Flow dynamics and wake past nature-inspired obstacle arrangements: an experimental study

Spatial arrangements of solid structures obstructing a flow plays an important role in determining the force experienced by the members of the arrangement as well as in affecting the downstream wake. Such spatial arrangements are vital to understand fish schools, bird flight formations, or flow around vegetation patches in flood plains. A systematic study of flow past such an array of obstacles can help optimize airplane/drone flight formations. In this talk, we present an experimental investigation of flow past arrays of 3D-printed rigid cylinders with square and airfoil-like cross-sections. Measurements are done in a water tunnel and velocity field and forces on the objects are obtained simultaneously using high resolution particle image velocimetry (PIV) and a 2-axis load cell. For each cross-sectional shape, effects of array population, packing density, and orientation (regular vs. staggered) are studied at various freestream speeds. The velocity field obtained is used to determine the contribution of the viscous and pressure effects on the forces on the cylinders, and the total drag force is verified using the load-cell. Near-field and far-field wakes are studied qualitatively as well as quantitatively by analyzing various terms of turbulent kinetic energy transport. Turbulent transport for the flow within the cylinder array is also analyzed. This study aims to achieve two objectives: first, establish empirical relations showing functional dependence of total drag on parameters of interest, and second, obtain high resolution velocity field measurements to study turbulent transport which can also be used for further theoretical and numerical modeling.