Objectivity Requirement for Fluid Dynamics

A new flow theory is established through the objectivity requirement on the fluid dynamics. It was known that inhomogeneous fluid motion gave rise to viscous force while the selection of observers on different space-time points would change such an inhomogeneous character. Therefore, when the viscous force was considered as an objective existence foreign to the selection of observers, the form invariances of viscous force and momentum equation under local rotation transformation required a new dynamic field, namely the vortex field to be introduced. Then the dynamical equations of all flow fields were obtained through constructing the Lagrangian density of fluid system and using the variational approach of energy.