bluuebunny/crossref_metadata_2025_split 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.
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.
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.
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.
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.