4 . 



/ \ • 

 2 ,r-^ N;;^-i 



Rod Diometers, Y/D 



Figure 1 - Distribution of Intensity of Turbulence 91 

 Diameters Downstream from 3/32-inch Rod 



The solid line is due to Townsend (/? = 850); the points are TMB hot-wire data (i? = 1050) 



turbulence intensity and correlation were made. Although the wake intensities are very sensi- 

 tive to the magnitude of the background turbulence, the intensity measurements made in the 

 TMB model circulating water channel are of the same magnitude as those obtained in the wind 

 tunnel at the National Bureau of Standards. ^'^ The validity of the correlation data obtained 

 in the TMB facility is uncertain owing to experimental difficulties. 



In the second experiment the sensing element was mounted downstream from a rod 

 mounted horizontally across the water channel. As seen in Figure 1, the data obtained from 

 wake traverses behind the cylinder are in good agreement with Townsend's data,^ if allowance 

 is made for the rather high level of background turbulence in the water channel (about 1 per- 

 cent). 



Preliminary measurements were also made of the decay of turbulence in the TMB towing 

 basin after the passage of a full-form ship model. ^ Although it was difficult to make quantita- 

 tive measurements under such conditions, it was estimated that after a waiting period of 10 

 minutes between runs the turbulence level in the basin had decayed to such an extent that it 

 would not affect the resistance measurements. 



Although quantitative turbulence measurements in water were difficult and sometimes 

 of doubtful accuracy, the hot wire has been used with great success for qualitative measure- 

 ments. After the wire has been submerged in water for a few minutes it accumulates a film 

 at a slower rate and it becomes a useful instrument for detecting turbulence where a calibra- 

 tion is not required. 



A useful qualitative application of the hot wire was made in an experimental study of 

 various methods of artificially stimulating turbulence in the boundary layer of a tani.er mod- 

 el. ^'^ For the purpose of mapping out regions of laminar, transitional, and turbulent flows, 



