This group works on many important fluid dynamics problems involving multiphase flows (involving bubbles, droplets, and particles), fogs (marine, advection) and the effect of radiation on it, fluid-structure interactions, and wind-wave interactions. These problems are studied using cutting-edge CFD tools and have widespread applications in geophysical flows, renewable energy harvesting, and atmospheric and oceanographic studies. The researchers are also involved in developing numerical schemes to efficiently and accurately devise fluid flow simulations for their research. They use an in-house code for simulation, which is based on a finite-difference method or pseudo-spectral method for spatial discretization and a second-order Runge-Kutta algorithm for time integration. They perform high-fidelity simulations using High-resolution DNS as well, and large-eddy simulation (LES) is adopted to solve the fluid flows and turbulence involved.
- The group will perform the simulations on sediment transportations using PR-DNS (Particle resolved direct numerical simulations). For particle-laden flows, they rely on the Navier-Stokes equation with IB (Immersed Boundary) framework to solve fluid flow coupled with the Newton-Euler equations to solve the spherical particle motion. The solver also contains the adaptive collision time modeling (ACTM) which helps the researchers to perform sophisticated simulations with realistic collisions of particles with a lubrication force model involved. Their fully coupled system will be used to study the important physics of sediment transportation and particle segregation. The data extracted from these simulations will help us to understand the role of air/water flows in dunes and ripples formation on desert sands and underwater sand beds in rivers, lakes, and oceans.
- Another key focus of the group's research is the simulation of marine fog using advanced computational methods. They will employ a unique LES-LCM (Large-Eddy Simulation-Lagrangian Cloud Model) approach to capture the intricacies of fog formation and evolution. This method allows for a detailed study of the fog lifecycle, including the integration of short-wave radiation parameterization. So far, simulations have successfully replicated the development of advection fog, and the results demonstrate a realistic evolution of advection fog, which continues to develop throughout the simulation period, providing valuable insights into the dynamics of marine fog formation. Additionally, the group will concentrate on simulating the impact of land topography on fog using the Immersed Boundary Method (IBM). This technique enables them to model complex landforms at the LES grid resolution accurately. They will combine IBM with an unstructured triangular mesh to incorporate high-resolution LiDAR elevation data, creating detailed topographic maps for the simulations. This approach allows the researchers to simulate the activation of cloud condensation nuclei (CCN) and the development of fog droplets in environments where periodic boundary conditions are not feasible due to topographical variations.
- The group is also investigating turbulence flows over waves. Turbulent flows over waves are complex and fascinating phenomena frequently observed in various natural and engineered systems. Understanding and accurately simulating these flows have significant implications for coastal and offshore engineering, oceanography, renewable energy harnessing, and environmental studies. At the air–sea interface, the interaction between air turbulence and ocean waves plays a critical role in determining wave growth. In order to resolve the boundary layer near the water surface, the equations are solved on a boundary-fitted grid. The Cartesian space is mapped to the computational domain with the algebraic mapping. A hybrid finite-difference and pseudo-spectral method is used for spatial discretization. The pseudo-spectral method based on the fast Fourier transform (FFT) is used for the horizontal directions. A second-order finite-difference scheme is used in vertical direction $\zeta$ with refinement near the top and bottom boundaries.
Research by this group was featured on the MSI website in August 2018: Modeling an Air-Pollution Filtration System.