Sevik 



-10- 



-20- 



-30 



-40 



-50- 



-60 



40 80 120 ISO 200 240 280 320 360 400 440 480 520 560 600 

 FREQUENCY (Hz) 



Fig. 13 - Power spectral density of the response of a ten- 

 bladed, 8 -inch -diameter propeller to turbulence (Test 5530, 

 Run Z: distance between the grid and the propeller = 20M = 

 IZO inches; measured water -tunnel turbulence level without 

 the grid u = 0.00 IIU; turbulence level at the propeller due 

 to the grid u = 0.03U; tunnel velocity u = 15.1 ft/sec; pro- 

 peller advance ratio J = 1.22) 



310 



