bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection of Precursor Event Before Blowout in a Gas Turbine Type Combustor at Atmospheric Pressure
Authors: Aditya K. P. , Muruganandam T. M.
Published: October 2013

The need for stringent emission requirements compel modern gas turbine (GT) combustors to work under lean conditions and lower temperatures, thereby reducing NOx emissions. The operation of a combustor close to lean blowout limit increases the risk of a complete flame blowout posing a safety hazard in aircraft engines. A study was carried out on a divergent gas turbine combustor, in order to sense and detect a similar blowout phenomenon in a non/partially premixed swirl flame. Inside combustor, 45° vane angle swirler created weak recirculation zone. New swirler with 5° and 60° at entry and exit respectively was used as replacement. 5 bar and 6 bar of stagnation pressure of air were used as loading parameters during the experimentation. Photodiode sensors and high speed imaging camera were used to record data of flame. It was observed that, bursts (or unsteady events) characterized by an almost complete loss of flame i. e. abrupt extinctions were followed by re-occurrence of flame. ‘Precursor events’ before flame blowout were detected. These events occurred and reoccurred in an interval of several milliseconds. In both scenarios, high speed visualization was recorded at 1000 Hz for 16–20 seconds. Detection of precursor events for the liquid fuelled combustor will assist in carrying out further research using sensing methods to estimate the proximity of the combustor to LBO.
Parametric Study of Axial Flow Turbine for Mean-Line Design and Blade Elements
Authors: Murthy S. V. Ramana , Kumar S. Kishore
Published: October 2013

A parametric study is carried out for aerodynamic performance of turbines including geometrical requirements, thermal requirements, mechanical integrity and manufacturing requirements. Life cycle costs, product cycle time and weight are additional, possible criteria during the parametric study. Preliminary design plays an important role in reaching the final design of the turbine. Preliminary design steps calculate the mean dimensions of the machine. The main step in the aerodynamic design which is instrumental in providing desired performance is blade element profile generation. During the profile generation, in addition to aerodynamic performance, additional constraints for castability, structural requirements and thermal requirements need to be considered. Thus profile generation is a trade-off between contradicting requirements of aerodynamic performance, structural and thermal performance.
Research on Structural Design and Optimization of Turbine Blade Shroud
Authors: Fan Jiang , Han Le , Wang Rongqiao , Shen Xiuli , Zeng Weiwei , Chang Zhipeng
Published: October 2013

An automatic optimization approach for the structural design of turbine blade shroud is presented and applied to the optimal design of a zigzag shroud in this paper. It integrates commercial CAD and CAE softwares into optimization procedure iSIGHT. According to the normal rules of the shroud design and experience, this paper advises a zigzag shroud which is fit for a kind of turbine blade. The parametric model of the shroud is established and the pre-twist angle parameter is taken into consideration. The structural intensity performance of the shroud, which is used to compute the optimal objective and constraints during optimization, is determined by conducting coupled thermal-structural analysis of shrouded turbine blade using the commercial Finite Element code ANSYS. Two application examples of the optimization approach are presented, with optimal objective functions of shrouded blade mass and maximum shroud contact pressure respectively. The latter includes the pre-twist angle as one of design variables. Mechanical and geometry constraints are applied on the design to ensure that the optimized design meets requirements for feasibility of engineering criteria. Simulation results from shroud optimizations by means of the optimization approach prove that the performance of the shroud can be improved significantly through structure optimization. The optimization approach provides an effective method to design and optimize the similar complicated models.
Form Factor for the Top-Level Comparison of the Condition of Supply of High-Pressure Compressor Blades
Authors: Schrade Marcus , Staudacher Stephan , Weißschuh Matthias , Voigt Matthias
Published: October 2013

High-pressure compressor (HPC) performance and maintenance of gas turbines is influenced by blade production scatter and in-service deterioration. Complex geometries in HPC, especially at blades, yield to a large amount of component features, which individually influence performance and maintenance characteristics. This results in a highly complex and poorly observable system. Hence, the correlation of a single component feature to performance or maintenance characteristics is not purposeful and a reduction of the parameter space is advantageous.

A form factor is introduced that reduces geometric deviations of component features to a scalar. Principal component analysis (PCA) of measured HPC blades is used to support the form factor concept. The meaningfulness of this approach is shown in identifying process capabilities of different forges based on the form factor.
Numerical Simulation to Characterize Homogeneity of Air-Fuel Mixture for Premixed Combustion in Gas Turbine Combustor
Authors: Chatterjee Kamalika , Kumar Arkadeep , Chatterjee Souvick , Mukhopadhyay Achintya , Sen Swarnendu
Published: October 2013

Homogeneity in mixing of air and fuel in premixed combustion for a gas turbine combustor is a critical criterion to ensure efficient combustion and less environmental hazards. The current work deals with determining this homogenous characteristic of air-fuel mixture through computational simulation to specify homogeneity for a particular premixing length and equivalence ratio required for gas turbine combustion. A 3-D geometry of combustion chamber with combustion zone of internal diameter 6 cm is constructed. A premixing tube is augmented with the combustion chamber which has one air inlet port at the bottom and 3 fuel inlet ports. Air-fuel mixture is considered to enter the combustion zone with inlet swirl. The homogeneity of the mixture is found out at the dump plane and other important planes from simulation done with ANSYS FLUENT® for the meshed geometry. The results show whether mixing of air and fuel is full or partial and the extent of partial premixing. The parameters varied in the ANSYS FLUENT®. based simulation are the premixing length i.e. port of entry of fuel, the fuel flow rate i.e. the equivalence ratio and the air flow rate.
Experimental Characterization of Premixed Flame in Gas Turbine Combustor With Spectroscopy and RGB Analysis
Authors: Kumar Arkadeep , Chatterjee Kamalika , Mukhopadhyay Achintya , Sen Swarnendu
Published: October 2013

Gas turbine combustion has been one of the principal sources for power generation and propulsion systems. Recent research thrust on flame monitoring for characterization of flame behavior has gained prominence for several reasons — notably for performance of combustor in aerospace propulsion and power plant applications, reduction in pollutant levels like NOx, and fire safety engineering, Lean air-fuel mixture leads to efficient combustion with lesser emissions, albeit with risk of Lean blow out (LBO). Flame monitoring is done to find out LBO point-which occurs by progressively varying the Air-fuel ratio or equivalence ratio. The current paper monitors the characteristics of lean premixed, swirl-stabilized, LPG fueled, dump combustor with the help of spectroscopy and high resolution camera images. Chemiluminescence is being used for determination of combustion characteristics. The spectroscopic peaks for chemical species like - OH* and CH* radicals and water vapor are found at varying parameters like air-fuel premixing and equivalence ratio. Blow off characteristics which occur in gas turbine combustor when going from rich to lean mixture are investigated. The comparison of the averaged red, green and blue (R, G, B) values has been done by graphical representation. The spectroscopic data are co-related with the RGB analysis results- and the location of spectroscopic peaks of intensities and their correspondence with electromagnetic spectrum in investigated. The behavior of peak intensities of Red, Green, Blue alongwith irradiation by chemical species – with the change in parameters like air flow rate, fuel flow rate or equivalence ratio and the extent of air-fuel premixing are investigated. Metrics for detecting the approach of impending LBO are proposed from the spectroscopic results.
CFD Simulation of Steam Ejector System in High Altitude Test (HAT) Facility
Authors: Sreekireddy Pavani , Reddy T. Kishen Kumar , Dadi Venugopal , Bhramara P.
Published: October 2013

In the present work, the performance of Steam Ejector System in High Altitude Test (HAT) facility is numerically studied, in the absence of the condenser. Steam is used as secondary fluid to eject the burnt gases into atmosphere.

Experimental visualization of mixing of burnt gas and steam and subsequent flow pattern is difficult, hence numerical simulation using FLUENT was done and the resulting flow stream lines, static and total pressures, shock patterns are computed along the ejector system to understand the physics of the problem. Three burnt gas flow rates of 9.17, 27.5 and 45.8 kg/s corresponding to lower, mid and upper limits of ejection from the HAT facility with the steam flow rate of 50 kg/s from Ejector I and 130 kg/s from Ejector II are studied. This corresponds to three cases of Entrainment Ratios for each of the ejector.

Results show that for a burnt gas flow rate of 27.5 and 45.8 kg/s with the given dimensions of the HAT facility provided by ASL, DRDO, the gas and steam start mixing in the converging duct, pass through the mixing tube and attains atmospheric pressure at the exit of the HAT facility. For the burnt gas flow rate of 9.17 kg/s, reverse flow is observed in the Ejector II, indicating the malfunction mode of the system for the given design parameters.
Effect of Some Design Parameters on Performance of a Shutter Type Vertical Axis Wind Turbine
Authors: Wangikar Sandeep S. , Misal Nitin D.
Published: October 2013

Renewable energy generation in the rural environment has been receiving an increased attention over the recent years due to the proximity with the point of use. This paper presents the effect of design parameters on the performance of a Shutter Type Vertical Axis Wind Turbine (STVAWT). A STVAWT has been designed, manufactured and tested. The turbine performance has been investigated by varying the design parameters such as shutter angle and form of the shutter. The results were used for the comparison between the performance achieved while changing the design parameters. Significant numbers of experiments have been performed by changing the above mentioned parameters for different wind speeds. The effect of each parameter on the torque and power has been analyzed. It has been found that the shutter angle has a significant effect on the power of the turbine. The maximum power obtained in this investigation was 103 watts using a turbine with radius 150 cm, height 45 cm, shutter angle 30 degree and curved shutter form. The torque and power increases with increase in shutter angle up to 30 degree starting from 12 degree and then decreases with increase in shutter opening angle up to 48 degree. From this investigation, it is clear that the newly developed STVAWT is working efficiently at 30 degree shutter opening angle and the curved shutter form is found to be more efficient as compared to the straight shutter form.
Improved Analytical Model for Bolted Joint Evaluation in Gas Turbines
Authors: Prasanna Kumar H. S. , Mayuram M. M. , Raghavan K. S.
Published: October 2013

Modern day gas turbines are very complex in construction consisting of a large number of smaller components connected and kept together by means of bolted joints. These joints operate at high temperatures, pressures and speeds. It is essential that the structural behavior of all the joints be assessed to address issues such as fatigue, creep and flange opening. During the preliminary design and concept optimization stage it is prudent to use simple analytical approaches rather than full fledged finite element simulation models. A number of analytical models are available in literature. Prominent among them are analytical model for “Flat Faces Flanges with Metal-to-Metal Contact beyond the Bolt Circle” by Schneider, which later become standard in ASME code and more recent one is by Galai and Bouzid that uses annular plate theory and thin cylinder theory in conjunction to simulate flange. However such analytical models do not account for all the operating parameters and it is essential to assess their adequacy. The main purpose of the proposed paper is to carry out critical assessment of the simpler analytical approaches and document the findings. The purpose is also to refine the approaches so that the shortcomings are addressed. To this end a 3D high fidelity finite element model including flanges, bolt and nut along with threads is developed simulating bolted joints in gas turbine cases and analyzed for different preload and external operating load conditions like pressure and axial blow off loads. The model is also analyzed for different geometric configuration by varying flange thickness, height and bolt spacing ratio. Different analytical approaches for fastener and member stiffness calculation are evaluated and identified the right combination for the complete model. Existing analytical model for flange opening and bolt stress is then updated by including the right stiffness models. The updated analytical model is compared with high fidelity FE model for different geometry configurations. Results show that the bolt stress variation between the updated analytical model and 3D FE model is around 10% as against 20% in the existing analytical model. Improved analytical method also provides good agreement with the 3D FE results for external loads up to about 60% of the bolt preload, which is well above the normal operating load.
A Detailed Validation Study of Multi-Environment Eulerian PDF Transport Method for Modeling Turbulent Non-Premixed Combustion
Authors: Yadav Rakesh , Kushari Abhijit , Eswaran Vinayak , Verma Atul K.
Published: October 2013

PDF transport modeling has been known to be the most accurate for modeling turbulence chemistry interactions with finite rate chemistry effects. But, this is computationally very expensive. The Direct quadrature method of moments with Interaction by exchange with mean closure (DQMOM-IEM) can be a potential alternative to solve the PDF transport equation in an efficient manner.

The current work involves the validation of presumed shape multi-environment Eulerian PDF Transport method (MEPDF) using DQMOM-IEM approach for modeling turbulence chemistry interactions in non-premixed combustion problems. The joint composition PDF is represented as a collection of finite number of Delta functions. The PDF shape is resolved by solving the governing transport equations for probability of occurrence of each environment and probability weighted mass fraction of species and enthalpy in Eulerian frame for each environment. A generic implementation of the MEPDF approach is carried out for an arbitrary number of environments.

In the current work, the MEPDF approach is used for a series of problems to validate each component of MEPDF approach in an isolated manner as well as their combined effect. First of all, a non reactive turbulent mixing problem with two different Reynolds number (Re = 7000, 11900) is used for validation of the mixing and correction terms appear in the MEPDF approach. The second problem studied is a diffusion flame with infinitely fast chemistry having an analytical solution. The reaction component is validated by considering a 1D premixed laminar flame. In order to validate the combined effect of mixing and turbulence chemistry interactions, two different turbulent non premixed problems using global one step chemistry are used. The first reactive problem used is H2 combustion (DLR Flame H3) while the second reactive validation case is a pilot stabilized CH4 flame. The current predictions for all validation problems are compared with experimental data or published results. The study is further extended by modeling a turbulent non premixed H2 combustion using finite rate chemistry effects and radiative heat transfer. The current model predictions for different flame lengths as well as minor species are compared with experimental data. The current model gave excellent predictions of minor species like OH. The differences in the current predictions with experimental data are discussed.
Effects of Blade Manufacturing Deviations on Turbine Performance
Authors: Fathi Alireza , Alizadeh Mohammad
Published: October 2013

In the manufacturing process of turbine blades and vanes, there are some deviations from design criteria. These geometry variations have negative effects on turbine performance. In the present paper, influences of these variations (listed below) on turbine performance are investigated. For precise calculation of turbine performance, a three-dimensional CFD code, which solves Reynolds Average Navier-Stokes (RANS) equations, is used. The code is validated against existing Hannover turbine experimental data. The test case for studying geometry variations is second stage of Avon turbine. The investigated variations are: (I) twist, (II) offset, (III) trailing edge and leading edge thickness, (IV) tilt, (V) lean, and (VI) bow. Results show that blade twist and offset have significant effect on the stage mass flow rate. In addition, blade offset has much more negative effect on stage efficiency than other defections. On the other hand, blade bow and leading edge and trailing edge thickness have minor effect on the stage efficiency. In addition, the combination of aforementioned deviations is also studied. The results show that combination of all of these deviations causes the stage mass flow rate and efficiency to change, significantly.
Thermodynamic Optimization and Off-Design Performance Analysis of a Toluene Based Rankine Cycle for Waste Heat Recovery From Medium-Sized Gas Turbines
Authors: Carcasci Carlo , Ferraro Riccardo
Published: October 2013

In the last years, the accelerated consumption of fossil fuels has caused many serious environmental problems such as global warming, the depletion of the ozone layer and atmospheric pollution. Similarly, low-temperature waste heat which is discharged in several industrial processes, contributes to thermal pollution and damages the environment. Furthermore, many industrial applications use low enthalpy thermal sources, where the conventional systems for the conversion of thermal energy into electrical energy, based on a Rankine water cycle, work with difficulty. Thus, the Organic Rankine Cycle can be considered a promising process for the conversion of heat at low and medium temperature whenever the conventional water cycle causes problems. Using an organic working fluid instead of water, the ORC system works like the bottom cycle of a conventional steam power plant. This kind of cycle allows a high utilization of the available thermal source. Moreover, the choice of the working fluid is critical, because it should meet several environment standards and not only certain thermophysical properties.

This paper illustrates the results for the simulations of an Organic Rankine Cycle based on a gas turbine with a diathermic oil circuit. The selected working fluid is toluene. The design is performed with a sensitivity analysis of the main process parameters, the organic Rankine cycle is optimized by varying the main pressure of the fluid at different temperatures of the oil circuit. The off-design is performed by varying the temperature of the air condenser.
Investigation of Outlet-Pressure Adaptation Mechanisms for Steam-Turbine Rotor Section
Authors: Amiri H. Beheshti , Piroozi A. A. , Kermani M. J.
Published: October 2013

In this paper, employing an Eulerian-Eulerian method, based on a non-equilibrium point of view, the simulation of a two-phase vapor-liquid flow in the blade to blade passage has been numerically studied. In the following, the governing phenomena in blade to blade passage as well as important parameters in the blade design procedure have been investigated.

In the first section, after introducing the physical governing phenomenon in the subsonic and supersonic outflows, the mechanisms will be discussed which play a way more important role in changing the outlet pressure compared to the other less important ones. In the next section, the blade loading distribution, which is one of the most important parameters in designing the steam-turbine blades, has been studied. At the last part noting the significance of gas mass phase fraction on the blade surface, this parameter is comprehensively investigated. In order to perform a more successful analysis, the blade to blade passage has been simulated by a convergent-divergent nozzle. Taking into account the governing phenomena in the convergent-divergent nozzle and using the developed simulation model, most of experimental observations could be reproduced and also successfully understood.
A Numerical Investigation on Effects of the Gap Between Plates of Savonius Vertical Axis Wind Turbines With Different Shapes on Their Performance
Authors: Abbaszadeh Morteza , Doroodian Fatemeh
Published: October 2013

Present study introduces the vertical gap between the blades of a Savonius rotor’s blades as a parameter that can enhance performance of the rotor. To provide comprehensive concept about application of gap between blades, two different models were tested in different working conditions and working regimes. The study completed by using R.S.M. turbulence model through ANSYS Fluent commercial software package. Utilization of the method was validated by comparing results of a conventional model with experimental data from one of the references. Results of the study proved that application of a proper gap between blades can improve rotor’s moment coefficient by 20 percent; however, the amount of enhancement and optimum gap are associated with the shape of the blade. Results also demonstrated that the application of vertical gap in a Savonius rotor doesn’t contribute to any change in the optimum velocity coefficient.
Transpiration Boundary Conditions for a Steady Inverse Method
Authors: Yang Jinguang , Wu Hu
Published: October 2013

Computational fluid dynamics has been widely used in the analysis of turbomachinery blades, however, its use as a design tool is far from sophisticated. The inverse method is such a design approach, which lends it self to the latter category. One application of the inverse method is the so called “pure inverse methd”, which differs from common analysis solver mainly in the boundary conditions on the blade surfaces. For this application, the usual non-penetration boundary conditions on the blade surfaces are aborted, instead, some aerodynamic constraints are imposed, and the flow is allowed to transpire through the actual solid wall. A camber line generation equation is added to periodically re-generate the blade camber line and drive the normal velocities on the blade surfaces to zero. When converged, the inverse method should obtain the blade shapes which satisfy the specified aerodynamic performance.

In the present paper, three transpiration boundary conditions for turbomachinery blades design are compared in terms of time cost, robustness, capability of coping separation flow etc. The first inverse boundary condition is based on the flow-tangency condition on the blade surfaces, the second relys on the propagating characteristics in the flow field, and the third is a hybrid version of the first and the second. The computation is validated for 2D Navier-Stokes equation. Two compressor cascades are taken as examples to compare the performance of the three transpiration boundary conditions. Finally some conclusions are drawn.
Integration and Performance Assessment of Hydrogen Fired Combined Cycle Power Plant With PSA Process for CO2 Capture in a Pre-Combustion IGCC Power Plant
Authors: Dave Ashok D. , Rezvani Sina , Huang Ye , McIlveen-Wright David , Hewitt Neil
Published: October 2013

The Pre-combustion IGCC Power Generation technology presents novel challenges in terms of gas turbine operation. The hydrogen-rich gaseous fuel has much higher heating value than conventional syngas. In a state of the art precombustion IGCC power plant, the fuel utilised in a gas turbine is generated on-site by a coal gasification unit followed by gas clean-up, water-gas (sour) shift reaction and CO2 sequestration. The Pressure Swing Adsorption (PSA) process is techno-economically promising option for separation of hydrogen from the syngas. However, the PSA process is inherently transient in nature. Performance of PSA process is dependent on the process configuration and various devised different PSA process configurations and reported the purity and recovery rate of hydrogen and carbon dioxide rich product gas streams. However, these process configurations published in literature are not directly adaptable to the state of the art pre-combustion IGCC power plant due to variations in the feed composition and condition. Moreover, the current research works have not addressed the impact of varying amount of hydrogen recovery on the power generation characteristics. Two important configurations of the PSA process are identified and their CAPEX is estimated.
Studies on Optimization of a Liquid Fuel Based Low Emission Combustor
Authors: Reddy V. Mahendra , Sawant Darshan , Kumar Sudarshan
Published: October 2013

This paper presents experimental and numerical results on a single stage burner configuration with flameless/MILD combustion with liquid fuel. The proposed burner configuration is designed for 20 kW thermal input with heat intensity of ∼ 5 MW/m3 using kerosene as fuel and air at ambient conditions as the oxidizer. Air is injected through four tangential injection holes near the bottom of the combustor results high swirl flow in the combustor helps to enhance the internal recirculation of the combustion products. Computational and experimental analysis is carried out simultaneously for optimization of combustor configuration. In swirl combustor configurations the reactants dilution ration (recirculation) is function of combustor geometry, exit diameter and inlet velocity of air. In the first step of study four different combustor configurations are considered, one cylindrical and three conical combustors with diverging angles of 30°, 45° and 60°. In the second step the effect of exit port diameter on the recirculation and quality of flameless combustion is studied. The exit port diameter varied from 80 mm to 25 mm. In the third step the inlet velocities of air varied by inserting different inlet diameters of 2 to 7 mm in a step of 1mm. Based on combustion completeness and emission analysis, the 60° diverging angle combustor with air inlet diameter of 4 or 5 mm and 25 mm exit diameter is considered as optimistic configuration to obtain flameless combustion mode with liquid fuels. The acoustic emissions and the emissions of CO and NOX are measured for different configurations.
Non-Axisymmetric Flow Structure in Vaneless Diffuser of Centrifugal Compressor for Turbochargers
Authors: Lan Chuanjie , Zheng Xinqian , Tamaki Hideaki
Published: October 2013

Turbocharger technology is widely used in internal combustion engines. With the downsizing of internal combustion engines and the introduction of strict emission regulations, there is urgent demand for turbochargers featuring centrifugal compressors with a wide flow range. The flow in a centrifugal compressor of a turbocharger is non-axisymmetric due to the inherent asymmetry of the discharge volute. The asymmetric flow field inside the diffuser has great influence on the performance of centrifugal compressor. In order to develop a flow control method that facilitates a wider flow range of turbocharger compressors, further understanding of the asymmetric flow structure is very important. The main subject of this study is to reveal the asymmetrical characteristics of the flow field in the vaneless diffuser of a centrifugal compressor followed by a volute. Oil flow visualizations and numerical simulations were used. The results of the numerical simulations are consistent with that of the oil flow visualizations near choke and at designed flow rate. The results show that a “dual-zone mode” asymmetric flow structure exists near the shroud of the vaneless diffuser at near choke condition. A bifurcation point at the volute tongue that divides the flow and creates two distinct flow patterns was found. The asymmetry of the flow structure near the hub was much less significant than that near the shroud. At the design flow rate, asymmetric flow patterns are found neither near shroud nor near hub. At near surge condition, the pattern of the oil flow traces near the shroud is very different from those near choke.
The Effect of Reduced Frequency on Transition and Separation at the Leading Edge of a Compressor Stator
Authors: Perkins Samuel C. T. , Henderson Alan D.
Published: October 2013

Studies on the effects of stator reduced frequency in low pressure turbines have shown that periodic wake-induced unsteadiness can increase steady flow circulation by as much as 15% and reduce losses compared to a steady flow datum. A large separation bubble downstream of peak suction that formed under steady flow conditions was periodically suppressed by wake passing events, resulting in significantly reduced losses within the boundary layer.

This research extends this concept to a controlled diffusion compressor stator blade with a circular arc leading edge. The blade was placed inside a large scale, two-dimensional, cascade with a rotating bar mechanism used to simulate an upstream rotor blade row. The blade profile has been shown to experience leading edge separations and subsequent transition on both the pressure and suction surfaces due to a velocity overspeed caused by discontinuities in surface curvature.

Testing was carried out at reduced frequencies of 0.47, 0.94 and 1.88 at the design inlet flow angle 45.5° and Reynolds number based on chord of 230,000. The freestream turbulence intensity was 4.0%.

A range of experimental measurements were used to look at the blade’s performance: high resolution time-averaged blade surface static pressure measurements, inlet and exit 3-hole probe traverses and instantaneous, ensemble averaged and time average surface mounted hot-film measurements for the calculation of turbulent intermittency and quasi wall-shear stress.

Results showed that increasing the stator reduced frequency from, 0–1.88, increased the overall blade pressure loss. The losses generated by the pressure surface and suction surface differed significantly and are affected very differently. The pressure surface demonstrated a clear reduction in loss with an increase in reduced frequency whereas the opposite trend was seen on the suction surface.

Wake-induced turbulent strips suppressed the formation of leading edge separation bubbles that formed under steady flow conditions and in between wake passing events. Wake-induced turbulent strips reduced in width and level of turbulent intermittency through the favorable pressure gradients leading to peak suction and grew in the adverse pressure gradient of the velocity overspeed. The flow between wake-induced turbulent strips partially relaminarised through the favorable pressure gradient leading to peak suction.
Filtration of Gas Turbine Lube Fluid Using Anti-Static Filters
Authors: Farooq Khalid , Arwindekar Meghdoot S.
Published: October 2013

Requirement for higher turbine performance and lower costs has resulted in smaller lubrication and control fluid systems operating at higher cleanliness levels, thus requiring higher fluid flux and finer filtration levels. Triboelectric Charge (TEC) generation by fine filters and its eventual discharge is considered to be a source of lubricating fluid breakdown and the resulting formation of resinous byproducts. These fluid breakdown byproducts form deposits or ‘varnish’ on the metallic surfaces causing servo-valve stiction along with other adverse consequences.

TEC generation occurs in fluid systems as a result of friction between the fluid and mainly the filtration media fibers. The friction causes charge separation between the filtration medium and the fluid, with the fluid oppositely charged to the filtration medium. The magnitude of charge generated depends on many interrelated factors, including the nature of the filter material and the fluid, fluid velocity, viscosity, conductivity and the contact area. The electrostatic discharge manifests itself in several ways, the most easily noticeable way being an audible clicking noise as the discharge of the accumulated electrostatic charge causes sparking internally within the system. In addition to lubricant degradation and varnish formation, the electrical charge can travel downstream with the fluid causing damage to system components, including the filter. There have been reports of heat exchanger damage, located downstream of the filters, due to the electrostatic charging of the fluid. The use of metal support meshes or other methods to dissipate the electrostatic charge to prevent its build-up in the filter cartridge may prevent the discharge within the filter assembly and the resulting filter damage, but it does not prevent the charging of the fluid, and the migration of the charge downstream causing damage to the fluid and the downstream components. In 2005 Pall Corporation introduced filter cartridges that mitigate charge generation and dissipate the small charge generated at its inception, thus offering the advantage of eliminating filter damage entirely, and significantly reducing the migration of the charge into the fluid and its associated damage to the fluid and the resulting varnish formation. This paper discusses the experience with the electrostatic charge dissipating filtration for the gas turbine lubrication application.
LCT and PIV Investigations Behind Trapezoidal-Rib With a Slit Mounted on Bottom Wall of a Rectangular Duct
Authors: Ali Md. Shaukat , Tariq Andallib , Gandhi B. K.
Published: October 2013

Various rib turbulator geometries have been used earlier to investigate the heat transfer and fluid flow characteristics owing to its vast industrial applications. Permeable ribs are reported to provide better performance in terms of heat transfer enhancement and pressure penalty. The trapezoidal rib with variable downstream chamfering and a centrally placed longitudinal slit has been used for the detailed flow field and heat transfer investigations using particle image velocimetry and liquid crystal thermography. Objective of the present work is to study the combined effect of rib chamfering along with a continuous slit and establish an understanding of the underlying flow mechanism and the corresponding heat transfer distribution. Experiments were carried out for hydraulic diameter based Reynolds numbers of 61480 in a rectangular duct for flow over rib with 12.5% blockage ratio and 25% open area ratio. The chamfer angles were varied from 0 to 20 degree. It has been observed that the slitted rib cause shorter reattachment length and reduced pressure penalty as compared to its solid counterpart.
Numerical Optimization of Thermo-Compressors Based on Non-Dimensional Geometrical Parameters
Authors: Sharifi Navid , Boroomand Masoud
Published: October 2013

Thermo-compressors are essential parts in desalination units and using the high pressure motive steam to compress large amounts of low pressure steam without any moving parts or blades. One of the current challenging issues in thermo-compressor design is the correct size selection for different dimensions to achieve the maximum entraining capability at a given compression ratio. The conventional design methods are based on varying shape parameters such as lengths, angles and diameters of internal parts and select a particular geometry which yields the best performance under given boundary conditions. The major characteristics of thermo-compressors which have to be compromised during such design procedures are “compression ratio” and “entrainment ratio”. In the current study, a new method of size selection for different geometrical parameters of thermo-compressors will be introduced. The basis of this method is to define two new non-dimensional parameters in terms of geometrical parameters. The effect of varying these parameters on both characteristics of thermo-compressors has been studied numerically via a CFD method and subsequently, a practical correlation has been developed to express the relationship between the characteristics and the geometrical parameters. The expression obtained from numerous simulations can be applied to evaluate the performance of a given geometry prior to manufacturing. The numerical simulation has been performed on more than 320 different models with different geometries according to the finite-volume steady-state method. The structured meshes were generated within the computational domain. In addition, several mesh concentrations have been studied to develop a mesh-independent model. Moreover, a modified k-epsilon method has been adopted to model the turbulent flow. Steam was taken as the working fluid and it was assumed a real gas with a nonlinear relationship between pressure and density. All governing equations have been discretized with a second-order upwind scheme and solved by implicit method. The numerical results verified with experimental measurements obtained from a real life model of thermo-compressor. The outcomes of applying the validated method on several models enable us to develop the practical characteristic curves based on non-dimensional parameters which further leading to achieve optimized shape selection for thermo-compressors.
Numerical Simulation of the Aerodynamic Behavior of Propeller Blades at Subsonic Conditions
Authors: Farghaly Mohamed B. , El-Sayed Ahmed F. , Salem Galal B.
Published: October 2013

The Organization of the Petroleum Exporting Countries (OPEC) oil crisis of the mid 1970s led to a revival in interest in the propeller as a possible fuel-efficient propulsion for aircraft operating at subsonic cruise speeds. A propeller aerodynamics is complex and should be analyzed carefully to ensure maximum propellers efficiency. Detailed knowledge of flow patterns and aerodynamics loads is necessary for blade material and manufacturing process.

In this study, an isolated propeller blade is chosen as the base of analysis, the geometry of the propeller: twist and chord variation with radius, are taken from real case module. The boundary conditions of the computational domain are set corresponding to that exist in the propeller manuals.

A three dimensional unstructured grid was generated and adopted using commercial grid generator GAMBIT software. The governing equations are solved using FLUENT6.3.26 a commercial CFD code, which uses a control volume approach on a grid over the computational domain. Results identified that the propeller efficiency, power coefficient are increases to reach maximum values and then decreases with increase Mach number. The thrust coefficient decreases with increase Mach number.
Fast B1 mapping based on interleaved‐three‐flip‐angle (ITFA) excitation
Authors: Kang Lae Hoon , Kim Dong Eun , Lee Soo Yeol
Published: October 2013

Purpose:

Fast B1 mapping based on short‐TR sequences is prone to T1‐induced errors. The purpose of this study is to develop a novel fast B1 mapping method that is less prone to T1‐induced errors.

Methods:

The authors acquired three gradient echoes by applying three RF pulses of different flip angles in an interleaved manner. The new method, named interleaved‐three‐flip‐angle (ITFA) method, employs a short TR for fast scan. Since the pixel intensity of the gradient echo images is dependent on both B1 and T1, the authors could compute a B1 map from the three gradient echo images with excluding the T1‐effects. The authors simulated the proposed B1 mapping method for various T1 values, and they found optimal flip angles for ITFA experiments for a given repetition time. To evaluate the B1 mapping performance, the authors made a human‐brain‐mimicking phantom that had six compartments with different T1 and T2. The authors performed B1 mapping experiments at 3T on the phantom and a volunteer using the ITFA method, the actual flip angle imaging (AFI) method, and the double angle method (DAM), and then, the authors compared the B1 mapping results.

Results:

Using a birdcage coil as a transceiver at 3T, the authors performed ITFA scans of the phantom and a volunteer with TR of 60 ms and the nominal flips angles of (25°, 70°, 80°). The authors also performed AFI scans with TR1/TR2 of 30/150 ms and the nominal flip angle of 60°. In both the phantom and human head imaging performed with the same scan times for ITFA and AFI, ITFA showed smaller average B1 errors than AFI when they were compared to DAM.

Conclusions:

ITFA excitations made it possible to reduce the T1‐effects on B1 mapping of the human‐brain‐mimicking phantom and the human brain at 3T. The authors expect the ITFA method can be used for B1 shimming once the optimal flip angles have been predetermined for the target imaging region and for the preferred TR.
An automated voxelized dosimetry tool for radionuclide therapy based on serial quantitative SPECT/CT imaging
Authors: Jackson Price A. , Beauregard Jean‐Mathieu , Hofman Michael S. , Kron Tomas , Hogg Annette , Hicks Rodney J.
Published: October 2013

Purpose:

To create an accurate map of the distribution of radiation dose deposition in healthy and target tissues during radionuclide therapy.

Methods:

Serial quantitative SPECT/CT images were acquired at 4, 24, and 72 h for 28177Lu‐octreotate peptide receptor radionuclide therapy (PRRT) administrations in 17 patients with advanced neuroendocrine tumors. Deformable image registration was combined with an in‐house programming algorithm to interpolate pharmacokinetic uptake and clearance at a voxel level. The resultant cumulated activity image series are comprised of values representing the total number of decays within each voxelˈs volume. For PRRT, cumulated activity was translated to absorbed dose based on Monte Carlo‐determined voxel S‐values at a combination of long and short ranges. These dosimetric image sets were compared for mean radiation absorbed dose to at‐risk organs using a conventional MIRD protocol (OLINDA 1.1).

Results:

Absorbed dose values to solid organs (liver, kidneys, and spleen) were within 10% using both techniques. Dose estimates to marrow were greater using the voxelized protocol, attributed to the software incorporating crossfire effect from nearby tumor volumes.

Conclusions:

The technique presented offers an efficient, automated tool for PRRT dosimetry based on serial post‐therapy imaging. Following retrospective analysis, this method of high‐resolution dosimetry may allow physicians to prescribe activity based on required dose to tumor volume or radiation limits to healthy tissue in individual patients.
Evidence that the Fosfomycin-Producing Epoxidase, HppE, Is a Non–Heme-Iron Peroxidase
Authors: Wang Chen , Chang Wei-chen , Guo Yisong , Huang Hui , Peck Spencer C. , Pandelia Maria E. , Lin Geng-min , Liu Hung-wen , Krebs Carsten , Bollinger J. Martin
Published: October 2013

Just Add Peroxide

The HppE enzyme uses iron to catalyze oxidation of an alcohol to an epoxide ring in the biosynthesis of the antibiotic fosfomycin. Because this process is a two-electron oxidation, it has been unclear how the enzyme reduces its presumed oxidative partner O
2
all the way to water. Where do the two extra electrons come from?

Wang
et al.

(p.
991
, published 10 October; see the Perspective by

Raushel

) now show that HppE is actually a peroxidase, and thus reduces H
2
O
2
, for which just two electrons are sufficient. The result expands the structural scope of iron-bearing peroxidase enzymes beyond heme motifs.
Complete Genome Sequence of Pseudomonas aeruginosa Podophage MPK7, Which Requires Type IV Pili for Infection
Authors: Bae Hee-Won , Cho You-Hee
Published: October 2013

We report the complete genome sequence of
Pseudomonas aeruginosa
podophage MPK7. It displays synteny to the
P. aeruginosa
phages of the
Phikmvlikevirus
genus, which includes phiKMV and LKA1. MPK7 requires type IV pili (TFP) for infection, suggesting the role of functional TFP as the receptor for this phage genus.
Draft Genome Sequences of Strains of Pasteurella multocida Isolated from the United Kingdom and the United States
Authors: Lainson Frederick A. , Dagleish Mark P. , Fontaine Michael , Bayne Colin , Hodgson J. Christopher
Published: October 2013

Pasteurella multocida
is a major pathogen of farm animals and has worldwide distribution. Here we report the draft genome sequences of four strains that were isolated from animals in the United Kingdom and the United States and represent pathogenic and commensal presentation of the bacterium.
SOME ATTRACTORS IN THE EXTENDED COMPLEX LORENZ MODEL
Authors: GÓMEZ-MONT X. , FLORES-GODOY J.-J. , FENANDEZ-ANAYA G.
Published: October 2013

We address the question of finding the attractors of the extended complex Lorenz model (ℂLM), which is obtained by extending the space from ℝ3 to ℂ3, and defining the model by the same equations as the classical Lorenz model (LM). We have numerical evidence of two strong attractors unrelated to the Lorenz attractor. We calculate its Lyapunov exponents and show that two of them are 0, and the other four are double and negative. Hence the attractors are nonchaotic. We show that they have a quasi-periodic nature. To decipher the structure of these attractors, we introduce the imaginary Lorenz model (𝕀LM), which is defined in the same space ℂ3 by multiplying with [Formula: see text] the Lorenz equations. Both models locally commute, and with its help we account for the double Lyapunov exponent 0 and show evidence that the basin of attraction of each attractor is a big open set of ℂ3. The chaotic limit set Lℂ ⊂ ℂ3 obtained from the classical Lorenz attractor L0 of (LM) by moving it with the (𝕀LM) has two positive Lyapunov exponents, but only captures a set of 6D-volume 0 in its basin of attraction. Hence this attractor may be hyperchaotic in ℝ5.
LOCALLY COMPACT GROUPS ADMITTING FAITHFUL STRONGLY CHAOTIC ACTIONS ON HAUSDORFF SPACES
Authors: SCHNEIDER FRIEDRICH MARTIN , KERKHOFF SEBASTIAN , BEHRISCH MIKE , SIEGMUND STEFAN
Published: October 2013

In this paper we provide a geometric characterization of those locally compact Hausdorff topological groups which admit a faithful strongly chaotic continuous action on some Hausdorff space.
ASYMPTOTIC BEHAVIOR AND RATIOS OF COMPLEXITY IN CELLULAR AUTOMATA
Authors: ZENIL HECTOR , VILLARREAL-ZAPATA ELENA
Published: October 2013

We study the asymptotic behavior of symbolic computing systems, notably one-dimensional cellular automata (CA), in order to ascertain whether and at what rate the number of complex versus simple rules dominate the rule space for increasing neighborhood range and number of symbols (or colors), and how different behavior is distributed in the spaces of different cellular automata formalisms. Using two different measures, Shannon's block entropy and Kolmogorov complexity, the latter approximated by two different methods (lossless compressibility and block decomposition), we arrive at the same trend of larger complex behavioral fractions. We also advance a notion of asymptotic and limit behavior for individual rules, both over initial conditions and runtimes, and we provide a formalization of Wolfram's classification as a limit function in terms of Kolmogorov complexity.