bluuebunny/crossref_metadata_2025 huggingface dataset:
PIV Study of Adverse and Favorable Pressure Gradient Turbulent Flows Over Transverse Ribs
Authors: Agelinchaab M. , Tachie M. F.
Published: September 2008

This paper reports an experimental study of the combined effects of rib roughness and pressure gradient on turbulent flows produced in asymmetric converging and diverging channels. Transverse square ribs with pitch-to-height ratio of 4 were attached to the bottom wall of the channel to produce the rib roughness. A particle image velocimetry technique was used to conduct measurements at several streamwise-transverse planes located upstream, within, and downstream of the converging and diverging sections of the channel. From these measurements, the mean velocities and turbulent statistics at the top plane of the ribs and across the channel were obtained. The data revealed non-negligible wall-normal motion and interaction between the cavities and overlying boundary layers. The different drag characteristics of the rough bottom wall and the smooth top wall produced asymmetric distributions of mean velocity and turbulent statistics across the channel. The asymmetry of these profiles is most extreme in the presence of adverse pressure gradient. Because of the manner in which pressure gradient modifies the mean flow and turbulence production, it was found that the streamwise turbulence intensity and Reynolds shear stress in the vicinity of the ribs are lower in the adverse pressure gradient than in the favorable pressure gradient channel. The results show also that the combined effects of rib roughness and adverse pressure gradient on the turbulent intensity statistics are significantly higher than when roughness and adverse pressure gradient are applied in isolation.
Recognition and Prevention of Distillate Fuel Emulsions
Authors: Newbound T. D. , Al-Nasser A. N. , Sang M. P. , Carrigan W. J.
Published: September 2008

This paper describes a case study involving chronic plugging of 5μm particulate filters in a gas turbine diesel fuel system in a Red Sea refinery. Rapid plugging of the filters was caused by water-in-diesel emulsions generated in diesel fuel supply tanks. Sludge with a wax-like appearance recovered from the 5 μm filters was, in fact, found to be composed of up to 50 percent water with no significant wax content. X-ray studies of the filter catch solids revealed a variety of iron oxide phases, sodium chloride, and high concentrations of sodium sulfate. Microbial cultures inoculated from storage tank ‘rag’ layers yielded moderate to high counts of general aerobic bacteria (GAB), moderate fungal cultures (yeast and molds) and low sulfate reducing bacteria (SRB). Elemental analysis of water in supply tanks where microbial activity was highest revealed ion concentrations similar to those found in Red Sea water. Sulfur isotope ratios in sulfate from filter catches suggest that much of the sulfate was derived from microbial metathesis of sulfur-bearing hydrocarbons. Frequent contamination of on-shore liquid hydrocarbon fuel tanks with sea water can cause corrosion and create a favorable environment for bacterial growth. Surfactant byproducts of microbial activity are capable of stabilizing emulsions, suspending water soluble salts such as sodium sulfate, and metals such as lead and copper. Copper is well known to promote gum formation, while all of these contaminants are potentially corrosive to gas turbine hot gas path components.
Experimental Results From Controlled Blade Tip/Shroud Rubs at Engine Speed
Authors: Padova Corso , Barton Jeffery , Dunn Michael G. , Manwaring Steve
Published: September 2008

Experimental results obtained for an Inconel compressor blade rubbing a steel casing at engine speed are described. Load cell, strain gauge and accelerometer measurements are discussed and then applied to analyze the metal-on-metal interaction resulting from sudden incursions of varying severity, defined by incursion depths ranging from 13 μm to 762 μm (0.0005-in to 0.030-in). The results presented describe the transient dynamics of rotor and casing vibro-impact response at engine operational speed similar to those experienced in flight. Force components at the blade tip in axial and circumferential directions for a rub of moderate incursion depth (140 μm) are compared to those for a severe rub (406 μm). Similar general trends of variation during the metal-to-metal contact are observed. However, in the nearly three-fold higher incursion the maximum incurred circumferential load increases significantly, while the maximum incurred axial load increases much less, demonstrating the non-linear nature of the rub phenomena. Concurrently, the stress magnification on the rubbing blade at root mid-chord, at tip leading edge, and at tip trailing edge is discussed. The results point to the possibility of failure occurring first at the airfoil trailing edge. Such a failure was in fact observed in the most severe rub obtained to date in the laboratory, consistent with field observations. Computational models to analyze the non-linear dynamic response of a rotating beam with periodic pulse loading at the free-end are currently under development and are noted.
Additional Engine Testing of an Advanced Alloy for Microturbine Primary Surface Recuperators
Authors: Matthews Wendy J.
Published: September 2008

HAYNES ® alloy HR-120 ® is being evaluated as a replacement for type 347 stainless steel for use in Microturbine Primary Surface Recuperators. The material has been characterized after being subjected to both steady-state and cyclic engine exposure in a Capstone C60 MicroTurbine™ operating at 100°F above the normal operating temperature. Oxide scale growth and elemental depletion has been analyzed and documented after 1,800 and 2,500 hours of exposure. A preliminary estimate of the remaining usable oxidation life has been made using a simplified parabolic model. Engine test results indicate that HR-120 has improved oxidation resistance and elemental stability.
Asymmetric Solution for Compressor Station Spare Capacity
Authors: Kurz Rainer , Lubomirsky Matt
Published: September 2008

Arranging compressor units in series rather than in parallel can offer a number of advantages in many applications. However, especially if the compression ratio is rather high, it is desirable to use different impellers for the low-pressure and the high-pressure compressor. Otherwise, one or both operate off their best efficiency points. This leaves however the problem of the staging of a spare unit. In the paper, a solution to this dilemma is described. To understand the underlying constraints, the relationships between the system resistance, the compressor characteristic, and the power turbine characteristic are analytically derived.
Pulsations in Centrifugal Compressor Installations
Authors: Kurz Rainer , McKee Robert , Brun Klaus
Published: September 2008

Compressor stations where both centrifugal and reciprocating compressors operate can exhibit operational problems due to low frequency pulsations. Avoiding these problems requires an understanding of the mechanisms that generate the pulsations, the transmission and attenuation of the pulsation, as well as their effect on the operation of the centrifugal compressor and the accuracy and reliability of flow measurements. The pulsation frequencies in question are typically lower than vortex shedding frequencies and blade passing frequencies. This paper will provide insight into the mechanisms and effects of pulsations and will describe approaches to avoid them.
Computation of Eigenvalues and Eigenvectors of a Mistuned Bladed Disk
Authors: Sinha Alok
Published: September 2008

This paper deals with fundamental aspects of variations in eigenvalues and eigenvectors of a bladed disk due to mistuning. First, the existence of derivatives of repeated eigenvalues and corresponding eigenvectors is thoroughly examined. Next, an algorithm is developed to compute these derivatives. It is shown how a Taylor series expansion can be used to efficiently compute eigenvalues and eigenvectors of a mistuned system. This methodology is developed for perturbations in both repeated and unrepeated eigenvalues of the tuned system. Lastly, numerical examples are presented.
Dynamic Behavior of Spherical Friction Dampers and Its Implication to Damper Contact Stiffness
Authors: Koh K.-H. , Griffin J. H.
Published: September 2008

A model that predicts the quasi-static behavior of a friction damper that has spherical contacts was developed using Mindlin’s theory. The model was integrated into a dynamic analysis that predicts the vibratory response of frictionally damped blades. The analytical approach was corroborated through a set of benchmark experiments using a blades/damper test fixture. There was good agreement between the theoretical predictions of amplitude and the values that were measured experimentally over a wide range of test conditions. It is concluded that it is possible to predict the vibratory response of frictionally damped vibrating systems using continuum mechanics, provided that the contact geometry is clearly defined and the local nonlinear contact is correctly taken into account.
Advanced Degradation Rates for High Power LM2500 Applications
Authors: Driscoll Matthew J. , Habib Thomas
Published: September 2008

Since the early 1970’s, the United States Navy has utilized the General Electric LM2500 gas turbine engine for propulsion aboard its surface combatants including its newest DDG 51 Class Destroyer. These ships have generally operated at a part power operational profile under a COGAG arrangement which has offered system redundancy while exceeding life projections for the gas turbine engines. For its newest ships still in the design phase (LHD 8/LCS/LSC(X)) the Navy intends to continue to utilize gas turbine engines but in different applications including electric drive, high power boost applications in tandem with both diesel engines and electric motor arrangements. Although this paper focuses on the LM2500, its conclusions are meant to apply to a broader scope of future propulsion applications. Specific conclusions are provided describing potential operating profile considerations.
Investigation of Compressor Rear Frame Cracking of United States Navy LM2500 Gas Turbine Engines
Authors: Driscoll Matthew J. , Descar Peter D.
Published: September 2008

In December 2000, a 7” long axial crack was visually identified on the compressor rear frame of an LM2500 propulsion gas turbine engine aboard the USS MITSCHER (DDG 57). This was originally thought to be a unique failure mode possibly caused by misaligned brackets external to the engine imparting undo thermal stresses onto the engine casing and flange. Since that time, 17 additional engines in the Navy fleet have been identified with either the large axial crack on the compressor casing or a small craze crack on the CRF flange, which appears to be the origination point prior to crack propagation. This paper discusses the extent of the cracking problem in the US Navy, the engineering investigation undertaken by the OEM and Navy to determine the root cause of the cracks and development of a field repair strategy to mitigate the impact of these cracks. The focus of the paper includes metallurgical analysis of failed compressor rear frame hardware, vibratory evaluation of the engine’s external piping system as a contributory failure mode and results of strain gage testing of the mid flange region.
Heat Transfer and Pressure Losses in a Narrow Dimpled Channel Structured With Spherical Protrusions
Authors: Borisov I. , Khalatov A. , Kobzar S. , Glezer B.
Published: September 2008

Achieving a high heat transfer effectiveness at low pressure losses in narrow channels continue to present a significant challenge for designers of gas turbine components and heat exchangers. The task of low pressure losses often requires that some of these components, particularly heat exchangers, have to operate at a flow rate that corresponds to relatively low Reynolds numbers ranging from 200 to 800. The operation at higher Reynolds numbers permits to improve the recuperator performance, however it leads to unacceptable pressure losses. Introduction of hemispherical dimples for heat transfer augmentation has become recently one of the promising techniques for achieving higher heat transfer performance in narrow channels at an acceptable pressure loss level. A structural support between the primary heat transfer surfaces is usually required for a double walled back-side cooled turbine components and multichannel heat exchangers (recuperators), operating with pressure differential between cold and hot channels. For this purpose in the current study spherical protrusions (reversed dimples) were employed on a panel opposing a dimpled panel. This structural arrangement was expected to result in additional blockage of the channel cross-section and certain increases in a pressure loss. The experimental study has been performed to assess the effect of spherical dimples and protrusions on heat transfer and pressure losses in a formed narrow channel. The airflows in the experiments corresponded to the Reynolds number ranging from 800 to 6,500. A dimple diameter and depth were 10.0 mm and 2.0 mm, correspondingly; the protrusions established the 2.0 mm height of the channels. Both the in-line and staggered dimple arrangements were studied with the x-pitch ranging from 9.0 to 18.0 mm and z-pitch changing from 13.0 to 18.0 mm. The data presented in this paper include results for measurements of average heat transfer coefficients and pressure losses. Reynolds analogy factor and thermal performance of the primary surface were obtained and discussed in the paper. Considering potential application of studied surfaces for gas turbine heat exchangers, the paper provided a comparison between a “pure” dimpled channel, dimpled channel with protrusions against a more traditional channel with sinusoidal corrugated primary surface. As expected, the protrusions in the channel enhanced the heat transfer, but led to increased pressure losses due to the partial destruction of the dimple-generated vortex structures. Nevertheless, it was demonstrated that the Reynolds analogy factor of 0.4 could be achieved in a dimpled channel with protrusions, resulting in overall pressure losses of under 5% for the application in a recuperator core.
Development of a One-Dimensional Modular Dynamic Model for the Simulation of Surge in Compression Systems
Authors: Morini M. , Pinelli M. , Venturini M.
Published: September 2008

The paper deals with the development of a non-linear one-dimensional modular dynamic model for the simulation of transient behavior of compression systems. The model is based on balance equations of mass, momentum and energy, which are derived through a general approach and are written by using the finite difference method. The model also takes rotating mass dynamics into account through a lumped parameter approach. Moreover, it reproduces the behavior of the system in the presence of the surge phenomenon through steady-state performance maps, which represent the compressor operation in the inverse flow region by means of a third degree polynomial curve. The model is implemented through the Matlab Simulink tool, where the system of ordinary differential equations is solved by using a fourth and fifth order Runge-Kutta method. A sensitivity analysis is carried out to evaluate the influence on compressor outlet pressure oscillations of the model parameters, of the supplied torque, of ambient conditions and of the shape of the compressor characteristic curves. The results show that the model proves effective in capturing the physical essence of surge phenomenon without being computationally too heavy.
Direct Parametric Analysis of Resonance Regimes for Nonlinear Vibrations of Bladed Discs
Authors: Petrov E. P.
Published: September 2008

A method has been developed to calculate directly resonance frequencies and resonance amplitudes as functions of design parameters or as a function of excitation levels. The method provides, for a first time, this capability for analysis of strongly nonlinear periodic vibrations of bladed discs and other structures with nonlinear interaction at contact interfaces. A criterion for determination of major, sub- and superharmonic resonance peaks has been formulated. Analytical expressions have been derived for accurate evaluation of the criterion and for tracing resonance regimes as function of such contact interface parameters as gap and interference values, friction and contact stiffness coefficients, normal stresses. High accuracy and efficiency of the new method have been demonstrated on numerical examples including large-scale nonlinear bladed disc model and major types of contact interfaces including friction contact interfaces, gaps and cubic nonlinearities.
3D Viscous Flutter in Turbomachinery Cascade by Godunov-Kolgan Method
Authors: Rza¸dkowski Romuald , Gnesin Vitally , Kolodyazhnaya Luba
Published: September 2008

In this study, numerical simulations of 3D viscous flutter were performed and compared with the available experimental results. The calculations were carried out for bending oscillations of the cascade known as the Eleventh Standard Configuration. The developed numerical algorithm solves the 3D Reynolds-averaged Navier-Stokes equation together with the Baldwin-Lomax turbulence model, using the explicit monotonous second-order accurate Godunov-Kolgan finite-volume scheme and moving hybrid H-O structured grid. Comparison of the calculated and the experimental results for the Eleventh Standard Configurations has shown sufficient quantitative and qualitative agreement for local performances (unsteady pressure amplitude and phase distribution) at off-design conditions. Benchmark solutions are provided for various values of the inter-blade phase angle.
Forced Vibration of Several Bladed Discs on the Shaft
Authors: Rza¸dkowski Romuald , Drewczynski Marcin
Published: September 2008

The effect of multistage coupling on the dynamics of a rotor consisting of eight bladed discs on a solid shaft is considered. Free vibrations are examined using finite element representations of rotating single blades, bladed discs, and the complete rotor. In this study, the global rotating mode shapes of flexible tuned bladed discs-shaft assemblies are calculated. Rotational effects, such as centrifugal stiffening are accounted for. The calculated natural frequencies obtained from the blade, the shaft, the bladed disc, and the complete shaft with discs are carefully examined to discover resonance conditions and the coupling effects. It was found that the flexible modes of the tuned bladed discs affected by shaft motion are those with zero, one and two nodal diameters. In these modes the shaft deflection is clearly visible. Different EO excitation is applied for particular stages in forced vibration analysis.
Numerical Study of the Heat Transfer in Micro Gasturbines
Authors: Verstraete T. , Alsalihi Z. , Van den Braembussche R. A.
Published: September 2008

This paper presents a numerical investigation of the heat transfer inside a micro gasturbine and its impact on the performance. The high temperature difference between turbine and compressor in combination with the small dimensions results in a high heat transfer causing a drop in efficiency of both components. Present study aims to quantify this heat transfer and to reveal the different mechanisms that contribute to it. A conjugate heat transfer solver has been developed for this purpose. It combines a 3D conduction calculation inside the rotor and the stator with a 3D flow calculation in the radial compressor, turbine and gap between stator and rotor. The results for micro gasturbines of different size and shape and different material characteristics are presented and the impact on performance is evaluated.
Comparison of Recuperator Alloy Degradation in Laboratory and Engine Testing
Authors: Pint Bruce A. , More Karren L. , Trejo Rosa , Lara-Curzio Edgar
Published: September 2008

In order to increase the efficiency of advanced microturbines, durable alloy foils are needed for their recuperators to operate at 650°–700°C. Prior work has demonstrated that water vapor in the exhaust gas causes more rapid consumption of Cr from austenitic alloys leading to a reduction in lifetime for the thin-walled components in this application. New commercial alloy foils are being tested in both laboratory tests in humid air and in the exhaust gas of a modified 60kW microturbine. Initial results are presented for a commercial batch of 80μm alloy 120 foil. The Cr consumption rates in laboratory testing were similar to those observed in previous testing. The initial results from the microturbine indicate a faster Cr consumption rate compared to the laboratory test but longer term results are needed to quantify the difference. These results will help to verify a Cr consumption model for predicting lifetimes in this environment based on classical gas transport theory.
Creep Strength and Microstructure of AL20-25+Nb Alloy Sheets and Foils for Advanced Microturbine Recuperators
Authors: Maziasz Philip J. , Shingledecker John P. , Evans Neal D. , Yamamoto Yukinori , More Karren L. , Trejo Rosa , Lara-Curzio Edgar , Stinner Charles P.
Published: September 2008

The Oak Ridge National Laboratory (ORNL) and ATI Allegheny-Ludlum began a collaborative program in 2004 to produce a wide range of commercial sheets and foils of the new AL20-25+Nb stainless alloy, specifically designed for advanced microturbine recuperator applications. There is a need for cost-effective sheets/foils with more performance and reliability at 650–750°C than 347 stainless steel, particularly for larger 200–250 kW microturbines. Phase I of this collaborative program produced the sheets and foils needed for manufacturing brazed plated-fin (BPF) aircells, while Phase II provided foils for primary surface (PS) aircells, and modified processing to change the microstructure of sheets and foils for improved creep-resistance. Phase I sheets and foils of AL20-25+Nb have much more creep-resistance than 347 steel at 700–750°C, and foils are slightly stronger than HR120 and HR230. Preliminary results for Phase II show nearly double the creep-rupture life of sheets at 750°C/100 MPa, with the first foils tested approaching the creep resistance of alloy 625 foils. AL20-25+Nb alloy foils are also now being tested in the ORNL Recuperator Test Facility.
High Pressure Turbocharger for Solid Oxide Fuel Cells
Authors: Berenyi Steven G.
Published: September 2008

Rolls-Royce has designed, built, and continues to test a high pressure (HP) turbocharging system specifically designed for a hybrid solid oxide fuel cell system being developed by Rolls-Royce Fuel Cell Systems, Ltd. This turbocharger is comprised of a two-spool machine with a shaft speed motor/generator on the low speed spool. Each spool contains a centrifugal compressor driven by a radial inflow turbine. The two spools run independently, but are physically close coupled for a smaller, more efficient system. The spools are mounted into a basic structure to provide structural rigidity, as well as sound and heat isolation. In its current test rig form, the system runs on oil lubricated bearings; is equipped with a liquid fueled slave combustor; and is controlled with a digital control system. Although never intended to be a “stand alone” microturbine — it is simply a high pressure turbocharger; if one wanted to — with a proper fuel and control system installed, it is capable of operation in such a stand alone mode. However, without heat recovery it would be a highly inefficient microturbine and therefore, was not considered in this application. Multiple units have been built and continue developmental testing. Initial matching to a fuel cell stack is scheduled for operation later in 2006.
Thermodynamic Analysis of Different Configurations for Microturbine Cycles in Simple and Cogeneration Systems
Authors: Sadeghi Ehsan , Khaledi Hiwa , Ghofrani Mohammad Bagher
Published: September 2008

In recent years, the development of distributed power generation has resulted in significant reduction in network losses and transmission costs while it has increased reliability. Microturbine is one of these power generators that has the ability of relatively high power generation in spite of its small volume [1], [2]. In this paper, different layouts for advanced microturbine cycles are analyzed. In order to modify cycle characteristics such as power and efficiency, and reduce exergy destruction, different configurations including intercooler, aftercooler, and heat recovery boiler are separately and synthetically analyzed and compared. The effects of various parameters, such as compressor pressure ratio, vapor pressure, and bypass ratio on the cycle performance are studied. For configurations including inter/aftercooling, the possibility of use of heat recovery boiler is surveyed, depending on the temperature of the coolers outlet water and the recuperator outlet gas. Each part of the cycle is analyzed based on first and second laws of thermodynamics. Results show that microturbine with intercooler and recuperator (MTC-IC) is the best option, with regard to efficiency and power criteria, but its steam production is less than simple cycle with recuperator (MTC). MTC-IC has higher total exergetic efficiency in higher pressure ratios, because of the priority of power versus heat. This configuration is also more suitable than MTC with heat recovery boiler for variable thermal loads especially with bypass ratio between 0 and 0.5.
Thermal Design of Heat Exchanger With Fins Inside and Outside Tubes
Authors: Xie G. N. , Chen Q. Y. , Zeng M. , Wang Q. W.
Published: September 2008

Compact heat exchangers such as tube-fin types and plate-fin types are widely used for gas-liquid or gas-gas applications. Some examples are air-coolers, fan coils, regenerators and recuperators in micro-turbines. In this study, thermal design of fin-and-tube (tube-fin) heat exchanger performance with fins being employed outside and inside tubes was presented, with which designed plate-fin heat exchanger was compared. These designs were performed under identical mass flow rate, inlet temperature and operating pressure on each side for recuperator in 100kW microturbine as well as specified allowable fractions of total pressure drop by means of Log-Mean Temperature Difference (LMTD) method. Heat transfer areas, volumes and weights of designed heat exchangers were evaluated. It is shown that, under identical heat duty, fin-and-tube heat exchanger requires 1.8 times larger heat transfer area outside tubes and volume, 0.6 times smaller heat transfer area inside tubes than plate-fin heat exchanger. Under identical total pressure drop, fin-and-tube heat exchanger requires about 5 times larger volume and heat transfer area in gas-side, 1.6 times larger heat transfer area in air-side than plate-fin heat exchanger. Total weight of fin-and-tube heat exchanger is about 2.7 times higher than plate-fin heat exchanger, however, the heat transfer rate of fin-and-tube heat exchanger is about 1.4 times larger than that of plate-fin heat exchanger. It is indicated that, both-sides finned tube heat exchanger may be used in engineering application where the total pressure drop is severe to a small fraction and the operating pressure is high, and may be adopted for recuperator in microturbine.
More Efficient Applications for Naval Gas Turbines: Addressing the Mismatch Between Available Technology and the Requirements of Modern Naval Gas Turbine Inlets
Authors: Oswald Alan D. , Hiner Stephen D.
Published: September 2008

The US Navy has operated gas turbines (GT’s) on board different types of vessel for several decades. To safe guard these engines against the harsh marine atmosphere several types of air inlet filtration system have been employed, with varying degrees of success. The purpose of this paper is to explore the various filtration technologies which are currently used in all GT inlet filtration applications; point out the benefits of each; and debate how these may be practically applied to the “Modern” Naval GT application. The changing vessel operational requirements; environmental requirements; advances in GT design; and how these impact the design of the GT inlet filtration system will be discussed. The current trends in Naval GT inlet filtration system specifications will also be detailed. The significant divergence of these from the capabilities of current marine GT filtration technology used will be highlighted. Recommendations will be proposed regarding how this situation may be addressed with the use of filtration technologies currently used in other GT applications.
Coriolis Forces in Forced Response Analysis of Mistuned Bladed Discs
Authors: Nikolic M. , Petrov E. P. , Ewins D. J.
Published: September 2008

The problem of estimating the mutual interaction of the effects of Coriolis forces and of blade mistuning on the vibration characteristics of bladed discs is addressed in this paper. The influence of different degrees of mistuning on forced response and amplification factors are studied in the presence of Coriolis forces and then compared to their non-Coriolis counterparts using a computationally inexpensive, yet representative, model of a bladed disc. The primary objective of the study reported in this paper is to establish whether current mistuned bladed disc analyses should incorporate Coriolis effects in order to represent accurately all the significant factors that affect the forced response levels.
Genetic Algorithm Optimization for Primary Surfaces Recuperator of Microturbine
Authors: Liang H. X. , Xie G. N. , Zeng M. , Wang Q. W. , Luo L. Q. , Feng Z. P.
Published: September 2008

Recent years, Genetic Algorithm (GA) technique has been gotten much more attention in solving real-world problems, more successful genetic algorithms applications to engineering optimization have shown the technique has strong ability of global searching and optimizing based on various objectives for their optimal parameters. The technique may be applied to more complicated heat exchangers and is particularly useful for new types. It is important to optimize heat exchanger, for minimum volume/weight to save fabrication cost or for improved effectiveness to save energy consumption, under requirement of allowable pressure drop; simultaneously it is mandatory to optimize geometry parameters of heat plate from the technical and economic standpoints. In this paper, GA is used to optimize the Cross Wavy Primary Surface (CWPS) and Cross Corrugated Primary Surface (CCPS) geometry characteristic of recuperator in 100kW microturbine, in order to get more compactness and minimum volume and weight. Two kinds of fitness assignment methods were considered. Furthermore, the GA parameters were set optimally to yield smoother and faster fitness convergence. The comparison shows the superiority of GA and confirms its potential to solve the objective problem. When the rectangular recuperator core size and corrugated geometries are evaluated, in the CWPS the weight of recuperator decreases 12% or more, the coefficient of compactness increases by up to 19%, with an increase of total pressure drop by a percentage of 0.84 compared to the original design data, the total pressure drop as a percentage of the operating pressure is controlled to be less than 3%. In the CCPS area compactness is increased to 70% the initial design result by decreasing pitch and relatively high height of the passage, the weight decreases by 17% to 36%, depending on different inclination angle (θ). Comparatively the CCPS shows superior performance for use in compact recuperators of the future. The GA technique chooses from a variety of geometry characters, optimizes them and picks out the one which provides the closest fit to the recupertor for microturbine.
Rotordynamic Stability Predictions for Centrifugal Compressors Using a Bulk-Flow Model to Predict Impeller Shroud Force and Moment Coefficients
Authors: Gupta Manoj K. , Childs Dara W.
Published: September 2008

An analysis is developed for a compressible bulk-flow model of the leakage path between a centrifugal-compressor impeller’s shroud and its housing along the impeller’s front and back sides. This development is an extension of analyses performed first by Childs [15] for pump impellers. The bulk-flow model is used to predict reaction force and moment coefficients for the impeller shroud. A labyrinth seal code developed by Childs and Scharrer [21] is used to calculate the rotordynamic coefficients developed by the labyrinth seals in the compressor stage and also provides a boundary condition for the shroud calculations. Comparisons between the measured shroud moment coefficients by Yoshida et al. [18] and model predictions show reasonable agreements for the clearance flow and reaction moments. For the conditions considered, low Mach number flow existed in the shroud clearance areas and compressible-flow and incompressible-flow models produced similar predictions. Childs’ model predictions for the direct damping and cross-coupled stiffness coefficients of a pump impeller produced reasonable agreement; hence the present model was validated to the extent possible. A rotor model consisting of an overhung impeller stage supported by a nominally cantilevered rotor was analyzed for stability using the present bulk-flow model and an API standard Wachel-formula model [10]. The bulk-flow model predicted significantly higher onset speeds of instability. Given that some compressors have been predicted to be comfortably stable using API standard Wachel-formula but have been unstable on the test stand, these results suggest that unidentified destabilizing forces and or moments are present in compressors. Seal rub conditions that arise from surge events and increase the seal clearances are simulated, showing that enlarged clearances increase the preswirl at the seals, thus increasing these seal’s destabilizing forces and reducing stability margins. These results are consistent with field experience. Predictions concerning the back shroud indicate that shunt-hole injection mainly acts to enhance stability by changing the flow field of the division wall or balance piston seals, not by influencing the back-shroud’s forces or moments. Effective swirl brakes at these seals also serves this purpose.
Dynamic Response of a Geared Rotor-Bearing System Under Residual Shaft Bow Effect
Authors: Shiau T. N. , Lee E. K. , Chen Y. C. , Young T. H.
Published: September 2008

The paper presents the dynamic behaviors of a geared rotor-bearing system under the effects of the residual shaft bow, the gear eccentricity and excitation of gear’s transmission error. The coupling effect of lateral and torsional motions is considered in the dynamic analysis of the geared rotor-bearing system. The finite element method is used to model the system and Lagrangian approach is applied to derive the system equations of motion. The dynamic characteristics including system natural frequencies, mode shapes and steady-state response are investigated. The results show that the magnitude of the residual shaft bow, the phase angle between gear eccentricity and residual shaft bow will significantly affect system natural frequencies and steady-state response. When the spin speed closes to the second critical speed, the system steady state response will be dramatically increased by the residual shaft bow for the in-phase case. Moreover the zero response can be obtained when the system is set on special conditions.
The Estimation of the Contact Stiffness for Directly and Indirectly Coupled Turbine Blading
Authors: Siewert Christian , Panning Lars , Schmidt-Fellner Annika , Kayser Andreas
Published: September 2008

Forced vibrations can lead to a substantial damage of the blading. To reduce the vibrational amplitudes to reasonable magnitudes, several coupling concepts, like shroud coupling or underplatform dampers, have been developed in the past. Mechanical models for the analysis of the forced response of coupled turbine blading are available. These models include an appropriate contact model to account for the contact effects like frictional damping, for example. These contact models demand for a stiffness type parameter, this is the so-called contact stiffness. Unfortunately, there is no straight-forward way for the determination of this parameter. In this paper, simple mechanical models are used for the estimation of the contact stiffness. The estimated contact stiffnesses are then used in forced response computations. The results of these computations are compared to measurements in order to find the most appropriate method for the contact stiffness estimation.
Erosion Lifetime Prediction for a Radial Turbine Operation in a Low Dust Stream
Authors: Zimmermann Peter , Hirsch Christoph , Sattelmayer Thomas
Published: September 2008

This study is part of the work performed for the pilot plant of an innovative indirect fired gas turbine cycle for biomass incineration using the Pebble-Heater technology and a microturbine. A Pebble-Heater is a regenerative heat exchanger consisting of an annular bed with radial flow, which implements an unsteady counterflow heat exchanger. It captures the flue gas enthalpy during the atmospheric heating phase and heats compressed air for the turbine during the blowing phase. During the heating phase ash particles from the incinerator deposit on the bulk material and are segregated by periodic exchange and cleaning of the bed. Like this a high degree of de-dusting and cooling of the flue gas is achieved upstream of the emission control filters. In the blowing phase, however, a small amount of ash (< 3mg/mN3) is re-suspended and condensables re-sublimate into the hot air stream, which feeds the turbine. In this paper we develop a simple procedure to estimate how the size distribution and concentration of the dust load decrease the lifetime of the radial turbine due to erosion. It is based on the consideration of single particles following the gas flow. To obtain a lifetime estimate the focus was set on the erosion of the radial turbine blade tips, which are identified as the most critical parts with respect to particle impacts. On the basis of the particle relative velocity and trajectory determined with the flow model the turbine lifetime was calculated with an erosion rate model. The paper discusses the influence of particle size and distribution on turbine lifetime. For the current turbine it was found that equivalent particle diameters above 3–4μm and dust loads greater than 1 mg/mN3 reduce the nominal turbine lifetime drastically.
Numerical and Experimental Analysis of the Thermo-Mechanical Load on Turbine Wheels of Turbochargers
Authors: Heuer Tom , Engels Bertold , Klein Achim , Heger Horst
Published: September 2008

CFD, FEA, and experimental testing have been combined in order to investigate the lifetime limiting design deficiencies of a turbine wheel in a turbo charger. Thermocouples have been applied to the same radial turbine wheel to provide boundary conditions and validation data for the simulations. The tests have been performed on a turbocharger gas-stand. Based on two steady state CHT-calculations for two distinctly different operating points the heating process of the wheel has been simulated in a transient temperature calculation. Since the resulting temperature gradients induce thermal stresses, the temperature distribution serves as a boundary condition for the subsequent structural analysis. To obtain realistic stress distributions, centrifugal forces also need to be accounted for. In this way, the influence of the thermal stress on the overall stress can be evaluated.
Automatic Integration in the Design of a Microturbine Compact Recuperator
Authors: Manzan Marco , Micheli Diego , Pieri Stefano
Published: September 2008

The first phase of the development of an automatic methodology for the design process of small gas turbine recuperators is presented. The different software tools are selected in order to be managed, in a successive step of the research, by means of a design-optimization platform, according to the concept of Multi Disciplinary Optimization (MDO). The methodology has been developed integrating a geometrical parametric model of the heat transfer surfaces, built inside an industrial CAD, a three dimensional meshing tool and a CFD solver. Final objectives of the research will be an optimization process designed to maximize the heat exchange rate and to minimize costs and fluid dynamics losses. The paper deals with the parameterization technique and the numerical model validation.
Upgrading of Aged Turbomachinery Through Modernization, Uprate and Selective Replacement in Oil and Gas Processing Plants
Authors: Quercioli Valter
Published: September 2008

Revamping a plant in the oil&gas industry is needed whenever the company’s management seeks improvements on plant availability, production output, energy efficiency or operational life, to quote the most common needs. The achievements of those objectives are reached through business programs usually known as “modernization”, “rejuvenation”, “debottlenecking”. Revamping actions over the compression trains that are within the plants are key for the success of those programs, achieving the business and operational objectives sought by the management. This paper is aimed to show how a revamping program works for turbocompression trains; three real-life examples are shown too. Focus is mainly on debottlenecking and upgrade projects, for which it is more necessary to act extensively on the compression trains.
Mistuning Identification and Model Updating of an Industrial Blisk
Authors: Laxalde Denis , Thouverez Fabrice , Sinou Jean-Jacques , Baumhauer Ste´phane , Lombard Jean-Pierre
Published: September 2008

The results of a complete study of mistuning identification on an industrial blisk are presented. The identification method used here is based on a model-updating technique of a reduced-order model where measured modal data are taken as input. This reduced-order model is build using component mode synthesis and mistuning is introduced as perturbations of the cantilevered-blade modes. The measured modal data are extracted from global measurements of the blisk’s forced response. As we use a one point excitation, this measurement procedure allows the acquisition of the all modes of a given family with a quite simple experimental setup. A selection of the best identified modal data is finally performed. During the mistuning identification procedure, these measured data are regularized using an eigenvector assignment technique which reduces the influence of eventual measurement errors. An inverse problem is defined based on the perturbed (mistuned) modal equation, with measured modes as input and mistuning parameters as unknown. Then, the reduced-order model is updated with the identified mistuning, we first perform a correlation on modal responses (using eigenfrequency deviation criteria and MACs). Finally, correlation results on forced responses are presented and discussed.
Investigation of Transient Performance of an Auxiliary Power Unit Microturbine Engine
Authors: Kim SooYong , Park JunYoung , Goldenberg Victor L.
Published: September 2008

Prevention of compressor surge is one of the most important tasks in operation of gas turbine engine. The easiest way to see the phenomena is to show the static and dynamic operation characteristic on the map. Its operation zone will be restricted by the surge limit and, static and transient process must have some margin for it. Surge margin of a static regime is normally chosen during its design stage. Safe operation during part load condition without facing the surge is an indispensable task for control system design and a swift response from the engine is required to avoid it. Effect of rotor moment of inertia, air/gas volumes and heat transfer are factors to cause the transition from the static line. In case a large volume such as heat exchanger exists in the system it will exert a substantial influence to dynamic characteristics. In the present paper, influence of air volume bled from the compressor exit on transient process is investigated with an example of an auxiliary power unit micro-turbine engine. A typical compressor characteristic with scaling was used for the calculation. Turbine mass, pressure ratio, rotation speed, power and moment are calculated based on mass and work conservation. Result from the present study can give a guidance to design the control system. A computer program is developed to calculate the dynamic process using the MathCAD commercial software. Air volume is changed from 0.02 to 6 m3.
Experimental Contribution to High Precision Characterization of Magnetic Forces in Active Magnetic Bearings
Authors: Kjo̸lhede Klaus , Santos Ilmar F.
Published: September 2008

Parameter identification procedures and model validation are major steps towards intelligent machines supported by active magnetic bearings (AMB). The ability of measuring the electromagnetic bearing forces, or deriving them from measuring the magnetic flux, strongly contributes to the model validation and leads to novel approaches in identifying crucial rotor parameters. This is the main focus of this paper, where an intelligent AMB is being developed with the aim of aiding the accurate identification of damping and stiffness coefficients of active lubricated journal bearings. The main contribution of the work is the characterization of magnetic forces by using two different experimental approaches. Such approaches are investigated and described in detail. A special test rig is designed where the 4 pole - AMB is able to generate forces up to 1900 N. The high precision characterization of the magnetic forces is conducted using different experimental tests: (a) by using hall sensors mounted directly on the poles (precise measurements of the magnetic flux) and by an auxiliary system, composed of strain gages and flexible beams attached to the rotor, (b) by measuring the input current and bearing gap variations, monitoring the bearing input signals. Advantages and drawbacks of the different methodologies are critically discussed. The linearity ranges are experimentally determined and the characterization of magnetic forces with a high accuracy of less than 1% is achieved. (%error is normalized with respect to the instantaneous measured force obtained from the strain gauges signals).
A Methodology for the Vibration Amplitude Prediction of Self-Excited Rotors Based on Dimensional Analysis
Authors: Corral Roque , Gallardo Juan Manuel
Published: September 2008

The dimensional analysis of a simple model that represents the vibration of aerodynamically unstable rotor blades is presented. Based on this analysis a methodology to determine the rotor blade vibration amplitude is outlined. The method assumes that the forcing is due solely to the self-excitation of the airfoil and that the vibration amplitude is small enough to represent the unsteady aerodynamics associated to the airfoil motion using the linearized Navier-Stokes equations. The vibration amplitude is saturated due to the non-linearity of fir-tree dry friction which is modelled using a simplified approach. To compensate for the limitations of the friction model several hypotheses need to be done, among them, the geometric similarity of the different configurations and that the aspect ratio of the rotor blades is high. The application of the method to a low-pressure-turbine bladed-disk is discussed in detail. A comparison of the present method against experimental data is presented.