Computational Study of the Effects of Shroud Geometric Variation on Turbine Performance in a 1.5-Stage High-Loaded Turbine

Generally speaking, main flow path of gas turbine is assumed to be perfect for standard 3D computation. But in real engine, the turbine annulus geometry is not completely smooth for the presence of the shroud and associated cavity near the end wall. Besides, shroud leakage flow is one of the dominant sources of secondary flow in tur- bomachinery, which not only causes a deterioration of useful work but also a penalty on turbine efficiency. It has been found that neglect shroud leakage flow makes the computed velocity profiles and loss distribution signifi- cantly different to those measured. Even so, the influence of shroud leakage flow is seldom taken into considera- tion during the routine of turbine design due to insufficient understanding of its impact on end wall flows and tur- bine performance. In order to evaluate the impact of tip shroud geometry on turbine performance, a 3D computa- tional investigation for 1.5-stage turbine with shrouded blades was performed in this paper. The following ge- ometry parameters were varied respectively：

Development and application of a throughflow method for high-loaded axial flow compressors

In this paper, a novel engineering platform for throughflow analysis based on streamline curvature approach is developed for the research of a 5-stage compressor. The method includes several types of improved loss and deviation angle models, which are combined with the authors' adjustments for the purpose of reflecting the influences of three-dimensional internal flow in high-loaded multistage compressors with higher accuracy. In order to validate the reliability and robustness of the method, a series of test cases, including a subsonic compressor P&W 3S1, a transonic rotor NASA Rotor 1B and especially an advanced high pressure core compressor GE E^3 HPC, are conducted. Then the computation procedure is applied to the research of a 5-stage compressor which is designed for developing an industrial gas turbine. The overall performance and aerodynamic configuration predicted by the procedure, both at design- and part-speed conditions, are analyzed and compared with experimental results, which show a good agreement. Further discussion regarding the universality of the method compared with CFD is made afterwards. The throughflow method is verified as a reliable and convenient tool for aerodynamic design and performance prediction of modern high-loaded compressors. This method is also qualified for use in the further optimization of the 5-stage compressor.

LiTFSI salt concentration effect to digest lithium polysulfides for high-loading sulfur electrodes

Sulfur utilization improvement and control of dissolved lithium polysulfide(LiPS;Li_(2)S x,2<x≤8)are cru-cial aspects of the development of lithium-sulfur(Li-S)batteries,especially in high-loading sulfur elec-trodes and low electrolyte/sulfur(E/S)ratios.The sluggish reaction in the low E/S ratio induces poor LiPS solubility and unstable Li_(2)S electrodeposition,resulting in limited sulfur utilization,especially under high-loading sulfur electrode.In this study,we report on salt concentration effects that improve sulfur utilization with a high-loading cathode(6 mgs ulfurcm^(-2)),a high sulfur content(80 wt%)and a low E/S ratio(5 m L gs ulfur^(-1)).On the basis of the rapid LiPS dissolving in a low concentration electrolyte,we estab-lished that the quantity of Li_(2)S electrodeposition from a high Li+diffusion coefficient,referring to the reduction of LiPS precipitation,was significantly enhanced by a faster kinetic.These results demonstrate the importance of kinetic factors for the rate capability and cycle life stability of Li-S battery electrolytes through high Li_(2)S deposition under high-loading sulfur electrode.

小型涡轮平面叶栅试验段设计

Performance improvement of the high-load transonic turbine is the key method of improving the thrustto-weight ratio or the power density of gas turbine engines. In order to investigate the flow behaviors inside the high load turbine cascades, a linear turbine cascade test section is designed, which enables the Schlieren photography and static pressure measurement along the cascade profile can be conducted. Variable pitch is realized in the test section to achieve different Zweifel coefficients. Due to the capability limitation of the air supplier, the test section is designed to have only5 blade channels with shortened blade height to achieve high Mach number flow conditions. Numerical investigations were carried out to investigate the wall effect and its in fluences on the flow fields inside the test section. The result indicates that the shape of the connecting part of the test section has a significant influence on the flow similarity among different blade passages. With the proper design, a good repetition flow is achieved between neighbored blade passages.

Fabricating high-loading Fe-N4 single-atom catalysts for oxygen reduction reaction by carbon-assisted pyrolysis of metal complexes

Iron-based single-atom catalysts with nitrogen-doped carbon as support(Fe-SA/NPC)are considered effective alternatives to replace Pt-group metals for scalable application in fuel cells.However,synthesizing high-loading Fe-SA catalysts by a simple procedure remains challenging.Herein,we report a high-loading(7.5 wt%)Fe-SA/NPC catalyst prepared by carbon-assisted pyrolysis of metal complexes.Both the nitrogen-doped porous carbon(NPC)support with high specific surface area and ο-phenylenediamine(o-PD)play key roles role in the preparation of high-loading Fe-SA/NPC catalysts.The results of X-ray photoelectron spectroscopy,high-angle annular dark-field scanning transmission electron microscopy,and X-ray absorption fine structure spectroscopy experiments show that the Fe atoms are anchored on the carbon carriers in a single-atom site configuration and coordinated with four of the doped nitrogen atoms of the carbon substrates(Fe-N_(4)).The activities of the Fe-SA/NPC catalysts in the oxygen reduction reaction increased with increasing iron loading.The optimized 250Fe-SA/NPC-800 catalyst exhibited an onset potential 0.97 V of and a half-wave potential of 0.85 V.Our study provides a simple approach for the large-scale synthesis of high-loading single-atom catalysts.

Dielectric polymer based electrolytes for high-performance all-solid-state lithium metal batteries

Solid polymer electrolytes (SPEs) are urgently required for achieving practical all-solid-state lithium metal batteries (ASSLMBs) but remain plagued by low ionic conductivity.Herein,we propose a strategy of salt polarization to fabricate a highly ion-conductive SPE by employing a high-dielectric polymer that can interact strongly with lithium salts.Such a polymer with large dipole moments can guide lithium cations (Li^(+)) to be arranged along the chain,forming a continuous pathway for Li^(+) hopping within the SPE.The as-fabricated SPE,poly(vinylidene difluoride)(PVDF)-LiN(SO_(2)F)_(2)(LiFSI),has an extraordinarily high dielectric constant (up to 10^(8)) and ultrahigh ionic conductivity (0.77×10^(-3)S cm^(-1)).Based on the PVDF–LiFSI SPE,the assembled Li metal symmetrical cell shows excellent Li plating/stripping reversibility at 0.1 m A cm^(-2),0.1 m Ah cm^(-2)over 1500 h^(-1) the ASS LiFePO_(4) batteries deliver long-term cycling stability at 1 C over 350 cycles (2.74 mg cm^(-2)) and an ultralong cycling lifespan of over 2600 h(100 cycles) with high loading (11.5 mg cm^(-2)) at 28°C.First-principles calculations further reveal the ion-dipole interactions-controlled conduction of Li^(+) in PVDF–LiFSI SPE along the PVDF chain.This work highlights the critical role of dielectric permittivity in SPE,and provides a promising path towards high-energy,long-cycling lifespan ASSLMBs.

Designandconstructionof athree-dimensionalelectrodewith biomass-derived carbon current collector andwater-soluble binder for high-sulfur-loading lithium-sulfur batteries

Lithium-sulfur batteries attract lots of attention due to their high specific capacity,low cost,and environmental friendliness.However,the low sulfur utilization and short cycle life extremely hinder their application.Herein,we design and fabricate a three-dimensional electrode by a simple filtration method to achieve a high-sulfur loading.Biomass porous carbon is employed as a current collector,which not only enhances the electronic transport but also effectively limits the volume expansion of the active material.Meanwhile,an optimized carboxymethyl cellulose binder is chosen.The chemical bonding restricts the shuttle effect,leading to improved electrochemical performance.Under the ultrahigh sulfur load of 28mg/cm2,the high capacity of 18mAh/cm2 is still maintained,and stable cycling performance is obtained.This study demonstrates a viable strategy to develop promising lithium-sulfur batteries with a three-dimensional electrode,which promotes sulfur loading and electrochemical performance.

A 0.5-meter-scale,high-load,soft-enclosed gripper capable of grasping the human body

Developing large,soft grippers with high omnidirectional load(above 40 kg)has always been challenging.We address this challenge by developing a powerful soft gripper that can grasp the human body based on a soft-enclosed grasping structure and a soft-rigid coupling structure.The envelope size of the proposed soft gripper is 611.6 mm×559 mm×490.7 mm,the maximum grasping size is 417 mm,and the payload on the human body is more than 90 kg,which has exceeded most existing soft grippers.Furthermore,the grasping force prediction of the gripper is achieved through theoretical modeling.The primary contribution of this work is to overcome the size and payload limits of current soft grippers and implement a human-grasping experiment based on the soft-grasping method.

Rational design of Co nano-dots embedded three-dimensional graphene gel as multifunctional sulfur cathode for fast sulfur conversion kinetics

Lithium-sulfur(Li-S)batteries hold great promises to serve as next-generation energy storage devices because of their high theoretical energy density and environmental benignity.However,the shuttle effect of the soluble lithium polysulfides(LiPS)and intrinsic insulating nature of sulfur lead to low sulfur utilization and coulombic efficiency,leading to poor cycling performance.The impeded charge transportation and retard LiPS catalytic conversion also endows the Li-S batteries with sluggish redox reaction,leading to unsatisfied rate capability.In this study,Co-based MOF material ZIF-67 is used as the precursor to prepare Co nano-dots decorated three-dimensional graphene aerogel as sulfur immobilizer.This porous architecture establishes a highly conductive interconnected framework for fast charge/mass transportation.The exposed Co nano-dots serve as active sites to strongly trap LiPS,which endows CoNDs@G with low decomposition energy barrier for fast LiPS conversion reaction and promote the completely Li2 S catalytic transformation.Li-S cells based on the Co-NDs@G cathode exhibits excellent cyclability and a high capacity retention rate of 91.1%in 100 cycles.This strategy offers a new direction to design sulfur immobilizer for accelerated LiPS conversion kinetics of Li-S batteries.

Effects of Boundary Layer Suction on Aerodynamic Performance in a High-load Compressor Cascade

This article is aimed to experimentally validate the beneficial effects of boundary layer suction on improving the aerodynamic performance of a compressor cascade with a large camber angle. The flow field of the cascade is measured and the ink-trace flow visualization is also presented. The experimental results show that the boundary layer suction reduces losses near the area of rnidspan in the cascade most effectively for all suction cases under test. Losses of the endwall could remarkably decrease only when the suction is at the position where the boundary layer has separated but still not departed far away from the blade surface. It is evidenced that the higher suction flow rate and the suction position closer to the trailing edge result in greater reduction in losses and the maximum reduction in the total pressure loss accounts to 16.5% for all cases. The suction position plays a greater role in affecting the total pressure loss than the suction flow rate does.

A combined application of micro-vortex generator and boundary layer suction in a high-load compressor cascade

In the current study, the effects of a combined application between micro-vortex generator and boundary layer suction on the flow characteristics of a high-load compressor cascade are investigated. The micro-vortex generator with a special configuration and the longitudinal suction slot are adopted. The calculated results show that a reverse flow region, which is considered the main reason for occurring stall at 7.9° incidence, grows and collapses rapidly near the leading edge and leads to two critical points occurring on the end-wall with the increasing incidence in the baseline. As the micro-vortex generator is introduced in the baseline cascade, the corner separation is switched to a trailing edge separation by the thrust from the induced vortex. Meanwhile, the occurrence of failure is delayed due to the mixed low energy fluid and main flow. The synergistic effects between the micro-vortex generator and the boundary layer suction on the performance of the cascade are superior to the baseline at all the incidence conditions before the occurrence of failure, and the sudden deterioration of the cascade occurs at 10.3° incidence. The optimal results show that the farther upstream suction position, the lower total pressure loss of the cascade with vortex generator at the near stall condition. Moreover, the induced vortex with a leg can migrate the accumulated low energy fluid backward to delay the occurrence of stall.

Hierarchical-structure anatase TiO2 with conductive network for high-rate and high-loading lithium-ion battery

Titanium dioxides have been extensively investigated as promising anodes for Lithium ion batteries(LIBs)because of the high–rate capacity and cyclability,as well as the improved safety over graphite anode(1,2)However,as a typical insertion–type anode,anatase TiO2 exhibits low conductivity(10–12S cm-1 for electron conductivity[3]and 10–17–10–10 cm2 s1 for Li+ion diffusion coefficient[4])and poor specific capacity(only accommodate<0.5 Li per bulk TiO2 unit[5]),severely limiting its practical applications.

Recent advances in high-loading catalysts for low-temperature fuel cells: From nanoparticle to single atom

Low-temperature fuel cells(LTFCs)are considered to be one of the most promising power sources for widespread application in sustainable and renew-able energy conversion technologies.Although remarkable advances have been made in the mass activity of catalysts,mass transport impedance needs to be urgently addressed at a well-designed membrane electrode assembly(MEA)scale.Increasing the loading of electrocatalysts is conducive to prepare thinner and more efficient MEAs owing to the resulting enhanced reactant permeability,better proton diffusion,and lower electrical resistance.Herein,recent progress in high-loading(≥40 wt.%)Pt nanoparticle catalysts(NPCs)and high-loading(≥2 wt.%)single-atom catalysts(SACs)for LTFC applications are reviewed.A summary of various synthetic approaches and support materials for high-loading Pt NPCs and SACs is systematically presented.The influences of high surface area and appropriate surface functionalization for Pt NPCs,as well as coordina-tion environment,spatial confinement effect,and strong metal-support interac-tions(SMSI)for SACs are highlighted.Additionally,this review presents some ideas regarding challenges and future opportunities of high-loading catalysts in the application of LTFCs.

Numerical Investigation of the Load Distribution between the Main Blade and the Splitter Blade in a High-Loading Centrifugal Compressor

In the traditional design of the centrifugal compressor,the splitter blade and the main blade always keep the same shape.However,to enable high efficiency of the high-loading centrifugal compressor,the matching of design parameters of the splitter blade and the main blade needs to be optimized.In this paper,the influence of the load distribution between the main blade and the splitter blade on the aerodynamic performance,the flow field,and the internal vortices of a high-loading centrifugal compressor were studied by means of CFD prediction.Four cases with different values of the variable CR which is defined as the load-ratio of splitter blade to main blade were set up.In each case,the splitter blade and the main blade were shaped according to different laws of circulation distribution(_(r)V_(u))while the average circulation of the splitter blade and the main blade at any meridional position were consistent with that of the prototype.The results showed that a proper reduction of the load-ratio of splitter blade to main blade is beneficial to suppress the leakage vortex of the splitter blade and reduce the scale of the wake in the channel near the suction-side of the splitter blade,which consequently improves the flow uniformity at the impeller outlet and enhances the aerodynamic performance of both the stage and the component.The stage isentropic efficiency of the optimal case was found to be 0.7%higher than that of the prototype and the stage total pressure ratio was also improved.The optimal value of CR,which in this investigation is 94%,is supposed to be the result of the trade-off between the development of the wake and the leakage vortices in adjacent two channels.The optimization of the load distribution between the main blade and the splitter blade provides an opportunity to further improve the high-loading centrifugal compressor performance.

Cobalt single atom site catalysts with ultrahigh metal loading for enhanced aerobic oxidation of ethylbenzene

The oxidation of hydrocarbons to produce high value-added compounds(ketones or alcohols)using oxygen in air as the only oxidant is an efficient synthetic strategy from both environmental and economic views.Herein,we successfully synthesized cobalt single atom site catalysts(Co SACs)with high metal loading of 23.58 wt.%supported on carbon nitride(CN),which showed excellent catalytic properties for oxidation of ethylbenzene in air.Moreover,Co SACs show a much higher turn-over frequency(19.6 h^(−1))than other reported non-noble catalysts under the same condition.Comparatively,the as-obtained nanosized or homogenous Co catalysts are inert to this reaction.Co SACs also exhibit high selectivity(97%)and stability(unchanged after five runs)in this reaction.DFT calculations reveal that Co SACs show a low energy barrier in the first elementary step and a high resistance to water,which result in the robust catalytic performance for this reaction.

Combined Experimental and Numerical Investigations on the Roughness Effects on the Aerodynamic Performances of LPT Blades

The aerodynamic performance of a high-load low-pressure turbine blade cascade has been analyzed for three different distributed surface roughness levels(Ra) for steady and unsteady inflows. Results from CFD simulations and experiments are presented for two different Reynolds numbers(300000 and 70000 representative of take-off and cruise conditions, respectively) in order to evaluate the roughness effects for two typical operating conditions. Computational fluid dynamics has been used to support and interpret experimental results, analyzing in detail the flow field on the blade surface and evaluating the non-dimensional local roughness parameters, further contributing to understand how and where roughness have some influence on the aerodynamic performance of the blade. The total pressure distributions in the wake region have been measured by means of a five-hole miniaturized pressure probe for the different flow conditions, allowing the evaluation of profile losses and of their dependence on the surface finish, as well as a direct comparison with the simulations. Results reported in the paper clearly highlight that only at the highest Reynolds number tested(Re=300000) surface roughness have some influence on the blade performance, both for steady and unsteady incoming flows. In this flow condition profile losses grow as the surface roughness increases, while no appreciable variations have been found at the lowest Reynolds number. The boundary layer evolution and the wake structure have shown that this trend is due to a thickening of the suction side boundary layer associated to an anticipation of transition process. On the other side, no effects have been observed on the pressure side boundary layer.