There are several situations in which the Newtonian mechanisms are taken over by
non-Newtonian ones, e.g. when viscous flows viscosity are found not be in direct relation to stresses. With what parameters or properties can one identify this transition to non-Newtonian mechanics?
In the context of fluid mechanics here is a simple definition: a fluid is said to be non-Newtonian if the shear stress is no longer proportional to the rate of strain, and the fluid does not have a yield stress. A plot of shear stress versus rate of strain ( also called the shear rate) should be a straight line. Deviations from a straight line indicate shear thinning behavior, or shear thickening behavior ( depending on the change in slope). A non-newtonian fluid can also exhibit viscoelastic behavior: For example the strain-rate or stress depends on time, or there is a hysteresis effect in the stress- strain curve. A polymer solution in which molecular arrangement can occur during deformation is an example of viscoelastic behavior. Note for pure elastic materials stress and strain are in phase ( e.g. Hooke's law). This is not the case with viscoelastic fluids that exhibit the concept of fading memory.
.
Just adding a small detail responses from Brian and Joachim.
.
When the apparentt Reynolds number decrease is more evident the rheological properties of non-Newtonian fluids.
.
At high Reynolds number the apparente dinamical effects are more important than the viscous effects (mainly for rough turbulent flow)..
.
- Badges
- Science topic
- Similar topics
- Engineering
- Thermal Engineering
- Thermofluid
- Fluid Mechanics
- Fluid Dynamics