Plane Liquid Jet Research Articles

Flow analysis of plane liquid jet with a controlled shear layer using temporal numerical simulation by diffuse interface model

Flow analysis of plane liquid jet with a controlled shear layer using temporal numerical simulation by diffuse interface model

Erosion threshold of a liquid immersed granular bed by an impinging plane liquid jet

Erosion threshold of a model granular bed by a jet in a quasi bidimensional configuration has been studied experimentally in both laminar and turbulent regimes. The jet is a liquid sheet which impinges normally a packing of immersed beads monodisperse in size and density. The erosion threshold has been characterized at different impact distances of the jet on the sediment and for different grain size and fluid viscosity. In the explored range of parameters, we show that the erosion threshold is well described by a critical inertial Shields number based on the local flow velocity at the impinging point. This has been done by a careful analysis of the different jet flow regimes taking into account the position of the virtual origin of the jet.

Simultaneous Measurements of Velocity and Reactive Scalar in Plane Liquid Jet with the Second-Order Chemical Reaction

In this study, the liquid plane jet with the second-order chemical reaction (A×B→R) is investigated experimentally. The reactants are 1-naphthol (A) and diazotized sulfanilic acid (B), and the product is 4-(4'-sulphophenylazo)-1-naphthol (R), briefly monoazo dyestuff. The main flow contains the species B and the water solution of species A is issued into the main stream by the plane jet. The blue dyestuff (C: Acid Blue 9) is also added into the jet flow and the concentration of species C can be treated as the conserved scalar (which is independent of the above chemical reaction). The concentrations of species C and the product species R are measured simultaneously by the optical fiber probe based on the light absorption spectrometric method, and the concentrations of species A and B are obtained from the conserved scalar theory. The streamwise velocity is measured by the I-type hot-film anemometer. We attempt to measure the concentrations of reactive species and the streamwise velocity simultaneously by the new combined probe which consists of the optical fiber probe and the I-type hot-film probe. First, it is examined whether it is possible to use the combined probe for simultaneous measurement. And then, the concentrations of the reactive species and the streamwise velocity in the plane jet are measured by the combined probe. It is found that the mass flux of reactant species involved in the jet flow (<uγA>) becomes larger and the mass flux of reactant species involved in the main flow (<uγB>) becomes smaller than nonreactive case due to the chemical reaction near the jet exit, while the influence of the chemical reaction on these mass fluxes in the downstream and outer regions is opposite to the influence near the jet exit. The results also show that the mass flux of product species (<uγR>) has negative value near the jet exit and positive value in the other region.

Numerical analysis of flow-induced gas entrainment in roll coating

Gas entrainment by plane liquid jets which plunge into a liquid pool is analyzed by numerical simulations. The numerical model is based on the equations of incompressible newtonian fluids flow. The two-phase flow problem is described with the volume-of-fluid method. The dynamic behaviour of the interface is characterized by two similarity parameters, the capillary number Ca = uη/ σ and the property number Γ = σ( ρ/ η 4 g) 1/3 where u is the velocity, η the dynamic viscosity, σ the interface tension, ρ the density and g the gravitational constant. Numerical simulations are performed with the open source CFD code OpenFOAM. In the simulations the stability of the gas–liquid meniscus is tested for different sets of Ca and Γ. Critical values of Ca which indicate the beginning gas entrainment are deduced from the inspection of the simulation results. The findings of the numerical investigations agree well with corresponding experimental results.

Two-dimensional and axisymmetric viscous flow in apertures

The flow in a plane liquid jet from an aperture is obtained by direct simulation of the Navier–Stokes equations. The gas–liquid interface is tracked using the level set method. Flows are calculated for different Reynolds and Weber numbers. When We = ∞, the maximum value of the discharge coefficient appears around Re = O(100). The regions that are vulnerable to cavitation owing to the total stress are identified from calculations based on Navier–Stokes equations and viscous potential flow; the two calculations yield similar results for high Reynolds numbers. We prove that the classical potential flow solution does not give rise to a normal component of the rate of strain at the free streamline. Therefore, the normal component of the irrotational viscous stresses also vanishes and cannot change the shape of the free surface. The results of calculations of flows governed by the Navier–Stokes equations are close to those for viscous potential flow outside the vorticity layers at solid boundaries. The Navier–Stokes solutions for the axisymmetric aperture are also given for two values of Reynolds numbers. The results for axisymmetric and planar apertures are qualitatively similar, but the axisymmetric apertures have a lower discharge coefficient and less contraction.

Absolute and convective instability of a relaxational plane liquid jet

The stability of a plane relaxational liquid jet has been studied theoretically and experimentally through linear stability analysis and flow visualizations. The relaxational liquid jet is obtained by the outflow of a liquid from a plane channel with an upstream fully developed Poiseuille flow into an ambient stagnant gas. Linear spatial stability calculations show that there are five convectively unstable modes, three sinuous and two dilatational. The spatial stability calculations are compared to experimental results for wavenumber variation and the growth of waves found in the visualizations. These variations have been quantified with a wavelet transform and through a comparison with the spatial stability results the type of mode observed in the visualizations has been determined. For this type of mode the calculated wavenumber variation is in good agreement with the experimental results. Also, in the experiments the breakup of the jet has been observed when the Reynolds number reaches a certain value, and as the Reynolds number increases this breakup moves closer to the channel exit. This upstream movement of the breakup can be explained by the linear stability results. Finally the relaxational liquid jet is shown to be absolutely unstable for a certain parameter region. Close to the nozzle both a sinuous mode and a dilatational mode are shown to be absolutely unstable. As the jet profile relaxes to uniform, the sinuous mode is shown to be the only unstable mode. This occurs for Weber numbers , which is in agreement with the theory for liquid jets with uniform velocity profile. The frequency selection for the observed waves is believed to be related to the region of absolute instability located closest to the channel exit.

Energy growth of initial perturbations in two-dimensional gravitational jets

The potential for transient growth of small perturbations to plane liquid jets falling under gravity in a still gas atmosphere is studied extending concepts thus far exclusively applied to one phase shear flows. The relevant initial value problem in time is formulated keeping into account the effect of the liquid viscosity, besides those of surface tension and gravity. The numerical counterpart of the differential operator, obtained by means of a spectral discretization, is examined focusing attention on both eigenvalues and pseudospectra with the aim of highlighting its non-normal character. The trend of an opportunely defined energy of perturbations is computed as a function of time in different flow regimes. The far field behavior is always recovered according to the classical temporal modes analysis, whereas non-normality is shown to amplify perturbations energy over short time scales even in situations where the spectrum is entirely confined to the stable half-plane.

Impingement of an inviscid plane liquid jet on a porous wall: a fixed domain method

Impingement of an inviscid plane liquid jet on a porous wall: a fixed domain method

Experimental and theoretical stability investigations of plane liquid jets

The present investigation has been undertaken in order to better understand the development of free, plane liquid jets. Both the development of the basic laminar flow as well as its stability have been investigated theoretically and experimentally. The velocity field and free surface location of a liquid jet emanating from a plane channel was calculated numerically and the velocity and surface relaxation lengths were determined. Calculated velocity profile distributions were in good agreement with Pitot tube measurements. Temporal linear stability calculations were performed using the calculated velocity distributions. The calculations showed five unstable modes, three sinuous and two dilatational. Four of these modes have been reported earlier and one of the sinuous modes is considered to be ‘new’. The linear stability calculations include surface tension as well as viscosity in the liquid and gas. Hot wire anemometry measurements of controlled forced disturbances showed that waves in the experimental jet also were sinuous and that the amplitude distribution was in fair agreement with theoretical results. Shadowgraph visualisations showed the evolution of the waves on the surface of the jet and it was found that the waves break up downstream the nozzle. This break-up was visualized by particle visualisations, which showed that it creates strong streamwise streaks in the jet.

Air entrainment upon liquid impact

The impact of round and plane liquid jets on plane liquid surfaces is simulated numerically on the basis of a potential flow model. It is found that the mass of the jet is as important as its momentum in determining the flow. For sufficiently long jets and small Froude numbers air cavities are entrained. Entrainment is more unlikely in two dimensions than in three.

Experimetnal observation of fine interfacial waves on a plane liquid jet.

A fine striped interfacial wave pattern was observed on the thin liquid sheet jet in a cocurrent gas stream. The experiment revealed that this wave pattern affected the disintegration of a liquid sheet. In order to clarify the significant factor of the liquid jet wave motion, the fine interfacial waves on a plane liquid jet in a stationary atmosphere were also investigated experimentally. The interfacial waves were classified into the following five patterns: smooth, two-dimensional wave, modified two-dimensional wave, pebble wave and sandpaperlike wave. The fundamental mechanism of the fine interfacial wave was investigated by developing an optical measuring device.

Instability analysis of a plane liquid jet in a stationary gas.

The instability of a thin liquid jet in a stationary atmosphere was analyzed by solving numerically the Orr-Sommerfeld equation for both sinuous disturbances and dilational disturbances. It was found that the thin liquid jet had hard mode and soft mode instability for both disturbances. Comparing theoretical results with experimental results, we discuss the possibility of the occurrence of the interfacial disturbances wave on the plane liquid jet. It could be suggested that the interfacial disturbance wave was mainly caused by the internal instability in the liquid jet flow and that the disturbance wave corresponded to the hard mode instability for the sinuous disturbance.