Arezoo Motavalizadeh Ardekani
O’Hara, C.S.C., Assistant Professor
369 Fitzpatrick Hall
Notre Dame, IN 46556
574.631.6676
aardekan@nd.edu
Research in our group focuses on understanding fundamental properties of multiphase flows of Newtonian and non-Newtonian fluids that are relevant to complex fluids, biofluids, and micro/nanofluids used in biomimetic applications, biomedical devices, alternative energy, and environmental remediation.
I'm co-organizing a winter conference on "Active Fluids: Bridging Complex Fluids and Biofluids" at the Aspen Center for Physics. The organizing committee members are: A. Ardekani (Notre Dame), Y. Renardy (Virginia Tech), J. Zhang (New York University and Courant Institute), E. Lauga (Cambridge), D. Saintillan (University of Illinois Urbana Champaign). Join us Jan 27-Feb 1 2014!
Funded by NSF Grant No. CBET-1150348- CAREER
Microbial habitats are rarely at rest (e.g. ocean, blood stream, flow in porous media and flow through membrane filtration processes). In order to study the hydrodynamics of bacterial response in a vortical flow, we utilize a microfluidic system to mimic some of the important microbial conditions at ecologically relevant spatiotemporal scales. We experimentally demonstrate the formation of “ring”-shaped bacterial collection patterns and subsequently the formation of biofilm streamers in a microfluidic system. Acoustic streaming of a microbubble is used to generate a vortical flow in a microchannel. Due to bacteria’s finite-size, the microorganisms are directed to closed streamlines and trapped in the vortical flow. The collection of bacteria in the vortices occurs in a matter of seconds and, unexpectedly, triggers the formation of biofilm streamers within minutes.
Funded by NSF Grant No. CBET-1150348- CAREER
Spatial distribution of
microorganisms
in a vortical flow of a complex fluid.
We have shown that the rheological properties of exopolysaccharides secreted by microorganisms play an important role in their interaction with background flow field. The normal stresses generated due to the presence of polymer molecules lead to aggregation of microorganisms in a vortical flow field. The shape and formation rate of these aggregation patterns depend on motility, vorticity, and rheological properties of exopolysaccharides. Given the viscoelastic nature of extracellular polymeric substances, these results suggest new mechanisms for ubiquitous processes among microorganisms, such as bacterial aggregation and biofilm formation.
Funded by NSF grant No. CBET-1066545
Propulsion speed of small organisms is strongly
affected by unsteady hydrodynamic forces.
Small planktonic organisms ubiquitously display unsteady or impulsive motion to attack a prey or escape a predator in natural environments. Despite this, the role of unsteady forces such as history and added mass forces on the low Reynolds number propulsion of small organisms, e.g. Paramecium, is poorly understood. In this paper, we derive the fundamental equation of motion for an organism swimming by the means of surface distortion in a nonuniform flow at a low Reynolds number regime. We show that the history and added mass forces are important as the product of Reynolds number and Strouhal number increases above unity.
Funded by NSF grant No. CBET-1066545
Flow field generated by small organisms is
markedly affected by stratification.
Swimming of microorganisms, a topic of long-standing interest for both biologists and physicists, has been mostly studied in homogeneous fluids. However, many aquatic environments, including oceans, lakes and the interstitial fluid in sea ice, are routinely stratified, due to salt- or temperature-induced variations in fluid density. We have analytically showed that stratification dramatically alters the flow field induced by the organism, generating recirculation cells in the velocity field. The size of these cells scales with Ra-1/4 where the Rayleigh number, Ra, measures the relative importance of buoyancy and diffusion. For stronger stratification, cells are more compressed and the velocity field decays faster with distance from the organism. These less conspicuous flow fields could affect those predator-prey interactions based on sensing of hydromechanical signals, potentially acting as a ‘silencer’ for swimming prey or a ‘stealth’ mechanism for approaching predators. We use a combination of methods that range from simple scaling laws to detailed computational models and sophisticated experimental equipments to explore the effects of stratification on swimming of small organisms.
Funded by Schlumberger
Jet Extensional Rheometry enables evaluation of
transient extensional rheological properties for even
very weakly elastic fluids.
Understanding the instability and breakup of polymeric jets is important for a wide variety of applications including inkjet printing, and spraying of fertilizers and paint. Such fluids are typically only weakly viscoelastic and the jetting/breakup process involves a delicate interplay of capillary, viscous, inertial and elastic stresses. The initial growth of disturbances can be predicted using linear instability analysis for small perturbations. A viscoelastic jet is initially more unstable when compared to a Newtonian fluid of the same viscosity and inertia. As the radius of the jet thins under the action of surface tension, elastic stresses grow and become comparable to the capillary pressure, leading to formation of a uniform thread connecting two primary drops. This beads-on-a-string structure can be captured by the Oldroyd-B model, and the radius of the thin cylindrical ligament connecting the beads necks down exponentially in time. The finite time breakup of the jet observed experimentally can be captured using the nonlinear Giesekus model. We show that by understanding the physical processes that control each phase of the temporal evolution in the jet profile it is possible to extract transient extensional viscosity information even for very low viscosity and weakly-elastic liquids. This is especially useful since filament-stretching and capillary breakup elongational rheometers face challenges for low-viscosity elastic polymer solutions.
Particles Interaction, Deformation, and Collision in Viscous and Viscoelastic Fluids, funded by NSF grant No. CBET-0828104
