I was going through some basic description of streamlines in which I noticed that streamlines in an Ideal fluid where shown "equidistant" from each other at a place . whereas in the real fluid somewhere they where dense and somewhere rarer at the same place...why is it so ?? Which assumption we too while taking the streamlines equidistant from each other in a small area in Ideal fluid??
The stream function is defined such that there is a constant volumetric flow rate between two stream lines of constant value. If two stream lines converge towards each other and become more 'dense', it indicates that the velocity of the fluid increases so that the volumetric flow rate remains unchanged.