Moving in steady, parallel layers, laminar flow is the most frequent type of movement used in aquariums. Typically easy to produce in aquariums with pumps called powerheads, laminar flow helps fish by providing steady movement in one direction. In actual bodies of water, laminar flow is found in areas with greater depths. In fluid dynamics, laminar flow is described as bullet-shaped, with more velocity at its center than toward its sides.
Surge flow is perhaps best described as wave motion. Surge flow, like laminar flow, moves in one parallel layers, but its flow is stronger and isn't as steady as laminar. Surge flow is followed by a weaker flow in the opposite direction. This back-and-forth flow is reflective of the waves found in the ocean and other bodies of water. Typically, surge flow is created by an outside force, such as wind or weather.
In turbulence flow, water moves unpredictably in all directions. This happens when currents or outside forces push water into itself. There is very little velocity in this type of flow, which doesn't allow it to help propel ships or fish, since the water loses energy colliding with itself. For an aquarium, this random activity actually works best for fish, as it moves food and oxygen throughout a tank.
Many different devices are available for aquarium hobbyists who want to change water flows. Powerheads can create a laminar flow to give some movement to the water in the tank. These are the simplest tools to create water flow. Other devices, such as an oscillating pump or even a small wavemaker, add additional movements to aquariums. Wavemakers can replicate ocean-like currents, benefiting aquarium life.