function of frequency was found to be 1 percent at 10 kHz and 5 percent at 



20 kHz. The axial velocity fluctuation u' was recorded on magnetic tape 



for 30 sec at a tape speed of 152.4 cm/s using a multichannel recorder. 



This tape recorder had a rapid fall-off in response above 20 kHz. The 



recorded data for u' were played back to determine the mean square values 



2 2 



of u' and (9u'/9t) (with the signal passing through the differentiation 



X X 



amplifier) by a true RMS voltmeter. 



The measured values of turbulence Reynolds number R, at various axial 

 locations of Afterbody 5 are shown in Figure 14. The value of R, decreases 



- 



▲^ 



O 



D O 

 A^ O D O 





o 



D 



o 



X 



L 

 0.831 

 0.873 

 0.909 



d 



\/u-2U, 





aaO D O 



AZ^ D O 





A 



A 



0.951 

 0.987 



\/er 



" 



1 



1 



A A O D 



1 1 1 



O 



1 



1 



1 



100 200 300 400 



600 700 800 900 1000 



'iT^A 



Figure 14 - Measured Turbulent Reynolds Numbers 



with increasing axial distance x, which is a distinguishing characteristic 

 of a thick stern boundary layer. For a given x/L, the measured values of 



R, are almost constant for distances less than 60 percent of the boundary 



A 



layer thickness. The measured values of R, in this thick stern boundary 



14 

 layer are higher than those generated by most turbulence grids. The 



turbulence Reynolds number R, in the present thick stern boundary layer is 



43 



