Forces acting on control volumes in fluid dynamics are considered compressive due to the nature of pressure as an isotropic component of the stress tensor. In the context of incompressible fluids, the stress tensor is defined as σ = -pI + σ_v, where σ_v represents the viscous stress component and I is the identity tensor. The Cauchy stress relationship confirms that the pressure term contributes to a compressive traction vector on surfaces of arbitrary orientation, which is fundamental in the derivation of the Navier-Stokes equations.
Students and professionals in fluid dynamics, mechanical engineers, and researchers focusing on continuum mechanics and fluid behavior under pressure conditions.
Hi Masshakar. Welcome to Physics Forums!masshakar said:Why is it that forces (for changes in pressure across a fluid) on the control volume are generally considered compressive? Even in the derivation of the Navier-Stokes equation, it is assumed that forces from fluid pressure will be compressive? Why?