Uncertainty analysis of acoustic flow measuring instruments for characterization of high energetic river flow

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Bhuyan, Kaisar Ahmed
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Velocity and turbulence measurement uncertainty using acoustic methods in highly energetic river flows are quantified by performing measurements to isolate specific error terms, and by applying analytical methods and statistical analysis to recorded data. A MATLAB code is developed for motion compensation and data filtering. The methodology adopted is to perform acoustic measurements in a controlled laboratory setting and in an energetic river test site at Reynolds number from 0.05x10^7 to 3x10^7. As the performance of hydrokinetic turbines operating in highly energetic flows depends on localized velocity and turbulence parameters, uncertainty analysis contributes to improving river site characterization for the marine industry. The uncertainty analysis applies to acoustic instruments deployed from a stationary platform, a moving vessel, or alternatively, suspended in the water column via a cabling system in energetic river flows, which are typical configurations required by this industry. A methodology to conduct measurement and estimate the uncertainty is presented for these three configurations. The uncertainty analysis results are dependent on multiple inputs which are processed using algorithms made accessible online. A typical result of the error analysis at a velocity of 1.10 m/s a maximum deviation of 23% is observed between the measured and expected streamwise velocity at an instrument pitch angle of 45 degree. After implementing angle compensation the uncertainty reduces to 4%. Furthermore, by applying an IMU correction algorithm, the maximum velocity error is reduced by 29.3% and the turbulence by 77.0% after applying the motion compensation to river surface measurements. Processed flow results from an energetic river test site show the ADV overestimate streamwise mean time-averaged velocity and underestimate turbulence intensity measurements with an average of 4.6% and 27.4%, respectively.
Flow characterization, ADV, Uncertainity analysis, River, Hydrokinetic turbine