NOVEL USAGE OF FIVE-HOLE PROBES: TIDAL CHANNEL TURBULENCE MEASUREMENTS
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Abstract
A fast-response five-hole probe has been developed for the measurement of turbulent flow structures in tidal channels. Such measurements are vital for accurate prediction of unsteady loads on tidal turbines. Existing field-based velocimeters are unable to capture the required range of frequencies or are too expensive to profile the variation of turbulence across a typical tidal power site, and thus the data they provide is inadequate for turbine design. This work adapts an established measurement technique from the turbomachinery community – a fast-response, multi-hole pneumatic probe – to achieve a low cost device which covers the required frequency range for tidal turbine applications. The main issues to be overcome in the marine environment are: the fact that, at depth, the ambient hydrostatic pressure is much higher than the dynamic pressure, and the need for devices to be water-tight and robust. These issues have been addressed by using novel calibration coefficients and by installing the sensors and amplifier board within the probe head. A prototype device has been tested in a flume tank using LDV measurements for comparison. The probe can now be developed for trials in the marine environment.