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National Advisory Committee for Aeronautics, Report - Experimental and Theoretical Studies of Area Suction for the Control of the Laminar Boundary Layer on an NACA 64A010 Airfoil

The stability theory for the incompressible laminar
boundary layer is an analysis of the damping or amplifica—
tion of vanishingly small two-dimensional aerodynamicslly
possible disturbances in the boundary layer (reference 1).
A possible definition in the physical sense of a small dis-
turbance is one that does not produce transition from laminar
to turbulent flow at its origin in contrast- with a large
disturbance, which does cause immediate transition. Small
disturbances may either amplify as they progress down-
stream and eventually grow large enough to cause turbulence
or they may be damped and cause no change in the down-
stream flow; if small disturbances of all frequencies are
damped rather than amplified, the laminar boundary layer
is considered stable (reference 2).

Theoretical investigations have been made of the character—
istics of flows past a flat plate through which there is a. small
normal velocity and, in addition, the stability theory has
been used to calculate the stability of the laminar boundary
layer for this type of flow. Examples of some of this theo—
retical work. can be found in references 3 to 7 and in British
work (not generally available). The results of these analy-
ses indicate that a small normal velocity into the surface
at all points along the surface has a. large stabilizing efl’ect on
the laminar layer. Inasmuch as there appear to be no data
that show this effect experimentally, an investigation of the _
effect- of area suction on the boundary—layer stability is being
made in the Langley low-turb ulence pressure tunnel. Three_
suction arrangements were investigated on an NACA 645010
airfoil that had porous sintered-bronze surfaces Measurer
ments were made up to a Reynolds number of approximately
20><106 and included wake drags, suction-flow quantities,
suction losses, and a few boundary—layer velocity profiles.