Hydrodynamic Characteristics and Supercavity Shape of Supercavitating Projectiles Launched with Supersonic Speed

A supercavitating projectile is launched underwater with supersonic speed,and then,the speed decreases to transonic and subsonic conditions orderly because of the drag coming from surrounding water.The flow regime and hydrodynamic characteristics are significantly influenced by the flying speed,the influence laws in supersonic,transonic,and subsonic regions are totally different.These issues aren’t well studied.A numerical model consisting of VOF model,moving frame method and state equation of liquid is established to calculate the compressible supercavitation flow field,and validated by comparing with a published result.The influences of water compressibility and Mach number on supercavity shape and hydrodynamic characteristics are quantitatively summarized.The results show that the flying speed of supercavitating projectiles exerts significant influences on the flow regime,supercavity shape and hydrodynamic characteristics for the transonic and supersonic conditions.With the decrease of flying speed,the drag coefficient decreases gradually,and the dimensions of the supercavity near supercavitating projectiles significantly increases in the high-speed conditions.An underwater bow shock is numerically observed before the disk cavitator in supersonic condition.However,no obvious changes are found for the incompressible water cases with different speeds.For supersonic conditions,the supercavity near supercavitating projectiles of compressible water is smaller than that of incompressible water,the drag coefficient is larger,and the relative difference significantly increases with the flying speed.For the case of Ma 1.214,the relative difference of supercavity diameter at the tail section 3.98%,and the difference of the drag coefficient is 23.90%.

Multiferroic oxide BFCNT/BFCO heterojunction black silicon photovoltaic devices

Multiferroics are being studied increasingly in applications of photovoltaic devices for the carrier separation driven by polarization and magnetization.In this work,textured black silicon photovoltaic devices are fabricated with Bi_(6)Fe_(1.6)Co_(0.2)Ni_(0.2)Ti_(3)O_(18)/Bi_(2)FeCrO_(6)(BFCNT/BFCO)multiferroic heterojunction as an absorber and graphene as an anode.The structural and optical analyses showed that the bandgap of Aurivillius-typed BFCNT and double perovskite BFCO are 1.62±0.04 eV and 1.74±0.04 eV respectively,meeting the requirements for the active layer in solar cells.Under the simulated AM 1.5 G illumination,the black silicon photovoltaic devices delivered a photoconversion efficiency(η)of 3.9%with open-circuit voltage(Voc),short-circuit current density(Jsc),and fill factor(FF)of 0.75 V,10.8 mA cm^(-2),and 48.3%,respectively.Analyses of modulation of an applied electric and magnetic field on the photovoltaic properties revealed that both polarization and magnetization of multiferroics play an important role in tuning the built-in electric field and the transport mechanisms of charge carriers,thus providing a new idea for the design of future high-performance multiferroic oxide photovoltaic devices.