A Water Velocity Sensor for the Measurement of Three Dimensional Turbulence

This paper discusses the Mk IV version of the original three-dimensional drag sphere velocity probe developed jointly by staff at the National Water Research Institute and Canadian industry. The sensor is intended for field turbulence studies; it has a bandwidth of 75 Hz and a spatial resolution of 27 cm at a SNR (on a turbulent length scale) of 10. The performance of this latest improved version is evaluated on the basis of the results obtained from various tests and calibrations performed with static forces and in the Canada Centre for Inland Waters´ towing tank facility. Force, flow and temperature sensitivity coefficients are presented and discussed. Flow vector measurement errors resulting from residual, second-order non-linearities are minimized by the redundancy of the defining transfer function equations. Work is currently in progress to further reduce these residual effects. Nevertheless, this sensor provides a useful measurement capability for the oceanographic and limnological communities.