<DOC>
<DOCNO>
484
</DOCNO>
<TITLE>
the influence of two-dimensional stream shear for airfoil
maximum lift .
</TITLE>
<AUTHOR>
vidal,r.j.
</AUTHOR>
<BIBLIO>
j. ae. scs. 29, 1962, 889.
</BIBLIO>
<TEXT>
  the effects of stream velocity gradients on airfoil maximum
lift are defined with experimental data obtained in a simulated
two-dimensional slipstream .  the experimental results show
that when positioned near the slipstream plane of symmetry, the
airfoil maximum lift varies markedly with location in the slipstream
.  in moving the airfoil from above to below the slipstream
plane of symmetry through a total distance corresponding
to the airfoil thickness, force data and boundary-layer observations
show that boundary-layer separation is delayed to higher
angles of attack, and the airfoil maximum lift is doubled .
  it is concluded that the destalling effect observed in the nonuniform
slipstream is not associated with slipstream boundary
interference, but stems from the influence of the large local slipstream
shear on airfoil characteristics .  the effects of uniform
and nonuniform shear on airfoil lift and pressure distribution are
discussed, within the framework of existing first-order, smallshear
theory, to show that these effects of shear tend to promote
stall .  a pohlhausen calculation of the laminar boundary layer
in a stream with shear is used to identify and to assess the effects
of stream shear on boundary-layer separation criteria .  it is
demonstrated that these effects are negligibly small, and that the
uniform-flow criterion applies .  it is concluded on the basis of
the experimental data that the observed destalling phenomenon
stems from a shear effect of higher order than those treated in the
inviscid theories .  it is hypothesized that it is a second-order
effect, fixed by the product of the stream shear and the derivative
of the shear, which was large in the present experiments .
</TEXT>
</DOC>
