Forced Shear Layers
Shear layer vortices over a rectangular body
Evolution of shear layers, the frequency of the structures, their dependence on Reynolds numbers etc are studied with (and without) perturbations; the aim is to understand the instability mechanism and the transition to turbulence.
Insect Flight
Numerical simulation of insect Drosophila
Numerical simulation of insect Drosophila in hovering condition along horizontal stroke plane. The moving geometry is simulated using immersed boundary method. The picture shows the major features of flow field such as initial shedding of Trailing Edge Vorticity, growth of Leading Edge Vorticity and formation of dipole vortices.
Interfacial Phenomena
Satellite drop formation due to capillary waves
Interfaces are thin boundaries between fluid-phases having an excess of free energy. The research include studies on surface waves and their breakup, transport across interfaces, stability of interfaces, motion of drops on surfaces and thin film flows. The image shows dripping from a horizontal thin film of fluid, showing satellite drop formation due to capillary waves.
Convection
Flows driven by density differences occur in phenomena ranging from earth's climate to day to day cooking. The transport of fluid near the wall occurs in the form of sheets of rising lighter fluid and falling heavier fluid. The lighter lines in the image are the top view of rising sheets of fluid above a hot surface in turbulent convection; these sheets move and merge.
Bio-Fluid Dynamics
Streamtraces for the case of offset in artery
The Flow pattern in a Cavopulmonary vascular system are analysed for different geometry and flow parameters. The results from a finite element computation is validated with dye flow visualization and PIV. The image shows the resulting flow lines of haemodynamics.
Direct Simulation of Turbulence
DNS of flow past a square cylinder
Direct numerical simulation of flow past square cylinder by a code developed in-house. The inflow is embedded with high shear. The instantaneous -λ2 contours capture fine details of Mode B type transition in the wake.
Active Flow Control Algorithms
Vortex shedding control
Flow control is important in a wide range of systems and devices. Often active flow control is required to handle both internal and external disturbances to achieve desired goals. A closed loop feedback control system includes, sensors, actuators and a control algorithm. This approach is central to all types of laminar and turbulent shear flows. In the context of free shear flows, Karman vortex shedding past a circular cylinder is gradually stabilized through a simple momentum injection strategy as shown.
Phase-Field Modeling
Efficient Phase-field simulation.
Phase-field models are popular for moving boundary problems, where high throughput interface tracking is involved. Here, nucleation, crystal growth and dissociation are simulated using stochastic Phase-field Gillespie algorithm. The RHS is maintained at a higher temperature than the LHS. A progressively expanding band of crystallinity can be noticed.
Thermal Hydraulics
Streamlines, pressure and temperature contours in complex 180-degree turn around spallation target module
Thermal hydraulics related to the design of the spallation target module of an Accelerator Driven Sub-critical (ADS) nuclear reactor system was investigated numerically using a Finite Element - RANS approach by predicting fluid flow and heat transfer characterstics. The research focus is towards utilizing appropriate FEM based CFD techniques for simulating industrially complex flows to predict fluid flow and heat transfer in laminar and turbulent regimes.
Large Eddy Simulation
Turbulent flow in a curved square duct
In Large Eddy Simulation (LES) of turbulent flows the unsteady large scale turbulent motion are explicitly computed and the small scales are modeled through a sub-grid scale model independent of the flow behavior. The present work aims at the prediction of the wall heat exchanges in a curved square duct for high Reynolds number turbulent flow.
Aerodynamics
A decambering approach is used to study the post-stall aerodynamics of wings of different taper ratios. The result show that at α=170o, the rectangular wing (taper ratio=1) has stalled at the root. At α=18o, the tapered wings also stall but near the tips as shown in the inset.
Unsteady Aerodynamics
A numercial scheme is implemented using a lumped vortex model for an airfoil with wake relaxation to account for unsteadiness. The unsteadiness is introduced through the zero-normal boundary condition and at each time step a steady state potential flow equation is solved. On-going research is directed towards better prediction of the wake model, wake roll-up and separated wake.
Thermal Hydraulics
Evolution of aperture field due to dissolution and buoyant convection
Upward flow through vertical fractures in limestone formations under a geothermal gradient favors dissolution and permeability growth. We investigate the transition from conductive and forced convective regimes to instability and buoyant convection as a result of permeability growth. This is an example of evolving natural system which may occur during geothermal heat extraction or carbon sequestration.
Heterogeneous Porous Media
Transport in heterogeneous porous media: Mean and standrad deviation of concerntration at different locations.
Multi-scale heterogeneity is the striking feature of subsurface hydrological systems, and is often modeled using random field concepts. This results in scale-dependent dispersivity and uncertainty in flow and transport processes. Higher order stochastic finite element method in Bayesian framework is used to for reducing conditional prediction uncertainty. This provides a guideline for optimal measurements to monitor the contaminant spreading.
