bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Bubble Size on the Microbubble Drag Reduction of a Turbulent Boundary Layer
Authors: Kawamura Takafumi , Moriguchi Yasuhiro , Kato Hiroharu , Kakugawa Akira , Kodama Yoshiaki
Published: February 2009

Three different methods have been investigated for generating microbubbles to control the bubble diameter separately from the main flow velocity. The first two methods achieve this by adjusting the local shear stress where bubbles are generated, while the third method uses foaming of dissolved air to generate very small bubbles. The average diameter of bubbles was successfully controlled by the first two method within the range of 0.5–2 mm for the fixed main flow velocity of U = 3 m/s, while the very small bubbles of 20–40 μm were generated by the third method. The influence of the bubble diameter on the frictional drag reduction was found to be insignificant for the diameter range of 0.5–2 mm, while we also obtained experimental results suggesting that smaller bubbles on the order of 10 μm in diameter can be effective for the drag reduction.
MEMS-Based Electrolytic Microbubbler in a Water Channel
Authors: Lee S. , Sutomo W. , Liu C. , Loth E.
Published: February 2009

This study investigated the development of microbubble injection using a MEMS-based electrolytic device capable of generating small bubbles introduced with nearly zero injection velocity. Three generations of electrolytic microbubblers with gold electrodes and photoresist (PR) as an insulator were fabricated. The objective for the first-generation microbubbler was to understand the influence of voltage and flow speed. The goal of the second-generation microbubbler was to understand the influence of electrode area and spacing, the distance between the cathode and anode. The purpose of the third generation device was to investigate the effect of electrode shape as well as further reduction in the size and spacing of the electrodes. Measurements of the sizes of the bubbles and the bubble generation rates of a first-generation device in a square water channel at different voltages and under different flow conditions were taken. At all but the lowest applied voltage, more than 65% of the observed bubbles were less than 50 μm in diameter. As the applied voltage was increased, the mean bubble diameter and the variation from the mean decreased while bubble generation rates increased. As the flow increased, mean bubble diameter and the deviation from the mean decreased as well. For the second-generation devices, the largest mean bubble diameter and smallest percentage of bubbles smaller than 50 μm occurred at an intermediate value of the ratio between the electrode size and the electrode spacing of approximately 0.7. For the third generation devices, increased detachment frequency occurred with the circular geometries, compared to triangular or square node shapes. The minimum allowable spacing between two electrodes to avoid coalescence was approximately 1.5 times the electrode diameter.
Void Fraction Measurement in the Boundary Layer of Training Ship Seiun-Maru
Authors: Kato Hiroharu , Ikemoto Akihiko , Toda Yasuyuki
Published: February 2009

The full-scale experiment of microbubbles was performed using the training ship Seiun-Maru in 2001. The void fraction was successfully measured in the turbulent boundary layer under the bottom surface, using an optical void measurement device developed by the authors. The void distribution had a peak in the region 5–10mm from the hull surface. The device also could be used to measure the bubble size distribution. The number-averaged bubble diameter was about 0.5mm.
Boundary Layer Studies on Polymer Drag Reduction Using PIV and PLIF
Authors: Somandepalli V. S. R. , White C. M. , Mungal M. G.
Published: February 2009

The structure of turbulence in a drag reduced flat plate boundary layer has been studied with particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF). Drag reduction was achieved by injection of a solution of water-soluble polymer through a spanwise slot near the leading edge of the flat plate. Velocity and concentration data were obtained using PIV and PLIF, respectively, in planes parallel to the wall (x-z plane) and perpendicular to the wall (x-y plane). Measurements of velocity, vorticity and streak spacing were obtained and trends analyzed. For increasing drag reduction, damping of streak oscillations, suppression of streak splitting and merging, streak stabilization and coarsening of the low speed streaks was observed. PLIF measurements of the injected polymer solution showed that regions of high polymer concentration are correlated with the low speed streaks. PIV measurements in the x-y plane showed that there are significant differences in the statistics of turbulence between boundary layers with polymer injection and channel flow with an ocean of polymer.
CFD Simulation of Single-Phase and Dilute Particulate Turbulent Flows in 90° Duct Bends
Authors: Kuan Benny T. , Schwarz M. Philip
Published: February 2009

Single-phase and two-phase (gas-solid) turbulent flow calculations are performed for 90° duct bends having radii of curvature ranging from 1.5 to 2.0 duct diameter, and with either a square or circular cross-section. The considered flow Reynolds number is between 6×104 and 3×105, and the particulate flows examined pertain to two different solid mass loading ratios: 1.5×10−4 and 0.33. Numerous turbulence models have been utilized to simulate the turbulent fluid motion within the duct bend while particle trajectories are calculated on the basis of a Lagrangian approach. Reasonable agreement with the experimental data is achieved for the continuous phase in the cases tested. In contrast, significant disparities with the measurements arise in particle tracking calculations, especially in regions where particle rope dispersion is predominant. Results of this investigation indicate the need for more experimental testing of mill-duct flows of similar configuration in order to facilitate a better understanding and modeling of strongly curved gas-solid duct flows.
Simulation of Altitude Influence on Piston Ring Movement and Blow-By Effects in Piston Engines (Keynote)
Authors: Abanteriba Sylvester
Published: February 2009

The compression and oil rings of the piston engine play a very important role in the performance and reliability of the piston engine. The rings are required to accomplish three main distinct tasks: 1. Sealing the combustion chamber gas from the crankcase to eliminate blow-by phenomenon, which constitutes the flow of some of the contents of the combustion chamber into the crankcase. 2. Proper distribution of the lubricating oil film over the piston skirt and cylinder liner. 3. Transfer of heat from piston to cylinder liner. Unfortunately the piston ring pack contributes to the highest proportion of the frictional losses in the engine and is more prone to high wear rates. In the engine, the compression rings are designed to provide effective sealing of the crankcase against the gases from the combustion chamber. The oil-rings provide an effective means of distributing the lubricating oil over the cylinder liner while keeping it from flowing into the combustion chamber. The ability of the compression rings to serve as a gas seal depends on their axial position within the groove. The ring needs to be in contact with the lower flank in order to provide the requisite sealing effect. Once the ring lifts itself from the lower flank its ability to act as an effective seal is compromised. The axial motion of the piston rings during the operation of the engine engenders blow-by and therefore has deteriorating effect on the engine performance. Not much work has, hereto, been done to study the impact of altitude on the movement of the piston rings and hence the blow-by phenomenon. This papers presents a simulation model to investigate this effect.
Experimental Study of a Constant-Area Ejector With Two-Phase Fluids
Authors: Bray J. A. , Lear W. E. , Sherif S. A.
Published: February 2009

The authors are presently involved in developing a design code to optimize an active space thermal management system that includes as a key component an ejector, which operates with fluids in the two-phase regime. In order to validate this code, and for other applications of two-phase ejectors, a comprehensive experimental data set is needed for this device. This paper deals with the conceptual design and implementation of a constant-area ejector experimental rig intended to provide the required data set. The system has been designed to implement the same thermodynamic cycle as the proposed thermal management system, allowing a preliminary performance database to be developed upon testing, in addition to the ejector data. The ejector itself will be an interchangeable part in this system, allowing geometrical variables to be manipulated.
Calvin W. Rice Lecture 2002: Two-Phase Oxymoron
Authors: Bataille J. , Lance M.
Published: February 2009

Mr. Chairman, Ladies and Gentlemen, Dear Colleagues: Mr. Chairman!... I am aware of the fact that this is French-speaking Canada, but this particular plenary lecture is associated with an American award. Accordingly, may I take the First Amendment and claim Freedom of Speech — within very reasonable limits, of course! In other words, may I impose a somewhat special sort of plenary lecture on the audience? Thank you, Mr. Chairman !
Comparison of Recent Model Equations for Particle Deposition in a Turbulent Boundary Layer With Those Based on the PDF Approach
Authors: Reeks Michael W.
Published: February 2009

Comparisons are made between the Advection-Diffusion Equation (ADE) approach for particle transport and the two fluid model approach based on the PDF method. In principal the ADE approach offers a simpler way of calculating the inertial deposition of particles in a turbulent boundary layer than that based on the PDF approach. However the ADE equations that have recently been used are only strictly valid for a simple Gaussian process when particle inertia is small. Using a prescribed but in general non-Gaussian random particle velocity field, it is shown that the net particle mass flux contains an extra drift term to that from the mean velocity of the particle velocity field, associated with the compressibility of the velocity field. Furthermore the diffusive flux in general depends not only upon the gradient of the mean concentration (true only for a Gaussian random flow field) but also upon higher order derivatives whose relative contribution depends on diffusion coefficients Dijk... etc. These coefficients depend upon the statistical moments associated with random displacements and compressibility of the particle flow field along particle trajectories which in turn depend upon particle inertia. In contrast the PDF approach offers the advantage of using a simple gradient (Gaussian) approximation in particle phase space which can lead to a non-Gaussian spatial dispersion process when particle inertia is important. Conditions based on the particle mean free path are derived for which a simple ADE is appropriate. Some of the features of particle transport in an inhomogeneous turbulent flow are illustrated by examining particle dispersion in a random flow field composed of pairs of counter rotating vortices which has an rms velocity which increase linearly from a stagnation point.
Large Eddy Simulation of a Particle-Laden Turbulent Backward-Facing Step Flow
Authors: Wang Bing , Zhang Hui-Qiang , Wang Xi-Lin , Guo Yin-Cheng , Lin Wen-Yi
Published: February 2009

Numerical simulations of the two-dimensional backward facing step gas-particle turbulent flow are reported. Both the evolution of large eddy coherent structures in spatially and temporally and the vortex-particle interactions are researched. Effects of the particle Stokes number and the initial two-phase velocity slip on the instantaneous concentration distribution of the particles with and without the influence of gravity are discussed. Continuous phase simulation is performed by the method of large eddy simulation (LES) while the particle phase is solved by a Lagrangian method. Simulations of the gas phase reproduce the character of the separation and reattachment flow and the essential features of the coherent structures. It is shown that the vortex structures become extraordinary abundant and complex under the high Reynolds number. Further more, the simulation shows the initial two-phase velocity slip plays an important role in enforcing particle dispersion and sharply changes the instantaneous particle distribution under the different particle Stokes numbers. Even more, results demonstrate the influence of gravity on particle dispersion and sedimentation. Such pronounces effect of gravity on instantaneous concentration of particles with increased Stokes number and initial slip coefficients emphasize the need for the consideration of gravity for horizontal particle-laden flow. Either the continuous phase results or particle phase results obtained from LES agree well with the experiment data both in quantitative and qualitative.
Computer Modeling and Experimental Verification of Mold Filling in Counter-Gravity Lost Foam Casting Process
Authors: Bakhtiyarov Sayavur I. , Overfelt Ruel A.
Published: February 2009

A dynamics of the molten metal-polymeric foam interface has been experimentally observed in “window counter-gravity lost foam casting” of standard GM plates. The observations allowed revealing the effect of the pyrolisis of polymeric foam material on molten metal propagation velocity. FLOW-3D software (Flow Science, Inc.) has been used to simulate liquid metal filling dynamics and the molten metal-polymeric foam interface velocity in foam plates. The effect of the degradation gaseous products on the molten metal-polymeric foam interface velocity was taken into consideration through specially written sub-routing program. The results of the simulations are compared with the experimental data obtained in this study.
Theoretical and Experimental Characterization of Emulsion Flow in a Cavity Transfer Mixer
Authors: Raza A. H. , Lai-Fook R. A. , Lawrence C. J.
Published: February 2009

A theoretical model of time-dependent flow based on Reynolds equation using emulsion processing in a Cavity Transfer Mixer (CTM) has been developed in Mathematica and is presented in this work. It is a continuum model, which allows the study of materials undergoing rapid deformation. The flow of a fluid in a CTM is examined using a finite difference analysis (FDA) to solve the flow equations for an unwound section with cavities arranged in a rectangular pattern. Periodic boundary conditions are included in the model to predict the pressure distribution, which allows subsequent determination of the flow field. The solution procedure gives a smooth function for the pressure field, with equal pressures at the boundaries in the y-direction and an overall mean pressure gradient in the x-direction. Once the pressure has been found, several flow properties follow directly. The flow in the downstream axial direction is seen to consist of purely pressure-driven flow. In contrast, the flow in the cross-cavity direction is a recirculating flow driven by the drag velocity of the moving rotor surface. These two flows taken together combine into a helical flow travelling through the cavity. Because of this, there is likely to bre a high degree of laminar and distributive flow in this type of machine. The experimental part of this work addresses the processing of an emulsion in the CTM when it is run under batch and continuous modes of operation. The flow characteristics have been studied for varying rotor speeds of 0 rpm, 16 rpm, 32 rpm, 48 rpm and 64 rpm. Also studied were the changes that the emulsion exhibits along the mixer length and with time in the mixer. The experiments indicate that increase in the rotational speed causes the viscosity to reduce systematically in both batch and continuous modes of operation.
Development of the Exhaust Systems Radiation Noise Simulation Technology
Authors: Sakurai Masato , Endo Masaki , Perie Fred
Published: February 2009

The purpose of this paper is to present a Finite Element method able to simulate and predict exhaust radiation noise. The simulation takes into account fluid flow pulsation, aeroacoustic noise sources; flow induced structural vibration as well as noise radiation in the far field. All those phenomena are directly calculated in a fully coupled manner. By applying measured values at the model inflow, accurate radiation noise from the exhaust system is obtained. Locations of noise sources as well as mechanisms of noise generation are clarified. The method enables the investigation of exhaust noise radiation at early development stages. The use of semiconductor pressure sensors with 1-MHz sampling as well as Laser Doppler Velocimetry contributed greatly to the measurement accuracy required for the definition of inflow conditions.
A Study of Flow Field in Vacuum Ejector Driven by Air
Authors: Endo Masaki , Iwamoto Junjiro
Published: February 2009

A vacuum ejector driven by the air is used for handling the products in industries. The flow field in the ejector is tiny and its flow pattern very complicated, and moreover the main jet is supersonic and noisy. In this paper, the flow field is analyzed using the method of water table analogy and the results are compared with the numerical simulation. Additionally, the similarity is discussed, of the flow in the ejector with that in the channel with an abrupt area enlargement.
Dynamics of Bubbles Rising in Finite and Infinite Media
Authors: Maneri Charles C. , Vassallo Peter F.
Published: February 2009

The dynamic behavior of single bubbles rising in quiescent liquid Suva (R134a) in a duct has been examined through the use of a high speed video system. Size, shape and velocity measurements obtained with the video system reveal a wide variety of characteristics for the bubbles as they rise in both finite and infinite media. This data, coupled with previously published data for other working fluids, has been used to assess and extend a rise velocity model given by Fan and Tsuchiya. As a result of this assessment, a new rise velocity model has been developed which maintains the physically consistent characteristics of the surface tension in the distorted bubbly regime. In addition, the model is unique in that it covers the entire range of bubble sizes contained in the spherical, distorted and planar slug regimes.
Experiments in Active Stall Control of a Twin-Spool Turbofan Engine
Authors: Leinhos Dirk C. , Scheidler Stephen G. , Fottner Leonhard , Grauer Frank , Hermann Jakob , Mettenleiter Manuel , Orthmann Armin
Published: February 2009

The aerodynamic stability of aero engine compressors must be assured by active control systems in all operating conditions when the design surge margin is reduced in order to improve efficiency. While this has been investigated only on compressor rigs and single-spool engines in the past, this study focuses on the active control of the LARZAC 04 twin-spool turbofan. The objective is to demonstrate potential benefits, problems and solutions and also to provide a data base for numerical modeling and simulation of the capabilities of active control. Three different control strategies have been employed each of which refers to a specific operating condition and instability inception of the engine: The attenuation of disturbances travelling at rotor speed by modulated air injection into the LPC in the high speed range, the recovery of fully developed LPC stall at low speeds with a minimized amount of air and finally a constant air recirculation (HPC exit to LPC inlet) for stabilizing the compression system at different speeds based on the monitoring of a stability parameter. The injector is mounted upstream of the LPC and has ten circumferentially distributed nozzles for air injection into the tip region of the first rotor. The injected air which is either taken from an external source or from bleed air ports at the HPC exit is controlled by high-bandwidth direct-drive-valves. Disturbances travelling at rotor speed can be detected and attenuated with modulated air injection leading to a delay of stall onset. Fully developed rotating stall in the LPC was eliminated by asymmetric injection based on modal control strategies with less air than needed with constant air injection. By using online-stability-monitoring it is possible to initiate constant air recirculation when approaching the surge line, though the current design of the injector does not allow for large extension of the operating range for all spool speeds.
A Method for On-Line Temperature Calculation of Aircraft Engine Turbine Discs
Authors: Botto D. , Zucca S. , Gola M. M. , Salvano S.
Published: February 2009

On-line calculation methods are currently used to evaluate stress and temperature of engine components in order to assess fatigue damage accumulation and residual life. On-line temperature calculation algorithms are necessary because temperature affects fatigue damage curves. Since it is neither possible nor necessary to compute on-line temperature on the whole component, a number of critical nodes are selected and their temperatures are evaluated with simplified algorithms. A well-known technique used to reduce the degrees of freedom of dynamic structural FE models is the component modes synthesis (CMS). By this technique the nodal degrees of freedom are divided into two sets: active and omitted. Active degrees of freedom are translated into the reduced model, while omitted ones are replaced by the most important modal shapes, in order to evaluate the dynamic behavior of the system. In the present work CMS has been applied to thermal transient analyses, in order to compute temperatures in low-pressure turbine discs critical areas. Due to the complexity of the geometry, the disc has been sub-structured into super-elements. The methodology has been tested on axi-symmetric FE model of a low-pressure turbine disc, comparing thermal transients performed by complete FE model with those evaluated by the sub-structured model.
MBM (Meat and Bonemeal) Co-Gasification in IGCC Technology
Authors: Garci´a-Pen˜a Francisco , Mun˜oz-Mozos Alejandro , Casero-Cabezo´n Pedro
Published: February 2009

The potential use of MBM (Meat and Bone Meal) as fuel in a power plant has been recently originated by the mad cow disease, affecting not only Europe (the origin of the disease) but also other continents. MBM manufacturing companies have been forced to change their traditional ways of distribution due to the current ban of using MBM as cattle feed, therefore using a dumping site or an incinerator. To be considered as a fuel, several studies should be carried out. Preliminary characterisation of MBM showed a heating value higher than existing in coal, and a grain size acceptable to be mixed with regular fuel, hence appropriate to be brought into a boiler or a gasifier. Additionally, an expected advantage of using MBM in a gasification process was the possibility of using it as adequate slag/ash fusion agent (instead of traditional limestone), due to the high presence of Ca compounds. Related to environmental issues, the conventional thermal oxidation process (like incineration) shows several inconveniences, associated to the presence of hazardous compounds (like furans and dioxins) expected in organic matter combustion. There are few references of the existence of this kind of compounds in gasification process, but it is known that the existing reducing environment in a gasifier does not benefit its formation at all. Some of these issues were analysed in short duration full-scale tests developed in Puertollano IGCC Power Plant, owned by ELCOGAS, in which several MBM/regular fuel mixtures were tested. This paper describes the methodology used in these tests, fuel characteristics, main systems performance, and general conclusions about the viability of IGCC co-gasification using alternative fuels.
Performance Monitoring on the A˚sgard “A” FPSO as Part of an Integrated Monitoring Strategy
Authors: So̸rli Arne , Langnes Kyrre , Laagland Geert , Hastings Mike
Published: February 2009

An integrated machine condition monitoring system was developed, installed, tested, commissioned and successfully operated on a floating production, storage and offloading vessel (FPSO) in the North Sea. This system combines an existing vibration and process monitoring system with focused performance monitoring capability that has been implemented with the cooperation of the oil company end-user, a thermodynamics specialist consultant and a monitoring system supplier. Implementation of this integrated monitoring system strategy with advanced performance monitoring is partly based on the end-user’s requirements to optimize their operation and maintenance functions to improve competitiveness. The system has already been in use for one year and has demonstrated the ability to detect faults at an early stage of development, such as the compressor degradation and gas turbine fouling described in this paper. The same system has also been implemented in other oil & gas and power applications around the world with similar, positive results.
Gas Turbine Data Validation Using Gas Path Analysis
Authors: Escher Patrick C.
Published: February 2009

A new method for the data validation of gas turbines is introduced that allows to assess engine degradation. The degree of degradation is derived from the analytical method of Gas Path Analysis (GPA). The method, built on GPA, allows to isolate faulty measurements. The method repeatedly estimates degradation from a set of measurement values. By systematically excluding measurement values from the calculation, differing estimations are evoked which indicate faulty measurement sets. The procedure also allows to distinguish between state changes and measurement errors in an easy fashion.
Study of the Optimisation of Measurement Sets for Gas Path Fault Diagnosis in Gas Turbines
Authors: Ogaji S. O. T. , Singh R.
Published: February 2009

The reliability of the gas path components (compressor, burners and turbines) of a gas turbine (GT) is usually high when compared with other GT systems such as fuel and control. However, their availability could be relatively low as high downtimes are normally associated with these components when subjected to forced outages. One way of improving availability is by improved maintenance practices that involve applying such approaches as condition based monitoring (CBM). Unfortunately, this cannot be achieved without the existence of a proper instrumentation set that can adequately and repeatedly track down the levels of deterioration in these components, thereby allowing for optimally scheduled maintenance. Different engine handles (operating point or parameter that is held constant with respect to other parameters) would require different instrumentation sets for proper gas path fault diagnosis. Sometimes, the instrumentation sets used makes the required diagnostic analysis impossible. Furthermore, allowing redundancy in instrumentation, unless specified with knowledge of the diagnostic technique to be used, is not only unnecessary but also cost ineffective. The central theme of this paper is to present a means of attaining an optimum instrumentation set using a non-linear gas path analysis (NLGPA) programme. Firstly, some of the common gas path faults are considered, some theoretical backing is given to the principles involved in this work, the implications of unoptimised instrumentation set as viewed from the users’ perspective is examined and finally, results presented for the NLGPA approach when applied to a two-shaft and a three-shaft industrial gas turbine. Also, we show how the engine handle can affect the choice of the instrumentation set.
Measurements of Equivalence Ratio Fluctuations in a Lean Premixed Prevaporized (LPP) Combustor and Its Correlation to Combustion Instability
Authors: Nguyen Quang-Viet
Published: February 2009

Experimental evidence correlating equivalence ratio fluctuations with combustion instabilities and NOX emissions in a jet-A fueled lean premixed prevaporized (LPP) combustor utilizing a non-proprietary ‘generic’ fuel injector is presented. Real-time laser absorption measurements of equivalence ratio, together with dynamic combustor pressure, flame luminosity and fuel pressure were obtained at inlet air conditions up to 16.7 atm and 817 K. From this data, an extensive database of real-time variables was obtained for the purposes of providing validation data for future studies of LPP combustion modeling. In addition, time and frequency space analysis of the data revealed measurable levels of acoustic coupling between all variables. Equivalence ratio and dynamic pressure cross-correlations were found to predict the level of combustion instability. Furthermore, NOX production was found to follow the root-mean-square (RMS) flame luminosity and RMS combustor dynamic pressure. However, the unmixedness of the fuel-air mixture was not found to predict NOX production in this combustor. The generic LPP injector, although not optimized for low-emissions or combustion stability, provides some of the essential features of real injectors for the purposes of studying the relationship between fluctuations in equivalence ratios and combustion instability. In particular, the fuel premixer advection time was found to have a significant and direct impact on the level of combustion instability. The results of this work support the time-lag concept for avoiding combustion instability when designing injector/premixers in LPP combustors.
Active Control of Combustion Dynamics for Lean Premixed Gas Fired Systems
Authors: Anson B. , Critchley I. , Schumacher J. , Scott M.
Published: February 2009

The present paper describes an active control system consisting of a fast-acting actuator valve, coupled with a control algorithm capable of adaptive phase and amplitude control for pressure oscillation suppression. Experiments were conducted using two separate combustion test rigs: a small, lean premixed, tubular combustor (75 kW) and a larger premixed annular DLE system (4 MW). Active control of pressure oscillations at frequencies of approximately 90 Hz and 300 Hz was demonstrated on the 75 kW rig. Up to 90% reduction in single-frequency dynamic pressure amplitude and 70% reduction in peak-mean was achieved. Simultaneous suppression of these two distinct modes was also demonstrated. The system was also demonstrated on a full-scale 4 MW combustion rig, with peak-mean dynamic pressure reductions between 33–45%. Instability reductions were achieved by pulsing fuel supplied to either a diffusion or a premixed flame. The response of the flame was notably better for the premixed case. For the premixed flame, combustor pressure pulses were realizable up to a frequency of about 400Hz, while the diffusion flame could only induce combustor pressure pulses up to approximately 50Hz. Adaptive frequency, phase and amplitude logic were developed, allowing automatic selection of the optimal values of these parameters to maximize suppression efficacy to suit the particular operating condition.
High Power Density Silicon Combustion Systems for Micro Gas Turbine Engines
Authors: Spadaccini C. M. , Lee J. , Lukachko S. , Waitz I. A. , Mehra A. , Zhang X.
Published: February 2009

As part of an effort to develop a micro-scale gas turbine engine for power generation and micro-propulsion applications, this paper presents the design, fabrication, experimental testing, and modeling of the combustion system. Two radial inflow combustor designs were examined; a single-zone arrangement and a primary and dilution-zone configuration. Both combustors were micro-machined from silicon using Deep Reactive Ion Etching (DRIE) and aligned fusion wafer bonding. Hydrogen-air and hydrocarbon-air combustion was stabilized in both devices, each with chamber volumes of 191 mm3. Exit gas temperatures as high as 1800 K and power densities in excess of 1100 MW/m3 were achieved. For the same equivalence ratio and overall efficiency, the dual-zone combustor reached power densities nearly double that of the single-zone design. Because diagnostics in micro-scale devices are often highly intrusive, numerical simulations were used to gain insight into the fluid and combustion physics. Unlike large-scale combustors, the performance of the micro-combustors was found to be more severely limited by heat transfer and chemical kinetics constraints. Important design trades are identified and recommendations for micro-combustor design are presented.
Design of High Performing Duct-Burners for Combined-Cycle Plants Using Progressive Optimization
Authors: Catalano L. A. , Dadone A. , Manodoro D.
Published: February 2009

A general efficient strategy for the design optimization of duct-burners for combined-cycle plants is presented. This methodology combines a widely employed commercial code, used for the flow analysis, with a progressive optimization strategy, whose efficiency relies on the simultaneous convergence of both the flow solution and the optimization process, as well as on the use of progressively finer grid levels. The proposed strategy has been initially tested versus two inverse design examples with known solutions; then, it has been employed to flatten the outlet thermal profile of a new enhanced-mixing after-burner. The presented results show that the overall optimization process requires a computational time compared to that required by 5 ÷ 14 flow analyses.
CFD-Based, Parametric, Design Tool for Gas Turbine Combustors From Compressor Deswirl Exit to Turbine Inlet
Authors: Lai Mark K. , Reynolds Robert S. , Armstrong Jeffrey
Published: February 2009

Since 1998, the Honeywell Engines & Systems, Combustion & Emissions Group has been developing an advanced, CFD-based, parametric, detailed design-by-analysis tool for gas turbine combustors called Advanced Combustion Tools (ACT). ACT solves the entire flow regime from the compressor deswirl exit to the turbine stator inlet, and can be used for combustor diagnostics, design, and development. ACT is applicable to can, through-flow, and reverse-flow combustors, and accommodates features unique to different combustor designs. The main features of ACT are: 1. Reduction of Analysis Cycle Time: Geometry modeling and grid generation are fully parametric and modular, using an inhouse feature-based technology. Each geometrical feature can be deleted, replaced, added, and modified easily, quickly, and efficiently. 2. Elimination of Inter-Feature Boundary Assumptions: All the complex combustor features, such as wall cooling configuration, details of the air swirler assemblies and fuel atomizer systems, dome-shroud/cowl wall, and splash cooling plate, are considered and fully coupled into the CFD calculations. This allows the plenum and annulus aerodynamics to interact directly with the combustor internal flow. 3. Ease of Use: To reduce setup time and errors and to facilitate parametric studies, ACT is highly customized for engineers. 4. Accurate and Efficient CFD Solutions: Advanced physical submodels of combustion and spray have been implemented. This paper provides an overview and development experiences of ACT. Application of ACT to a through-flow combustor system is presented to illustrate the approach as applied to real-world combustors. Validation of the ACT system, by comparison to test cell data, is in-progress and will be the subject of a future paper.
The ALSTOM GT13E2 Medium BTU Gas Turbine
Authors: Reiss Frank , Griffin Timothy , Reyser Karl
Published: February 2009

ALSTOM Power’s GT13E2 gas turbine has been successfully commissioned in a refinery residual oil gasification process (api Energia, Italy) operating on Medium Btu gas (GT13E2-MBtu). The modification of the standard GT13E2 to operate with MBtu fuel has resulted in an improvement in the performance of the GT13E2 to exceed 192 MW and 38% efficiency (simple cycle) at ISO conditions. The GT compressor has been upgraded to incorporate an extra-end stage to boost the pressure ratio to 17:1 and improve performance. Syngas from residual oil gasification has a typical volumetric composition of 45% H2, 48% CO and 7% CO2 and a lower heating value of 13.9 MJ/kg. This syngas has been diluted with N2 to reduce the heating value to 7 MJ/kg lowering reactivity and allowing partially premixed operation. In order to operate with syngas a redesign of the standard EV burners was necessary to deal with the associated high flame velocities and volume fluxes. The fuel injection for syngas operation was placed at the burner end and the gas injected radially inward to obtain inherently safe operation. The gas turbine demonstrated successful operation with both syngas and oil No. 2 fuels. At the standard dilution of 7MJ/kg NOx emissions are in the 20–25 vppm range and the CO emissions are below 5 vppm independent of load. The modified burners demonstrated safe operation on syngas with and without dilution of nitrogen in a tested LHV range from 6.8 to 14 MJ/kg. This behavior allows high flexibility of the entire power plant. Changeover from oil no. 2 to syngas and vice versa can be done between 50 and 100% load. The gas turbine components have been inspected several times during the commissioning period and shown to be in good condition.
Steady and Dynamic Performance and Emissions of a Variable Geometry Combustor in a Gas Turbine Engine
Authors: Li Y. G. , Hales R. L.
Published: February 2009

One of the remedies to reduce the major emissions production of nitric oxide (NOx), carbon monoxide (CO) and unburned hydrocarbon (UHC) from conventional gas turbine engine combustors at both high and low operating conditions without losing its performance and stability is to use variable geometry combustors. This type of combustor configuration provides the possibility of dynamically controlling the airflow distribution of the combustor based on its operating conditions and therefore controlling the combustion in certain lean burn conditions. Two control schemes are described and analyzed in this paper: both are based on airflow control with variable geometry, the second including fuel staging. A model two-spool turbofan engine is chosen in this study to test the effectiveness of the variable geometry combustor and control schemes. The steady and dynamic performance of the turbofan engine is simulated and analyzed using an engine transient performance analysis code implemented with the variable geometry combustor. Empirical correlations for NOx, CO and UHC are used for the estimation of emissions. Some conclusions are obtained from this study: • With variable geometry combustors significant reduction of NOx emissions at high operating conditions and CO and UHC at low operating condition is possible; • Combustion efficiency and stability can be improved at low operating conditions, which is symbolized by the higher flame temperature in the variable geometry combustor; • The introduced correlation between non-dimensional fuel flow rate and air flow ratio to the primary zone is effective and simple in the control of flame temperature; • Circumferential fuel staging can reduce the range of air splitter movement in most of the operating conditions from idle to maximum power and have the great potential to reduce the inlet distortion to the combustor and improve the combustion efficiency; • During transient processes, the maximum moving rate of the hydraulic driven system may delay the air splitter movement but this effect on engine combustor performance is not significant.
An Alternative Cruising Method (Constant Speed) for the Hercules C-130H: Relative Life Savings When Compared to the Constant Power One and the Effect of Several Engine Physical Faults
Authors: Kotsiopoulos Petros , Singh Riti , Templalexis Ioannis
Published: February 2009

The total cost to purchase and operate a gas turbine engine is indeed quite substantial. Out of this, the biggest portion is the operating cost. In order to keep it as low as possible, a prime concern is to keep temperatures at the entry of the turbine at low levels. Therefore the effect of engine degradations should be understood and analysed, as well as the impact of the major hot section failure modes. This paper examines an alternative cruising method of constant speed for the Hercules C-130H, powered by the Alison T56-A-15 turboprop engine. This study is being done on a comparative basis to the constant power cruising method, which is applied until now. It is concerning the life savings deduced out of creep. Moreover, the effect of several engine degradations on engine life, for both constant speed and constant power cruising methods has been investigated.
Component Matching Analysis for a Power Generation Gas Turbine: Classroom Applications
Authors: Flack Ron
Published: February 2009

One analysis that is often overlooked in the gas turbine classroom is that of component matching. Some “student friendly” analyses have been published for gas turbines with propulsion applications, including modeling of the components for computer analyses. To complement the propulsion analyses, a method of matching gas turbine components for an aeroderivative power generation gas turbine is presented in this paper. Matching is the process by which components are integrated to allow predictions of overall gas turbine performance. The fundamental method of matching components with generalized characteristic maps is first described. A single shaft power generation gas turbine (inlet/gas generator/regenerator/exhaust/shaft/load) is used. Matching is accomplished by simultaneously solving the matching closure equations along with the component maps (either mathematical models or graphical data). The method is demonstrated for an example moderate sized power generation unit with given inlet, compressor, burner, turbine, regenerator, exhaust, load, and shaft maps. Improvements with the inclusion of the regeneration unit are included. For the example, a range of fuel ratios was used and the unit was shown to increase in rotational speed and the compressor eventually surged as the fuel ratio was increased. Overall thermodynamic efficiency, power output, mass flow rate, rotational speed, and other overall and component parameters are shown as functions of the fuel flow rate. The technique lends itself well in the classroom so that students can appreciate the interdependence of the component performances. The technique is a tool in which a student can select components to optimize the overall performance and can predict off-design performance of a power generation unit.
Steam-Gas Condensing Turbine in the Dual-Fuel Arrangement With a Circulating Fluidized Bed Boiler
Authors: Chodkiewicz Ryszard , Porochnicki Jerzy , Gruszczynski Jerzy , Rostkowski Robert
Published: February 2009

This study deals with a new internal combustion power system with a condensing steam-gas turbine (CSGT) and a circulating fluidized bed coal boiler (CFB) to produce electricity. Heat is delivered to the system by burning gaseous fuel in the CSGT combustor and by using coal combustion heat to generate the superheated steam for injection into the CSGT combustor. The optimization analysis of this novel dual-fuel energy system addresses the thermal efficiency of electric power generation and electric power generated by the system while offering the possibility of premium gaseous fuel saving. The ecological advantages are also identified.
Film Cooling Effectiveness and Heat Transfer of Rectangular-Shaped Film Cooling Holes
Authors: Rhee Dong Ho , Lee Youn Seok , Cho Hyung Hee
Published: February 2009

An experimental study has been conducted to measure the local film-cooling effectiveness and the heat transfer coefficient for a single row of rectangular-shaped holes. The holes have a 35° inclination angle with 3 hole diameter spacing of rectangular cross-sections. Four different cooling hole shapes such as a straight rectangular hole, a rectangular hole with laterally expanded exit, a circular hole and a two-dimensional slot are tested. The rectangular cross-section has the aspect ratio of 2 at the hole inlet with the hydraulic diameter of 10 mm. The area ratio of the exit to the hole inlet is 1.8 for the rectangular hole with expanded exit, which is similar to a two-dimensional slot. A thermochromic liquid crystals technique is applied to determine adiabatic film cooling effectiveness values and heat transfer coefficients on the test surface. Both film cooling effectiveness and heat transfer coefficient are measured for various blowing rates and compared with the results of the cylindrical holes and the two-dimensional slot. The flow patterns inside and downstream of holes are calculated numerically by a commercial package. The results show that the rectangular holes provide better performance than the cylindrical holes. For the rectangular holes with laterally expanded exit, the penetration of jet is reduced significantly, and the higher and more uniform cooling performance is obtained even at relatively high blowing rates. The reason is that the rectangular hole with expanded exit reduces momentum of coolant and promotes the lateral spreading like a two-dimensional slot.
A Model for Diffusion of Turbulent Kinetic Energy for Calculation of Momentum and Heat Transfer in High FST Flows
Authors: Yavuzkurt Savas , Iyer Ganesh R.
Published: February 2009

A modified low-Reynolds number k-ε model (named YI-diffn. model) for predicting effects of high free stream turbulence (FST) on momentum transport and heat transfer in a flat plate turbulent boundary layer is presented. An additional turbulent kinetic energy (TKE) diffusion term incorporating the effects of FST intensity (velocity scale) and length scale was included in the TKE equation. This model was developed with experience from many years of experimental and theoretical studies in the area of high FST flows. The constant cμ in the equation for the transport coefficient μt was modified using experimental data. These modifications were applied to a well-tested k-ε model (K-Y Chien called KYC in this study) under high FST conditions (initial FST intensity, Tui > 5%). Models were implemented in a 2-D boundary layer code. The high FST zero pressure gradient data sets against which the predictions (in the turbulent region) were compared had initial FST intensities of 6.53% and 25.7%. In a previous paper, it was shown that predictions of the original k-ε models became poorer (over prediction up to more than 50% for skin friction coefficient and Stanton number, and under prediction of TKE up to more than 50%) as FST increased to about 26%. In comparison, the new model developed here provided excellent results (within ±3% of experimental data) for skin friction coefficient and Stanton number for both the data sets. TKE results were excellent for Tui = 6.53%, but have scope for improvement in the case of Tui = 25.7%. The present model incorporates physics of transport of free stream turbulence in turbulence modeling and provides a new method for simulating flows with high FST. Future work will focus upon improving the model further and applying it to practical applications like flow over gas turbine blades.
Low-Pressure Turbine Separation Control: Comparison With Experimental Data
Authors: Garg Vijay K.
Published: February 2009

The present work details a computational study, using the Glenn-HT code, that analyzes the use of vortex generator jets (VGJs) to control separation on a low-pressure turbine (LPT) blade at low Reynolds numbers. The computational results are also compared with the experimental data of Bons et al. [1] for steady VGJs. It is found that the code determines the proper location of the separation point on the suction surface of the baseline blade (without any VGJ) for Reynolds numbers of 50,000 or less. Also, the code finds that the separated region on the suction surface of the blade vanishes with the use of VGJs. However, the separated region and the wake characteristics are not well predicted. The wake width is generally over-predicted while the wake depth is under-predicted.