Some general characteristics of fluid flow:
-
Fluid flow can be steady or nonsteady. If variables such as pressure, density, and flow velocity are constant in time throughout the fluid, the flow is steady. If not, it is nonsteady flow. In nonsteady flow, the velocities
are functions of time. -
Fluid flow can be compressible or incompressible If density
is constant, its flow is incompressible. Liquids are often incompressible, but even for highly compressible gasses changes in density are often insignificant. -
Fluid flow can be viscous or nonviscous. Viscosity is similar to friction for liquids. Kinetic Energy with the fluid flow can be transformed into internal energy by viscous forces. The greater the viscosity. the greater the external force needed to maintain flow.
-
Fluid flow can be rotational or irrotational. Imagine a leaf carried by the fluid flow. If it is rotated about an axis through its center of mass, it is rotational. Otherwise, it is irrotational.