Experimental investigation of flow past three-cylinder rotating system

Wake interactions from a three-cylinder system arranged in an intermediate-spacing setting in static and rotating conditions are investigated. The complex flows generated are relevant to fundamental fluid flow phenomena and engineering applications and merit investigation. In this study, experiments using hot-wire and two-dimensional (2D) Particle Image Velocimetry (PIV) are conducted in order to characterize the fluid flow at various Reynolds numbers and rotational speeds. The three-cylinder system setup is in equidistant triangular arrangement, each cylinder having diameter of 3.1 mm with a 9.7 mm circumscribed-circle diameter among them. To elucidate the cylinder system flow phenomena occurring during static and rotating conditions, the PIV measurement campaign was conducted in two stages. Firstly, a very close view of the flow was used to capture wake interaction between three cylinders in detail at a representative case of low Reynolds number, Re = 57, at three static orientations. Secondly, the experiment was conducted using a larger field of view to capture far field flow characteristics at increased Reynolds numbers, Re = 310 and 1250, for three static orientations and various rotating conditions. For static cases, the results show some flow phenomena that has been reported in several computational studies before, but new experimental evidence of early mixing and breakdown of the wake through a variety of flow patterns are revealed. With the addition of the new parameter of continuous rotation, the three-cylinder system further evolves into new scenarios, including cases with resembling single-cylinder wake patterns. Time-resolved characteristics of the flow are obtained from point-wise hot-wire anemometry and are presented as a function of cylinder system rotational speed, Re number, and non-dimensional frequency or Strouhal (St) number.