Flow over a cylinder with a small triangular bump

The surface pressure distribution over a circular cylinder with a small, full-span, triangular bump is examined. The geometry of the bump is an isosceles triangle, the height of which is varied from 1.33 % to 5.33 % of the diameter of the cylinder and positioned between $60^{\circ }$ and $120^{\circ }$ . The Reynolds number ( $Re = V_{\infty}D/\nu$ , where $V_\infty$ is the velocity of the freestream, $D$ is the diameter of the cylinder and $\nu$ is the kinematic viscosity) is varied between $1.1 \times 10^5$ and $1.8 \times 10^5$ . The lift and drag are estimated through the surface integral of pressure over the cylinder. The results show that the smallest bump acts as a trip for the lower Re and orientations before $70^{\circ }$ , leading to a separation farther upstream than in the case of no bump. For larger bumps, Re and orientation angles, the bump acts as a spoiler and fully separates the boundary layer at the bump. In addition, the surface pressure upstream of the bump is strongly dependent on the bump position. The lift is highest for bump position less than $90^{\circ }$ and decreases significantly with increasing bump location angle. The drag is less sensitive to the position of the bump. These findings have implications for predicting the forces on bluff bodies due to small asymmetric surface geometry features and extension to applications such as atmospheric flow over topography.