28.1. Introduction

Despite the fact that there are more linear techniques and methods than nonlinear ones, the physical world is a nonlinear place. Fluid mechanics frequently exhibits nonlinearity, including the following:

  • The material parameters used in modeling heat conduction, such as conductivity or specific heat, may be temperature dependent, and thus cause a nonlinearity.

  • In Newtonian flows, inertia terms are quadratic in terms of the velocity components; also, the shear-rate dependence of the viscosity causes nonlinearity.

  • In nonisothermal flow problems, heat convection generates terms that are products of velocity components and temperature gradients.

  • In viscoelastic flows, the constitutive equations are highly nonlinear.

The evolution procedure in Ansys Polyflow greatly simplifies the handling of the computational difficulties of nonlinear problems.