Advances and applications of the digital mask technique in particle imagevelocimetry experiments

Abstract

Some advancements of the digital mask technique, which was first described byGui and Merzkirch (1996a ERCOFTAC Bull. 30 45–8) for a phase-separatedevaluation of two-phase flow particle image velocimetry (PIV) recordings, arepresented in this paper. The originally minimum-quadratic-difference- (MQD-)based mask technique is accelerated by using the fast Fourier transformationalgorithm. In order to further increase the evaluation speed and the measurementaccuracy, the digital mask technique is modified so that it can be combined withthe correlation-based central difference image correction (CDIC) method, which isproved to be a more accurate and less peak-locked evaluation algorithm than boththe MQD tracking method and the correlation-based tracking method. Anellipse-shaped interrogation window is constructed with the digital masktechnique to improve the spatial resolution of the evaluation without loss of theevaluation accuracy. Applications in PIV measurements of solid/water two-phaseflow, bubbly water flow, flow around a human blood cell and airflow near the tipof a vibrating cantilever demonstrate that the combination of the digital masktechnique, the CDIC algorithm and the ellipse interrogation window makes apowerful tool for evaluating digital PIV recordings of complex flows.