SUMMARY AND CONCLUSIONS 



As a result of research done at the Taylor Model Basin and the Iowa Institute of Hydrau- 

 lic Research over the years, a hot-wire instrument for making turbulence measurements in 

 water under controlled conditions has been developed. It is essential that the wire be heated 

 with an alternating current to prevent electrolytic action and that only the wire metal be ex- 

 posed to the water. Unless the wire supports and joints are of the same metal as the wire 

 these must be covered with a good waterproof insulation to prevent galvanic action. With these 

 precautions the wire is stable enough for quantitative turbulence measurements in well-filtered 

 dust-free water. 



Although the wire is stable in clean water it acquires a surface film when it is used in 

 ordinary water such as that found in most test facilities. The rate at which the film forms de- 

 pends upon the degree of contamination of the water. The usefulness of the hot-wire element 

 for practical purposes appears to depend upon the development of a satisfactory method of 

 dynamic calibration. Although film formation will decrease the wire sensitivity and frequency 

 response, a coated wire may still be useful for turbulence measurements. If the wire is used 

 in a constant-temperature circuit the decrease in frequency response should not be serious 

 until the film thickness exceeds half the wire diameter. 



REFERENCES 



1. "Progress Report on Research in Frictional Resistance," David Taylor Model Basin Re- 

 port 726 (Sep 1950). 



2. Macovsky, M.S., "The Measurement of Turbulence in Water," David Taylor Model Basin 

 Report 670 (Oct 1948). 



3. Schubauer, G.B. and Klebanoff, P.S., "Theory and Application of Hot-Wire Instruments 

 in the Investigation of Turbulent Boundary Layers," ARC No. 5K27 (Mar 1946). 



4. Dryden, H.L. et al, "Measurements of Intensity and Scale of Wind-Tunnel Turbulence 

 and Their Relation to the Critical Reynolds Number of Spheres," National Advisory Comm.it- 

 tee for Aeronautics Report 581 (1937). 



5. Townsend, A. A., "Measurements in the Turbulent Wake of a Cylinder," Roy. Soc. Lon- 

 don, Proc. A., Vol. 190, (Sep 1947). 



6. Breslin, J. P. and Macovsky, M.S., "Effects of Turbulence Stimulation on the Boundary 

 Layer and Resistance of a Ship Model as Detected by Hot Wires," David Taylor Model Basin 

 Report 724 (Aug 1950). 



7. Roshko, Anatol, "On the Development of Turbulent Wakes from Vortex Streets," Na- 

 tional Advisory Committee for Aeronautics TN 2913 (Mar 1953). 



14 



