  A general set of fluid equations that allow for energy-conserving momentum
transport by gyroscopic motion of fluid elements is obtained. The equations are
produced by a class of action principles that yield a large subset of the known
fluid and magnetofluid models, including gyroviscosity. Analysis of the action
principle yields broad, model-independent results regarding the conservation
laws of energy and linear and angular momenta. The formalism is illustrated by
studying fluid models with intrinsic angular momentum that may appear in the
contexts of condensed matter, biological, and other areas of physics.
