Effect of Mach Number on Boundary-Layer Transition in the Presence of Pressure Rise and Surface Roughness on an Ogive-Cylinder Body with Cold Wall Conditions Page: 3 of 31

                                
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very different for laminar and turbulent boundary layers. Therefore, it
is a primary concern of the designer to know the extent to which the
boundary-layer flow is laminar or turbulent so that cooling requirement
calculations for the vehicle can be made. If the operating conditions
of the vehicle are such that heating is of little concern, knowledge of
the extent of laminar flow can nevertheless be important in determining
the efficiency of flight.
The theoretical work of Lees and Lin (ref. 1) and Van Driest (ref. 2)
predicts that for small two-dimensional disturbances the stability and
extent of laminar flow will be increased by heat flow from the boundary
layer to the body. This same analysis shows that on a flat plate with
zero pressure gradient for Mach numbers between 1 and 9, if the heat trans-
fer is sufficient, the laminar boundary layer will be stabilized for all
values of Reynolds number. Investigations such as those of Scherrer
(ref. 3) and Czarnecki (ref. 4) have confirmed experimentally the benefi-
cial effect of heat transfer to the body. The experiments of reference 5
in the predicted regime of infinite laminar stability showed that transi-
tion will occur in this regime on roughened surfaces or in the presence
of adverse pressure gradient. However, the amount of data collected in
this regime, references 5, 6, and 7, is thus far rather small, and to the
author's knowledge, is limited to Mach numbers below 3.7.
The present investigation was initiated at the NACA Ames Laboratory
primarily to determine how Mach number affects transition within the pre-
dicted regime of infinite laminar stability. Previous wind-tunnel data, *
reference 8, had shown a decrease in transition Reynolds number with ris-
ing Mach number for the condition of small heat transfer.l A limited
number of observations had been made also of the effect of Mach number
on transition Reynolds number for the condition of constant wall tempera-
ture near stream static temperature. These observations, from the super-
sonic free-flight wind tunnel and other sources, showed a strong stabiliz-
ing influence on the laminar boundary layer of increasing Mach number.
A purpose of the present test, then, was to investigate systematically
the effect of Mach number on transition Reynolds number for the condition
of constant, low wall to free-stream temperature ratio. In addition, the
results obtained provide information on the effect of surface roughness,
since roughness was varied to position transition in the field of view
on the model and therefore became a necessary part of the investigation.
As was the case in reference 5, it was observed that pressure rise was
also affecting transition position when transition was not controlled by
roughness. This effect became a part of the investigation and is con-
sidered along with the effects of Mach number and surface roughness.
1Potter (ref. 9) had suggested that the .observed effect of Mach number
on transition in the Naval Ordnance Laboratory wind tunnels was influenced
by other factors in addition to Mach number.
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