Extensional viscosity
Extensional viscosity is a viscosity coefficient when applied stress is extensional stress.
Extensional viscosity can be measured using rheometers that apply extensional stress. Acoustic rheometer is one example of such devices.
where
For a Newtonian Fluid, the uniaxial elongational viscosity is three times the shear viscosity which can be derived using the continuity equation for incompressible fluids.
