Understanding biases in the near-field region of LDA two-point correlation measurements

Two-point laser Doppler anemometry (LDA) measurements are shown to be strongly affected by both geometric and coincidence timing parameters, some effects of which are akin to those previously documented for nonorthogonal three-component LDAs. High spatial resolution is shown to be a necessity for small scale two-point measurements. It is suggested that a maximum effective probe volume dimension of one Kolmogorov length be considered as an upper bound for lateral and spanwise correlation measurements if microscale estimates are intended. However, if the effective probe volume shape is roughly spherical and a proper coincidence window is chosen, the spatial resolution of longitudinal correlation measurements appears to be independent of probe dimension. (Author)