2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/125000In the above paper by Bechtel, Cai, Rooney and Wang, Physics of Fluids, 2004, 16, 3955-3974 six different theories of a Newtonian viscous fluid are investigated and compared, namely, the theory of a compressible Newtonian fluid, and five constitutive limits of this theory: the incompressible theory, the limit where density changes only due to changes in temperature, the limit where density changes only with changes in entropy, the limit where pressure is a function only of temperature, and the limit of pressure a function only of entropy. The six theories are compared through their ability to model two test problems: (i) steady flow between moving parallel isothermal planes separated by a fixed distance with no pressure gradient in the flow direction (Couette flow), and (ii) steady flow between stationary isothermal parallel planes with a pressure gradient (Poiseuille flow). The authors found, among other, that the incompressible theory admits solutions to these problems of the plane Couette/Poiseuille flow form: a single nonzero velocity component in a direction parallel to the bounding planes, and velocity and temperature varying only in the direction perpendicular to the planes.Comment on S. Bechtel, M. Cai, F. Rooney and Q. Wang [Physics of Fluids, 2004, Vol. 16, pp. 3955-3974]Fluid Dynamicstext