Effects of Freestream Turbulence on the Flow past a Circular Cylinder

초록

Effects of freestream turbulence on the flow past a circular cylinder are investigated by means of LES. Especially, we focus on how the laminar-turbulent transition of the separated shear layers is affected by the intensity of freestream turbulence. The code uses the Cartesian coordinate system with the immersed boundary method implemented. The numerical results for Re=3,900 (based on the bulk mean velocity and the cylinder diameter) without freestream turbulence are in excellent agreement with other authors’ experimental and numerical results, even though only 1.17 million grid points were used. A 'prescribed power spectrum' methodology was employed to generate isotropic turbulence at the inlet of the computational domain at each time step. Effects of the freestream turbulence are reported for Re=3,900 and Re=10,000, respectively. Statistical study reveals that the Reynolds stresses in the near-wake region increase as the intensity of freestream turbulence increases. On the other hand, the bubble size behind the cylinder shrinks with the increased intensity of freestream turbulence. The separation angle is not significantly affected by the freestream turbulence. It seems that freestream turbulence helps the mean flow be recovered fast.