Amplitudes of three-dimensional waves in a nonisothermal falling liquid film

The amplitudes of three-dimensional (3D) waves in a water film flowing down a vertical plate with a local heater have been measured. Thermocapillary forces that arise on heating lead to the formation of rivulets separated by thin-layer troughs, with 3D waves propagating over the crests of rivulets. The film thickness and 3D wave amplitudes on the heater grow with increasing heat flux density and distance downstream the flow, but the relative wave amplitude remains unchanged. In the heated regions between rivulets, the relative amplitude of waves increases with decreasing average thickness (or local Reynolds number). Analysis of results obtained for large Reynolds numbers showed that the relative amplitudes of waves in the regions between rivulets at high heat flux densities are much greater than those for small Reynolds numbers in isothermal falling films.     

Effect of thermocapillary perturbations on the wave motion in heated falling liquid film

The transformation of hydrodynamic perturbations into thermocapillary-wave structures in a locally heated water film flowing down a vertical plate has been experimentally studied using a high-speed IR imager for monitoring the temperature field and a fluorescent technique for determining the liquid film thickness. It is established that a three-dimensional (3D) front of the hydrodynamic wave acquires inhomogeneous temperature profile, which leads to a deformation of the liquid film under the action of thermocapillary forces and results in the formation of rivulets. Distances between the 3D waves and rivulets are determined as functions of the heatflux density. The experimental data are compared to the theoretical results.     

Controlling interaction of hydrodynamic waves with thermocapillary instability in falling liquid film

The interaction of hydrodynamic-wave and thermocapillary perturbations in a locally heated water film flowing down a vertical plate has been experimentally studied using a high-speed IR imager. It is established that, in the presence of fairly high heat fluxes, artificial disturbances can significantly influence the formation of wave structures and the wave flow in the liquid film. Depending on the parameters of waves passing the heater, various scenarios of their transformation into rivulets are possible.     

The wave characteristics of a nonisothermal film of liquid under conditions of jets forming on its surface

An eight-channel capacitive sensor is used for the first time, which enables one to investigate the dynamics of three-dimensional wave flows and the variation of the transverse profile of a nonisothermal film of liquid during formation of jets. Measurements are performed of the wave characteristics of the flow of a film of water on a vertical plate with a heater 150 × 150 mm in size. During the heating of falling liquid, the thermocapillary forces cause the formation of jets and of a thin film between them. The film thickness and wave amplitude in the interjet region decrease with increasing heat flux. Two ranges of the effect of the heat flux on the characteristics of wave flow are identified. Under conditions of low heat fluxes, the film flow hardly differs from isothermal. Under significant heat loads, an intensive formation of jets occurs. Three-dimensional waves propagate over the jet crests, where the film thickness and wave amplitude increase with increasing heat flux. In the interjet region of the film being heated, the average relative amplitude of waves increases with decreasing average thickness, and in the isothermal region this amplitude decreases. Comparison of the obtained results with experimental data for isothermal film reveals that the values of relative amplitude differ significantly in the interjet region at high densities of heat fluxes. Transverse temperature gradients cause a decrease in the liquid film thickness, and longitudinal gradients cause an increase in the relative amplitude of waves compared to isothermal flows. In the end, this leads to the emergence of dry spots and breakdown of film. The relative amplitude of waves on the jet surface decreases with increasing heat flux; this is true of isothermal film flows.     

Evolution of the temperature field at the three-dimensional wave front in a heated liquid film

An experimental study of the transformation of three-dimensional waves into thermocapillarywave structures in the flow of water film on a vertical plate with a heater was carried out using the fluorescent thickness measurement technique and a high-speed infrared recording technique in order to measure the temperature field on the liquid film surface. It was shown that the temperature disturbances occur in the residual layer of the wave film. Then, as the film flows along the heater, temperature inhomogeneities appear transverse to the flow at the three-dimensional wave front; and these inhomogeneities cause deformation of the liquid film and formation of rivulet due to the action of thermocapillary forces.     

Specific features of three-dimensional wave regimes development in a vertically falling liquid film

This Letter presents the results of an experimental study of the wave regimes of the liquid film flow over the vertical plate within a range of moderate Reynolds numbers using liquids with different physical properties. The analysis of statistical characteristics of wave fields has made it possible to elaborate the classification of three-dimensional wave regimes in a range of liquid flow rates under study. Steady-state threedimensional wave regimes are shown to occur at Reynolds numbers that are significantly higher than the Reynolds number of a transition from a two-dimensional to three-dimensional wave flow.     

Thermocapillary effects in nonisothermal liquid film at high Reynolds numbers

The temperature and wave characteristics of the water film flowing down a vertical plate with a heater at Re = 300 are studied. The field of film thicknesses at different heat flux values was measured using the fluorescence method. The temperature field on the film surface was measured by an infrared scanner. The experimental data were obtained for variations in temperature over the liquid film surface with time during the propagation of waves. When the falling liquid is heated, the thermocapillary forces lead to formation of rivulets and a thin film between them. Averaging of measurements allowed the value of the transverse film deformation to be determined. Two mechanisms of influence of thermocapillary forces on the motion of the wavy liquid film are marked. For the first time, the exhibition of such a strong thermocapillary effects is revealed in the heated liquid film at high Reynolds numbers.     

The effect of mutual location of heaters on the falling film dynamics

Thin nonisothermal liquid film flowing down under action of gravity is considered. Investigation of the influence of the spanwise and streamwise arrangement of the rectangular heaters on 3-D structures, occurring at the film surface, is the main objective of the present work. Three-dimensional time-dependant mathematical model for calculation of gas-liquid interface deformations and evolution of temperature fields was developed. Our numerical investigations have shown that interaction, imposition and mutual influence of the 3D structures (bumps, lateral waves ...) takes place. In the case of streamwise arrangement of the heaters film rupture is most likely on the second heater. There is a critical backlash between the heaters, at which film deformations, including film thinning, are the largest. For the spanwise arrangement of the heaters distance between them practically do not effect on the minimum film thickness, but mutual imposition of the lateral waves and film thickening exists.     

Reconstruction of Charged Hydrogen Surface

The evolution of shape of the surface of equipotentially charged liquid hydrogen film condensed on lower or upper plate of a horizontally placed diode in external electric fields has been studied experimentally under the conditions of total compensation of the applied field by the surface charge. Reconstruction phenomenon — the formation of a solitary wave (soliton) — has been observed in an electric field higher than some critical value for the film covering the lower plate.     

String wave spraying of liquid

It is established that an impact-excited string partly immersed into a liquid at an angle to its surface produces wave transport and spraying of the liquid. The liquid is sprayed from some regions on the string excited at definite frequencies. A law governing the conditions of liquid spraying is found and explained in terms of the phase difference between transverse and longitudinal waves in various regions of the oscillating string.     

Rivulet dynamics at isothermal film flow

Averaged fields of thickness of an isothermal vertically flowing liquid film, obtained by the laserinduced fluorescence method, have been analyzed. The chosen minimum averaging time interval, at which the wave motion is completely averaged, allows one to observe rivulet dynamics in a transverse direction. It is found that short-lived rivulets, which are chains of no less than five to eight waves with similar transverse coordinates, are dominant structures on the film surface at Reynolds number Re > 50.     

Experimental study of the evolution of solitary three-dimensional waves on the surface of a heated liquid film

Results of an experimental investigation of the features of evolution of a solitary three-dimensional (3D) wave on the surface of a vertically falling liquid film heated by a constant heat flux are presented. It is established that the wave weakly influences the film surface temperature. The interaction of a 3D wave with thermocapillary rivulet structures on the falling film surface results in that the wave is pulled toward the center of a rivulet.     

Transformation of acoustic waves in periodic metal grating sandwiched between piezoelectric and dielectric

The mechanism of SAW transformation with variation of film thickness is investigated in a piezoelectric substrate with a metal grating overlaid by a dielectric film, via simulation and visualization of the acoustic fields. By way of example, two orientations of lithium niobate substrates are analyzed, YX-LN and 128°YX-LN, with a Cu grating and an isotropic silica glass overlay. The motions, which follow the wave propagation in the sagittal plane, are visualized within two periods of the grating, with added contour plots showing the shear horizontal displacements. The continuous transformation of the wave's nature is investigated for each wave propagating in the analyzed material structures when the film thickness is increased from zero to a few wavelengths. The examples of the SAW transformation into boundary waves and into plate modes of different polarization have been found and investigated. The behavior of the SAW characteristics in the grating is correlated with transformation of the wave structure with increasing overlay thickness.     

On the propagation of Lamb waves in viscothermoelastic plates under fluid loadings

In this paper the propagation of plane and circular crested viscothermoelastic waves in a homogeneous isotropic, Kelvin-Voigt type viscoelastic thermally conducting, plate sandwiched between inviscid liquid layers is investigated in the context of classical and non-classical theories of thermoelasticity. The secular equations for the symmetric and skew-symmetric modes of plane and circular crested waves are derived in closed form and isolated mathematical conditions. It is noticed that the motion for both the plane and cylindrical waves in plates is governed by Rayleigh-Lamb-type secular equations. The secular equations for thin plate and short wave length waves are also obtained and discussed. The results in the absence of fluid loading, coupled and uncoupled theories of thermoelasticity have been obtained as particular cases from the derived secular equations. The dispersion curves, attenuation profiles and specific loss in case of symmetric and skew-symmetric wave modes are also presented graphically for a polymethyl methacrylate material plate under fluid loadings. The effect of dissipation due to viscosity is noticed to be quite significant and clearly visible from various curves in the graphs.     

Decay of large waves naturally forming in a heated liquid film

The mechanism of transformation of developed naturally formed large waves into thermocapillary wave structures on a vertical downflow of heated water film is experimentally studied. It is shown that the combination of thermocapillary and inertial effects in a wavy liquid film leads to deformation of large waves and their decay into narrower waves.     

Effect of artificial perturbations on the formation of structures in a nonisothermal liquid film

The effect of artificial perturbations on the formation of structures in a nonisothermal liquid film flowing down a vertical plate with a 150 × 150 mm heater has been experimentally studied. The action of heat flux on the wave flow leads to the formation of periodic flowing rivulets separated by thin film regions. Artificial perturbations in a certain interval of wavelengths produce a change in the number of rivulets formed on the heater surface. The “most dangerous” wavelength of artificial perturbations altering the flow structure is determined.     

Effects of a liquid layer on thickness-shear vibrations of rectangular AT-cut quartz plates

Thickness-shear vibrations of rectangular AT-cut quartz with one face in contact with a layer of Newtonian (linearly viscous and compressible) fluid are studied. The two-dimensional (2D) governing equations for vibrations of piezoelectric crystal plates given previously are used in the present study. The solutions for 1D shear wave and compressional wave in a liquid layer are obtained, and the stresses at the bottom of the liquid layer are used as approximations to the stresses exerted on the crystal surface in the plate equations. Closed form solutions are obtained for both free and piezoelectrically forced thickness-shear vibrations of a finite, rectangular AT-cut quartz plate in contact with a liquid layer of finite thickness. From the present solutions, a simple and explicit formula is deduced for the resonance frequency of the fundamental thickness-shear mode, which includes the effects of both shear and compressional waves in the liquid layer and the effect of the thickness-to-length ratio of the crystal plate. The formula reduces to the widely used frequency equation obtained by many previous investigators for infinite plates. The resonance frequency of a rectangular AT-cut quartz, computed as a function of the thickness of the adjacent liquid layer, agrees closely with the experimental data measured by Schneider and Martin (Anal. Chem., vol. 67, pp. 3324-3335, 1995)     

直立堤上任意方向入射波的波压力研究

为了研究在不同入射波向时直立堤上的波压力,基于FLOW-3D,该文建立了三维数值波浪水池,并进行了物理模型试验。模型采用推板造波及孔隙消波的方法形成稳定的波浪场,数值模拟结果与试验结果吻合较好。研究表明:墙面测点的波压力与波吸力均随入射角度的增大而增大;墙底各测点浮托力的变化规律较为复杂,合田公式不能准确描述;墙面波压力的分布与合田公式基本相符;墙底浮托力的分布并不是合田公式描述的三角形,而是近似梯形分布;斜向波作用下的墙面波吸力分布图相似于正向入射时的分布。研究结论可为防波堤设计提供参考依据。     

Experimental study of the wave flow of a liquid film on a heated surface

The wave flow of a water film over the surface of a vertical plate with a 150×150-mm heater has been experimentally studied. The action of heat flux on the wave flow of the liquid film is manifested by the formation of periodic flowing rivulets separated by thin film regions. The thickness of the film between rivulets was measured using a fiber optical reflection probe. As the heat flux grows, the average film thickness h continuously decreases. However, when the thickness reaches h≈0.5 h₀, where h₀ is the value given by the Nusselt formula for a laminar liquid film, the film exhibits spontaneous rupture. It was found that, as the local flow rate decreases, the wave amplitude in the region between rivulets drops more rapidly than expected according to the laws of “cold hydrodynamics.”     

Development of artificial perturbations in a nonisothermal liquid film

The effect of artificial perturbations on the formation of structures in a water film flowing over a vertical plate with a heater has been experimentally investigated. Attention has been focused on the study of the propagation of nonstationary perturbations in time immediately after their creation on the surface of the liquid film. The fluorescence method has been used to measure the film thickness field. The temperature field on the film surface has been measured by a high-speed infrared scanner. It has been shown that the passage of the wave front after the action of a perturbation system with the “most dangerous” distance between the cylinders leads to a change in the distance between the rivulets. It has been found that the intensity of introduced perturbations (cylinder diameters) and the characteristics of waves flowing to the heater significantly affect the change in the distance between the rivulets. An increase in the amplitude of the waves at the front of propagating perturbation has been detected. The coalescence of the rivulets in the lower part of the heater has been observed. It has been shown that the passage of several wave fronts is necessary for the complete rearrangement of the flow even when the intensity of perturbations is high.