Question

What are the Newtonian constitutive assumptions regarding relationship between stress tensor and velocity gradients?

(a) Linear and isotropic

(b) Constant

(c) Linear

(d) Non-Uniform

The question was posed to me in a national level competition.

My question is from Navier-Stokes Equations of Motion topic in portion Fluid Dynamics of Fluid Mechanics

Answer 1

Right answer is (a) Linear and isotropic

To explain I would say: Newtonian fluid is a fluid in which the viscous stresses arise due to its flow. The flow experiences a strain rate at every point. The strain rate is related to the constant viscosity tensor that does not depend upon the stress and velocity of the flow. Thus, the relationship is linear and isotropic.