Professor Fletcher and his team of students from the Centre for Advanced Computational Engineering and Science discovered that the behaviour of the bubbles varies not only with the shape of the glass, but with the size of the bubbles themselves. Bubbles in the centre of the glass move upwards relatively quickly and drag liquid with them. Therefore the liquid moving upwards must eventually move downwards again. The researchers found that near the walls of the glass, the liquid indeed moved downwards. This downward-moving liquid has a dragging effect on the bubbles.
Larger bubbles are more buoyant than smaller bubbles, and continue to move upwards.
Of course, the primary use of our software is solving far more serious fluid flow problems - optimising vehicle aerodynamics, speeding up the mixing process in chemical reactors, improving the performance of ventilation fans, that sort of thing. The full story, in PDF format. Animated illustrations of the flow in a pint of Guinness. The mathematics used to solve the problem of a pint of Guinness is the same as that used for weather forecasting - they're both fluid dynamics. One of the interesting aspects of the flow diagrams above is the presence of eddies .