Polymer addition in a turbulent flow is the most effective drag reduction strategy available for liquid flows. Polymers are for instance used in the Trans-Alaskan Pipeline to reduce the energy required to move crude oil from the fields to refineries. Using numerical methods that capture the small scale dynamics of polymer dynamics and parallel algorithms, we study polymer drag reductions at larger Reynolds numbers than previously simulated: (based on bulk), (based on viscous scales). These simulations enable us and our collaborators to further the understanding of the mechanisms of polymer drag reductions toward the derivation of predictive theory and models.
The effects of polymer additives in convection flows are anticipated to provide a new approach to the control of heat transfer. We conduct fundamental numerical simulations of natural convection flows in the presence of polymers to investigate the interactions between polymer dynamics and convection cells. This contour plot shows the existence of horizontal elastic instabilities emerging from the boundary layers of convection cells and propagating within the core of convection cells, and circular elastic instabilities in the plumes of convection cells. The identification of elastic instabilities is critical to the understanding of chaotic behavior observed in natural convection flows with polymer additives.
Turbulence is one of the remaining great challenges of physics. We use high-fidelity numerical techniques to simulate a large variety of flows to study the structure and predictability of turbulence. The figure shows vortices in a Kolmogorov flow forced at two wavenumbers. This fundamental study has highlighted the asymptotic behavior of turbulent dissipation.
Using molecular dynamics, we study novel approaches to lubrication in human joints and for engineering applications based on intermolecular and surface forces.
We work with Prof. Ken Mann to implement Prof. Mann's biochemistry models of the blood coagulation cascade in our flow simulation. This is a quintessential multiscale problem where as little as 2nM of thrombin (a small molecule) may create a deadly blood clot in an artery. Blood is also a particulate flows with a complex rheology, which adds to the modeling challenge. We use numerical techniques and knowledge gained from turbulence simulations, ablation research toward the development of a comprehensive model of the biochemistry of blood coagulation in physiological flows.
We did it! We abused Skype and filled our mailboxes with enormous threads of emails for a year, and now… more