Paper Number
IN42 

Session
Flow Induced Instabilities and Non-Newtonian Fluids

Title
Non-linear dynamics of turbulence and re-laminarization of dilute polymer solution jets

Presentation Date and Time
October 24, 2019 (Thursday) 10:50

Track / Room
Track 4 / Room 305B

Authors (Click on name to view author profile)

  1. Yamanidouzisorkhabi, Sami (Massachusetts Institute of Technology, Department of Mechanical Engineering)
  2. McKinley, Gareth H. (Massachusetts Institute of Technology, Department of Mechanical Engineering)
  3. Bischofberger, Irmgard (Massachusetts Institute of Technology, Mechanical Engineering)

Author and Affiliation Lines (in printed abstract book)
Sami Yamanidouzisorkhabi, Gareth H. McKinley, and Irmgard Bischofberger
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

Speaker / Presenter 
Yamanidouzisorkhabi, Sami

Text of Abstract
Dilute synthetic and biopolymer solutions have been shown to reduce turbulent drag in pipelines and around marine vehicles due to their viscoelasticity. The very low concentrations of polymer employed in drag reduction studies makes direct imaging of the mixing and turbulent flow structures an outstanding challenge and motivates novel experimental techniques to track the spatiotemporal evolution in the dilute polymer solution phase. In this work, we combine particle image velocimetry (PIV) and Schlieren imaging protocols to enable direct velocity measurement and flow visualization of the mixing dynamics and vortical structures that develop in turbulent jets of dilute aqueous polymer solutions injected into quiescent water. At the interface of the viscoelastic jet and water a shear layer develops leading to momentum transfer between the two fluids. This momentum transfer can result in formation of turbulent vortical structures. It is shown that under certain conditions, an increase in viscoelasticity completely eliminates the vortical structures of a turbulent jet resulting in re-laminarization. A comprehensive state diagram is proposed to fully characterize transition to turbulence, turbulence, and re-laminarization based on the viscoelastic properties of the fluid jet. In this state diagram, Reynolds number, elasticity number, and polymer viscosity ratio (βp = ηp ⁄ η0) characterize the interaction between inertial, elastic, and viscous forces. It is shown that the elasticity number criterion suggested by Rallison and Hinch (J. Fluid Mech., 1995) for eliminating the linear modes of instability, together with a high polymer viscosity ratio are necessary and sufficient conditions for re-laminarization. Finally, to illustrate how the viscoelastic properties of the fluid modify the mixing dynamics of the flow, we use the PIV results to compute local values of the Finite Time Lyapunov Exponent (FTLE) characterizing the evolution of material lines in the jet.