The viscosity terms in x-momentum equation is \(\frac{\partial\tau_{xx}}{\partial x}+\frac{\partial\tau_{yx}}{\partial y}+\frac{\partial\tau_{zx}}{\partial z}\). In a more general form, this becomes div(μ gradu). Which of these relations is used for this transformation?
(a) Thermodynamic relations
(b) Stress-strain relations
(c) Fluid flow relations
(d) Geometric relations
The question was posed to me during an online interview.
The query is from Navier Stokes Equation topic in portion Governing Equations of Fluid Dynamics of Computational Fluid Dynamics