Effect of anomalous particle light scattering on PIV image quality

摘要

Abstract: Optical mastermind techniques, such as PIV, are finding more frequent use in experimental fluid mechanics laboratories. The continuing development of both imaging technology and image processing algorithms over the past twenty years have extended its measurement capabilities. Developments in high power pulsed lasers, such as Nd:YAG have also contributed to extending the applicability of the technique to a variety of flows. It has been found that for measurements in water, problems arise due to a combination of the very high light intensity supplied by a high powered pulsed Nd:YAG laser and Mie scattering effects of sub-micron sized particles inherently present in un-distilled water (e.g. mains water supply). This creates problems for obtaining consistent PIV images. These problems arise when using large water tunnel facilities for which it is not feasible to use distilled water. In addition to this, particle selection is of prime importance when one wishes to use orthogonally polarized dual laser systems. Experimental results will be presented to illustrate the degradation in image quality due to these ubiquitous effects. Recommendation regarding particle selection and optimum laser polarization states will be presented for conditions in distilled and typical mains water supply. !5