2003 IRISH SCIENTIST YEAR BOOK

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Loreto College, Coleraine, Co. Derry
Mairead Mary McCloskey
Chaotic fluids - an examination of phase transitions in Taylor-Couette flow

Mairead McCloskey

An experimental apparatus to study the behaviour of the Taylor-Couette system was designed, built and tested. By means of computer controlled stepper-motors, the apparatus allows precisely controlled driving of independently rotating, co-axial cylinders, between which the fluid under study was confined. Drive speeds were controlled to an accuracy of better than 0.5%.

The flow of the fluid was visualised using Kalliroscope, a suspension of mica crystals which exposes fluid flow directions by differential light scattering. Flow regimes were initially identified qualitatively and then characterised by measuring the time variation of the intensity of light scattered from the fluid, using a digital video camera. Phase transitions between the flow regimes were mapped on a phase plane whose co-ordinates are Reynold's numbers (which relate density, velocity and pipe diameter) of the inner and outer cylinders (Ro-Ri space). The predicted rapid onset of chaotic behaviour over very small increments in Reynolds numbers was observed.


Wavy Vortex flow

Twelve distinct flow regimes were identified and the corresponding phase transitions were mapped on the Ro-Ri phase plane. Significant departures from published research were observed. In particular a number of phase transitions appear to be gradational over significant ranges in Ro and Ri. Detailed investigations of selected transitions showed locally strong hysteresis which was shown to vary systematically with Reynold's number in the counter rotating condition. Hysteresis was not observed for co-rotating cylinders. Modulation of the driving Reynolds numbers, by the periodic forcing of either cylinder, was found to have no measurable effect on the location of phase transitions in Ro-Ri space.

Mairead Mary McCloskey, who entered her project in the Senior Individual Section in the Chemical, Physical & Mathematical Sciences Category at the Esat BT Young Scientist & Technology Exhibition in January 2003, won one of the top prizes - Runner-up Individual.

She also won the Intel Student Award, and went on to win five top prizes at The Intel International Science and Engineering Fair in Cleveland, Ohio, in May 2003.
Her teacher was Mr Brian McKenna.

This article was sponsored by Oldbury Publishing