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National Advisory Committee for Aeronautics, Technical Notes - Experimental Investigation of the Pressure Distribution About a Yawed Circular Cylinder in the Critical Reynolds Number Range

An experimental investigation has been made of the pressure dis—
tribution about a circular cylinder at yaw angles of 0°, 159, 30°, #50,
and 60° for Reypolds numbers from'below the critical value up to
about 5.0 X 10 . The Reynolds number is based on the cylinder diameter
and the component of velocity normal to the leading edge of the cylinder.

The Mach number of the flow normal to the cylinder was less than 0.2 for
all tests. The results of the investigation indicated that, for the range
of'Reynolds number near and above the critical value, the flow and force
characteristics of a yawed circular cylinder cannot be determined only
by the component of flow normal to the axis of the cylinder. For example
the critical Reynolds number decreased from 3.65 x 105 for the unyawed
cylinder to 1.00 X 105 for the 600 yawed cylinder, and the supercritical
drag coefficient, based on the flow normal to the leading edge of the
cylinder, increased from approximately 0.18 for 00 yaw to approximately
0.7# for 600 yaw. In addition, the localized regions of laminar sepa-
ration that appeared in the supercritical range of Reynolds number on
the unyawed cylinder were not as well defined at yaw angles of 15° and
300 and completely disappeared at yaw angles of #5° and 60°.

Theoretical investigations of the boundary layer on yawed, infi-
nitely long wings and bodies (references 1 to 3) have shown that the
characteristics of laminar boundary layers in planes at right angles
to the axis of the body can be considered as independent of the axial
flow. For those cases in which regions of turbulent flow exist, the
flow in normal planes cannot be shown to be independent of the axial
velocity. The degree to which flow fields in planes normal to the axis
of yawed, infinite bodies can be approximated by assuming that the normal
and axial components of the flow are independent, however, is not known
for those cases in which turbulent flow exists. The accuracy of such
an approximation would be expected to depend on such variables as the
relative extents of laminar and turbulent flow in the boundary layer,
the width of the wake and the degree of turbulence in the wake, the
existence and size of localized regions of laminar separation, and the
presence and extent of separation of the turbulent boundary layer.