Modeling Turbulent Multiphase Flows

simulation of flow breakup

 

Aerosol sprays are a major area of study because of the many industrial, agricultural, and pharmaceutical (among others) applications of such work. The research group of Sean Garrick (Mechanical Engineering; MSI Fellow) in the Computational Transport Phenomena Laboratory has a long history in the direct numerical simulation and large eddy simulation of turbulent, reacting, multiphase flows. The researchers develop physical models (and their mathematical representations) and software in-house that can be used to numerically simulate a wide-variety of physical and chemical problems.

 

Wanjiao Liu, a graduate student in the Garrick group, presented a poster at the MSI 2012 Research Exhibition describing her work in advanced modeling of turbulent sprays. She is studying the size distributions and breakup patterns of droplets in a spray, as these characteristics determine the spray’s performance, efficiency, or safety. Studying these droplets is challenging and the characteristics of sprays and droplets are not completely understood. Ms. Liu’s poster was one of the finalists in the poster competition.

 

Using various numerical modeling techniques, Ms. Liu is investigating the best way to simulate atomization and spray behavior. The Garrick group runs the highly parallel computer codes necessary for these models on Itasca.

 

The image shows two views of a turbulent multiphase flow simulation. A liquid column is injected from the left of the domain into gas and starts to break up. The colored contour at the top shows volume of fluid (VOF). VOF equaling 1 means the local space is occupied by liquid, while VOF equaling 0 means the local space is occupied by gas. The black-and-white image at the bottom shows the magnitude of surface tension force for the same flow. In this image, darker color indicates larger surface tension, while white color indicates zero surface tension. Surface tension force acts on the liquid-gas interface, playing a critical role in droplet formation in turbulent sprays.

 

The ligaments formed due to Rayleigh-Taylor instability (instability induced by two contacting fluids with different densities) are visible, beginning at the left of the image. After formation of these thin, long ligaments, Plateau-Rayleigh instability (instability induced by the effect of surface tension) takes over and small pieces of fluid fragment are pinched off from the jet. Further downstream, flow becomes turbulent. Towards the end of domain, there are coherent structures as well as small-scale droplets and ligaments.

 

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