bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid Tracking With Automatic Trajectory Optimization for Speed
Authors: Ma C. C. H. , Qian T. W. T.
Published: February 2008

An automatic trajectory optimization scheme, which takes the system dynamics into account, is presented in this paper. It is developed for use in conjunction with the rapid-tracking learning control. It optimizes the reference trajectory such that tracking will be speeded up whenever the actuator capability is not fully utilized, and slowed down whenever the actuator would otherwise saturate. This yields not only excellent fast tracking performance but also a new reference trajectory which accommodates the saturation constraint of the control actuator. Application of the proposed strategy in control practice will ease the burden of having to precisely design the timing of a reference trajectory in a tracking control problem. The resulting controlled system is able to precisely track short but highly complex trajectories at the highest speed physically possible. Simulation and experimental results of simultaneously controlling two motors to emulate servoing an x-y table are given to demonstrate the effectiveness of the proposed methodology.
Development of Proper Models of Hybrid Systems
Authors: Ferris J. B. , Stein J. L. , Bernitsas M. M.
Published: February 2008

A method to improve the ability of design engineers to generate proper dynamic models of systems from sets of component models is developed. This two stage method, called Eigenvalue MODA, is a new model deduction procedure for developing proper models of hybrid systems. The first stage in Eigenvalue MODA consists of using a previously published Model Order Deduction Algorithm (MODA) to systematically increment the complexity of each component model in the system. The first stage continues until a set of Critical System Eigenvalues (CSE) has been defined. During the second stage, the complexity component models is incremented based on the convergence of the CSE. The second stage continues until each CSE has converged to within a user specified tolerance. Component models may be represented by first-order (state space) or second-order equations and may be modal expansion or finite segment models. An example shows that the deduction of the proper system model depends on the interactions between the component model representations and the model deduction method. Eigenvalue MODA is a model deduction method that facilitates the generation of models of sufficient accuracy with physically meaningful parameters and states. This makes the models useful for system design and, as such, Eigenvalue MODA would be a useful tool in an automated modeling environment for design engineers.
Reduced Model Control of a Plasma Deposition Process
Authors: Pandit S. M. , Demeny T. M.
Published: February 2008

This preliminary study, relating plasma stagnation pressure to the current level, provided an initial step toward the development of feedback control of the plasma deposition process. Data consisting of an input voltage and output stagnation pressure were collected about a nominal operating point. Data Dependent Systems (DDS) methodology was utilized to obtain a high-order adequate model and then to reduce it to a first-order model suitable for feedback control. The power supply inductance was credited as the source of the single root characterizing the system. A minimum mean squared control strategy was employed to develop a control equation for the reduced system model. The simulation of the reduced order controller compared favorably with that of an optimal controller, based on the full model.
Dynamics of Axisymmetric Rockets in Free Flight
Authors: Eke F. O. , Cervantes E.
Published: February 2008

The attitude behavior of an axisymmetric, solid-propellant rocket in a torque-free environment is examined. The focus is on assessing the impact of substantial mass variation on the behavior of such systems. The main finding is that both the spin rate and the transverse angular velocity can differ substantially from those that would be observed if mass variation were neglected. The deviation is exacerbated by the presence of large amounts of propellant (variable mass) in the system. The attitude motion of such systems is also greatly influenced by the shape of the propellant grain.
Comparison of Coriolis and Turbine-Type Flowmeters for Fuel Measurement in Gas Turbine Testing
Authors: MacLeod J. D. , Grabe W.
Published: February 2008

The Machinery and Engine Technology (MET) Program of the National Research Council of Canada (NRCC) has established a program for the evaluation of sensors to measure gas turbine engine performance accurately. The precise measurement of fuel flow is an essential part of steady-state gas turbine performance assessment. Prompted by an international engine testing and information exchange program, and a mandate to improve all aspects of gas turbine performance evaluation, the MET Laboratory has critically examined two types of fuel flowmeters, Coriolis and turbine. The two flowmeter types are different in that the Coriolis flowmeter measures mass flow directly, while the turbine flowmeter measures volumetric flow, which must be converted to mass flow for conventional performance analysis. The direct measurement of mass flow, using a Coriolis flowmeter, has many advantages in field testing of gas turbines, because it reduces the risk of errors resulting from the conversion process. Turbine flowmeters, on the other hand, have been regarded as an industry standard because they are compact, rugged, reliable, and relatively inexpensive. This paper describes the project objectives, the experimental installation, and the results of the comparison of the Coriolis and turbine-type flowmeters in steady-state performance testing. Discussed are variations between the two types of flowmeters due to fuel characteristics, fuel handling equipment, acoustic and vibration interference, and installation effects. Also included in this paper are estimations of measurement uncertainties for both types of flowmeter. Results indicate that the agreement between Coriolis and turbine-type flowmeters is good over the entire steady-state operating range of a typical gas turbine engine. In some cases the repeatability of the Coriolis flowmeter is better than the manufacturer’s specification. Even a significant variation in fuel density (10 percent), and viscosity (300 percent) did not appear to compromise the ability of the Coriolis flowmeter to match the performance of the turbine flowmeter.
Eigenvector Derivatives of Generalized Nondefective Eigenproblems With Repeated Eigenvalues
Authors: Zhang Y.-Q. , Wang W.-L.
Published: February 2008

A new method is presented for computation of eigenvalue and eigenvector derivatives associated with repeated eigenvalues of the generalized nondefective eigenproblem. This approach is an extension of recent work by Daily and by Juang et al. and is applicable to symmetric or nonsymmetric systems. The extended phases read as follows. The differentiable eigenvectors and their derivatives associated with repeated eigenvalues are determined for a generalized eigenproblem, requiring the knowledge of only those eigenvectors to be differentiated. Moreover, formulations for computing eigenvector derivatives have been presented covering the case where multigroups of repeated first eigenvalue derivatives occur. Numerical examples are given to demonstrate the effectiveness of the proposed method.
Damage-Mitigating Control of Power Systems for Structural Durability and High Performance
Authors: Wu M.-K. , Ray A.
Published: February 2008

A major goal in the control of complex power systems such as advanced aircraft, spacecraft, and electric power plants is to achieve high performance with increased reliability, availability, component durability, and maintainability. The state of the art in the synthesis of control systems for complex mechanical processes focuses on improving performance and diagnostic capabilities under constraints that do not often adequately represent the dynamic properties of the materials. The reason is that the traditional design is based upon the assumption of conventional materials with invariant characteristics. In view of high performance requirements and availability of improved materials, the lack of appropriate knowledge about the properties of these materials will lead to either less than achievable performance due to overly conservative design, or overstraining of the structure leading to unexpected failures and drastic reduction of the service life. The key idea of the research work reported in this paper is that a significant improvement in service life can be achieved by a small reduction in the system dynamic performance. The concept of damage mitigation is introduced and, to this effect, a continuous-time model of fatigue damage dynamics is formulated. Finally, the results of simulation experiments are presented for transient operations of a reusable rocket engine.
Assessment of Damage in Ceramics and Ceramic Matrix Composites Using Ultrasonic Techniques
Authors: Rokhlin S. I. , Chu Y. C. , Baaklini G. Y.
Published: February 2008

This paper addresses the application of ultrasonic methods to damage assessment in ceramics and ceramic matrix composites. It focuses on damage caused by thermal shock and oxidation at elevated temperatures. The damage-induced changes in elastic constants and elastic anisotropy are determined by measuring the velocities of ultrasonic waves in different propagation directions within the sample. Thermal shock damage measurement is performed in ceramic samples of reaction bonded silicon nitride (RBSN) and aluminum oxide. Thermal shock treatment from different temperatures up to 1000°C is applied to produce the microcracks. Both surface and bulk ultrasonic wave methods are used to correlate the change of elastic constants to microstructural degradation and to determine the change in elastic anisotropy induced by microcrack damage. Oxidation damage is studied in silicon carbide fiber/reaction bonded silicon nitride matrix (SCS-6/RBSN) composites. The oxidation is done by exposing the samples in a flowing oxygen environment at elevated temperatures, up to 1400°C, for 100 hours. Significant changes of ultrasonic velocities were observed for composites before and after oxidation. The elastic constants of the composites were determined from the measured velocity data. The Young’s modulus in the fiber direction as obtained from ultrasonic measurements decrases significantly at 600°C but retains its original value at temperatures above 1200°C. This agrees well with the results of destructive tests by other authors. The transverse longitudinal and shear moduli obtained from ultrasonic measurements decrease continually until 1200°C. The results of this work show that the damage-induced anisotropy in both ceramics and ceramic matrix composites can be determined successfully by ultrasonic methods. This suggests the possibility of assessing damage severity using ultrasonic techniques.
Effects of Variational Particle Restitution Characteristics on Turbomachinery Erosion
Authors: Hamed A. , Kuhn T. P.
Published: February 2008

This paper presents the results of an investigation to determine the effects of variational particle rebounding models on surface impacts and blade erosion patterns in gas turbines. The variance in the particle velocities after the surface impacts are modeled based on the experimental measurements using Laser-Doppler Velocimetry (LDV) under varying flow conditions. The probabilistic particle trajectory computations simulate the experimental variance in the particle restitution characteristics using cumulative distribution functions and random sampling techniques. The results are presented for the particle dynamics through a gas turbine flow field and are compared to those obtained with deterministic rebound models based on experimental mean values.
Forging of Compressor Blades: Temperature and Ram Velocity Effects
Authors: Saigal A. , Zhen K. , Chan T. S.
Published: February 2008

Forging is one of the most widely used manufacturing process for making high-strength, structurally integrated, impact and creep-resistant Ti-6A1-4V compressor blades for jet engines. In addition, in modern metal forming technology, finite element analysis method and computer modeling are being extensively employed for initial evaluation and optimization of various processes, including forging. In this study, DEFORM, a rigid viscoplastic two-dimensional finite element code was used to study the effects of initial die temperature and initial ram velocity on the forging process. For a given billet, die temperature and ram velocity influence the strain rate, temperature distribution, and thus the flow stress of the material. The die temperature and the ram velocity were varied over the range 300 to 700°F and 15-25 in./sec, respectively, to estimate the maximum forging load and the total energy required to forge compressor blades. The ram velocity was assumed to vary linearly as a function of stroke. Based on the analysis, it was found that increasing the die temperature from 300 to 700°F decreases the forging loads by 19.9 percent and increases the average temperature of the workpiece by 43°F. Similarly, increasing the initial ram velocity from 15 to 25 in./sec decreases the forging loads by 25.2 percent and increases the average temperature of the workpiece by 36°F. The nodal temperature distribution is bimodal in each case. The forging energy required to forge the blades is approximately 18 kips *in./in.
Experimental Analysis of Journal Bearings
Authors: Elkholy A. H. , Elshakweer A.
Published: February 2008

This study presents a comprehensive technique, which could be applied to almost any rotating equipment to identify and diagnose journal bearing problems that relate to metal-to-metal bearing surface contact. Orbital measurements that describe bearing parameters in different modes of operation were experimentally obtained and analyzed. Such parameters may include: attitude angle, minimum oil film thickness, and the possibility of metal-to-metal rubbing occurrence. The general outline of the presented experimental technique was substantiated using the Raimondi–Boyd well-documented design charts and good correlation between experimental and analytical results was obtained.
Comparison of Emissions and Efficiency of a Turbocharged Lean-Burn Natural Gas and Hythane-Fueled Engine
Authors: Larsen J. F. , Wallace J. S.
Published: February 2008

An experiment was conducted to evaluate the potential for reduced exhaust emissions and improved efficiency, by way of lean-burn engine fuelling with hydrogen supplemented natural gas (Hythane). The emissions and efficiency of the Hythane fuel (15 percent hydrogen, 85 percent natural gas by volume), were compared to the emissions and efficiency of pure natural gas using a turbocharged, spark ignition, 3.1 L, V-6 engine. The feasibility of heavy duty engine fueling with Hythane was assessed through testing conducted at engine speed and load combinations typical of heavy-duty engine operation. Comparison of the efficiency and emissions at MBT spark timing revealed that Hythane fueling of the test engine resulted in consistently lower brake specific energy consumption and emissions of total hydrocarbons (THC), carbon monoxide (CO), and carbon dioxide (CO2), at a given equivalence ratio. There was no clear trend with respect to MBT oxides of nitrogen (NOx) emissions. It was also discovered that an improved NOx-THC tradeoff resulted when Hythane was used to fuel the test engine. Consequently, Hythane engine operating parameters can be adjusted to achieve a concurrent reduction in NOx and THC emissions relative to natural gas fueling.
Modeling of Gas Turbine Fuel Nozzle Spray
Authors: Rizk N. K. , Chin J. S. , Razdan M. K.
Published: February 2008

Satisfactory performance of the gas turbine combustor relies on the careful design of various components, particularly the fuel injector. It is, therefore, essential to establish a fundamental basis for fuel injection modeling that involves various atomization processes. A two-dimensional fuel injection model has been formulated to simulate the airflow within and downstream of the atomizer and address the formation and breakup of the liquid sheet formed at the atomizer exit. The sheet breakup under the effects of airblast, fuel pressure, or the combined atomization mode of the airassist type is considered in the calculation. The model accounts for secondary breakup of drops and the stochastic Lagrangian treatment of spray. The calculation of spray evaporation addresses both droplet heat-up and steady-state mechanisms, and fuel vapor concentration is based on the partial pressure concept. An enhanced evaporation model has been developed that accounts for multicomponent, finite mass diffusivity and conductivity effects, and addresses near-critical evaporation. The presents investigation involved predictions of flow and spray characteristics of two distinctively different fuel atomizers under both nonreacting and reacting conditions. The predictions of the continuous phase velocity components and the spray mean drop sizes agree well with the detailed measurements obtained for the two atomizers, which indicates the model accounts for key aspects of atomization. The model also provides insight into ligament formation and breakup at the atomizer exit and the initial drop sizes formed in the atomizer near field region where measurements are difficult to obtain. The calculations of the reacting spray show the fuel-rich region occupied most of the spray volume with two-peak radial gas temperature profiles. The results also provided local concentrations of unburned hydrocarbon (UHC) and carbon monoxide (CO) in atomizer flowfield, information that could support the effort to reduce emission levels of gas turbine combustors.
Dynamic Fatigue Testing of Candidate Ceramic Materials for Turbine Engines to Determine Slow-Crack-Growth Parameters
Authors: Osborne N. R. , Graves G. A. , Ferber M. K.
Published: February 2008

The purpose of this study was to evaluate the mechanical strength and slow-crack-growth parameter values for two commercially available silicon nitrides, SN-88 and NT164, at three high-temperature conditions. Weibull analysis and dynamic fatigue slow-crack-growth parameters were used to characterize the material strength and resistance to slow crack growth at high temperatures for use in life prediction models. Although both materials are commercially available Si3N4, their high-temperature behavior was found to be significantly different.
The Negative Information Problem in Mechanical Diagnostics
Authors: Hall D. L. , Hansen R. J. , Lang D. C.
Published: February 2008

Condition-based maintenance (CBM) is an emerging technology, which seeks to develop sensors and processing systems aimed at monitoring the operation of complex machinery such as turbine engines, rotor craft drivetrains, and industrial equipment. The goal of CBM systems is to determine the state of the equipment (i.e., the mechanical health and status), and to predict the remaining useful life for the system being monitored. The success of such systems depends upon a number of factors, including: (1) the ability to design or use robust sensors for measuring relevant phenomena such as vibration, acoustic spectra, infrared emissions, oil debris, etc.; (2) real-time processing of the sensor data to extract useful information (such as features or data characteristics) in a noisy environment and to detect parametric changes that might be indicative of impending failure conditions; (3) fusion of multi-sensor data to obtain improved information beyond that available to a single sensor; (4) micro and macro level models, which predict the temporal evolution of failure phenomena; and finally, (5) the capability to perform automated approximate reasoning to interpret the results of the sensor measurements, processed data, and model predictions in the context of an operational environment. The latter capability is the focus of this paper. Although numerous techniques have emerged from the discipline of artificial intelligence for automated reasoning (e.g., rule-based expert systems, blackboard systems, case-based reasoning, neural networks, etc.), none of these techniques are able to satisfy all of the requirements for reasoning about condition-based maintenance. This paper provides an assessment of automated reasoning techniques for CBM and identifies a particular problem for CBM, namely, the ability to reason with negative information (viz., data which by their absence are indicative of mechanical status and health). A general architecture is introduced for CBM automated reasoning, which hierarchically combines implicit and explicit reasoning techniques. Initial experiments with fuzzy logic are also described.
Balanced Model Reduction and Control of Rotor-Bearing Systems
Authors: Sawicki J. T. , Gawronski W. K.
Published: February 2008

An effective technique is applied to the suppression of vibrations in flexible rotor-bearing systems with small gyroscopic effects. A balanced linear-quadratic-Gaussian (LQG) controller design procedure is implemented. The size of the controller is reduced in two stages by using (i) a balanced model reduction, and (ii) an LQG balanced reduction. The condition for a gyroscopic matrix is developed that allows one to ignore the rotor gyroscopic effects in the process of the controller design, although they are included in the rotor dynamics. The approach is illustrated on a typical rotor-bearing system represented by a 48 degree-of-freedom finite element model.
Effect of Air Extraction for Cooling and/or Gasification on Combustor Flow Uniformity
Authors: Wang T. , Kapat J. S. , Ryan W. R. , Diakunchak I. S. , Bannister R. L.
Published: February 2008

Reducing emissions is an important issue facing gas turbine manufacturers. Almost all of the previous and current research and development for reducing emissions has focused, however, on flow, heat transfer, and combustion behavior in the combustors or on the uniformity of fuel injection without placing strong emphasis on the flow uniformity of fuel injection without placing strong emphasis entering the combustors. In response to the incomplete understanding of the combustor’s inlet air flow field, experiments were conducted in a 48 percent scale, 360 deg model of the diffuser-combustor section of an industrial gas turbine. In addition, the effect of air extraction for cooling or gasification on the flow distributions at the combustors’ inlets was also investigated. The following three different air extraction rates were studied: 0 percent (baseline), 5 percent (airfoil cooling), and 20 percent (for coal gasification). The flow uniformity was investigated for the following two aspects: (a) global uniformity, which compared the mass flow rates of combustors at different locations relative to the extraction port, and (b) local uniformity, which examined the circumferential flow distribution into each combustor. The results indicate that even for the baseline case with no air extraction there was an inherent local flow non uniformity of 10 ∼ 20 percent at the inlet of each combustor due to the complex flow field in the dump diffuser and the blockage effect of the cross-flame tube. More flow was seen in the portion further away from the gas turbine center axis. The effect of 5 percent air extraction was small. Twenty percent air extraction introduced approximately 35 percent global flow asymmetry diametrically across the dump diffuser. The effect of air extraction on the combustor’s local flow uniformity varied with the distances between the extraction port and each individual combustor. Longer top hats were installed with the initial intention of increasing flow mixing prior to entering the combustor. However, the results indicated that longer top hats do not improve the flow uniformity; sometimes, adverse effects can be seen. Although a specific geometry was selected for this study, the results provide sufficient generality to benefit other industrial gas turbines.
Distributed Flight Control and Propulsion Control Implementation Issues and Lessons Learned
Authors: Schley W. R.
Published: February 2008

This paper addresses the motivations for using a distributed control system architecture, technical challenges, typical functions which are off-loaded to remote terminals, sensor/effector interface issues, data bus selection, technology insertion issues, lessons learned, and objectives for future distributed control implementations. Typical design requirements, constraints, environmental conditions, and operational challenges will be described. Examples of various distributed control system implementations will be discussed, including both propulsion control and flight control examples.
Effects of Bearing and Shaft Asymmetries on the Resonant Oscillations of a Rotor-Dynamic System
Authors: Ganesan R.
Published: February 2008

Parametric steady-state vibrations of an asymmetric rotor while passing through primary resonance and the associated stability behavior are analyzed. The undamped case is considered and the equations of motion are rewritten in a from suitable for applying the method of multiple scales. Sensitivity to the bearing as well as shaft asymmetries of the oscillations due to unbalance excitation is evaluated. Expressions for amplitude and frequency modulation functions are obtained and are specialized to yield the steady-state solutions near primary resonance. Frequency-amplitude relationships that result from combined parametric and mass unbalance excitations are derived. Stability regions in the parameter space are obtained based on the time evolution of the amplitude and phase of the steady-state motions. The effects of bearing asymmetry on the amplitude and phase of the resonant oscillations are brought out. The sensitivity of vibrational and stability characteristics to various rotor-dynamic system parameters is illustrated through a numerical investigation.
Instability Threshold and Stability Boundaries of Rotor-Bearing Systems
Authors: Chen W. J.
Published: February 2008

A direct numerical method for the determination of instability threshold and stability boundaries of flexible rotor-bearing systems is presented. The proposed procedure can also be used to improve the system stability by considering the design variables as operating parameters. The finite element method is utilized in the formulation of system equations of motion. The numerical algorithm is based on nonlinear optimization techniques. Two examples are presented to illustrate the feasibility, desirability, and ability of the proposed algorithm. A simple journal bearing system is used for the parametric study. An industrial high-speed compressor is employed to demonstrate the ability of this algorithm to deal with practical applications. The stability boundaries calculated from this algorithm are in agreement with the experimental results.
A General Simulation Model for Stirling Cycles
Authors: Schulz S. , Schwendig F.
Published: February 2008

A mathematical model for the calculation of the Stirling cycle and of similar processes is presented. The model comprises a method to reproduce schematically any kind of process configuration, including free piston engines. The differential balance equations describing the process are solved by a stable integration algorithm. Heat transfer and pressure loss are calculated by using new correlations, which consider the special conditions of the periodic compression/expansion respectively of the oscillating flow. A comparison between experimental data achieved by means of a test apparatus and calculated data shows a good agreement.
A Catalytic Combustor for High-Temperature Gas Turbines
Authors: Vortmeyer N. , Valk M. , Kappler G.
Published: February 2008

Catalytic combustion has been the subject of thorough research work for over two decades, mainly in the U.S. and Japan. However, severe material problems in the ceramic or metallic monolith prevented regular operation in most cases. Still, during these two decades, turbine inlet temperatures were raised remarkably, and lean premix combustors have become standard in stationary gas turbines. In view of these facts, a simple “monolith-in-tube” concept of a catalytic combustor was adapted for the use in high-temperature gas turbines. Its essential feature is the fact that a considerable portion of the homogeneous gas phase reaction is shifted to the thermal reactor, thus lowering the catalyst temperature. This is achieved by the employment of very short catalyst segments. The viability of this concept has been demonstrated for a variety of pure hydrocarbons, alcohols as well as common liquid fuels. Extensive experimental investigations of the atmospheric combustor led to the assessment of parameters such as reference velocity, fuel-to-air ratio, and fuel properties. The maximum combustor exit temperature was 1673 K with a corresponding catalyst temperature of less than 1300 K for diesel fuel. Boundary conditions were in all cases combustion efficiency (over 99.9 percent) and pressure loss (less than 6 percent). Additionally, a model has been developed to predict the characteristic values of the catalytic combustor such as necessary catalyst length, combustor volume, and emission characteristics. The homogeneous reaction in the thermal reactor can be calculated by a one-dimensional reacting flow model.
A Spinning Finite Beam Element of General Orientation Analyzed With Rayleigh/Timoshenko/Saint-Venant Theory
Authors: Abrahamsson T. J. S. , Sa¨llstro¨m J. H.
Published: February 2008

Linear vibrations are studied for a straight uniform finite beam element of general orientation spinning at a constant angular speed about a fixed axis in the inertial space. The gyroscopic and circulatory matrices and also the geometric stiffness matrix of the beam element are presented. The effect of the centrifugal static axial load on the bending and torsional dynamic stiffnesses is thereby accounted for. The Rayleigh/Timoshenko/Saint-Venant theory is applied, and polynomial shape functions are used in the construction of the deformation fields. Nonzero off-diagonal elements in the gyroscopic and circulatory matrices indicate coupled bending/shearing/torsional/tensional free and forced modes of a generally oriented spinning beam. Two numerical examples demonstrate the use and performance of the beam element.
Nondimensional Schmidt Analysis for Optimal Design of Stirling Engines
Authors: Impero Abenavoli R. , Carlini M. , Kormanski H. , Rudzinska K. , Sciaboni A.
Published: February 2008

General directions for rough optimal calibration of Stirling machines can be given by a non-dimensional Schmidt model (nDSM). Since different relative parameters and performance indices have been analyzed by nDSM models, there is lack of uniform conclusions in the literature. This paper describes a new nDSM of six parameters and compares four performance indices as functions of relative parameters. Two optimization tasks of two and five parameters are formulated and solved using the nDSM. Maximized criterion is cycle work per unit of mean pressure and total swept volume. An optimization code based on the algorithm of conjugate gradients with projection on linear constraints is described. The optimal values of volume phase angle, nondimensional swept volume, and dead volume are presented for different constraints imposed on temperature ratio and relative dead volumes.
Thermal Shock Analysis and Testing of Simulated Ceramic Components for Gas Turbine Applications
Authors: Rajiyah H. , Inzinna L. P. , Trantina G. G. , Orenstein R. M. , Cutrone M. B.
Published: February 2008

A ceramic gas seal for a utility gas turbine was designed and analyzed using ANSYS and CARES/LIFE. SN-88 silicon nitride was selected as the candidate material. The objective was to validate the failure prediction methodology using rectangular plates, which were thermally shocked in a fluidized bed. The failure prediction methodology would then be applied to the representative component geometry. Refined ANSYS finite element modeling of both the plate and component geometries was undertaken. The CARES/LIFE reliability analysis of the component geometry for fast fracture was performed for two cases: (I) steady-state thermomechanical loads during normal gas turbine operation and (II) transient thermal shock loading during a turbine trip. Thermal shock testing of alumina disks was performed in order to gain confidence in the testing and analysis procedures. Both notched and unnotched SN88 plates were then tested. Failure modes were identified through flexure tests and data censoring was performed using SAS. Weibull modulus was assumed to be invariant with temperature and the scale parameter was assumed to vary through a scaling variable such that multiple data could be pooled.
Combined Helium and Combustion Gas Turbine Plant Exploiting Liquid Hydrogen (LH2) Physical Exergy
Authors: Bisio G. , Massardo A. , Agazzani A.
Published: February 2008

The aim of this work is the energy and exergy analysis of a combined plant made up of a conventional gas turbine (heavy-duty or aeroderivative) and a closed helium turbine cycle, which exploits liquid hydrogen (LH2) as a lower energy source. A helium turbine with the characteristics of the fluid allows us to operate between the usual temperatures of the top turbine waste gas and those of the liquid hydrogen available. In this way the combined system reaches efficiency values greater than every combined system proposed to date. The work contains a detailed analysis of the relative entropy productions of the helium cycle and considerations about the realization and technological aspects of helium turbines.
Evolution of Westinghouse Heavy-Duty Power Generation and Industrial Combustion Turbines
Authors: Scalzo A. J. , Bannister R. L. , DeCorso M. , Howard G. S.
Published: February 2008

This paper reviews the evolution of heavy-duty power generation and industrial combustion turbines in the United States from a Westinghouse Electric Corporation perspective. Westinghouse combustion turbine genealogy began in March of 1943 when the first wholly American designed and manufactured jet engine went on test in Philadelphia, and continues today in Orlando, Florida, with the 230 MW, 501G combustion turbine. In this paper, advances in thermodynamics, materials, cooling, and unit size will be described. Many basic design features such as two-bearing rotor, cold-end drive, can-annular internal combustors, CURVIC clutched turbine disks, and tangential exhaust struts have endured successfully for over 40 years. Progress in turbine technology includes the clean coal technology and advanced turbine systems initiatives of the U.S. Department of Energy.
A Probabilistic Method for the Fatigue Life Assessment of Powder Metallurgy Parts of Aircraft Engines
Authors: Krafft R. , Mosset S.
Published: February 2008

This paper will present a probabilistic approach developed in order to assess the fatigue life of aircraft engine parts (turbine disks) obtained by powder metallurgy technique. First of all, the main issues will be pointed out and the theoretical principles of the method will be described. Then the design implications and the experimental correlation will be emphasized. The scale effect is a major concern for the fatigue life assessment of a powder metallurgy part. It no longer allows the designer to evaluate the life of a massive part directly from experimental results based on small specimen fatigue tests as is done in the classical methodology. In order to describe this scale effect correctly, incubation sites (inhomogeneities like ceramic inclusions) must be characterized. The size of these inhomogeneities and their positions in the part appeared to be the most relevant parameters. Hence the methodology developed at SNECMA integrates the scale effect scatter through a binomial probability distribution as well as a temperature and stress-dependent life evaluation for each inhomogeneity size and position. The life calculation of a part implies an analysis of its whole volume and surface. An iterative process determines the number of cycles corresponding to a global reliability level requirement for the part. The complete methodology is then validated by comparing the calculated initiation distribution with experimental results on small specimens and test disks.
Fluid Mechanics of Membrane-Coated Ceramic Filters
Authors: Ahluwalia R. K. , Geyer H. K.
Published: February 2008

Analytical models are formulated for evaluating the fluid mechanics of membrane-coated, dead-end ceramic filters. The models are applicable to forward flow as in the filtration mode and reverse flow as in the back-pulse cleaning mode. General criteria are derived to size the filter passages from considerations of Darcy pressure drop, friction pressure drop, and the dynamic head. These criteria together with Reynolds numbers are shown to provide measures of nonuniformities in face velocity and pressure that develop in the filter passages for atmospheric and high-pressure applications. A methodology is presented for optimizing the venturi geometry from the standpoint of minimizing pulse gas usage and controlling the thermal load imposed on the filter assembly.
A Second-Law-Based Optimization: Part 2—Application
Authors: El-Sayed Y. M.
Published: February 2008

This paper deals with an application of the second-law-based optimization methodology described in Part 1 of this paper. The methodology is applied to a simple energy system of 10 components and 19 manipulated decision parameters. The system is treated once as a single-purpose combined cycle and once as a power-heat cogenerating system. The results of the application are summarized and evaluated. The required computer programs are described. Further investigations are suggested.
Operation of Gas Turbine Engines in Volcanic Ash Clouds
Authors: Dunn M. G. , Baran A. J. , Miatech J.
Published: February 2008

Results are reported for a technology program designed to determine the behavior of gas turbine engines when operating in particle-laden clouds. There are several ways that such clouds may be created, i.e., explosive volcanic eruption, sand storm, military conflict, etc. The response of several different engines, among them the Pratt & Whitney JT3D turbofan, the Pratt & Whitney J57 turbojet, a Pratt & Whitney engine of the JT9 vintage, and an engine of the General Electric CF6 vintage has been determined. The particular damage mode that will be dominant when an engine experiences a dust cloud depends upon the particular engine (the turbine inlet temperature at which the engine is operating when it encounters the dust cloud), the concentration of foreign material in the cloud, and the constituents of the foreign material (the respective melting temperature of the various constituents). Further, the rate at which engine damage will occur depends upon all of the factors given above, and the damage is cumulative with continued exposure. An important part of the Calspan effort has been to identify environmental warning signs and to determine which of the engine parameters available for monitoring by the flight crew can provide an early indication of impending difficulty. On the basis of current knowledge, if one knows the location of a particle-laden cloud, then that region should be avoided. However, if the cloud location is unknown, which is generally the case, then it is important to know how to recognize when an encounter has occurred and to understand how to operate safely, which is another part of the Calspan effort.
Adaptive Vibration Control of a Rigid Rotor Supported by Active Magnetic Bearings
Authors: Lang O. , Wassermann J. , Springer H.
Published: February 2008

In this paper a digital numerical simulation is carried out in which active magnetic bearings (AMB) are applied to control nonlinear and nonsynchronous vibrations of a rigid rotor excited by nonconservative cross-coupling mechanisms. Through an adaptive control algorithm of the AMB controller, unknown cross-coupling parameters of a rotor are estimated on-line by a standard least-square estimator along with a time-varying so-called forgetting factor. The parameters of the AMB controller are adapted in order to compensate for the cross-coupling effects and to stabilize the rotor system. Transient cross-coupling response characteristics are calculated by numerical simulation of a rigid rotor supported by two active magnetic bearings. With this kind of control strategy, the stability of the system can be guaranteed for much higher values of cross-coupling coefficients than with common nonadaptive feedback controllers, designed with pole placement or least square algorithms.
Investigation of Wedge Probe Wall Proximity Effects: Part 1—Experimental Study
Authors: Smout P. D. , Ivey P. C.
Published: February 2008

Conventional three-hole wedge probes fail to measure the correct static pressure when operating in close proximity to a wall or boundary through which the probe is inserted. The free-stream pressure near the outer wall of a turbomachine may be overindicated by up to 20 percent dynamic head. This paper reports a series of experiments aimed at quantifying this so-called “wall proximity effect.” It is shown from a factorial experiment that probe wedge angle, stem design, and free-stream Mach number all have a significant influence. The yaw angle sensitivity of wedge probes is also found to depend on the proximity of the probe to the wall of introduction. Flow visualization studies on large-scale probe models are described, and a qualitative model of the probe local flow structures is developed. This model is used to explain the near-wall characteristics of the actual size wedge probes. In Part 2 of this paper, the experimental data are used to validate CFD calculations of the flow field around a wedge probe. A simple analytical model of the probe/flow interaction is developed from the CFD solutions.
PI Control of HSFDs for Active Control of Rotor-Bearing Systems
Authors: Hathout J. P. , El-Shafei A.
Published: February 2008

This paper describes the proportional integral (PI) control of hybrid squeeze film dampers (HSFDS) for active control of rotor vibrations. Recently it was shown that the automatically controlled HSFD based on feedback of rotor speed can be a very efficient device for active control of rotor vibration when passing through critical speeds. Although considerable effort has been put into the study of steady-state vibration control, there are few methods in the literature applicable to transient vibration control of rotor-bearing systems. Rotating machinery may experience dangerously high dynamic loading due to the sudden mass unbalance that could be associated with blade loss. Transient run-up and coast down through critical speeds when starting up or shutting down rotating machinery induces excessive bearing loads at criticals. In this paper, PI control is proposed as a regulator for the HSFD system to attenuate transient vibration for both sudden unbalance and transient runup through critical speeds. A complete mathematical model of this closed-loop system is simulated on a digital computer. Results show an overall enhanced behavior for the closed-loop rotor system. Gain scheduling of both the integral gain and the reference input is incorporated into the closed-loop system with the PI regulator and results in an enhanced behavior of the controlled system.
Numerical Investigation of the Grinding Process in a Beater Wheel Mill With Classifier
Authors: Anagnostopoulos J. , Bergeles G.
Published: February 2008

A numerical investigation is presented for a two-dimensional simulation of the gas flow field and of the dynamic behavior of lignite particles inside Beater Wheel mills with classifier, installed in large coal-fired plants. A large number of representative particles are tracked using Lagrangian equations of motion, in combination with a stochastic model for particle turbulent dispersion. All the important mechanisms associated with the particle motion through the mill (particle-surface collisions and rebounding phenomena, fuel moisture evaporation and erosion wear of internal surfaces) are modeled. A special model is constructed to simulate the fragmentation of impacting particles and to calculate the size distribution of the final mill product. The models are regulated on the basis of available data from grinding mills of the Greek lignite power stations. The numerical code is capable of predicting the locations of significant erosion and to estimate the amount of particle mass that circulates through the mill via the classifying chamber. Mean impact velocity and impingement angle distributions along all the internal surfaces are also provided. The results indicate remarkable differences in the extent of the erosion caused at different locations of the mill. Also, the significant role of the leading blades arrangement inside the classifier on its classification performance and efficiency is elucidated.
Efficient District Heat Production by Heat Extraction From Combined Cycle Plants
Authors: Haselbacher H. , Frutschi H. U.
Published: February 2008

Among cogeneration facilities, block heating stations and large combined cycle plants are two extreme examples of district heating technologies. In this paper, these two alternatives will be applied to one and the same representative district heating task. The thermodynamic differences will be made clear and the advantages of heating by extracting steam from a combined cycle plant will become evident. An important conclusion from an engineering point of view is that extracting heat from a combined cycle plant should be considered even if this plant is located at greater distances from the heat consumers.
Thermocyclic Behavior of Variously Stabilized EB-PVD Thermal Barrier Coatings
Authors: Schulz U. , Fritscher K. , Peters M.
Published: February 2008

The demand for increasing gas inlet temperatures in modern gas turbines up to 1500°C and above is the main reason for the need for more reliable thermal barrier coatings. New ceramics should provide higher phase stability and better resistance against chemical attack by pollutants in the combustion gas. Electron-beam physical vapor deposition (EB-PVD) processed, ZrO2-based TBCs were generated on bond-coated superalloy directionally solidified (DS) samples. Common yttria-stabilized zirconias of two different compositions, as well as novel stabilizers like CeO2 and La2O3, were investigated. A columnar structure was established during high-rate deposition in all cases. Diameter, degree of ordering of the columns, and phase composition depended on stabilizer oxide and content. The role of differences of vapor pressures is addressed with regard to chemical homogeneity of the coatings. The performance of the TBCs having various stabilizers was investigated in a cyclic oxidation furnace test and in a burner rig at Mach 0.3. The results were correlated to the type and content of stabilizer with special emphasis on phase analyses. Evaporation of new ceramic compositions necessitates special precautions because the vapor pressures of the components may differ too much. A new dual-source evaporation coater allows the production of these innovative TBCs with close control of chemistry. The potential of the equipment will be discussed.