On 2D Liquid Sheet Atomization

Liquid sheet atomization by coflowing air flows appears in a broade range of industrial process, but still remains not well understood. This paper is devoted to the numerical investigation of the air-assisted disintegration of a planar liquid sheet by two parallel air streams flowing on both sides. To do that, a DNS solver for two-phase incompressible viscous flows with interface capturing feature for non miscible fluids has been developped and validated [1]. The interface is captured by a Level-Set method, which has become very popular during the last ten years. However, unlike classical approaches, stress tensor jump conditions across the interface are explicitly taken into account without introducing any smoothing. Although the physical phenomenon is tridimensional, experimental studies show that the initial stage of the liquid sheet oscillations is mainly two-dimensional which justifies the two dimensional simulations done in this paper. We present a first two-dimensional spatial simulation which shows the gas flow dynamics in interaction with the liquid sheet oscillations. By separation of the air boundary layer behind the liquid sheet at its maximum amplitude location, vortical structures are created and evolve in time with the frequency of the liquid sheet global oscillation. We investigate the effects of the main flow parameters such as outer air velocity, air boundary layer thickness on the main characteristics of the flow and the global oscillation frequency. The first result from our study concerning the frequency oscillation shows a linear variation of the frequency with air velocity. This is in complete agreement with experimental results of [2], whereas inviscid linear stability theory predicts a quadratic evolution. Evidence from those results shows that two-dimensional spatial simulations can provided relevant information on the early stage of liquid sheet atomization.