In-flight Behavior Research Articles

Multi-scale modeling and analysis of an industrial HVOF thermal spray process

A hybrid (deterministic/stochastic) fundamental model is proposed for the major physico-chemical processes involved in an industrial HVOF thermal spray process (Diamond Jet hybrid gun, Sulzer Metco, Westbury, NY, USA). The model includes continuum type differential equations that describe the evolution of gas and particle temperature and velocity, and a rule-based stochastic simulator that predicts the evolution of the coating microstructure. Regarding gas/particle dynamics, the Reynolds- and Favre-averaged Navier–Stokes equations and the energy balance equations are solved with the renormalization group (RNG) k– ε turbulence model, and the particle trajectories, temperature histories and melting degrees are determined using the fourth-order Runge–Kutta method. On the microscopic particle deposition process, the formation of coating microstructure is captured by the Madejski deformation model and several rules that govern splat formation, solidification and coating growth. Based on the proposed model, a detailed comprehensive parametric analysis is carried out to study the relationship between the key process parameters and the particle in-flight behavior as well as the resulting coating properties.

MULTISCALE MODELING OF HVOF THERMAL SPRAY PROCESS

The major physicochemical processes involved in an industrial HVOF thermal spray process (Diamond Jet hybrid gun, Sulzer Metco, Westbury NY) are studied by a comprehensive multiscale model. The model includes continuum type differential equations that describe the dynamics of gas phase and particles of different sizes, and a rule-based stochastic simulator that predicts the evolution of coating microstructure. On the macroscopic gas/particle dynamics side, the Favre-averaged Navier-Stokes equations and energy balance equations are solved with the renormalization group (RNG) k-ɛ turbulence model, and the particle trajectories, temperature histories and melting degrees are determined using the 4th order Runge-Kutta method. On the microscopic particle deposition side, the formation of coating microstructure is captured by certain rules that encapsulate the main physical features of particle deposition, deformation, solidification and coating growth. Parametric analysis based on the developed multiscale model is carried out to study the relationship between the macroscopic operating conditions and the particle in-flight behavior as well as the resulting coating microstructure.

A particle image velocimetry investigation of in-flight and deposition behaviour of steel droplets during electric arc sprayforming

Abstract Gas and Fe–0.8 wt.% C droplet dynamics during electric arc spraying have been characterised using particle image velocimetry (PIV). This study has shown that the flow of N2 atomising gas was well-collimated, with an exit velocity of 255 m s−1, decaying to 75 m s−1 at an axial distance of 150 mm, where the jet diameter was ∼50 mm. The presence of atomised steel droplets increased spray divergence. Droplet mode velocity measurements equalled the gas-only velocity measurement of ∼120 m s−1 at an axial distance of 95 mm, and then further increased to 135 m s−1 at 150 mm. Close to the substrate, droplet splashing dominated the flow field with upward and then lateral flow of splashed droplets. In the presence of a vertical step feature, the flow field became complex, with some splash droplets having trajectories that caused secondary deposition on the vertical step wall.

Confusion in travellers

Acute onset long haul in-flight confusion, restlessness, disorientation and abnormal behaviour in a 24 year old lady who had recent typhoid fever is reported. Confusion in travelers within the context of infections, including typhoid psychosis, and other causes, is discussed to enlighten practitioners on the problem, and ensuing potential medico-legal and ethical issues.

ISGRI: The INTEGRAL Soft Gamma-Ray Imager

For the first time in the history of high energyastronomy, a large CdTe gamma-ray camera is operating in space. ISGRI is the low-energy camera of the IBIS telescope on board the INTEGRAL satellite. This paper details its design and itsin-flight behavior and performances. Having a sensitive area of 2621 cm$^2$ with a spatial resolution of 4.6 mm, a low threshold around 12 keV and an energy resolution of $\sim$ 8\% at 60 keV, ISGRI shows absolutely no signs of degradation after 9 months in orbit. All aspects of its in-flight behavior and scientific performance are fully nominal, and in particular the observedbackground level confirms the expected sensitivity of 1 milliCrab for a 10$^6$s observation.

Modeling and analysis of HVOF thermal spray process accounting for powder size distribution

This work focuses on the high velocity oxygen–fuel (HVOF) thermal spray processing of coatings and presents a fundamental model for the process which explicitly accounts for the effect of powder size distribution. The model describes the evolution of the gas thermal and velocity fields, as well as the motion and temperature of agglomerate particles of different sizes. In addition to providing useful insight into the in-flight behavior of particles with different sizes, the model is used to make a control-relevant parametric analysis of the HVOF thermal spray process. This analysis allows us to systematically characterize the influence of controllable process variables such as combustion chamber pressure, oxygen/fuel ratio, as well as the effect of powder size distribution, on the values of particle velocity and temperature at the point of impact on substrate. Specifically, the study shows that particle velocity is primarily influenced by the combustion chamber pressure, and particle temperature is strongly dependent on the fuel/oxygen ratio. Furthermore, it shows that the particle velocity and temperature at the point of impact depend strongly on particle size. These findings are consistent with available experimental observations and set the basis for the formulation of the control problem for the HVOF process.

Analysis of In-Flight Behavior of Truncated Plug Nozzles

Plug nozzles are usually designed to achieve altitude adaptation in a wide range of chamber/ambient pressure ratios.In actual in-e ight operationsofplug nozzles, this phenomenon musttakeplacein a e owing airstream,which can affect the performance. To understand the e ow behaviorin such conditionsand to evaluate the departure from the ideal nozzle performance, an investigation is carried out with a validated numerical tool based on the solution of turbulent Navier ‐Stokes equations and on shock e tting. A sample rocket plug nozzle is analyzed parametrically to evaluate the effect of varying Mach number at constant pressure and the effect of varying pressure ratio at constant Mach number. The results indicate that the interaction with a e owing airstream reduces the pressure of the external air, as seen from the nozzle exhaust jet, yielding a reduction of the performance. In particular, a dramaticdecrease of nozzleperformance may takeplacein the transonicregion iftheslipstream effect is neglected in thedesign. Theresults also provide useful indications on how the Mach numberand the shroud shapecan affect the value of ambient pressure where the transition from open to closed wake takes place.

The effect of particle size and morphology on the in-flight behavior of particles during high-velocity oxyfuel thermal spraying

A one-way coupled mathematical model is formulated to simulate the effects of particle size and morphology on the momentum and thermal energy transfer of particles during high-velocity oxyfuel (HVOF) thermal spraying. First, computational fluid dynamic techniques are implemented to solve the Favre-averaged mass, momentum, and energy conservation equations in the gas phase. The gas dynamic data are then used to model the behavior of particles in the gas field. The concept of sphericity is used to incorporate the effect of particle morphology into the model. The calculated results show that the particle velocity and temperature, before impinging onto the substrate, are strongly affected by particle size, morphology, and spray distance. Smaller particles are accelerated to a higher velocity but slowed down rapidly due to their smaller momentum inertia, while the larger particles are accelerated with some difficulty. The same tendency is observed regarding the effect of particle size on its thermal history.

A principal component feedforward algorithm for active noise control: flight test results

An in-flight evaluation of a principal component algorithm for feedforward active noise control is discussed. Cabin noise at the first three harmonics of the blade passage frequency (103 Hz) of a Raytheon-Beech 1900D twin turboprop aircraft was controlled using 21 pairs of inertial force actuators bolted to the ring frames of the aircraft; 32 microphones provided error feedback inside the aircraft cabin. In a single frequency noise control test, the blade passage frequency was reduced by 15 dB averaged across the microphone array. When controlling the first three harmonics simultaneously, reductions of 11 dB at 103 Hz, 1.5 dB at 206 Hz, and 2.8 dB at 309 Hz were obtained. For single frequency feedforward control problems, the principal component algorithm is shown to be useful for reducing the computational burden and simplifying the implementation of control effort penalties in high channel count control systems. Good agreement was found between the in-flight behavior of the controller and the predicted optimal control solution.

In-flight behaviour of steel particles during plasma spraying

A mathematical model of the powder particle in-flight behaviour during plasma spraying is further developed by including the influence of the particle mass loss due to evaporation on the mechanical behaviour of the particle. The effects of the particle mass loss and plasma–particle interactions are included in the model in a simple analytical form. Analytical equations for estimating the particle mass loss, the time of complete particle melting and the degree of plasma cooling caused by the plasma–particle interaction are obtained and are shown to be consistent with the modelling results. The kinetics of particle melting are studied in detail. On the basis of the model developed, mathematical simulation of the mechanical and thermal behaviour of the powder particles made of alloyed steel 316 L has been undertaken.

Modelling of the in-flight behaviour of stainless steel powder particles in high velocity oxy-fuel spraying

Modelling of the mechanical and thermal behaviour of stainless steel 316L powder particles during high velocity oxy-fuel (HVOF) spraying is presented. This modelling accounts for the combustion process, the gas dynamics inside and outside of the spray gun, gas-particle interactions, acceleration and deceleration of the gas flow, internal heat conduction in the powder particles and particle heating, melting, cooling and solidification. Variations of the times of flight and melting of the particles are studied. Optimal conditions of spraying are predicted. The results agree with experimentally-established HVOF spraying practice.

Dynamic processes during high velocity oxyfuel spraying

High velocity oxyfuel spraying is a new, rapidly developing technology for coating formation which is now challenging plasma spraying. Dynamic processes during HVOF spraying have considerable influence on the coating quality. The dynamic processes considered are as follows: combustion and gas dynamics, mechanical and thermal inflight behaviour of the powder particles, and droplet flattening. The corresponding literature is also reviewed. The following points are taken into account: fluid behaviour inside and outside a spraying gun; fluid-particle interactions; particle shape and morphology; internal heat conduction in powder particles; mass transfer (dissolution, diffusion, etc.) inside the composite particles; particle heating, fusion, cooling, and solidification; surface roughness, splat solidification, and mass loss of the droplet liquid phase during droplet flattening. Good agreement between theoretical and experimental results is shown to exist. The results obtained can be used for prediction of the optimum conditions of spraying.

Influence of plume structure and pheromone concentration on upwind flight of Cadra cautella males

Abstract. The effects of pheromone plume structure and its concentration on the pheromone‐mediated flight of male Cadra cautella (Lepidoptera: Phycitinae) were investigated in a laminar‐flow wind tunnel. When two C. caurella males flew simultaneously along a ribbon plume of mixed smoke and pheromone, their inflight behaviour was dependent on the instantaneous structure of the plume they encountered. When a male intercepted an intact ribbon filament, he sustained a crosswind course, whereas when he intercepted a turbulent filament (created by an upwind male fragmenting the ribbon plume), he adopted a flight course more due upwind. These results indicate that C. cautella males altered their in‐flight manoeuvres in response to instantaneous changes in the fine structure of the pheromone plume. We also demonstrated that differences in the fine structure of the plume had more influence on the flight pattern of C. cautella males than a 1000‐fold range in pheromone dose. The size of the plume was increased by adding wind deflectors upwind of the pheromone source, independent of source dosage, males following ribbon plumes flew slow zigzag tracks, whereas males following large, turbulent plumes flew directly to the source in fast, straight tracks with less counterturning.

Talking to bats: what do arctiids say?

Certain tiger moths (Arctiidae) generate trains of high-frequency clicks from specialized structures (tymbals) on their thorax. Although social functions for the sounds have been demonstrated, debate continues on their anti-bat defensive role with aposematism, startle, and/or echolocation disruption being offered as to how the sounds operate. The controversy arises primarily from the near impossibility of observing natural, in-flight behavior of moths and hunting bats. As a result, most of the experiments attempting to explain the sounds have used indirect methods to infer their actions. These studies include examinations of the structure of the sounds, stimulation of stationary moths with artificial bats, and stimulation of trained, laboratory bats with artificial moths. Other laboratories have attempted to exploit the foraging behavior of wild bats in controlled conditions. These studies have not yet satisfactorily explained why arctiids talk but one observation that has become clear is that the defenses of tiger moths, as with most animals, are directed against a variety of predators and that single explanations do not exist for complex behaviors.

Personality and occupational success: 16PF correlates of cabin crew performance

One hundred and thirty-six cabin crew completed the Cattell 16PF at the beginning of their training as the personnel department wanted to determine the effectiveness of the test in predicting occupational success. Over the course of a 6-month period detailed daily reports were kept on their in-flight behaviour. These reports were later used to categorize the subjects into above average, average, below average and to note those who left the airline. Pearson correlations and one-way ANOVAs across various groups (i.e. above vs below average; stayed vs left) failed to yield significant differences, though some clear trends were apparent. Results were discussed in terms of current studies examining personality trait correlates of occupation behaviour.

Homing behavior of hippocampus and parahippocampus lesioned pigeons following short-distance releases

The avian hippocampal formation has been proposed to play a critical role in the neural regulation of a navigational system used by homing pigeons to locate their loft once in the familiar area near home. In support of this hypothesis, the homing performance of pigeons with target lesions of either the hippocampus or parahippocampus was found to be impaired compared to controls following releases of about 10 km. Further, radio tracking revealed that the in-flight behavior of the hippocampal lesioned homing pigeons was characterized by numerous direction changes and generally poor orientation with respect to the home loft. The results identify a local navigational impairment on the part of the hippocampal lesioned pigeons in the vicinity of the loft where landmark cues are thought to be important. Additionally, target lesions of the hippocampus or parahippocampus were found to be similarly effective in causing homing deficits.

Threshold hypothesis for pheromone perception

Field results have shown that male moths of some species are not always trapped by the ratio of pheromone components produced by the female moths. For cases involving a binary mixture of geometrical or positional isomers, this phenomenon may be explained by use of a threshold diagram in which the isomer ratio in the mixture is plotted against release rate (concentration). In this diagram an “attraction area” is bounded by the threshold for flight activation over the full range of binary mixtures and by the threshold for alteration of in-flight behavior (disorientation) by each pheromone component. A low release rate of the natural mixture may fall within this “attraction area,” or a high release rate of mixtures in certain other ratios may fall within this area and would be expected to attract male moths. This hypothesis has been used to explain heretofore anomalous trapping data with some moth species, and it can be useful in future studies on defining pheromone blends, species specificity, and potentially disruptive mixtures for insect control.