Stochastic sub-grid scale model for LES of secondary atomization - assessment and evaluation for ECN Spray-A conditions

Mikhael Gorokhovski,Surya Kaundinya Oruganti

doi:10.2218/iclass.2021.5962

Abstract

Stochastic sub-grid scale model for LES of secondary atomization - assessment and evaluation for ECN Spray-A conditions

Highlights

In order to ensure efficient fuel-air mixing on short time scales in diesel engines, the liquid fuel jet is atomized into very small droplets by injecting at relatively high velocities of the order of 300-500 m/s
The liquid spray tip “penetration length” is the most commonly used global parameter to characterize temporal evolution of spray. It is defined as the distance where the accumulated liquid droplet mass reaches 95% of the total liquid mass injected at any given instance of time
From the comparison of the penetration length evolution shown on left hand side of Figure 1, it can be seen that the model constant has no influence on the spray evolution

Summary

Introduction

In order to ensure efficient fuel-air mixing on short time scales in diesel engines, the liquid fuel jet is atomized into very small droplets by injecting at relatively high velocities of the order of 300-500 m/s. Since in Diesel-like conditions, the high speed injection generates strong turbulence, with highest frequencies of order of characteristic times in KH-RT instabilities, the conditions for droplets breakup become stochastic, and thereby the atomization can be viewed as a stochastic random process To this end, in [4] the child droplet size is generated from the numerical solution of the master equation for the size distribution function. It was shown that at large times under scaling symmetry at the constant fragmentation frequency, the fragmentation equation reduces exactly to the Fokker-Plank equation with two model parameters i.e., the first and second logarithmic moments of the fragmentation intensity spectrum Based on these principles [7,8] formulated a stochastic breakup model for LES modelling of sprays with the closures for the logarithmic moments expressed in terms of local flow field properties. In this paper, in the context of LES modelling of the gas phase, the stochastic log-normal process [10] is used to model the evolution of dissipation rate field along each droplet trajectory

Objectives

Methods

Results

Conclusion