Experimental investigation on de-icing by an array of impact rod-type plasma synthetic jets

Since flight accidents due to aircraft icing occur from time to time,this paper proposes an array of impact rod-type plasma synthetic jet de-icing methods for aircraft icing problems.The impact rod-type plasma synthetic jet actuator(PSJA)is based on the traditional PSJA with an additional impact rod structure for better de-icing in the flight environment.In this work,we first optimize the ice-breaking performance of a single-impact rod-type PSJA,and then conduct an array of impact rod-type plasma synthetic jet ice-breaking experiments to investigate the relationship between crack expansion and discharge energy,ice thickness and group spacing.The results show that the impact force and impulse of a single-impact rod-type PSJA are proportional to the discharge energy,and there exists a threshold energy Qmin for a single actuator to break the ice,which is proportional to the ice thickness.Only when the discharge energy reaches above Qmin can the ice layer produce cracks,and at the same time,the maximum radial crack length produced during the ice-breaking process is proportional to the discharge energy.When the ice is broken by an array of impact rod PSJAs,the discharge energy and group spacing together determine whether the crack can be extended to the middle region of the actuator.When the group spacing is certain,increasing the energy can increase the intersection of cracks in the middle region,and the ice-fragmentation degree is increased and the ice-breaking effect is better.At the same time,the energy estimation method of ice breaking by an array of impact rod-type PSJAs is proposed according to the law when a single actuator is breaking ice.

高速催泪射流轨迹分析及抗风性能实验研究

目的探究高速催泪射流轨迹和外界风环境对催泪剂着靶性能的影响。方法通过搭建高速射流瞬态采集和抗风性能测试平台,系统研究射流动态特征及抗风性能,并与现行单警催泪喷射器进行对比。结果高速催泪喷射器射流初始直径达5.5mm,呈较为规整的柱状,初始速度达138.9m/s。在1m处,射流中心仍有明显的集束状,周围出现空泡现象,速度降为88.3 m/s。在3 m处,射流轨迹呈发散的胶丝状,速度降为42.9 m/s。单警催泪喷射器射流在0.2、1、3 m处的速度分别为7.9、20.7、7.5 m/s,射流在前进过程中逐渐分散成小颗粒状的液珠,并在3 m处出现整体轨迹向下偏移。在抗风性能上,使用模拟人体上躯干600mm×900mm靶标(瞄准脸部),在0~4级侧向风作用下,高速催泪喷射器射流的着靶率为85.2%~57.4%,中心侧向偏移小于10cm,而单警催泪喷射器射流着靶率为78.8%~4.2%,中心侧向偏移超过20cm。结论相比单警催泪喷射器,高速催泪喷射器的射流轨迹具有良好的集束性和定向性,射流速度整体更高,同时在抗风性能方面也具有明显优势。另外,射流轨迹特征对其抗风稳定性起到了关键作用。

High-speed measurement of thickness of a water film formed by a jet obliquely impinging onto a plate using an LED-induced fluorescence method

A transient thickness distribution measured with a high temporal resolution is elemental for exploring the flow characteristics and mechanism of a liquid film formed by an impinging jet.Therefore,this paper develops a high-speed Light-Emitting Diode-Induced Fluorescence(LEDIF)system based on the brightness measured directly above the liquid film.An Ultraviolet(UV)LED lamp is used to provide sufficient and continuous excitation light.Then,a system performance analysis proves that the system can continuously measure the global film thickness at a high acquisition frequency of 5000 Hz when the dye concentration is 200 mg/L.The influence of the irregularity of the excitation intensity,including the spatial non-uniformity,temporal instability,and long-term instability,on the measurement uncertainty is analyzed in detail.The analysis indicates that the system has an acceptable uncertainty of 10%.Compared with theoretical results,experimental results verify that the LEDIF system can accurately measure the global thickness of a liquid film formed by a water jet obliquely impinging onto a plate.An experimental investigation of the radial section of the raised zone demonstrates that the radial section changes from a sewing needle to an oval when the azimuth angle increases from 10°to 90°.Meanwhile,the dynamic contact angle exponentially decreases from 41.4°to 30.1°.A dynamic analysis of surface waves shows that the measured wave velocity decreases from 12 m/s to 1 m/s and the dominant frequency decreases from 1000 Hz to 10 Hz along the flow direction.

High Speed Observation of Periodic Cavity Behavior in a Convergent-Divergent Nozzle for Cavitating Water Jet

Cloud cavitation shows an unsteady periodic tendency under a certain flow condition. In a cavitating water jet flow with cavitation clouds, the cavities or the clouds produce high impact at their collapse. In order to make clear a mechanism of the periodic cavity behavior, we experimentally examine the behavior in a transparent cylindrical convergent-divergent nozzle using a high-speed video camera. An effect of upstream pressure fluctuation due to a plunger pump is investigated from a viewpoint of unsteady behavior in a cavitating water jet. As a result, it is found that the cavitating flow has two kinds of oscillation patterns in the cavity length (cavitation cloud region). One is due to the upstream pressure fluctuation caused by the plunger pump. The other is much shorter periodic motion related to the characteristic oscillation of cavitation clouds accompanied with the shrinking (reentrant), growing and shedding motion of the clouds.

Flow and penetration behavior of submerged side-blown gas

To assess the widely used submerged side-blowing in pyrometallurgy,a high-speed camera-digital image processing-statistical approach was used to systematically investigate the effects of the gas flow rate,nozzle diameter,and inclination angle on the space-time distribution and penetration behavior of submerged side-blown gas in an air-water system.The results show that the gas motion gradually changes from a bubbling regime to a steady jetting regime and the formation of a complete jet structure as the flow rate increases.When the flow rate is low,a bubble area is formed by large bubbles in the area above the nozzle.When the flow rate and the nozzle diameter are significant,a bubble area is formed by tiny bubbles in the area above the nozzle.The increased inclination angle requires a more significant flow rate to form a complete jet structure.In the sampling time,the dimensionless horizontal and vertical penetration depths are Gaussian distributed.Decreasing the nozzle diameter and increasing the flow rate or inclination angle will increase the distribution range and discreteness.New correlations for a penetration depth with an error of±20%were obtained through dimensional analysis.The dimensionless horizontal penetration depth of an argon-melt system in a 120 t converter calculated by the correlation proposed by the current study is close to the result calculated by a correlation in the literature and a numerical simulation result in the literature.

Determination of the shedding frequency of cavitation cloud in a submerged cavitation jet based on high-speed photography images

To accurately determine the shedding frequency of the cavitation cloud in a submerged cavitation jet,the spectral analysis and the proper orthogonal decomposition(POD)for high-speed photography images are performed.The spectrums of 6 different kinds of image signals(the area-averaged gray level,the line-averaged gray level,the point gray level,the cavitation length,width,and area)are calculated and compared.The line-averaged gray level is found to be optimal in determining the shedding frequency but an accurate frequency can only be obtained in the stable-frequency zone where the cavitation cloud sheds.In repeated experiments,the plateau-shape distribution of the main frequency is established with a deviation of 10.8%.A revised Reynolds number Re'is defined and the shedding frequency can be correlated to Re'by a power law when the cavitation number is less than 0.02.This relationship is validated by the experimental data in literature.The first mode of the POD characterizes the ensemble-average of the cavitation cloud while the second mode is the major part of the cavitation cloud transient components.The modes 2-5 are organized in pairs,which confirms the periodic feature of the cavitation cloud in the submerged cavitation jet.Near the nozzle exit,the modes 2-5 are symmetrically distributed in the jet shear layer.The shedding frequency of the cloud cavitation can also be precisely determined by performing the spectral analysis of the weighting coefficients of the mode 2.This paper shows that the two parameters,namely,the line-averaged gray level and the weighting coefficients of the mode 2,can be confidently used to calculate the shedding frequency of the cavitation cloud in a submerged cavitation jet.

EVALUATION OF THE CUMULATIVE FORMATION OF HIGH-SPEED LIQUID JETS

This paper describes the generation of pulsed, high-speed liquid jets usingthe cumulation method. This work mainly includes (1) the design of the nozzle assembly, (2) themeasurement of the jet velocity and (3) flow visualization of the injection sequences. Thecumulation method can be briefly described as the liquid being accelerated first by the impact of amoving projectile and then further after it enters a converging section. The experimental resultsshow that the cumulation method is useful in obtaining a liquid jet with high velocity. The flowvisulization shows the roles of the Rayleigh-Tay-lor and Kelvin-Helmholtz instabilities in thebreakup of the liquid depend on the jet diameter and the downstream distance. When the liquid jetfront is far downstream from the nozzle exit, the jet is decelerated by air drag. Meanwhile, largecoherent vortex structures are formed surrounding the jet. The liquid will break up totally by theaction of these vortices. Experimental results showing the effect of the liquid volume on the jetvelocity are also included in this paper. Finally, a method for measuring the jet velocity bycutting two carbon rods is examined.

Mathematical modelling and numerical optimization of particle heating process in copper flash furnace

A mathematical model of the particle heating process in the reaction shaft of flash smelting furnace was established and the calculation was performed.The results indicate that radiation plays a significant role in the heat transfer process within the first 0.6 m in the upper part of the reaction shaft,whilst the convection is dominant in the area below 0.6 m for the particle heating.In order to accelerate the particle ignition,it is necessary to enhance the convection,thus to speed up the particle heating.A high-speed preheated oxygen jet technology was then suggested to replace the nature gas combustion in the flash furnace,aiming to create a lateral disturbance in the gaseous phase around the particles,so as to achieve a slip velocity between the two phases and a high convective heat transfer coefficient.Numerical simulation was carried out for the cases with the high-speed oxygen jet and the normal nature gas burners.The results show that with the high-speed jet technology,particles are heated up more rapidly and ignited much earlier,especially within the area of the radial range of R=0.3−0.6 m.As a result,a more efficient smelting process can be achieved under the same operational condition.

Experimental investigations of mechanical and reaction responses for drop-weight impacted energetic particles

Low-velocity drop-weight impact experiments on individual and multiple Cyclotetramethylene tetranitramine (HMX) energetic particles were performed using a modified drop-weight machine equipped with high-speed photography components. Multiple particles experienced more severe burning reactions than an individual particle. Comparisons between impacted salt and HMX particle show that jetting in HMX is mainly due to the motion of fragmented particles driven by gaseous reaction products. Velocity of jetting, flame propagation, and area expansion were measured via image processing, making it possible to quantify the chemical reaction or mechanical deformation violence at different stages.

Influences of nozzle parameters and low-pressure on jet breakup and droplet characteristics

Experiments were carried out to investigate the influences of nozzle geometric parameters and injection pressure on jet breakup characteristics using a high-speed photography(HSP)technique.The flow rates and spraying ranges of sprinkler with different nozzles were measured.In this research,HSP technique was also used to photograph the drops emitted by sprinkler with different nozzles at different pressures,photographs were taken at different horizontal distances from the sprinkler and the equivalent circle diameter was used to represent the particle sizes.Based on HSP technology,the effects of flow velocity and nozzle geometric parameters on jet breakup length were studied,and the droplet diameters with different nozzle types were obtained.The result showed that for the sprinkler with different nozzles,the breakup length decreased with the increases of pressures.At the nearby(3-9 m)region and distant(12-18 m)region of sprinkler,the droplet diameters of sprinkler with type B nozzle were the largest,which meant the sprinkler with type B nozzle was the optimal choice by synthesizing the droplet diameter distribution.The fitting relationship of jet breakup length with Reynolds number and Weber number(Re and We),and the regression equation of the end droplet diameters were deduced with errors of less than 5%and 4%respectively.

STUDY ON FLUID MECHANICS OF HYPERVELOCITY LIQUID JETS

The fluid mechanics in the generation of hyper veloeity water jets, light oiljets and glycerin jets was studied. Framing high-speed photography and single-shot photography wereused to observe the jets directly. The purposes of this study is to investigate the disintegrationand atomization processes at the velocity of 2km/s-3km/s as well as the auto-ignition andself-combustion of the light oil jets. Therefore, in the jet velocity measurement in addition to thehigh-speed photography, the results by other methods such as the laser beams cutting method and theshock wave detection using pressure transducers were also given. In the observation of the jetsevents, the illumination phenomenon was found, which may be regarded as the result of theauto-ignition and combustion of the light oil jets. Finally, the Munroe jet was studied.

Experimental study of the dynamics of a single cavitation bubble excited by a focused laser near the boundary of a rigid wall

Based on high-speed photographic experiments,this study presents a detailed qualitative and quantitative analysis of the dynamics of a single cavitation bubble near the boundary of a rigid wall in asymmetric settings.The main findings are reported as follows:(1)The non-sphericity of the bubble interface decreases with increasing spacing between the bubble and the boundary,and the asymmetry of the bubble becomes more significant with increasing asymmetry angle.(2)The motion mode of the bubble cluster in the second oscillation cycle can be divided into two typical modes depending on the direction of movement.(3)The angle between the oblique jet pointing towards the upper wall surface and the horizontal direction in the second oscillation cycle decreases as the dimensionless spacing decreases.