Fluid flows are categorized by dimensionality and behavior, with one-dimensional flow being the simplest form, where properties like velocity and pressure change only along a single axis. Water moving through straight pipes exemplifies this flow type, as variations in other directions are minimal. One-dimensional analysis helps simplify understanding such flows, focusing solely on changes along the pipe's length.

Two-dimensional flow involves changes in both length and height, as seen in air moving over flat surfaces like a bridge deck. Variations occur in two directions, making calculations more complex than in one-dimensional flow. Three-dimensional flow, which is the most intricate, involves variations in all three spatial dimensions: length, height, and depth. The wind circulating around buildings demonstrates this type of flow, where fluid properties differ across multiple directions.

Flows are also classified by how fluid properties change over time. Steady flow describes situations where properties like velocity and pressure remain constant at any point over time. A pipeline in a municipal water supply system is a typical example. In contrast, unsteady flow, such as stormwater runoff, features changes in fluid properties over time. Analyzing unsteady flows requires attention to time-dependent variations in velocity and pressure.

The distinction between laminar and turbulent flow is also essential. Laminar flow features smooth, orderly fluid movement, with fluid layers moving in parallel with minimal mixing. Groundwater seeping through soil layers often exhibits laminar flow. Turbulent flow, however, involves chaotic and irregular motion, often seen in rivers during floods. Fluid particles interact in complex ways, creating swirling eddies and vortices, which greatly complicates the analysis of such flows.