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National Advisory Committee for Aeronautics, Technical Notes - A Method of Rapidly Estimating the Position of the Laminar Separation Point

A method is described of rapidly estimating the posi-
tion of the laminar separation point from the given pres—
sure distribution along a body; the method is applicable
to a fairly wide variety of cases. The laminar separation
point is found by the von Karman-Millikan method for a
series of velocity distributions along a flat plate, which
consist of a region of uniform velocity followed by a re-
gion of uniformly decreasing velocity. It is shown that
such a velocity distribution can frequently replaCe the
actual velocity distribution along a body insofar as the
effects on laminar separation are concerned:

An example of the application of the method is given
by using it to calculate the position of the laminar sepe
aration point on the N.A.C.A. 0012 airfoil section at zero
lift. The agreement between the position of the separa-
tion point calculated according to the present method aid
that found from more elaborate computations is very good.

Of the various available methods of calculating the
characteristics of the laminar boundary layer in two-
dimensional flow and, in particular, the pesition of the
laminar separation point. the von Karman— Millikan method
(reference 1) seems to be the most reliable. This method,
when applied to the boundary—layer flow about an elliptic
cylinder, showed good agreement with experiment when other
methods failed (reference 2). The von Karman—Millikan
method, however, has the disadvantage that the computa- "'5
tions are usually cumbersome and lengthy. Because of the
growing importance of the boundary-layer problem, some
method of rapidly finding the position of the laminar sep—
aration point is needed.

Although the calculations given in reference 1 for a
family of "double—roof" velocity distributions, consisting
of a region in which the outside velocity increases lin—
early with distance along the surface followed by a region
in which the velocity decreases linearly, partly satisfy
the need, some easy method having more general applicabil:
ity is required.