Coupled Level set moment of fluid method for simulating multiphase flows

International audienceA coupled level set moment of fluid (CLSMOF) method for numerical simulation of multiphase flows is presented in this paper. This numerical method of liquid/gas interface capture is a hybrid of classical moment of fluid (MOF) method and coupled level set volume of fluid (CLSVOF) method. In this CLSMOF method, MOF interface reconstruction is used only for the under-resolved liquid structures while the level set function is used for the interface reconstruction for the resolved structures. This method combines the advantages of accurate capture of under-resolved liquid strucutres from MOF method and sharp interface representation by the level set function. The results presented in this paper demonstrates the ability and accuracy of the CLSMOF method to be as high as that of the MOF method while incurring relatively less computational expense. Finally, the application of CLSMOF method to simulation of turbulent diesel jet yeilded a very satisfactory volume conservation

A 3D Moment of Fluid method for simulating complex turbulent multiphase flows

International audienceThis paper presents the moment of fluid method as a liquid/gas interface reconstruction method coupled with a mass momentum conservative approach within the context of numerical simulations of incompressible two-phase flows. This method tracks both liquid volume fraction and phase centroid for reconstructing the interface. The interface reconstruction is performed in a volume (and mass) conservative manner and accuracy of orientation of interface is ensured by minimizing the centroid distance between original and reconstructed interface. With two-phase flows, moment of fluid method is able to reconstruct interface without needing phase volume data from neighboring cells. The performance of this method is analyzed through various transport and deformation tests, and through simple two-phase flows tests that encounter changes in the interface topologies. Exhaustive mesh convergence study for the reconstruction error has been performed through various transport and deformation tests involving simple two-phase flows. It is then applied to simulate atomization of turbulent liquid diesel jet injected into a quiescent environment. The volume conservation error for the moment of fluid method remains small for this complex turbulent case

A comparative study of DNS of airblast atomization using CLSMOF and CLSVOF methods

International audienceThe results from direct numerical simulations (DNS) of planar pre-filming airblast atomization are presented in this paper. The configuration of the airblast atomization is inspired from a published experimental configuration of Gepperth et al (2012, "Ligament and Droplet Characteristics in Prefilming Airblast Atomization", ICLASS 2012). The simulations have been performed using our in-house Navier-Stokes solver ARCHER. Two DNS have been performed each respectively using coupled level moment of fluid (CLSMOF) and coupled level set volume of fluid (CLSVOF) methods for liquid/gas interface reconstruction. The operating point investigated in the simulations correspond to aircraft altitude relight conditions. The DNS data are post-processed consistent to that of the experimental data to extract droplet and ligament statistics. The droplet diameter distribution from the simulations is found to be having satisfactory agreement with the experimental data. Two breakup mechanisms of atomization are observed: sheet breakup producing small droplets and ligament breakup producing medium and bulgy droplets. The CLSMOF method is observed to produce more medium and bulgy droplets owing to dominant ligament breakup while CLSVOF method produced more number of small droplets owing to predominant sheet breakup mechanism. A good agreement was found between simulations and experiments for Sauter Mean Diameter (SMD) of the droplets. The droplet diameter distribution from the simulations are found to under-predict the peak of the distribution but displays similar profile as that of the experiments. The droplet velocity distribution from the simulations is found to agree well with that of the experiments. The liquid ligaments formed at the trailing edge of the pre-filmer plate are characterized by their lengths. The breakup length of the ligaments, defined as arithmetic mean of the ligament lengths, computed from the simulations agree satisfactorily with the value computed from the experimental data

Detailed numerical simulations of primary atomization of airblasted liquid sheet

International audienceThis paper investigates the primary atomization of airblasted liquid sheet using detailed numerical simulations. The atomization of liquid sheet under airblasting conditions involve complex mechanisms and a thorough understanding is necessary. A planar pre-filming airblast atomization configuration have been chosen to study the breakup of liquid sheet/film injected on a solid flat plate. We have investigated an operating point directly relevant for high altitude relight condition of the aircraft. This configuration has been chosen based on the experimental investigation of Gepperth et al [S. Gepperth, A. Müller, R. Koch, H.-J. Bauer, Ligament and droplet characteristics in pre-filming airblast atomization, Proceedings of the ICLASS, 12th Triennial International Conference on Liquid Atomization and Spray Systems, September 2-6, Heidelberg, Germany, 2012] for the airblast atomization. The numerical simulations have been performed using in-house Navier-Stokes solver that uses consistent mass and momentum flux computation technique. The purpose of this work is to provide a comprehensive database and analyses of the airblast atomization of liquid sheet. This include studies on the effect of velocity profile on the atomization characteristics, occurrence of secondary atomization and drop coalescence, and extraction of near-field atomization characteristics. The qualitative analyses of the results from the simulations showed that there are two major atomization mechanisms of liquid film breakup -- sheet/bag breakup and ligament breakup. The drop diameter and velocity distributions computed from the simulations was found to be of the same order of magnitude although under-predicting the experimental data. Based on the atomized drop data, both the secondary atomization and drop coalescence have been observed to occur in the simulations. The quantitative analyses of the near-field liquid ligaments results revealed the lengths of these ligaments are of the same order of magnitude as the experimental data while an under-prediction in the ligament velocity has been observed. Finally, an excellent agreement between simulations and experimental data has been found for the Sauter Mean Diameter (SMD) of the atomized droplets

Interface reconstruction method for multiphase flows in under-resolved regions

International audienceThis paper presents an interface reconstruction method called moment of uid (MOF) method for two-phase ows using statistical moments of liquid volume fraction. In each ow solver grid cell, the liquid volume fraction and liquid center of mass are used for computing the interface unit normal. The transport of the liquid volume fraction and center of mass is performed by a directionally split advection scheme. This method is validated, results are compared with those from coupled level set volume of uid (CLSVOF) method for 2D and 3D test cases, and is found to be at least secondorder accurate in spatial resolution. Furthermore, MOF method is shown to outperform CLSVOF method in terms of interface reconstruction for thin and underresolved liquid ligaments and laments thereby conserving mass in the domain

A comparative study of DNS of airblast atomization using CLSMOF and CLSVOF methods

International audienceThe results from direct numerical simulations (DNS) of planar pre-filming airblast atomization are presented in this paper. The configuration of the airblast atomization is inspired from a published experimental configuration of Gepperth et al (2012, "Ligament and Droplet Characteristics in Prefilming Airblast Atomization", ICLASS 2012). The simulations have been performed using our in-house Navier-Stokes solver ARCHER. Two DNS have been performed each respectively using coupled level moment of fluid (CLSMOF) and coupled level set volume of fluid (CLSVOF) methods for liquid/gas interface reconstruction. The operating point investigated in the simulations correspond to aircraft altitude relight conditions. The DNS data are post-processed consistent to that of the experimental data to extract droplet and ligament statistics. The droplet diameter distribution from the simulations is found to be having satisfactory agreement with the experimental data. Two breakup mechanisms of atomization are observed: sheet breakup producing small droplets and ligament breakup producing medium and bulgy droplets. The CLSMOF method is observed to produce more medium and bulgy droplets owing to dominant ligament breakup while CLSVOF method produced more number of small droplets owing to predominant sheet breakup mechanism. A good agreement was found between simulations and experiments for Sauter Mean Diameter (SMD) of the droplets. The droplet diameter distribution from the simulations are found to under-predict the peak of the distribution but displays similar profile as that of the experiments. The droplet velocity distribution from the simulations is found to agree well with that of the experiments. The liquid ligaments formed at the trailing edge of the pre-filmer plate are characterized by their lengths. The breakup length of the ligaments, defined as arithmetic mean of the ligament lengths, computed from the simulations agree satisfactorily with the value computed from the experimental data

Coupled Level set moment of fluid method for simulating multiphase flows

International audienceA coupled level set moment of fluid (CLSMOF) method for numerical simulation of multiphase flows is presented in this paper. This numerical method of liquid/gas interface capture is a hybrid of classical moment of fluid (MOF) method and coupled level set volume of fluid (CLSVOF) method. In this CLSMOF method, MOF interface reconstruction is used only for the under-resolved liquid structures while the level set function is used for the interface reconstruction for the resolved structures. This method combines the advantages of accurate capture of under-resolved liquid strucutres from MOF method and sharp interface representation by the level set function. The results presented in this paper demonstrates the ability and accuracy of the CLSMOF method to be as high as that of the MOF method while incurring relatively less computational expense. Finally, the application of CLSMOF method to simulation of turbulent diesel jet yeilded a very satisfactory volume conservation