Sub-grid effects in atomisation process using stochastic fields

Liquid atomization involves the interaction of a broad range of length and time scales, which make impractical the use of Detailed Numerical Simulation to resolve all scales. In the present work we use Large Eddy Simulations, where large scales are resolved directly and small scales require closure models. To model sub-grid liquid breakup, the paper use a novel framework, Σ-Y-PDF. The model solves the sub-grid joint probability density function of the liquid volume fraction and surface density. The probability density function allows an instantaneous statistical description of the two variables, and therefore provides sub-grid droplets (or fragments) distribution. The probability density function equation is solved using the Monte Carlo method of Eulerian stochastic fields. The method is used to investigate the influence of sub-grid liquid structures on spray dynamics in two academic configurations: 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 major spray characteristics: spray liquid penetration, liquid break-up point and droplet distribution. The sensitivity of the suggested framework to the number of stochastic fields and model parameter is also investigated.