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H. D. Pite

Abstract

When a Savonius rotor is used on a current meter as a sensor for fluid speed, it is usually surrounded by a number of support rods. These rods interfere with the flow to the rotor and, depending on their orientation to the flow, can be found to cause quite large variations in rotor speed. Experimental results show that generally the rotor speed asymmetries are larger for the rotor used by Aanderaa Instruments than for a true Savonius rotor. The asymmetries can be reduced to near zero if the number of rods used is such that near cancellation of the positive and negative asymmetries occurs. The asymmetry pattern for one support rod can be used to deduce the pattern for any number of rods; thus, for a specified rotor, support rod diameter and pitch circle, the number of rods can be chosen to give the minimum azimuthal asymmetry.

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H. D. Pite, D. R. Topham, and B. J. van Hardenberg

Abstract

A review of the upper structure of the Arctic Ocean and its overlying ice cover suggests that significant potential exists for the generation of internal wave fields by the deeper drafts of the pressure ridge keels. Laboratory measurements are presented of the drag force on two-dimensional ice keel models of varying degrees of slenderness in both homogeneous and two-layer fluid systems. The experiments were performed in a towing tank 10 m long and covered the range from subcritical to fully supercritical flows. MW results show that the two-layer stratification increases the drag dramatically over that in a corresponding homogeneous flow, reaching a maximum in the transcritical flow regime as a result of the establishment of a system of internal waves. The increase in drag was greatest for the most slender obstacle, approaching the values to be expected from simple hydraulic theory. For the more steeply sloped obstacles, the wave growth is limited by dispersion, with a corresponding reduction in the peak drag force, Comparison with both simple hydraulic theory and the forced, extended Korteweg-de Vries equation shows that while the trend of the measurements is reproduced, a good description of the flows over the obstacles is obtained only for a limited range of conditions. Scaling the laboratory measurements to the Arctic Ocean suggests that the deeper ice keels may exert a considerable influence on the ice-ocean drag forces.

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