Trantision of a compressible square cylinder wake structures subjected to free-stream disturbance*

The flow around a square cylinder and its three-dimensionalization which leads to a turbulent wake are analyzed by a series of high-resolution simulations of the subsonic wake at Mach 0.3.
By examining the effects of upstream velocity disturbances on the wake flow structure, the following results are obtained.
In the preprimary study, the two-dimensional numerical simulation indicates that the Karman vortex street behind the cylinder is generated, when the base flow loses its symmetry around the critical point in the near wake region of the squire cylinder due to the round-off error.
The wake is well stimulated by the disturbance with an angular frequency close to the most unstable frequency of the wake.
The disturbances with an antisymmetric feature are well amplified, even if the angular frequency of the disturbance is far from the most unstable one. Bypassing secondary instability of the wake column structure, Roller-like structures which are often observed in the far wake flow.
A phase diagram of u and v fluctuations in the region indicates a turbulent state.