Effect of Initialized Method on the Three-dimensional Secondary Wake Instability of Elongated Bluff Body

Direct numerical simulation (DNS) is used to calculate the three-dimensional cases of elongated bluff body under low Reynolds numbers (Re=1000). Primary instabilities such as Von Karman vortices and secondary instabilities including Mode A and Mode C are identified in the numerical results to investigate the physical mechanism of the wake region. Besides, vortex formation length and wave length of secondary instabilities are also characterized to reveal the flow structures. In the cases where Re=1000, Mode A is the dominant secondary instability in RANS initialized calculation. The spanwise and streamwise wavelength of Mode A is about 3D and 4D respectively, where D is the thickness of trailing edge. The sense of rotation alternates every half shedding cycle, which exhibits out-phase symmetry. However, Mode A and Mode C coexist in free-stream-condition initialized calculation. The spanwise wavelength of Mode C is about 0.5D. Conclusion is reached that difference in initialization method may result in difference in wake flow instabilities.