EDDY VISCOSITY AND MIXING LENGTH 



The experimental values of eddy viscosity e and mixing length £ 



across the thick stern boundary layer are derived from the measured values 



8u 



of Reynolds stress -u'v' and the mean velocity gradient -r — , using the 



, .. . . 1,5,13 '^^ 



definitions 



-u V = e 



9u 

 J 



(13) 



and 





o2 



du 



3u 









-u'v' 



= i 













dr 



dr 



(14) 



where the Reynolds stress -u'v' and the axial velocity u are measured by 

 the "X" hot-film probe. By fairing the measured velocity profile u with 



X 



a 'spline' curve, the value of 9u /9 can be computed numerically. 



The experimentally-determined distributions of eddy viscosity e/U- 6 



6 p 



are given in Figure 11 for the axisymmetric body under consideration. 



The 



U.d* 



/ □ 

 / ^<>° 



/ o O 



THIN 



BOUNDARY 



LAYER15 



- EXPERIMENTS 

 O 0.704 





D 0.831 



g 



O 0.873 



\ 



A 0.909 



V 



A 0.951 



\ 



O 0.987 



o 



0.6 



Figure 11 - Measured Distributions of Eddy Viscosity for 

 Afterbody 5 



39 



