ID 391

Numerical simulation on the impact of advanced droplet collision models on an interacting spray

 

Abstract:

Spray systems have numerous industrial applications from combustion systems to food and pharmaceutical industries. Additionally, the fluid to be atomised ranges from low to high viscosity liquids as well as solutions or suspensions. However, the spray structure is greatly affected by droplet collisions and their outcome (bouncing, coalescence or separation) whose boundaries are summarised in so-called collisions maps. Such diagrams are obtained experimentally (Kuschel and Sommerfeld 2013, Sommerfeld and Kuschel 2016) and the boundaries between the different collision outcomes depend on the physical properties (viscosity, surface tension) of the involved liquid. Therefore, knowledge of the collision map is a requirement to perform reliable numerical computations of the spray behaviour by the Euler-Lagrange approach. Previously often, the numerical calculation of for example Diesel sprays was based on using boundary lines established for water (Post and Abraham 2002), which of course is not appropriate. Different correlations of the location of the triple point and the critical weber number in terms of the Ohnesorge number have been recently developed (Sommerfeld 2016; Sommefeld 2017; Sommerfeld and Lain 2017) that can be employed to build collision maps including the effect of physical properties such as viscosity.

The effect of the proposed collision maps and liquid physical properties on the produced droplet size spectrum is analysed in a configuration of two side by side mounted interacting sprays inspired by the nozzle employed in Rüger et al. (2000). Droplet collision modelling is performed on the basis of the stochastic droplet collision model (Sommerfeld 2001), also considering the influence of impact efficiency (Ho and Sommerfeld 2002), which so far was neglected for most spray simulations. As shown by Sommerfeld and Lain (2017) the consideration of the impact efficiency, where small droplet might move around larger ones with the relative velocity, will drastically reduce the collision rate in sprays.