ID 279

Sub-grid effects in atomisation process using Stochastic Fields

 

Abstract:

The atomisation process involves a broad range of length and time scales, which make impractical from computation point of view the use of Detail Numerical Simulation to describe atomisation phenomena at all scales. In this work we use Large Eddy Simulations, where the large scales are resolved but the small scales require closure. For the small scales, we introduce a novel approach, namely the Σ-Y-PDF, which is an extension of the well-known Eulerian-Lagrangian Spray Atomization approach. The model solves the sub-grid (SGS) joint probability density function of the liquid volume fraction and the surface density, allowing an instantaneous statistical description of the two variables and therefore provides sub-grid droplets (or fragments) distribution. This is an improvement over previous attempts that describe atomisation based only on the filtered values. The SGS PDF is solved using the computationally efficient Monte Carlo method of stochastic fields. The present work investigates the influence of the sub-grid liquid structures on the whole spray dynamics. Two different popular configurations are studied: a liquid flow in a cross jet (prototype of a gas-turbine injector) and a liquid turbulent jet (akin to a diesel injector). The same approach is used in both configurations to investigate the influence of small scales in the spray break-up mechanism. The liquid penetration, the break-up point and droplet distribution are extracted are analysed. The sensitivity of the suggested framework to the number of stochastic fields and turbulence model is also investigated.