Research

3-D Large Eddy Simulation of Cavitation of a Bluff Body (Sphere & DARPA Sub-off)

The simulation shows cavitating flow passing a Submarine Hull at a Reynolds number of 1.36x10^5 and a cavitation number of 0.1. In the video, the water volume fraction contour is colored by the velocity magnitude. We can see a stable vapor bubble forming around the body. When the local liquid pressure drops below the saturation pressure, vapor bubbles form, called cavitation. The Cavitation number quantifies the potential of cavitation. A low cavitation number, such as 0.1, suggests that the flow exhibits supercavitation, where a stable bubble layer forms around the object. This phenomenon of supercavitation, or cavitation in general, helps in drag reduction. This drag reduction helps achieve higher traverse speeds, especially in the case of torpedoes.

Numerical Investigation of Water Entry of Hydrophobic Spheres. 

We perform numerical simulations to study the dynamics of the entry of hydrophobic spheres in a pool of water. To track the air-water interface during the translation of the sphere in the pool of water, we use the volume of fluid (VOF) model. The continuum surface force (CSF) method computes the surface tension force. To simulate the hydrophobic surface properties, we also include wall adhesion. We perform simulations with different diameters and impact speeds of the sphere. Our simulations capture the formation of different types of air cavities, pinch-offs of these cavities, and other finer details similar to the experiments performed at the same parameters. Finally, we compare the coefficient of drag among the different hydrophobic cases. We further perform simulations of hydrophilic spheres impacting the pool of water and compare the drag coefficient with the analogous hydrophobic cases. We conclude that the spheres with hydrophobic surfaces have a lower drag coefficient than their hydrophilic counterparts. This lower drag of the hydrophobic spheres is attributed to the formation of the air cavity by the hydrophobic surfaces while translating through the pool of water, which reduces the area of the sphere in contact with water. In contrast, no such air cavity forms in the case of hydrophilic spheres. 

Zonal Jets in Geophysical Flows

Flows around the equatorial regions of gas giants such as Jupiter are known as Zonal flows. The formation of zonal winds on the onset is characterized by the annihilation of the convective rolls by uni-directional winds at both the top and bottom plates, the winds are in opposite directions as well. The below LES simulation using the Dynamic Samagorinsky Model depicts the formation of zonal jets.

Viscous Fingering and Carbon dioxide Sequestration

Three-dimensional simulations have been performed to understand the role of viscous fingering in sweeping High viscous fluid using Low viscosity fluid. This type of fluid flow instability occurs in various processes, including oil and natural gas extraction, the sequestration of CO2, the lubrication of industrial machinery, etc. We are able to capture the variation in finger growth based on several dependent parameters that can be improved to provide efficient flow. 

Prediction of  Turbulence Using Machine Learning Models

Faraday Instability in Miscible Fluids

This animation demonstrates that the Coriolis force delays the onset of the sub-harmonic instability responsible for the turbulent mixing, which is driven by the Faraday instability when the interface of two miscible fluids is subjected to vertical time-periodic accelerations. F1f/$\omega$0 corresponds to the non-rotating case, and F1f/$\omega$48 and F1f/$\omega$59 correspond to the rotating case. F1f/$\omega$48 represents that the forcing amplitude is $F=1$ and the ratio of the Coriolis frequency and the forcing frequency is $f/\omega=0.48$. $\omega t$ denotes the non-dimensional time.