<DOC>
<DOCNO>
710
</DOCNO>
<TITLE>
the smallest height of roughness capable of affecting boundary-layer
transition .
</TITLE>
<AUTHOR>
smith, a.m.o. and clutter, d.w.
</AUTHOR>
<BIBLIO>
j. aero. sc. april, 1959. p.229-245, 256 .
</BIBLIO>
<TEXT>
an investigation was made to determine the smallest size of isolated
roughness that will affect transition in a laminar-boundary layer .
critical heights for three types of roughness were found in a low-speed
wind tunnel . the types were /1/ two-dimensional spanwise wires, /2/
three-dimensional discs, and /3/ a sandpaper type . in addition to type
of roughness, test variables included the location of roughness, pressure
distribution, degree of tunnel turbulence, and length of natural
laminar flow .
the most satisfactory correlation parameter was found to be the roughness
reynolds number, based on the height of roughness and flow properties
at this height . the value of this critical reynolds number was
found to be substantially independent of all test variables except the
shape of roughness . this parameter also correlates well other published
 data on critical roughness in low-speed flow . the value of the roughness
reynolds number necessary to move transition forward to the roughness
itself was also determined for the three types of roughness and was
 found to be approximately constant for a given type of roughness .
an investigation of the limited amount of available data on critical
roughness in supersonic flow indicates that the effects of roughness may
 still be correlated by the roughness reynolds number . the value of
this reynolds number depends primarily on the mach number at the top of
the roughness . when this mach number is greater than 1.0, the roughness
 reynolds number based on conditions behind a shock is probably the
characteristic parameter .
</TEXT>
</DOC>
