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1. A Dual Scale Approach to Modeling Sub-Filter Shear-Induced Instabilities with a Vortex Sheet Method

   Goodrich, A.; Herrmann, M. (May 2021, ILASS-Americas 31st Annual Conference on Liquid Atomization and Spray Systems)

   null (Ed.)

   A method to predict sub-filter shear-induced velocities on a liquid-gas phase interface for use in a dual scale LES model is presented. The method reconstructs the sub-filter velocity field in the vicinity of the interface by introducing a vortex sheet at the interface. The vortex sheet is transported by an unsplit geometric volume and surface area advection scheme with a Piecewise Linear Interface Construction (PLIC) representation of the material interface. At each step and desired location the shear-induced velocities can be calculated by integrating the vortex sheet and other relevant quantities over the liquid-gas interface with the sub-grid velocity reconstruction limited to a small number of cells near the phase interface. The vortex sheet method is tested and compared against prior literature. 

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2. A Dual Scale Model for Reconstructing Sub-Filter Shear-Induced Instabilities Using a Vortex Sheet Method

   Goodrich, A.; Herrmann, M. (August 2021, ICLASS 2021, 15th Triennial International Conference on Liquid Atomization and Spray Systems)

   null (Ed.)

   A method to predict sub-filter shear-induced velocities on a liquid-gas phase interface for use in a dual scale LES model is presented. The method reconstructs the sub-filter velocity field in the vicinity of the interface by introducing a vortex sheet at the interface. The vortex sheet is transported by an unsplit geometric volume and surface area advection scheme with a Piece- wise Linear Interface Construction (PLIC) representation of the material interface. At each step and desired location the shear-induced velocities can be calculated by integrating the vortex sheet and other relevant quantities over the liquid-gas surface with the sub-grid velocity recon- struction limited to a small number of cells near the phase interface. The vortex sheet method is tested and compared against prior literature. 

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3. A Dual Scale Approach to Modeling Sub-Filter Velocities due to Shear-Induced Instabilities

   Goodrich, A.; Herrmann, M. (May 2020, ILASS-Americas 31st Annual Conference on Liquid Atomization and Spray Systems)

   null (Ed.)

   A method to compute sub-filter velocities due to shear induced instabilities on a liquid-gas interface for use in a dual scale LES-DNS model is presented. The method reconstructs the sub-filter velocity field as the sum of a prescribed base velocity profile and a perturbation velocity field determined by the Orr-Sommerfeld equations. The base velocity profile is approximated as an error function appropriately scaled with flow parameters, and the perturbation velocity field is computed by solving the Orr-Sommerfeld equations with appropriate boundary and interface conditions. The perturbation velocities of the Orr-Sommerfeld equations are expanded into Chebyshev polynomials to create a linear eigenvalue problem as outlined by Schmid and Henningson (2001). Finally the eigenvalue problem is solved using a standard linear algebra package and used to evaluate the perturbation velocities. The Chebyshev method is tested under a variety of flow parameters and initial interface disturbances. Results are presented and compared against prior literature and asymptotic solutions. 

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4. High-Fidelity Modeling and Simulation of Primary Breakup fo a Gasoline Surrogate Jet

   Zhang, Bo; Ling, Yue (May 2019, Proc. ILASS-Americas 30th Annual Conference on Liquid Atomization and Spray Systems 30th Annual Conference on Liquid Atomization and Spray Systems)

   In the present work, we model and simulate the injection and atomization of a gasoline surrogate jet by detailed numerical simulation. The surrogate fuel has a low volatility and thus no phase change occurs in the process. The nozzle geometry and operation conditions are similar to the Engine Combustion Network (ECN) “Spray G”. We focus the present study on the near field where inter-jet interaction is of secondary importance. Therefore, we have considered only one of the eight jets in the original Spray G injectors. The liquid is injected from the inlet into a chamber with stagnant gas. A tangential component of velocity is introduced at the inlet to mimic the complex internal flow in the original spray G injector, which leads to the jet deflection. A parametric study on the inlet tangential velocity is carried out to identify the proper value to be used. Simulations are performed with the multiphase flow solver, Basilisk, on an adaptive mesh. The gas-liquid interface is captured by the volume-of-fluid method. The numerical results are compared to the X-ray experimental data for the jet deflection angle and the temporal variation of penetration length. The vortex dynamics in the near field are also presented by the assistance of the vortex-identification criterion. 

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5. Impact of inlet gas turbulence on the formation, development and breakup of interfacial waves in a two-phase mixing layer

   https://doi.org/10.1017/jfm.2021.481  

   Jiang, D.; Ling, Y. (August 2021, Journal of Fluid Mechanics)

   Understanding the development and breakup of interfacial waves in a two-phase mixing layer between the gas and liquid streams is paramount to atomization. Due to the velocity difference between the two streams, the shear on the interface triggers a longitudinal instability, which develops to interfacial waves that propagate downstream. As the interfacial waves grow spatially, transverse modulations arise, turning the interfacial waves from quasi-two-dimensional to fully three-dimensional. The inlet gas turbulence intensity has a strong impact on the interfacial instability. Therefore, parametric direct numerical simulations are performed in the present study to systematically investigate the effect of the inlet gas turbulence on the formation, development and breakup of the interfacial waves. The open-source multiphase flow solver, PARIS, is used for the simulations and the mass–momentum consistent volume-of-fluid method is used to capture the sharp gas–liquid interfaces. Two computational domain widths are considered and the wide domain will allow a detailed study of the transverse development of the interfacial waves. The dominant frequency and spatial growth rate of the longitudinal instability are found to increase with the inlet gas turbulence intensity. The dominant transverse wavenumber, determined by the Rayleigh–Taylor instability, scales with the longitudinal frequency, so it also increases with the inlet gas turbulence intensity. The holes formed in the liquid sheet are important to the disintegration of the interfacial waves. The hole formation is influenced by the inlet gas turbulence. As a result, the sheet breakup dynamics and the statistics of the droplets formed also change accordingly. 

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