Incompressible Flow 5 - Strain, Deformation and Rotation of a Fluid Particle

Question 1

Relationship between shear stress and velocity

Answer 1

Shear stress in a fluid flow is directly proportional to the velocity gradient (or shear strain rate)

Question 2

What is the shear strain rate?

Answer 2

Related to how far the fluid deforms

Question 3

Fluid element deformation steps

Answer 3

Solid translate
Stretch
Rotate
Deform

Question 4

Define shear strain rate

Answer 4

Rate of closure of two opposite lines in fluid element (to measure how fast the shape deforms)

Question 5

What is vorticity?

Answer 5

Indicates how fast the fluid element is turning around itself

Question 6

Define irrotational flow

Answer 6

If the vorticity is 0 and this is held everywhere in the flow (otherwise it is rotational)

Question 7

What equation can be applied everywhere in an irrotational, incompressible flow field?

Answer 7

Bernoulli’s equation (with the same constant)

Question 8

What is vorticity related to and used for?

Answer 8

Related to the local angular rate of rotation
Used in flow analysis (e.g. PIV)