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이진(J. Lee),장성재(S.J. Jang),성형진(H.J. Sung) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.5
Direct numerical simulations were carried out to investigate the turbulence statistics and coherent structures in a fluid flow through a conical diffuser for three opening angles of 2°, 4°, and 8°. To simulate the flow in the conical diffuser, we introduced the generalized coordinates for the streamwise and radial directions and used a cylindrical coordinate along the azimuthal direction. The adverse pressure gradient affected, the axisymmetric flow such that the streamwise component of the turbulence intensity was sensitive to the diffuser in the outer region. The maximum Reynolds shear stress increased as the opening angle increased. The premultiplied energy spectra showed that the most energetic wall-normal height and its wave length increased when the opening angle increased. Time-resolved instantaneous flow fields and two-point correlation functions provided evidence for the streamwise merging of low-speed streaking structures. The outer vortical structures shifted toward the diffuser axis as the flow passed the diffuser throat. The swirling motions of the individual hairpins in the outer region were stronger in the diffuser flow than in the straight pipe flow.