When you pour liquid into liquid, things get pretty complicated. It is true that you often can manage to maintain bubbles in the stream for a few seconds, but the situation is far too complex for useful measurement.
Exactly where to go with this question and experiments suited to answering it, is up to you, but the simplest approach would be to measure the speed of bubbles of fixed sizes rising up through the fluids in question. You would need to control for temperature, the size of the bubble, the nature of the fluid (viscosity, density, sugar content and so on). It would make a thoroughly manageable and sensible school science project, requiring no dramatic expenditure on apparatus, little risk, good sense, and fairly simple arithmetic.
Personally I would start with stopwatches and suitably fizzy fluids in cylindrical glasses on which we had drawn calibration lines equal distances apart, say 50 mm or so, depending on what is convenient. Pour in some fizzy wine, beer, or soda, wait for the main effervescence and turbulence to subside, and then locate a convenient site on the sides of the glass where a slow stream of well-separated bubbles is rising. Take repeated readings of how long it takes successive bubbles, to pass between two lines. With a digital camera and suitable calibrations, you should be able to get a good estimate of the size of the bubbles. With repeated readings of the time between marks, you should be able to get very good figures for speed.Once you've got that going, getting more elaborate figures and relationships should not be very difficult. You can draw yourself some capillary tubes of various diameters with U-shapes at the bottom, and blow bubbles out of them one at a time for measurement of their speeds of rising.
Have fun, and let us know what you discover!
