bluuebunny/crossref_metadata_2025 huggingface dataset:
CFD Simulation of Lab Seal Tooth Tip Geometry Variations to Reduce Leakage
Authors: Chougule Hasham H. , Mirzamoghadam Alexander
Published: August 2015

A modification of a conventional straight four-tooth labyrinth seal with inclined teeth including single and double stepped notches is proposed. The variants are to be numerically modeled and evaluated for potential leakage reduction through the seal as a result of the developing flow field. The CFD methodology for numerical investigation is first validated by comparison with literature data from static labyrinth seal experiments. The objective is to numerically analyze the proposed “Notched Inclined Teeth” with solid and honeycomb lands and verify the leakages. Another objective is to compare these leakages with the “Stepped Double Notched Straight Tooth” variant discussed by the present authors in a previous paper.

Results indicate that the proposed modifications — single and double stepped notched inclined teeth, systematically reduce the seal leakage compared to the baseline straight and forward inclined teeth due to higher turbulence, higher blockages by introducing vortex in leakage flow through step and cavities, and higher flow resistance as compared to baseline model.
Application of Data Reconciliation Method to Increase CCPP Performance Test Result Accuracy
Authors: Wang Zengqian , Ji Jingjin , Wang Xinghao , Sun Bo , He Lei , Xu Qiang
Published: August 2015

Performance acceptance test for gas-steam Combined Cycle Power Plant (CCPP) is of great significance for both equipment manufacturer and customer. The influence of measurement error on the calculation of guaranteed performance data as power output and heat rate can lead to unnecessary loss for either party. Commonly used uncertainty analysis method based on ASME PTC 19.1 would require all measuring instrumentation working at designed accuracy range. Meanwhile, due to the complexity of CCPP system and large number of measuring items, and as well the propagation of measurement and data reduction error, the uncertainty of corrected performance data could be significant. In this paper, process data reconciliation method based on VDI 2048 is introduced. With access to complete performance test data from a CCPP project, data reconciliation calculation is performed with an appropriate thermodynamic model. Several measurement values with gross error are identified and verified in heat balance calculation. Moreover, after recalculating with the reconciled data instead of raw data for the corrected power output and heat rate, comparison with the common uncertainty analysis method is also carried out. It is shown that with this reconciliation method, it is not only possible to find out gross errors such as instrumentation drift, but also able to dramatically increase the test result accuracy, which is of great value for both manufacturer and customer.
Numerical Simulation of the Auto Ignition Process in Inlet-Injection Shock-Induced-Combustion Scramjet Engines
Authors: Huang Wei , Yan Li , Liu Jun , Jin Liang , Tan Jian-guo
Published: August 2015

Fuel injection in the inlet surface of the scramjet engine can promote the fuel/air mixing process, resulting in a decrease in skin friction as well as vehicle length and structural weight. In the current study, the two-dimensional Reynolds-averaged Navier-Stokes (RANS) equations and the SST k-ω turbulence model have been employed to simulate the auto-ignition process in a shock-induced-combustion scramjet engine. Combustion is simulated by a one-step hydrogen-air mechanism and the Laminar Finite-Rate reaction model. The numerical approach has been validated through a grid independency analysis and a comparison with the available experimental data in the open literature. The influences of the injection angle and jet–to–crossflow pressure ratio on the auto–ignition process of the shock–induced–combustion scramjet engine have been investigated. The predicted results show good agreement with the experimental data, and the grid scale has only a slight impact on the wall pressure distribution of the scramjet engine. The cases with an injection angle of 90° are more beneficial to the auto-ignition process, and the reaction process occurs mainly at the entrance of the combustor when the jet-to-crossflow pressure ratio is 2 and 3. At the same time, two large separation regions are formed on the upper and lower walls of the scramjet engine, and their sizes increase with the increase of the jet-to-crossflow pressure ratio. However, when the jet-to-crossflow pressure ratio is 4.0, the flame is pushed forward, and the reaction process occurs mainly upstream of the injection port. This may be induced by the intensive combustion.
Aerodynamic Turbine Upgrade for W501D5, and SGT6-3000E (W501D5A) Gas Turbines
Authors: Ayoung-Chee Frank , Bhatia Akash , Humphrey Chris , Abdel-Karim Hisham
Published: August 2015

The W501D5, W501D5A, and SGT6-3000E gas turbines have been in operation for almost 30 years and continue to be a reliable workhorse for many power suppliers. As these units age, operating costs and power production become key drivers in order to maximize profits and improve dispatch rates. Performance upgrades for this mature frame allows customers to benefit from proven technology used in advanced frames in order to lower their overall combustion turbine operating costs and provide improved thermal performance.

The W501D5 and W501D5A fleet contain approximately 150 units with the fleet leader having over 235,000 reported operating hours. These units are configured in both combined and simple cycle operation, and are located in 60 Hertz power markets throughout the world. This upgrade product focuses on improving efficiency and increasing power for both frames.

The purpose of this paper is to describe the Si3D Aerodynamic Turbine Upgrade for the W501D5, W501D5A and SGT6-3000E Gas Turbines. This product is intended to improve turbine performance with an upgrade to the turbine stage 1 and 2 components (row 1 blade, row 1 vane, and row 2 vane) using the latest 3D aerodynamic tools. The Si3D product will provide customers with an increase in engine power and improved thermal efficiency through a combination of improved aerodynamic design, advanced sealing, cooling improvements, and advanced materials.

This product uses the same concept, analytical tools, and processes as the SGT5-2000E and SGT6-2000E Si3D upgrade, which to date has been installed in over 80 new apparatus and service units achieving over 840,000 equivalent operating hours. While actual results may vary, installation of this product in a W501D5, W501D5A, or SGT6-3000E may provide up to 8.0 MW gas turbine power and 320 BTU/kW-hr gas turbine heat rate improvement. Recent verification testing of the first time application of the Si3D upgrade has just been completed on a W501D5 unit with favorable results.
Simplified Osculating Cone Method for Design of a Waverider
Authors: Ding Feng , Liu Jun , Shen Chi-bing , Huang Wei
Published: August 2015

Hypersonic vehicles have become one of the key areas for development in the aerospace industry, particularly in reference to long-range precision strike capabilities. A waverider is any supersonic or hypersonic lifting body that is characterized by an attached, or nearly attached, bow shock wave along its leading edge. Previous studies have shown that an osculating cone waverider can be used as the forebody of a hypersonic airframe-engine integrated aircraft. It enables sufficient pre-compression for the inlet system. Usually, an osculating cone waverider is designed using the streamline tracing technique. In this work, a simplified osculating cone method is proposed, termed the geometric relationship method. Two types of osculating cone waveriders are obtained applying the simplified and the conventional approach, respectively. Numerical methods are employed to analyze the differences between both types of waveriders. The obtained results show that the proposed approach in this paper can simplify the design process of the osculating cone waverider with a bit larger drag, lower lift-to-drag ratio, worse homogeneous flow properties at the inlet position, but improved internal volume and volumetric efficiency.
Build Direction Effects on Additively Manufactured Channels
Authors: Snyder Jacob C. , Stimpson Curtis K. , Thole Karen A. , Mongillo Dominic
Published: August 2015

With the advances of Direct Metal Laser Sintering (DMLS), also generically referred to as additive manufacturing, novel geometric features of internal channels for gas turbine cooling can be achieved beyond those features using traditional manufacturing techniques. There are many variables, however, in the DMLS process that affect the final quality of the part. Of most interest to gas turbine heat transfer designers are the roughness levels and tolerance levels that can be held for the internal channels. This study investigates the effect of DMLS build direction and channel shape on the pressure loss and heat transfer measurements of small scale channels. Results indicate that differences in pressure loss occur between the test cases with differing channel shapes and build directions, while little change is measured in heat transfer performance.
Evaluating the Immersed Boundary Method in a Ribbed Duct for the Internal Cooling of Turbine Blades
Authors: He Long , Tafti Danesh
Published: August 2015

In this paper, immersed boundary method (IBM) is evaluated in a ribbed duct geometry to show the potential of simulating a complex geometry with a simple structured grid. In this framework, instead of resolving the geometry with a body conforming grid, the geometry is immersed into a volume background grid, and the immersed boundary cuts through the background grid and catches the geometry features. A fully developed rib roughed duct geometry is simulated with IBM at a bulk Reynolds number of 1.5 × 104. Three cases have been examined: a stationary case; a case of positive rotation at a rotation number (Ro = ΩDh/U) of 0.3 (destabilizing); and a case of negative rotation at Ro = −0.3 (stabilizing). The dynamic Smagorinsky subgird stress model is used with a second-order central difference discretization. Time averaged mean, turbulent quantities are presented, together with heat transfer. It is found that in general, the simulation with IBM resolves the bulk mean features of the flow with very good accuracy. In the stationary and positive rotation cases, the recirculation patterns and reattachment point predicted by IBM agree very well with the experiment data. In the negative rotation case, prediction of the recirculation zone shows some differences with the experiment. The IBM approach over predicts the turbulent statistics under destabilizing conditions. The overall good agreement between IBM and experimental results suggests that IBM is a promising method to apply to complex blade geometries.
Laser Consolidation: A Novel Additive Manufacturing Process for Making Net-Shape Functional Metallic Components for Gas Turbine Applications
Authors: Xue Lijue , Li Yangsheng , Chen Jianyin , Wang Shaodong
Published: August 2015

Laser consolidation (LC) is a novel additive manufacturing process being developed by the National Research Council Canada (NRC) at its London facility. LC offers unique capabilities in the production of net-shape functional metallic parts requiring no further post-machining. NRC’s LC technology has achieved dimensional accuracy of up to +/−0.05 mm with a surface finish up to 1 μm Ra (depending on the materials used in the manufacturing process). The LC process differs from other additive manufacturing technologies by its high precision deposition system that can build functional parts or features on top of existing parts using various high performance materials and alloys. In this paper, laser consolidation of various high performance materials (such as Ni-base super alloys and Ti-6Al-4V alloy) will be discussed and the examples will be given on building complex functional components and repairing parts otherwise unrepairable for gas turbine and other applications.
Evaluation of RANS and ZDES Methods for the Prediction of Three-Dimensional Separation in Axial Flow Compressors
Authors: Scillitoe Ashley D. , Tucker Paul G. , Adami Paolo
Published: August 2015

Regions of three-dimensional separations are an inherent flow feature of the corner formed by the suction surface and endwall of axial compressors. RANS turbulence models, common in industrial CFD codes, often struggle in these regions. This paper investigates the use of two hybrid RANS/LES methods as alternatives to pure RANS methods.

SA and SST based Zonal DES (ZDES) are applied to a linear blade cascade case, studied experimentally by Gbadebo [1]. The time-averaged results are compared to steady SA, SST and RSM RANS results. SA model corrections for streamline curvature, anisotropy and non-equilibrium effects are also examined. For the ZDES computations the solver is modified to reduce dissipation at low Mach numbers.

Significant uncertainty is observed in the RANS results, with the origin of the suction surface corner separation occurring too far upstream, and the extent of the corner separation significantly over-predicted. The laminar separation bubble and the turbulent reattachment are also missed. Consequently the surface pressure distribution, exit flow angle and total pressure loss predictions are poor. Conversely, the ZDES results were encouraging; with much better predictions of the pressure distribution, exit flow angle and trailing edge boundary layer displacement thickness. Some RANS corrections proved effective, such as the SA model with Rotation/Curvature correction (SA-RC), however all had deficiencies in some areas.

Although the ZDES results are encouraging it is noted that these computations were two orders of magnitude more computaionally expensive due to the high mesh densities and small time-steps required. For the ZDES results quality indexes are examined in order to determine whether the computational mesh used is sufficient in different flow regions. Mesh generation strategies based on using a pre-cursor RANS solution to obtain a modelled energy spectrum and various turbulent length scales to guide mesh refinement are considered. These can provide a quick estimate of the potential computational cost of LES or hybrid RANS/LES computations from a RANS solution.
Performance Degradation of Wind Turbine Airfoils due to Dust Contamination: A Comparative Numerical Study
Authors: Diab Aya , Alaa Moataz , Hossam El-Din Ahmed , Salem Hassan , Ghoneim Zakaria
Published: August 2015

Sand accumulation can pose significant problems to wind turbines operating in the dusty Saharan environments of the Middle East and North Africa. Despite its difficulty, sand particles can be to a great extent avoided using sealed power drive trains; however, surface contamination of the blades is certainly unavoidable. As a result, aerodynamic losses and even premature separation can be incurred. To mitigate such advert consequences and avoid significant power losses, the choice of properly designed airfoil sections with low contamination sensitivity is a must. Alternatively, mitigation techniques for premature separation may also be considered. In this paper the contamination sensitivity of a number of airfoil sections widely used in the wind turbine industry is compared. Additionally, the possibility of deploying a leading edge slat to mitigate the contamination-driven performance degradation of wind turbine airfoils is explored. A two dimensional CFD model of the particle laden flow over an airfoil section is developed by solving Navier-Stokes equations along with the SST k-ω turbulence model. Additionally, a particle deposition model has been deployed via FLUENT’s discrete phase modeling capability to simulate dust particles trajectories and hence predict their accumulation rate. The preliminary results obtained indicate that airfoil sections with low surface contamination sensitivity specifically designed for wind turbines perform better under dusty conditions. Furthermore installing a leading edge slat affects the aerodynamics of the particle laden flow and may therefore be used to mitigate the adverse effects of surface contamination that otherwise would require frequent cleaning which can be expensive.
Heat Transfer and Pressure Drop in a Rotating Two-Pass Square Channel With Different Ribs at High Rotation Numbers
Authors: Li Yang , Deng Hongwu , Xu Guoqiang , Tian Shuqing
Published: August 2015

Rotation effects on heat transfer and pressure drop in a rotating two-pass square channel with ribs is experimentally investigated. The cooper plate heating technique is applied to obtain the regional average heat transfer coefficients. The Reynolds number and rotation number varies from 10000 to 60000, and 0 to 2.0, respectively. Rib turbulators are placed on the leading and trailing walls of the channel at an angle of 90 deg or 45 deg to the flow direction. The rib pitch-to-height (P/e) ratio is 10 and the height-to-hydraulic diameter (e/Dh) ratio is 0.1 for all tests.

The detailed comparisons between smooth wall case and ribbed wall cases are presented. At stationary, increasing the Reynolds number decreases heat transfer and thermal performance ratios, but raises the friction factor ratios dramatically. Rotation shows the strongest effect on heat transfer in smooth case, and then 90 deg rib case, and the least in 45 deg rib case. Channel friction in smooth case is increased by rotation monotonously, but decreases with Ro in ribbed case when Ro increases up to 0.5. The similar thermal performances trends are observed for smooth and ribbed cases at rotation but with different peak point. The 45 deg rib channel has the superior thermal performance because it incurs the highest heat transfer and moderate pressure penalty.
Transient Analysis of a Transonic Compressor Rotor With Aeroelastic Effects
Authors: Tan Yan Han , van Rooij Michel , Prananta Bimo
Published: August 2015

High fidelity aeroelastic analysis of gas turbine blading is becoming increasingly common. It is used in vibration analysis and prevention, to increase accuracy of off-design flow analysis and performance prediction, and in damage investigation. Here, an aeroelastic analysis is performed of the transient response of a transonic rotor to a change in operating point.

An existing aeroelastic method is used that was originally developed and validated for aircraft applications. The method consists of a time-accurate CFD-method coupled with a modal approach for geometry deformation. The validity of the aeroelastic method is confirmed using the standard aeroelastic test case STCF4. Next, the transient behavior of a transonic rotor due to a change in operating point is investigated. Two scenarios are analyzed: from design point to near stall, and from design point to near choke conditions. These scenarios were analyzed using time-accurate U-RANS calculations with rigid and deformable blading, using six vibration modes to describe the blade deformation in the latter case.

In the case of a rigid blade, the shock quickly moves from the original position to the position associated with the new operating point. The duration of this process is approximately one rotor revolution, but a small oscillatory movement remains after three rotor revolutions. With deformable blading, the changing pressure distribution deforms the blade shape during the transient process. The geometric displacement is very small, on the order of 10 μm, and has only a minor effect on the observed shock movement. The final extent of deformation is reached within 0.5 rotor revolutions, but the blade continues to vibrate after three rotor revolutions.

The oscillatory displacements of both the shock and the blade are very small for this particular geometry. For different configurations, the blade deformations might be large enough to influence the shock motion, possibly giving rise to noise and fatigue problems.
Ceramic Matrix Composite Interlaminar Fracture Toughness (Mode I-II) Characterization
Authors: Abdi Frank , Baid Harsh , Ahmad Jalees , Gonczy Steve , Morscher Gregory N. , Choi Sung , Godines Cody
Published: August 2015

The objective of this effort is to develop and demonstrate innovative interlaminar Mode I and Mode II fracture toughness analysis and test methods for ceramic matrix composites (CMC). Currently, there are number of American Society for Testing and Materials (ASTM) test standards for CMC’s at both ambient and elevated temperatures, including interlaminar tension and shear strength test methods. However, there are no standardized test methods for determination of interlaminar fracture toughness in CMC’s. Although research work exists on interlaminar Mode I and Mode II fracture toughness of various types of CMC’s, the test methods applied particularly in Mode II fracture toughness testing showed definite drawbacks and limitations. ASTM test standards for CMC’s may exhibit a zig-zag (wavy) crack path pattern, and fiber bridging. The experimental parameters that may contribute to the difficulty can be summarized as: specimen width and thickness, interface coating thickness, mixed mode failure evolution, and interlaminar defects. Modes I and II crack growth resistances, GI and GII, were analytically determined at ambient temperature using double cantilever beam (DCB) and End Notched Flexure (ENF) geometries. Three (3) CMC material systems were analyzed (Sylramic/IBN/MI, SiC/SiC CVI, and SiC/CAS). Several Finite Element (FE) based potential techniques were investigated: a) Multi-scale progressive failure analysis (MS-PFA); b) Virtual Crack Closure Technique (VCCT); and c) Contour Integral (CI). Advantages and disadvantages of each were identified. The final modeling algorithm recommended was an integrated damage and fracture evolution methodology using MS-PFA and VCCT. The analysis results (Fracture energy vs. crack length, Fracture energy vs. load, Fracture energy vs. crack opening displacement) matched the Mode I and Mode II coupon tests and revealed the following key findings. Mode I-DCB specimen: 1) Sylramic/IBN/MI failure mode is due to interlaminar tension (ILT) only in the interface section and a zig-zag pattern observed 2) VCCT crack growth resistance of Sylramic/IBN/MI is well matched to the test data and 3) SiC/SiC CVI failure mode is a mixed mode behavior (ILT to interlaminar shear (ILS). Mode II ENF specimen MS-PFA analysis suggests mixed mode behavior and the zig-zag pattern similar to Mode I coupon tests.
Performance Evaluation of Last Stage Bucket Tip Section Using Non-Equilibrium Wet Steam CFD Tool
Authors: Sreedharan Sai S. , Mistry Hiteshkumar , Ostrovskiy Vsevolod , Guo Tao
Published: August 2015

In order to develop the next generation of low pressure steam turbines, it is imperative to understand the moisture effects and their impact on performance. The objective of the current study is to apply the recently developed in-house multiphase CFD code to the analysis of the tip section of the last stage bucket (LSB), and propose design improvements based on insights gained into wet steam flow physics. 2D simulations were first carried out with equilibrium and non-equilibrium condensation models, showing significant differences in losses which were attributed to non-equilibrium condensation. Details of the shock structures in the transonic blade tip passage under equilibrium and non-equilibrium condensation models were captured with best in class split blade grid topology. Sensitivity studies of major airfoil design parameters such as un-guided turning and trailing edge angle were carried out and their impact quantified on the basis of wetness losses. Based on the detailed investigation of the flow field, a new design feature on the suction side of the LSB was proposed. Numerical results show higher performance benefit of the new design at design point operation.
Premixed Pilot Flames for Improved Emissions and Flexibility in a Heavy Duty Gas Turbine Combustion System
Authors: York William D. , Romig Bryan W. , Hughes Michael J. , Simons Derrick W. , Citeno Joseph V.
Published: August 2015

Operators of heavy duty gas turbines desire more flexibility of operation in compliance with increasingly stringent emissions regulations. Delivering low NOx at base load operation, while at the same time meeting aggressive startup, shutdown, and part load requirements for NOx, CO, and unburned hydrocarbons is a challenge that requires novel solutions in the framework of lean premixed combustion systems. The DLN2.6+ combustion system, first offered by the General Electric Company (GE) in 2005 on the 9F series gas turbines for the 50 Hz market, has a proven track record of low emissions, flexibility, and reliability. In 2010, GE launched a program to incorporate the DLN2.6+ into the 7F gas turbine model. The primary driver for the introduction of this combustion system into the 60 Hz market was to enable customers to capitalize on opportunities to use shale gas, which may have a greater Wobbe range and higher reactivity than traditional natural gas.

The 7F version of the DLN2.6+ features premixed pilot flames on the five outer swirl-stabilized premixing fuel nozzles (“swozzles”). The premixed pilots have their roots in the multitube mixer technology developed by GE in the US Department of Energy Hydrogen Gas Turbine Program. A fraction of air is extracted prior to entering the combustor and sent to small tubes around the tip of the fuel nozzle centerbody. A dedicated pilot fuel circuit delivers the gas fuel to the pilot tubes, where it is injected into the air stream and given sufficient length to mix. Since the pilot flames are premixed, they contribute lower NOx emissions than a diffusion pilot, but can still provide enhanced main circuit flame stability at low-load conditions. The pilot equivalence ratio can be optimized for the specific operating conditions of the gas turbine.

This paper presents the development and validation testing of the premixed pilots, which were tested on E-class and F-class gas turbine combustion system rigs at GE Power & Water’s Gas Turbine Technology Lab. A 25% reduction in NOx emissions at nominal firing temperature was demonstrated over a diffusion flame pilot, translating into more than 80% reduction in CO emissions if increased flame temperature is employed to hold constant NOx. On the new 7F DLN2.6+, the premixed pilots have enabled modifications to the system to reduce base load NOx emissions while maintaining similar gas turbine low-load performance and bringing a significant reduction in the combustor exit temperature at which LBO occurs, highlighting the stability the pilot system brings to the combustor without the NOx penalty of a diffusion pilot. The new combustion system is scheduled to enter commercial operation on GE 7F series gas turbines in 2015.
Stall, Surge and 75 Years of Research
Authors: Day I. J.
Published: August 2015

Work on rotating stall and its related disturbances has been in progress since the Second World War. During this period, certain ‘hot topics’ have come to the fore — mostly in response to pressing problems associated with new engine designs. This paper will take a semi-historical look at some of these fields of study (stall, surge, active control, rotating instabilities etc.) and will examine the ideas which underpin each topic. Good progress can be reported, but the paper will not be an unrestricted celebration of our successes because, after 75 years of research, we are still unable to predict the stalling behaviour of a new compressor or to contribute much to the design a more stall resistant machine. Looking forward from where we are today, it is clear that future developments will come from CFD in the form of better performance predictions, better flow modelling and improved interpretation of experimental results. It is also clear that future experimental work will be most effective when focussed on real compressors with real problems — such as stage matching, large tip clearances, eccentricity and service life degradation. Today’s topics of interest are mostly associated with compressible effects and so further research will require more high speed testing.
Vibration Modeling and Experimental Results of Two Phase Flow Twin-Screw Pump
Authors: Muhammed Ameen R. A. , Childs Dara W.
Published: August 2015

In turbomachines, the transfer of energy between the rotor and the fluid does not — in theory — result in lateral forces on the rotor. In positive displacement machines, on the other hand, the transfer of energy between the moving and stationary components usually results in unbalanced pressure fields and forces. In [1] the authors developed a model to predict the dynamic forces in twin screw pumps, showing that the helical screw shape generates hydraulic forces that oscillate at multiples of running speed.

The work presented here attempts to validate the model in [1] using a clear-casing twin screw pump. The pump runs in both single and multiphase conditions with exit pressure up to 300 KPa and a flow rate 0.6 liter per second. The pump was instrumented with dynamic pressure probes across the axial length of the screw in two perpendicular directions to validate the dynamic model. Two proximity probes measured the dynamic rotor displacement at the outlet to validate the rotordynamics model and the hydrodynamic cyclic forces predicted in [1].

The predictions were found in good agreement with the measurements. The amplitude of the dynamic pressure measurements in two perpendicular plans supported the main assumptions of the model (constant pressure inside the chambers and linear pressure drop across the screw lands). The predicted rotor orbits at the pump outlet in the middle of the rotor matched the experimental orbits closely. The spectrum of the response showed harmonics of the running speed as predicted by the model.

The pump rotor’s calculated critical speed was at 24.8 krpm, roughly 14 times the rotor’s running speed of 1750 rpm. The measured and observed excitation frequencies extended out to nine times running speed, still well below the 1st critical speed. However, for longer twin-screw pumps running at higher speed, the coincidence of a higher-harmonic excitation frequency with the lightly damped 1st critical speed should be considered.
Numerical Evaluation of the Performance of the Sister–Shaped Single–Hole Schemes on Turbine Blade Leading Edge Film Cooling
Authors: Khajehhasani Siavash , Jubran Bassam
Published: August 2015

In the present study, a numerical evaluation of the performance of the sister-shaped single-hole (SSSH) schemes (downstream, upstream and up/downstream) on the leading edge of AGTB-B1 high pressure turbine blade cascade is carried out. Simulations are performed at three blowing ratios of 0.7, 1.1 and 1.5. Predicted results are compared to the single cylindrical hole and a 15° forward-diffused shaped hole. The realizable k-ε model combined with the standard wall function is used to model the flow field; wherein, the predicted pressure field was in a good agreement with the available experimental data. At the high blowing ratios of 1.1 and 1.5, a noticeable improvement in the film cooling effectiveness and the lateral spread of the cooling jet has been observed for the upstream and up/downstream SSSH schemes, in particular on the suction side. The downstream SSSH configuration provided almost similar film cooling effectiveness values to that of the forward diffused shaped hole for all blowing ratios on both the pressure and suction sides of the blade. Note that the obtained film cooling effectiveness for the downstream SSSH scheme at high blowing ratios was disappointing in comparison with other SSSH schemes where much higher film cooling effectiveness values were obtained. The mixing of the coolant with the high mainstream flow at the leading edge of the blade is considerably decreased for the upstream and up/downstream SSSH schemes and more adhered coolant to the blade’s surface is observed than with other configurations. Moreover, the jet lift-off is notably diminished for the upstream and up/downstream SSSH compared to other hole geometries.
Effect of Microstructure on Mechanical Behavior of a Combined Steam Turbine Rotor Steel
Authors: Zhu Ming-Liang , Mei Lin-Bo , Xuan Fu-Zhen
Published: August 2015

High-pressure low-pressure (HLP) combined rotors have been gradually used in advanced power plants. In the present work, tensile, impact, fatigue and creep experiments were conducted to comprehensively investigate mechanical properties of a newly developed combined rotor steel 25Cr2NiMo1V based on microstructure influence. Fatigue crack growth (FCG) rates were obtained by both constant amplitude method and the load-shedding technique. A new method based on cyclic plastic zone size being equalling to grain size was introduced to defferentiate corresponding FCG data in the Paris regime and the near-threshold regime. Results show that 25Cr2NiMo1V steel has sufficient lower temperature strength and toughness in LP zone, and good high temperature creep properties in HP zone. Fracture Appearance Transition Temperature (FATT) at center core of LP is lower than 3°C with a tensile strength of 850 MPa, and creep rupture strength of HP for 105 h is respected to reach 165 MPa at 566°C. By comparison with other combined rotor materials in literature, the properties of 25Cr2NiMo1V steel enable it particularly suitable to HLP rotor material for advanced combined cycle power plants.
Uncertainty Quantification of Thermoacoustic Instabilities in a Swirled Stabilized Combustor
Authors: Ndiaye A. , Bauerheim M. , Moreau S. , Nicoud F.
Published: August 2015

Combustion instabilities can develop in modern gas-turbines as large amplitude pressure oscillations coupled with heat release fluctuations. In extreme cases, they lead to irreversible damage which can destroy the combustor. Prediction and control of all acoustic modes of the configuration at the design stage are therefore required to avoid these instabilities. This is a challenging task because of the large number of parameters involved. This situation becomes even more complex when considering uncertainties of the underlying models and input parameters. The forward uncertainty quantification problem is addressed in the case of a single swirled burner combustor. First, a Helmholtz solver is used to analyze the thermoacoustic modes of the combustion chamber. The Flame Transfer Function measured experimentally is used as a flame model for the Helmholtz solver. Then, the frequency of oscillation and the growth rate of the first thermoacoustic mode are computed in 24 different operating points. Comparisons between experimental and numerical results show good agreements except for modes which are marginally stable/unstable. The main reason is that the uncertainties can arbitrary change the nature of these modes (stable vs unstable); in other words, the usual mode classification stable/unstable must be replaced by a more continuous description such as the risk factor, i.e. the probability for a mode to be unstable given the uncertainties on the input parameters. To do so, a Monte Carlo analysis is performed using 4000 Helmholtz simulations of a single experimental operating point but with random perturbations on the FTF parameters. This allows the computation of the risk factor associated to this acoustic mode. Finally, the analysis of the Monte Carlo database suggests that a reduced two-step UQ strategy may be efficient to deal with thermoacoustics in such a system. First, two bilinear surrogate models are tuned from a moderate number of Helmholtz solutions (a few tens). Then, these algebraic models are used to perform a Monte Carlo analysis at reduced cost and approximate the risk factor of the mode. The accuracy and efficiency of this reduced UQ strategy are assessed by comparing the reference risk factor given by the full Monte Carlo database and the approximate risk factor obtained by the surrogate models. It shows a good agreement which proves that reduced efficient methods can be used to predict unstable modes.
Multiphase Flow LES Study of the Fuel Split Effects on Combustion Instabilities in an Ultra Low-NOx Annular Combustor
Authors: Bauerheim M. , Jaravel T. , Esclapez L. , Riber E. , Gicquel L. Y. M. , Cuenot B. , Cazalens M. , Bourgois S. , Rullaud M.
Published: August 2015

This paper describes the application of a coupled Acoustic model/LES approach to assess the effect of fuel split on combustion instabilities in an industrial ultra low-NOx annular combustor. Multiphase flow LES and an analytical model (ATACAMAC) to predict thermoacoustic modes are combined to reveal and compare two mechanisms leading to thermoacoustic instabilities: 1) a gaseous type in the multi-point zone where acoustics generates vortex shedding, wrinkling the flame front and 2) a multiphase flow type in the pilot zone where acoustics can modify the liquid fuel transport and the evaporation process leading to gaseous fuel oscillations. The aim of this paper is to investigate these mechanisms by changing the fuel split (from 5% to 20%, mainly affecting the pilot zone and mechanism 2) and therefore assess which mechanism controls the flame dynamics. First, the eigenmodes of the annular chamber are investigated using the analytical model and validated by 3D Helmholtz simulations. Then, multiphase flow LES are forced at the eigenfrequencies of the chamber for three different fuel split values. Key features of the flow and flame dynamics are investigated. Results show that acoustic forcing generates gaseous fuel oscillations which strongly depend on the fuel split parameter. However, the global correlation between heat release fluctuations and acoustics highlights no dependency on the fuel split staging. It suggests that vortex shedding in the multi-point zone, almost not depending on the fuel split here, is the main feature controlling the flame dynamics for this LEMCOTEC engine.
Centrifugal Compressors Return Channel Optimization by Means of Advanced 3D CFD
Authors: De Bellis Fabio , Guidotti Emanuele , Rubino Dante Tommaso
Published: August 2015

In the Oil&Gas industry, the quest for turbomachinery high efficiency is continuously pushing technology towards new improvements. Rotor (impeller) optimization is a rather established practice in the centrifugal compressors design both in the scientific literature and in the industrial experience, but the same focus is not always applied to statoric components optimization. This is due to the smaller impact of plenums and return channels on the overall compressor performance in comparison to the impeller. However, further improvements in the design of centrifugal compressors stage have to deal with the loss minimization of statoric parts, also considering the advanced level of aerodynamic detail reached by Original Equipment Manufacturers (OEMs).

In the present paper, the optimization of the return channel is performed by means of 3D Computational Fluid Dynamics (CFD) with the objective of loss coefficient minimization. The CFD simulations are run with a non-commercial proprietary software (Tacoma) considering steady flow with Reynolds Averaged Navier Stokes (RANS) approach and turbulence k-ω model with strain correction; full validation of the employed method was performed in the past against experimental campaigns and is available in the literature.

In order to reproduce as much as possible full stage operating conditions, simulations should include impeller, diffuser and return channel, but the computational cost of an optimization with many iterations required the reduction of the domain. In order to preserve simulation accuracy at the same time, flow profiles at impeller exit have been imposed at the considered computational domain inlet (i.e. diffuser inlet), whilst cavity effects and secondary flows have been considered adding source terms taken from the full stage simulation of the baseline geometry.

Return channel blades have been parameterized in terms of angle distributions with Bézier curves at hub and shroud, for a total of 18 Bézier poles. Each different design has been simulated with its speedline consisting of 7 operating conditions, whereas progressive optimization based on response surfaces have been considered starting from an initial Design of Experiment (DOE). Over 100 designs have been simulated and the most efficient allows a 20% loss coefficient reduction on a real case stage design at design point.
Numerical Validation of Empirical Formula for Estimating Airfoil Drag Coefficient at Extreme Angles of Attack in Wind Turbine Applications
Authors: Loganathan Jaikumar , Narayanamurthy Srinath
Published: August 2015

For optimal structural design of wind turbine blades, aerodynamic loads need to be estimated at all wind and operating conditions. Under parked conditions or during an emergency stop or in the event of a sudden gust, the blades can experience very high angles of attack (AOA). Generally, loads at these high AOA are design driving and hence an accurate estimation of force coefficients at these conditions are critical for efficient design. Experimental investigation of airfoils at high AOA in a wind tunnel is always a challenge due to blockage effects, Reynolds number limitation and large unsteady wake motion. Numerical simulations have their own deficiencies mainly associated with the limitations of turbulence models. Empirical formulas which are derived from experimental data for a variety of airfoils have been used with some degree of success. One such empirical formula proposed by C. Lindenburg is based on a limited set of airfoil geometry parameters like leading edge radius and wedge angles. In this study a CFD based numerical investigation is carried out on simplified airfoil geometries to validate the assumptions made in Linderburg’s formula.
A-10 Wing Leading Edge Effects on Engine Stability: Part 2 — Identifying Total Pressure Distortion Sources and the Effects on Engine/Airframe Integration
Authors: Binkley Brian A. , Patterson Grant T. , Jenkins Jerome C.
Published: August 2015

The A-10 aircraft has fuselage mounted engines with inlets just above the rear of the wing. A deployable slat system is used on the A-10 to delay wing stall directly in front of the engines. Wing stall can lead to high inlet distortion and ultimately engine stall for this aircraft. Many alternate wing leading-edge designs were recently considered for replacement of the slat system to reduce maintenance cost, reduce system complexity and increase system reliability. Fifteen potential wing leading-edge proposals for replacing the A-10 slat system were evaluated through test and analysis. Performance of the wing leading-edge candidates was characterized by the effect of inlet/engine distortion on loss of stability pressure ratio (ΔPRS) for the TF-34 engine fan and compressor. The many protuberances and non-aerodynamic shapes of the A-10 outer mold lines can generate flow structures that cause significant inlet/engine total pressure distortion. Thorough understanding of these flow structures and their impact on inlet/engine distortion was necessary to fully assess the performance of candidate wing leading edge configurations. The paper discusses the integrated test and evaluation tools and methods used to identify the sources of inlet/engine total pressure distortion and the associated impact to engine/airframe integration.
Reverberation time estimation from speech signals based on blind room impulse response identification
Authors: Wu Lifu , Qiu Xiaojun , Burnett Ian , Guo Yecai
Published: August 2015

A reverberation time (RT) estimation method is presented which consists of three steps, the anechoic speech is first recovered by maximizing the skewness of the linear prediction residual of the reverberant speech, then room impulse response (RIR) is identified using the recovered anechoic and reverberant speech, finally RIR is truncated to compensate the estimation errors and RT is estimated using the Schroeder's method. Simulations show that the proposed method successfully estimates RT less than 1.4 s and is insensitive to the speech content such as the number of long pauses and sharp offsets.
Fat-Free Mass Changes During Ketogenic Diets and the Potential Role of Resistance Training
Authors: Tinsley Grant M. , Willoughby Darryn S.
Published: August 2015

Low-carbohydrate and very-low-carbohydrate diets are often used as weight-loss strategies by exercising individuals and athletes. Very-low-carbohydrate diets can lead to a state of ketosis, in which the concentration of blood ketones (acetoacetate, 3-β-hydroxybutyrate, and acetone) increases as a result of increased fatty acid breakdown and activity of ketogenic enzymes. A potential concern of these ketogenic diets, as with other weight-loss diets, is the potential loss of fat-free mass (e.g., skeletal muscle). On examination of the literature, the majority of studies report decreases in fat-free mass in individuals following a ketogenic diet. However, some confounding factors exist, such as the use of aggressive weight-loss diets and potential concerns with fat-free mass measurement. A limited number of studies have examined combining resistance training with ketogenic diets, and further research is needed to determine whether resistance training can effectively slow or stop the loss of fat-free mass typically seen in individuals following a ketogenic diet. Mechanisms underlying the effects of a ketogenic diet on fat-free mass and the results of implementing exercise interventions in combination with this diet should also be examined.
Effect of Practicing Soccer Juggling With Different Sized Balls Upon Performance, Retention, and Transfer to Ball Reception
Authors: Raastad Olav , Aune Tore Kristian , van den Tillaar Roland
Published: August 2015

The aim of this study was to investigate if making the skill acquisition phase more difficult or easier would enhance performance in soccer juggling, and if this practice has a positive intertask transfer effect to ball reception performance. Twenty-two adolescent soccer players were tested in juggling a soccer ball and in the control of an approaching ball at a pre, post and retention test. The participants were randomly divided in a small ball size and bigger ball size training group that both trained four times per week for 6 weeks. At the post and retention test both groups enhanced performance in soccer juggling test with no difference between groups and no increase in ball reception performance at these tests. It was concluded that about intra task transfer and retention of soccer juggling skills, it does not matter if you increase (small balls) or decrease the difficulty (larger balls) when using the same amount of practice time within the skill acquisition phase in soccer juggling. In addition that for ball juggling and ball reception (inter task) these two tasks differ too much in afferent information and movement characteristics that no positive transfer between these two skills no positive intertask transfer can be expected.
Testing the Effects of a Self-Determination Theory-Based Intervention with Youth Gaelic Football Coaches on Athlete Motivation and Burnout
Authors: Langan Edel , Toner John , Blake Catherine , Lonsdale Chris
Published: August 2015

We conducted a cluster randomized controlled trial (RCT) to test the effects of a self-determination theory-based intervention on athlete motivation and burnout. In addition, we examined the feasibility and acceptability of the intervention. We randomly assigned youth Gaelic football coaches (N = 6) and their teams to an experimental or a delayed treatment control group (n = 3 each group). We employed linear mixed modeling to analyze changes in player motivation and burnout as a result of their coach participating in a 12-week SDT-based intervention. In addition, we conducted a fidelity assessment to examine whether the intervention was implemented as planned. The findings demonstrated the feasibility and acceptability of implementing a self-determination theory-based intervention in the coaching domain. In addition, this study demonstrated favorable trends in the quality of player motivation and burnout symptoms as a result of an SDT-based intervention.