7.0 



3.0 



U 



Uj 0.7 



<n 



> 0. 5 



111 



K 



>- 



<■> 0.3 



Z 

 111 



3 



2 0.2 



Z 



o 



< 0.1 



o 



Or 



0.07 



0.05 — 



0.03 — 



0.01 



I I I I 



"1 1 1 1 I I I I 



"i r 



ROTOR CS-2, CLEAN SURFACE 



ROTOR CS-2, PET 

 JELLY SURFACE 



ROTOR HT-I, FOULED SURFACE 



NOTES: 



I. DATA POINTS SHOWN AS DOTS ARE FOR 

 ROTOR HT-I WITH CLEAN SURFACE. 



2 CROSSES ARE FOR ROTOR HT-I SURFACE 

 COVERED WITH ABOUT 1/8 INCH THICK- 

 NESS OF NATURAL FOULING. 



3. SOLID CURVE IS FOR ROTOR CS-2 WITH 

 CLEAN SURFACE 



4 CIRCLED DOTS ARE FOR ROTOR CS-2 

 COATED WITH PETROLEUM JELLY. 



5 DATA TAKEN JULY 1962, HYTECH TOW 

 TANK. 



■ROTOR HT-I, CLEAN SURFACE 



I I I I I 



J I 



0.05 0.07 



0.1 0.2 0.3 0.5 0.7 1.0 



TOW CARRIAGE SPEED (KNOTS) 



2.0 



3.0 



5.0 



Fig. 10. Calibration curves showing influence of rotor surface roughness. 



an acceleration step change the rotor is not 

 anomalously affected in this manner so results 

 are likely to be more consistent. Harmonic 

 cycling experiments have been performed by 

 Marine Advisers" with a maximum lateral displace- 

 ment of about k.'j feet and a period of 10 seconds. 

 Output failed to return to zero and the output 

 oscillation was modulated with a period twice 

 that of the forcing function. 



Besides being convenient to perform, the step 

 function is useful as a standard response test 

 which allows interpretation in terms of the well 

 known "time constant." The time constant 

 strictly applies only to non-inertial systems 

 that respond exponentially. In such cases the 



time constant is independent of the magnitude of 

 the step change and is equal to the time required 

 for approximately 63$ response. The Savonius 

 rotor is definitely inertial but for convenience 

 and uniformity rotor response to the first 63$ of 

 a step change in towed speed is taken as its 

 "time constant. " 



It must be emphasized that the response tests 

 described were for a step change between zero 

 and a steady speed. The results of anemometer 

 tests? indicate that rise and decay character- 

 istics may be radically different when step 

 changes are between steady speeds rather than 

 between zero and a steady speed. This is espe- 

 cially true for the negative step (meter 



122 



