A minute addition of long-chain, flexible, polymer molecules to Newtonian fluid strongly affects both laminar and turbulent flows. Polymers being stretched by a velocity gradient, particularly in a flow with curvilinear streamlines, engender elastic (hoop) stress that modifies the flow via a feedback mechanism. It results in pure elastic instabilities and elastic turbulence (ET), observed at Reynolds number Re <<1 and Weissenberg number Wi>>1. I will discuss a sequence of elastic instabilities and ET observed in a wake between two widely-spaced obstacles, hindering the channel flow. Further, I will present first quantitative evidence of elastic waves in ET.
In the second part of my talk, I will discuss viscous electron flow in graphene and our analogous experiments with Newtonian fluid. Electron transport in two- dimensional conducting materials, with dominant electron-electron interaction, exhibits unusual current vortices that result in negative resistance (nonlocal current-field relation). The transport behavior of these materials is best described by low Reynolds number hydrodynamics, where constitutive pressure-speed relation is the Stoke's law. I will present evidence of such vortices in a ow of viscous Newtonian fluid in a microuidic device analogous to the electronic system.
Atul Varshney obtained his B.Sc. (Hons.) Physics at Aligarh Muslim University, and he was awarded the University medal in 2005. He received MHRD-UGC Post Graduate award from 2005-2007 for being the University Rank Holder. In 2007 he obtained his M.Sc. Physics from IIT Delhi. He completed his PhD from TIFR Mumbai in 2013, thesis entitled â€œStructure Formation and Mechanical Response of Model Amorphous Systemsâ€. He was awarded PBC fellowship in 2013 for his postdoctoral research in the area of polymer hydrodynamics at Weizmann Institute of Science, Israel. In 2017 he joined Institute of Science and Technology (IST) Austria as ISTplus (Marie Curie) fellow. His present research focuses on hydrodynamic instabilities in blood flow.