Paper Number
IN15 

Session
Flow-induced Instabilities and Non-Newtonian Fluids

Title
Instabilities and turbulence in planar jets of dilute polymer solutions

Presentation Date and Time
October 13, 2021 (Wednesday) 11:30

Track / Room
Track 4 / Meeting Room C-D

Authors (Click on name to view author profile)

  1. Yamanidouzisorkhabi, Sami (Massachusetts Institute of Technology, Mechanical Engineering)
  2. Raj, Yashasvi (Massachusetts Institute of Technology, Mechanical Engineering)
  3. Zaki, Tamer A. (Johns Hopkins University, Mechanical Engineering)
  4. McKinley, Gareth H. (Massachusetts Institute of Technology, Mechanical Engineering)
  5. Bischofberger, Irmgard (Massachusetts Institute of Technology, Mechanical Engineering)

Author and Affiliation Lines (in printed abstract book)
Sami Yamanidouzisorkhabi1, Yashasvi Raj1, Tamer A. Zaki2, Gareth H. McKinley1 and Irmgard Bischofberger1
1Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139; 2Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218

Speaker / Presenter 
Yamanidouzisorkhabi, Sami

Keywords
experimental methods; flow-induced instabilities; non-Newtonian fluids; polymer solutions

Text of Abstract
Fluid turbulence enhances the mixing of regions with high and low momentum but viscous effects also result in high dissipative energy losses that are notoriously difficult to mitigate. Dilute polymer solutions, typically containing less than 100 parts per million of polymer, are important exceptions; they can fundamentally modify the flow dynamics and reduce the turbulent losses that cause frictional drag. Jets are canonical shear-flow configurations to examine the spatially developing instabilities and turbulence of dilute polymer solutions. In this work, we study high aspect ratio (i.e. 1:10 and 1:20) planar jets using stereo-Schlieren imaging. Synchronous side- and front-view Lagrangian visualizations reveal the dynamical changes in the flow structure arising from the presence of small amounts of polymer. We apply dynamic mode decomposition to identify the dominant unstable, spatially growing modes due to viscoelasticity that are stable for a Newtonian jet. The advective growth of these inertio-elastic modes leads to a turbulent region downstream of the jet. In this region, we map the Schlieren images to a concentration fluctuation profile and perform laser Doppler velocimetry to measure the local velocity fluctuations. We discuss how viscoelasticity produces elongated turbulent structures in the direction of the flow and modifies the power-law spectral decay of local velocity and concentration fluctuations.