Date of Award

Spring 2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Mechanical Engineering

Committee Director

Shizhi Qian

Committee Member

Xiaoyu Zhang

Committee Member

Venkat Maruthamuthu

Committee Member

Yan Peng

Abstract

Micro/Nanofluidic devices often involve use of biological fluids or polymeric solutions that cannot be simply treated as Newtonian fluids. The numerical simulation for the complex fluids at micro/nanoscale presents a significant computational challenge, and the inclusion of electrokinetic body force further increases the complexity. Specifically, the well-known High Weissenberg Number Problem (HWNP) has become a challenge for the numerical simulation of viscoelastic fluid. This dissertation is aimed to develop a numerical tool to simulate the behavior of viscoelastic fluid in the micro/nanochannel. The most popular log-conformation reformulation to solve the HWNP is presented and implemented in a finite volume scheme. The implemented solver is validated by applying to several classical viscoelastic fluid benchmark problems, ranging from 2D to 3D, stationary to transient problems.

Then, flow behavior of viscoelastic fluid in a three-dimensional curvy channel is investigated. A Finitely Extensible Nonlinear Elastic with Peterlin closure (FENE-P) constitutive model is utilized to describe the viscoelastic fluid. The characterization of viscoelastic instability and elastic turbulence at a relatively high Weissenberg number is identified from the fluctuation of velocity field, streamlines, secondary flow patterns, and the intensity of secondary flow. The mechanism of this phenomenon is analyzed from the interaction between the flow and polymer molecules. Parametric study shows that the level of elastic turbulence decreases with viscosity ratio and becomes stronger with the extensibility parameter.

The implemented solver is further applied to investigate the electroosmotic flow (EOF) of viscoelastic fluid with a linear Phan-Thien and Tanner (LPTT) model in nanoslit and nanochannel with reservoirs. Under the condition in which the Electrical Double Layer (EDL) thickness is comparable to the characteristic length of the nanochannel and the surface charge density is relatively high, the effects of viscoelasticity on EOF, ionic current, and ion transport are investigated. Obvious enhancement of velocity, flow rate and ionic current is observed for viscoelastic fluid compared to the Newtonian fluid. The EDL thickness and the presence of microscale reservoirs also have significant influence on the EOF of viscoelastic fluid.

DOI

10.25777/z40q-at07

Available for download on Thursday, June 10, 2021

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