Micro/Bio/Nanofluidics (Shen) Unit would like to invite you to the seminar by Dr. Richard Hodgkinson on September 16 (Tuesday).
 
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Date:   September 16, 2025
Time:  11:00-12:00
Venue: L4E01, OIST
Zoom: https://oist.zoom.us/j/94222191180?pwd=hSfUK2P0ZssllchIyW2L9naAV29mmi.1
Meeting ID: 942 2219 1180
Passcode: 220377
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Speaker:

Richard Hodgkinson
NFFDy (National Fellowships in Fluid Dynamics) Fellow
School of Chemical, Materials and Biological Engineering
University of Sheffield, UK

Title:

The impasse of strain rate quantification in arbitrary and kinematically mixed flow fields

Abstract:

The quantification of strain rates being experienced by a fluid element is fundamental to the field of rheology. When a flow field is kinematically pure, or we assume a flow field is kinematically pure, then our standard measure of total strain rate can be used. However, as soon as our flow field is not kinematically pure and we desire separate measures of shear and extension rate across the entirety of even a 2D simulated flow, the situation is much more complex with no currently accepted way to achieve this. This problem contains particular parallels with the identification of rotating flows and vortexes in turbulence.

Connecting with a special session being organised by the presenter at the 2025 UK Fluids Conference aiming to bring together the rheology and turbulence communities on this specific issue, this seminar will present existing methods, note their shortcomings, as well as highlight an apparent disconnect with our current experimental practices in rheometry. Following this, two areas of interest to the presenter will be introduced that exemplify the importance of this issue: a. the design of channels for constant extension rate flow where we are interested in extension rate not at the channel centreline but across the entire flow field, and b. experimentally studying the effect of extensional flow on shear viscosity/rheology, using a technique that relies on quantifying shear and extension rates to perform both strain rate and stress measurement within the core of a kinematically mixed flow.

Host:
Prof. Amy Shen