Start
Jan 07, 2010 - 16:00
End
Jan 07, 2010 - 17:30
Venue
Room No 118 (Creativity Hall)
Event Type
Speaker
Dr. Prashant Valluri University of Edinburgh Scotland
Title
Spatiotemporal instabilities in two-phase flows
Abstract: This talk is motivated by a long standing problem faced by the FMCG industry wherein highly viscous soils are displaced by a cleaning fluid and also in the oil-and-gas industry wherein oil and gas mixtures are transported via pipelines. Integral to these applications is the formation and growth of waves the nature of which governs the flow regime and therefore throughput. In this work the linear and nonlinear spatio-temporal stability of an interface separating two Newtonian fluids in pressure-driven channel flow at moderate Reynolds numbers is analysed both theoretically and numerically. Inertia interfacial tension and gravity are also accounted for in the study. In the linear regime our theoretical (Orr-Sommerfeld-type) analysis reveals that the interface is absolutely unstable over an intermediate range of Reynolds numbers and ratios of the thicknesses of the two layers; convectively unstable regimes are present in the complimentary ranges of these parameters. Increasing the viscosity ratio promotes the absolute nature of the interfacial instability. Results obtained from direct numerical simulations of the Navier-Stokes equations for long channels elucidate significantly large spatial growth rates in the absolute regime and the nonlinear evolution of the interface which is accompanied by wave coalescence towards the downstream end of the channel.The transition point from a convective to an absolute regime predicted by simulations also agrees well with the theoretical analysis.Bio-sketch: I am a lecturer in chemical engineering at the University of Edinburgh Scotland. I am based in the Institute for Materials and Processes and my research interests centre around tackling industrial and biological multiphase flows using numerical and theoretical means. These flow problems concern with the environment energy and the health sectors which are crucial for our future – some examples being oil-gas flows industrial cleaning and cancer treatment. A brief summary of my work so far - My PhD research at Imperial College London dealt with numerical investigation of countercurrent multiphase flows in structured packings. This was followed by my postdoctoral work concerning multiphase flows in oil-gas pipelines and towards minimising environmental footprint in industrial cleaning-in-place processes. My ongoing work at University of Edinburgh focuses on cooling of microelectronic devices and solid-liquid flows in pipelines. My research work at Unilever Research India (prior to my PhD studies at Imperial College London) involved development and processing of novel patented detergent formulations.