Showing papers on "Ohnesorge number published in 1997"

The impact of a single drop on a wetted solid surface

Abstract: The impact of single drops on a thin liquid film was studied to understand the mechanism of secondary atomisation of sprays colliding on a wetted, cold, solid surface. To span a wide range of conditions various mixtures of water and glycerol were used. The use of Weber number, Ohnesorge number and non-dimensional film thickness to describe the peculiarities of the phenomenon allowed to carry out the experiments under appropriate similarity conditions. The impact of millimetric drops was analysed in detail by photographic means, using both still photography to study impact morphology, and laser sheet visualisation to investigate secondary droplet formation. Two mechanisms of splash were identified, depending essentially on the liquid viscosity (Ohnesorge number), a parameter which appears to play an important role also in defining the splash morphology. A photographic documentation is annexed. The characteristic times of the crown formation, the non-linear evolution of cusps (jet formation) and the surface roughness influence are further discussed. The experimental results allow to propose an empirical correlation for the splashing/deposition limit, for a wide range of conditions, and a comparison to available previous works is presented. The influence of the film thickness and liquid viscosity on the splash is confirmed and quantified.

Damped Oscillations of a Liquid/Gas Surface upon Step Reduction in Gravity

Abstract: The reorientation and settling of a liquid/gas interfacein a right circular cylinder upon step reduction in gravity is investigated numerically. A modie ed dynamic contact angle boundary condition is implemented where the hysteresis parameter ° is employed as an adjustable parameter representing the degree of relative slip at the contact line. The effect of the boundary condition on the axial interface oscillation is studied and the dependence thereon of the resonant frequency and settling time is given. Results are shown regarding the behavior of the dynamic contact angle and the penetration of the surface oscillations into the bulk liquid. The numerical results aretuned via comparisons with existing experimentaldata, and a method forestimating theappropriateboundary condition providing good agreement is suggested. An accompanying scale analysis depicts ° as a function of the Ohnesorge number, the cylinder radius, and the static contact angle. These independent parameters are measures of the system damping, characteristic surface dee ection, and effective stiffness of the interface. Applications of the results may be made to spacecraft e uids management and the use of spacecraft and/or drop towers for e uids experimentation.

Asymmetric Instability of a Viscous Liquid Jet

Abstract: The spatial instability of a viscid liquid jet issued into an inviscid surrounding gas medium is considered. The numerical solution of the governing equations is used to study the evolution of axisymmetrical and asymmetrical disturbances. It is found that asymmetrical disturbances may become dominant at high Weber number. Increasing gas to liquid density ratio and/or decreasing Ohnesorge number enhances the dominance of asymmetrical disturbances. A high gas to liquid density ratio is sufficient to sustain the prevalence of asymmetrical disturbances at moderate values of Weber number.