AN EFFICIENT DRAG REDUCTION OF BLUFF BODIES BY TESSELLATION

In this work a new method of passive drag reduction on bluff bodies by tessellation is presented. Wind-tunnel measurements on tessellated spheres reveal that the variation of the drag coefficient is similar to dimpled spheres, manifested by a sudden decrease in the drag coefficient at a critical Reynolds number followed by a nearly constant drag value in the post-critical regime. However, tessellated spheres can achieve a further 10%-15% drag reduction compared to dimples without shifting the critical Reynolds number. To further investigate the underlying physics leading to this reduction we also conducted Direct Numerical Simulations of both tessellated and dimpled spheres at Re = 1.50 × 10⁵. The predicted values of drag coefficient agree very well with the experiments and confirm the drag reduction. Analysis of the flow reveals that the tessellated panels introduce a smaller pressure”penalty” compared to dimples at the front part of the body. In addition, transition to turbulence occurs later and near the top of the body. As a result the boundary layer grows thinner and global separation is delayed by approximately 10°.