The discussion clarifies that viscosity can vary with temperature in compressible flow without violating the principles of Newtonian fluids. Shear stress remains linearly proportional to strain rate as long as viscosity does not depend on strain rate. High Mach numbers are necessary for noticeable temperature-induced viscosity changes. The conversation also highlights that many fluids, including heavy oils, can be Newtonian even when their viscosity changes with temperature.
PREREQUISITESFluid dynamics engineers, mechanical engineers, and researchers in thermodynamics will benefit from this discussion, particularly those focusing on the behavior of fluids under varying temperature and pressure conditions.
Oh, so if the viscosity becomes a function of the strain rate. In that case, it would violate Newtonian fluid?boneh3ad said:No. The shear stress is still linearly proportional to the strain rate through the viscosity. It's simply the case that viscosity may not be constant. That said, viscosity varies quite slowly with temperature so the Mach number has to be relatively high to start getting the kind of heating required for the effect to be all that noticeable.
Yes. We call such fluids non-Newtonian fluids.charlies1902 said:Oh, so if the viscosity becomes a function of the strain rate. In that case, it would violate Newtonian fluid?
But even if the viscosity varies with temperature, it doesn't necessarily mean it is a non-Newtonian fluid right?Chestermiller said:Yes. We call such fluids non-Newtonian fluids.
Incidentally, for liquids, the viscosity varies pretty rapidly with temperature. Typical values are a few percent per degree C.
Chet
There are all sorts of fluids where the viscosity varies with temperature and these fluids are Newtonian. Many heavy oils are heated to make them easier to pump by reducing their viscosity.charlies1902 said:But even if the viscosity varies with temperature, it doesn't necessarily mean it is a non-Newtonian fluid right?
As long as the viscosity does not vary with the strain rate, the shear stress is still a linear function of the strain rate, even if the viscosity is varying with other parameters?
Right (like SteamKing said).charlies1902 said:But even if the viscosity varies with temperature, it doesn't necessarily mean it is a non-Newtonian fluid right?
As long as the viscosity does not vary with the strain rate, the shear stress is still a linear function of the strain rate, even if the viscosity is varying with other parameters?