bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of a Real-Time Simulator Based on Recurrent Neural Networks for Compressor Transient Behavior Prediction
Authors: Venturini M.
Published: September 2008

In the paper, feed-forward Recurrent Neural Networks with a single hidden layer and trained by using a back-propagation learning algorithm are studied and developed for the simulation of compressor behavior under unsteady conditions. The data used for training and testing the RNNs are both obtained by means of a non-linear physics-based model for compressor dynamic simulation (simulated data) and measured on a multi-stage axial-centrifugal small size compressor (field data). The analysis on simulated data deals with the evaluation of the influence of the number of training patterns and of each RNN input on model response, both for data not corrupted and corrupted with measurement errors, for different RNN configurations and different values of the total delay time. For RNN models trained directly on experimental data, the analysis of the influence of RNN input combination on model response is repeated, as carried out for models trained on simulated data, in order to evaluate real system dynamic behavior. Then, predictor RNNs (i.e., those which do not include among the inputs the exogenous inputs evaluated at the same time step as the output vector) are developed and a discussion about their capabilities is carried out. The analysis on simulated data led to the conclusion that, to improve RNN performance, it is beneficial the adoption of a one-time delayed RNN, with an as low as possible total delay time (in the paper, 0.1 s) and trained with an as high as possible number of training patterns (at least 500). The analysis of the influence of each input on RNN response, conducted for RNN models trained on field data, showed that the single-step-ahead predictor RNN allowed very good performance, comparable with that of RNN models with all inputs (overall error for each single calculation equal to 1.3% and 0.9% for the two test cases considered). Moreover, the analysis of multi-step-ahead predictor capabilities showed that the reduction of the number of RNN calculations is the key factor for improving its performance over a significant time horizon. In fact, when a high test data sampling time is chosen (in the paper, 0.24 s), prediction errors were acceptable (lower than 1.9%).
Centrifugal Rotor Tri-Hub Burst For Containment System Validation
Authors: Manavi B.
Published: September 2008

The following paper outlines a methodology for accurately predicting the burst of a centrifugal rotor, for the purpose of certifying the tri-hub containment capability of an Auxiliary Power Unit gas turbine engine. The tri hub burst is achieved by introducing three equally spaced slots into a centrifugal rotor. Using 2D and 3D finite element analysis, the slot geometry was optimized to ensure burst of the centrifugal rotor at the desired speed, through spin pit testing, and to account for thermal and centrifugal growth for operation in an engine with proper tip clearances. In order to validate the versatility of this methodology, two centrifugal rotor geometries with different material properties (Ti6Al4V and Ti6Al2Sn4Zr6Mo) and operating conditions were analyzed. The analytical predictions were confirmed with isothermal spit pit tests using temperatures that approximate the bulk average temperature in the high stressed bore for an un-slotted centrifugal rotor. The results of spin pit tests were found to be within 0.4% of predicted values. Burst tests were subsequently conducted on a gas generator rig and a full engine test, where results were found to be within 2% of predicted values.
Improvement of Microturbine Recuperators Using Taguchi Methodology
Authors: Escola George , Bucey Charles W. , Montague Preston , Telfer Michael J. , McClain John , Patel Mahesh , Miars Chad , Shockley Michael
Published: September 2008

The fabrication of primary surface recuperators for gas turbines and microturbines is a complex process involving a multitude of variables, which are highly interactive. After over 25 years of improvements to recuperator manufacture at Solar Turbines Incorporated, fabrication of the recuperator primary sheet is still prone to scatter of output measures within drawing requirements caused by variations in raw foil properties and changes in environmental conditions. This paper outlines a systematic analysis and improvement of the primary sheet fin folding process using Taguchi methodology. The approach was to break the overall system into subsystems, analyze each subsystem using computer simulation for fin folding and then to analyze the complete system in actual use. The goal was to improve the fabrication process so that multiple drawing requirements for primary recuperator sheet are consistently met with minimum variation and the time needed for subsequent manufacturing steps is reduced. An improved system is more robust, meaning total variability in the primary sheet is minimized and outputs are more insensitive to noise (inputs that are not controllable or are very expensive to control). Improvement is measured by calculating the ratio of desired output to undesired output (noise), i.e. the signal to noise (S/N) ratio. More consistent primary sheet will improve overall recuperator system performance and reduce the cost of this critical gas turbine system component. A secondary objective was to increase the durability of the fin-folding blades, which are subject to wear and breakage. As this paper goes to press, analysis of the final design of experiment on the actual system is in progress.
Advanced Modelling of Underplatform Friction Dampers for Analysis of Bladed Disc Vibration
Authors: Petrov E. P. , Ewins D. J.
Published: September 2008

Advanced structural dynamic models for both wedge and split underplatform dampers have been developed. The new damper models take into account inertia forces and the effects of normal load variation on stick-slip transitions at the contact interfaces. The damper models are formulated for the general case of multiharmonic forced response analysis. An approach for using the new damper models in the dynamic analysis of large-scale finite element models of bladed discs is proposed and realised. Numerical investigations of bladed discs are performed to demonstrate the capabilities of the new models and an analysis of the influence of the damper parameters on the forced response of bladed discs is made.
Analysis of Variation of Natural Frequency and Resonant Stress of Blade
Authors: Kaneko Yasutomo , Mori Kazushi , Yamashita Hiroyuki , Sato Kenji
Published: September 2008

A compressor blade of low aspect ratio is a typical shell-type structure and its natural frequency and vibratory stress are sensitive to a manufacturing tolerance. In designing a blade, the designer should take the variation of the vibration characteristics into account, and evaluate the mechanical strength of the blade. This paper, first, proposes an analysis method for predicting the resonant stress due to the interaction force between the vane and blade, using 3-D CFD and the modal analysis method based on 3-D FEM. Rig tests of the compressor are carried out, and the measured frequencies and vibratory stresses are compared to predicted values, and the validity of the proposed method is verified. In the second place, a practical analysis method for predicting the variation of the natural frequency and vibratory stress of the blade is proposed, where the variation of the vibration characteristics such as a natural frequency and a resonant stress is evaluated by the first order second moment method in addition to 3-D CTD and 3-D EEM. The calculated results are compared with measured ones. From the results, it is confirmed that the variation of the vibration characteristics can be predicted by the simple method proposed in this paper.
Mistuning Phenomena on Bladed Disk: Industrial Methods and Applications
Authors: Lombard Jean-Pierre , Dupeux Je´roˆme , Dupont Christian , Garcin Francois , Baumhauer Ste´phane
Published: September 2008

This paper deals with the methods used at Snecma (SAFRAN Group) to simulate the real mistuned dynamic behavior of bladed disks. Many applications of the method on industrial cases are also presented. The dissymmetry of a real bladed disk, which is mainly generated by small deviations in its geometry, leads to different dynamic impedances of the blades. These variations in impedance cause significant amplification of the forced response of the bladed disk. We propose to focus on industrial methods that can be used to simulate the mistuned dynamic behavior of a bladed disk in the case of small “frequency mistuning” or of greater “large mistuning”. This method, based on the modal synthesis technique (Benfield and Hruda family), can be classified as a “first generation method”. The first originality of this method consists in taking into account major mistuning, such as that induced by an FOD event. A second innovation concerns the use of these methods to assess in probabilistic terms the correction factor to apply to the maximum dynamic level measured during engine certification tests. The first part of the paper relates to the proposed method and its validation for large-scale “shape” mistuning on an academic test case. In the second section, we present a number of industrial applications: • An application of “geometric mistuning” is presented on a bladed disk after an FOD event. The same kind of analysis as previously described is carried out and the numerical results are commented. • The mistuning analyses are carried out on an industrial blisk with a local defect. The sensitivity of the response amplification factor is calculated versus the mistuning rate using a probabilistic approach. • Another application of the mistuning strategy is discussed: it concerns the use of the mistuning method to specify the correction factor of partial dynamic strain gauge measurements in order to assess the maximum level of a bladed disk. • The last application is dedicated to the simulation of intentional mistuning to increase the aeroelastic stability of an industrial test case.
Transient Rotor/Active Magnetic Bearing Control Using Sampled Wavelet Coefficients
Authors: Cade Iain S. , Keogh Patrick S. , Sahinkaya M. Necip
Published: September 2008

A novel method for transient rotor/ active magnetic bearing control using sampled wavelet coefficients is proposed. Control currents are formulated in the wavelet transform domain, prior to signal reconstruction. The wavelet based controller is designed from target transient responses due to step changes in wavelet co-efficients of applied forces. Transient system dynamics are embedded in the controller and evaluated from on-line system identification. Experimental validation is undertaken using a flexible rotor/active magnetic bearing system. Mass loss tests were performed at two critical speeds corresponding to near sudden changes in unbalance that are capable of exciting rotor dynamic modes in a transient manner. The controller is shown to suppress the transient responses within a finite settling time.
LM500: Packaged Power for the All-Electric Ship
Authors: Willett Fred T. , Patel Mark
Published: September 2008

Increased shipboard electricity demand, for propulsion, navigational electronics, reduced crew size, and other purposes, has created a need for marinized gas turbine generator sets. The LM500 is a versatile 4 MW class aeroderivative gas turbine with a solid track record. The LM500 gas turbine is now equipped with a dual-redundant 21st century digital control system, which also manages the gas turbine generator set. In addition, to improve combustor life at a rated power, the marinized LM500 was modified for the engineering development model (EDM), and the turbine hot section components proven in the CF34-3B — the life improved model of its aero engine counterpart, may be offered for production. The gas turbine has been fully integrated on a common base with a 4 MW generator and all auxiliary equipment. An epicyclic gearbox was used to reduce power turbine output speed from 7000 RPM to the 1800 RPM required at the four-pole generator. The auxiliary equipment layout was designed to minimize weight and allow for ease of maintenance. Gas turbine engine testing was completed in August 2004. Operational string testing of the integrated gas turbine generator set was completed in January 2005, with full power plant testing scheduled for 2005 at the Land Based Test Site, in Philadelphia, Pennsylvania, by the customer. This paper describes and discusses the gas turbine generator set (genset) design, development, and production plans, as well as the benefits of the packaged power plant and potential applications.
CFD Optimization of Gas Inlet Configuration for 100kW Microturbine Recuperator
Authors: Zhang D. J. , Wang Q. W. , Zeng M. , Luo L. Q. , Wu F. , Feng Z. P.
Published: September 2008

Compact and efficient recuperator is an important component of a microturbine system. To ascertain the optimum gas cavity configuration of the recuperator in a 100kW-microturbine system, a numerical study of flow performance has been done. The main parameters to change in different cases are cone angle of the gas pipeline, α and depth of the pipeline in the gas cavity, L. By comparing the gas pressure drop, Δp and the gas outlets velocity nonuniformity, Su, we found that the case with α = 5° and L = 370mm is the best configuration. Comparing with the worst case, it may greatly decrease the velocity nonuniformity by 73.3% while the corresponding pressure drop increases only 8%.
Flywheel Energy Storage System for Naval Applications
Authors: Huynh Co , McMullen Patrick , Filatov Alexei , Imani Shamim , Toliyat Hamid A. , Talebi Salman
Published: September 2008

A recent trend in designing naval ships is to improve performance through using more electric equipment. The reliability and quality of the onboard electric power, therefore, becomes critical as the ship functionality would entirely depend on its availability. This paper investigates the possibility of using Flywheel Energy Storage Systems (FESS), similar to those earlier developed for commercial applications, to address issues related to onboard power supplies. A design of a FESS for onboard power backup and railroad electrical stations is presented. The FESSs power output parameters are 500kWx30sec in high-duty mode and up to 2MW in pulse mode. High power output is one of the main advantages of FESS over commercially available electrochemical batteries. The other advantages include essentially an unlimited number of charge/discharge cycles, observable state of charge and environmental friendliness. Designs of the main FESS components are discussed: low-loss magnetic bearings, an energy-storage hub, a high-efficiency motor/generator and power electronics.
Dynamic Properties of Tilting-Pad Journal Bearings: Experimental and Theoretical Investigation of Frequency Effects Due to Pivot Flexibility
Authors: Dmochowski Waldemar
Published: September 2008

Tilting-pad journal bearings (TPJB) dominate as rotor supports in high speed rotating machinery. The paper analyzes frequency effects on the TPJB’s stiffness and damping characteristics based on experimental and theoretical investigations. The experimental investigation has been carried out on a five pad tilting-pad journal bearing of 98 mm in diameter. Time domain and multifrequency excitation has been used to evaluate the dynamic coefficients. The calculated results have been obtained from a three-dimensional computer model of TPJB, which accounts for thermal effects, turbulent oil flow, and elastic effects, including that of pad flexibility. The analyzes of the TPJB’s stiffness and damping properties showed that the frequency effects on the bearing dynamic properties depend on the operating conditions and bearing design. It has been concluded that the pad inertia and pivot flexibility are behind the variations of the stiffness and damping properties with frequency of excitation.
Test Results and Analytical Predictions for Rotor Drop Testing of an AMB Expander/Generator
Authors: Hawkins Lawrence , Filatov Alexei , Imani Shamim , Prosser Darren
Published: September 2008

A cryogenic gas expander system that incorporates a high performance, high-speed permanent magnet, direct-drive generator and low loss magnetic bearings is described. Flow loop testing to 30,000 rpm was completed at the system manufacturer’s facility in January 2005, and field installation is scheduled for October 2005. As part of the system testing, the rotor was dropped onto the backup bearings multiple times at an intermediate speed and at 30,000 rpm. Orbit and time-history data from a full speed drop and spin down are presented and discussed in detail. A transient, nonlinear rotordynamic analysis simulation model was developed for the machine to provide insight into the dynamic behavior. The model includes the dead band clearance, the flexible backup bearing support and hard stop. Model predictions are discussed relative to the test data.
Comparative Analysis of Microturbines Performance Deterioration and Diagnostics
Authors: Gomes E. E. B. , McCaffrey D. , Garces M. J. M. , Polizakis A. L. , Pilidis P.
Published: September 2008

The interest in microturbines and new distributed generation technologies is growing in the entire world because of the many potentially beneficial characteristics they can offer and the developments achieved so far. This paper investigates the performance and degradation effects of microturbines for electric power generation. Diagnostics investigation is also carried out to obtain optimal instrumentation sets for degradation faults. Here the capacity of the gas turbines analyzed is 29kW simple and regenerative cycles. The engine performance is also analyzed operating at constant and variable speed. To simulate the gas turbine performance and carry out the diagnostic analysis the software Pythia and Turbomatch, developed by Cranfield University, were used. In this paper the engines above are simulated at degraded conditions. The effects of the degradation in the compressor, turbine and recuperator on the performance of the engines were investigated. Despite of the improvement on performance achieved with regenerative cycle and variable speed operation the results show that the performance of variable speed microturbines is more sensitive to components degradation than constant speed engines. Also recuperator degradation has greater effect on variable speed than constant speed engines. Due the effects of degradation on each engine different diagnostic approaches are observed.
Micro Gas Turbine With Ceramic Nozzles and Rotor: Part 2
Authors: Iki Norihiko , Inoue Takahiro , Matsunuma Takayuki , Yoshida Hiro , Sodeoka Satoshi , Suzuki Masato , Ebara Takumi , Lee Yoonhwan
Published: September 2008

In order to develop a micro gas turbine with high turbine inlet temperature and thermal efficiency, a series of running tests has been carried out. J-850 jet engine (Sophia Precision Co., Ltd.) was chosen as a baseline machine. The turbine nozzle and the rotor are replaced by type SN-01 (Otsuka Ceramics Co., Ltd.) and type SN-235 (Kyocera Corporation) ceramic elements, respectively. By using type 3a engine, we succeeded one-hour running test of the engine without cooling and severe damages. The turbine inlet temperature was higher than 1000 °C. The rotating speed was about 120,000 rpm. Performances of the type 3a engine (with ceramic nozzle and rotor) and the type 1 (with Inconel alloy nozzle and ceramic rotor) were compared as follows: At the same rotation speed, turbine inlet temperature of the type 3a became higher than that of the type 1. Simultaneously, fuel consumption of type 3a was larger than that of the type 1. Thrust of the type 3a was slightly larger than that of the type 1. Those results imply that the thermal efficiency of type 3a is slightly, 2%, lower than that of the type 1. The present sealing configurations between ceramic nozzle-vanes and their holder plate and ceramic rotor-housing and metal combustion chamber were found to work well.
Steady-State Off-Design Thermodynamic Performance Analysis of a Humid Air Turbine Based on a Micro Turbine
Authors: Zhang Shijie , Xiao Yunhan
Published: September 2008

This paper presents a steady-state on-design and off-design thermodynamic performance investigation of a Humid Air Turbine (HAT) cycle and other competitive gas turbine cycles based on a simple cycle micro turbine. First of all, several stand-alone softwares and programs were integrated to achieve the computational capability of mass and energy balancing and optimization at on-design and off-design conditions. Later on, this paper shows the simulated on-design performance of a micro turbine in three different modified configurations: 1) recuperated cycle, 2) Recuperated Water Injected (RWI) cycle and 3) HAT cycle. The micro turbine is a 90.10 kW single-shaft simple cycle gas turbine with the electrical efficiency of 12.8%. After transformation, the electrical efficiencies of the recuperated, the RWI and the HAT cycle are 26.21%, 29.26% and 29.92%, respectively; the power outputs are 82.52 kW, 106.22 kW and 109.92 kW, respectively. Finally, the effects of load reduction (part-load at ISO conditions) and ambient temperature on the thermodynamic off-design performance of the simple, the recuperated, the RWI and the HAT cycle were investigated and compared. Simulation results indicate that the HAT cycle and the RWI cycle have similar off-design performance. In addition, the two evaporative cycles have more favorable off-design performance compared with the other two cycles with waste heat utilization of converting to power. It is concluded that the adjustment of the water vapor added to the compressed air has beneficial effect on the stability of the off-design performance. However, because of the absence of intercooler, as well as the limited amount of available waste exergy inside the micro gas turbine cycle, the advantages of the on-design and off-design performance of the transformed HAT cycle on the other competitive cycles are not completely displayed.
The Importance of Batch Effects When Considering Damaged Holes in Manufacture
Authors: Corran R. S. J.
Published: September 2008

Anomalies in material condition can arise for Critical Rotating Parts in gas turbines in melt, manufacture and handling. To use a probabilistic approach when designing against burst from such anomalies it is necessary to gather data describing their frequency of occurrence and their size when they do occur. Because of the rare occurrence of such anomalies it is likely that industry data compiled from a wide number of manufacturers will be used to define the exceedance curve. However anomalies may not occur in isolation. Certain causes, such as a worn drill in holemaking, will likely lead to a sequence of damaged holes possibly with increasing depths of distorted material. It is shown that the presence of a batch effect can make a significant difference to the probability of a large anomaly. A method of translating between averaged data gathered from a number of sources and specific component data that recognises the batch effect is described. The examples used here are similar to data gathered from manufacturing anomalies in holes.
Stability Increase of Aerodynamically Unstable Rotors Using Intentional Mistuning
Authors: Martel Carlos , Corral Roque , Llorens Jose´ Miguel
Published: September 2008

A new simple asymptotic mistuning model (AMM), which constitutes an extension of the well known Fundamental Mistuning Model for groups of modes belonging to a modal family exhibiting a large variation of the tuned vibration characteristics, is used to analyze the effect of mistuning on the stability properties of aerodynamically unstable rotors. The model assumes that both, the aerodynamics and the structural dynamics of the assembly are linear, and retains the first order terms of a fully consistent asymptotic expansion of the tuned system where the small parameter is the blade mistuning. The simplicity of the model allows the optimization of the blade mistuning pattern to achieve maximum rotor stability. The results of the application of this technique to realistic welded-in-pair and interlock low-pressure-turbine rotors are also presented.
Characterization of Commercially Available Turbochargers for Possible Application in the UPS System Scenario
Authors: Facchini Bruno , Tarchi Lorenzo , Piccardi Pier Francesco
Published: September 2008

Standard uninterruptible power supply (UPS) systems for radio base stations use lead acid batteries stacks as energy storage device; the fairly short life cycle of such systems, not more than 3 years, together with the presence of highly polluting components make it costly in terms of money and environmental aspects. From these considerations originate the idea to develop an alternative UPS system based on compressed air storage able to replace the battery stacks and to satisfy more restrictive environmental requirements. This work is developed within the European project PNEUMA (PNEumatic Uninterruptible Machine - LIFE 04 ENV/IT/00595) with the final aim to develop some UPS demonstrators for an on site experimentation. In this paper it is described the way followed to set up an air turboalternator with a maximum power of 10.0 kW. Starting from the selection of the turbine, we decided to extract it from an ICE turbocharger because its size and its low cost matches our requirements. First of all, an experimental survey has been realized to test two turbines of different size: expansion ratio, corrected mass flow and efficiency have been measured varying inlet pressure and temperature. This activity led us to select the smaller turbine to develop the first pilot demonstrator; the turbine has been coupled to an high speed alternator (max. 60’000 rpm) by means of an elastic coupling. Some shakedown testing have been performed to verify the mechanical resistance and to test the power conversion system and the control system.
The Effect of Stagger Variability in Gas Turbine Fan Assemblies
Authors: Wilson Mark J. , Imregun Mehmet , Sayma Abdulnaser I.
Published: September 2008

Fan blades of high bypass ratio gas turbine engines are subject to substantial aerodynamic and centrifugal loads, producing the well-known phenomenon of fan blade untwist. The accurate prediction of the running geometry, as opposed to the cold geometry at rest, is crucial in the assessment of aerodynamic performance, vibratory response and noise production of the fan. The situation is further complicated by the fact that some geometric variation is inevitable even for the state-of-the-art manufacturing processes used. The aim of this paper is to investigate the effect of static stagger variability on the dynamic untwist behaviour of fan assemblies. An aeroelastic model was used to show that under certain conditions the stagger pattern changes significantly, both in form and amplitude, relative to the static configuration. At other conditions, a strong correlation between the running and static patterns is demonstrated.
Evolution of Slip Through the Thickness of a Single-Crystal Nickel-Base Superalloy Notched Specimen
Authors: Siddiqui Shadab , Arakere Nagaraj K. , Ebrahimi Fereshteh
Published: September 2008

Deformation mechanisms and failure modes of FCC (face centered cubic) single crystal components subjected to triaxial states of static and fatigue stress are very complicated to predict, because plasticity precedes fracture in regions of stress concentration, and the evolution of plasticity on the surface and through the thickness is influenced by elastic and plastic anisotropy. The triaxial stress state at regions of stress concentration results in the activation of many slip systems that otherwise would not be activated during uniaxial testing. We recently presented [1] results from a numerical and experimental investigation of evolution of slip systems at the surface of notched FCC single crystal specimens, as a function of secondary crystallographic orientation. Results showed that the slip sector boundaries have complex curved shapes with several slip systems active simultaneously near the notch. We extend our work on slip at the surface to investigating the evolution of slip or plastic deformation through the thickness of the specimen. A single crystal double-edge-notched rectangular specimen of a Ni-base superalloy, under the tensile loading ([001] load orientation and [110] notch direction) is considered. A three dimensional (3-D) finite element model (FEM) including elastic anisotropy is used for the numerical investigation. Results indicate that the stress distribution and slip fields are a strong function of axial location through the thickness. Numerical results are verified by comparing them with experimentally observed slip fields. We demonstrate that inclusion of three dimensional analysis and elastic anisotropy is important for predicting evolution of slip at the surface and through the specimen thickness. The resolved shear stresses (RSS) on the dominant slip systems and the normal stress on the dominant planes are shown to vary significantly from the surface to the midplane of the specimen. Based on the consideration of RSS, normal stress and the number of activated slip systems at each thickness level, it is concluded that fatigue cracks most likely start in the midplane, for the orientation reported here.
Rotordynamic Analysis of a Large Industrial Turbo-Compressor Including Finite Element Substructure Modeling
Authors: Moore J. Jeffrey , Vannini Giuseppe , Camatti Massimo , Bianchi Paolo
Published: September 2008

A rotordynamic analysis of a large turbo-compressor that models both the casing and supports along with the rotor-bearing system was performed. A three-dimensional (3-D) finite element model of the casing captures the intricate details of the casing and support structure. Two approaches are presented, including development of transfer functions of the casing and foundation, as well as a fully coupled rotor-casing-foundation model. The effect of bearing support compliance is captured, as well as the influence of casing modes on the rotor response. The first approach generates frequency response functions (FRF’s) from the finite element case model at the bearing support locations. A high-order polynomial in numerator-denominator transfer function format is generated from a curve-fit of the FRF. These transfer functions are then incorporated into the rotordynamics model. The second approach is a fully coupled rotor and casing model that is solved together. An unbalance response calculation is performed in both cases to predict the resulting rotor critical speeds and response of the casing modes. The effect of the compressor case and supports caused the second critical speed to drop to a value close to the operating speed and not compliant with API 617 7th edition requirements. A combination of rotor, journal bearing, casing, and support modifications resulted in a satisfactory and API compliant solution. The results of the fully coupled model validated the transfer function approach.
An Experimental Investigation Into Turbine Flutter Characteristic at Different Tip-Clearances
Authors: Huang X. Q. , He L. , Bell D. L.
Published: September 2008

This paper documents an investigation into unsteady flow in a three-dimensional oscillating turbine cascade with emphasis on the influence of tip clearance. Systematic experimental measurements were performed on a low-speed turbine cascade rig. The cascade consists of seven prismatic turbine blades, with the middle blade being driven to oscillate in a three-dimensional bending/flapping mode. Blades were instrumented with pressure tappings at six span-wise sections to facilitate three dimensional steady and unsteady pressure measurements on the blade surface. The steady pressure measurements are complemented by CFD simulations. Both are in a good agreement and indicate a marked local pressure suction peak at 70–90% chord on the suction surface resulting from the tip-clearance vortex. The measured unsteady pressure shows that this tip-clearance induced suction peak has a significant destabilising influence on the aerodynamic damping at a large tip-clearance (5% chord). Whilst at a small tip clearance (1.25–2.5% chord), the tip-clearance actually has a stabilising effect. The behaviour is in line with a quasi-steady analysis.
An Integrated Design Approach for Micro Gas Turbine Combustors: Preliminary 0-D and Simplified CFD Based Optimization
Authors: Fuligno Luca , Micheli Diego , Poloni Carlo
Published: September 2008

The present work presents a novel approach for the optimised design of small gas turbine combustors, that integrates a 0-D code. CFD analyses and an advanced game theory multi-objective optimization algorithm. The output of the 0-D code is a baseline design of the combustor, given the required fuel characteristics, the basic geometry (tubular or annular) and the combustion concept (i.e. lean premixed primary zone or diffusive processes). For the optimization of the baseline design a parametric CAD/mesher model is then defined and submitted to a CFD code. Free parameters of the optimization process are position and size of the liner holes arrays, their total area and the shape of the exit duct, while different objectives are the minimisation of NOx emissions, pressure losses and combustor exit Pattern Factor. As a first demonstrative example, the integrated design process was applied to a tubular combustion chamber with a lean premixed primary zone for a recuperative methane-fuelled small gas turbine of the 100 kW class.
Inlet Air Supercharging of a 70 kW Microturbine
Authors: Brandon Robert , Halliday Bryan , Hoffman John S.
Published: September 2008

The significant reduction in power output of small gas turbines at high ambient temperatures places the technology at a significant disadvantage compared with reciprocating engines. On site power applications in many jurisdictions are experiencing high power costs during summer peak times. A variable speed industrial fan combined with an evaporative cooler has been constructed and operated in the CETC laboratory in Ottawa, Canada to supply supercharged inlet air to a microturbine rated at 70 kW at ISO conditions. The supercharging system can raise the inlet air pressure by 10.5 kPa (42” wc). A mapping of the turbine performance has been done as a function of boost pressure, relative humidity and ambient air temperature. A net power increase has been observed from 57 kW to 70 kW at an ambient air temperature of 33°C (91°F) and RH of 60%, a 23% increase. Supercharging at lower temperatures yields lower net power increases since the microturbine generator rating is the limiting factor; for example an 11% increase in net power was observed at an inlet air temperature of 11°C (52°F) and RH of 60%. Supercharging was shown to decrease net fuel-to-electricity efficiency of this recuperated turbine by about 3%, at an air temperature of 33°C (91°F). An economic analysis using published power prices and weather data from Toronto explores the business case of using supercharging, with the best economies likely for multiple units or larger microturbines, such as 250 kW units. The objective of the project was to demonstrate the concept leading to a field trial in Toronto or in Calgary where the altitude offers a further benefit to the inlet air supercharging concept. Work is underway to design a control system suitable for field deployment for the concept.
Test Evolution and Oil-Free Engine Experience of a High Temperature Foil Air Bearing Coating
Authors: Lubell Daniel , DellaCorte Christopher , Stanford Malcolm
Published: September 2008

During the start-up and shut-down of a turbomachine supported on compliant foil bearings, before the bearings have full development of the hydrodynamic gas film, sliding occurs between the rotor and the bearing foils. Traditional solid lubricants (e.g., graphite, Teflon®) readily solve this problem at low temperature. High temperature operation, however, has been a key obstacle. Without a suitable high temperature coating, foil air bearing use is limited to about 300°C (570°F). In oil-free gas turbines, a hot section bearing presents a very aggressive environment for these coatings. A NASA developed coating, PS304, represents one tribological approach to this challenge. In this paper, the use of PS304 as a rotor coating operating against a hot foil gas bearing is reviewed and discussed. During the course of several long term, high cycle, engine tests, which included two coating related failures, the PS304 technology evolved and improved. For instance, a post deposition thermal treatment to improve dimensional stability, and improvements to the deposition process to enhance strength resulted from the engine evaluations. Largely because of this work, the bearing/coating combination has been successfully demonstrated at over 500°C (930°F) in an oil-free gas turbine for over 2500 hours and 2900 start-stop cycles without damage or loss of performance when properly applied. Ongoing testing at Glenn Research Center as part of a long term program is over 3500 hours and 150 cycles.
Quantification of Uncertainty Related to Stress Estimation in Turbine Engine Blades
Authors: Calanni Giorgio , Volovoi Vitali , Ruzzene Massimo , Cento Peter , Vining Charlie
Published: September 2008

Stress prediction in turbine blades is affected by limitations in the measurement setup as well as by various sources of uncertainty in the model-based inference techniques. The presence of uncertainty diminishes the confidence in the estimated response, whose fidelity lowers further when results are extrapolated to operating conditions or systems other than the tested ones. A procedure is being developed with a twofold objective: maximization, under given computational constraints, of a system’s model accuracy and quantification of any remaining uncertainty associated with the estimation technique. A probabilistic analysis, in which uncertainties are explicitly modeled has been carried out to investigate the effects of modeling and input parameter uncertainties, and to evaluate their contribution to a system’s vibratory response prediction. Results and considerations are herein described and discussed.
Forced Response Analysis of Shrouded Blades by an Alternating Frequency/Time Domain Method
Authors: Yajie Shi , Jie Hong , Yingchun Shan , Zigen Zhu
Published: September 2008

In turbine jet engine, the rotating blades are subjected to cyclic loading, which makes the blades experience the so-called High Cycle Fatigue (HCF). Dry friction is often employed in turbine design to attenuate the blade vibration and increase aeroclastic stability of the turbine. The dry friction dampers are often classified into four types, i.e., blade-to-blade, blade-to-ground, shrouds, and wedge damper, respectively. Compared with the under-platform dampers, shrouds make fan behavior be significantly more complex. It is very difficult to model and predict the nonlinear response of shrouded blades. In the present study, an efficient approach to investigate the nonlinear response of the shrouded blades is suggested using an alternating frequency/time domain (AFT) method. On one hand, the friction force between shrouds is numerically solved in time-domain. The trajectory of relative motion of the moving contact point is traced, and the stick-slip-separation transition for 3-D relative motion of the shroud-contact interface is considered. On the other hand, the response of the shrouded blades is iteratively solved in frequency-domain using Harmonic Balance Method (HBM). In this approach, the influence of high frequency modes of blade, and the coupling of each harmonic component on damping behavior can be taken into account. As an application, the performance of shroud damper is systematically investigated using the AFT method. The influence of shroud-to-shroud preload and contact stiffness on the shroud damping potential is studied. Some valuable results are got to the design of the shroud contact.
Vibration Reduction Investigation of a Squeeze Film Damper With Valvular Metal Rubber
Authors: Yanhong Ma , Jie Hong , Yin Deng
Published: September 2008

A new-style squeeze film damper with valvular metal rubber squeeze film ring (SFD/VMR) was designed to improve characteristics of the squeeze film force of the SFD. The immobile squeeze film ring of the SFD was replaced by the elastic squeeze film ring with the valvular metal rubber subassembly (VMR). When the unbalance force was smaller, the displacement of the journal changed little, and then the squeeze film force was smaller too, so as to the squeeze film ring of the SFD/VMR was nearly immobile. The working condition was similar with the SFD. When the unbalance force was larger, the displacement of the journal changed bigger, and then the squeeze film force rapidly increased, so as to the VMR deformed, which made the film thickness changed correspondingly, until it reached a balanceable state of the squeeze film force and elastic force of the VMR. Theoretical and experimental investigations showed that the SFD/VMR had optimal effect on reducing vibration, comparing with the SFD, because it could passively adjust the squeeze film clearance by taking advantage of the elastic deformation of the VMR. The SFD/VMR could control the squeeze film clearance in a suitable range, which made the characteristics of the squeeze film force of the SFD/VMR better than the SFD. The SFD/VMR could suppress the occurrence of the nonlinear vibration phenomenon markedly, such as bistable jump up.
Characterization of Porous Carbon Foam as a Material for Compact Recuperators
Authors: Straatman A. G. , Gallego N. C. , Yu Q. , Thompson B. E.
Published: September 2008

Experiments are presented to quantify the convective heat transfer and the hydrodynamic loss that is obtained by forcing water through blocks of porous carbon foam (PCF) heated from one side. The experiments were conducted in a small-scale water tunnel instrumented to measure the pressure drop and the temperature rise of the water passing through the blocks and the base temperature and heat flux into the foam block. In comparison to similar porosity aluminum foam, the present results indicate that the pressure drop across the porous carbon foam is higher due to the large hydrodynamic loss associated with the cell windows connecting the pores, but the heat transfer performance suggests that there may be a significant advantage to using PCF over aluminum foam for extended surface convection elements in recuperators and electronic cooling devices.
Fracture Analysis of Cracks in Orthotropic Materials Using ANSYS®
Authors: Ayhan A. O. , Kaya A. C. , Loghin A. , Laflen J. H. , McClain R. D. , Slavik D.
Published: September 2008

A methodology for performing two and three-dimensional fracture analyses in orthotropic materials using ANSYS software (“ANSYS”) is presented. The methodology makes use of analytically known crack tip fields in orthotropic materials and is implemented into a general purpose ANSYS macro. The ANSYS analysis, which takes into account the material orthotropy is performed in a regular manner by including the quarter point elements near the crack front. Then, in the post-processing module, the developed macro is run to associate the crack tip displacements with the orthotropic crack tip displacement fields to compute the mixed-mode stress intensity factors. Numerical examples are also presented that demonstrate application and validation of the procedure. These examples include an edge crack in an orthotropic strip and a surface crack in a transversely isotropic plate. The results show how the orthotropic fracture results may differ from those of isotropic fracture analysis. It is also shown that this difference can be dramatically big when the stress analysis is done using the orthotropic properties, whereas the fracture calculations are performed considering the crack tip fields for a crack in an isotropic material.
An Internal Flow Measurement That Senses a Pre-Cursor to Surge in Centrifugal Compressors
Authors: McKee Robert J.
Published: September 2008

Centrifugal compressors are critical for moving large volumes of gas in the natural gas pipeline, hydrocarbon processing, and general energy industries. The operation of centrifugal compressors is limited by a number of factors including the occurrence of surge at low flows. The exact low flow conditions at which surge occurs cannot be determined from external measurements. The precise flow and head at which surge occurs is effected by factors including the installed piping configuration, the dynamic impedance of the piping system, the pulsating pressures in the piping, and the gas properties such as compressibility among other variables. The results of the many factors affected when surge occurs and the sudden nature of surge onset are such that there are no previously identified reliable ways to detect an approaching surge. Current surge control methods rely on external measurements of head or speed and flow to estimate the conditions at which surge will occur and then recycle flow at some margin above the expected surge conditions in order to avoid surge. However, this type of surge control is inefficient and frequently leads to recycling more flow than necessary with the result that fuel and energy are wasted. If a means were available to measure a fundamental pre-cursor to surge then a reliable indication of the operating margin above surge could be developed and the amount of recycle flow and the loss of efficiency could be minimized. Such a pre-cursor has been found and a sensor technique base on drag probe technology has been developed. This paper presents some of the background on pre-surge detection in centrifugal compressors and then describes the known behavior of the impeller inlet outer wall re-circulating flow that develops as surge approaches. In addition, this paper reports on the development of a drag probe sensor to measure these internal flow components. Evidence from direct surge control testing is presented to support the finding that these internal flows are a basic surge pre-cursor and a useful control for centrifugal compressors. The measured flow changes prior to surge are identified and data is shown. The result of this research will lead to an improved surge control system for a significant class of signal stage modern centrifugal compressors and will increase the operating range and overall efficiency of such machines.
Scaling of Turbine Blade Unsteady Pressures for Rapid Forced Response Assessment
Authors: Green J. S. , Fransson T. H.
Published: September 2008

High Cycle Fatigue caused by high vibration levels continues to be a major concern in gas turbine design. The use of Computational Fluid Dynamics methods is becoming more commonplace for calculating the vibration amplitude of turbomachinery blades during the design process. A typical calculation approach would be to calculate the unsteady aerodynamic loads at the resonance condition for each vibration mode of interest. In this paper it is proposed that, for a choked high pressure (HP) turbine, an unsteady flow prediction can be scaled across a wide engine operating range using a few simple parameters. There is a fixed relationship between the turbine inlet pressure and the HP shaft speed (when expressed non-dimensionally) which can be used to scale the flow conditions. The effects of altitude variation in the ratio of shaft speeds, compressor bleed flows and schedule of the variable vanes are secondary, having only a small influence on the behaviour. This paper demonstrates that the steady flow distribution around both stator and rotor is virtually constant across the speed range of the engine and the rotor unsteady surface pressure distribution shows only small differences. Further, the parameter which is of prime interest for vibration assessment, the modal force, can be scaled very well using turbine inlet pressure. For modes of vibration with high amplitudes the errors introduced by scaling are of the order of 6% which is considered acceptable for design predictions.