| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1993: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1992: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Research Abstract |
First, two types of two-equation heat transfer models are developed along with an accurate prediction of wall turbulent thermal fields, which are often encountered in a large helical device. One has a simpler model formulation and is applicable to the cases where wall temperature fluctuations are negligible. The other has more rigorous foundations and reproduces the correct wall limiting behavior of turbulence under arbitrary wall thermal conditions, though the computing time required is usually longer than that needed in the former model. On the other hand, to calculate heat transfer in free shear flows, a second-rank eddy diffusivity tensor for heat is essential. A proposal for closing the energy equation is presented at the two-equation level of turbulence modeling. Secondly, the effects of mean shear enforced in decaying isotropic turbulence have been investigated by numerical experiments with the direct numerical simulation (DNS) of Navier-Stokes equations. In flows rapidly distor
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ted from isotropy, it is important to elucidate the behavior of turbulent quantities, in particular, the pressure-strain correlations contributing to the origin of the anisotoropic state. The pressure-strain term in the reynolds stress equations becomes positive only in the spanwise velocity fluctuations, and hence turbulence energy is extracted from components in both streamwise and shear directions. The redistribution process as well as the anisotropic behavior of turbulence statistics are accurately evaluated with a linear analysis based on the rapid distorton theory. Furthermore, from the assessment of turbulence models for pressure-stain correlations ushing the present DNS data, it is found that none of the existing models represent the energy sink from the shear direction except for model using the Langevin equation, and the destruction of the Reynolds shear stress is described rather well using a classical linear model. Thirdly, a k - epsilon model has been reconstructed with t
The models developed in the present study must be quite useful in heat removal technology of high heat flux components for fusion experimental reactors. Less
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