| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2003: ¥1,500,000 (Direct Cost: ¥1,500,000)
Fiscal Year 2002: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
We begun our study with the generation of the DNS data for the decaying and forced homogeneous isotropic turbulence. Grid points up to 512^3 were employed, and we utilized the SX-5 supercomputer located at the Cyber-media Center, Osaka University, and its user fee was paid by this grant-in aid. In the next step, we investigated on the process of formation of the vortex tube structures along the vortex sheets using the DNS data. We have shown that the tubes are formed through the interaction of the dual vortex sheets, which intersect to each other forming the τ shaped configuration. It was shown that three modes of configuration exist depending on the relative alignment of the vorticity vectors on the two sheets. When the vorticity vectors on the two sheets were placed perpendicular to each other, compression of the strain-rate tensor in the stretching direction arose in the vicinity of the dual sheets. Thus the direction of the axis of the vortex tube generated in this configuration was in the transverse direction against the vorticity vector along the vortex sheet. As the frequency of occurrence of this transformation process increased, intense generation of turbulent energy cascade took place. Then, we investigated the effect of viscoelasticity on the occurrence of this transformation process using the Oldroyd constitutive equation. Using the steady state solution of this equation, we have shown that the viscoelastic effect is primarily exerted on the vortex sheet, and occurrence of its transformation into the tube was annihilated, and the turbulence generation was markedly reduced. It was shown that the steady solution is similar to the nonlinear model which is used in LES of the Newtonian fluid, but to take into the viscoelastic effect in the non-Newtonian fluid, a sign of the one specific term should be reversed.
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