SUHAS S. JAIN

1. Eulerian formulation for the simulation of soft-solids in a fluid

In this study an incompressible 2D Eulerian Finite volume solver has been developed on a fully collocated grid. We have adopted the Reference Map Technique by Valkov et. al (J. Appl. Mech., 82, 2015) as an approach to fully resolve hyperelastic solids in a fluid on an Eulerian grid. Multiple improvements for this technique are assessed. The extrapolation of the reference map field outside the solid region is performed using a cost effective Least Square Approach. Following recent adoptions, level-set field is constructed using the reference map field at every time step. These modifications allow simulations without artificial viscosity in solid regions while maintaining numerical robustness and have completely eliminated the striations of the interface that was seen before, hence eliminating the additional routines that were required for the smoothing of the interface. An approximate projection method has been used to project the velocity field onto a divergence free field. Cost and accuracy analysis of the solver has been performed.

Collision of two hyperelastic solids placed in a Taylor-Green vortex.

2. Detailed numerical study of primary atomization of a liquid jet in swirling crossflow

This study involved VOF based numerical simulations of a liquid jet injected into gas-crossflow in swirling motion. The liquid is injected radially outwards from a central tube to a confined annular space with gas crossflow. Simulations are conducted at high liquid-to-gas density ratio ($\rho^*$) of 180:1 and different liquid-to-gas momentum ratios ($Q$) upto 25. The Swirl Number ($SN$) of the gas crossflow was varied between 0 and 0.84. The liquid jet undergoes column and shear modes of breakup as observed in experimental studies. Spray characteristics such as drop size distribution, velocity of the drops, shape factor and column breakup length were analyzed. Simulations effectively captured the influence of swirl flow on the spray characteristics.

This project was carried out under the guidance of Prof. Gaurav Tomar, Prof. R. V. Ravikrishna and Prof. Raghunandan B. N. and was supported by Pratt and Whitney, USA.

No swirl case.

Swirl case with Swirl Number = 0.84.

3. Density ratio and Reynolds number effect in the secondary breakup of drops at moderate Weber numbers

In this study fully resolved VOF simulations were performed to understand the physics involved in the breakup of an initially spherical droplet in a gas flow. In particular, we focused on the effect of density ratio, Reynolds number and viscosity ratio on drop morphology and the breakup mechanism. We used scaling analysis to explain these characteristics of the drop breakup. We also studied the role of the dynamics of the droplet rim and the Rayleigh-Taylor instability, at different density ratios in the bag formation process. Finally, we presented a density ratio - Weber number phase plot reflecting the drop behavior at various density ratios and Weber numbers.

This project was carried out under the guidance of Prof. Gaurav Tomar and Prof. R. V. Ravikrishna.

Density ratio = 10, Weber number = 20.

Density ratio = 1000, Weber number = 20.

4. Development of a general block-based AMR library for a CFD solver

A block-based adaptive mesh refinement (AMR) library with multigrid poisson solver for the in-house CFD solver was developed with an aim of developing a massively parallelable physics-based adaptive two-phase flow solver. Library is written in C++ and extensively uses STL. Parallelization is done using MPI and were tested on the supercomputer (SahasraT - Cray XC40).

This project was carried out under the guidance of Prof. Gaurav Tomar.

Gradient-based refinement with Block nesting (adjacent block refinement ratio = 2)

5. Development of bubble coalescence and breakup models for Euler-Euler Two-fluid modeling

Effects of surfactants and salts on bubbly flows were studied to investigate the coalescence inhibition process. This property was then used to suppress the coalescence and to validate the breakup closure models in an Euler-Euler Two-fluid approach. This models tested were part of the iMUSIG model(inhomogeneous MUltiple SIze Group model) and GENTOP model(GENeralized TwO Phase model - DNS and Euler-Euler coupled multiscale model for high void fraction regime multiphase flows).

This project was done under the guidance of Dr. Dirk Lucas and Dr. Roland Rzehak and was supported by the Helmholtz-Zentrum Dresden-Rossendorf scholarship.

Simplified model for bubble breakup in wake

Benchmarking for bubble breakup models against the FRAME experimental results

6. Development of a 3D two-phase flow solver

I worked on developing a two-phase flow solver for my Bachelor's Thesis. The idea was to build a solver that included the solution of the Navier-Stokes (NS) equations n general to better understand solver development and also to deal with some basic aspects of numerical methods for multiphase flows. I solved a three-dimensional NS equations with the finite volume method and used an algebraic VOF method with CICSAM advection scheme to capture sharp interfaces. Further, I implemented CSF model for surface tension as well as Kernel K8 convolution for curvature calculation. I successfully validated the solver with Lid driven cavity, mixed convection in cavity, rotation of slotted disk, drop in shear flows, static drop and dynamic drop test cases. Results from test cases prompted a few modifications to improve the accuracy and convergence. I replaced CICSAM with STACS which in turn was replaced with HiRAC with pseudo-time stepping to effectively avoid the unbounded solution. Kernel convolution was replaced by the height function method to improve the accuracy of curvature calculation. Balanced-force algorithm was implemented to eliminate spurious currents and to obtain an accurate balance between surface and pressure forces. Hybrid deferred correction method was developed and implemented with QUICK scheme for convective terms to improve the convergence of the solver.

Lid driven cavity at Re 1000

Pressure jump inside the drop (Height function)

Rotation of a slotted disk with on grid 100x100. Simulation was performed at a courant number of 0.25. Results obtained using CICSAM and STACS were almost same at Courant number (Co) 0.25 and STACS performed better at Co 0.9.

Initial Condition

After Half Rotation

After One Full Rotation

7. Implementation of level-set method in OpenFOAM

A conservative level-set method was implemented in the interFOAM solver of OpenFOAM with third-order WENO advection interpolation scheme. Modified solver was validated using droplet coalescence and jet breakup. Comparative study of the effects of kothe, harmonic and arithmetic viscosity interpolation models was done.

This project was done under the guidance of Prof. -Ing. Eugeny Kenig at the University of Paderborn, Germany and was supported by the DAAD (German Academic Exchange Program) - IAESTE summer research fellowship.