Centre of pressure
k(cp) = x(ac)/c =
Cm
--------------------------------
Cl.cos(alpha) + Cd.cos(alpha)
= centre of pressure position.
Aerodynamic Centre
Work out k(cp) for a series of values of Cl. Then plot a graph of k(cp) on the horizontal axis against Cl on the vertical axis. Cl will apparently diverges to infinity at a value of k(cp) that is likely to be somewhere between 0.15 and 0.3 - for most aerofoils about the quarter chord point.
That value of k(cp) is the position of the aerodynamic centre, k(ac).
(If you want to look at it another way, k(cp) asymptotes to k(ac) at normal to high Cl values.
G
Suggestion to the moderator, would this thread not be better off in tech-log?