Numerical investigation on the end effects of the flow past a finite rotating circular cylinder with two free ends

This paper studies the impact of the aspect ratio and free end shape on the end effects in the flow past a rotating circular cylinder with two flat, radiused, hemispherical, and conical ends, using the large eddy simulation method at a Reynolds number of $4.6\times {10}^4$. The aspect ratio in the range of 6–30 and the rotation rate in the range of 0–3, are investigated. The results show that the mean drag coefficient initially decreases slightly before rapidly increasing with the rotation rate, with a critical rotation rate that rises from 1 to 1.5 as the aspect ratio increases from 6 to 30. In contrast, the mean lift coefficient increases with both the rotation rate and the aspect ratio. When the rotation rate increases and the aspect ratio decreases, the differences between the aerodynamic coefficients of the four end shapes become more pronounced. The flat end results in the highest mean drag and lift coefficients, while the hemispherical end yields the lowest ones. In addition, when the rotation rate increases, the alternate shedding vortices shift to the opposite side. They even disappear and increase the elongated streamwise vortices. Due to the combined impacts of the rotation and end effects, large-scale tip vortices are formed, significantly altering the wake structure. The intense rotation effect results in expanding the strong influence region of the end effects and shrinking (or even removing) the weak influence region.