In this study, we clarified a formation process of coherent structures of turbulent flow around a three dimensional rectangular solid. The flow around the rectangular solid with the aspect ratio L/H of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 and 5.5, has been computed by the large eddy simulation at Reynolds number of 4 000. The computational results of the distribution of spectrum and Strouhal number correspond well with the flow around a two dimensional cylinder except for variation of

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... k value. And, in terms of Strouhal number, the result (L/H=1.0) corresponds with experimental result. In large aspect ratios, the visualization results show that a pair of hair pin vortex structures is shed from the vortex formation region alternately and periodically. The rectangular solid has two free ends. So, the aspects of the flow field around the three dimensional solid are different from that around the two dimensional cylinder, especially concerning the vortex formations. And, some characteristics of shear layer and vortex structures in a wake are found to be remarkably different with the aspect ratio. As for some vortices with characteristic aspect ratio, the formation and kinetic mechanisms of some vortices are described in details. LES Re (1) (8)