Experimental results are presented concerning the spontaneous oscillations observed when a high-viscosity fluid jet flows vertically against a flat surface. The two jet shapes investigated were the axisymmetric jet and the plane jet. The minimum distance from the jet orifice to the flat surface for which these oscillations are observed, termed the ‘buckling height’, was determined experimentally. The frequency of the subsequent oscillations was also determined. Both were measured as functions of fluid and flow variables. It is found that surface tension effects are the dominant factors influencing the buckling height, while the rate of oscillation is affected by both surface tension effects and by viscous, gravity and inertia effects. The major results are presented in non-dimensional form. Photographs of the buckling phenomenon are provided for representative jet geometries. It is also established experimentally that there is an upper limit to the flow Reynolds number above which buckling does not occur.

A theoretical model is developed for predicting the critical plate-orifice distances for viscous fluid buckling in plane and axisymmetric low-Reynolds-number bounded jets in stagnation flow. The theory is based on a hypothesis that treats the spatial growth of perturbation to the jet in a manner that distinguishes between the near-wall and far-field regions of the jet. This perturbation growth rate is shown to be the important parameter in the determination of the critical plate-orifice distances.This study also uses a one-dimensional model of the fluid column when it is displaced from equilibrium to determine the frequency at which buckling is first initiated in the case of the plane jet.

Simple solutions are presented for the equation governing one-dimensional flow of very viscous jets that issue from a round orifice and fall against a flat plate. Due to the viscous axial stresses developed, the jet may be either in tension or compression, depending on the values of various dimensionless parameters involved. The comparison of the theoretical and experimental results is good.

A jet of viscous fluid falling against a flat plate may become unstable and buckle. The buckling process is postulated as a discontinuity, and a simple model is developed that indicates a loss of energy in the fluid buckling. Experimental values of the energy loss coefficient are presented.

No abstract