ABSTRACT 



A summary is given of the wori< done since 1946 at the Taylor Model Basin 

 to develop a hot-wire turbulence-sensing element for use in water and of some of 

 the uses to which the wire has been put. Recent efforts to determine the causes 

 of wire instability and to eliminate them are described. As a result it was deter- 

 mined that these wires should be heated with an alternating carrier current and 

 that the exposure of dissimilar metals in the probe assembly should be eliminated. 

 With these precautions the wire could be stabilized in well-filtered water. In or- 

 dinary water, instability from the accumulation of dirt and surface film on the 

 wire could not be controlled except by removing the wire frequently for cleaning. 

 It appears that the only satisfactory solution to this problem lies in the develop- 

 ment of a dynamic calibration technique. Theoretical expressions for the sensi- 

 tivity and frequency response of a coated hot wire are included. 



INTRODUCTION 



Since 1946 experimenters at the David Taylor Model Basin and elsewhere have attempt- 

 ed to apply the principles of hot-wire anemometry to turbulence measurements in water. Al- 

 though many hydrodynamic problems can be simulated in wind tunnels and studied with con- 

 ventional hot-wire methods, there are a few important problems, particularly where surface 

 effects are important, which are not amenable to this procedure. Although the techniques for 

 the use of a hot-wire turbulence-sensing element in air are now well developed and widely 

 used, some very serious difficulties arise when efforts are made to adapt this instrument for 

 use in water. 



It is the purpose of this report to review the efforts of various investigators at the Mod- 

 el Basin who have contributed to the development of a hot-wire element for use in water, to 

 discuss the problems and difficulties involved and to report on current investigations. M.S. 

 Macovsky and W.L. Stracke developed the first element and made a few quantitative turbulence 

 measurements with it. The wire has been used by Macovsky and J. P. Breslin in qualitative 

 experiments in turbulence detection. Mr. Stracke worked out a method for a dynamic calibra- 

 tion of the element and made preliminary experiments for developing the technique. Recent 

 experimental investigations to develop a more stable wire have been carried out by R.G. Stev- 

 ens and P.E. Strausser. Dr. Borden has made theoretical studies of the sensitivity and fre- 

 quency response of hot wires on which a surface film has formed. 



