bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Optimization of Geometry Parameters for Shaped Film Cooling Holes
Authors: Alshehaby Mohammad M. , Ragab Kasem E. , El-Gabry Lamyaa
Published: August 2017

Film cooling, along with other approaches, are essential to control the very high gas temperatures passing over gas turbine blades. The abundant research in film cooling characteristics and parameters reveals the importance of the topic as an integral part of blade cooling. Although these extensive studies have identified the important parameters that influence both aerodynamics and thermal performance of film cooling, optimization research is continuing to enhance overall system design. Owing to the simplicity in manufacturing, the circular hole shape has been studied more than any other shaped coolant hole. However, data from literature shows that shaped hole may limit coolant jet separation, resulting in less aerodynamic losses and better cooling effect. The purpose of the present study is to numerically verify aeroslot (rectangular slot with fully round ends) superiority over circular one by neutralizing other important parameters, and to optimize the aeroslot aspect ratio (straight length over thickness) to maximize cooling effect. After confirming model validity, a comparison between aeroslot and circular hole showed a superiority of the former in terms of adiabatic film effectiveness. In addition, aspect ratio optimization was evaluated in terms of both adiabatic film effectiveness and Nusselt number indications. Aspect ratios from 2.5 to 8 were tested. It was found that the optimum aspect ratio for overall cooling performance is 7. The influence of velocity and thermal diffusion on surface temperature was examined.
Numerical Investigation of Local Cooling Enhancement Using Pin-Finned Channel With Incremental Impingement
Authors: Singh Susheel , Acharya Sumanta , Ames Forrest
Published: August 2017

Flow and heat transfer in a low aspect ratio pin-finned channel, representative of an internally cooled turbine airfoil, is investigated using Large Eddy Simulations (LES). To achieve greater control of surface cooling distribution, a novel approach has been recently proposed in which coolant is injected incrementally through a series of holes located immediately behind a specially designed cutout region downstream of the pin-fins. Sheltering the coolant injection behind the pin-fins avoids the impact of the cross-flow buildup that deflects the impingement jet and isolates the surface from cooling. The longitudinal and transverse spacing of the pin-fins, arranged in a staggered fashion, is X/D = 1.046 and S/D = 1.625, respectively. The aspect ratio (H/D) of pin-fin channel is 0.5. Due to the presence of the sequential jets in the configuration, the local cooling rates can be controlled by controlling the jet-hole diameter which impacts the jet mass flow rate. Hence, four different hole diameters, denoted as Large (L), Medium (M) , Small (S), Petite (P) are tested for impingement holes, and their effects are studied. Several patterns of the hole-size distributions are studied. It is shown that the peak Nusselt number in the stagnation region below the jet correlates directly with the jet-velocity, while downstream the Nusselt numbers correlate with the total mass flow rates or the average channel velocity. The local cooling parameter defined as (Nu/Nu0)(1-ε) correlates with the jet/channel mass flow rates.
Analytical Investigation of a Thermal-Supercharged Internal Combustion Engine Compounded With Organic Rankine Cycle for Waste Heat Recovery
Authors: Jiménez-Arreola Manuel , Dal Magro Fabio , Romagnoli Alessandro , Chiong Meng Soon , Rajoo Srithar , Martinez-Botas Ricardo F.
Published: August 2017

Waste heat recovery is seen as one of the key enablers in achieving powertrain of high efficiency. The exhaust waste heat from an internal combustion engine (ICE) is known to be nearly equivalent to its brake power. Any energy recovered from the waste heat, which otherwise would be discarded, may directly enhance the overall thermal efficiency of a powertrain. Rankine cycle (indirect-recovery method) has been a favorable mean of waste heat recovery due to its rather high power density yet imposing significantly lesser back pressure to the engine compared to a direct-recovery method.

This paper presents the analytical investigation of a thermal-supercharged ICE compounded with Rankine cycle. This system removes the turbocharger turbine to further mitigate the exhaust back pressure to the engine, and the turbocharger compressor is powered by the waste heat recovered from the exhaust stream. Extra caution has been taken when exchanging the in/output parameters between the engine and Rankine cycle model to have a more realistic predictions. Such configuration improves the engine BSFC performance by 2.4–3.9%. Water, Benzene and R245fa are found to be equally good choice of working fluid for the Rankine cycle, and can further advance the BSFC performance by 4.0–4.8% despite running at minimum pressure setting. The off-design analyses suggested the operating pressure of Rankine cycle and its expander efficiency have the largest influence to the gross system performance.
An Experimental Study of Stall Suppression and Associated Changes to the Flow Structures in the Tip Region of an Axial Low Speed Fan Rotor by Axial Casing Grooves
Authors: Chen Huang , Li Yuanchao , Koley Subhra Shankha , Doeller Nick , Katz Joseph
Published: August 2017

The effects of axial casing grooves on the performance and flow structures in the tip region of an axial low speed fan rotor have been studied experimentally in the JHU refractive index-matched liquid facility. The four-per-passage semicircular grooves are skewed by 45° in the positive circumferential direction, and have a diameter of 65% of the rotor blade axial chord length. A third of the groove overlaps with the blade front, and the rest extends upstream. These grooves have a dramatic effect on the machine performance, reducing the stall flow rate by 40% compared to the same machine with a smooth endwall. However, they reduce the pressure rise at high flow rates. The flow characterization consists of qualitative visualizations of vortical structures using cavitation, as well as stereo-PIV (SPIV) measurements in several meridional and (z,θ) planes covering the tip region and interior of the casing grooves. The experiments are performed at a flow rate corresponding to pre-stall conditions for the untreated machine. They show that the flow into the downstream sides of the grooves and the outflow from their upstream sides vary periodically. The inflow peaks when the downstream end is aligned with the pressure side (PS) of the blade, and decreases, but does not vanish, when this end is located near the suction side (SS). These periodic variations have three primary effects: First, substantial fractions of the leakage flow and the tip leakage vortex (TLV) are entrained periodically into the groove. Consequently, in contrast to the untreated flow, The TLV remnants remain confined to the vicinity of the entrance to the groove, and the TLV strength diminishes starting from the mid-chord. Second, the grooves prevent the formation of large scale backflow vortices (BFVs), which are associated with the TLV, propagate from one blade passage to the next, and play a key role in the onset of rotating stall in the untreated fan. Third, the flow exiting from the grooves causes periodic variations of about 10° in the relative flow angle around the blade leading edge, presumably affecting the blade loading. The distributions of turbulent kinetic energy provide statistical evidence that in contrast to the untreated casing, very little turbulence originating from a previous TLV, including the BFVs, propagates from the PS to the SS of the blade. Hence, the TLV-related turbulence remain confined to the entrance to groove. Elevated, but lower turbulence is also generated as the outflow from the groove jets into the passage.
The Effect of Coating Composition and Geometry on TBC Lifetime
Authors: Pint Bruce A. , Lance Michael J. , Haynes J. Allen
Published: August 2017

Several factors are being investigated that affect the performance of thermal barrier coatings (TBC) for use in land-based gas turbines where coatings are mainly thermally sprayed. This study examined high velocity oxygen fuel (HVOF), air plasma sprayed (APS) and vacuum plasma sprayed (VPS) MCrAlYHfSi bond coatings with APS YSZ top coatings at 900°–1100°C. For superalloy 247 substrates and VPS coatings tested in 1-h cycles at 1100°C, removing 0.6wt.%Si had no effect on average lifetime in 1-h cycles at 1100°C, but adding 0.3%Ti had a negative effect. Rod specimens were coated with APS, HVOF and HVOF with an outer APS layer bond coating and tested in 100-h cycles in air+10%H2O at 1100°C. With an HVOF bond coating, initial results indicate that 12.5 mm diameter rod specimens have much shorter 100-h cycle lifetimes than disk specimens. Longer lifetimes were obtained when the bond coating had an inner HVOF layer and outer APS layer.
Comparison of Temperature Fields and Emissions Predictions Using Both an FGM Combustion Model, With Detailed Chemistry, and a Simple Eddy Dissipation Combustion Model With Simple Global Chemistry
Authors: Gauthier Pierre Q.
Published: August 2017

The detailed modeling of the turbulence-chemistry interactions occurring in industrial flames has always been the leading challenge in combustion Computational Fluid Dynamics (CFD). The wide range of flame types found in Industrial Gas Turbine Combustion systems has exacerbated these difficulties greatly, since the combustion modeling approach must be able to predict the flames behavior from regions of fast chemistry, where turbulence has no significant impact on the reactions, to regions where turbulence effects play a significant role within the flame. One of these combustion models, that is being used more and more in industry today, is the Flamelet Generated Manifold (FGM) model, in which the flame properties are parametrized and tabulated based on mixture fraction and flame progress variables. This paper compares the results obtained using an FGM model, with a GRI-3.0 methane-air chemistry mechanism, against the more traditional Industrial work-horse, Finite-Rate Eddy Dissipation Model (FREDM), with a global 2-step Westbrook and Dryer methane-air mechanism. Both models were used to predict the temperature distributions, as well as emissions (NOx and CO) for a conventional, non-premixed, Industrial RB211 combustion system. The object of this work is to: (i) identify any significant differences in the predictive capabilities of each model and (ii) discuss the strengths and weakness of both approaches.
Research on Fluid Flow Stability With Baffles of Different Size in a Hydrodynamic Coupling During Partially Liquid-Filled Operating Conditions
Authors: Yan Qingdong , An Yuanyuan , Wei Wei
Published: August 2017

The hydrodynamic coupling is a power transmission device dependent on the liquid medium momentum change with the advantage of slow shock, isolation of torsional vibration, start light load and overload protection, which is applied in engineering, mining, construction, lifting the transport machinery, et al[1]. The hydrodynamic coupling without inner ring usually works in partially liquid-filled operating conditions, when the flow state changes suddenly with the rotating speed ratio changing. This may lead to unstable gas-liquid two-phase flow in a hydrodynamic coupling in a certain ratio range. To improve the stability of two-phase flow, a baffle is set inside the circulatory circle of a hydrodynamic coupling. The baffle blocks part of the flow area between two wheels in the hydrodynamic coupling. The size of baffle plays an important role on the effect for improving the flow stability.

To investigate the influence of the baffle to the internal flow stability, the two-phase flow (liquid-filling rate is 80%) in hydrodynamic couplings with baffles in different sizes and without baffles were studied by Computational Fluid Dynamics (CFD) numerical simulation with the rotating speed of pump at constant 2200 r/min and rotating speed of turbine changing from 0 to 2200r/min. The corresponding distributions of streamlines and characteristics curves were obtained.

Through the analysis of turbine torque and efficiency, it is verified that the baffle could improve the flow stability, and the different distributions of streamline could explain the reason. In addition, optimal range of baffle size c = 30% ∼ 40% is obtained by analyzing the simulation results. This will provide a basis for the improvement of design in the hydrodynamic coupling.
Effect of Azimuthal Velocity Fluctuation on Hollow Cone Spray
Authors: I. Babu Aravind , Chakravarthy Satya
Published: August 2017

This paper reports an experimental investigation on the effect of imposed azimuthal velocity fluctuation on the spray characteristics of a hollow cone spray produced from a pressure-swirl nozzle. This effect is inferred by performing experiments separately on 0° and 60° axial straight vane swirlers oriented concentric to the spray nozzle for the air-flow subjected to upstream acoustic forcing. The hollow cone spray is subjected to external excitation using a loudspeaker at two different frequencies and two amplitudes. These frequencies correspond to the resonant frequencies of the plenum. The 60° vane swirler, when subjected to acoustic excitation, produces axial and azimuthal velocity fluctuation downstream of the swirler, whereas the 0° swirler produces only axial velocity fluctuation downstream of the swirler. In both 60° and 0° swirlers, the downstream velocity fluctuation due to acoustic disturbances propagate at the speed of sound. In addition, the velocity fluctuations produced due to the excitation are convected by the mean flow. This results in a combined effect of velocity fluctuations at the swirler exit. The hollow cone spray responds more readily to excitation at low frequencies than higher frequencies. This is observed from the high-speed shadowgraph images. The high-speed shadowgraph images acquired are processed to extract spray cone angle. The phase averaged spray cone angle fluctuates for different phase angle within an acoustic cycle. The analysis of the high-speed shadowgraph images shows that the cone angle fluctuation amplitude is higher for the 0° swirler as compared to the 60° swirler. The variation of the liquid sheet thickness and breakup length due to excitation is captured using high-speed planar laser induced fluorescence. The study clearly demonstrates that azimuthal velocity fluctuation affects the spray formation process.
Measurements and Characterization of Turbulence in the Tip Region of an Axial Compressor Rotor
Authors: Li Yuanchao , Chen Huang , Katz Joseph
Published: August 2017

Modeling of turbulent flows in axial turbomachines is challenging due to the high spatial and temporal variability in the distribution of the strain rate components, especially in the tip region of rotor blades. High-resolution stereo PIV measurements performed in a refractive index matched facility in a series of closely-spaced planes provide a comprehensive database for determining all the terms in the Reynolds stress and strain rate tensors. Results are also used for calculating the turbulent kinetic energy production rate and transport terms by mean flow and turbulence. They elucidate some but not all of the observed phenomena, such as the high anisotropy, high turbulence levels in the vicinity of the tip leakage vortex (TLV) center, and in the shear layer connecting it to the blade suction side (SS) tip corner. The applicability of popular Reynolds stress models based on eddy-viscosity is also evaluated by calculating it from the ratio between stress and strain components. Results vary substantially, depending on which components are involved, ranging from very large positive to negative values. In some areas, e.g., in the tip gap and around the TLV, the local stresses and strains do not appear to be correlated at all. In terms of effect on the mean flow, for most of the tip region, the mean advection terms are much higher than the Reynolds stress spatial gradients, i.e., the flow dynamics is dominated by pressure-driven transport. However, they are of similar magnitude in the shear layer, where modeling would be particularly challenging.
Mode Shapes and Dominant Frequency Predictions in a Swirl Stabilized Premixed Air-Methane Combustor Using Modal Analysis and Large Eddy Simulations (LES)
Authors: Jadhav Tushar , Orsino Stefano , Patwardhan Saurabh , Nakod Pravin
Published: August 2017

Stringent emission regulations force the gas turbine combustor community to come up with new designs. Lean Premixed (LPM) combustion is gaining popularity to meet the emission regulations. However, lean combustion process is prone to other issues like combustion instabilities and noise. Self-excited combustion instabilities in a gas turbine play vital role in the life cycle of combustor, noise generation and pollutant formation. If the instabilities in combustor dominate at natural modes, there are risks of resonance which can lead to bursting damage to the combustors.

In the present work, modal analysis is carried out to predict the longitudinal and the transverse modes in a swirl-stabilized premixed methane-air combustor. The geometrical details and the boundary conditions used in this work are described in Broda et al. [1]. In addition to the modal analysis, Large Eddy Simulations (LES) with Flamelet Generation Manifold (FGM) combustion model are carried out to find out the instabilities and their sources. In the large eddy simulation, at the inlet of the combustor, a broadband impedance boundary condition is used. This will consider the effect of upstream travelling acoustic waves at the inlet. The outlet of combustor is specified with non-reflecting boundary condition. The inlet mass flow rate and the temperature conditions are consistent with Broda et al. [1]. The longitudinal and transverse modes predicted by the modal analysis and the dominant frequency predicted in the LES case are compared with the experimentally observed values. The predicted first longitudinal mode at ∼1760 Hz compares well with the experimental value of 1760 Hz. Predicted values of first and second tangential modes at 10459 Hz and 17344 Hz are also in good agreement with the experimental measurement. The dominant frequency predicted by the LES simulation is 1940 Hz. After applying the appropriate correction to this value for the wall heat transfer effect, it is in-line with that obtained from the modal analysis and the experiments. The spectral analysis at different probe location in LES simulation shows higher thermo-acoustic coupling at natural frequencies. In this work, the effect of variation in inlet swirl number and the temperature is also studies. The predicted trends in the change in dominant frequency with the increase in inlet swirl number and inlet temperature are captured accurately. For each condition, calculations were performed for about four flow-through times (around 12 ms) after the flow field had reached to its limit cycle to obtain statistically steady condition.
A Novel Experimental Method for LCF Measurement of Nickel Base Super Alloys in High Pressure High Temperature Supercritical CO2
Authors: Thatte Azam , Martin Etienne , Hanlon Tim
Published: August 2017

CSP plants using supercritical CO2 (sCO2) power cycle can potentially achieve high thermal conversion efficiency at low capital cost due to compact turbomachinery and other components. An sCO2 expander and improved heat exchanger is expected to provide a major stepping stone for achieving CSP power at $0.06/kW-hr LCOE, energy conversion efficiency > 50%, and total power block cost < $1,200/kW installed. However the life limiting mechanisms of these turbomachines in high pressure, high temperature sCO2 environment are not well understood. To understand the effect of high pressures, high temperatures and sCO2 chemical kinetics on crack initiation, crack propagation and low cycle fatigue (LCF) life of these turbomachines, a novel experimental setup is developed. Advanced microstructure and spectroscopic analyses are conducted that shed light on some key differences between various Ni base alloys in terms of oxidation morphology, chemical species diffusion and trapping, the formation of protective corrosion resistant layers and changes in surface properties. An experimental technique for low cycle fatigue experiments in high pressure, high temperature supercritical CO2 environment is developed. The test setup allows for pressurized LCF testing of alloys being considered for MW scale sCO2 turbine development. Results show that the LCF life remains the same (within the scatter band) irrespective of the location of crack initiation site whether at the OD (non shot-peened bars in air and sCO2), or at the ID (shot peened bars). Total fatigue life, for all conditions, lie within the normal variation in LCF results (± 2X life variation). No significant LCF life debit is observed in IN718 by sCO2 at 550 °C, 0.7% max strain, 20 cpm. Similar conclusion is reached during 0.6% max strain tests. The effect of sCO2 is found not to be significantly more damaging than air at these strain levels. However, the results can be different for lower % max strains due to longer exposure times involved, resulting from larger number of cycles to failure. Similarly at higher temperatures and/or longer hold-times, sCO2 environment may be more aggressive, resulting in lower total fatigue life.
Aerodynamic Inverse Blade Design of Axial Compressors in Three-Dimensional Flow Using a Commercial CFD Program
Authors: Arbabi Araz , Ghaly Wahid , Medd Adam
Published: August 2017

An aerodynamic inverse design method is developed for the simulation of three-dimensional viscous flow over blades, it is implemented into a commercial CFD program, namely ANSYS-CFX, and it is applied to the design of a transonic compressor stage. The implementation is validated for Rotor 37; it is then assessed in the redesign of Stage 67 stator. One set of design choices is to prescribe a target blade pressure loading and blade thickness distributions and a stacking line from hub to tip. The blade walls are assumed to be moving with a virtual velocity that would asymptotically drive the blade to the shape that would correspond to the specified target pressure distribution. This virtual velocity distribution is computed from the difference between the computed and the target pressure distributions. This inverse design approach is fully consistent with the viscous flow assumption and is independent of the CFD approach taken. The Arbitrary Lagrangian-Eulerian formulation of the unsteady Reynolds-Averaged Navier Stokes equations is solved in a time accurate fashion with the blade motion being the source of unsteadiness. At each time step, the blade shape is modified and dynamic meshing is used to remesh the fluid flow domain. To demonstrate the ability of this approach, it is applied to redesign the stator of a transonic axial fan, Stage 67, to improve its performance.
Large Eddy Simulation of Combustion Instability of Low-Swirl Flames in a Multi-Nozzle Combustor
Authors: Liu Weijie , Ge Bing , Zang Shusheng , Li Mingjia , Xu Wenyan
Published: August 2017

Large eddy simulation of self-induced combustion instability of low-swirl flames in a multi-nozzle combustor is carried out. The unsteady behaviors in the multi-nozzle burner including pressure fluctuation, velocity oscillation, PVC and triggering mechanism are studied in detail. Numerical result is compared with experimental measurement in terms of frequency and amplitude of pressure fluctuation. Results show LES successfully predicts the longitudinal instability mode in the multi-nozzle combustor with a reasonable agreement with experimental data. Flow parameters in the burner, such as pressure, axial velocity and CH4 mass fraction oscillate with the same frequency but different phases. Combustion instability leads to flame flashback into the burner due to the reversal flow. Vortex generation and shedding off in the outer shear layer result in unsteady heat release at the tail edge of the outer flame near combustor wall. Meanwhile, the unsteady heat release feedback to the pressure and flowfield, which is the main reason for inducing combustion instability.
A Framework to Predict Combustion Noise and Instability: Case Study of a Partially Premixed Flame in a Backward-Facing Step Combustor
Authors: Kannan Ashwin , Chakravarthy S. R.
Published: August 2017

Incompressible large eddy simulations coupled with acoustics are performed to predict combustion noise and instability in a partially premixed based backward facing step combustor. The computational analysis adopts a simultaneous multi-scale spatio-temporal framework for flow and acoustics such that the flow/acoustics varies at a shorter/longer length scale and a longer/shorter time scale respectively. This engenders flow dilatation and acoustic Reynolds stress (ARS) as the external source terms in the acoustic energy and flow momentum respectively. Numerical results are presented for three cases, at a particular Reynolds number, wherein two of them constitute acoustically coupled (coupled long duct case) and its uncoupled counterpart (no acoustic feedback). The third corresponds to a shorter combustor length (coupled short duct case). These three cases contrast the strong acoustic feedback in the short duct case, both of which are compared with the acoustically uncoupled LES that is common to them. It is found that combustion occurs predominantly in the large-scale vortical structures in the coupled long duct case due to enhanced mixing between the reactants brought about by the strong acoustic feedback (ARS). Thus, the present work is able to not only distinguish between the flow and acoustic processes, but also handle both combustion noise and instability within the same framework.
Design of Casing Treatment on a Mixed-Flow Compressor
Authors: Du Juan , Seume Joerg R.
Published: August 2017

Casing treatments (CTs) have been proved to beneficially affect the behavior of tip clearance flow and compressor stability. This paper presents the design of casing treatment for a mixed-flow compressor with a very small tip gap of 0.1mm. In the first part, the potential of applying two traditional types of casing treatments, i.e. circumferential grooves and axial slots, to enhance the stability of a mixed-flow compressor is investigated. The flow details in the reference compressor with smooth casing are examined first. It is found that a separating vortex is formed due to the reversed flow on the blade suction side near the rotor trailing edge at the near-stall point. It is supposed to be responsible for the decrease in total pressure ratio when the compressor approaches to stall. The numerical stall, i.e. the breakdown of the simulation, is initiated from the spillage of tip leakage flow over the rotor blade leading edge. The effect of circumferential grooves on the compressor performances is not remarkable. The implement of axial slots ameliorates the total pressure ratio and extend the flow range substantially, but with higher efficiency penalty than the circumferential grooves. The recirculation formed in the axial skewed slots eliminates the separation vortex near the trailing edge and suppresses the spillage of the tip leakage flow forward the rotor leading edge simultaneously. The axial skewed slots are further designed and optimized numerically by DoE (Design of Experiments). As DoE factors the axial length, the height, the open area ratio, and the number per blade passage of the slots are varied. Their effects on the two target values stall margin and polytropic efficiency are investigated. The plot of stall margin improvement (SMI) with a function of the peak efficiency improvement (PEI) indicates that the SMI changes reversely with the PE. There are two trends in the correlation curves of SMI with PE. For the configurations with the open area ratio of 20%, the SMI is changed from 9% to 23% with 1% decrease in PE by varying other three factors. For the CTs with the open area ratio of 60% the augment in SMI from 17.8% to 26.3% produces extra efficiency loss of 4.2%.
Including Pivot Friction in Pad Motion for a Tilting Pad Journal Bearing With Ball-Socket Pivots
Authors: He Feng
Published: August 2017

Tilting pad journal bearing has its wide application in turbomachinery. For years, frictionless contact has been assumed for all the contact types in bearing coefficients prediction of tilting pad bearings. Existing experimental data demonstrates contact friction does present in pivots and can prevent pads from effective tilting, which is especially true for the surface contact pivot, e.g. ball-socket pivot. However, no open literature is available to discuss individual pad motion with consideration of pivot contact friction and document the effects on the dynamic behaviors of tilting pad bearings. This paper tries to improve the understanding in this area by discussing the pad motion of a tilting pad bearing with ball-socket pivots subject to pivot friction. A model, which couples the journal motion, hydrodynamic pressure from oil film and contact pressure within the pivots, is established. Instead of Hertz contact, a conformal contact model is applied for the ball-socket contact. Through the coupled transient analyses, the effects of contact friction coefficients, bearing dynamic and static loading, and pivot size on pads motion of a 5-pads load-on-pad bearing are considered and compared.

The results show that the presence of friction within ball-socket pivots does not guarantee “locked up” pads motion, but only limits pads from effective tilting for a given range of friction coefficients. Larger dynamic load increases pad tilting amplitude; this does not mean that enlarged tilting magnitudes reduce pivot friction moments for the pads. With varying bearing loads, the pivot friction could result in non-synchronous motion of pads tilting and pivots deformation and bring these non-synchronous components into the journal vibration. Size-reduced pivots are found to diminish the effects of pivot friction and offer preferred pads dynamics and journal vibration.
Evaluation of Using Supercritical Rankine Cycles in Integrated Coal Gasification Combined Cycles (IGCC)
Authors: Long Henry A. , Wang Ting , Thomas Arian
Published: August 2017

Coal is a prominent energy resource in the modern world, particularly in countries with emerging economies. In order to reduce emissions, it is necessary to find a way to utilize coal in a cleaner manner, such as through supercritical and ultra-supercritical Rankine cycles and the Integrated Gasification Combined Cycle (IGCC). Two approaches — raising the boiler pressure and using a reheat scheme — have been proven to notably increase the Rankine cycle efficiency. Thus, this study aims to investigate the effects of implementing reheat and supercritical or ultra-supercritical pressure in the bottom Rankine cycle on the IGCC cycle efficiency. First, reference cases of a standalone Rankine cycle were studied with single and double reheat, including boiler pressure levels from subcritical to ultra-supercritical conditions, followed by similar combined cycle cases, and finally IGCC systems. The results indicate that the notable efficiency enhancement in the standalone subcritical Rankine cycle do not prevail in the studied IGCC systems. Thus, it is not economically worthwhile to implement supercritical or ultra-supercritical bottom Rankine cycles in IGCC applications.
Large Eddy Simulations of a Pressurized, Partially-Premixed Swirling Flame With Finite-Rate Chemistry
Authors: Jella Sandeep , Gauthier Pierre , Bourque Gilles , Bergthorson Jeffrey , Bulat Ghenadie , Rogerson Jim , Sadasivuni Suresh
Published: August 2017

Finite-rate chemical effects at gas turbine conditions lead to incomplete combustion and well-known emissions issues. Although a thin flame front is preserved on an average, the instantaneous flame location can vary in thickness and location due to heat losses or imperfect mixing. Post-flame phenomena (slow CO oxidation or thermal NO production) can be expected to be significantly influenced by turbulent eddy structures. Since typical gas turbine combustor calculations require insight into flame stabilization as well as pollutant formation, combustion models are required to be sensitive to the instantaneous and local flow conditions. Unfortunately, few models that adequately describe turbulence-chemistry interactions are tractable in the industrial context. A widely used model capable of employing finite-rate chemistry, is the Eddy Dissipation Concept (EDC) model of Magnussen. Its application in large eddy simulations (LES) is problematic mainly due to a strong sensitivity to the model constants which were based on an isotropic cascade analysis in the RANS context.

The objectives of this paper are: (i) To formulate the EDC cascade idea in the context of LES; and (ii) To validate the model using experimental data consisting of velocity (PIV measurements) and major species (1-D Raman measurements), at four axial locations in the near-burner region of a Siemens SGT-100 industrial gas turbine combustor.
Testing Protruding Studs As a Form of Casing Treatment on a Transonic Turbofan: A Computational Study
Authors: Collao M. David , Webster Robert S. , Sreenivas Kidambi
Published: August 2017

This paper presents the findings of an ongoing CFD study of using protruding studs as a form of casing treatment on a transonic turbofan stage. Simulations have been performed on the subject turbomachine with and without the casing treatment in order to validate computations with available experimental results and to compute any difference in performance. The results of the simulations with the casing treatment suggest that protruding studs have the potential to extend the stall margin of the turbofan while resulting in a slight reduction in pressure rise and efficiency. From the use of an initial configuration of studs, the computed increase in stall margin based on mass flow rate was 5.46%, and the greatest decrease in pressure ratio and adiabatic efficiency were 0.25% and 1.59%, respectively. Flowfield visualizations of simulations at computed near-stall conditions without casing treatment show regions of low momentum flow near the casing in the rotor blade passage, and low momentum regions near the hub in the stator section. Visualization from simulations with casing treatment at computed near-stall conditions show a large blockage imposed by the studs in the rotor blade passage, and a low momentum region near the casing in the stator section. Computed performance maps obtained from using other configurations of studs suggest that further increase in stall margin is possible at other levels of protrusion of the studs.
Optimal Gas Turbine Power Plant Operation Regarding Fuel and Maintenance Cost
Authors: Waniczek Phillip , Therkorn Dirk , Lilley Darrel
Published: August 2017

This paper describes a method that optimizes the commercial benefit by modifying gas turbine control parameters like turbine inlet temperature and variable inlet guide vane position for any dispatched power plant load. The method is a trade-off between best efficiency in the component characteristic together with higher efficiency due to increased turbine inlet temperature and lifetime. With commercial data, both effects are transferred into costs and an optimization routine identifies controller settings for minimum power plant operation cost.

Test cases demonstrate the advantage of the operational cost optimization. Costs are calculated based on historic plant data with the original and the optimized operation concept. Although savings per operating hour are small, the accumulated savings over years or major inspection intervals are significant. It could be demonstrated that in regions with high fuel prices the commercial benefit of the optimized gas turbine operating concept sums up to “several million dollars” of savings. Parametric and sensitivity studies show the effect of the main parameters.

Dispatch power optimization is not subject of the presented model, but can be implemented on top of the proposed concept.

All in all, this work demonstrates and quantifies the commercial benefits when todays and future digital industrial capabilities are applied to gas turbine operation concepts and strategies. The proposed digital approach has the advantage of minimum investment and is attractive for gas turbine operators to generate electricity at lower costs and fuel consumption, increasing revenues and minimizing environmental impact.
The role of floridoside in osmoadaptation of coral-associated algal endosymbionts to high-salinity conditions
Authors: Ochsenkühn Michael A. , Röthig Till , D’Angelo Cecilia , Wiedenmann Jörg , Voolstra Christian R.
Published: August 2017

In response to high salinity, algal endosymbionts of corals produce floridoside, an osmolyte with antioxidant potential.
From the surface to the seafloor: How giant larvaceans transport microplastics into the deep sea
Authors: Katija Kakani , Choy C. Anela , Sherlock Rob E. , Sherman Alana D. , Robison Bruce H.
Published: August 2017

Larvaceans can filter microplastics from the water and package them into their fecal pellets, transporting them into the deep sea.
Impaired DNA replication derepresses chromatin and generates a transgenerationally inherited epigenetic memory
Authors: Klosin Adam , Reis Kadri , Hidalgo-Carcedo Cristina , Casas Eduard , Vavouri Tanya , Lehner Ben
Published: August 2017

Inhibiting DNA replication in
C. elegans
embryos causes loss of repressive histone modifications and generates epialleles.
U.S.-Mexico water pact aims for a greener Colorado delta
Authors: Cornwall Warren
Published: August 2017

Experimental flood in 2014 helped shape plan for targeted flows to restoration sites in long-parched ecosystem.
What do revised U.S. rules mean for human research?
Authors: Nichols Lisa , Brako Lois , Rivera Suzanne M. , Tahmassian Ara , Jones Martha F. , Pierce Heather H. , Bierer Barbara E.
Published: August 2017

The updated Common Rule raises many questions
Beyond the museum's mandate
Inside the Lost Museum: Curating, Past and Present
Steven Lubar
Harvard University Press, 2017. 416 pp.
Authors: Brinkman Paul D.
Published: August 2017

A behind-the-scenes tour of iconic institutions offers insight into their once and future roles
Playing marble run to make methane
Authors: Dobbek Holger
Published: August 2017

A crystal structure elucidates a key step in methane generation by archaea
Revisit NIH biosafety guidelines
Authors: Oye Kenneth A. , O'Leary Maureen , Riley Margaret F.
Published: August 2017

To celebrate the anniversary of an arcane federal guideline is a rare event. For an agency to use that moment to invite reflection on modifying policies is even rarer. Last month, the U.S. National Institutes of Health (NIH) did just that, with a workshop that marked the 40th anniversary of its Guidelines for Research Involving Recombinant or Synthetic Nucleic Acid Molecules. The meeting was an inspiring start for charting future oversight of nonclinical applications.
A new therapeutic target for myelofibrosis is cause for Gli
Authors: Jonas Brian A.
Published: August 2017

Myeloproliferative neoplasm cells recruit Gli1 positive mesenchymal stromal cells to transdifferentiate into fibrosis-causing myofibroblasts, a process that can be inhibited by a Gli inhibitor.
A vitamin to D-crease sunburn
Authors: Scharschmidt Tiffany C.
Published: August 2017

High doses of oral vitamin D
3
attenuate skin inflammation following experimentally induced sun damage.
Flipping the kill switch
Authors: Christenson Stephanie A.
Published: August 2017

Alveolar macrophages display an impairment in delayed bacterial killing in chronic obstructive pulmonary disease (COPD) that may contribute to an increased susceptibility to bacterial infection.
When they go low, we go high
Authors: Dzirasa Kafui
Published: August 2017

High-frequency electrical interference can be used to drive activity deep in the brain.
“AMP”(K)ed up recovery from ischemia-reperfusion injury
Authors: Levi Benjamin
Published: August 2017

Aging decreases tolerance to ischemia-reperfusion injury, which is mitigated by sestrin2-driven substrate metabolism.
Neutrophils: Double agents for TB
Authors: Philips Jennifer A.
Published: August 2017

Nitric oxide restricts growth of
Mycobacterium tuberculosis
by repressing neutrophilic inflammation.
Congenital Zika virus infection: More than just microcephaly
Authors: Miner Jonathan J.
Published: August 2017

A nonhuman primate model demonstrates efficient vertical transmission of Zika virus.
Rett syndrome modeling goes simian
Authors: Novarino Gaia
Published: August 2017

Rett syndrome modeling in monkey mirrors the human disorder.
Equine Arteritis Virus Elicits a Mucosal Antibody Response in the Reproductive Tract of Persistently Infected Stallions
Authors: Carossino Mariano , Wagner Bettina , Loynachan Alan T. , Cook R. Frank , Canisso Igor F. , Chelvarajan Lakshman , Edwards Casey L. , Nam Bora , Timoney John F. , Timoney Peter J. , Balasuriya Udeni B. R.
Published: August 2017

Equine arteritis virus (EAV) has the ability to establish persistent infection in the reproductive tract of the stallion (carrier) and is continuously shed in its semen. We have recently demonstrated that EAV persists within stromal cells and a subset of lymphocytes in the stallion accessory sex glands in the presence of a significant local inflammatory response. In the present study, we demonstrated that EAV elicits a mucosal antibody response in the reproductive tract during persistent infection with homing of plasma cells into accessory sex glands. The EAV-specific immunoglobulin isotypes in seminal plasma included IgA, IgG1, IgG3/5, and IgG4/7. Interestingly, seminal plasma IgG1 and IgG4/7 possessed virus-neutralizing activity, while seminal plasma IgA and IgG3/5 did not. However, virus-neutralizing IgG1 and IgG4/7 in seminal plasma were not effective in preventing viral infectivity. In addition, the serological response was primarily mediated by virus-specific IgM and IgG1, while virus-specific serum IgA, IgG3/5, IgG4/7, and IgG6 isotype responses were not detected. This is the first report characterizing the immunoglobulin isotypes in equine serum and seminal plasma in response to EAV infection. The findings presented herein suggest that while a broader immunoglobulin isotype diversity is elicited in seminal plasma, EAV has the ability to persist in the reproductive tract, in spite of local mucosal antibody and inflammatory responses. This study provides further evidence that EAV employs complex immune evasion mechanisms during persistence in the reproductive tract that warrant further investigation.
Multiplex Real-Time PCR Assay for Simultaneous Identification of Neisseria gonorrhoeae and Its Ciprofloxacin Susceptibility Status
Authors: Perera Sumudu R. , Khan Nurul H. , Martin Irene , Taheri Ali , Parti Rajinder P. , Levett Paul N. , Horsman Greg B. , Kusalik Anthony , Dillon Jo-Anne R.
Published: August 2017

A real-time PCR (RT-PCR) assay was designed for the simultaneous identification of
Neisseria gonorrhoeae
and its ciprofloxacin susceptibility status. A SYBR green-based multiplex RT-PCR format was used; it comprised two different forward primers and a common reverse primer to detect single nucleotide polymorphisms (SNPs) in
gyrA
of
N. gonorrhoeae
. The primer pairs were evaluated for their sensitivity and specificity using genomic DNA from 254
N. gonorrhoeae
isolates (82 were ciprofloxacin susceptible and 172 were ciprofloxacin resistant) and 23 non-
N. gonorrhoeae
species isolates. The performance of the primers was validated using genomic DNA from 100 different
N. gonorrhoeae
isolates (46 were ciprofloxacin susceptible and 54 were ciprofloxacin resistant) and 52 non-
N. gonorrhoeae
isolates. The latter panel was revalidated by testing 99 (46 isolates were ciprofloxacin susceptible and 53 isolates were ciprofloxacin resistant) of the
N. gonorrhoeae
isolates and 23 non-
N. gonorrhoeae
isolates. These primers detected
N. gonorrhoeae
and its ciprofloxacin susceptibility status with over 99% sensitivity and specificity for all panels tested. This assay has the potential to be an inexpensive and rapid test for the simultaneous identification of
N. gonorrhoeae
and its ciprofloxacin susceptibility status.
Contributions of Individual Domains to Function of the HIV-1 Rev Response Element
Authors: O'Carroll Ina P. , Thappeta Yashna , Fan Lixin , Ramirez-Valdez Edric A. , Smith Sean , Wang Yun-Xing , Rein Alan
Published: August 2017

The HIV-1 Rev response element (RRE) is a 351-base element in unspliced and partially spliced viral RNA; binding of the RRE by the viral Rev protein induces nuclear export of RRE-containing RNAs, as required for virus replication. It contains one long, imperfect double helix (domain I), one branched domain (domain II) containing a high-affinity Rev-binding site, and two or three additional domains. We previously reported that the RRE assumes an “A” shape in solution and suggested that the location of the Rev binding sites in domains I and II, opposite each other on the two legs of the A, is optimal for Rev binding and explains Rev's specificity for RRE-containing RNAs. Using small-angle X-ray scattering (SAXS) and a quantitative functional assay, we have now analyzed a panel of RRE mutants. All the results support the essential role of the A shape for RRE function. Moreover, they suggest that the distal portion of domain I and the three crowning domains all contribute to the maintenance of the A shape. Domains I and II are necessary and sufficient for substantial RRE function, provided they are joined by a flexible linker that allows the two domains to face each other.

IMPORTANCE
Retroviral replication requires that some of the viral RNAs transcribed in the cell nucleus be exported to the cytoplasm without being spliced. To achieve this, HIV-1 encodes a protein, Rev, which binds to a complex, highly structured element within viral RNA, the Rev response element (RRE), and escorts RRE-containing RNAs from the nucleus. We previously reported that the RRE is “A” shaped and suggested that this architecture, with the 2 legs opposite one another, can explain the specificity of Rev for the RRE. We have analyzed the functional contributions of individual RRE domains and now report that several domains contribute, with some redundancy, to maintenance of the overall RRE shape. The data strongly support the hypothesis that the opposed placement of the 2 legs is essential for RRE function.