The discussion revolves around the behavior of Newtonian fluids in the context of compressible flow, particularly focusing on how viscosity may vary with temperature and its implications for the definition of Newtonian versus non-Newtonian fluids.
Participants express differing views on the implications of varying viscosity with temperature for classifying fluids as Newtonian or non-Newtonian. There is no consensus on whether temperature-dependent viscosity inherently leads to non-Newtonian behavior, as some maintain that it does not if strain rate remains constant.
Participants discuss the nuances of viscosity behavior in relation to temperature and strain rate, indicating that definitions and classifications may depend on specific conditions and assumptions that are not fully resolved in the discussion.
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?