## inviscid flow and viscous flow

viscous flows are always rotational because of shear stress that is exerted on the fluid element due to viscosity.

what about the inviscid flows? can they be rotational ? if yes then what are the factors which makes the inviscid flows rotational?
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Recognitions:
By rotational do you mean have vorticity? If so then yes, in fact the fundamental equations can be written in terms of vorticity rather than velocity by taking the curl of the equations.

 Quote by http://en.wikipedia.org/wiki/Vorticity For any flow, you can write the equations of the flow in terms of vorticity rather than velocity by simply taking the curl of the flow equations that are framed in terms of velocity (may have to apply the 2nd Fundamental Theorem of Calculus to do this rigorously). In such a case you get the vorticity transport equation which is as follows in the case of incompressible (i.e. low mach number) fluids, with conservative body forces
$$\frac{D\omega}{Dt} = \omega \cdot \nabla u + \nu \nabla^2 \omega$$
 okay fine but what is it that is making it to rotate? like in viscous flows its the shear stress that causes the rotation of the fluid element.

Recognitions: