Wake interactions in the flow past side-by-side elliptic cylinders

The wake resulting from an incident flow over two elliptic cylinders involves complex interactions of the separated flow with the inner/outer shear layers and the gap flow close to the cylinders as well as vortex street interactions further downstream. The wake dynamics in such configurations can help understand bio-inspired locomotion, forces and moments on offshore structures, among other applications. This study uses experiments and computations to characterize the wake structures in the flow over two side-by-side ellipses of various eccentricities at different gaps (the shortest distance between cylinder surfaces) and Reynolds numbers. The experiments are conducted in a water tunnel, where the flow structures are investigated using dye visualization as well as Particle Image Velocimetry (PIV) measurements. The computations in the incompressible regime help expand the parameter space for the investigation. Based on the gap size at a given Reynolds number, the wake flow regimes can be classified into single, asymmetric, or coupled wakes. At small gap sizes, the two ellipses act as a single bluff body leading to one vortex street. With an increase in the gap size, vortex shedding from individual ellipses forms two vortex streets. At intermediate gap values, the wake is asymmetric with one cylinder wake dominating over the other. Further increase in the gap leads to coupled wakes where vortex streets with in-phase or anti-phase shedding are observed. The parameter values for transition between these wake regimes will be discussed for different ellipse eccentricities.