Strain Rate Components

• Consider a fluid element of original lengths dx, dy and dz along the coordinate axes x, y and z respectively.

• The rate of volumetric dilatation per unit original volume of the element can be written as

[ is a small interval of time]

• The left hand side of the Eq. (9.7) or (9.8) can be physically identified as the rate of volumetric dilatation per unit volume of a fluid element in motion which is obviously zero for an incompressible flow.