Spatially correlated precision error in digital particle image velocimetry measurements of turbulent flows

The purpose of the current paper is to describe an experimental study of the spatially correlated precision errors associated with particle image velocimetry (PIV) measurements made in turbulent flows. A free jet was used as the base flow for the study. The precision error of time-averaged statistics of the mean and turbulent flowfield is governed by the probability distribution function of the various quantities and the finite sample size of the data sets. Spatial measurements that are separated by a distance that is shorter than the size of the large turbulent scales will not be independent, resulting in a correlated precision error. The characteristics of the precision error for various statistics will be described. It is found that mean vorticity has a correlated precision error that is limited to a much smaller length scale. The results demonstrate the importance of understanding the role of error correlation in the interpretation of PIV data.