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National Advisory Committee for Aeronautics, Research Memorandum - Experimental Investigation of the Effects of Viscosity on the Drag of Bodies of Revolution at a Mach Number of 1.5

Tests were conducted to determine the effects of viscosity
on the drag and base pressure characteristics of various bodies of
revolution at a Mach number of 1.5. The models were tested both
with smooth surfaces and with roughness added to evaluate the
effects of Reynolds number for both laminar and turbulent boundary
layers. The principal geometric variables investigated were after—
body shape and length—diameter ratio. For most models, force tests
and base pressure measurements-were made over a range of Reynolds
numbers, based on model length, from 0.6 million to 5.0 millions.
Schlicrcn photographs were used to analyze the effects of viscosity
on flow separation and shockkwnve configuration near the base and
to verify the condition of the boundary layer as deduced from force
tests. The results are discussed and compared with theoretical
calculations.

The results show that viscosity effects are large and depend
to a great degree on the body shape. The effects differ greatly for
laminar and turbulent flow in the boundary layer, and within each
regime depend upon the Reynolds number of the flow. Laminar flow
was found up to a Reynolds number of 6. 5 millions and may possibly
exist to higher values.

The flow over the afterbody and the shockuwavo configuration
near the base are shown to be very much different for laminar than
for turbulent flow in the boundary layer. The base pressure is much
higher with the turbulent layer than with the laminar layer, result—
ing in a negative base drag in some cases. The total drag cheracter~
istics at a given Reynolds number are affected censiderebly by the
transition to turbulent flow. The fore drag of bodies without heat
tailing or of boat—tailed bodies for which the effects of flow
separation are negligible can be calculated by adding the skin"
friction drag based upon the assumption of the lowhspoed friction
characteristics to the theoretical were drag.

For laminar flow in the boundary layer the effects of varying
the Reynolds number were found to be large, approximately doubling
the base drag in many cases and increasing the total drag about
20 percent over the Reynolds number range investigated. For
turbulent flow in the boundary layer, the effects of varying the
Reynolds number usually changed the base drag and total drag coeffi—
cients considerably.