Validation and Analysis of 3D DNS of planar pre-filming airblast atomization simulations

Abstract : In this paper, results from direct numerical simulations (DNS) of published experimental configuration of planar pre-filming airblast atomization are presented. The simulations have been performed using our in-house multiphase Navier-Stokes equations solver ARCHER. The coupled level set volume of fluid (CLSVOF) method has been used for capturing the liquid/gas interface within the context of multiphase flows. This numerical method has been proved to well capture the interface from many of our previous works. A kerosene based fuel at an operating point corresponding to aircraft altitude relight conditions have been used in DNS. The results are analyzed in two parts: analysis of liquid droplets and analysis of liquid ligaments at the trailing edge of the pre-filmer plate. The analyses of the liquid droplets diameter and velocity distributions revealed that the results from the simulations are agreeing with the experimental data very satisfactorily. Moreover, the observation from these distributions is that the sheet breakup mechanism is dominant over the ligament breakup mechanism of atomization. Ligament analysis has been carried out by reducing the 3D DNS data to 1D liquid/gas interface contour. The frequency distribution of the liquid ligaments shows the under-prediction on their lengths in comparison to experiments. Overall, a satisfactory agreement has been achieved between the DNS and experiments. Introduction Pre-filming planar airblast atomization involves destabilization of liquid sheet by a high speed coflow-ing gas stream. Such a type of atomization process is commonly employed in aircraft engines. Quite often , the velocity of the gas stream is about one order of magnitude larger than that of the liquid fuel. With the idea of airblast atomization first introduced by Lefebvre and Miller [1], there has been multiple experimental investigations [2, 3, 4] to understand the physical processes of atomization occurring in the atomizing edge. Most of these experimental analyses focused on the far downstream properties such as droplet diameter and velocity distribution analysis. But the characteristics of atom-ization near the pre-filmer plate have not been extracted from experiments. The work of Bilger and Stewart Cant [5] focused on the airblast atomiza-tion and regime classification for different gas and liquid phase velocities. This work used laminar velocity profile for the phases thus might not necessarily represent the real time fuel injection scenarios. In the past years, multiple works on airblast atom-ization using numerical simulations are performed, such as, Fuster et al. [6] studied the primary break up of planar coflowing sheets of water and air at dynamic pressure ratios of 0.5 to 32; Chiodi et al [7] studied the cylindrical and planar airblast atomiza-tion using semi-Lagrangian geometric VOF method and accurate conservative level set (ACLS) method and showed the cascade of instabilities from Kelvin-Helhmholtz to Rayleigh-Taylor to Rayleigh-Plateau in the breakup mechanism; and Agbaglah et al [8] studied the destabilization of the air/water planar liquid sheet and found excellent agreement between experiments and simulations for liquid cone length, spatial growth of primary instability, and maximum wave frequency. A recent work by Braun et al [9] used meshless smoothed particle hydrodynamics (SPH) for numerically predicting the air-assisted at-omization and compared their results with that from the work of Gepperth et al [10]. Recently, the works of Gepperth et al [10] and Warncke et al [11] on planar pre-filming airblast at-omization extracted experimentally and numerically the information close to the plate such as ligament lengths and deformation velocity. Although a good agreement between experiments and simulations had been observed in the work of Warncke et al [11], the results displayed the limitation of the diffused interface capturing methods used in their simulations. Thus, to this end, in our work we have used direct numerical simulations (DNS) approach to simulate the planar pre-filming airblast atomization for same
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Anirudh Asuri Mukundan, Thibaut Ménard, A. Berlemont, Jorge César Brändle de Motta, Ruud Eggels. Validation and Analysis of 3D DNS of planar pre-filming airblast atomization simulations. In Proceedings of ILASS Americas, 30th Annual Conference on Liquid Atomization and Spray Systems. May 12th-15th, Tempe, Arizona, USA, May 2019, Tempe, United States. ⟨hal-02178046⟩

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