Flume studies of the response of various current meter rotor/propellers to combinations of unidirectional and oscillatory flow

Hammond, Thomas M. and Collins, Michael B. (1979) Flume studies of the response of various current meter rotor/propellers to combinations of unidirectional and oscillatory flow. Deutsche Hydrographische Zeitschrift, 32 (2), 39-58.

Abstract

The effects of wave-induced oscillatory currents may cause impeller-style current meters to produce records which incorrectly represent the unidirectional current fields in which they are placed. The impellers from five oceanic current meters and one miniature laboratory current meter were tested, using a horizontally oscillating carriage, in an otherwise unidirectional flume. Differences between the indicated velocity (under the combined flow) and the unidirectional current velocity were found to be small only when the magnitude of the wave-induced currents was smaller than that of the unidirectional currents. Larger errors, approaching or even exceeding the unidirectional current being measured, occurred when the velocity of the oscillatory flow exceeded that of the unidirectional flow. The velocities indicated by the Savonius (rotor-type) impeller exceeded those indicated by the propellers.
Graphs are presented to aid in estimating the magnitude of possible exaggeration in readings of unidirectional current in the presence of superimposed wave energy.
Finally, the effect of the housing of a current meter on the response of its impeller to oscillatory flow was also briefly investigated.

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