ADV Data Analysis for Turbulent Flows: Low Correlation Problem

Abstract

This study was motivated by difficulties encountered when analysing ADV measurements taken in turbulent flows in which correlations were often lower than 70% in the bottom 5 cm of flow. The low correlations were attributed to an increase in turbulence for flows over rough boundaries and this assumption was confirmed experimentally. The influence of the ADV velocity range setting on correlation values was also examined. It was confirmed that a higher velocity range setting resulted in higher correlations for measurements away from the boundary, but in the near-bed region this was not always the case. Given the low correlation for much of our data, it was necessary to determine the variability in average velocities and Reynolds stresses for different degrees of filtering based on correlation. It was found that average velocities were much less sensitive to the value of the correlation filter than Reynolds stresses. In conclusion, for turbulent flows, ADV measurements could be used to calculate average velocities and generate velocity profiles if measured data were edited based on the correlation filter set to as low as 40%, provided that after filtering 70% or more data were retained for analysis.