On the scale of stretched vortical structures in the forward stagnation region of a bluff body

Stretched vortical structures in the forward stagnation region of a two-dimensional bluff body were studied by a smoke-wire flow visualization method conducted in a wind tunnel. Four bluff bodies with different shapes and widths, W, were employed in this study. For each of the cases, the length scales of the stretched vortical structures in the stagnation region were estimated from the visualization results obtained. Additionally, the streamwise velocity distribution along the stagnation streamline for each of the four bluff bodies was measured and numerically computed. According to the velocity distributions, the slope, a*, of each of the velocity distributions near the stagnation point was reduced. For the cases analyzed, the normalized length scales of the vortical structures based on W (characteristic dimension of a bluff body) and 1/a* (bluffness of a bluff body) are in good agreement to each other, suggesting that the vortical scale is proportional to W and 1/a*.