In-flight Behavior Research Articles

Fuelbed ignition potential and bark morphology explain the notoriety of the eucalypt messmate 'stringybark' for intense spotting

In south-eastern Australia, bark of the ‘stringybark’ eucalypt group, and notably that of messmate (Eucalyptus obliqua L’Hér.), is notorious for intense spotting and it is likely that firebrands of this type contribute significantly to loss of life and property during major wildfires. The fuelbed ignition potential by glowing samples was laboratory tested on excised sections of Pinus radiata D. Don litterbed at moisture contents between 2 and 8% and for ‘no-wind’ or for ‘wind’ of 1 m s–1. Prepared samples of outer bark between 0.5 and 1.6 g were combusted until they attained ~20% of initial mass before placement. For ‘no-wind’, flaming ignition did not occur and the probability of glowing ignition appeared to depend on the chance of contact with needles. For ‘wind’, the probability of flaming ignition was a function of sample glowing mass and fuelbed moisture content. Its ignition probability, weight-for-weight, appears to exceed that reported for other forest firebrands, including bark of E. globulus Labill. However, it is likely that the notoriety of messmate bark is also due, in part, to its morphology and in-flight behaviour. It is argued that firebrand laboratory tests to date may poorly reflect the ignition potential of similar samples after flight.

In-Flight Behaviors and Properties of Plasma-Sprayed Tungsten Coatings

Tungsten is one of the most promising candidates for the plasma facing materials (PFM) in fusion experiment devices. In this study, tungsten coatings were fabricated on copper alloy substrates via air plasma spraying technology. The in-flight behaviors of tungsten particles in the spraying process were investigated. The microstructure and some properties of the as-sprayed coatings, including surface roughness, bonding strength, microhardness and thermal property, were evaluated. The results showed that the temperature and velocity of the in-flight tungsten particles increased by enhancing the spraying power. Un-melted particles and microcracks were found for the coatings prepared under the low (32.7kW) and high (47.6kW) spraying powers, respectively. The highest bonding strength and microhardness were obtained for the coating prepared under a medium spraying power (42.5kW) by reason of its good in-flight behaviors. The thermal conductivity of tungsten coatings was 32.2 W٠K-1٠m-1 at room temperature, which was much lower than that of bulk tungsten.

Research on In-Flight Property of Particles in Plasma Spray Forming

Plasma spraying has been carried out under different spraying parameters, the particle in-flight behaviors have been measured to analyze the influence of argon flow rate, hydrogen flow rate and electrical current on the particle temperature and velocity. The particle velocity increased remarkably with the increase of the argon flow rate. The particle temperature was mainly influenced by the hydrogen flow rate, and increasing electrical current resulted in the increase of the particle temperature and velocity to some extent.

Computational and Experimental Studies on Cavity Filling Process by Cold Gas Dynamic Spray

Time-dependent computational simulations on cavity filling process by cold gas dynamic spray and powder jet deposition process ranging from microscale to macroscale were carried out in order to give an insight for their advanced applications to joining, crack repair, and dental treatment. Shock wave appears in front of the substrate due to underexpansion of jet and in-flight particles interact with the shock wave before their impact. The relation between shock wave, cavity configuration, and particle in-flight behavior in supersonic jet has been discussed in detail. Based on numerical and experimental studies, it was found that when the shock wave covers up the cylindrical cavity, the cavity cannot be filled at all by deposited powders. Moreover, under the condition of shock wave appearing inside the cylindrical cavity, conical deposition was formed due to the secondary back flow jet along the cavity side wall. By adopting conical cavity, cavity can be filled completely resulting from the suppression of the secondary back flow jet along the cavity side wall.

Numerical Study of the Plasma Flow Field and Particle In-flight Behavior with the Obstruction of a Curved Substrate

A three-dimensional numerical model is developed using computational fluid dynamics software FLUENT v6.3.26 to investigate the influence of curved substrate on the plasma flow fields and subsequent in-flight particle behavior. The curved substrates have two different dimensional shapes and are positioned in two orientations (convex or concave). It is found that inclusion of the substrates with different shapes in different directions significantly affects the plasma flow fields at the vicinity of the substrate, although the most upstream region of the plasma field remains unaffected. Plasma temperature and velocity contours and flow vectors in the computational domain, especially at regions near substrates are presented. Investigations on the size effect on the in-flight particle parameters are carried out, which show that smaller particles tend to acquire higher velocities and temperatures. Moreover, smaller particles are more susceptible to the flow change by the substrate inclusion. However, for the size range of the zirconia feedstock we used later, there is no obvious effect of the substrate inclusion on the particle distribution on the substrate surface.

Modeling and Control of High-Velocity Oxygen-Fuel (HVOF) Thermal Spray: A Tutorial Review

This work provides a tutorial overview of recent research efforts in modeling and control of the high-velocity oxygen-fuel (HVOF) thermal spray process. Initially, the modeling of the HVOF thermal spray, including combustion, gas dynamics, particle in-flight behavior, and coating microstructure evolution is reviewed. The influence of the process operating conditions as predicted by the fundamental models on particle characteristics and coating microstructure is then discussed and compared with experimental observations. Finally, the issues of measurement and automatic control are discussed and comments on potential future research efforts are made.

Simulations of galactic cosmic ray impacts on the Herschel/PACS bolometer arrays with Geant4 code

The effects of the in-flight behaviour of the bolometer arrays of the Herschel/Photo-conductor Array Camera and Spectrometer (PACS) instrument under impacts of Galactic cosmic rays are explored. This instrument is part of the ESA-Herschel payload, which will be launched at the end of 2008 and will operate at the Lagrangian L2 point of the Sun-Earth system. We find that the components external to the detectors (the spacecraft, the cryostat, the PACS box, collectively referred to as the ‘shield’) are the major source of secondary events affecting the detector behaviour. The impacts deposit energy on the bolometer chips and influence the behaviour of nearby pixels. 25% of hits affect the adjacent pixels. The energy deposited raises the bolometer temperature by a factor ranging from 1 to 6 percent of the nominal value. We discuss the effects on the observations and compare simulations with laboratory tests.

Patterns of praying mantis auditory system evolution based on morphological, molecular, neurophysiological, and behavioural data

Some praying mantids have sensitive ultrasonic hearing arising from a unique ‘cyclopean’ ear located in the ventral metathorax. The present study explores the evolutionary history of the mantis auditory system by integrating large anatomical, neurophysiological, behavioural, and molecular databases. Using an ‘auditory phylogeny’ based on 13 morphological characters, we identified a primitively earless form of metathoracic anatomy in several extant taxa. In addition, there are five distinct mantis auditory systems. Three of these can be identified anatomically, and the other two can only be detected neurophysiologically. Superimposing these results onto a phylogenetic tree derived from molecular data from seven genes shows that the cyclopean mantis ear evolved once approximately 120 Mya. All the other auditory system types are either varying degrees of secondary loss, or are recent innovations that each occurred independently multiple times. The neurophysiological response to ultrasound is remarkably consistent across all taxa tested, as is the multicomponent, in-flight behaviour triggered by ultrasound. Thus, mantids have an ancient, highly conserved auditory neural–behavioural system. Although ultrasonic hearing in several insect groups evolved in response to bat predation, mantis hearing predates the appearance of bats (approximately 63 Mya) and must originally have functioned in communication, prey detection, or avoidance of nonbat predators. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 541–568. ADDITIONAL KEYWORDS: acoustic startle – bat evasion – cyclopean ear – insect ear – insect hearing – molecular phylogeny – tympanum.

519 ナノ・マイクロ粒子高速流動の衝突過程とキャビティー充填加工の高度化(T07-4 流体及び界面におけるナノ構造と流動特性(4),大会テーマセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

A real-time and realistic computation on the entire cold gas dynamic spray process has been carried out by the integrated model of flow considering shock wave, splat formation, and coating formation. The in-flight behavior of nano/micro particle in the supersonic jet impinging on the substrate with a cavity, and also the interaction between a particle and shockwave has been made clear from this study. By clarifying the effect of cavity shapes on a coating formation inside the cavity, optimum cavity shape was proposed for cavity filling process. Then, the fundamental data has been provided for the advanced application of a high performance cold gas dynamic spray process to a dental treatment or structural repair.

Particle in-flight behavior and its influence on the microstructure and mechanical properties of plasma-sprayed Al 2O 3 coatings

This paper aims to elaborate the particle characteristics during their flight into the spray and its significance in determining the microstructure and mechanical properties of resultant coatings. Study of plasma spraying of Al 2O 3 using three different grain fractions of feedstock was done by an on-line monitoring system (SprayWatch 2i). The as-sprayed coatings were characterized in terms of the microstructure and composition, microhardness, adhesion strength and porosity. In addition, a statistic study of Weibull analysis was employed to further examine the microstructural homogeneity of coatings. It was found that particle in-flight behaviors are strongly influenced by feedstock particle size. Improved particle velocity and temperature as well as melting extent can be obtained for the finer feedstock. This contributes to produce increasingly bonded splats resulting in coating with compact microstructure, where low porosity and increased microhardness and adhesion strength were realized.

Computational simulation of cold spray process assisted by electrostatic force

The integrated model of compressible thermofluid, splat formation and coating formation for the cold spray process has been established. In-flight behavior of nano-micro particles and the interaction between the shock wave and the particles in a supersonic jet flow impinging onto the substrate and further effect of electrostatic force on the particle acceleration are clarified in detail by carrying out a real-time computational simulation. The optimal particle diameters for an impinging particle velocity exceeding critical velocity exist. Particles with the diameter of submicron interact with shock wave and particles are decelerated prior to the impact. However, the particles can be accelerated considerably by utilizing electrostatic forces even in the presence of unavoidable shock waves. Finally, based on the integrated model, the coating thickness in an electrostatic assisted cold spray process is evaluated.

Study of Injection Angle and Carrier Gas Flow Rate Effects on Particles In-Flight Characteristics in Plasma Spray Process: Modeling and Experiments

This paper investigates the influence of particle injection angle on particle in-flight behaviors and characteristics at different primary and carrier gas flow rates through an integrated modeling and experimental approach. Particle in-flight status such as temperature, velocity, size and their distribution are analyzed to examine particle’s melting status before impact. Results from the experiments and numerical simulations both show that, when carrier gas flow rate is fixed, a small injection angle favors the particle melting and flattening. This behavior is independent of primary and secondary gas flow rates, spray distance and carrier gas flow rate. When both carrier gas flow and injection angle vary, a high carrier gas flow rate and a small injection angle are recommended for high particle temperature and velocity.

In-Flight Behavior of Ceramic Particle in Plasma Spray Forming

In-Flight Behavior of Ceramic Particle in Plasma Spray Forming

An Empirical Method to Evaluate the In-Flight Particle Behaviors within a Cross Section of Mass Flux during Atmospheric Plasma Spraying

In order to enhance understandings of the coating formation in the plasma spraying, an empirical method known as the spot spraying bead formation, was designed. This study is focused on the applicability of the proposed empirical method to explain the microstructural inhomogeneity during the process. Based on the in-flight particle diagnostics using DPV-2000, two different plasma gas compositions were chosen to evaluate the plasma gas effect on the microstructural evolution of Al2O3-TiO2 composite feedstock. A blended NiCr-Cr2O3-Ag-Ca/BaF2 feedstock was sprayed in order to examine the effects of particle parameters on the particle trajectory and the coating microstructures. Through the empirical approach, impacting particle properties and particle trajectory depending on process parameters could be directly shown and coating microstructures could be deduced from the characteristics of the spot spraying bead.

119 DC-RFハイブリッドプラズマ流動システムの熱流動構造と飛行微粒子特性との相関(流体IV)

119 DC-RFハイブリッドプラズマ流動システムの熱流動構造と飛行微粒子特性との相関(流体IV)

Computational Simulation on Optimization of Micro/Nano Particle-Laden Micro Jet by Electrostatic Acceleration

In-flight behavior of micro-nano particles and the interaction between shock wave and particles in a supersonic jet which impinges onto the substrate in a micro space are clarified in detail by computational simulation. The optimal particle diameter for maximum impinging particle velocity exists. Particles smaller than the optimal diameter are decelerated drastically prior to the impact on the cavity as a result of unavoidable particle-shock interaction. The larger deceleration through shockwave is observed with decrease in particle diameter. The particle less than 100 nm cannot penetrate the shockwave and carried by wall jet without impinging on the tooth cavity. The electrostatic force in the vicinity of tooth cavity acts effectively for the acceleration of submicron particles even in the presence of unavoidable shockwave in micro space.

In-flight behaviors of ZrO 2 particle in plasma spraying

In recent years, on-line measurement of particle in-flight behaviors including temperature, velocity and spatial distribution is one of the most important research fields, which can be used to directly analyze the influence of spray parameters and to control the coating quality real-time during plasma spray forming. According to the method of orthogonal experiments, plasma spraying of ZrO 2 has been carried out under different spray parameters in this paper. The particle in-flight behaviors have been measured by a two-color emission technique to analyze the influence of argon flow rate, hydrogen flow rate and electrical current on the particle temperature and velocity. The molten state of the particle has been analyzed. The results showed that the particle velocity increased remarkably with the increase of the argon flow rate. The particle temperature was mainly influenced by the hydrogen flow rate, and increasing electrical current resulted in the increase of the particle temperature and velocity to some extent. The molten state of the particle, affected by the particle in-flight behaviors in the plasma jet, could be used to analyze the deposition efficiency and coating quality.

Computational study of particle in-flight behavior in the HVOF thermal spray process

A computational framework is developed for the multiphase flow in a high velocity oxygen-fuel (HVOF) thermal spray coating process with steel powders as the feedstock. The numerical model includes continuum-type differential equations that describe the evolution of gas dynamics and multi-dimensional tracking of particle trajectories and temperature histories in the turbulent reacting flow field. The numerical study shows that the particle temperature is strongly affected by the injection position while the particle velocity is less dependent on this parameter. Moreover, both particle velocity and temperature at impact are strongly dependent on particle size, although the spatial variation of these two variables on the substrate is minimal. It is also found that not all the particles are deposited on the substrate perpendicularly (even if the spray angle is 90°), due to substantial radial fluid velocities near the stagnation point. A statistical distribution of particle velocity, temperature, impinging angle and position on the substrate as well as particle residence time is obtained in this work through independent random tracking of numerous particles by accounting for the distributed nature of particle size in the feedstock and injection position as well as the fluctuations in the turbulent gas flow.

Modeling and control of HVOF thermal spray processing of WC–Co coatings

This work focuses on the modeling and feedback control of the high velocity oxygen fuel (HVOF) thermal spray processing of WC–Co coatings. A first-principles-based process model is proposed to explore the fluid dynamics and particle inflight behavior in the HVOF flow field. Rule-based stochastic simulation, which encapsulates the main features involved in the deposition process, is used to capture the evolution of coating microstructure. The multiscale modeling of HVOF thermal spray process reveals that the velocity and melting degree of particles at the point of impact on the substrate play a very important role in the formation of coating microstructure, which in turn, can be almost independently controlled by pressure and fuel/oxygen ratio, respectively. Based on model predictions and available experimental observations, the control problem is formulated as the one of regulating volume-based averages of particle velocity and melting degree at impact on the substrate by manipulating the feed rate of air, oxygen and fuel at the entrance of the thermal spray gun, through which the pressure and oxygen/fuel ratio can be independently adjusted. A feedback control system is then developed and applied to a detailed mathematical model of the process. Closed-loop simulations show that the feedback controller is effective in driving the controlled outputs to the desired set-point values and also robust with respect to various kinds of disturbances in the operating environment.

In-flight particle behaviour and its effect on co-spraying of alumina–titania

The present paper investigate and illustrate the importance of plasma–particle interaction in controlling the plasma spray process while spraying alumina–titania powder blend. Plasma sprayed coatings of alumina–titania (60–40 μm) have been prepared at different operating parameters. Phase composition of the coatings has been studied by X-ray diffraction technique. It is observed that chemical composition of alumina–titania coatings, prepared at low input power, is significantly different from that of the feed stock powder. Coating composition progressively approaches that of the feedstock powder at higher power inputs. Experimental results are explained in terms of the in-flight behaviour of alumina and titania particles in the plasma jet using a one-dimensional model to predict the thermal state of the particles. In particular, the effect of particle size and input power are considered in this study.