<DOC>
<DOCNO>
363
</DOCNO>
<TITLE>
an alternative formulation of the problem of flutter
in real fluids .
</TITLE>
<AUTHOR>
chu,w.h. and abramson,h.n.
</AUTHOR>
<BIBLIO>
j. ae. scs. 26, 1959.
</BIBLIO>
<TEXT>
it is well known, in steady flow, that the actual lift curve
slope is somewhat less than that predicted by inviscid flow
theory, even at small angles of attack .  as the stall angle is approached,
the lift curve slope continually decreases and thus deviates
even more from the theoretical value .  pinkerton employed
the measured circulation to determine the pressure distribution
and found that the resulting prediction of the moment
is considerably improved over that given by the classical theory .
this amounts to replacing the conventional kutta-joukowski
condition with the condition that the total lift should agree with
the measured value, and this, in turn, completely determines the
flow pattern .  practically, this is accomplished by giving a
fictitious camber to the profile .  since potential flow theory is
valid outside of the boundary layer, once the boundary-layer
thickness is known, the potential flow may be corrected for the
displacement thickness and the viscous wake by appropriate
source distributions .  the boundary layer cannot be evaluated,
of course, until the potential flow is known and the circulation is
applied .  a criterion to determine the circulation, by generalizing
the kutta-joukowski condition, was proposed by preston
and spence by assuming that the pressure at the trailing edge
shall have the same value when determined from the potentialflow
values above and below the airfoil .  this procedure gives
qualitative information concerning viscous effects in steady
flow .
</TEXT>
</DOC>
