Direct Computation of an Annular Liquid Jet

Abstract

An Eulerian approach with mixed-fluid treatment has been used to study the flow field of an annular liquid jet in a compressible gas medium. A mathematical formulation is developed which is capable of representing the two-phase flow system with the gas phase treated as compressible and liquid as incompressible, where the volume of fluid method has been adapted to take into account the gas compressibility. The mathematical formulation is then applied to the computational analysis of an annular liquid jet, in order to achieve a better understanding on the flow physics by providing detailed information on the flow field. The gas-liquid two-phase flow system has been examined by direct solution of the governing equations using highly accurate numerical schemes. The numerical simulation shows that the dispersion of the annular liquid jet is characterised by a recirculation zone adjacent to the nozzle exit. Without applying perturbation at the domain inlet, vortical structures develop at the downstream locations of the flow field due to the Kelvin-Helmholtz instability. The flow becomes more energetic at progressive downstream locations with the dominating frequencies becoming smaller.

Direct numerical simulation of the near-field dynamics of annular gas-liquid two-phase jets

“…Klein 26 performed DNS of a liquid sheet exhausting into a gaseous incompressible atmosphere under moderate Reynolds number. Direct computations of two-phase gas-liquid flows have been performed in axisymmetric and planar configurations [27][28][29] and good agreement with linear theories has been obtained. An extended study in full three dimensions is needed for detailed realization of the mixing.…”

“…In this study, the original VOF method has been adapted to solve an equation for the liquid mass fraction Y rather than the volume fraction ⌽ in order to suit the compressible gas phase formulation. [27][28][29] From their definitions, a relation between liquid volume fraction and liquid mass fraction can be derived as…”

“…The 3D parallel DNS code used was developed from the 3D parallel DNS code for gas jets 48,49 based on the gas-liquid two-phase flow formulation used in the axisymmetric and planar simulations. [27][28][29] The excessive computational cost needed to perform the complex two-phase DNS ͑around 300 000 allocation units on HPCx per simulation͒ limits the computation to regions close to the jet nozzle exit. The results are discussed in terms of the instantaneous and time-and spatialaveraged flow properties.…”

“…2, it is evident that the dispersion of the liquid is dominated by large-scale vortical structures formed at the jet primary stream due to the Kelvin-Helmholtz-type shear layer instability. The presence of streamwise vorticity, which is absent in idealized axisymmetric and planar configurations, [27][28][29] is generated by 3D vortex stretching and interaction. The flow vorticity dominates the dispersion of the liquid as indicated by the similar structures of the enstrophy and liquid volume fraction.…”

Application of gentle annular gas veil for electrospinning of polymer solutions and melts

“…An annular jet has significantly different flow characteristics. The presence of an inner wall induces the occurrence of a specific recirculation zone close to the die orifice [28]. The dominant characteristic of this zone is the occurrence of an area where the flow is traveling in the opposite direction relative to the jet [29].…”