fluid parcel

But also other ways of labeling the fluid parcels are possible.

Another name for fluid parcel is material element of fluid.

Another approach is by using the Lagrangian frame of reference, following the fluid parcels.

On the other hand, in the Lagrangian specification, individual fluid parcels are followed through time.

In this reference frame, fluid parcels are labelled and followed through space and time.

The end position in the Lagrangian description is obtained by following a specific fluid parcel during the time interval.

The motion of a fluid parcel, or trajectory, is given by the following system of ordinary differential equations:

This Lagrangian drift of the fluid parcels is known as the Stokes drift.

As it moves, the mass of a fluid parcel remains constant, while-in a compressible flow-its volume may change.

Note that in an incompressible flow the volume of the fluid parcel is also a constant (isochoric flow).

The fluid parcels, as used in continuum mechanics, are to be distinguished from microscopic particles (molecules and atoms) in physics.

The zonal pressure gradient and eddy stresses cause torque that changes the absolute angular momentum of fluid parcels.

Thus, as a fluid parcel moves equatorward (βy approaches zero), the relative vorticity must increase and become more cyclonic in nature.

Conversely, if the same fluid parcel moves poleward, (βy becomes larger), the relative vorticity must decrease and become more anticyclonic in nature.

Under the assumption of incompressibility, the density of a fluid parcel is constant and it follows that the continuity equation will simplify to:

When the flow is incompressible, does not change for any fluid parcel, and its material derivative vanishes: The continuity equation is reduced to:

In astrophysics, particularly the study of accretion disks, the epicyclic frequency is the frequency at which a radially displaced fluid parcel will oscillate.

Conservative tracers remain constant following fluid parcels, whereas reactive tracers (such as compounds undergoing a mutual chemical reaction) grow or decay with time.

Then the material derivative describes the temperature evolution of a certain fluid parcel in time, as it is being moved along its pathline (trajectory) while following the fluid flow.

The concept derives from Newton's Second Law when applied to a fluid parcel in the presence of a background stratification (in which the density changes in the vertical).

Since a fluid parcel with label α traverses along a path of many different Eulerian positions x, it is not possible to assign α to a unique x.

For a pure wave motion in fluid dynamics, the Stokes drift velocity is the average velocity when following a specific fluid parcel as it travels with the fluid flow.

The potential density of a fluid parcel at pressure is the density that the parcel would acquire if adiabatically brought to a reference pressure , often 1 bar (100 kPa).

In fluid dynamics, within the framework of continuum mechanics, a fluid parcel is a very small amount of fluid, identifiable throughout its dynamic history while moving with the fluid flow.

In most flows of liquids, and of gases at low Mach number, the density of a fluid parcel can be considered to be constant, regardless of pressure variations in the flow.