Paper Number
IN17 

Session
Flow-induced Instabilities and Non-Newtonian Fluids

Title
Axisymmetric numerical simulations of viscoelastic jets

Presentation Date and Time
October 13, 2021 (Wednesday) 1:55

Track / Room
Track 4 / Meeting Room C-D

Authors (Click on name to view author profile)

1. Zinelis, Konstantinos (Imperial College London, Chemical Engineering)
2. Abadie, Thomas (Imperial College London, Chemical Engineering)
3. McKinley, Gareth H. (Massachusetts Institute of Technology, Mechanical Engineering)
4. Matar, Omar K. (Imperial College London, Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Konstantinos Zinelis¹, Thomas Abadie¹, Gareth H. McKinley² and Omar K. Matar^1
1Chemical Engineering, Imperial College London, London, United Kingdom; ²Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA

Speaker / Presenter 
Zinelis, Konstantinos

Keywords
computational methods; flow-induced instabilities; interfacial rheology; non-Newtonian fluids; polymer solutions

Text of Abstract
Droplet formation in a non-Newtonian fluid is central to numerous industrial applications such as spray-drying, atomisation and paint application. The flows associated with spray formation involve large interfacial deformations and complex spatio-temporal dynamics. The aim of the present work is to establish a robust numerical basis for systematic examination of viscoelastic fluid sprays. To achieve this, we begin with two-dimensional axisymmetric simulations of an impulsively-started jet exiting a nozzle and entering a stagnant gas phase. We use an adaptively-refined volume-of-fluid technique to capture the interface and the log-conformation transformation for stable and accurate solution of the viscoelastic constitutive equation. We simulate, for the first time, the entire jetting and breakup process of a viscoelastic fluid, including the flow through the nozzle which results in an initial radial stress distribution that is shown to affect the subsequent breakup dynamics. We validate the numerical simulations against the predictions of linear stability analysis. Subsequently, we explore the effect of shearing flow inside the nozzle on the thinning dynamics of the viscoelastic jet via analysis of the spatio-temporal evolution of the polymeric stresses. We also examine the role of the finite extensibility of the polymeric chains on the breakup process and demonstrate the capacity of the numerical formulation to resolve the elasto-capillary regime as a function of mesh resolution and the finite extensibility of the fluid. Finally, we investigate systematically the dependence of the rate of filament thinning on the axial momentum of the jet and the fluid relaxation time; this permits efficient exploration of the material parameter space, capturing the competing effects of elastic, viscous, and inertial forces on the ejected droplet size distribution.