bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of a Small Aircraft Combustor to Reduce NOx Emissions Under Practical Conditions
Authors: Makida Mitsumasa , Yamada Hideshi , Shimodaira Kazuo , Yamamoto Takeshi , Hayashi Shigeru
Published: March 2009

A series of research experiments under practical conditions has been conducted to develop a combustor for a small-class aircraft engine (with the pressure ratio of about 20). In the previous research experiments, including ignition and emission tests under atmospheric pressure, we applied a single airblast fuel nozzle and utilized the rich-burn quick-quench lean-burn (RQL) combustion approach. The combustor was tuned to show the behavior of the RQL under the atmospheric condition. In this paper, the results of single-sector combustor experiments under the practical temperature and pressure conditions are presented, in which RQL behavior is observed and NOx emissions in the ICAO (International Civil Aviation Organization) LTO (Landing and Take-Off) cycle are reduced to 45% of the ICAO CAEP4 (Committee on Aviation Environmental Protection 4) standard. Also the results of successive multi-sector combustor tests to optimize combustion performances with a more practical combustor configuration under the practical conditions are presented. The emission characteristics which are obtained are compared with those of the single-sector tests, and combustor size and configuration, air mass flow ratio and air hole positions are tuned through a series of multi-sector experiments. After the optimization, the combustor achieved the following performances; NOx emissions are reduced to less than 42% of the ICAO CAEP4 standard, CO and THC (Total Hydrocarbon) are reduced to those of 2% and 50% respectively, the lean blowout limit is kept over 220 AFR (Air to Fuel Ratio) at the idle condition and the exit temperature profile at the full load condition is sufficiently uniform (P.T.F.<0.15). The process of optimization will be discussed in this report.
Effects of Obstructions and Surface Roughness on Film Cooling Effectiveness With and Without a Transverse Trench
Authors: Somawardhana Ruwan P. , Bogard David G.
Published: March 2009

Recent studies have shown that film cooling with holes imbedded in a shallow trench significantly improve cooling performance. In this study, the performance of shallow trench configurations were investigated for simulated deteriorated surface conditions, i.e. increased surface roughness and near hole obstructions. Experiments were conducted on the suction side of a scaled-up simulated turbine vane. Results from the study indicated that as much as 50% degradation occurred with upstream obstructions, but downstream obstructions actually enhanced film cooling effectiveness. However, the transverse trench configuration performed significantly better than the traditional cylindrical holes, both with and without obstructions and almost eliminated the effects of both surface roughness and obstructions.
CFD Predictions of Film Cooling Adiabatic Effectiveness for Cylindrical Holes Embedded in Narrow and Wide Transverse Trenches
Authors: Harrison Katharine L. , Bogard David G.
Published: March 2009

Recent studies have shown that film cooling adiabatic effectiveness can be significantly improved when holes are embedded in shallow, transverse trenches. In this study computational simulations were made using the commercial CFD code FLUENT to determine if the dramatic improvement in film cooling performance was predictable. Simulations were made of a baseline cylindrical hole configuration, and narrow and wide trench configurations. Simulations correctly predicted that the narrow trench outperformed the baseline row of cylindrical holes and the wide trench at all blowing ratios. Furthermore, the simulations showed that enhanced performance with the trench could be attributed to decreased separation of the coolant jets. The success of these predictions show that computational simulations can be used as a tool for studying and identifying promising film cooling configurations.
Anomaly Detection Using Non-Parametric Information
Authors: Varma Anil , Bonissone Piero , Yan Weizhong , Eklund Neil , Goebel Kai , Iyer Naresh , Bonissone Stefano
Published: March 2009

Diagnostics and prognostics is particularly challenging in systems with a restricted suite of sensors; e.g., in aircraft engines where harsh operating conditions, weight considerations, and regulatory concerns limit the number of sensors. In this paper, we investigate anomaly detection techniques subject to these constraints. Specifically, we use as input to these techniques only controller-generated, log-data for the system. While such log-data is not designed to carry predictive information related to system health, we show that it is possible to extract early warning signals related to the failure of the system by looking for the presence or onset of anomalous or novel patterns in the log-data. We present preliminary results obtained by the application of this approach to some complex systems. We also provide a roadmap for extending this approach by the incorporation of minimal amount of system-specific knowledge of the kind that is typically available for complex systems. This extension is expected to strengthen the applicability of the approach to diagnostic and prognostic analysis at the level of the system components, as well as to the estimation of the root cause of a detected system anomaly.
Successful Trending and Diagnostics Technology Transition
Authors: Rendek Pete , Jaw Link , Smith Gary
Published: March 2009

Starting in 1998, the U.S. Air Force funded a Small Business Innovative Research (SBIR) contract to develop enhanced capabilities for trending, diagnostics, and health management for engines. The resulting technology platform, called ICEMS (Intelligent Condition-based Equipment Management System), includes an open-system architecture and a suite of tools to perform a full range of functions for engine health management, although the ICEMS technology platform is applicable to all types of equipment or systems [1]. The ICEMS technology is one of very few that have crossed the transition chasm in that it is being commercialized into the next generation of Air Force trending tool, the Diagnostic Analysis and Trending Tool (DATT), and into a commercial trending and analysis tool called I-Trend. This paper describes the tools and discusses some of the key factors in the successful commercialization of the SBIR technology.
Comparison of Measured Low-Frequency Engine Noise With Combustion and Jet Noise Predictions for a Turbofan Engine With an Internal Lobed Mixer Nozzle
Authors: Lieber Lysbeth S. , Weir Donald S.
Published: March 2009

This paper presents an examination of the low-frequency engine noise of a turbofan engine with an internal lobed mixer nozzle, and identifies the contributions of the combustion and exhaust jet component noise sources within the low frequency portion of the spectrum by applying recently developed modeling techniques. This investigation was performed as part of the NASA Quiet Aircraft Technology Program. Because the mixer reduces the total jet noise, the combustion noise source becomes a significant contributor. In addition, the character of the jet noise for the mixer nozzle is different from that for a single-stream or coannular nozzle. Although the internal mixer reduces the low-frequency shear-induced jet noise, it also produces an additional higher frequency contribution to the jet noise due to enhanced turbulence levels produced by the mixing process. Therefore, the modeling techniques that predict the low-frequency component source noise must capture sufficient physics of the noise generation process for the combustor and mixer nozzle to accurately represent the component spectral distributions. The improved modeling of component source noise for both combustor and jet sources was addressed as part of the NASA Quiet Aircraft Technology Program. This activity included development of a new narrowband combustion noise model, as well as the application of a recent jet noise model for nozzles with internal forced mixers. The noise data used in this study was taken during the NASA Engine Validation of Noise Reduction Concepts (EVNRC) Program. Both static and flight noise measurements were made at a range of power settings using the Honeywell TFE731-60 turbofan engine. The engine configuration of interest for this study employed a nozzle with an internal lobed mixer. Comparison of static and flight data with predictions from the combustion and jet noise models indicates that combustor noise has a significant contribution to lower-frequency engine noise (in the 400–1000 Hz range), particularly for flight conditions, where the jet noise is reduced due to flight effects, and also for lower power settings at static conditions. However, further calibration of the combustion and jet noise prediction techniques will be required, with isolated component noise data, before these models may be applied with certainty to model total engine noise in the low-frequency range.
Simulation of a Multi-Stage Cooling Scheme for Gas Turbine Engines: Part I
Authors: Ghorab M. , Hassan I. , Beauchamp M.
Published: March 2009

This paper presents heat transfer characteristics for a Multi-Stage Cooling Scheme (MSCS) design applicable to high temperature gas turbine engines in aerospace and electric power generation. The film cooling and impingement techniques are considered concurrently throughout this study. The proposed design involves passing cooling air from the inside of the turbine blade to the outside through three designed stages. The coolant air is passed through a circular hole into an internal gap creating an impingement of air inside the blade. It then exits through a sequence of two differently shaped holes onto the blade’s external surface. The film cooling effectiveness is enhanced by increasing the internal gap height and offset distance. This effect is significantly diminished however by changing the inclination angle from 90° to 30° at large gap height. The coolant momentum became more uniform by creating the internal gap consequently the coolant air is spread closer to the external blade surface. This reduces jet liftoff as the air exits its hole and also provides internal cooling for the blade. The hole exit positioned on the outer surface of the blade is designed to give a positive and a wide downstream lateral spreading. The MSCS demonstrates greater film cooling effectiveness performance than traditional schemes.
Aerodynamic Shape Optimization of Turbine Blades Using a Design-Parameter-Based Shape Representation
Authors: Mengistu Temesgen , Ghaly Wahid , Mansour Tarek
Published: March 2009

Currently, most shape optimization activities for 2D blade sections focus on modifying the blade shape locally to get an optimum one, which implicitly assumes that the global shape is near optimum. Moreover, the common design parameters in most cases are not the variables used in shape optimization, hence the designer does not have control over the parameters that he or she uses in the design. In this work, the turbine blade shape at any given radial location, is represented with the MRATD model (Modified Rapid Axial Turbine Design), which is a low-order representation that describes the blade profile using a maximum of 17 aerodynamic design parameters that are given (and used) by the turbine designer, e.g. the blade axial chord, stagger, maximum thickness, throat, uncovered turning, inlet and exit blade and wedge angles, LE and TE radii etc... This representation is used in an optimization scheme to sweep the design space and identify the design parameters that would accomplish a certain optimization objective (e.g. maximum adiabatic efficiency) subject to some constraints (e.g. fixed throat area or minimum TE radius or maximum TE wedge angle or metal angles etc...). The optimization scheme uses evolutionary optimization algorithm, Genetic Algorithm(GA) and, to save computing time, Artificial Neural Network (ANN) is introduced to approximate the optimization objectives and constraints; it is trained and tested using a relatively small number of high fidelity CFD flow simulations. This approach to geometry representation is used to carry out a sensitivity study of the effect of the different design parameters on the blade performance of a highly efficient subsonic turbine blade. Its impact on the design process is also demonstrated.
An Investigation of Tip Force Characteristics of Brush Seals
Authors: Demiroglu Mehmet , Gursoy Mustafa , Tichy John A.
Published: March 2009

Thanks to their compliant nature and superior leakage performance over conventional labyrinth seals, brush seals found increasing use in turbomachinery. Utilizing high temperature super-alloy fibers and their compliance capability these seals maintain contact with the rotor for a wide range of operating conditions leaving minimal passage for parasitic leakage flow. Consequently, the contact force/pressure generated at seal rotor interface is of importance for sustained seal performance and longevity of its service life. Although some analytical and numerical models have been developed to estimate bristle tip pressures, they simply rely on linear beam equation calculations and other such assumptions for loading cases. In this paper, previously available analytical and/or numerical models for bristle tip force/pressure have been modified and enhanced. The nonlinear cantilever beam equation has been solved and results are compared to a linear cantilever beam equation solution to establish application boundaries for both methods. The results are also compared to experimental data. With the support of testing, an empirical model has been developed for tip forces under operating conditions.
An Investigation of Heat Generation Characteristics of Brush Seals
Authors: Demiroglu Mehmet , Tichy John A.
Published: March 2009

Brush seals are considered as a category of compliant seals, which tolerate a great high level of interference between the seal and the rotor or shaft. Their superior leakage characteristics have opened many application fields in the turbo-machinery world, ranging from industrial steam turbines to jet engines. However, brush seal designers have to find a trade-off between the lower parasitic leakage but higher heat generation properties of brush seals for given operation conditions. As brush seals can maintain contact with the rotor for a wide range of operating conditions, the contact force/pressure generated at the seal-rotor interface becomes an important design parameter for sustained seal performance and longevity of its service life. Furthermore, due to this contact force at the interface, frictional heat generation is inevitable and must be evaluated for various design and operating conditions. In this paper, frictional heat generation at the sealrotor interface is studied. To capture temperature rise at the interface, a thermal image of the seal and rotor is taken with an infrared camera under various operating conditions. The temperature map of the rotor is compared to results from thermal finite element analysis of the rotor to back calculate the heat flux to the rotor. A closed form equation for frictional heat generation is suggested as a function of seal design parameters, material properties, friction coefficient and empirical factors from testing.
2D Parametric Study Using CFD of a Circulation Control Inlet Guide Vane
Authors: Hill H. E. , Ng W. F. , Vlachos P. P. , Guillot S. A. , Car D.
Published: March 2009

Circulation control inlet guide vanes (IGVs) may provide significant benefits over current IGVs that employ mechanical means for flow turning. This paper presents the results of a two-dimensional computational study on a circulation control IGV that takes advantage of the Coanda effect for flow vectoring. The IGV in this study is an uncambered airfoil that alters circulation around itself by means of a Coanda jet that exhausts along the IGV’s trailing edge surface. The IGV is designed for an axial inlet flow at a Mach number of 0.54 and an exit flow angle of 11 degrees. These conditions were selected to match the operating conditions of the 90% span section of the IGV of the TESCOM compressor rig at the Compressor Aero Research Laboratory (CARL) located at Wright-Patterson AFB, the hardware that is being used as the baseline in this study. The goal of the optimization was to determine the optimal jet height, trailing edge radius, and supply pressure that would meet the design criteria while minimizing the mass flow rate and pressure losses. The optimal geometry that was able to meet the design requirements had a jet height of h/Cn = 0.0057 and a trailing edge Radius R/Cn = 0.16. This geometry needed a jet to inflow total pressure ratio of 1.8 to meet the exit turning angle requirement. At this supply pressure ratio the mass flow rate required by the flow control system was 0.71 percent of the total mass flow rate through the engine. The optimal circulation control IGV had slightly lower pressure losses when compared with a reference cambered IGV.
Thermal Analysis of a Heat Recovery System for Externally Fired Micro Gas Turbines
Authors: Bahador Mehdi , Ito Takamasa , Sunde´n Bengt
Published: March 2009

Several serious problems such as material durability and fouling in the High Temperature Heat Exchanger (HTEH) for Externally Fired Micro Gas Turbines (EFMGT) cause the low thermal efficiency. In this study for increasing the thermal efficiency, a duct around a cylindrical fixed bed combustor which burns wood pellets is proposed and two different designs, empty and porous material filled, are investigated. A heat transfer model, based on coupling between radiative and convective modes at the combustor and duct sides is developed to evaluate the important geometrical parameters in the different designs. The predicted results for the empty duct show that although an increase of the combustion length increases the temperature of air at the duct outlet, an increase of the combustor diameter is more effective. In addition, an increase of the duct cross section is the most effective way and according to the predictions, the pressure drop in this case is still acceptable. The porous duct design shows a significant increase in the air temperature at the duct outlet. However, the pressure drop is high. The investigation shows the possibility of reduction of the pressure drop with the same amount of heat transfer by selecting suitable particle size and porosity.
Design and Analysis of a Planar 2-D Nozzle for a Small Jet-Engine
Authors: Moro´n Laura , Ghoreyshi Mehdi , Banazdeh Afshin , Pilidis Pericles
Published: March 2009

The thrust-vectoring in particular “Fluid” type is of increasing interest for the maneuverability and the agility of combat and fighter aircraft. This has been employed for different nozzles mainly axisymmetric and 2-dimensional. For the latter, the aspect ratio, i.e. the ratio of the long-to-short side of the nozzle has significant influence upon the exhaust and thrust-vectoring performance. The effectiveness of a high aspect-ratio nozzle in order to deflect the jet engine’s thrust has been demonstrated {Hiley, 1975} but, such large aspect ratios often causes increasing of the structure weight and internal pressure losses. Here, the design of a two-dimensional nozzle with respect to the thrust-loss factor of a small jet-engine is presented. Computational Fluid Dynamics (CFD) techniques were used in order to simulate the nozzle’s flow characteristics under various engine’s operating settings as well as different aspect-ratio designs. Computations results were obtained from the “Fluent” program. All developed models are 3-D and meshed by using “Gridgen” code. Moreover, the boundary conditions were obtained by using of the engine’s performance model developed in TURBOMATCH program. Also, the paper describes an experiment in order to predict the engine’s performance for a test case that has aspect ratio of 8.5. The CFD results were compared with experimental measurements. The results showed that nozzle with higher aspect-ratio results in larger pressure losses, while, its thrust discharge coefficient is not far from the moderate aspect-ratio nozzle.
Ignition and Propagation Characteristics of Hydrogen-Enriched Methane Flames
Authors: Briones Alejandro M. , Aggarwal Suresh K.
Published: March 2009

The effects of H2 enrichment on the ignition and propagation of laminar CH4-air flames in axisymmetric coflowing jets are numerically investigated. A comprehensive, time-dependent computational model, which employs a detailed description of chemistry and transport, is used to simulate the transient ignition and flame propagation phenomena. Because fuel-air mixtures can potentially be ignited due to the presence of either a high-temperature zone or a radical pool, we explore temperature-induced ignition and radical-pool-induced ignition. It is observed overall that radical-pool-induced ignition is more effective than temperature-induced ignition for igniting any H2-CH4-air mixture. With increasing the radical-pool concentration ignition is facilitated and the total ignition time for the mixture to reach the ignition conditions is significantly reduced. In addition, as H2 mole fraction in the fuel jet increases, the mixture is more easily ignited. To study the propagation characteristics of these flames only radical-induced ignition is used since it is more effective. Following ignition, a well-defined triple flame, containing a rich premixed, a nonpremixed, and a lean premixed reaction zone, is formed that propagates upstream with nearly constant flame displacement speed towards the burner. As the flame approaches the burner, it transitions to a double flame, and subsequently to a burner-stabilized nonpremixed flame. Predictions are validated using measurements of the flame displacement speed. Detailed simulations are used to examine the effects of H2 enrichment on the propagation characteristics of CH4-air triple flames. As H2 concentration in the fuel blend is increased, the flame displacement and propagation speeds increase progressively due to the enhanced chemical reactivity, diffusivity, and preferential diffusion caused by H2 addition. In addition, the flammability limits associated with the triple flames are progressively extended with the increase in H2 concentration. The flame structure and flame dynamics are also markedly modified by H2 enrichment, which substantially increases the flame curvature and mixture fraction gradient. For all the H2-enriched methane-air flames investigated in this study, there is a negative correlation between flame speed and stretch, with the flame speed decreasing almost linearly with stretch, consistent with previous studies. The effect of H2 addition is to modify the flame sensitivity to stretch, as it decreases the Markstein number (Ma) and increases the flame tendency towards diffusive-thermal instability (i.e. Ma→0). These results are consistent with the previously reported experimental results for outwardly propagating spherical flames burning a mixture of natural gas and hydrogen.
Dynamics, NOx and Flashback Characteristics of Confined Pre-Mixed Hydrogen Enriched Methane Flames
Authors: Tuncer Onur , Acharya Sumanta , Uhm Jong Ho
Published: March 2009

The operating regime of a gas turbine combustor is highly sensitive to fuel composition changes. In particular, the addition of hydrogen, a major constituent of syngas, has a major effect on flame behavior due to the higher burning rates associated with hydrogen. A laboratory scale pre-mixed test rig is constructed in order to study such effects. The fuel composition is incremented with increasing hydrogen starting from 100% methane. It is observed that increased RMS pressure levels and higher susceptibility to flashback occurs with increasing hydrogen volume fraction. Furthermore, hydrogen enrichment can cause an abrupt change in the dominant acoustic mode. Phase locked hydroxyl PLIF measurements have been performed with respect to the dominant acoustic instability limit cycle. These measurements are complemented with real time heat release, emissions and flashback measurements. Particular emphasis is put on time resolving the thermoacoustic instability induced flashback cycle of the wedgeshaped flame front and the temporal events associated with flashback.
High Rotation Number Heat Transfer of Rotating Trapezoidal Duct With 45-deg Staggered Ribs and Bleeds From Apical Side Wall
Authors: Chang Shyy Woei , Liou Tong-Minn , Chiou Shyr Fuu , Chang Shuen Fei
Published: March 2009

An experimental study of heat transfer in a radially rotating trapezoidal duct with two opposite walls roughened by 45° staggered ribs and mid-rib bleeds from the apical side wall is performed. Centerline heat transfer variations on two rib-roughened surfaces are measured for radially outward flows with and without bleeds at test conditions of Reynolds number (Re), rotation number (Ro) and density ratio (Δρ/ρ) in the ranges of 15000–30000, 0–0.8 and 0.04–0.31, respectively. Geometrical configurations and rotation numbers tested have considerably extended the previous experiences that offer practical applications to the trail edge cooling of a gas turbine rotor blade. A selection of experimental data illustrates the individual and interactive influences of Re, Ro and buoyancy number (Bu) on local heat transfer with and without bleeds. Local heat transfer results are generated with the influences of sidewall bleeds examined to establish heat transfer correlations with Re, Ro and Bu as the controlling flow parameters for design applications.
Performance Analysis of a Reheat Cycle Gas Turbine Based on Measured Data
Authors: Yoon Soo Hyoung , Jeong Dae Hwan , Lee Jong Joon , Kim Tong Seop
Published: March 2009

This study evaluated component characteristics of the reheat cycle gas turbine in a combined cycle power plant. High pressure ratio, sequential combustion, large amount of cooling flow and full utilization of the inlet guide vane distinguishes the engine from simple cycle engines. Considering the detailed engine configuration, performance analysis using an inverse calculation, based on measured performance data, has been carried out to estimate the component characteristic parameters that closely match the measured performance parameters. The measured parameters are power, fuel flow rates of two combustors, and temperatures and pressures at compressor discharge, exits of both high and low pressure turbines. The estimated parameters from the analysis include not only the compressor and turbine efficiencies but also the inlet air flow rate. The analysis has been performed for a wide operation range in terms of ambient temperature and load. Not only the absolute value of the inlet air flow rate but also its variation with the operating condition change correspond very well with the reference data from the manufacturer. The compressor and turbine efficiencies at each full load condition and their variations with the operating condition change were examined. The sensitivity of the estimated parameters to the uncertainties of the measured parameters has also been investigated.
Control of a Three-Pole Hybrid Active Magnetic Bearing With Three Hall Diodes
Authors: Park Sang-Hyun , Lee Chong-Won
Published: March 2009

In this paper, we propose an effective modeling and controller design scheme for the three-pole hybrid-type AMB recently develped in the laboratory, which consists of three permanent magnets, providing bias flux, and three Hall diodes, measuring rotor displacements. Along the three physical coordinates formed by three poles, we introduce the redundant coordinate system to design three identical decoupled controllers. The experiments are also carried out in order to verify the effectiveness of the proposed controller in stabilizing the transient and steady state responses of rotor.
Highly-Loaded Low-Reaction Boundary Layer Suction Axial Flow Compressor
Authors: Wang Songtao , Qiang Xiaoqing , Lin Weichun , Feng Guotai , Wang Zhongqi
Published: March 2009

In order to design high pressure ratio and highly loaded axial flow compressor, a new design concept based on Highly-Loaded Low-Reaction and boundary layer suction was proposed in this paper. Then the concept’s characteristics were pointed out by comparing with the MIT’s boundary layer suction compressor. Also the application area of this design concept and its key technic were given out in this paper. Two applications were carried out in order to demonstrate the concept. The first application was to redesign a low speed duplication-stage axial flow compressor into a single stage. The second one was a feasibility analysis to decrease an 11 stage axial compressor’s stage count to 7 while not changing its aerodynamic performance. The analysis result showed that the new design concept is feasible and it can be used on high pressure stage of the aero-engine, compressor of ground gas turbine (except the transonic stage) and high total pressure ratio blower.
Development of a 150kW Microturbine System Which Applies the Humid Air Turbine Cycle
Authors: Nakano Susumu , Kishibe Tadaharu , Araki Hidefumi , Yagi Manabu , Tsubouchi Kuniyoshi , Ichinose Masaya , Hayasaka Yasushi , Sasaki Manabu , Inoue Tomoaki , Yamaguchi Kazuyuki , Shiraiwa Hiroyuki
Published: March 2009

A prototype machine for a next generation microturbine system incorporating a simplified humid air turbine cycle has been developed for laboratory evaluation. Design targets of electrical output were 150 kW and of electrical efficiency, 35% LHV. The main feature of this microturbine system was utilization of water for improved electrical output, as lubricant for bearings and as coolant for the cooling system of the generator and the power conversion system Design specifications without WAC (Water Atomizing inlet air Cooling) and HAT (Humid Air Turbine) were rated output of 129 kW and efficiency of 32.5% LHV. Performance tests without WAC and HAT were done successfully. Electrical output of 135 kW with an efficiency of more than 33% was obtained in the rated load test. Operation tests for WAC and HAT were carried out under the partial load condition as preliminary tests. Water flow rates of WAC were about 0.43 weight % of inlet air flow rate of the compressor and of HAT, about 2.0 weight %. Effects of WAC and HAT were promptly reflected on electrical output power. Electrical outputs were increased 6 kW by WAC and 11kW by HAT, and efficiencies were increased 1.0 pt % by WAC and 2.0 pt % by HAT. Results of WAC and HAT performance tests showed significant effects on the electrical efficiency with an increase of 3.0 point % and electrical output with an increase of 20% by supplying just 2.4 weight % water as the inlet air flow rate of the compressor.
Benchmarking Diagnostic Algorithms
Authors: Sambasivan Lokesh Kumar , Mukherjee Joydeb , Mylaraswamy Dinkar
Published: March 2009

The problem of fault diagnosis has gained considerable significance in a cost conscious aerospace industry. This has resulted in the development of novel methods as well as novel approaches. Following a cost benefit analysis, wherein a diagnostic algorithm has to buy its way on an aircraft, the practitioner is faced with the difficult problem of choosing the best algorithm from among many candidates. Despite the appeal of multiple algorithm solutions, practical applications are limited by engineering resources—the practitioner is forced to pick few among many. Specifically, this paper addresses this important engineering decision making step. Our approach to evaluating diagnostic algorithms is based on two key elements—non recurring engineering cost and recurring engineering cost. Corresponding to each of these criterions, we define metrics. Since development data is a major cost element, non recurring engineering cost is derived using a metric that measures how well an algorithm has used this data. Recurring cost is measured with respect to the algorithm’s robustness and hence the cost associated with sustaining it. Further, we outline procedures for calculating these metrics, making minimal assumptions regarding algorithm internals; allowing the practitioner to evaluate both in-house as well as third party algorithms. The utility of this benchmarking procedure is illustrated using two sets of examples. One of them is a standard vowel recognition problem, while the second one is related to gas turbine diagnosis. For each of these problems, we evaluate a series of candidate algorithms and illustrate the utility of the proposed approach to filter out weak ones. Concluding sections discuss the use of these procedures for exiting technical feasibility and entering engineering feasibility on the technology readiness level (TRL).
Effects of Impeller Tip Clearance on Centrifugal Compressor Efficiency
Authors: Backman Jari L. H. , Reunanen Arttu , Saari Juha , Turunen-Saaresti Teemu , Sallinen Petri , Esa Hannu
Published: March 2009

The paper describes the results of tip clearance variation experiments in centrifugal compressors. The compressors work at different peripheral Mach number speeds either with vaneless or vaned diffusers. In the experiments, the compressors were operated in a thermally steady state after which the axial positions of the shafts were changed. The changes in the performance of the compressors were recorded and analyzed. The clearance between the impeller and its housing affects the efficiency of the centrifugal compressor. The clearance is optimized to adapt to various phenomena: thermal expansions, impeller tip deflections, shaft bending and gyroscopic motions. The compressors of this study are equipped with active magnetic bearings. They contain a control system, which constantly measures and controls the position of the shaft. This gives useful information about impeller clearance variation, and the measured results are precise within 1/100 millimeters.
Optimization of the Gas Turbine Engine Parts Using Methods of Numerical Simulation
Authors: Kuzmenko M. L. , Egorov I. N. , Shmotin Yu. N. , Fedechkin K. S.
Published: March 2009

Modern computer technologies now allow us to conduct rather complex mathematical calculations in a relatively short period of time. Thus, it has become possible to employ optimization methods in the design of various parts of aircraft engines, even when calculations require large computational resources (structural, thermal, and gasdynamics calculations). The designer may have to vary more than a hundred design variables and constraints during the optimization process. Therefore the procedure of preparing the initial data for optimization may take a long time. That is why we developed the optimization software system for designing turbomachines and their parts. This software system includes the IOSO optimization procedure and modules of automatic data preparation and handling. The data is represented in the format that is convenient and understandable for a designer. The optimization procedure is based on the response surface methodology, when response surfaces are constructed for objective functions and constraints and then optimized at each iteration in a current search region. The objective function and constraints are then evaluated at the optimal point using the mathematical model of the system under consideration. As the analysis tools the well-known commercial software package (FINE/Design3D) is used. The paper presents the results of optimizing a three-stage axial compressor. The optimization goal was to improve the compressor efficiency at two flight conditions by optimizing geometry of the 5 compressor rows (62 design parameters).
Computational Analysis of Scroll Tongue Shapes to Compressor Performance by Using Different Turbulence Models
Authors: Xu Cheng , Amano R. S.
Published: March 2009

A scroll is used to collect and transport swirling fluid produced by impeller or diffuser. Scroll or volute is one of the key components of centrifugal compressors. Design of the scroll not only impacts compressor efficiency but also influences operating range of the compressor. In this study, navier-stokes equations combined with both an zero-equation turbulence model and the k-ε turbulence model were used to simulate the flows inside a single stage compressor. Detailed flow simulations for a large cut back tongue scroll were presented and discussed. Studies showed that a large cut back rounded tongue scroll provided good operating range without dropping compressor peak efficiency dramatically. The turbulence model influences to the calculation were discussed and some suggestions for scroll flow modeling were made. The numerical results obtained using two turbulence models were compared and showed agreement reasonably well with experiments. Although the k-ε model behaves well inside the boundary layer, it was not decisively better than the zero-equation model for the performance predictions.
Computation of Unsteady Flowfield and Blade Response Due to Impeller-Diffuser Interaction
Authors: Srivastava R. , Lentz J. , Liu J. S. , Panovsky J.
Published: March 2009

Numerical analysis of a modern centrifugal compressor is carried out to calculate the high strains observed during testing at overspeed condition. Three-dimensional, viscous, time accurate, CFD analysis of the centrifugal compressor stage is carried out to obtain the unsteady forces on the impeller blades due to impeller-diffuser interaction. Analysis showed a strong interaction between the impeller and the diffuser with periodic shock impingement on the impeller pressure surface. The unsteady forces were found to be largely limited to last 20 percent of the impeller meridional chord. Strain calculations were carried out by applying the 1st harmonic of the diffuser blade count of the unsteady pressures and using ANSYS to perform a sweep through the frequencies of interest. It was found that the impeller mode shape contained a 25 nodal diameter vibration mode in the frequency of interest which was excited by the pressure waves from the 25 count diffuser resulting in high resonant stresses. Analysis also showed a strong interaction between various system modes. The response was found to be very sensitive to this interaction. Utilizing this interaction, an analytical redesign of the impeller predicted significantly reduced blade response.
Technical and Economic Assessment of Small to Medium Scale Bio-Ethanol Distilleries With Cogeneration Systems
Authors: Gonza´lez-Salazar Miguel Angel , Willinger Reinhard
Published: March 2009

This investigation presents an assessment of the potential use of sugar cane to support sustainable development in Colombia with a particular focus on devising ways of supplying electricity to regions without service (about 1.8 million people and 66% of the territory). The goal of this study is to evaluate the technical and economic feasibility of using small to medium scale modern technologies to exploit the co-production of two of the major forms of energy that can be derived from the sugar cane plant: ethanol (by fermentation and distillation of the cane juice) and electricity (by cogeneration of bagasse). The market potential for ethanol, electricity and carbon credits (for associated emissions reduction) is examined and a site selection analysis is performed to decide the most suitable location within the Non-Interconnected Zones (NZI) in Colombia. Development scenarios are constructed and analyzed in the context of the markets identified, combining different alternative technologies. Production costs of sugar cane, investment costs, operating costs, labour costs and maintenance costs are estimated for each development scenario, and economic and financial characteristics are quantified and compared, to determine which options are the most attractive. The study identifies that the key factors which affect the feasibility of distilleries with CHP systems in Colombia are: 1) specific location and conditions, 2) type of technologies used, efficiencies and maximum capacities of production, 3) total investment costs, 4) incomes for ethanol, electricity and emissions reduction and 5) national and global incentives.
Innovative Design of a Robust Turbine Stage Using Flow Analysis and Subcomponent Rig Testing With Rapid Prototypes
Authors: Kielb Jason , Weber Kurt , Crook Bruce
Published: March 2009

Designing turbine engine components for high cycle fatigue robustness can significantly reduce operating costs and improve safety. However, obtaining an optimum design and getting the new hardware into service using traditional methods is an expensive process. A process that combines state-of-the-art computational fluid dynamics (CFD) analytical simulations with subcomponent rig testing has been developed and demonstrated on a gas turbine engine. The analytical method involves spatial Fourier decomposition of vane exit total pressure from steady flow calculations. This provides an efficient method to reduce the design space and eliminate poor designs, resulting in a small subset of near-optimum designs. To confirm that the remaining candidate designs provide less unsteady forcing and to validate the CFD analysis, a unique experimental test rig was constructed. The experiments consisted of flowing ambient air through a subsection of the engine, while measuring the exit total pressure flow field around the turbine rotor exit annulus with a unique traversing probe. The measured exit total pressure was then Fourier decomposed in space to understand the resulting unsteady forcing on the blade. The costs of the flow rig and producing numerous sets of candidate hardware were much less expensive than full-scale engine or rotating rig tests. New hardware designs tested in the rig were manufactured using a rapid prototyping procedure, which allowed for extremely quick turn around in going from design concept to experimental validation. Good correlation between analysis and test was found, except in a few cases. The majority of these discrepancies were attributed to excitation sources that were impractical to include in the CFD models. This finding indicated that there are still circumstances for which the analytical tools were insufficient and hence experimental validation is still important. Both the analysis and experiments confirmed up to a 50% reduction in the amplitude of unsteady pressure for this particular engine test case.
Effect of Temperature Ratio on Jet Array Impingement Heat Transfer
Authors: Goodro Matt , Park Jongmyung , Ligrani Phil , Fox Mike , Moon Hee-Koo
Published: March 2009

Considered are the effects of temperature ratio on the heat transfer from an array of jets impinging on a flat plate. At constant Reynolds number of 18000, and constant Mach number of 0.2, different ratios of target plate temperature to jet temperature are employed. The spacing between holes in the streamwise direction X is 8D, and the spanwise spacing between holes in a given streamwise row Y is also 8D. The target plate is located 3D away from the impingement hole exits. Experimental results show that local, line-averaged, and spatially-averaged Nusselt numbers decrease as the Tw/Tj temperature ratio increases. This is believed to be due to the effects of temperature-dependent fluid properties, as they affect local and global turbulent transport in the flow field created by the array of impinging jets. The effect of temperature ratio on crossflow-to-jet mass velocity ratio and discharge coefficients are also examined.
Thermoeconomic Optimization of Heat Recovery Steam Generators
Authors: Sanaye Sepehr , Hamidkhani Omid , Shabanian Mostafa , Espanani Rohollah , Hoshyar Abdolreza
Published: March 2009

The combined cycle power plant (CCPP) is one of the efficient power producing technologies which includes both Brayton (topping) and Rankine (bottoming) cycles. The optimal design of heat recovery steam generator (HRSG) as an important part of a CCPP is a subject of interest. In this paper a thermoeconomic analysis has been applied to optimally design HRSGs in a combined cycle power plant. Two arrangements of heating elements are studied here. The method consists of both developing a simulation program and applying the Genetic Algorithm optimization scheme. The total cost per unit produced steam exergy was introduced as the objective function which included, capital or investment cost, operational cost, and the corresponding cost of the exergy destruction. The objective function per unit of produced steam exergy was minimized while satisfying a group of constraints. The decision variables (or design parameters as well as pinch point temperatures, pressure levels and, mass flow rates) are obtained. The variations of design parameters as well as the exergy efficiency and the total cost with the inlet hot gas enthalpy are shown.
System Identification of Multistage Turbine Engine Rotors
Authors: Song Sang Heon , Castanier Matthew P. , Pierre Christophe
Published: March 2009

Recently, an efficient approach for modeling the vibration of multistage rotors was developed by the authors [1, 2]. This reduced-order modeling technique employs component mode synthesis, with each stage (bladed disk) treated as a separate component. In addition, the component mode mistuning (CMM) projection technique was extended to multistage systems. In the CMM method, individual blade mistuning is transformed from a basis of cantilevered blade modes to the basis of tuned system modes used for the reduced-order model. In this paper, the component-based modeling framework developed for mistuned multistage turbine engine rotors is utilized for system identification. First, the identification of multistage mode types is considered. Strain energy ratios are used to identify which system modes are confined to mostly one stage and which modes show strong coupling among multiple stages. Simple approximations for these ratios are derived based on data from the component-level free response analysis that are performed during the model construction process. The component-level results are also utilized to identify the dominant nodal diameter number for each multistage mode, even though the multistage system does not possess cyclic symmetry because the stages have different numbers of blades. Second, the modes are further classified as to how much the blades participate in the response relative to the disk for each stage. As a systematic identification procedure, this is applicable to single-stage models as well. For multistage systems, this is used to determine operating conditions where coupled response among blades on adjacent stages is most likely to occur. Third, the application of mistuning identification techniques to multistage systems is considered. It is found that the proposed modal classification methods allow the determination of conditions under which deviations in individual blade properties may be observed indirectly from measurements of the disks and spacer.
Combustion Performance of Liquid Bio-Fuels in a Swirl-Stabilized Burner
Authors: Sequera Daniel , Agrawal Ajay K. , Spear Scott K. , Daly Daniel T.
Published: March 2009

Fuels produced from renewable sources offer an economically viable pathway to curtail emissions of greenhouse gases. Two such liquid fuels in common usage are biodiesel and ethanol derived from soybean, corn or other food crops. In recent years, significant effort has been devoted to identify alternate feedstock sources and conversion techniques to diversify the biofuels portfolio. In this study, we have measured emissions from flames of diesel, biodiesel, emulsified biooil, and diesel-biodiesel blends. Experiments are conducted in an atmospheric pressure burner with an air-atomized injector and swirling primary air around it to replicate typical features of a gas turbine combustor. Experiments were conducted for fixed air and fuel flow rates, while the airflow split between the injector and the co-flow swirler was varied. Results show a significant reduction in emissions as the fraction of total air fed into the atomizer is increased. Blue flames, reminiscent of premixed combustion and low emissions of nitric oxides and carbon monoxide were observed for all fuel blends. In general, the emissions from bio-fuel flames were comparable or lower than those from diesel flames.