Seminar"Tomographic Velocimetry of Time Dependent Flows of Complex Fluids"Kasra Amini

Micro/Bio/Nanofluidics (Shen) Unit would like to invite you to the seminar by Kasra Amini on July 17 (Thursday).
 
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Date:   July 17, 2025
Time:  11:00-12:00
Venue: B503, OIST
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Speaker:

Kasra Amini
PhD candiate
FLOW and Fluid Physics Laboratory, Dept. of Engineering Mechanics
KTH Royal Institute of Technology, Stockholm, Sweden

Title:

Tomographic Velocimetry of Time Dependent Flows  of Complex Fluids

Abstract:

The packed meso-scale ordered, or heterogeneous structural patterns required for essential attributes of non-Newtonian fluids, set challenges in their velocimetry. Conventional optical flow measurement techniques such as Particle Image Velocimetry (PIV) and Lagrangian Particle Tracking (LPT) fail due to lack of optical access through typically opaque or translucent fluids. Shear-induced migration of particles would lead to biased measurements with techniques such as PIV and Laser Doppler Velocimetry (LDV) in high shear regions of the field. And small-scale flow apparati (i.e., rheometric and micro-scale channel-type geometries) of prominent interest in the field of non-Newtonian fluid flow and soft matter physics do not allow for application of intrusive sensory such as Hot-Wire Anemometry (HWA).

Herein, Optical Coherence Tomography (OCT) is introduced as a non-intrusive, contactless, tomographic measurement technique, capable of depth probing into the stationary and flowing medium. It is shown that not only is OCT compatible with opaqueness of the medium, but also it relies on the contrast points for back-scattering the emitted light from its depth. With high spatial- (O (1) µm), and temporal (O (10) kHz) resolutions, OCT-based velocimetry is suitable for addressing a versatile spectrum of problems in time-dependent and near-wall flows of complex fluids, such as wall slippage, mixing, instabilities, and elastoinertial interactions.

In this talk, to elaborate on the abovementioned points, we first explore the working principles of OCT and crucial aspects of data curation and signal processing needed for extracting large-scale velocity fluctuation structures on the case of shear-banding driven instabilities in the duct flow of pNIPAM microgels on smooth and rough surfaces. Next, the duct flow of highly concentrated aqueous solutions (O (1000) ppm) of high molecular weight (MW > 15 × 106 Da) polyacrylamide (PAA) are investigated, disclosing a novel elastic instability in rectangular duct flows of viscoelastic fluids, occurring as an integral block of the flow/rheology/shear-induced structural morphology feedback loop of the concentrated, entangled network of the polymer chains.

Host:
Prof. Amy Shen