Influence of wall proximity on characteristics of wake behind a square cylinder: PIV measurements and POD analysis

摘要: Abstract Influence of wall proximity on characteristics the wake behind a two-dimensional square cylinder was experimentally studied in present work. A low-speed recirculation water channel established for experiment; Reynolds number based free-stream velocity and width ( D ) kept at Re  = 2250. Four cases with different gap width, e.g., G / D  = 0.1, 0.2, 0.4 0.8, were chosen comparison. Two experimental techniques, standard PIV high image-density CCD camera TR-PIV high-speed employed measuring field, enabling comprehensive view time-averaged pattern spatial resolution instantaneous flow field temporal resolution, respectively. For four cases, difference vicinity plane analyzed terms quantities measured by PIV, streamline pattern, vector streamwise fluctuation intensity reverse-flow intermittency. The proper orthogonal decomposition (POD) method extensively used to decompose measurements, giving close-up energetic POD modes buried wake. low-order model = 0.8 constructed using linear combination first two time-mean which reflected well vortex shedding process sense phase-dependent patterns. intermittent appearance weakly separated region near found = 0.4. On going from 0.4, remarkable variation longitudinal direction confirmed that constraint stretches vortices transfers energy component expense lateral one.