Large eddy simulation of spray atomization with stochastic modeling of breakup

Abstract

A stochastic sub-grid model for the droplet breakup in Large Eddy Simulation (LES) is developed. An Eulerian description of the continuous phase is adopted and fully coupled with a Lagrangian definition of the dispersed phase. A stochastic model is incorporated into the equation describing the evolution of the spray pdf in order to simulate the atomisation of sprays in the framework of uncorrelated breakup events.The results of the simulations are compared with experimental data from a diesel injector and in spray in cross flows.

Large Eddy Simulation of the two-phase flow in an experimental swirl-stabilized burner

“…The breakup constant C b was adjusted in order to reproduce the effects of the internal characteristic pressure and flow perturbations of the injector. The value of C b used in the present case is 14% larger than the value ffiffiffiffiffiffiffiffiffiffiffiffi ð1=3Þ p which was been found to give good results (Jones and Lettieri, 2010) for the breakup of individual kerosene droplets in air. This adjustment was found necessary in order to reproduce the effects on breakup of liquid pressurization and flow perturbations introduced by the atomizer.…”

“…For the two-phase results, a study of the effects of the total number of particles on the droplet statistics is unpractical for this application, where typically over two millions particles are simulated. However, the two-phase methodology has been previously validated in a less computationally expensive test case (Jones and Lettieri, 2010), where results show relative insensitivity to particle number.…”

“…In the present work, because of the lack of data regarding the fuel composition, injector discharge pressure, density and size distribution at the discharging nozzle, a was determined from an initial estimate that was then refined empirically by trial and error until the correct a 0 was reproduced at the 6 mm downstream location. Mono-dispersed droplets of diameter corresponding to the nozzle size (200 lm) were injected following the same injection methodology used in Jones and Lettieri (2010) and schematically represented in Fig. 17b.…”

A stochastic breakup model for Large Eddy Simulation of a turbulent two-phase reactive flow

“…Further details are given in [11]. In the following section, an improved version of the previously formulated breakup model [1] is described.…”

“…This atomization process plays a crucial role in determining the global performance of two-phase combusting flows in terms of the rate of fuel consumption and pollutant emissions. In the present work, a probabilistic model for the atomization of sprays [1] is adopted in combination with an LES of the gas phase and further developed to simulate the methanol spray flame, studied experimentally by [2,3]. The model for breakup consists of a stochastic formulation which reproduces the effects of the sub-grid scale (sgs) motions on droplet breakup with each breakup event being defined in a statistical manner through a Poisson release process.…”