A theory is built from the following materials or has a structure like:
In the Name of God
Dealing with viscous flow assumptions, one may consider the following aspects influencing aerodynamic characteristics as well as other influencing factors:
Therefore, the viscous flow is characterized by the following aspects:
1- Viscous Stress: the velocity gradient + viscosity (indicated by Re number)
Furthermore, turbulence also affects both velocity gradient and viscosity
2- Pressure Loss: the pressure gradient + separation or bubbles