Meaning of Irrotationality

It should be noted that the concept of Irrotationality applies to a fluid element in a given flow than to the flow itself. The main flow may be a vortex where the streamlines are circles. But the individual elements of fluid may not rotate or distort making the flow irrotational. This is shown in Fig. 4.10 where an irrotational flow about an aerofoil is sketched. Note that even though the main follows a path which seems to indicate distortion, the fluid elements are simply translated.

Figure 4.10: Meaning of Irrotationality.

(c) Aerospace, Mechanical & Mechatronic Engg. 2005
University of Sydney