University of Pennsylvania ScholarlyCommons Publicly Accessible Penn Dissertations 2018 Flow Behavior And Instabilities In Viscoelastic Fluids: Physical And Biological Systems Boyang Qin University of Pennsylvania, [email protected] Follow this and additional works at: https://repository.upenn.edu/edissertations Part of the Mechanical Engineering Commons Recommended Citation Qin, Boyang, "Flow Behavior And Instabilities In Viscoelastic Fluids: Physical And Biological Systems" (2018). Publicly Accessible Penn Dissertations. 3174. https://repository.upenn.edu/edissertations/3174 This paper is posted at ScholarlyCommons. https://repository.upenn.edu/edissertations/3174 For more information, please contact [email protected]. Flow Behavior And Instabilities In Viscoelastic Fluids: Physical And Biological Systems Abstract The flow of complex fluids, especially those containing polymers, is ubiquitous in nature and industry. From blood, plastic melts, to airway mucus, the presence of microstructures such as particles, proteins, and polymers, can impart nonlinear material properties not found in simple fluids like water. These rheological behaviors, in particular viscoelasticity, can give rise to flow anomalies found in industrial settings and intriguing transport dynamics in biological systems. The first part of my work focuses on the flow of viscoelastic fluids in physical systems. Here, I investigate the flow instabilities of viscoelastic fluids in three different geometries and configurations. Realized in microfluidic channels, these experiments mimic flows encountered in technology spanning the oil extraction, pharmaceutical, and chemical industries. In particular, by conducting high-speed velocimetry on the flow of polymeric fluid in a micro-channel, we report evidence of elastic turbulence in a parallel shear flow where the streamline is without curvature. These turbulent-like characteristics include activation of the flow at many time scales, anomalous increase in flow esistance,r and enhanced mixing associated with the polymeric flow. Moreover, the spectral characteristics and spatial structures of the velocity fluctuations are different from that in a curved geometry. Measured using novel holographic particle tracking, Lagrangian trajectories show spanwise dispersion and modulations, akin to the traveling waves in the turbulent pipe flow of Newtonian fluids. These curvature perturbations far downstream can generate sufficient hoop stresses to sustain the flow instabilities in the parallel shear flow. The second part of the thesis focuses on the motility and transport of active swimmers in viscoelastic fluids that are relevant to biological systems and human health. In particular, by analyzing the swimming of the bi-flagellated green algae {\it Chlamydomonas reinhardtii} in viscoelastic fluid, we show that fluid elasticity enhances the flagellar beating frequency and the wave speed. Yet the net swimming speed of the alga is hindered for fluids that are sufficiently elastic. The origin of this complexesponse r lies in the non-trivial change in flagellar gait due ot elasticity. Numerical simulations show that such change in gait reduces elastic stress build up in the fluid and increases efficiency. These results further illustrate the complex coupling between fluid rheology and swimming gait in the motility of micro-organisms and other biological processes such as mucociliary clearance in mammalian airways. Degree Type Dissertation Degree Name Doctor of Philosophy (PhD) Graduate Group Mechanical Engineering & Applied Mechanics First Advisor Arratia E. Paulo Keywords Complex fluids, Flow instability, Low Re Swimming, Polymer fluid, Rheology, Viscoelasticity Subject Categories Mechanical Engineering This dissertation is available at ScholarlyCommons: https://repository.upenn.edu/edissertations/3174 Flow behavior and instabilities in viscoelastic fluids: physical and biological systems Boyang Qin A DISSERTATION in Mechanical Engineering and Applied Mechanics Presented to the Faculties of the University of Pennsylvania in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy 2018 Supervisor of Dissertation Paulo E. Arratia, Professor, Mechanical Engineering and Applied Mechanics Graduate Group Chairperson Kevin T. Turner, Professor, Mechanical Engineering and Applied Mechanics Dissertation Committee Paulo E. Arratia, Professor, Mechanical Engineering and Applied Mechanics Howard H. Hu, Professor, Mechanical Engineering and Applied Mechanics Douglas J. Jerolmack, Associate Professor, Earth and Environmental Science Steven D. Hudson, Physical Scientist, Materials Science and Engineering Division, National Institute of Standards and Technology Flow behavior and instabilities in viscoelastic fluids: physical and biological systems c COPYRIGHT 2018 Boyang Qin ACKNOWLEDGEMENT I am truly grateful to many individuals whose support, encouragement, and wisdom have made the completion of this dissertation possible. I am deeply indebted to my advisor, Professor Paulo E. Arratia, for being an incredible mentor, for his passion and curiosity in research, and for showing me the importance of resilience in science. I'd like to also thank the entire faculty, students, and staff of the department of Mechanical Engineering and Applied Mechanics, particularly Professor Prashant Purohit for his wonderful lectures and generous advices, Peter Szczesniak for his help with many hours of parts machining, and Eric Johnston for his assistance and training on cleanroom micro-fabrication. My special acknowledgement extends to all the former and current group members for their supportive discussions and collaborative spirit. In particular, I'd like to thank Dr. Arvind Gopinath, Dr. Alison E. Koser, and Dr. David A. Gagnon for the many intellectual and philosophical discussions, many of which I deeply enjoyed. They and many other friends here at Penn have made my time as a doctoral student so much more rewarding, colorful, and endearing. I'd like to thank Dr. Paul Salipante and Dr. Steven Hudson for their generous help with holographic particle tracking techniques and the many insightful discussions on the flow of complex fluids. I'd like to also thank my collaborators Dr. Chuanbin Li, Dr. Becca Thomases, and Dr. Robert Guy for the many wonderful discussions, both face-to-face and remotely, on the study of flagellar kinematics in viscoelastic fluid. My work is generously supported by NSF-CBET-1336171 and NSF-DMR-1104705. Finally, I believe a fraction of my every minute of existence is connected to and shared with my parents. I cannot thank them enough for the lifetime of love, support, and guidance they generously offered me that continue to inspire and shape who I am today. iii ABSTRACT Flow behavior and instabilities in viscoelastic fluids: physical and biological systems Boyang Qin Paulo E. Arratia The flow of complex fluids, especially those containing polymers, is ubiquitous in nature and industry. From blood, plastic melts, to airway mucus, the presence of microstructures such as particles, proteins, and polymers, can impart nonlinear material properties not found in simple fluids like water. These rheological behaviors, in particular viscoelasticity, can give rise to flow anomalies found in industrial settings and intriguing transport dynamics in biological systems. The first part of my work focuses on the flow of viscoelastic fluids in physical systems. Here, I investigate the flow instabilities of viscoelastic fluids in three different geometries and con- figurations. Realized in microfluidic channels, these experiments mimic flows encountered in technology spanning the oil extraction, pharmaceutical, and chemical industries. In particu- lar, by conducting high-speed velocimetry on the flow of polymeric fluid in a micro-channel, we report evidence of elastic turbulence in a parallel shear flow where the streamline is without curvature. These turbulent-like characteristics include activation of the flow at many time scales, anomalous increase in flow resistance, and enhanced mixing associated with the polymeric flow. Moreover, the spectral characteristics and spatial structures of the velocity fluctuations are different from that in a curved geometry. Measured using novel holographic particle tracking, Lagrangian trajectories show spanwise dispersion and modu- lations, akin to the traveling waves in the turbulent pipe flow of Newtonian fluids. These curvature perturbations far downstream can generate sufficient hoop stresses to sustain the flow instabilities in the parallel shear flow. iv The second part of the thesis focuses on the motility and transport of active swimmers in viscoelastic fluids that are relevant to biological systems and human health. In particular, by analyzing the swimming of the bi-flagellated green algae Chlamydomonas reinhardtii in viscoelastic fluid, we show that fluid elasticity enhances the flagellar beating frequency and the wave speed. Yet the net swimming speed of the alga is hindered for fluids that are sufficiently elastic. The origin of this complex response lies in the non-trivial change in flagellar gait due to elasticity. Numerical simulations show that such change in gait reduces elastic stress build up in the fluid and increases efficiency. These results further illustrate the complex coupling between fluid rheology and swimming gait in the motility of micro-organisms and other biological processes such as mucociliary clearance in mammalian airways. v TABLE OF CONTENTS ACKNOWLEDGEMENT . iii ABSTRACT . iv LIST OF ILLUSTRATIONS