alt Hacker NewsHave you ever watched a movie with a fire or explosion just didn't look right because it was a scale replica? At a subconscious level, you may have picked up on how the dynamics of the smoke or debris didn't fit right with the scale. It's because the fluids in the model lacked "similitude" at the adjusted scale.
When building scaled models, adjustments have to be made to create that similitude, usually done by comparing some dimensionless number at the real scale and model scale. If you're using water, maybe you can't adjust the viscosity, so you may you have to adjust the velocity to get the same dimensionless number. Everything doesn't just scale linearly; you tweak the variables to achieve the dimensionless value so the whole system dynamics remain faithful.
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