bluuebunny/crossref_metadata_2025 huggingface dataset:
Benefits of Active Compressor Stability Management on Turbofan Engine Operability
Authors: Liu Yuan , Dhingra Manuj , Prasad J. V. R.
Published: August 2009

Active compressor stability management can play a significant role towards the intelligent control of gas turbine engines. The present work utilizes a computer simulation to illustrate the potential operability benefits of compressor stability management when actively controlling a turbofan engine. The simulation, called the Modular Aero-Propulsion System Simulation (MAPSS) and developed at NASA Glenn, models the actuation, sensor, controller, and engine dynamics of a twin-spool, low-bypass turbofan engine. The stability management system is built around a previously developed stability measure called the correlation measure. The correlation measure quantifies the repeatability of the pressure signature of a compressor rotor. Earlier work has used laboratory compressor and engine rig data to develop a relationship between a compressor’s stability boundary and its correlation measure. Specifically, correlation measure threshold crossing events increase in magnitude and number as the compressor approaches the limit of stable operation. To simulate the experimentally observed behavior of these events, a stochastic model based on level-crossings of an exponentially distributed pseudo-random process has been implemented in the MAPSS environment. Three different methods of integrating active stability management within the existing engine control architecture have been explored. The results show that significant improvements in the engine emergency response can be obtained while maintaining instability-free compressor operation via any of the methods studied. Two of the active control schemes investigated utilize existing scheduler and controller parameters and require minimal additional control logic for implementation. The third method, while introducing additional logic, emphasizes the need as well as benefits of a more integrated stability management system.
Investigation of Tip-Flow Based Stall Criteria Using Rotor Casing Visualization
Authors: Bennington Matthew A. , Cameron Joshua D. , Morris Scott C. , Legault Camille , Barrows Sean T. , Chen Jen-Ping , McNulty G. Scott , Wadia Aspi R.
Published: August 2009

Recent stall inception investigations have indicated that short-length scale stall initiates when the interface between the tip gap flow and the approach flow spills forward of the leading edge of the adjacent blade. This hypothesis was investigated in the present work using both numerical and experimental results from a range of compressor geometries and speed. First, full annulus unsteady computations of R35 were used to generate contours of entropy at the casing. It was found that a large gradient in entropy, which marked the leakage fluid, was aligned with the leading edge plane at the stalling mass flow. It was also observed that the flow direction in the region of increased entropy was in the reverse axial direction. The interface between the approach fluid and the reverse-direction leakage flow was related to a region in which the axial component of the wall shear stress was zero. The axial location of this line was measured experimentally using a surface streaking method using two separate facilities. It was found that the location of this line is determined by a momentum balance between the approach fluid and the tip leakage fluid. Measurements were acquired with varied tip clearance, radial distortion, and centerline offset to support these conclusions. In all cases the zero axial shear line was found to move upstream with decreased flow coefficient, and was in close proximity to the rotor leading edge at the stalling mass flow.
Large Eddy Simulation of Premixed Combustion With a Thickened-Flame Approach
Authors: De Ashoke , Acharya Sumanta
Published: August 2009

A Thickened Flame (TF) modeling approach is combined with a Large Eddy Simulation (LES) methodology to model premixed combustion and the accuracy of these model predictions is evaluated by comparing with the piloted premixed stoichiometric methane-air flame data of Chen et al. [Combust. Flame 107 (1996) 223–226] at a Reynolds number Re = 24,200. In the TF model, the flame front is artificially thickened to resolve it on the computational LES grid. Since the flame front is resolved, the combustion chemistry can be incorporated directly without closure approximations for the reaction rate. The response of the thickened flame to turbulence is taken care of by incorporating an efficiency function in the governing equations. The efficiency function, which is also known as a sub-grid flame wrinkling parameter, is a function of local turbulence and of the premixed flame characteristics, such as laminar flame speed and thickness. Three variants of the TF model are examined: the original Thickened Flame model, the Power-law flame wrinkling model, and the dynamically modified TF model. Reasonable agreement is found when comparing predictions with the experimental data and with computations reported using a probability distribution function (PDF) modeling approach by Lindstedt et al. [Combust. Flame 145 (2006) 495–511] and G-equation approach by Duchamp et al. [Annual Research Briefs, CTR (2000) 105–116].
Flame Speed and Velocity Measurements in Premixed Hydrogen-Enriched Flames
Authors: Zhu Shengrong , Acharya Sumanta
Published: August 2009

Measurements of the velocity field and burning velocity are reported for a swirl-stabilized premixed laboratory scale burner. Of specific interest in the present study is the role of hydrogen addition in premixed methane flames. Because of the high flame speeds associated with hydrogen, flames enriched with hydrogen are prone to flashback. Therefore detailed characterization of hydrogen enriched flames is of interest. In particular, measurements of turbulent flame speeds for different hydrogen contents are desired. In this study, we present detailed PIV measurements of the velocity field for two hydrogen concentrations in hydrogen-methane flames. The measured velocity fields are analyzed to extract flame speeds and these are correlated with measurements of CH chemiluinescence.
Effect of Hydrogen Combustion on the Combustion Dynamics of a Natural Gas Combustor
Authors: Singh Kapil , Varatharajan Bala , Yilmaz Ertan , Han Fei , Kim Kwanwoo
Published: August 2009

In a carbon-constrained world, Integrated Gasification Combined Cycle (IGCC) systems achieve excellent environmental performance and offer a more economical pre-combustion CO2 removal compared to other coal-based systems. The residual gas after carbon removal is comprised primarily of hydrogen and nitrogen mixtures. Achieving stable combustion of hydrogen-rich fuel mixtures while producing ultra-low NOx emissions (much lower than current diffusion combustion technology) is challenging. The goal of this study was to characterize the stability of lean premixed combustion systems operating with hydrogen and establish boundaries for stable operation. Modeling and experimental efforts were directed towards demonstration of the feasibility of such systems while meeting the emissions requirements. The higher flame speed and heat-release rate achievable with hydrogen-containing fuels can change the dynamics and stability characteristics of the combustors compared to natural gas. A combustion rig was modeled using an in-house combustion dynamics analysis code. In the model, flame heat-release fluctuations were captured by considering the effect of upstream fuel-air ratio fluctuations and flow speed fluctuations. CFD simulations were used to obtain combustion parameters. The results showed the effect of using hydrogen instead of methane and the simulations correctly predicted the combustor modes and their instability for hydrogen as well as methane combustion.
A Meanline Model for Impeller Flow Recirculation
Authors: Qiu Xuwen , Japikse David , Anderson Mark
Published: August 2009

Flow recirculation at the impeller inlet and outlet is an important feature that affects impeller performance, especially the power consumption at a very low flow rate. Although the mechanisms for this flow phenomenon have been studied, a practical model is needed for meanline modeling of impeller off-design performance. In this paper, a meanline recirculation model is proposed. At the inlet, the recirculation zone acts as area blockage to relieve the large incidence of the active flow at a low flow rate. The size of the blockage is estimated through a critical area ratio of an artificial “inlet diffuser” from the inlet to throat. The intensity of the reverse flow can then be calculated by assuming a linear velocity profile of meridional velocity in the recirculation zone. At the impeller outlet, a recirculation zone near the suction surface is established to balance the velocity difference on the pressure and suction sides of the blade. The size and the intensity of the outlet recirculation zone is assumed related to blade loading, which can be evaluated based on flow turning and Coriolis force. A few validation cases are presented showing a good comparison between test data and prediction by the model.
A Parametrical Study of a Seven Serpentine Channel PEM Fuel Cell
Authors: Carcadea Elena , Ingham D. B. , Ma L. , Pourkashanian M. , Ene H. , Stefanescu Ioan , Ionete Roxana Elena
Published: August 2009

Proton exchange membrane (PEM) fuel cells have been identified as a viable emerging technology for future power generation systems in terms of both stationary and mobile applications since it offers a significant economical and environmental potential in future power production. This paper presents the development of a PEM fuel cell system using a full three-dimensional computational fluid dynamics model for the system optimization. The fuel cell investigated is a seven serpentine channel cell of 100cm2 active area. The model includes a complete set of mathematical equations for the fluid flow, multi-component species transport, electrochemistry, and the transport of protons and electrical currents throughout the PEM fuel cell. The results obtained from the parametric analyses of the cell performance at different current loads have been presented. The model results provide us detailed information on the fluid dynamics and electrochemical processes that occur in the fuel cell. This generates a clear picture on the fuel/oxidant distribution, consumption, and the current density distribution in the fuel cell. This assists us in identifying the critical parameters that influence the cell performance and sheds light onto the physical mechanisms leading to the improvement of the fuel cell system performance.
Shipboard Mission Readiness Assessment
Authors: Cook Thomas C. , Valentine Scott G.
Published: August 2009

Gas turbines are widely used, highly critical, components for generating electrical power and propulsion on modern US Navy ships. Increasing numbers of sensors and sophisticated health management systems are being integrated into shipboard systems to enhance monitoring, performance, diagnostic, and maintenance planning capabilities. Development of a decision support tool to fuse multiple independent system health indicators provides the US military with a readily deployable technology for enabling comprehensive assessment of overall system platform health and mission readiness. This technology leverages existing open source data systems and on-board diagnostic and prognostic modules to efficiently and seamlessly employ advanced reasoning and self-learning techniques to predict high level system health and readiness from component level inputs. This paper summarizes the work associated with development of a software application to provide real-time mission readiness assessment for US Navy ships. The application incorporates several novel approaches including use of a uniform gray-scale method for identifying system health and readiness; fusion of multiple independent low-level indicators to predict overall system health and readiness; methodologies to account for the interactive effects of interconnected subsystems on overall system health and readiness; and use of self learning techniques to provide continuous refinement to future system health and readiness predictions.
Ceramic Gas Turbine Development: Need for a 10-Year Plan
Authors: van Roode Mark
Published: August 2009

Ceramic gas turbine development that started in the 1950s has slowed considerably since most of the large-scale ceramic gas turbine development programs of the 1970s–1990s ended. While component durability still does not meet expectations, the prospect of significant energy savings and emissions reductions, potentially achievable with ceramic gas turbines, continues to justify development efforts. Four gas turbine applications have been identified that could be commercially attractive: a small recuperated gas turbine (microturbine) with ∼35% electrical efficiency, a recuperated gas turbine for transportation applications with ∼40% electrical efficiency with potential applications for efficient small engine cogeneration, a ∼40% efficient mid-size industrial gas turbine and a ∼63% (combined cycle) efficient utility turbine. Key technologies have been identified to ensure performance and component durability targets can be met over the expected life cycle for these applications. These technologies include: a Si3N4 or SiC with high fracture toughness, durable EBCs for Si3N4 and SiC, an effective EBC/TBC for SiC/SiC, a durable Oxide/Oxide CMC with thermally insulating coating, and the Next Generation CMCs with high strength that can be used as structural materials for turbine components for small engines and for rotating components in engines of various sizes. The programs will require integrated partnerships between government, national laboratories, universities and industry. The overall cost of the proposed development programs is estimated at U.S. $100M over ten-years, i.e. an annual average of U.S. $10M.
Numerical Assessment of the Noise Signature Sidewall Contamination of a Linear Cascade With Moving Bars
Authors: Burgos Manuel A. , Corral Roque
Published: August 2009

The effect of the finite extent of a linear cascade on the acoustic and vortical modes generated at the cascade exit by a set of moving bars located at the inlet is assessed by means of a numerical study. The sidewall interference is studied for an airfoil which is representative of the mid-section of a low pressure turbine airfoil. The deviations from the purely periodic steady state have been also investigated. It is concluded that both, the unsteady pressure distributions on the airfoil, and the mode decomposition at the cascade exit show a reasonable matching with the purely periodic case, provided that the nominal inter-blade phase angle is taking into account to post-process the numerical data. This conclusion is a key element to the investigation of the scattering and propagation of pure tones in turbomachinery in high speed linear cascades.
Reliable Sub-5 ppm NOx Emissions: Field Experience on GE’s E-Class Industrial Gas Turbine Fleet
Authors: Venkataraman Krishna K. , Simons Derrick W. , Popovic Predrag , Thomas Larry L.
Published: August 2009

This paper describes the operational experience of GE’s 7EA DLN1+ combustion system that reliably meets the markets need for lower emissions. Currently, seven Frame 7’s with DLN1+ have over 48000 hrs and 340 starts of operational experience. The DLN1+ combustor has demonstrated its ability to reduce NOx emissions below 5 and 25ppm respectively for NOx and CO emissions over a wide ambient, humidity, and turndown range. The system has an advanced closed loop control system that greatly reduces emissions variation over the operational space. In addition, the DLN1+ is designed for 24K hour and 450 starts between combustion inspection intervals. To date, two fleet leader DLN1+ combustors have successfully completed 15000 hrs and 115 starts of continuous operation respectively.
Interdependence of Discharge Behavior, Swirl Development and Total Temperature Increase in Rotating Labyrinth Seals
Authors: Denecke J. , Fa¨rber J. , Dullenkopf K. , Bauer H.-J.
Published: August 2009

Leakage flows between stationary and rotating components are one of the main sources for losses in turbo machines. Therefore, their reduction is a main goal in the design of modern aircraft engines. Contactless seals, mainly labyrinth seals are key elements either to seal rotating parts or to control the amount of leakage flow for internal use in the secondary air system. Even though new seal types like, brush seals, carbon seals etc. will be seen more often in advanced gas turbines, labyrinth seals will continue to play an important role in the primary and secondary air system and thus improved design tools are a necessity for more efficient and reliable engines. In the design process but also during the life time of the engine the characterization of contactless seals e.g. their discharge behavior, the development of the circumferential velocity (swirl) and the loss induced total temperature increase (windage heating) are of special interest for designers and operators. Despite of today’s efficient CFD methods, analytical models remain a valuable tool as they provide for reasonably estimates fast with small computational effort. Additionally, analytical models are especially suited to improve the understanding of the complex interdependency of the aforementioned parameters. As one limit of the swirl in rotating seals, the equilibrium swirl is defined in this paper and a simple method to determine its value is presented. In this context, the influences of the rotor-stator area ratio and the stator roughness on the equilibrium swirl are taken into account. In the case the inlet swirl is known or can be estimated with reasonable confidence an analytical approach to determine the swirl development from chamber to chamber is proposed. Given this swirl development along the seal axis, the overall total temperature increase can be calculated. Based on the final dimensionless equation for the total temperature change the interdependent influences of discharge behavior, swirl development and the total temperature increase on each other are discussed.
Optimization of Intentional Mistuning Patterns for the Mitigation of the Effects of Random Mistuning
Authors: Han Yun , Mignolet Marc P.
Published: August 2009

This paper focuses on the optimization of intentional mistuning patterns for the reduction of the sensitivity of the forced response of bladed disks to random mistuning. Intentional mistuning is achieved here by using two different blade types (denoted as A and B) around the disk. It is thus desired to find the arrangement of these A and B blades (A/B pattern) that leads to the smallest 99th percentile of the amplitude of blade response in the presence of random mistuning. It is first demonstrated that there usually is a large number of local minima and further that the cost of a function evaluation is high. Accordingly, two novel, dedicated optimization algorithms are formulated and validated to address this specific problem. Both algorithms proceed in a two-step fashion. The first step, which consists of an optimization in a reduced space, leads to a series of good initial guesses. A local search from these initial guesses forms the second step of the methods. A detailed validation effort of this new procedure was next achieved on both a single-degree-of-freedom per blade model and a reduced order model of a blisk. In all validation cases, the two novel algorithms were found to converge to the global optimum or very close to it at a small computational cost. Finally, the results of this optimization efforts further demonstrate the value of intentional mistuning to increase the robustness of bladed disks to random mistuning.
Part-Load Performance of MCFC/APT Hybrid Power System
Authors: Tsujikawa Y. , Terashima S. , Yamauchi T. , Katsura S. , Kaneko K.
Published: August 2009

High temperature fuel cell such as SOFC or MCFC/turbo machinery hybrid power system has been theoretically demonstrated that it can achieve higher thermal efficiency than any other power generation schemes. Authors had already executed performance analysis of both outer and inner reforming type MCFC/APT (atmospheric pressure turbine) hybrid power systems. In the APT, turbine expansion, cooling by heat exchanger and draft by compressor are made in an open cycle mode. Results in those studies show the total thermal efficiency (electric efficiency) based on a MCFC/APT hybrid power system can be expected more than 65 percent at design point condition. In the present paper, part-load characteristics of MCFC/APT hybrid power system, of which total power output is 100 kW, are investigated for its prospective use in the small distributed energy systems. A cycle analysis of the hybrid system has been performed to obtain general strategies of highly efficient operation and control. A typical operation mode, i.e., variable rotational speed APT operation, is considered. It is found that the generation efficiency can be maintained over 50 percent (LHV) in the power output range from 50 to 100 percent.
Separated Flow Measurements on a Highly Loaded Low-Pressure Turbine Airfoil
Authors: Volino Ralph J.
Published: August 2009

Boundary layer separation, transition and reattachment have been studied on a new, very high lift, low-pressure turbine airfoil. Experiments were done under low freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Velocity profiles were acquired in the suction side boundary layer at several streamwise locations using hot-wire anemometry. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) ranging from 25,000 to 330,000. In all cases the boundary layer separated, but at high Reynolds number the separation bubble remained very thin and quickly reattached after transition to turbulence. In the low Reynolds number cases, the boundary layer separated and did not reattach, even when transition occurred. This behavior contrasts with previous research on other airfoils, in which transition, if it occurred, always induced reattachment, regardless of Reynolds number.
A High-Order LES Turbulent Model to Study Unsteady Flow Characteristics in a High Pressure Turbine Cascade
Authors: Jimbo Tomohiko , Biswas Debasish , Yokono Yasuyuki , Niizeki Yoshiki
Published: August 2009

In this work, unsteady viscous flow analysis around turbine blade cascade using a High-Order LES turbulent model is carried out to investigate basic physical process involved in the pressure loss mechanism. This numerical analysis is assessed to the wind tunnel cascade test. Basically, all the physical phenomena occurring in nature are the effect of some cause, and the effect can somehow be measured. However, to understand the cause, detail information regarding the visualization of the phenomena, which are difficult to measure, are necessary. Therefore, in our work, firstly the computed results are compared with the measured data, which are the final outcome of the cause (of the phenomena under investigation), to verify whether our physics-based model could qualitatively predict the measured facts or not. It was found that the present model could well predict measured data. Therefore, the rest of the computed information, which were difficult to measure, were used to visualize the overall flow behavior for acquiring some knowledge of the physical process associated with the pressure loss mechanism. Our study led to an understanding that the interaction of the vortex generated on the suction and pressure surface of the blade and the secondary vortex generated on the end-wall, downstream the trailing edge resulted in the formation of a large vortex structure in this region. This unsteady three-dimensional flow characteristic is expected to play an important role in the pressure loss mechanism.
Effect of Wake on Endwall Film Cooling Effectiveness for a Row of Cylindrical Holes Near the Stagnation Region of an Airfoil
Authors: Rodri´guez S. , Kersten S. , Krishnan V. , Kapat J. S.
Published: August 2009

Over the last decades, researchers have investigated many aspects of film cooling. The present study investigates the effect of transition wake near the stagnation region on endwall film cooling effectiveness. Experimental measurements are presented for a single row of cylindrical holes inclined at 35° with hole length to diameter ratio, L/D = 7.5, pitch to diameter ratio, PI/D = 3 with a constant density ratio of 1.26 and with nitrogen as the coolant. Nine different configurations were studied. The airfoil was positioned at x/D equal to (I) 6.4, (II) 12.7, and (III) 25.4. Configuration (IV-VI) consisted of the airfoil positioned at x/D = 6.4, 12.7 and 25.4 and a wake plate positioned at x/D = −12.7, upstream of the injection point. The presence of wake is also investigated on configuration VII through IX. Configuration (VII-IX) consisted of the airfoil positioned at x/D = 6.4, 12.7 and 25.4 and a wake plate positioned at x/D = −50.8, upstream of the injection point. Configuration 0, 0-b and 0-c are the baselines; these configurations consist of a single row of cylindrical holes with and without wake plate. In the absence of wake, the average effectiveness increases with increasing blowing ratio at a x/D further downstream of the injection point where the jet has reattached. Higher blowing ratio increases lateral spreading of the jet promoting jet to jet interaction and mainstream interaction enhancing mixing. The presence of wake promotes jet mixing with the mainstream resulting in faster decay of film cooling effectiveness. Effectiveness is higher for the cases where the plate is placed further upstream of the injection point.
Experimental and Simulation Study of Biodiesel Combustion in a Microturbine
Authors: Tan Ee Sann , Palanisamy Kumaran
Published: August 2009

Biodiesel, produced from the transesterification of renewable sources is one of the answers to today’s energy scarcity and environmental challenge. The success of biodiesel in transportation sector has shown that there is great potential for biodiesel to be used as an alternative fuel for gas turbine and microturbine. This paper presents the experimental and simulation results of performance test conducted in a 30kW microturbine to replicate the combustion of biodiesel derived from Waste Cooking Oil originated from palm oil source. The test was conducted using biodiesel, distillate and their blends up to a maximum of 20 percent biodiesel concentration. The study shows that the thermal efficiency and combustion efficiency increases when biodiesel blends increased. The fuel consumption for biodiesel blends are marginally higher compared to neat distillate. From the data obtained, a numerical analysis was conducted to simulate the thermal efficiency computation for biodiesel blends beyond 20 percent concentration. The predicted results showed that the thermal efficiency for B100 increased by 2 percent for the entire rated power output. This finding shows a promising potential for the application of biodiesel as an additive to gas turbine liquid fuel, to increase efficiency, in line with existing power augmentation works.
Optical Transfer Function Measurements for Technically Premixed Flames
Authors: Schuermans Bruno , Guethe Felix , Mohr Wolfgang
Published: August 2009

This paper deals with a novel approach for measuring thermo-acoustic transfer functions. These transfer functions are essential to predict the acoustic behavior of gas turbine combustion systems. Thermoacoustic prediction has become an essential step in the development process of low-NOx combustion systems. The proposed method is particularly useful in harsh environments. It makes use of simultaneous measurement of the chemiluminescence of different species in order to obtain the heat release fluctuations via an inverse method. Generally, the heat release fluctuation has two contributions: one due to equivalence ratio fluctuations, the other due to modulations of mass flow of mixture entering the reaction zone. Because the chemiluminescence of one single species depends differently on the two contributions, it is not possible to quantitatively estimate the heat based on this information. Measurement of the transfer matrix based on a purely acoustic method provides quantitative results, independent of the nature of the interaction mechanism. However, this method is difficult to apply in industrial full-scale experiments. The method developed in this work uses the chemiluminescence time traces of several species. After calibration, an over-determined inverse method is used to calculate the two heat release contributions from the time traces. The optical method proposed here has the advantage that it does not only provide quantitative heat release fluctuations, but it also quantifies the underlying physical mechanisms that cause the heat release fluctuations: it shows what part of the heat release is caused by equivalence ratio fluctuations and what part by flame front dynamics. The method has been tested on a full scale, swirl stabilized gas turbine burner. Comparison with a purely acoustic method validated the concept.
The Comparison of Two Species Film Cooling Characteristics Between Trenched and Shaped Holes
Authors: Zhang D. H. , Chen Q. Y. , Sun L. , Zeng M. , Wang Q. W.
Published: August 2009

The exit-shaped holes can result in lower coolant momentum injection with greater surface coverage. The exit-trenched holes can also lower the coolant momentum. Thus, the cooling and aerodynamic performance of laterally diffused shaped holes and laterally trenched holes were numerically compared with same depth and same hole length and the reasons for the difference were also analyzed from the viewpoint of flow mechanism. The both end-shaped holes and both end-trenched holes were also compared to the exit-shaped holes and exit-trenched holes respectively. Owing to the better heat transfer performance of steam than that of air, the cooling characteristics of super heated vapor film and pure air film were numerically investigated using the multi phase model of FLUENT to study the effect of different vapor volume fraction on film cooling characteristics. It appears that the shaped holes is superior to the trenched holes in cooling and aerodynamic performance for the cases in the present study; for shaped holes, the difference between the exit-shaped hole and both end-shaped hole is negligible; But for trenched holes, the cooling effectiveness of both end-trenched hole and the exit-trenched holes is heavily dependent on the hole length to diameter ratio; for shorter hole length to diameter ratio, the cooling effectiveness of both end-trenched hole is superior to that of exit-trenched hole. For all the cases studied, the mixture injectant is better than pure air coolant, and the mixture exhibits greater cooling advantage in the far downstream region of the holes than in the near hole region. The super heated vapor film can improve the film cooling effectiveness; the vapor volume fraction increased by 20%, and the area average cooling effectiveness can increase by 5%.
A Comparative Study of Fin-and-Tube Heat Exchangers With Various Fin Patterns
Authors: Tang L. H. , Xie G. N. , Zeng M. , Lin M. , Wang Q. W.
Published: August 2009

Air-side heat transfer and friction characteristics of five kinds of fin-and-tube heat exchangers, with the number of tube rows (N = 12) and the diameter of tubes (Do = 18 mm), have been experimentally investigated. The test samples consist of five types of fin configurations: Crimped spiral fin, plain fin, slit fin, fin with delta-wing longitudinal vortex generators and mixed fin with front 6-row vortex-generator fin and rear 6-row slit fin. The heat transfer and friction factor correlations for different types of heat exchangers are obtained with the Reynolds numbers ranging from 4000 to 10000. It is found that crimped spiral fin provides higher heat transfer and pressure drop than the other four fins. The air-side performance of heat exchangers with crimped spiral fin, plain fin, slit fin, fin with delta-wing longitudinal vortex generators and mixed fin with front 6-row vortex-generator fin / rear 6-row slit fin has been evaluated under four sets of criteria and it is shown that the heat exchanger with mixed fin (front vortex-generator fin and rear slit fin) has better performance than that with fin with delta-wing vortex generators, and the slit fin offers best heat transfer performance at high Reynolds numbers. Based on Genetic Algorithm optimization results it is indicated that the increase of length and decrease of height may enhance the performance of vortex generator fin.
Cycle Selection and Compressor Design of 600kW Simple Cycle Gas Turbine Engine
Authors: Nascimento Marco A. R. , Venturini Osvaldo J. , Lora Electo S. , Sierra Guido A. , Rodrigues Lucilene O. , Carvalho Hila´rio M. , Moura Newton R.
Published: August 2009

Distributed generation emerged as a new philosophy for electricity generation in our time, since then, it has been possible to see new concepts of technology following the idea of energy production away from the main producers or in remote areas, mainly in the countryside. Distributed generation technologies include small gas turbine engines, internal combustion reciprocating engines, photovoltaic panels, fuel cells, solar thermal conversion and Stirling engines using fossil and biofuels. Among them, the small gas turbine engine that generates electricity and heat working with fossil or renewable fuels is a promising technology for the near future. The aim of this work is the cycle analysis and preliminary compressor design of a 600kW simple cycle gas turbine engine that has been developed in Brazil. The 600kW engine will be the first prototype of its class in Brazil. A cycle performance calculation for different pressure ratios and turbine inlet temperature was carried out for fixed component efficiencies and losses. A selection of the design point was discussed and compared with the existing commercial engines of the same class. A compressor design point calculation was carried out with a mean line calculation CODE developed in FORTAN language. A CFD simulation was used for flow field analyses and design refinement.
Effect of Time and Temperature on TBC Failure Mode Under Oxidizing Environment
Authors: Cheruvu N. S. , Chan K. S. , Gandy D. W.
Published: August 2009

Thermal barrier coatings (TBC) have been recently introduced on hot section components; such as transition pieces and first two stages of turbine blades and vanes of advanced F, G, and H class land-based turbine engines. The TBC coating is typically applied on metallic coated components. The metallic bond coat provides oxidation and/or corrosion protection. It is generally believed that the primary failure mode of TBCs is delamination and fracture of the top ceramic coating parallel to the bond coat in the proximity of the thermally grown oxide (TGO) between the coatings. One of the concerns associated with the use of a TBC as a prime reliant coating is its long-term stability. The effect of long-term operation at typical land based turbine operating temperatures below 1010°C (1850°F) on the failure mode of TBCs is unknown. Long-term isothermal tests were conducted on the TBC coated specimens at three temperatures, 1010°C (1850°F), 1038°C (1900°F), and 1066°C (1950°F) to determine the effects of long term exposure on the TBC failure location (mode). Following isothermal testing, the samples were destructively examined to characterize the degradation of TBC and determine the extent of TGO cracking, TGO growth, bond coat oxidation, and TBC failure location after long term exposure for up to 18000 hours. Optical microscopy and scanning electron microscope (SEM) attached with an energy dispersive spectroscopy (EDS) system were used to study the degradation of the TBC and bond coatings. The results showed that long term isothermal exposure leads to a change in the TBC failure mode from delamination of TBC at the TGO/TBC interface to internal oxidation of the bond coat and the bond coat delamination. In this paper, the effect of long-term exposure on delamination of TBC and bond coat failure mode is discussed.
Simplified Approach to Predicting Rough Surface Transition
Authors: Boyle R. J. , Stripf M.
Published: August 2009

Turbine vane heat transfer predictions are given for smooth and rough vanes where the experimental data show transition moving forward on the vane as the surface roughness physical height increases. Consistent with smooth vane heat transfer, the transition moves forward for a fixed roughness height as the Reynolds number increases. Comparisons are presented with published experimental data. Some of the data are for a regular roughness geometry with a range of roughness heights, Reynolds numbers, and inlet turbulence intensities. The approach taken in this analysis is to treat the roughness in a statistical sense, consistent with what would be obtained from blades measured after exposure to actual engine environments. An approach is given to determine the equivalent sand grain roughness from the statistics of the regular geometry. This approach is guided by the experimental data. A roughness transition criterion is developed, and comparisons are made with experimental data over the entire range of experimental test conditions. Additional comparisons are made with experimental heat transfer data, where the roughness geometries are both regular as well as statistical. Using the developed analysis, heat transfer calculations are presented for the second stage vane of a high pressure turbine at hypothetical engine conditions.
Infestation by Brood Symbionts and Their Impact on Egg Mortality of the Red King Crab, Paralithodes camtschatica, in Alaska: Geographic and Temporal Variation
Authors: Kuris Armand M. , Blau S. Forrest , Paul A. J. , Shields Jeffrey D. , Wickham Daniel E.
Published: August 2009

Egg masses of 772 red king crab, Paralithodes camtschatica, were sampled to determine the prevalence, intensity, and patterns of cooccurrence of brood symbionts from 28 Alaskan localities. Carcinonemertes regicides and three other undescribed nemertean egg predators were recovered from many localities, as were an undescribed turbellarian and an amphipod, Ischyrocerus sp. A widespread outbreak of nemerteans occurred in the 1983–84 and 1984–85 red king crab brooding seasons. At some locations, nearly all of the eggs were consumed in the 1983–84 brood season. Feeding of C. regicides on eggs was documented in vitro and these worms caused substantial egg mortality at many locations. The amphipod was also an egg predator and may have had a significant impact at three locations. The turbellarian did not kill eggs. From the seasonal pattern of C. regicides infestation at Kachemak Bay, we postulate an abbreviated life cycle and autoinfection for C. regicides. Such life history features may have contributed to the peak intensities observed late in the 1983–84 and 1984–85 brooding seasons. At some localities, heavy brood mortality may reduce or eliminate recruitment of some year classes to the fishery.
Prey Selectivity by Age 0 White Perch (Morone americana) and Yellow Perch (Perca flavescens) in Laboratory Experiments
Authors: Parrish Donna L. , Margraf F. Joseph
Published: August 2009

We conducted prey selectivity experiments by age 0 white perch (Morone americana) and yellow perch (Perca flavescens) in the laboratory. Lake Erie zooplankters were introduced into tanks where both fishes were in single and combined species assemblages. We identified and counted the introduced plankton samples and the contents of fish stomachs after the feeding period. Our results showed no differences in prey consumed within a fish species, whether in single or combined assemblages (ANOVA, p > 0.05). There were a few differences between white perch and yellow perch consumption of each prey taxa (ANOVA); however, the arrays of organisms eaten were not different (MANOVA, p > 0.01). We note that the majority of prey consumed were smaller taxa, which is counter to optimal foraging predictions in relation to prey size, but is consistent with other research on young planktivore prey selectivities.
Using a Numerical Model of the Northeast Pacific Ocean to Study the Interannual Variability of the Fraser River Sockeye Salmon (Oncorhynchus nerka)
Authors: Hsieh William W. , Lee Warren G. , Mysak Lawrence A.
Published: August 2009

The hypothesis that numerical ocean circulation models could benefit fishery management was tested by first simulating the interannual variability of the northeast Pacific Ocean from 1955 to 1979 with the Bryan–Cox–Semtner ocean model (from the Geophysical Fluid Dynamics Laboratory, Princeton, NJ) and then relating the model output to the interannual variability found in the Fraser River sockeye salmon (Oncorhynchus nerka). Empirical orthogonal function (EOF) analysis was first used to condense the model output fields as well as the atmospheric forcing data. Next, the amplitude of the EOF's were regressed with the annual values of the sockeye variables (return migration route and timing, marine survival, and fork length) by stepwise multiple regression, with various time lags between the physical and the sockeye variables. The EOF modes associated with interannual variability (usually mode 2) were more often correlated with the sockeye variables than the other modes thought to contain mainly the seasonal cycle (mode 1) or else noise. The correlations between the physical variables and the sockeye variables were highest in the first and final few months of the sockeye marine life.
Phenotypic Differentiation in Seasonal Ecotypes of Chum Salmon, Oncorhynchus keta
Authors: Tallman Ross F. , Healey Michael C.
Published: August 2009

We compared the reproductive environments and phenotypes of early and late season breeding stocks of chum salmon, Oncorhynchus keta, to test the hypothesis that seasonal separation has resulted in phenotypically distinct forms. These were autumn- and winter-spawning populations from Bush Creek (Vancouver Island, B.C.) and a winter-spawning stock from nearby Walker Creek. All stocks had a similar time of downstream migration of the fry. No differences were found among the Walker Creek and the autumn-spawning stock of Bush Creek in age at maturity, length composition of spawners, egg size, vertebral counts of adults and fry, and time of fry migration. The winter-spawning stock of Bush Creek differed from the other stocks in egg size and vertebral counts. Discriminant analysis of 10 morphological features of the fry revealed considerable overlap in body form among the stocks. These results do not support the hypothesis that distinct life history morphs are associated with the season of reproduction. We propose that the large amount of similarity in terms of morphology and seasonality among the populations may be the product of selection. Genetic divergence may have occurred to compensate for the environmental differences experienced during embryonic development.
Vertical Size–Depth Distribution Properties of Midwater Fish off Bermuda, with Comparative Reviews for Other Open Ocean Areas
Authors: Brooks Albert L. , Saenger R. Alfred
Published: August 2009

The nighttime (N) and daytime (D) size–depth distributions of mesopelagic fish at Ocean Acre, a typical deepwater site in the North Sargasso Sea, are described using archival discrete-depth data from the surface to about 1500 m. The N/D abundance distributions n(z) for a representative group of 18 swtmbladdered species indicate that fish are concentrated in the 0–150 m euphotic zone at night and in the 400–1000 m zone during the day in spring, summer, and winter. Seasonal succession in the average life stage size classes of the bladdered group occurs, but all classes are present year-round due to the variety of specific spawning patterns. The noncoincident N/D depth niches of individual bladdered species apparently are organized to reduce competition. Normalized N/D depth distributions [Formula: see text] for the bladdered group are similar throughout the year, and appear to be determined, respectively, by the N distribution of zooplankton biomass and the D underwater light field, other hydrographic variables having little direct influence. Also, it seems likely that the form of [Formula: see text] is relatively insensitive to species composition for such groups. These hypotheses are verified qualitatively by comparing specific and group distribution properties at other ocean sites with those at Ocean Acre.
Influence of prehatch temperature on the development of muscle cellularity in posthatch Atlantic salmon (Salmo salar)
Authors: Nathanailides C. , Stickland N. C , Lopez-Albors O.
Published: August 2009

Previous work has shown that higher incubation temperatures produce newly hatched salmon (Salmo salar) with fewer but larger muscle fibres than salmon incubated at colder temperatures. Our purpose was to study the effect of differing incubation temperatures on the development of muscle cellularity in posthatch salmon. Eggs from a single pair of Atlantic salmon were incubated at either the stream ambient temperature (fluctuating around 5 °C prehatch and gradually rising to around 10 °C posthatch) or at 11 °C. From each group, samples were taken at hatching, first feeding, and at 3 weeks after first feeding. During the period of exogenous feeding under study, the ambient group grew faster. The number of muscle fibres remained lower in the 11 °C fish but there was more muscle fibre hypertrophy in the ambient group so that the difference in muscle fibre size seen at hatching was eliminated by 3 weeks after first feeding. It is suggested that reduced number of nuclei in the 11 °C fish at hatching may contribute to the relatively reduced fibre hypertrophy in these fish. The results indicate that embryonic myogenesis can affect the posthatch growth of salmon at least up to 3 weeks after first feeding.
Field transplantation of a freshwater bivalve, Pyganodon grandis, across a metal contamination gradient. I. Temporal changes in metallothionein and metal (Cd, Cu, and Zn) concentrations in soft tissues
Authors: Couillard Y. , Campbell P. G. C. , Tessier A. , Auclair J. C. , Pellerin-Massicotte J.
Published: August 2009

To test the response of the freshwater bivalve Pyganodon grandis (formerly Anodonta grandis) to increased metal exposure in the field, we transferred specimens (8 cm length; 4–6 years old) from a less to a more contaminated lake in the mining area of Rouyn-Noranda, in northwestern Québec. The transplanted bivalves were maintained in open enclosures placed in the bottom sediments of the contaminated lake. Up to 16 individuals were removed from pairs of enclosures at times t = 0 (June 1990), 5, 14, 30, 60, 90, and 400 d; tissue concentrations of metallothionein (MT) and metals were monitored over time. Measurements on control molluscs enclosed in their lake of origin showed that enclosure per se had no apparent effect on tissue [MT] or tissue metal levels, but did decrease shell growth. Metallothionein levels in specimens transplanted to the more contaminated lake showed a slow but steady increase with time; in contrast, MT levels in the control populations showed only modest seasonal fluctuations. The increase in MT over time in the transplanted bivalves was closely correlated with a similar slow increase in soft tissue [Cd]. We conclude that MT in the freshwater bivalve P. grandis is a promising biochemical indicator of metal exposure.