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National Advisory Committee for Aeronautics, Technical Notes - Study of the Pressure Rise Across Shock Waves Required to Separate Laminar and Turbulent Boundary Waves

A dimensional study and an experimental investigation have been
made on the pressure rise across shock waves required to cause separa-
tion of the boundary layer on a flat plate. The interaction of shock
wave and boundary layer was investigated experimentally when the bound-
ary layer was caused to separate from the surface of a tube of large
diameter compared with the boundary-layer thickness, by means of a
collar mounted on the tube. The investigation was conducted in a
Langley blowdown jet at a Mach number of 3.03, for a Reynolds number
range from about 2 x 106 to 19 X 106.

The dimensional study, based on certain simplifying assumptions,
indicates that the critical pressure rise across a shock wave which
just causes separation of the boundary layer is proportional to the
skin friction; The available experimental data on flat plates indicate
that the critical pressure rise varies as the Reynolds number to the
power for laminar boundary layers and as the Reynolds number to the
number for turbulent bdundary layers; therefore, these results are
in agreement with the prediction of the dimensional study. The Mach
number effect on the critical pressure coefficient for turbulent bound-
ary layers appears to follow that which is predicted for the skin-friction
coefficient on a flat plate. The significance of the results obtained
is discussed relative to certain practical design problems, such as
supersonic-diffuser design.

Increasing interest has been shown in recent years concerning the
phenomena associated with the interaction of shock waves and boundary
layers. A comprehensive review of the present status of the problem
from both experimental and theoretical considerations is given in
reference 1. Experimental investigations show that—the State of th
boundary layer, thatfiis, whether the boundary layeffis laminar or tur-
bulent, largely determines the resulting shock-wave_ configuration and
the upstream influence of the shock wave on the boundary layer. (See
references 1 to h. ) The studies up to the pr-esent—time have been con-
cerned primarily with the differences in shock—wave pattern for inter-
action with laminar and turbulent boundary layers; however, it was
desired in this investigation to determine the conditions under which
a boundary layer separates when a shock wave impinges upon it.