What is Self-similar solutions? Any online notes or books please..........

The similar solutions (this should be the right name) are solutions that are invariant under the proper scaling of the independent variables.

Some example are the round jet and the blasius profile, both solutions of the boundary layer equations.

In this case, if x is the axis of the jet or the direction of the wall and y the transverse direction, the two solutions are costant with x / h(x) with h(x) the scaling function and so a single solution of the form f(y) exists and is valid for each x / f(x).

Several books exists on similar solutions; actually every boundary layer section should, at least partially, contains some informations about it.

hope this helps

Scaling, self-similarity, and Intermediate Asymptotics by Barenblatt.