Comparative visualized investigation of impact-driven high-speed liquid jets injected in submerged water and in ambient air

This paper is a comparative study on the characteristics of high-speed liquid jets injected in surrounding water and air using shadowgraph technique. One of the main objectives is to investigate the effects of liquid’s physical properties, used to generate the high-speed liquid jets, on jet generation’s characteristics. Moreover, comparative investigations on effects of those liquid jets after injected in water and air are reported. The high-speed liquid jets were generated by the impact of a projectile launched by a horizontal single-stage power gun. The impact-driven high-speed liquid jets were visualized by shadowgraph technique and images were recorded by a high-speed digital video camera. The process of impact-driven high-speed liquid jet injection in air and water, oblique shock waves, jet-induced shock waves, shock waves propagation, the bubble behavior, bubble collapse-induced rebound shock waves and bubble cloud regeneration were clearly observed. It was found that different properties of liquid (surface tension and kinematic viscosity) affect the jet maximum velocity and shape of the jet. Bubble behaviors were only found for the jet injected in water. From the shadowgraph images, it is found that the maximum average jet velocity, expansion and contraction velocities of bubble in axial direction increase when the value of the multiplied result of surface tension by kinematic viscosity increases. Therefore, surface tension and kinematic viscosity are the significant physical properties that affect characteristics of high-speed liquid jets.     

Manifestation of the stochastic resonance in submerged jets under an acoustic action

A phenomenon that is similar to the well-known stochastic resonance in nonlinear oscillators but is caused by the turbulence in a circular submerged jet under a harmonic acoustic action, rather than by noise, is considered. It is shown that, at a fixed distance from the nozzle, a variation of the initial turbulence level leads to a non-monotonic variation of the wave amplitude at the frequency of the acoustic action, namely, to the appearance of an amplitude maximum at a certain level of the initial turbulence. The qualitative explanation of the phenomenon consists in that the initial turbulence acts on the system in a way similar to that of external noise: it changes the effective parameters of the system and, in particular, shifts the spectral maxima, which is equivalent to a change in a certain “eigenfrequency.” Such a change in the effective parameters of the jet leads to a phenomenon similar to the stochastic resonance.     

Numerical visualization of vortex flow behavior in square jets in cross-flow

Direct numerical simulations have been performed in this study to visualize the flow behavior of single and multiple square jets issuing normally into a cross-flow. Three configurations are considered, a single jet located in the centre of the domain, twin jets in side-by-side (SBS) arrangement in the spanwise direction and triple jets in tandem arrangement with twin jets at the front and a third jet in downstream along the centre line. Simulation uses a jet to cross-flow velocity ratio of 2.5 and the Reynolds number 225, based on the free-stream quantities and the jet width. While the vortical structures predicted from single jet case were in good qualitatively agreement with the findings of other researchers, our results show that the process of merging between two counter-rotating vortex pairs (CRVP) in twin jets configurations is strongly dependent on the jet-to-jet edge distance. Further downstream in the far-field, results from the SBS twin jets show a most dominating larger CRVP accompanied with a smaller inner vortex pair. The observations are in good qualitative agreement with the experimental findings in the literature. The resulting flow structures of triple jets in tandem configuration have revealed, for the first time, more complicated flow interactions between individual jets and cross-flow, providing further insights of complex flow physics and its potential engineering applications.     

Broadband shock noise reduction in turbulent jets by water injection

The concept of effective jet properties introduced by the author (Kandula M. Prediction of turbulent jet mixing noise reduction by water injection. AIAA J 2008;46(11):2714-22) has been extended to the estimation of broadband shock noise reduction by water injection in supersonic jets. Comparison of the predictions with the test data for cold and hot underexpanded supersonic nozzles shows a satisfactory agreement. The results also reveal the range of water mass flow rates over which saturation of mixing noise reduction and existence of parasitic noise are manifest.     

Coupled hydrodynamic-acoustic modeling of sound generated by impacting cylindrical water jets

A coupled hydrodynamic-acoustic model describing acoustic propagation in a fluid containing multiple bubbles is proposed and applied to simulate noise generated by impacting water jets. The total pressure is decomposed into a "hydrodynamic" part and an "acoustic" part and computed using different schemes. The hydrodynamic pressure field is calculated independently using a generalized hydrodynamic model, and the pressure variations serve as sources in the wave equation for the acoustic pressure. A numerical algorithm developed to calculate wave propagation in an irregular region is used to account for the existence of the cavities. Noise generated by the impact of two cylindrical water jets is predicted. The computed near-field pressure is compared with the experimental data.     

Transient behavior of superheated water jets boiling

Superheated water flowing out from high-pressure chamber through short cylindrical and slot channel has been studied experimentally. Relation of vaporization mechanisms in superheated liquid (boiling in single, not interacting centers, intense heterogeneous vaporization, and homogeneous fluctuating nucleation) and respective forms of superheated water jets has been determined. Temperature intervals with transient behavior of boiling have been determined. It is shown that at transient behavior of boiling the amplitude of pulsations of jet parameters increases, and in the spectra of pulsation power, the low-frequency component 1/f appears.     

使用莫尔条纹法测量气流密度

把莫尔条纹应用于对称的和非对称的流场，测出了从喷嘴喷出的不完全膨胀气流的密度分布。气流的内部密度分布通过使用数字表示的转化方法转变成了莫尔条纹图像数据，这些莫尔条纹图像数据表明了同种光在穿过气流时将会发生折射。这一现象可以通过改变气体喷口的压力比来完成并观察到。实验表明：不同形状的喷嘴喷出的气流密度分布各不相同，而且复杂程度也不同，但沿着喷嘴气流轴的气流密度变化大致相似。     

Dynamics of individual single-walled carbon nanotubes in water by real-time visualization

Individual single-walled carbon nanotubes (SWNTs) in aqueous suspension are visualized directly by fluorescence video microscopy. The fluorescent tagging is simple, biocompatible, and does not modify the SWNTs. The dynamics of individual SWNTs in water are observed and quantified for the first time. We measure the confined rotational diffusion coefficient and find it in reasonable agreement with predictions based on confined diffusion of dilute Brownian rods. We determine the critical concentration at which SWNTs in suspensions start interacting. By analyzing the fluctuating shape of SWNTs in the 3 to 5 microm range, we determine that their persistence length ranges between 32 and 174 microm, in agreement with theoretical estimates; thus, commonly available SWNTs in liquids can be considered as rigid Brownian rods in the absence of imposed external fields or self-attractive forces.     

Real-time coloured visualization of phase flows by the schlieren method

A coloured real-time visualizer of optical inhomogeneities comprising a bichromatic schlieren system, video camera and colour monitor has been developed. The schlieren system represents a function Foucault-Hilbert transformation provided with an amplitude spatial frequency filter, or a quadrant Foucault knife edge. Two colour-coded complementary Toepler-grams are obtained in the exit plane of this schlieren system. Their summed image is then recorded by the video camera and displayed on the screen of the colour monitor. The schlieren photograph of internal gravity waves, generated by the cylindrical body motion in the reservoir filled with the stratified liquid, is presented.     

The geometrical acoustic method for calculating the echo of targets submerged in a shallow water waveguide

A geometrical acoustic method based on image-source method and physical acoustic method was developed to calculate the echo of targets submerged in the shallow water waveguide.The incident rays and the scattering rays are reflected by two boundaries for many times,and then the back rays become countless.The total backscattering field is obtained through summing up the scattering field produced by each combination of incident rays and back rays.The echo of the 10m-radius pressure release sphere in Pekeris waveguide with the range is calculated by the geometrical acoustic method.Compared with the results calculated by the wave acoustic method in the available literature,it shows that both are in accordance on average value and descend trend.The following results indicate that the difference between Effective Target Strength(ETS) in shallow water and the Target Strength(TS) in free space for spheres and certain other rounded objects is small.However,the ETS of some targets such as cone-shaped is quite different from TS in free space,which can lead to large errors in estimating a target’s scattering property using traditional sonar equation.Compared with the method of wave acoustics,the geometrical acoustic method not only has the definite physical meaning but also can calculate the echo of complex objects in shallow water waveguide.     

浅海波导中目标回声计算的射线声学方法

建立一种基于虚源法和物理声学方法计算浅海波导中目标回声的射线声学方法。入射声线经过两个界面的多次反射有无限多条,每条入射声线由目标反射后又会产生无限多条到达接收点的声线。将各种组合的散射声场求和得到总的回波声场。用射线声学方法计算了Pekeris波导中半径10 m的绝对软球的回声随距离的变化。与已有文献中波动声学方法的计算结果对比,两者在平均值和下降趋势上符合。计算表明,波导中球和一些圆形目标的等效目标强度(ETS)与自由空间中目标强度(TS)差别很小。而像圆锥形这类目标的等效目标强度与自由空间中目标强度差别较大,导致传统的声呐方程误差较大。与波动声学方法相比,射线声学方法不但具有明确的物理意义,而且可以对浅海信道中复杂形状目标回声进行计算。     

Flow visualization by an improved double exposure method in holography

Some optical differential interferometric techniques were investigated in order to measure the density distribution in the air jet flow of a small scale flow cell while excluding the effects of the optical distortion of its glass windows. A technique using moiré fringe formation by rotating the reference wave in one exposure of the double exposure method was found to be most suitable for this purpose. High contrast and multiplication of moiré fringes can be obtained by a moiré fringe sharpening and multiplication method.     

Delta-wing vortex visualization using micro-sized water droplets generated by an ultrasonic humidifier

An off-surface visualization method using micro water droplets and a laser beam sheet was developed. The average size of the water droplets generated by the home-style ultrasonic humidifier was about 5–10 μ. This method was pollution-free, eliminated the problem of toxicity, and provided a sufficient density of tracing particles for good visibility. The method was successfully applied to a visualization of the complex vortex flow of a double-delta wing with strake.     

A qualitative evaluation of variable-angle ultrasonic transducers by the photoelastic visualization method

The technique of photoelastic visualization of ultrasound has been applied to study the waves generated by variable-angle transducers. Two particular transducer designs have been investigated. In the first, a compressional wave is launched through a liquid, whereas in the second a compressional wave propagates through perspex before striking the boundary of the testpiece. A comparison has been made between the waves generated, which have been visualized in glass testpieces, and those predicted by calculation.     

Photon production by gluon jets

The fragmentation function for photons from a gluon jet is uniquely calculable in QCD. A phenomenological investigation of its properties indicates that the best place to observe it is in the continuum photon spectrum in the two-gluon decays of heavy Q$\text{Q}$ P-wave or pseudo-scalar bound states. The fragmentation function may be observable in an experiment with sufficient efficiency in rejecting photons from π⁰ decay.     

Characteristics of water veil and verification of its healing effect by visualization of mind

A very thin water veil like a thin transparent sheet of vinyl has been produced by shaping a double-disk nozzle in such a way to accelerate the water flow inside the nozzle. Comparison of the simulated shape of the water veil with that of the experiment shows that they are almost identical. Human mind can be refreshed and relaxed by being inside of this water veil. In this paper, the application of water veil to healing mind and body is examined. The analysis of the brain wave data using the emotion spectrum analysis method (ESAM) elicited that the water veil is very useful to recover freshness and effective in healing mind and body.