SOME DYNAMICAL PROPERTIES OF THE SAVONIUS 

 ROTOR CURRENT METER 



R. D. GAUL 

 Agricultural and Mechanical College of Texas 

 College Station, Texas 



J. M. SNODGRASS 

 Scripps Institution of Oceanography 

 La Jolla, California 



D. J. CRETZLER 

 Hytech Division of Bissett-Berman Corporation 

 San Diego, California 



ABSTRACT 



BACKGROUND 



A series of steady state and acceleration 

 experiments has been performed with the Savonius 

 rotor current meter in a tow tank. From the 

 several models tested an evaluation has been 

 made of some of the effects of size and configu- 

 ration on rotor performance in the range of 0.05 

 to 3 knots. Rotor response to changes from zero 

 to a steady current speed and vice versa has 

 been shown to be significantly different and 

 dependent on current speed. Notable changes in 

 performance have also been found due to change 

 of rotor surface roughness by biological fouling. 



INTRODUCTION 



A commonplace failing in research is use of 

 a measurement device without complete under- 

 standing of its characteristics. Whether this 

 be by necessity or neglect, the danger exists 

 that subsequent misinterpretation or overvalua- 

 tion of data may contribute to confusion rather 

 than enlightenment. Such could be the case in 

 the realm of ocean current measurement and it is 

 evident that at least one device, the Savonius 

 rotor, deserves some attention in this regard. 



A major motivation for the studies summarized 

 herein has been the unprecedented rise to popu- 

 larity of the Savonius or "wing" rotor since its 

 introduction as a current meter in 1952. Sev- 

 eral commercial firms have become involved in 

 manufacture of the several hundred rotor meters 

 that have been widely used for oceanographic and 

 limnological research. It is interesting to 

 note that all of these meters employ the same 

 rotor design that was rather arbitrarily selected 

 for the first experimental model. There has been 

 a dual objective for our tow tank experiments: 



(1) to quantitatively evaluate the measurement 

 capabilities of the "standard" Savonius rotor and 



(2) to generate criteria for possible design 

 improvements . 



The Savonius rotor is not new. S. J. Savonius 

 devised the "wing rotor" in the early 1920 's as 

 an improvement over ocean-going sails^ and sub- 

 sequently as a wind and water driven power gen- 

 erator for a variety of applications. 3 In the 

 early 1950 's J. M. Snodgrass began experimenting 

 with the rotors as an ocean current sensing 

 device. By 1958 at least two U. S. companies 

 were beginning to manufacture rotor meters and 

 W. S. Richardson at Woods Hole Oceanographic 

 Institution was using rotors in instruments for 

 a major ocean current study. From that time to 

 the present application of the meters has steadily 

 broadened. Little has been published about these 

 applications; still less about characteristics 

 of the device itself. 



A series of tests was initiated jointly by 

 the authors in 1961 after earlier spot checks 

 had failed to explain the reasons for discrep- 

 ancies between calibrations of rotor meters . 

 Details of many of the initial studies have been 

 given in a previous report.^ This present paper 

 is limited mainly to results obtained during the 

 latest test period in July 1962. 



EXPERIMENTAL APPROACH 



The rotor models shown in Fig. 1 were used 

 for the July 1962 experiments. The 2 rotors on 

 the left are "standard" models consisting of 

 3 circular flat plates 6 3/8 inches in diameter 

 that enclose 2 tiers of 2-inch radius half- 

 cylindrical vanes placed in pairs with the hori- 

 zontal axis of symmetry rotated 90° between tiers. 

 Rotor CS-2 is a Hytech production unit made of 

 molded high impact polystyrene and ST-1 was 

 individually fabricated from cycolac at Scripps 

 Institution of Oceanography. Rotor ST-2 is 

 scaled down to one-half size, ST-3 is standard 

 diameter and height overall but has h- tiers of 

 standard diameter vanes. Rotor ST-4 has 2 tiers 



Superior numbers refer to similarly numbered references at the end of this paper. 



115 



