Research on Leading Edge Erosion and Aerodynamic Characteristics of Wind Turbine Blade Airfoil

The effects of the erosion present on the leading edge of a wind turbine airfoil(DU 96-W-180)on its aerodynamic performances have been investigated numerically in the framework of a SST k–ωturbulence model based on the Reynolds Averaged Navier-Stokes equations(RANS).The results indicate that when sand-induced holes and small pits are involved as leading edge wear features,they have a minimal influence on the lift and drag coefficients of the airfoil.However,if delamination occurs in the same airfoil region,it significantly impacts the lift and resistance characteristics of the airfoil.Specifically,as the angle of attack grows,there is a significant decrease in the lift coefficient accompanied by a sharp increase in the drag coefficient.As wear intensifies,these effects gradually increase.Moreover,the leading edge wear can exacerbate flow separation near the trailing edge suction surface of the airfoil and cause forward displacement of the separation point.

Influence of Surface Ice Roughness on the Aerodynamic Performance of Wind Turbines

The focus of this research was on the equivalent particle roughness height correction required to account for the presence of ice when determining the performances of wind turbines.In particular,two icing processes(frost ice and clear ice)were examined by combining the FENSAP-ICE and FLUENT analysis tools.The ice type on the blade surfaces was predicted by using a multi-time step method.Accordingly,the influence of variations in icing shape and ice surface roughness on the aerodynamic performance of blades during frost ice formation or clear ice formation was investigated.The results indicate that differences in blade surface roughness and heat flux lead to disparities in both ice formation rate and shape between frost ice and clear ice.Clear ice has a greater impact on aerodynamics compared to frost ice,while frost ice is significantly influenced by the roughness of its icy surface.

The effects of PM_(2.5)concentration on residents'health from the perspective of spatial economics

Ambient air quality is an important part of the ecological environment.Based on panel data from 192 countries for the period 2010–2016,our study applies spatial geography elements in a spatial panel model to analyze whether PM_(2.5)harms residents'health.We find a positive correlation between PM_(2.5)concentration and the prevalence of tuberculosis.Empirical testing shows that if residents live in environments with high PM_(2.5)concentrations for an extended period,it increases their probability of contracting tuberculosis.PM_(2.5)concentration and economic growth have an environmental Kuznets curve(EKC)relationship.Furthermore,PM_(2.5)concentration and prevalence of tuberculosis in different countries have a positive spatial correlation during the study period.The values of PM_(2.5)concentration in adjacent areas are similar,because PM_(2.5)can cross borders through airflow and as economic development levels in adjacent regions are similar.When regulating haze pollution,we should adopt regional joint governance,consider the specific characteristics of different regions,and coordinate these regulations with environmental protection policies to realize the goal of“lucid waters and lush mountains.”

Nanoscale Impact Ionization and Electroluminescence in a Biased Scanning-Tunneling-Microscope Junction

Electroluminescence from a p-type Ga As(110)surface was induced by tunneling electrons in a scanning tunneling microscope under both polarities of bias voltage.The optical spectra exhibit a polarity-independent luminescence peak at 1.47 eV resulting from the exciton recombination.However,the quantum yield of photon emission at negative bias voltage is two orders of magnitude weaker than that at positive bias voltage.Moreover,the luminescence at negative bias voltage shows the linear dependence of bias voltage,distinct from the rapid rise due to resonant electron injection at positive bias.Furthermore,the threshold bias voltage for electroluminescence at negative bias is nearly twice the bandgap of Ga As,not simply satisfying the energy conservation for the creation of an electron–hole pair.Through theoretical calculation,we propose an impact ionization model to nicely explain the newly observed electroluminescence at negative bias voltage.We believe that this mechanism of impact ionization could be readily applied to other nanoscale optoelectronics including 2D semiconductors and 1D nanostructures.

Hierarchical NiMoP_(2)-Ni_(2)P with amorphous interface as superior bifunctional electrocatalysts for overall water splitting

Producing highly efficient bifunctional catalyst for the generation of hydrogen and oxygen through overall water splitting is an emerging direction in electrocatalysis.Herein,a dandelion-like hierarchical NiMoP_(2)-Ni_(2)P(nanowire/nanoparticle)heterostructure was synthesized for efficient electrochemical water splitting.The NiMoP_(2)-Ni_(2)P heterostructures grown on carbon cloth as a freestanding integrated electrode exhibited excellent oxygen evolution reaction(OER)activity and hydrogen evolution reaction(HER)activities with low overpotentials(258 mV and 53 mV to reach 10 mA cm~(-2)for the OER and HER,respectively),and small Tafel slope(45 mV dec^(-1)and 58 mV dec^(-1)for the OER and HER,respectively).Moreover,the NiMoP_(2)-Ni_(2)P heterostructure can act as both anode and cathode catalysts for overall water splitting with low overall potential of 1.48 V at 10 mA cm~(-2).Density functional theory(DFT)combined with structural probes suggests that the amorphous heterogeneous interfaces play an essential role in enhanced catalytic performance.

Routing valley exciton emission of a WS_(2) monolayer via delocalized Bloch modes of in-plane inversion-symmetry-broken photonic crystal slabs

The valleys of two-dimensional transition metal dichalcogenides(TMDCs)offer a new degree of freedom for information processing.To take advantage of this valley degree of freedom,on the one hand,it is feasible to control valleys by utilizing different external stimuli,such as optical and electric fields.On the other hand,nanostructures are also used to separate the valleys by near-field coupling.However,for both of the above methods,either the required low-temperature environment or low degree of coherence properties limit their further applications.Here,we demonstrate that all-dielectric photonic crystal(PhC)slabs without in-plane inversion symmetry(C_(2) symmetry)can separate and route valley exciton emission of a WS2 monolayer at room temperature.Coupling with circularly polarized photonic Bloch modes of such PhC slabs,valley photons emitted by a WS_(2) monolayer are routed directionally and are efficiently separated in the far field.In addition,far-field emissions are directionally enhanced and have long-distance spatial coherence properties.

Selective laser melting of dense and crack-free AlCoCrFeNi_(2.1) eutectic high entropy alloy: Synergizing strength and ductility

Additively manufactured high-entropy alloys generally suffer from low strength and/or poor ductility.In this work,by leveraging the good castability of eutectic high entropy alloys and high cooling rate of selective laser melting(SLM),we report a nearly fully dense and crack-free as-SLM AlCoCrFeNi_(2.1) eutectic high entropy alloy with an exceptional strength-ductility synergy,showing an ultrahigh yield strength of 982.1±35.2 MPa and an ultimate tensile strength of 1322.8±54.9 MPa together with an elongation to fracture of 12.3±0.5%.Such strength-ductility enhancement is owing to the heterogeneous eutectic microstructure consisting of the columnar,equiaxed,and“L-shape”cells with much refined sizes down to nanoscales.The morphology of cells in the transition zone is related to the misorientation between the growth direction of adjacent layers.This heterogeneous eutectic microstructure is the result of the graingrowth behavior dominated by the mechanisms of the epitaxial growth and growth of heterogeneous nuclei in SLM.Our current results provide a new methodology for the future design of ultrahigh-strength and ductile SLM-fabricated metallic materials including HEAs,and other printable alloys for various structural applications.

Dual precipitate simultaneous enhancement of tensile and fatigue strength in(FeCoNi)_(86)Al_(7)Ti_(7) high-entropy alloy fabricated using selective laser melting

Recent studies have indicated that precipitation-strengthened high-entropy alloys(HEAs)show superior mechanical performance and have been successfully fabricated by additive manufacturing.However,the lack of fatigue and fracture research has limited the engineering applications of additive manufacturing HEAs.This work explored a dual precipitation-strengthened(FeCoNi)_(86)Al_(7)Ti_(7) HEA with excellent tensile and fatigue strength,prepared through selective laser melting and heat treatment.Compared with the as-built samples,the tensile properties and fatigue endurance limit improved through aging by 48.7%and 30%,respectively.The strengthening mechanism and enhanced fatigue performance were clarified in detail.The improvement in fatigue strength was attributed to the improved resistance of the L1_(2) and L2_(1) precipitates.During deformation,the dislocation shear coherent L1_(2) precipitates reduced slip band energy and inhibited slip band expansion,while the L2_(1) particles acted as obstructions for further slip band propagation,severely limiting the rapid formation and propagation of crack growth.In-situ TEM cyclic tensile-tensile testing also clarified the fatigue crack growth behavior,demonstrating that crack deflection due to L2_(1) precipitate obstruction slowed down the crack growth rate and efficiently promoted the closure of the microcrack tips.This work offers im plications for a new strategy to develop additive manufacturing HEAs.

A Photoelectric-Stimulated MoS_(2) Transistor for Neuromorphic Engineering

The von Neumann bottleneck has spawned the rapid expansion of neuromorphic engineering and brain-like networks.Synapses serve as bridges for information transmission and connection in the biological nervous system.The direct implementation of neural networks may depend on novel materials and devices that mimic natural neuronal and synaptic behavior.By exploiting the interfacial effects between MoS_(2) and AlOx,we demonstrate that an h-BN-encapsulated MoS_(2) artificial synapse transistor can mimic the basic synaptic behaviors,including EPSC,PPF,LTP,and LTD.Efficient optoelectronic spikes enable simulation of synaptic gain,frequency,and weight plasticity.The Pavlov classical conditioning experiment was successfully simulated by electrical tuning,showing associated learning behavior.In addition,h-BN encapsulation effectively improves the environmental time stability of our devices.Our h-BN-encapsulated MoS_(2) artificial synapse provides a new paradigm for hardware implementation of neuromorphic engineering.

Multistage strain-hardening behavior of ultrastrong and ductile lightweight refractory complex-concentrated alloys

Lightweight high-entropy alloys or complex-concentrated alloys have demonstrated great potential for engineering applications due to their high strength and lightweight.However,a weak strain-hardening ability and a limited tensile ductility remain their major hindrance.Here,a multistage strain-hardening effect is developed to ensure a high strength and still a sufficient ductility in a rolled and annealed(Ti_(44)V_(28)Zr_(14)Nb_(14))_(98.5)Mo_(1.5)(at.%)lightweight refractory complex-concentrated alloy(M1.5A-LRCCA).This multistage strain-hardening behavior is related to the microstructure and the corresponding initial aver-age dislocation density and distribution by comparison with rolled and annealed Ti_(44)V_(28)Zr_(14)Nb_(14)(M0-LRCCA)and as-cast(Ti_(44)V_(28)Zr_(14)Nb_(14))_(98.5)Mo_(1.5)(M1.5C-LRCCA).The microstructure,with homogeneously distributed submicron precipitations,a moderate initial average dislocation density,and uniform disloca-tion distribution(e.g.,M1.5A-LRCCA),is susceptible to producing various deformation substructures,such as dislocation substructures(slip bands,Taylor lattices,microbands,DDWs),shear bands,and deformation twins,which results in the multistage strain-hardening behavior.This method of achieving multistage strain hardening behavior through a microstructure modulation is significant for engineering applications of lightweight high-entropy alloys or complex-concentrated alloys,and it might be extended to other lightweight and high-strength alloys.

A promising new class of plasticine: Metallic plasticine

Soft, malleable, and non-dry on exposure in air are the typical features for plain plasticine, which lead plasticine to be widely used in many industrial fields and our daily life. As a kind of clay, poorly elec- tric conductivity and thermal conductivity of plain plasticine seriously limit its applications. Therefore, synthesizing a kind of plasticine having metallic bond is of importance for extending its applications in some special cases, such as thermal-cooling medium, anti-static electricity, electromagnetic shielding, etc. Here, we report a novel GalnSnCdZn2 alloy, which exhibits similar behavior as compared to those of plasticine at near room temperature （30-40 ℃）, and a good electrical conductivity due to its nature of metal. This new GalnSnCdZn2 alloy can be called as metallic plasticine that contains the near-eutectic structure with low melting point and the other relatively high melting point phases. In this metallic plas- ticine, the near-eutectic structure with low melting point plays the same role as the oily ingredient in plain plasticine, dominating the plastic deformation, while the other relatively high melting point phases act as the stuffing like the CaCO3 in plain plasticine. The creation of metallic plasticine offers a general strategy for designing/preparing a new class of plasticine which possesses both the nature of metal and plasticine.

Mechanism design of reverse auction on concession period and generalized quality for PPP projects

Reverse auctions of PPP projects usually require the bid to specify several characteristics of quality and the concession period to be fulfilled. This paper sets up a summary function of generalized quality, which contributes to reducing the dimensions of information.Thus, the multidimensional reverse auction model of a PPP project can be replaced by a two-dimensional direct mechanism based on the concession period and the generalized quality. Based on the theory of the revelation principle, the feasibility conditions, equilibrium solution and generalized quality requirements of such a mechanism,considering the influence of a variable investment structure are described. Moreover, two feasible multidimensional reverse auctions for implementing such a direct mechanism: Adjusting the scoring function and establishing a special reverse auction rule are built. The analysis shows that in these types of reverse auctions, optimal allocation can be achieved, the social benefit under the incomplete information will be maximized, and the private sector with the highest integrated management level wins the bid. In such a direct mechanism, the investment and financial pressure of the public sector can be reduced.