bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Surface Patterning on the Dynamic Response of Annular Hole-Pattern Seals
Authors: Jin Hanxiang , Untaroiu Alexandrina , Fu Gen
Published: August 2017

The performance of annular seals depends on the geometry of the leakage path as it facilitates the dissipation of the fluid kinetic energy. The goal of this study is to investigate potential correlations between the characteristics of the alternately arranged surface pattern and the corresponding rotor dynamic properties of the seal in addition to mapping its performance.

Various patterning arrangements lining the stator surface are considered and the relative seal performance change is investigated using a hybrid method that calculates the seal dynamic response for each point in the design space. The design parameters selected in this DOE study are: the diameters of alternately arranged holes that are replicated in both axial and circumferential direction to construct the pattern, the hole depths for both types of holes, and the number of holes in both axial and circumferential directions. A sensitivity study is conducted to analyze the influence of each geometrical parameter on the seal response. Regression models are then generated for each response, including the leakage rate and the rotor dynamic coefficients. Quadratic regression models are used in this study to represent the relationship between the objective functions and the design parameters. The goal is to achieve a minimum leakage rate as well as an improved dynamic response. The results of the baseline model and the best performing design are compared. The results show that the patterning arrangements have crucial effects on the leakage rate as well as the dynamic coefficients of the seal. The results of this study are found to be helpful in designing a hole-pattern seal that can concurrently satisfy constraints on both the leakage rate and the rotor dynamic response while maintaining same design envelope.
The Conductance Ratio Method for Off-Design Heat Exchanger Modeling and its Impact on an sCO2 Recompression Cycle
Authors: Crespi Francesco , Sánchez David , Hoopes Kevin , Choi Brian , Kuek Nicole
Published: August 2017

This paper presents a method to evaluate the off-design performance of a heat exchanger without specifying detailed heat exchanger geometry. Presently, off-design heat exchanger performance evaluation is often done by assuming one of the terms in a lumped volume approach is constant (such as UA, temperature difference, ε etc.) or by producing a draft heat exchanger geometry to evaluate the local heat transfer coefficients in off-design operation.

As opposed to these approaches, the method presented in this paper manages to accurately predict off-design heat exchanger performance with very limited information. The method relies on a single parameter beyond the design operating conditions, namely the conductance ratio which is the product of heat transfer coefficient and area on both sides of the heat exchanger. The method is particularly powerful as it allows for the exploration of different off-design scenarios for a given on-design operating point.

The paper presents a theoretical introduction of the method along with a validation using data provided by BMPC and Alfa Laval for different types of heat exchangers and working fluids, including supercritical CO2. The method is then used to model the off-design performance of a simple recuperated sCO2 cycle, showing its ability to capture the off-design performance of a heat exchanger without specifying its detailed geometry and the impact of conductance ratio on off-design cycle performance.
Computational Analysis of Windage Losses in an Epicyclic Gear Train
Authors: Bianchini Cosimo , Da Soghe Riccardo , D. Errico Jacopo , Tarchi Lorenzo
Published: August 2017

Aside from increasing the overall engine pressure ratio, current trends in the design of innovative aircraft propulsion systems focus also on improving the propulsive efficiency. In this context, research efforts have been devoted towards the implementation of a new family of Ultra-High Bypass Ratio (up to 20) engines. In order to take into account the new constraints set by this innovative fan concept, configurations able to guarantee an independent optimization of the low pressure spool modules are more promising. This framework however introduces new challenges for the transmission system in terms of heat management and power losses, since the amount of power transferred through the gearbox is largely increased. Among the various types of losses occurring within the gearbox, whose relative magnitude largely vary depending on the operating conditions, one of the most significant at high rotational speeds is certainly windage.

This paper studies windage losses within an epicyclic gear train by means of CFD simulations. Superposition effect is assumed for the various losses contributions hence gear meshing is avoided to simplify the computational domain and separate the effects. Results obtained in this computational campaign highlight the influence of most relevant parameters such as oil concentration, chamber pressure and rotational speed. The response of the system to increased oil concentration and chamber pressure is linear with density variation, while power losses on both sun and planetary gears are shown to scale well with the third power of rotational speed. Furthermore the effects of geometrical modifications, introduced to avoid gear meshing, are studied and guidelines to scale the effective power losses is provided.

Multi-phase simulations have been carried out in order to confirm obtained trends from single-phase analysis verifying the rationality of such a computational approach.
Regenerative Hydraulic Assisted Turbocharger
Authors: Zeng Tao , Upadhyay Devesh , Sun Harold , Curtis Eric , Zhu Guoming G.
Published: August 2017

Engine downsizing and down-speeding are essential in order to meet future US fuel economy mandates. Turbocharging is one technology to meet these goals. Fuel economy improvements must, however, be achieved without sacrificing performance. One significant factor impacting drivability on turbocharged engines is typically referred to as, “Turbo-Lag”. Since Turbo-lag directly impacts the driver’s torque demands, it is usually perceptible as an undesired slow transient boost response or as a sluggish torque response. High throughput turbochargers are especially susceptible to this dynamic and are often equipped with variable geometry turbines (VGT) to mitigate some of this effect. Assisted boosting techniques that add power directly to the TC shaft from a power source that is independent of the engine have been shown to significantly reduce turbo-lag. Single unit assisted turbochargers are either electrically assisted or hydraulically assisted. In this study a regenerative hydraulically assisted turbocharger (RHAT) system is evaluated. A custom designed RHAT system is coupled to a light duty diesel engine and is analyzed via vehicle and engine simulations for performance and energy requirements over standard test cycles. Supplier provided performance maps for the hydraulic turbine, hydraulic turbo pump were used. A production controller was coupled with the engine model and upgraded to control the engagement and disengagement of RHAT, with energy management strategies. Results show some interesting dynamics and shed light on system capabilities especially with regard to the energy balance between the assist and regenerative functions. Design considerations based on open loop simulations are used for sizing the high pressure accumulator. Simulation results show that the proposed RHAT turbocharger system can significantly improve engine transient response. Vehicle level simulations that include the driveline were also conducted and showed potential for up to 4% fuel economy improvement over the FTP 75 drive cycle. This study also identified some technical challenges related to optimal design and operation of the RHAT. Opportunities for additional fuel economy improvements are also discussed.
Comparison of Supercritical CO2 Power Cycles to Steam Rankine Cycles in Coal-Fired Applications
Authors: Miller Jason D. , Buckmaster David J. , Hart Katherine , Held Timothy J. , Thimsen David , Maxson Andrew , Phillips Jeffrey N. , Hume Scott
Published: August 2017

Increasing the efficiency of coal-fired power plants is vital to reducing electricity costs and emissions. Power cycles employing supercritical carbon dioxide (sCO2) as the working fluid have the potential to increase power cycle efficiency by 3–5% points over state-of-the-art oxy-combustion steam-Rankine cycles operating under comparable conditions. To date, the majority of studies have focused on the integration and optimization of sCO2 power cycles in waste heat, solar, or nuclear applications.

The goal of this study is to demonstrate the potential of sCO2 power cycles, and quantify the power cycle efficiency gains that can be achieved versus the state-of-the-art steam-Rankine cycles employed in oxy-fired coal power plants. Turbine inlet conditions were varied among the sCO2 test cases and compared with existing Department of Energy (DOE)/National Energy Technology6 Laboratory (NETL) steam base cases. Two separate sCO2 test cases were considered and the associated flow sheets developed. The turbine inlet conditions for this study were chosen to match conditions in a coal-fired ultra-supercritical steam plant (Tinlet = 593°C, Pinlet = 24.1 MPa) and an advanced ultra-supercritical steam plant (Tinlet = 730°C, Pinlet = 27.6 MPa). A plant size of 550 MWe, was selected to match available information on existing DOE/NETL bases cases.

The effects of cycle architecture, combustion-air preheater temperature, and cooling source type were considered subject to comparable heat source and reference conditions taken from the steam Rankine reference cases. Combinations and variants of sCO2 power cycles — including cascade and recompression and variants with multiple reheat and compression steps — were considered with varying heat-rejection subsystems — air-cooled, direct cooling tower, and indirect-loop cooling tower. Where appropriate, combustion air preheater inlet temperature was also varied.

Through use of a multivariate nonlinear optimization design process that considers both performance and economic impacts, curves of minimum cost versus efficiency were generated for each sCO2 test case and combination of architecture and operational choices. These curves indicate both peak theoretical efficiency and suggest practical limits based on incremental cost versus performance. For a given test case, results for individual architectural and operational options give insight to cost and performance improvements from step-changes in system complexity and design, allowing down selection of candidate architectures. Optimized designs for each test case were then selected based on practical efficiency limits within the remaining candidate architectures and compared to the relevant baseline steam plant. sCO2 cycle flowsheets are presented for each optimized design.
Experimental and Numerical Study of Honeycomb Tip on Suppressing Tip Leakage Flow in Turbine Cascade
Authors: Fu Yunfeng , Chen Fu , Liu Huaping , Song Yanping
Published: August 2017

In this paper, the effect of a novel honeycomb tip on suppressing tip leakage flow in a highly-loaded turbine cascade has been experimentally and numerically studied. The research focuses on the mechanisms of honeycomb tip on suppressing tip leakage flow and affecting the secondary flow in the cascade, as well as the influences of different clearance heights on leakage flow characteristics. In addition, two kinds of local honeycomb tip structures are pro-posed to explore the positive effect on suppressing leakage flow in simpler tip honeycomb structures.

Based on the experimental and numerical results, the physical processes of tip leakage flow and its interaction with main flow are analyzed, the following conclusions can be obtained. Honeycomb tip rolls up a number of small vortices and radial jets in regular hexagonal honeycomb cavities, increasing the flow resistance in the clearance and reducing the velocity of leakage flow. As a result, the structure of honeycomb tip not only suppresses the leakage flow effectively, but also has positive effect on reducing the associated losses in cascade by reducing the strength of leakage vortex. Compare to the flat tip cascade at 1%H gap height, the relative leakage flow in honeycomb tip cascade reduces from 3.05% to 2.73%, and the loss at exit section is also decreased by 10.63%. With the increase of the gap height, the tip leakage flow and loss have variations of direct proportion with it, but their growth rates in the honeycomb tip cascade are smaller. Consider the abradable property of the honeycomb seal, a smaller gap height is allowed in the cascade with honeycomb tip, and that means honeycomb tip has better effect on suppressing leakage flow. Two various local honeycomb tip structures has also been discussed. It shows that local raised honeycomb tip has better suppressing leakage flow effect than honeycomb tip, while local concave honeycomb tip has no more effect than honeycomb tip. Compare to flat tip cascade, the leakage flow in honeycomb tip cascade, local concave tip cascade and local raised honeycomb tip cascade decrease by nearly 17.33%, 15.51% and 30.86% respectively, the losses at exit section is reduced by 13.38%, 12% and 28.17% respectively.
Experimental and Numerical Investigation on Windage Power Losses in High Speed Gears
Authors: Massini D. , Fondelli T. , Andreini A. , Facchini B. , Tarchi L. , Leonardi F.
Published: August 2017

Enhancing the efficiency of gearing systems is an important topic for the development of future aero-engines with low specific fuel consumption. The transmission system in fact has a direct impact on the engine overall efficiency by means of its weight contribution, internal power losses and lubrication requirements. Thus, an evaluation of its structure and performance is mandatory in order to optimize the design as well as maximize its efficiency. Gears are among the most efficient power transmission systems, whose efficiencies can exceed 99 %, nevertheless in high speed applications power losses are anything but negligible. All power dissipated through losses is converted into heat that must be dissipated by the lubrication system. More heat leads to a larger cooling capacity, which results in more oil, larger heat exchangers which finally means more weight. Mechanical power losses are usually distinguished in two main categories: load-dependent and load-independent losses. The former are all those associated with the transmission of torque, while the latter are tied to the fluid-dynamics of the environment which surrounds the gears, namely windage, fluid trapping and squeezing between meshing gear teeth and inertial losses resulting by the impinging oil jets, usually adopted in high speed transmission for cooling and lubrication purposes. The relative magnitude of these phenomena is strongly dependent on the operative conditions of the transmission. While load-dependent losses are predominant at slow speeds and high torque conditions, load-independent mechanisms become prevailing in high speed applications, like in turbomachinery. Among fluid-dynamic losses, windage is extremely important and can dominate the other mechanisms. In this context, a new test rig was designed for investigating windage power losses resulting by a single spur gear rotating in a free oil environment. The test rig allows the gear to rotate at high speed within a box where pressure and temperature conditions can be set and monitored. An electric spindle, which drives the system, is connected to the gear through a high accuracy torque meter, equipped with a speedometer providing the rotating velocity. The test box is fitted with optical accesses in order to perform particle image velocimetry measurements for investigating the flow-field surrounding the rotating gear. The experiment has been computationally replicated, performing RANS simulations in the context of conventional eddy viscosity models. The numerical results were compared with experimental data in terms of resistant torque as well as PIV measurements, achieving a good agreement for all of the speed of rotations.
Lowering the Levelized Cost of Electricity of a Concentrating Solar Power Tower With a Supercritical Carbon Dioxide Power Cycle
Authors: Schmitt Joshua , Wilkes Jason , Allison Timothy , Bennett Jeffrey , Wygant Karl , Pelton Robert
Published: August 2017

In order to maintain viability as a future power-generating technology, concentrating solar power (CSP) must reduce its levelized cost of electricity (LCOE). The cost of CSP is assessed with the System Advisor Model (SAM) from the National Renewable Energy Laboratory (NREL). The performance of an integrally geared compressor-expander recuperated recompression cycle with supercritical carbon dioxide (sCO2) as the working fluid is modeled. A comparison of the cycle model to the integrated SAM cycle performance is made. The cycle model incorporates innovative cycle control methods to improve the range of efficiency, including inventory control. The SAM model is modified to accommodate the predicted cycle performance. The ultimate goal of minimizing the LCOE is targeted through multiple approaches, including the cost of the power block, the impact of system scale, the sizing of the thermal system relative to the power block system, the operating approach for changes in ambient temperature and availability of sunlight. Through reduced power block cost and a detailed cycle model, the LCOE is modeled to be 5.98 ȼ/kWh, achieving targeted techno-economic performance. The LCOE of the CSP system is compared to the cost of hybrid solar and fossil-fired systems. An analysis is made on the efficacy of a fossil backup system with CSP and how that relates to potential future costs of carbon dioxide emissions.
Heat Transfer Analysis of the Surface of Nonfilm-Cooled and Film-Cooled Nozzle Guide Vanes in Transonic Annular Cascade
Authors: Ragab Kasem E. , El-Gabry Lamyaa
Published: August 2017

One of the approaches adopted to improve turbine efficiency and increase power to weight ratio is reducing vane count. In the current study, numerical analysis was performed for the heat transfer over the surface of nozzle guide vanes under the condition of reduced vane count using three dimensional computational fluid dynamics (CFD) models. The investigation has taken place in two stages: the baseline nonfilm-cooled nozzle guide vane, and the film-cooled nozzle guide vane. A finite volume based commercial code (ANSYS CFX 15) was used to build and analyze the CFD models. The investigated annular cascade has no heat transfer measurements available; hence in order to validate the CFD models against experimental data, two standalone studies were carried out on the NASA C3X vanes, one on the nonfilm-cooled C3X vane and the other on the film-cooled C3X vane. Different modelling parameters were investigated including turbulence models in order to obtain good agreement with the C3X experimental data, the same parameters were used afterwards to model the industrial nozzle guide vanes. Three Shear Stress Transport (SST) turbulence model variations were evaluated, the SST with Gamma-Theta transition model was found to yield the best agreement with the experimental results; model capabilities were demonstrated when the laminar to turbulent transition took place.
Experimental Study of Transient Mechanisms of Bi-Stable Flame Shape Transitions in a Swirl Combustor
Authors: Stöhr Michael , Oberleithner Kilian , Sieber Moritz , Yin Zhiyao , Meier Wolfgang
Published: August 2017

Sudden changes of flame shape are an undesired, yet poorly understood feature of swirl combustors used in gas turbines. The present work studies flame shape transition mechanisms of a bistable turbulent swirl flame in a gas turbine model combustor, which alternates intermittently between an attached V-form and a lifted M-form. Time-resolved velocity fields and 2D flame structures were measured simultaneously using high-speed stereo-PIV and OH-PLIF at 10 kHz. The data analysis is performed using two novel methods that are well adapted to the study of transient flame shape transitions: Firstly, the linear stability analysis (LSA) of a time-varying mean flow and secondly the recently proposed spectral proper orthogonal decomposition (SPOD). The results show that the transitions are governed by two types of instability, namely a hydrodynamic instability in the form of a precessing vortex core (PVC) and a thermoacoustic (TA) instability. The LSA shows that the V-M transition implies the transient formation of a PVC as the result of a self-amplification process. The V-M transition, on the other hand, is induced by the appearance of a TA instability that suppresses the PVC and thereby modifies the flow field such that the flame re-attaches at the nozzle. In summary these results provide novel insights into the complex interactions of TA and hydrodynamic instabilities that govern the shape of turbulent swirl-stabilized flames.
Simulations of Slot Film-Cooling With Freestream Acceleration and Turbulence
Authors: Kanani Yousef , Acharya Sumanta , Ames Forrest
Published: August 2017

Slot film cooling in an accelerating boundary layer with high free-stream turbulence is studied numerically using Large Eddy Simulations (LES). Recent cooling designs of turbine airfoils (such as double-wall cooling) enable slot cooling configurations that are known to provide improved cooling effectiveness over discrete hole cooling systems. Calculations are done for a symmetrical leading edge geometry with the slot fed by a plenum populated with pin fins. To generate the inflow turbulence, the Synthetic Eddy Method (SEM) is used by which the turbulence intensity and length scales in each direction can be specified at the inflow. Different levels of turbulence are imposed at the inflow cross-plane. For the inflow at the plenum, an a priori simulation has been performed in the plenum with pin fins, and the velocity signals are stored at a plane downstream of the pin fins over a sufficient period of time, and are used as the inflow boundary condition in the plenum. Calculations are done for a Reynolds number of 250,000 and freestream turbulence levels of 0.7%, 3.5%, 7.8% and 13.7% are reported. These conditions correspond to the experimental measurements of Busche and Ames (2014). Numerical results show good agreement with experiment data and show the observed decay of thermal effectiveness with turbulence intensity. The turbulence and non-uniformity exiting the slot are shown to play an important role in the cooling effectiveness distributions downstream of the slot. To provide a better understanding of the flow physics and heat transfer, the mean flowfield and turbulence statistics are studied. Generation of freestream structures is observed at the leading edge, and the amplification of the corresponding fluctuations downstream is identified as one of the parameters influencing the slot cooling performance. Predictions show the higher growth rate of the thermal boundary layer with increasing turbulence which is a clear indication of the increase in turbulent thermal diffusivity and reduction of the effective turbulence Prandtl number. The self-similar temperature profiles deviate from those measured under low freestream turbulence condition.
Integrating Anode Recycle in a Solid Oxide Fuel Cell for Hybrid Applications: Design Considerations
Authors: Mcilvenna Amelia , Zaccaria Valentina , Harun Nor Farida , Tucker David
Published: August 2017

In Solid Oxide Fuel Cell (SOFC) hybrid systems, anode recycle allows us to reach high stack fuel utilization without causing anode re-oxidation, which is detrimental for the fuel cell. In addition, anode recycle also helps the system to mitigate the risk of carbon deposition within the fuel cell when employing fuel with high methane/CO content. This work incorporated anode recycle within a pre-existing fuel manifold model which is embedded in a larger real-time SOFC model. To optimize system performance, we considered fuel manifold design and anode recycle concurrently. The pre-existing manifold model contained a fuel valve, mixing volume, and pipe system for pressure losses. Because increasing anode recycle percentage increased fuel mass flow, pressure losses in the system also increased. Therefore, a sensitivity analysis on manifold pipe diameter and fuel composition was conducted with parametric variation in anode recycle percentage. This enabled both minimization of pressure loss to avoid damage to the SOFC, and minimization of manifold residence time to maintain acceptable control response. The updated model allowed for further investigation of the effects of anode recycle within the fuel cell and ultimately the entire hybrid system.
Crack Growth Resistance of CMC Attachment Element and Turbine Joint in Aircraft Engines
Authors: Abdi Frank , DorMohammadi Saber , Ahmad Jalees , Godines Cody , Morscher Gregory N. , Choi Sung , Mansour Rabih , Gonczy Steve , Ojard Greg
Published: August 2017

A Durability and Damage Tolerance (D&DT) analysis of an S200 Nicalon/SiNC CVI SiC/SiC attachment joint was conducted to determine the CMC components material structural integrity during service loading. A building block validation strategy is proposed that includes: (i) Room, and High Temperature (RT/HT) testing with AE (Acoustic Emission) and ER (Electrical Resistivity) strategies; (ii) Advanced multi-scale modeling; (iii) Interpretation test/model; and (iv) ASTM draft submittal of simplified beam equation supported by FEM/test compliance and round robin exercise.

The following building block calibration, verification, validation, and accreditation strategy were performed: 1) Material characterization analysis to determine the damage evolution under uniaxial tensile loads and compared with test; 2) Crack Growth Resistance (CGR) analysis and test of wedge loaded DCB (Double Cantilever Beam) to determine the crack growth length, zig-zag pattern, fracture, shift in failure mechanisms and derivation of fracture energy vs. crack length simple formulation at RT; 3) Joint loading multi scale modeling and comparison with observed test load displacement curve, and determination of fracture energy; and 4) blade structural integrity and response under service loading using Multi-Scale Progressive Failure Analysis (MS-PFA) and determination of contributing damage and delamination types and their locations. FE based MS-PFA of the material and structure studied addressed the critical damage events (damage initiation, damage propagation, fracture initiation, and fracture propagation) as the components were being loaded. All dehomogenized multi scale methods CMC parameters were implemented in the material and structural modeling strategy, such as crack density effects and architecture (2D, 3D orthogonal, and mixed) interphase thickness, and interfacial shear strength. Many parameters that contribute to specimen failure including interface coating thickness, mixed mode failure evolution, interlaminar defects, delamination damage, crack bridging, and fiber fracture were all studied in detail in this work. Several FE-based multi-scale modeling techniques were investigated: a) MS-PFA; b) Virtual Crack Closure Technique (VCCT); and c) integrated damage and fracture evolution methodology using combined MS-PFA and VCCT.
Effect of Combustor-Turbine Platform Misalignment on the Aerodynamics and Heat Transfer of an Axisymmetric Converging Vane Endwall at Transonic Conditions
Authors: Mayo David E. , Arisi Allan , Ng Wing F. , Li Zhigang , Li Jun , Moon Hee-Koo , Zhang Luzeng
Published: August 2017

This paper presents a detailed study on the effect of misalignment between the combustor exit and the nozzle guide vane endwall. The Nusselt number distribution and augmentation on an axisymmetric converging endwall as well as stage pressure losses were studied using experimental techniques and computational analysis. The analyzed endwall configurations are representative of the design intent and average off-design endwall configurations of a land-based high-pressure turbine nozzle guide vane. The studies were carried out at isentropic exit Mach number of 0.85, with an exit Reynolds number of 1.5 × 106 based on the true chord, and an inlet turbulence intensity of 16%. The experiment was conducted in a blowdown transonic linear cascade wind tunnel and an infrared camera was used to measure the surface temperature and subsequently the endwall heat transfer coefficient and Nusselt number distribution. Numerical computation analysis using ANSYS Fluent v.16 was used to provide further insight into the near-endwall flow field the predictions compared favorably to experimental data.

The findings show that at the two configurations there exist uniquely different endwall secondary flow systems throughout the NGV stage. The interaction of separated flow at the combustor-turbine interface with the vane potential field results in additional secondary flow that is vastly different from that associated with classical endwall flows. This increased secondary flow in the misaligned configuration was marked by a 25% increase in NGV stage losses. The presence of separated flow and additional secondary flows also resulted in flow reattachment inside the vane passage which augmented heat transfer. The region upstream of the vane gage/throat showed heat transfer augmentation of up to 60%, while the endwall region downstream of the throat did not show any considerable heat transfer augmentation.
Control of the Corner Separation in a Linear Cascade by Trailing Gaps
Authors: Zhao Wenfeng , Jiang Bin , Zheng Qun
Published: August 2017

Hub corner is the high-loss area in the blade passages of turbo machinery. It is well known that the flow separation and vortex development in this area affects directly not only the energy losses and efficiency, but also the stability of axial compressors. Linear compressor cascades with partial gaps and trailing gaps which can blow away the corner separation by the pressure difference between the suction surface and pressure surface are numerically simulated in this paper. A proposed linear cascade model with gaps has been built. The steady flow field in a linear cascade with different length gaps is studied by numerical simulation of RANS with SST turbulence model and γ-Reθ transition model focusing on the streamline structure between the corner separation vortex and the gap leakage vortex, especially the interaction of the two vertical vortex. When the length of trailing edge gaps is enough (in this paper, the optimal length of the gap is 30% chord), the corner vortex basically disappears completely. At the same time, the mode of flow field changes from the closed separation to the open separation.
Parametric Cooling Study of Single-Row Cylindrical Film Holes on Pressure Side of a Rotor Blade
Authors: Chi Zhongran , Liu Haiqing , Zang Shusheng
Published: August 2017

Film cooling of 1st stage rotor blades strongly relates to the aerodynamic performance and life expectation of gas turbine. In this piece of work, a parametric study was carried out based on 3D RANS CFD methods to systematically investigate both cooling performance and aerodynamic loss of various film holes’ arrangements on the pressure side (PS) of a realistic rotor blade. In each CFD case, cylindrical film holes were arranged in one row with P/D around 4.0. More than one hundred CFD cases were carried out with various dimensionless streamwise locations (0.1, 0.2, ..., and 0.7), compound angles (−60°, −30°, ..., and 90°), and relative coolant massflows (0.2%, 0.3%, 0.45%, 0.7%, and 1.0% of mainstream massflow).

Detailed distributions of adiabatic film cooling effectiveness on blade surface and aerodynamic loss with film cooling were computed for each case. It was found that coolant massflow was the decisive factor of aerodynamic efficiency φ. For near-LE film holes, −60° compound angle gave higher and more uniform η distributions at various coolant massflows. And the separation near LE could be suppressed, improving local cooling at near-hub on PS. For downstream film holes, 60° and −60° compound angles provided equivalent cooling performances, which were also better than other cases. The cooling characteristics of film holes with −30° compound angle were more susceptible to both coolant massflow and the location of ejection, which was mainly because of the blow-off and reattachment of coolant jets. For the cases with 90° compound angle, the distributions of η were generally similar, and the values increased monotonically as coolant massflows get larger.
Improved Hierarchical Modelling for Aerodynamically Coupled Systems
Authors: Watson Rob , Cui Jiahuan , Ma Yunfei , Tyacke James , Vadlamani Nagabhushana Rao , Alam Mohammed F. , Dai Yushuang , Tucker Paul G. , Cao Teng , Hield Paul , Wilson Mark , Menzies Kevin , Sheaf Christopher
Published: August 2017

Strong aerodynamic coupling can make the high fidelity simulation of a number of critical aero-engine components prohibitively expensive — particularly within the timeframes of industrial design cycles. This paper develops a body force based hierarchy of approaches to modelling the effects of blade rows. These are envisaged as allowing the computationally expensive parts of coupled systems to be resolved much more cheaply, rendering the cost of the overall simulation as more manageable. Simulation of the coupling that exists between the flow around an aero-engine intake and its fan is particularly emphasised, as this is becoming stronger and more performance critical with the modern trends towards the reduction of the relative diffuser length.

The use of the viscous smeared geometry level of fidelity is initially shown to be an effective model over a number of cases — a simple compressor blade row, a modern high bypass fan, and the Darmstadt rotor. After this, it is shown working as part of a coupled system in an intake experiencing cross-flow. Higher fidelity geometry representations are then considered, which mimic the effect of struts. Finally, a mix of various fidelity geometry representations and turbulence modelling approaches is shown to bring otherwise hugely expensive calculations within the realm of practical computation, in the form of a full fan-to-flap calculation.
Bottom profile degradation mechanism in high aspect ratio feature etching based on pattern transfer observation
Authors: Negishi Nobuyuki , Miyake Masatoshi , Yokogawa Ken'etsu , Oyama Masatoshi , Kanekiyo Tadamitsu , Izawa Masaru
Published: August 2017

The hypothetical mechanism of bottom profile degradation, such as distortion and twisting in high aspect ratio feature etching, was verified based on the pattern transfer observation of etched pattern. The authors mainly focused on trench pattern sample to make the investigation easier, that is, direct observation of the sidewall roughness, using an atomic force microscope, as well as analysis of the depth dependence of pattern deformation in high aspect ratio trench etching. Using Fourier transformation analysis for the trench sidewall roughness, it was found that lower spatial frequency component of the mask's sidewall roughness is amplified at the bottom region of the trench and that higher spatial frequency component of over 10 μm−1 disappears. However, the higher spatial frequency component is transferred directly to the upper sidewall of the trench. The observation of the pattern deformation profile, as a function of etch depth, revealed that the ratio of line width roughness to line edge roughness decreases linearly with increasing etch depth. This indicates that the deformation mode changes from “roughness” to “wiggling” as a function of etch depth. Also, the twisting depth, as determined by the cross section images, was found to be shallower when using lower wafer bias etching condition. Based upon these results, and previously proposed mechanisms, the authors conclude that the mask deformation should be considered as one of the root causes when bottom deformation occurs. This is due to the imbalance between ion flux and deposition amount created by mask asymmetric profile. In addition, the etching profile and etching direction should be affected by this phenomenon under polymer-rich process condition. In order to verify our assumed mechanism, the relationship between mask deformation degree, and bottom distortion and twisting amount was also evaluated by using different pitch hole patterns. As a result, the authors determined that the distortion is improved by 22% and the twisting is improved by 20% when the mask deformation is reduced by 50% with using a wider pitch pattern.
Hard AlN films prepared by low duty cycle magnetron sputtering and by other deposition techniques
Authors: Kohout Jiří , Qian Jincheng , Schmitt Thomas , Vernhes Richard , Zabeida Oleg , Klemberg-Sapieha Jolanta , Martinu Ludvik
Published: August 2017

Crystalline AlN films are very attractive due to their properties such as high thermal stability and relatively high hardness and piezoelectric response. However, the deposition of dense textured AlN films with superior quality at a high deposition rate remains a challenge. In the present work, a reactive low duty cycle pulsed direct current magnetron sputtering (LDMS) process was employed to deposit AlN films on glass and silicon substrates. An arc-free discharge on the Al target was achieved by using short voltage pulses of 10 μs at a low duty cycle of 10%. The authors optimized the deposition conditions in terms of reactive gas flow, working pressure, average target power, substrate temperature, substrate bias, and the level of target erosion. With the optimized deposition conditions, the authors were able to obtain transparent crystalline AlN films with strong (002) preferential orientation and very good optical and mechanical properties: The AlN films with the highest refractive index of 2.1 present a hardness of up to 22 GPa and a low residual stress of ≈+300 MPa. Meanwhile, a relatively high deposition rate of ≈45 nm/min was achieved. A systematic comparison of the LDMS process with five other magnetron sputtering approaches working at optimized conditions indicated superior performance of the LDMS technique. This approach leads to the most promising results in terms of discharge stability, deposition rate, and film properties, and thus, it shows much promise for reactive deposition of dielectric materials and hard optical coatings.
Calibration of focused ultrasonic transducers and absolute measurements of fluid nonlinearity with diffraction and attenuation corrections
Authors: Li Xiongbing , Zhang Shuzeng , Jeong Hyunjo , Cho Sungjong
Published: August 2017

This paper presents analytical and experimental techniques for absolute determination of the acoustic nonlinearity parameter (β) in fluids using focused transducers. When focused transducers are used for β measurements, the geometrical and mechanical calibrations are generally required for accurate determination of the receiver transfer function from which the absolute pressure can be calculated. The fundamental and second harmonic wave amplitudes in harmonic generation measurements should be modified to account for beam diffraction and material absorption. All these issues are resolved in this study and the proposed technique is validated through the β measurement in water. An experimental method is developed to determine the effective radius and focal length of focused transducers. A simplified self-reciprocity calibration procedure for a broadband focused receiver is described. The diffraction and attenuation corrections for the fundamental and second harmonic waves are explicitly derived using the multi-Gaussian beam model, and the effects on the β determination are discussed. When the diffraction and attenuation corrections are all properly made, the measurement of β over a large range of propagation distances is possible with errors less than 8%.
Entanglement relaxation time of polyethylene melts from high-frequency rheometry in the mega-hertz range
Authors: Szántó Levente , Vogt Robert , Meier Julia , Auhl Dietmar , Van Ruymbeke Evelyne , Friedrich Christian
Published: August 2017

The determination of relevant rheological properties and parameters in a very broad frequency range can be achieved for a number of thermoplastic polymers, for example, polystyrene, by applying the time-temperature-superposition principle. In contrast, polyethylene can only be explored rheologically in a limited frequency range, due to its fast crystallization below the crystallization temperature and its weak viscosity temperature-dependence. In this paper, various commercially available polydisperse and narrowly distributed linear and branched polyethylenes and ethylene-vinylacetate-copolymers were characterized. A piezoelectric- and a new quartz (crystal resonator) rheometer (QR) with an extended frequency range were utilized for the characterization. Introduction of high frequency rheological techniques and implementation of these new measurement methods are shown. For the first time, the entanglement relaxation time in the higher MHz frequency range was determined by applying the QR-technique and compared with those obtained by an alternative experimental method and numerical calculations.
Where has all the Zika gone?
Authors: Cohen Jon
Published: August 2017

The epidemic in the Americas has all but disappeared—at least for now.
‘Safe spaces’ may save the European mink
Authors: Karáth Kata
Published: August 2017

Spanish researchers create an ecological island free of American mink, a fierce competitor.
Preventing mussel adhesion using lubricant-infused materials
Authors: Amini Shahrouz , Kolle Stefan , Petrone Luigi , Ahanotu Onyemaechi , Sunny Steffi , Sutanto Clarinda N. , Hoon Shawn , Cohen Lucas , Weaver James C. , Aizenberg Joanna , Vogel Nicolas , Miserez Ali
Published: August 2017

When you don't want things to stick

During marine fouling, surfaces are encrusted with scale or biological organisms, which can be expensive to remove. Amini
et al.
used polymers infused with organic lubricants to prevent mussels from adhering to a submerged surface. The infused polymer presents a relatively soft surface to the mussel. This means that when the mussel probes the surface with its feet, it is less likely to release adhesive threads, which reduces its adhesion. The antifouling properties of the treatment were observed in both a laboratory setting and field testing.

Science
, this issue p.
668
An unusual white dwarf star may be a surviving remnant of a subluminous Type Ia supernova
Authors: Vennes S. , Nemeth P. , Kawka A. , Thorstensen J. R. , Khalack V. , Ferrario L. , Alper E. H.
Published: August 2017

Unusual star may be supernova debris

Type Ia supernovae occur when a white dwarf star is completely destroyed in a thermonuclear explosion. Recently, another class of supernova has been found, dubbed type Iax; these look like type Ia but are much fainter and may be the result of only partial destruction of a white dwarf. In support of this notion, Vennes
et al.
found a white dwarf star in our Galaxy that is low-mass, is moving quickly, and has an unusual composition. These properties suggest that it could be the predicted leftover remains from a type Iax supernova.

Science
, this issue p.
680
Deriving genomic diagnoses without revealing patient genomes
Authors: Jagadeesh Karthik A. , Wu David J. , Birgmeier Johannes A. , Boneh Dan , Bejerano Gill
Published: August 2017

Sharing data, protecting privacy

Although data-sharing is crucial for making the best use of genetic data in diagnosing disease, many individuals who might donate data are concerned about privacy. Jagadeesh
et al.
describe a solution that combines a protocol from modern cryptography with frequency-based clinical genetics used to diagnose causal disease mutations in patients with monogenic disorders. This framework correctly identified the causal gene in cases involving actual patients, while protecting more than 99% of individual participants' most private variants.

Science
, this issue p.
692
Vinculin forms a directionally asymmetric catch bond with F-actin
Authors: Huang Derek L. , Bax Nicolas A. , Buckley Craig D. , Weis William I. , Dunn Alexander R.
Published: August 2017

Making the right catch

Tension reveals cryptic vinculin-binding sites on α-catenin and talin at cadherin-based cell-cell and integrin-based cell-matrix adhesions, respectively. The enrichment of vinculin at cellular adhesions is thus an indicator of load-induced reinforcement of the cytoskeletal linkage. Huang
et al.
used a single-molecule optical trap assay to measure the binding lifetimes of vinculin to single actin filaments under load. The vinculin-F-actin interaction formed a directional catch bond—one that is very weak at low force but that greatly increases in lifetime with increasing force. This explains vinculin's role as a reinforcing linker at both cell-cell and cell-matrix adhesions.

Science
, this issue p.
703
A molecular spin-photovoltaic device
Authors: Sun Xiangnan , Vélez Saül , Atxabal Ainhoa , Bedoya-Pinto Amilcar , Parui Subir , Zhu Xiangwei , Llopis Roger , Casanova Fèlix , Hueso Luis E.
Published: August 2017

A spin-valve solar cell

Electronic spin currents can be measured with a spin valve—a device that injects charge carriers from one ferromagnetic electrode to another through a semiconductor layer. Some organic semiconductors can have long spin-carrier lifetimes and can also generate charge carriers through the photovoltaic effect. Sun
et al.
fabricated a spin valve based on C
60
and showed that the spin current could be modulated by the photocurrent. At certain light intensities, the sign of the photocurrent could be changed using an applied magnetic field, an effect that could potentially be harnessed for sensing applications.

Science
, this issue p.
677
Vortex generation reaches a new plateau
Authors: Qiu Cheng-Wei , Yang Yuanjie
Published: August 2017

Surface engineering provides a powerful platform for vortex and structured wave generation
Self-healing soft pneumatic robots
Authors: Terryn Seppe , Brancart Joost , Lefeber Dirk , Van Assche Guy , Vanderborght Bram
Published: August 2017

Soft robots manufactured out of self-healing polymers have the ability to repair macroscopic damage.
Complement C3 deficiency protects against neurodegeneration in aged plaque-rich APP/PS1 mice
Authors: Shi Qiaoqiao , Chowdhury Saba , Ma Rong , Le Kevin X. , Hong Soyon , Caldarone Barbara J. , Stevens Beth , Lemere Cynthia A.
Published: August 2017

C3 deficiency protects against hippocampal neurodegeneration and cognitive decline in aged APP/PS1 mice despite abundant Aβ plaques.
Infectivity of
Plasmodium falciparum
sporozoites determines emerging parasitemia in infected volunteers
Authors: McCall Matthew B. B. , Wammes Linda J. , Langenberg Marijke C. C. , van Gemert Geert-Jan , Walk Jona , Hermsen Cornelus C. , Graumans Wouter , Koelewijn Rob , Franetich Jean-François , Chishimba Sandra , Gerdsen Max , Lorthiois Audrey , van de Vegte Marga , Mazier Dominique , Bijker Else M. , van Hellemond Jaap J. , van Genderen Perry J. J. , Sauerwein Robert W.
Published: August 2017

Infectivity of
P. falciparum
sporozoites determines the course of primary malaria infection in human volunteers.
Sulforaphane reduces hepatic glucose production and improves glucose control in patients with type 2 diabetes
Authors: Axelsson Annika S. , Tubbs Emily , Mecham Brig , Chacko Shaji , Nenonen Hannah A. , Tang Yunzhao , Fahey Jed W. , Derry Jonathan M. J. , Wollheim Claes B. , Wierup Nils , Haymond Morey W. , Friend Stephen H. , Mulder Hindrik , Rosengren Anders H.
Published: August 2017

Sulforaphane, a natural compound identified by drug repurposing, reduces hepatic glucose production and improves glucose control in type 2 diabetes.