material. A passive piezo damper consists of a piezoelectric element and a passive electric network connected to its electrodes. The damping performance depends on the size and location of the piezoelectric element with respect to the mode shape of the mechanical strain. Numerical and experimental investigations are carried out on a rigidly clamped simplified compressor blade at stand still and ambient conditions. An optimization process incorporating electromechanical finite element calculations determines the optimal position of the piezo damper in regard to the mode shape of interest. By applying the computed and measured Frequency Response Functions, the damping performance with and without piezo-damper are compared and referred to the measured material damping. The obtained numerical results are in very good agreement with the measured data, leading to a promising damping performance in real application.
Design Philosophy and Dynamic Calculation Method for Optimized Load Rejection Characteristics of Steam Turbines
Authors: Schindler Christoph , Zimmer Gerta
Published: December 2013

A load rejection disconnects the generator from the electrical grid. The resulting power excess accelerates the turbo set. Reacting to the load rejection, the turbine governor rapidly closes the steam admission valves. The remaining entrapped steam expands, thereby continuing to power the turbine. Thus the turbine speed rises till a dynamic equilibrium of accelerating and braking forces is reached. Thereafter the turbine speed decreases. If the maximally attained turbine speed remains below the trip threshold, immediate re-synchronization to the electrical grid is possible. Consequently, a forced outage of the steam turbine can be avoided and operational reliability is increased. Furthermore, functional safety requirements demand that the maximum turbine speed remains below test speed under all failure conditions. Accordingly, steam turbine design has to account for the impact of overspeed for a reliable and safe operation of the turbo set.

In order to manage load rejection requirements for steam turbine operation, the design engineer applies standard rules and overspeed calculation methods. These rules limit standardized overspeed estimation by defining maximum steam volumes, valve closing times, and I&C reaction times, as well as type and number of non-return valves.

A more thorough turbine overspeed investigation is necessary for several reasons, such as to evaluate this behavior under undesired failure conditions e.g. failure of non-return valves or blocking of control valves. A second justification for this investigation would be to predict changes resulting from turbine modifications — e.g. turbine upgrade or change at I&C systems.

In this paper, basic and advanced overspeed calculation tools are illustrated and compared, with respect to required effort as well as accuracy of prediction. It is shown how system parameters which are most sensitive with respect to overspeed can be identified and their influence assessed. Thus, firstly it is already possible to identify and improve critical overspeed behavior during design. Secondly, the impact of particular failures can be accurately predicted, thus allowing for due implementation of appropriate counter measures.

The methods, presented in this paper, were developed by the authors and their predecessors at SIEMENS AG for large steam turbo sets with a power range between 100 MW and 1500 MW.
Full-Annulus Multi-Row Flutter Analyses
Authors: Hsu Kwen , Hoyniak Dan , Anand M. S.
Published: December 2013

Flutter analysis for a first stage rotor of a compressor assembly was performed using the traditional Single-Passage, Single-Row (SPSR) flow model, and the prediction results did not correlate well with the test findings. In the tests flutter was observed but the SPSR simulation results indicated no flutter. It was suspected that influences from the upstream and downstream rows, which were omitted by the use of the SPSR model, might have significantly altered the flutter behavior of this rotor in a multistage environment. To confirm this hypothesis and to better understand the multistage turbomachinery flutter problem, FAMR (Full-Annulus, Multi-Row) models were employed in the current study to accurately take into account the interferences generated by the presence of the neighboring rows and to capture the time-varying flow variations in all directions.

It was found that the flutter performance predicted by a FAMR model can be dramatically different from that predicted by a SPSR model of the same design. The FAMR model showed that flutter can occur for this design, as indicated by test results. Present results indicate the potential impact of complex blade row interactions and aliasing on flutter behavior in a multi-blade row turbomachinery configuration. A simple sine-wave model was also used to better explain the FAMR simulation results and help the analyst in judging the efficacy of the FAMR simulation.
Parametric Evaluation of Compressor Blade Blending
Authors: Day W. David , Fiebiger Stephen W. , Patel Hitesh N.
Published: December 2013

This paper presents a methodology for rapidly analyzing the effect of blending damaged compressor blades on structural integrity. Heavy duty gas turbine compressor blades are subjected to damage from numerous sources. Compressor blades are blended in the field to allow continued operation with minimal risk of failure. By constructing analysis models parametrically, blend limits may be rapidly and reliably established for an entire compressor.

Erosion from washing or fogging, foreign object impacts, icing, tip rubs, and clash can damage both stator vanes and blades. Replacement of blades and stator vanes is very costly. The blades on some engines cannot be removed without de-stacking the rotor. The high cost of replacement provides an incentive to determine blend limits that do not compromise mechanical integrity. Field service support of compressor hardware includes the evaluation of compressor damage and the determination of whether such damage can be blended out in situ. Compressors on F-class engines have more than 15 stages, so at least 30 different airfoils must be analyzed when stator vanes are included. One must consider damage in the tips as well as leading and trailing edges at numerous radii. The variation in sizes, locations, and combinations of blends coupled with the number of airfoils results in a intense analytical task. Field service must also support multiple design configurations that include original engine manufacturer (OEM) blades as well as more robust aftermarket designs.

By setting up parametric analysis models of each blade, PSM has been able to provide its field service support group with accurate blend limits and has created a tool with which nonstandard blends may be evaluated in nearly real-time. This paper presents a methodology which has been applied to an entire compressor. A pre-stressed large-displacement modal analysis was performed which includes contact effects and considers a wide range of operating speeds using the linear perturbation technique. Combinations of parametrically defined blends are analyzed automatically. The effects of the blends on the modal frequencies were evaluated against in-house criterion. Plots of vibratory stress capability were produced to highlight which airfoils and which portions of airfoils are vulnerable in case of damage. The parametric nature of the analysis allows the user to easily change the position size and shape of the blends. With this methodology PSM is able to rapidly evaluate blends of stator vanes and blades for whole compressors and provide reliable and timely guidance to our field service representatives.
Rotor Model Updating and Validation for an Active Magnetic Bearing Based High-Speed Machining Spindle
Authors: Wroblewski Adam C. , Sawicki Jerzy T. , Pesch Alexander H.
Published: December 2013

This paper presents an experimentally-driven model updating approach to address the dynamic inaccuracy of the nominal finite element (FE) rotor model of a machining spindle supported on active magnetic bearings. Modeling error is minimized through the application of a numerical optimization algorithm to adjust appropriately selected FE model parameters. Minimizing the error of both resonance and antiresonance frequencies simultaneously accounts for rotor natural frequencies as well as for their mode shapes. Antiresonance frequencies, which are shown to heavily influence the model’s dynamic properties, are commonly disregarded in structural modeling. Evaluation of the updated rotor model is performed through comparison of transfer functions measured at the cutting tool plane, which are independent of the experimental transfer function data used in model updating procedures. Final model validation is carried out with successful implementation of robust controller, which substantiates the effectiveness of the model updating methodology for model correction.
Performance Optimization of a 3kW Microturbine for CHP Applications
Authors: Visser W. P. J. , Shakariyants S. , de Later M. T. L. , Haj Ayed A. , Kusterer K.
Published: December 2013

Combined heat and power (CHP) concepts for small scale distributed power generation offer significant potential for saving energy and reducing CO2 emissions. Microturbines are an interesting candidate for small CHP systems with advantages in terms of performance, size, noise and costs.

MTT has developed a 3kW recuperated microturbine for micro CHP applications, using turbocharger technology for the turbomachinery. In 2010, the development towards a 12.2% efficient demonstrator has been described in [1]. The underlying paper describes the subsequent performance optimization work done to obtain the 18% turbogenerator electric efficiency target.

The work included research focused on improving several components and auxiliary systems resulting in many small loss reduction steps. Combustor performance was improved and emissions reduced. Large steps were made by improving compressor and turbine performance. Compressor efficiency and pressure ratio were optimized to obtain maximum cycle efficiency. Turbine efficiency was improved by a redesign of the turbine scroll.

A detailed CFD study was performed to predict compressor design adaption effects on performance. A 60° sector model was used including inlet duct, impeller (including tip clearance) and diffusor. With prescribed inlet total pressure and total temperature and by varying the outlet static pressure boundary condition, the stationary flow field has been calculated for several operating points. The calculations have been carried out for both the original design and the adapted design.

Results showed that pressure ratio could be increased from 2.9 up to 3.2 using simple adaptations (from the turbocharger original design) while maintaining isentropic efficiency.

Finally, results of the test program and test analysis work are presented.
Numerical Investigation of the Flow in a Hydrodynamic Thrust Bearing With Floating Disk
Authors: Fischer Magnus , Mueller Andreas , Rembold Benjamin , Ammann Bruno
Published: December 2013

In this paper we present a novel method for the numerical simulation of flow in a hydrodynamic thrust bearing with floating disk. Floating disks are commonly employed in turbochargers and are situated between the thrust collar, which is rotating at turbocharger speed, and the static casing. A floating disk reduces wear, improves the skew compensating capacity of the bearing and is freely movable in the axial direction.

The simulation model presented combines a commercial flow solver (ANSYS CFX) with a control unit. Based on physical principles and a predefined axial thrust, the control unit automatically sets the rotational speed of the floating disk, the mass flow of the oil supply and the oil film thickness between the rotating disk and the casing wall and collar respectively. The only additional inputs required are the temperature and the pressure of the oil at the oil feed and the turbocharger speed. The width of the computational grid of the thin lubricating oil film in the gaps is adjusted using a mesh-morphing approach. The temperature-dependent variation in viscosity is included in the model. The calculated solution of the flow field in the domain, the oil film thickness and the resulting rotational velocity of the floating disk are validated against experimental data and demonstrate favorable agreement. The influence of uncertainties in the measurements and the behavior of the systems are thoroughly investigated in parametric studies which reveal the key influencing factors. These are the temperature-dependent viscosity of the oil, the axial thrust and turbulence effects in the supply grooves and ducts of the floating disk. Using the model presented here, it is now possible to predict design variants for this type of bearing.
Integrated Training Solutions: An Effective Tool to Synchronize People and Maintenance (U.S. Navy LCAC Case Study)
Authors: Hartey Maurice , Bodman Thomas , Korn Arlene
Published: December 2013

Maintenance, especially in a Marine environment, is continuous and costly. Life Cycle Management of a Marine Gas Turbine system encompasses many costs, of which repair parts, labor and equipment downtime associated with failures and maintenance are a significant portion. In fact, people (labor) make up the largest component of overall maintenance costs. Investing in people the largest cost driver to life cycle cost has a direct return in the long run, in terms of maintenance effectiveness and efficiencies. Applying and reinforcing knowledge and skills in a maintenance environment translates to improved reliability outcomes, longer operating time, fewer parts needs, and ultimately costs savings. However, given today’s constrained fiscal environment, the value of spending money for training rather than buying more parts or applying more maintenance, may not appear obvious. Such thinking is short sighted, and ultimately leads to reduced reliability and increased maintenance in the long run. This paper will explore these areas, and recommend how training programs can be effective predictive, proactive and responsive.
2500 KW Ship Service Turbine Generator Casing Welded Inconel Plug Failure and Repair Analysis
Authors: Shields John S. , Shapiro William H. , Kolb Eric C.
Published: December 2013

Six of seven US Navy Wasp Class (LHD) ships have 2500 KW Ship Service Turbo Generator (SSTG) steam turbine casings that were mistakenly manufactured with in-place first stage balancing holes in both the inboard and outboard sides of the upper casing half. These holes were intended for in-place balancing of the turbine rotor; however, the US Navy did not request the access holes since in-place balancing is typically not accomplished on in-service surface ship SSTGs. To correct the mistake, the OEM, developed a procedure to weld plugs into the holes. Unfortunately, cracks developed in the plug weld heat affected zones (HAZs) on many of the in-service units. Some cracks propagated entirely through the plug and leaked steam in service. A failure analysis determined that the original plug (Inconel X750) should have received post weld heat treatment (PWHT) to avoid embrittlement and the subsequent cracking of the HAZ. If PWHT was not to be accomplished, an alloy such as Inconel 600 should have been selected. It is noted that PWHT risks warping the casing and cannot be performed in-place. Inconel 600 repair plug installations were performed in-place, permitting a fast repair turnaround time, which allowed the affected ships to meet operational schedules.

To evaluate the repair integrity, the US Navy reviewed the failure analysis data and repair procedure and performed a Finite Element Analysis (FEA) and Fracture Analysis. Various “improved plug” designs were also studied in parallel to determine if a different geometry plug would better resist future cracking. During repairs, minor radial cracks were discovered in the welding “inlay” originally installed between the casing and plug weld. Because the inlay had to be fully preserved to avoid complex and time consuming additional repairs to the casing including PWHT, minor cracks were left in place and consumed by the new weld.

An important objective of this effort was to prove that if any cracking ever reoccurred only minor steam leakage would result. The leakage would be apparent to the operators long before there was potential for the plug to fail catastrophically; moreover, a “leak-before-break” determination was requested to be proven and validated.
Application of a Smooth Approximation of the Schmid’s Law to a Single Crystal Gas Turbine Blade: Part 1—Theory and Governing Equations
Authors: Ramaglia Alessandro D.
Published: December 2013

In industrial practice, the choice of the most suitable material model does not solely rely on the ability of the model in describing the intended phenomena. Most of the choice is often based on a trade-off between a great variety of factors. Robustness, cost and time for the minimum testing campaign necessary to identify the model and pre-existing standard practices are only a few of them. This is particularly true in the case of nonlinear structural analyses because of their intrinsic difficulties and the higher level of skills needed to carefully exploit their full potential. So, despite the great progress in this field, in certain cases it is desirable to use plasticity models that are rate-independent and possess very simple hardening terms. This is for example the case in which long term creep can be an issue or when the designer may want to treat separately different phenomena contributing to inelastic deformation.

If the material to be modelled is isotropic, commercial FE packages are able to deal with such problems in almost every case. On the contrary for anisotropic materials like Ni-based super-alloys cast as single crystals, the choice of the designer is more limited and despite the large amount of research literature on the subject, single crystal constitutive models remain quite difficult to handle, to implement into FE codes, to calibrate and to validate. Such difficulties, coupled with the unavoidable approximations introduced by any model, often force the practice of using oversimplifications of the material behaviour. In what follows this problem is addressed by showing how single crystal plasticity modelling can be reduced to the adoption of an anisotropic elastic behaviour with a sort of von Mises yield surface.
An Energy-Based Axial Isothermal-Mechanical Fatigue Lifing Method
Authors: Wertz John , Letcher Todd , Shen M.-H. Herman , Scott-Emuakpor Onome , George Tommy , Cross Charles
Published: December 2013

An energy-based fatigue lifing method for the determination of the full-life and critical-life of in-service structures subjected to axial isothermal-mechanical fatigue (IMF) has been developed. The foundation of this procedure is the energy-based axial room-temperature lifing model, which states: the total strain energy dissipated during both a quasi-static process and a dynamic (fatigue) process is the same material property. The axial IMF lifing framework is composed of the following entities: (1) the development of an axial IMF testing capability; (2) the creation of a testing procedure capable of assessing the strain energy dissipated during both a quasi-static process and a dynamic process at elevated temperatures; and (3), the incorporation of the effect of thermal loading into the axial fatigue lifing model. Both an axial IMF capability and a detailed testing procedure were created. The axial IMF capability was employed to produce full-life and critical-life predictions as functions of temperature, which were shown to have excellent correlation with experimental fatigue data. For the highest operating temperature, the axial IMF full-life prediction was compared to lifing predictions made by both the Universal Slopes and the Uniform Material Law prediction and was found to be more accurate at elevated temperature.
Uncontained Failure of a U.S. Navy Rolls-Royce 250-KS4, Root Cause Investigation and Subsequent Corrective Actions
Authors: Viercinski John , Hoffman Matthew , Pineiro Ivan , Russom Dennis
Published: December 2013

In 2008, a US Navy DDG-51 Class destroyer experienced an uncontained failure of a Rolls Royce 250-KS4 turbine engine which serves as a starter for the Ship Service Gas Turbine Generator (SSGTG). This paper discusses the events that preceded the failure, the root cause and contributing factors. It also describes multiple corrective actions, including design improvements that have been implemented with the goal of preventing this type of failure in the future.
A View to the Energy Dissipation Mechanism of a Gas Foil Bearing’s Structure due to Dry Friction
Authors: Matute José A. , Ruiz Rafael O. , Diaz Sergio E.
Published: December 2013

The purpose of the present work consists on improving the understanding of the energy dissipation mechanism in the structure of a gas foil bearing. The analysis is based on an analytical model capable of predicting bumps deformation due to a load on the top coupled with dry friction forces at the top and bump ends. Models of mass-individual bump and mass-bump foil subject to a harmonic force are predicted numerically. The nonlinear behavior due to dry friction results in the possibility of stick-slip conditions over the surfaces in contact. The Variation of parameters such as excitation amplitude, mass magnitude, coefficient of friction, and bump geometry were considered. Equivalent dynamic coefficients of stiffness and damping are estimated through a least squares curve fitting, which constitutes a linearization of the system with dry friction. A computer program was developed in order to consider the effect of stick-slip. As a final product of this research the nonlinear model of the structure support was used to obtain a linear and simplified equivalent model. In most studied cases it is possible to represent the system with a linearized model of constant stiffness and viscous damping which is a variable function of the studied parameters and the frequency.
Numerical Simulation of Spin Testing for Turbo Machine Disks Using Energy-Based Fracture Criteria
Authors: Nozhnitsky Yu. A. , Karimbaev K. D. , Servetnik A. N.
Published: December 2013

The results of numerical simulation of spin testing of disks of different structures including those made from different alloys are presented. Stress strain state (SSS) of disk during loading was determined using the MSC.Software and ANSYS commercial finite element method (FEM) software. As an integral assessment of disk burst speed, it has been suggested that a local energy fracture criterion be used. The results of calculation made using this criterion were compared with the results of disk testing carried out at special spin test rigs and also with the results of calculations made using different local strain and stress fracture criteria. Numerical simulation is effectively usable to assess the load-carrying capability of disks taking into account possible adverse combination of mechanical material properties and other factors and also to optimize structures of rotors including the welded ones.
Controlled Deflection Approach for Rotor Crack Detection
Authors: Kulesza Zbigniew , Sawicki Jerzy T.
Published: December 2013

A transverse shaft crack is a serious malfunction that can occur due to cyclic loading, creep, stress corrosion, and other mechanisms to which rotating machines are subjected. Though studied for many years, the problems of early crack detection and warning are still in the limelight of many researchers. This is due to the fact that the crack has subtle influence on the dynamic response of the machine and still there are no widely accepted, reliable methods of its early detection.

This paper presents a new approach to these problems. The method utilizes the coupling mechanism between the bending and torsional vibrations of the cracked, non-rotating shaft. By applying an external lateral force of constant amplitude, a small shaft deflection is induced. Simultaneously, a harmonic torque is applied to the shaft inducing its torsional vibrations. By changing the angular position of the lateral force application, the position of the deflection also changes opening or closing of the crack. This changes the way the bending and torsional vibrations are being coupled. By studying the coupled lateral vibration response for each angular position of the lateral force one can assess the possible presence of the crack.

The approach is demonstrated with a numerical model of a rotor. The model is based on the rigid finite element method (RFE), which has previously been successfully applied for the dynamic analysis of many complicated, mechanical structures. The RFE method is extended and adopted for the modeling of the cracked shafts. An original concept of crack modeling utilizing the RFE method is presented. The crack is modeled as a set of spring-damping elements (SDEs) of variable stiffness connecting two sections of the shaft. By calculating the axial deformations of the SDEs, the opening/closing mechanism of the crack is introduced.

The results of numerical analysis demonstrate the potential of the suggested approach for effective shaft crack detection.
Qualification of Duct Resonator Array for Noise Reduction in Offshore Installations
Authors: Palacios Sandra Rodiño , Liu Zheji , Peikli Vegard , Skorping Roald , Melvær Asle , Haaheim Ole Georg , Enger Jørund , Newman Michael J. , Syverund Elisabet
Published: December 2013

A compressor noise reducing device was investigated in connection with internal qualification of the technology for use in offshore installations in the Norwegian Continental Shelf. The acoustic performance of two duct resonator arrays applied to the inlet and discharge pipes as spool pieces was studied by means of sound insertion loss measurements. This array configuration minimizes the acoustical energy propagating to the inlet/discharge pipes and can be an optimal solution in modification cases where it is not feasible to mount the device inside the compressor. Laboratory verification measurements demonstrated that the duct resonator array reduces 14–18 dB the noise level at designed frequency (2–3 kHz). Correlation between insertion loss and effective length and a comparative study of the arrays installed in series or separated 90° with a bend were additionally performed. The investigation showed that this technology allows further flexibility of implementation often required in piping layouts with limited space.
Analysis of Offshore Wind Turbine Operation and Maintenance Using a Novel Time Domain Meteo-Ocean Modeling Approach
Authors: Dinwoodie I. , Quail F. , McMillan D.
Published: December 2013

This paper presents a novel approach to repair modeling using a time domain Auto-Regressive model to represent meteo-ocean site conditions. The short term hourly correlations, medium term access windows of periods up to days and the annual distribution of site data are captured. In addition, seasonality is included. Correlation observed between wind and wave site can be incorporated if simultaneous data exists. Using this approach a time series for both significant wave height and mean wind speed is described. This allows MTTR to be implemented within the reliability simulation as a variable process, dependent on significant wave height. This approach automatically captures site characteristics including seasonality and allows for complex analysis using time dependent constraints such as working patterns to be implemented. A simple cost model for lost revenue determined by the concurrent simulated wind speed is also presented. A preliminary investigation of the influence of component reliability and access thresholds at various existing sites on availability is presented demonstrating the ability of the modeling approach to offer new insights into offshore wind turbine operation and maintenance.
Analysis of the Operating Mode Influence Onto Energy Consumption of a Natural Gas Storage Plant
Authors: Arnulfi Gianmario L. , Cravero Carlo , Marini Martino
Published: December 2013

Natural gas carrying from production sites to users’ facilities is made by marine shipping in liquid phase or by terrestrial pumping in gaseous phase through long pipelines. In the latter case several storage stations are distributed along the pipeline nets to move the natural gas from its deposits to users’ terminals. Storage stations are set up to compensate seasonal fluctuations of the consumer demand versus methane supply, storing the gas in various kinds of reservoirs.

In most of such plants centrifugal compressors are used, where the energy and the time that a complete charge takes are affected by the operation scheduling of the compressor from the minimum to the maximum storage levels. While the pressure in the reservoir enforces the instant operation pressure, the flow rate is limited within a quite wide range. Here an in-house code, based on the lumped parameter approach and a quasi-steady dynamics, is applied to a complete charge. The natural gas behavior is modeled by the pseudo-ideal gas in order to get a fair accuracy keeping the usual gas dynamics equations.

The compression path has been parameterized and a multi objective optimization, embedding the simulation code, has been implemented to find the most suitable management of the compression station for the minimization of time and energy. The most significant paths are analyzed to pick out the effects of the compression strategy.
Optimization of Advanced Liquid Natural Gas-Fuelled Combined Cycle Machinery Systems for a High-Speed Ferry
Authors: Tveitaskog Kari Anne , Haglind Fredrik
Published: December 2013

This paper is aimed at designing and optimizing combined cycles for marine applications. For this purpose, an in-house numerical simulation tool called DNA (Dynamic Network Analysis) and a genetic algorithm-based optimization routine are used. The top cycle is modeled as the aero-derivative gas turbine LM2500, while four options for bottoming cycles are modeled. Firstly, a single pressure steam cycle, secondly a dual-pressure steam cycle, thirdly an ORC using toluene as the working fluid and an intermediate oil loop as the heat carrier, and lastly an ABC with inter-cooling are modeled. Furthermore, practical and operational aspects of using these three machinery systems for a high-speed ferry are discussed.

Two scenarios are evaluated. The first scenario evaluates the combined cycles with a given power requirement, optimizing the combined cycle while operating the gas turbine at part load. The second scenario evaluates the combined cycle with the gas turbine operated at full load.

For the first scenario, the results suggest that the thermal efficiencies of the combined gas and steam cycles are 46.3% and 48.2% for the single pressure and dual pressure steam cycles, respectively. The gas ORC and gas ABC combined cycles obtained thermal efficiencies of 45.6% and 41.9%, respectively. For the second scenario, the results suggest that the thermal efficiencies of the combined gas and steam cycles are 53.5% and 55.3% for the single pressure and dual pressure steam cycles, respectively. The gas ORC and gas ABC combined cycles obtained thermal efficiencies of 51.0% and 47.8%, respectively.
Differentiating Benign and Unstable Vibrations in Integral Geared Centrifugal Compressors
Authors: Srinivasan Anand
Published: December 2013

Industrial turbomachinery pose several rotordynamic challenges with the ever expanding envelope of design parameters. Monitoring and understanding vibration signatures of rotating equipment remains to be more of an art, despite the availability of state-of-the-art design and diagnostic techniques. Vibration characteristics of any machine can broadly be classified as synchronous or non-synchronous spectra. While synchronous vibrations can be fairly easily mitigated by balancing, non-synchronous vibrations typically necessitate a more involved treatment and analysis based on the nature of the problem. A rotor-bearing system is said to be unstable if the amplitude of vibration increases with time in an outward spiraling orbit, until the rotor contacts the stator. In the rotordynamics literature, a sub-synchronous vibration is typically associated with rotor-bearing instability. However, although it seems counter intuitive, not all non-synchronous vibrations are necessarily unstable (i.e., of the self-excited type). This paper focuses on classifying and differentiating benign sub-synchronous vibrations from potentially unstable ones, based on vibration data collected on integral geared centrifugal compressors. Guidelines have been suggested to appropriately correlate sub-synchronous vibrations with the health of a turbomachine. Both design techniques and measured vibration spectra have been presented to augment the discussions.
Experimental Investigation of the TurboClaw® Low Specific Speed Turbocompressor
Authors: Pullen K. R. , Etemad S. , Cattell R.
Published: December 2013

For both radial and axial turbocompressors there are well established design methods which direct the designer to the optimum shaft speed for a given flow rate and pressure rise. This shaft speed is relatively narrow in range if the highest efficiency is to be obtained. However, there are many reasons why shaft speed is dictated by other considerations and it is more common to find that the turbocompressor must operate far below the preferred shaft speed. The present contribution describes numerous applications where this occurs, the majority of which are when volume flow rates are relatively low.

Many researchers have attempted to find solutions to this problem and the starting point is to take a radial compressor and design it for operation at lower than optimal speed. This creates high windage and tip leakage losses relative to the useful work component which becomes punitive as the exit blade width is reduced. In addition to this, for small machines, the size of the exit blade width itself becomes an issue as it reduces to less than around 3mm leading to high relative tip clearances and narrow passages.

The purpose of this paper is to describe a novel solution that has been developed which is based on a combination of a partial entry rotor and extremely high forward sweep, a new class of machine denoted TurboClaw®. The level of forward sweep is substantial, at almost 90° that it is beyond the experience of fully bladed machines with levels of forward sweep below 30°. The machine is stable with extremely high tangential to radial Mach number ratios well over 20 being achieved. Experimentally produced maps for various sizes of machine are presented which demonstrate that the characteristic is very similar to that of an equivalent radial machine which would have to operate at speeds between two to four times greater.

Further experimental work is described which has taken place on both small prototype machines and on a larger version using a specially designed test rig capable of producing accurate performance measurements based on shaft torque. The test rig has been designed to allow flow visualization and non intrusive flow measurements. A selection of results from these tests is also described. At the levels of performance reached to date this class of machine is already suitable for a number of commercial applications including fuel cell air management systems, electric supercharging, and other industrial applications. Results of research and development programs in these areas are also described.
Rotordynamics of a 105,000 rpm Oil-Free Compressor-Expander for Subsurface Natural Gas Compression and Reinjection
Authors: Rimpel Aaron M. , Moore J. Jeffrey , Grieco Joseph S. , Shy Perry C. , Klein John M. , Brady Jerry L.
Published: December 2013

An aerodynamic and rotordynamic performance test stand has been developed to test a 105,000 rpm compressor-expander which is intended for subsurface natural gas reinjection. The machine consists of a two-stage centrifugal compressor which is driven by a single-stage expansion turbine, and the rotor is supported by foil gas journal bearings and a spiral-groove gas thrust bearing. The test stand is configured for open-loop testing of the overall compressor and turbine performance with air as the working fluid and atmospheric pressure at the compressor suction and turbine discharge locations. The dynamic performance of the test rig was monitored with proximity probes (relative rotor displacements) and accelerometers (housing acceleration) during tests. An instability of the conical rigid rotor mode was observed at or near the designed operating speed of 105,000 rpm which prevented testing of the machine at the maximum speeds required by the aerodynamic performance test matrix (110% of the designed operating speed). Various rotordynamic analyses investigated the effects of hole-pattern and labyrinth seals on stability, including a hole-pattern seal taper sensitivity study and the effect of higher compressor discharge densities. Based on the conclusions of the low-pressure condition rotordynamic analyses, the hole-pattern seals were replaced with labyrinth seals in the open-loop test rig, and the stability issue was no longer present up to the maximum speed.
Synchronous Analysis in Wind Turbine Gearbox Condition Monitoring
Authors: Luo Huageng , Luo Mingqi , Zhang Shaobo
Published: December 2013

This paper summarizes the application of “synchronous sampling” technique in the digital domain to enhance the signal-to-noise ratio in detection of wind turbine gear and bearing damage signatures. In this technique, only a once-per-revolution Key Phaser or a low-count Encoder signal is required. High-count synchronous sampling is achieved by resampling in the digital domain. Implementation and demonstration of the aforementioned techniques are illustrated in two current wind turbine field operation examples. The improvement in the accuracy and precision of damage feature extractions is demonstrated.
Design Analysis of a Micro Gas Turbine Combustion Chamber Burning Natural Gas
Authors: de Campos André Perpignan V. , Sacomano Filho Fernando L. , Krieger Filho Guenther C.
Published: December 2013

Gas turbines are reliable energy conversion systems since they are able to operate with variable fuels and independently from seasonal natural changes. Within that reality, micro gas turbines have been increasing the importance of its usage on the onsite generation. Comparatively, less research has been done, leaving more room for improvements in this class of gas turbines. Focusing on the study of a flexible micro turbine set, this work is part of the development of a low cost electric generation micro turbine, which is capable of burning natural gas, LPG and ethanol. It is composed of an originally automotive turbocompressor, a combustion chamber specifically designed for this application, as well as a single stage axial power turbine. The combustion chamber is a reversed flow type and has a swirl stabilized combustor. This paper is dedicated to the diagnosis of the natural gas combustion in this chamber using computational fluid dynamics techniques compared to measured experimental data of temperature inside the combustion chamber. The study emphasizes the near inner wall temperature, turbine inlet temperature and dilution holes effectiveness. The calculation was conducted with the Reynolds Stress turbulence model coupled with the conventional β-PDF equilibrium along with mixture fraction transport combustion model. Thermal radiation was also considered. Reasonable agreement between experimental data and computational simulations was achieved, providing confidence on the phenomena observed on the simulations, which enabled the design improvement suggestions and analysis included in this work.