Flow visualization around two staggered square cylinders

Smoke flow visualization tests in a vertical wind tunnel are carried out to investigate the flow characteristics around two infinite staggered square cylinders at a staggered angle ( = 45) for different gap distances between cylinders at Re = 750. Quantitative results like separation angle, wake width and shedding frequency were obtained for each cylinder and consequently three distinct flow regimes were recognized, namely, single body, periodic gap flow and modulated periodic flow regime. In a single body flow regime, vortex shedding occurs only from the outer layers of both cylinders and a single vortex shedding mechanism can be detected. In the periodic gap flow regime, the vortices shed from the outer shear layers of both cylinders, each with two similar frequencies. In addition, in the modulated periodic flow regime, the main features are that the frequencies of Karmann vortices and the Kelvin Helmholtz instabilities are attributed to each cylinder and not to the shear layers (the frequencies of both inner and outer layers are the same for each cylinder), however, the frequency of each cylinder is different from the other one.