When: Apr 19 2019 @ 4:00 PM
Where: 132 Gilman Hall
132 Gilman Hall

4:10 pm Presentation
“Deformation and Breakup of Bubbles in Strong Turbulence”
Presented by ASHIK ULLAH MOHAMMAD MASUK (Adviser: Prof. Rui Ni)
In oceanic wave breaking, a large amount of air bubbles are produced in the turbulent upper layer of the ocean, which controls many important natural processes such as ocean-atmosphere gas exchange and aquatic environment for marine life. One of the limiting factors to understand such processes is our knowledge on the behavior of bubbles in such a violent turbulent environment. Therefore, we experimentally study the dynamics of bubble deformation and breakup in a turbulent flow with high energy dissipation rate ( ) through simultaneous measurements of both carrier and dispersed phases. In this presentation, a novel method to reconstruct the 3D geometry of bubbles from optical measurements of turbulent multiphase flow will be introduced. Furthermore, experimental observations of the breakup mechanism of Hinze scale bubbles will be discussed.

4:35 pm Presentation
“Energy-Based Control of Wall-Bounded Shear Flows”
Presented by CHANG LIU (Adviser: Prof. Dennice Gayme)
This work examines the use of energy methods to design a feedback control law for channel flow. This approach has advantages over linear methods that may lead to control law that are only effective in small regions of attraction around a base state. In particular, we design a control law based on the Lyapunov stability applicable to nonlinear systems, allowing them to enlarge the controllable flow region. The fluctuation energy in the shear flows is a typical candidate for a Lyapunov function(al) to prove stability of a base flow, resulting in the classical Reynolds-Orr equation. This work uses this framework to design a control law that achieves stability through suppressing the shear production term in this energy equation. This control law is initially illustrated in a nine-dimensional Galerkin model of plane Couette flow and then demonstrated in the Direct Numerical Simulation (DNS) of turbulent channel flows. The results reveal that the base flow is stabilized through this control law, which has the potential to relaminarize a turbulent flow.