Stress waves propagation in solids under high-speed liquid impact

The high-speed liquid/solid impact phenomenon is often seen in many technicalfields such as, water jet cutting technology[1], rain erosion of aviation vehicles[2] and ro-tor blades erosion in large steam turbines[3]. Recently, China Aerodynamics ResearchCenter reported experimental results of rain erosion of hypervelocity projectile[4]; Xi’anJiaotong University reported numerical simulation of high-speed liquid drop impact on asolid surface[5]. In analyzing the mechanism of material’s dama…     

The turbulence of capillary waves on the surface of liquid hydrogen

It is experimentally demonstrated that the surface excitation of liquid hydrogen at a low frequency results in the turbulent mode in a system of capillary waves. The experimental results are in good agreement with the theory of weak wave turbulence. The pair correlation function of the surface deviations is described by the exponential function ω^m. The exponent m decreases in magnitude from m=?3.7±0.3 to ?2.8±0.2 when the pumping at a single resonant frequency changes to broadband noise excitation. Measurements are made of the dependence of the boundary frequency ω_b of the upper edge of the inertial range in which the Kolmogorov spectrum is formed on the wave amplitude η_p at the pumping frequency. It is demonstrated that the obtained data are well described by a function of the form ω_b∝η _p ^4/3 ω _p ^23/9 .     

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.     

The measurement of ultraweak liquid surface wave by laser interferometry

We describe a simple experiment on the interference of refraction light by ultraweak liquid surface wave at low frequency. The surface wave profile is generated by electrically driven vertical oscillations exciters. The high visibility and stable laser interference fringes were gathered experimentally. The theoretical light intensity distribution agrees well with the observations. In particular, we show the relation between the light intensity distribution and the characteristic features of the surface wave. In addition, we can measure the amplitude and wavelength of the ultraweak liquid surface wave at low frequency by this means.     

SEM imaging of liquid jets

We present a technique for the study of liquid jets in an environmental scanning electron microscope (ESEM). By using a two-fluid stream consisting of a water inner core and a co-flowing outer gas sheath, we are able to produce liquid streams of sufficiently low flow rate to be compatible with ESEM vacuum requirements. We have recorded ESEM images of water jets down to 700 nm diameter. Details of the jet structure, such as the point of jet breakup and size and shape of the jet cone, can be measured with ESEM to far greater accuracy than with optical microscopy. ESEM imaging of liquid jets offers a valuable research tool for the study of aerosol production, combustion processes, ink-jet generation, and many other attributes of micro- and nanojet systems.     

Finite-amplitude waves on the surface of a viscous deep liquid

For the first time a rigorous solution to the problem on time evolution of the periodic wave shape on the surface of a viscous infinitely deep liquid is found in the quadratic approximation with respect to the wave amplitude. It is found, in particular, that the damping rate of the quadratic component with respect to the wave amplitude is twice as high as the damping rate of the linear term. It is shown that inclusion of viscosity leads to asymmetry of the wave profile.     

Nonlinear internal resonance interaction between surface waves and internal waves in an inhomogeneous laminated liquid

Eight nonlinear resonances may arise in a two-layer liquid with a free surface, as follows from asymptotic calculations of the second order of smallness. Two of them involve waves generated by either surface, and six mixed resonances involve waves generated by different surfaces. Of these six resonances, two are degenerate and the remaining four are secondary combination resonances. However, not all of them are observed in practice. In the mixed combination resonances, interaction arises only between surface waves provided that the internal wave (which does not change its parameters but is necessary for the resonance to occur) has a catalytic influence.     

Temperature dependence of surface tension and capillary waves at liquid metal surfaces

The temperature dependence of the surface tension γ(T) is treated theoretically and experimentally. The theoretical model based on the Gibbs thermodynamics of a one-component fluid relates ∂γ/∂T to the surface excess entropy density −ΔS. All specific surface effects, namely ordering, capillary waves, and double layer influence the surface entropy, which in turn governs the sign and the magnitude of ∂γ/∂T. Experimental data collected at a free Hg surface in the temperature range from 0°C to 30°C show that ∂γ/∂T is negative. Zh. éksp. Teor. Fiz. 114, 2034–2042 (December 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

液面微幅波动的激光干涉测量

对于低频微幅的液面波动,提出了一种激光干涉测量方法.实验上观察到了清晰、稳定的激光干涉图样.干涉图样受到调制,光强在两边界位置达到极大,形成两个极亮条纹.干涉条纹被限制在两个极亮条纹之间的确定区域内.根据光干涉理论推导出了调制干涉条纹光强度、相邻条纹角宽度、干涉区域角宽度与液面波物理参量之间的解析关系,该理论分析与实验...     

Prediction of interface states in liquid surface waves with one-dimensional modulation

We theoretically study the interface states of liquid surface waves propagating over the heterojunctions formed by a bottom with one-dimensional periodic undulations. By considering the periodic structure as a homogeneous one, our systematic study shows that the signs of the effective depth and gravitational acceleration are opposite within the band gaps whether the structure is symmetric or not. Those effective parameters can be used to predict the interface states which could amplify the amplitudes of liquid surface waves. These phenomena provide new opportunities to control the localization of water-wave energy.     

Nonlinear degenerate resonance interaction of waves on a charged liquid surface

The physics of nonlinear degenerate resonance energy exchange between waves on the flat free charged surface of a conducting liquid is analytically (asymptotically) studied up to the second order of smallness. A set of differential equations for the evolution of the amplitudes of nonlinearly resonantly interacting waves is derived. It turns out that nonlinear computations (taking into account the dependence of the wave frequency on the finite amplitude) yield an infinite number of degenerate resonances, although computations based on frequencies found in the linear theory give a finite number of resonances. In nonlinear computations, the positions of the degenerate resonances depend on the surface charge density (or on the external electric field normal to the free surface of the liquid) in contrast to the results of linear computations (based on frequencies found in the linear theory). It is found that as the wavenumber of an exact degenerate resonance is approached (that is, in the vicinity of this number), the direction of energy transfer changes sign: now the energy is transferred from a shorter wave to a longer one and not the reverse.     

A study on generation of noise by high-speed pulsating jets

This paper describes the noise generation in an exhaust system of a reciprocating engine and focuses on the noise generated by shock/vortex interaction. The pulsating flow through the exhaust pipe consists of the compression and expansion wave, shock wave being generated by the non-linearity of the compression wave at its head. The jet noise is produced when the pulsating flow is discharged from the pipe end into atmosphere. The numerical simulation based on a finite difference method and experiment were made, the result of both of them being compared. First, the flow field in the pipe was obtained to easily discuss the characteristic of the pulsating jet in terms of the pressure history in the pipe. The jet structure was visualized by using schlieren and shadowgraph techniques. Sound pressure measurements at various locations were made in order to survey the directivity of the noise. The comparison between the result of numerical calculation and experiment showed a good agreement. A noise source related to shock/vortex interaction was confirmed by the numerical study clearly.     

The attenuation of rayleigh surface waves by surface roughness

This paper presents a calculation of the attenuation length of Rayleigh surface waves in the presence of surface roughness. We consider Rayleigh waves on the surface of a semi-infinite isotropic elastic continuum, and the method we use produces the contribution to the attenuation rate proportional to the square of the rms amplitude of the roughness. We obtain explicit expressions for the contribution to the attenuation rate from roughness-induced scattering into bulk transverse and longitudinal acoustic waves, and into Rayleigh waves. Our derivation makes use of a Green's function method. When the wavelength λ of the Rayleigh wave is long compared to the transverse correlation length a that characterizes the surface roughness, all contributions to the attenuation rate are proportional to the fifth power of the frequency. When λ is comparable to or smaller than a, the attenuation constant varies more slowly with frequency. For a model of the surface roughness, we present numerical calculations of the relative magnitude and frequency dependence of the various contributions to the attenuation rate. The Green's functions used here may be applied to a number of calculations. A derivation of their form is provided in an Appendix.