TMB results with those obtained by Hall (5) and Schubauer (1) 
shows that the data for water are not only in agreement with 
the slope of the decay curve, but also in order of magnitude, 
Differences between Hall's curve and Schubauer's curve have been 
attributed (5) to differences in initial wind-tunnel turbulence. 
PRINCIPAL DIFFICULTY OF THE HOT WIRE IN WATER 
It has been found in wind tunnel applications of the 
hot-wire anemometer that frequent brushing of the wire is com- 
pulsory for maintainance of a constant calibration. The rate of 
dirt accumulation in water, even drinking water, is many times that 
for air and the calibration of the wire changes within a matter of 
minutes in water. Constancy of calibration is accomplished only 
by very frequent brushing. Consistency of results where a constant 
calibration is required, such as in the measurement of intensity, 
ean only be obtained by observing data immediately after the wire 
has been cleaned. In measurement of correlation, however, it was 
assumed that both wires were accumulating dirt at approximately the 
same rate, and hence, changing calibration at the same rate. Al- 
though their sensitivities were gradually diminishing, the wires 
could still measure correlation provided their response character= 
istics remain nearly alike. Even in the correlation measurements, 
however, the two wires were frequently cleaned. 
APPLICATION OF HOT WIRES TO TURBULENT 
BOUNDARY-LAYER INVESTIGATIONS 
Turbulence in boundary layers has been a subject for in- 
vestigation for some time in wind tunnel work. Only recently, 
however, has research been undertaken at TMB to investigate the 
nature of the boundary layer on ship models. Not only is it of 
importance to know the characteristics of the laminar and turbu- 
lent regions, but locating the region of transition from laminar 
to turbulent boundary layer is essential in estimating frictional 
resistance. 
Locating the region of transition under variable opera- 
ting conditions, therefore, was the first phase of the investiga- 
tion undertaken with the hot wire. Preliminary tests have been 
conducted on a wood friction plane 6 feet long, 12 inches wide, 
and 0.50 ineh thick with ends tapering to a thickness of 0.04 
inch, The plane,fitted with 6 fixed hot wires, was towed in the 
deep water basin at Carderock. The hot wires were platinum; 
0.0015 inch in diameter and 0.25 inch in length. The normal dis- 
tance of the wires from the surface was measured, and the average 
distance was 0.016 inch which was well within the laminar boundary 
layer at the wire locations. 
Sun GH ee 
