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CHARACTERISTICS AND STRUCTURES OF TURBULENT BOUNDARY LAYER WITH COUNTER DIFFUSION GRADIENT PHENOMENON

Hirofumi Hattori
Information and Analysis Technologies Division, Department of Mechanical Engineering, Nagoya Institute of Technology, Gokiso-cho, Showaku, Nagoya 466-8555, JAPAN

K. Hotta
Department of Mechanical Engineering Nagoya Institute of Technology Gokiso-cho, Showa-ku, Nagoya 466-855, JAPAN

Tomoya Houra
Department of Electronical and Mechanical Engineering, Department of Environmental Technology, Nagoya Institute of Technology, Gokiso-cho, Showa-ки, Nagoya 466-8555, JAPAN

Masato Tagawa
Department of Electronical and Mechanical Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, JAPAN

Resumo

The objectives of this study are to investigate a counter diffusion phenomenon (CDP) in a stably thermally-stratified turbulent boundary layer by means of direct numerical simulation (DNS). In this study, four cases of stably thermally-stratified turbulent boundary layer are simulated in order to reproduce the CDP, in which two Reynolds numbers and four Richardson numbers are set. The CPD is discovered in both the velocity and thermal fields in three cases. DNS clearly shows the CDP which indicates the negative sign of the Reynolds shear stress and the wall-normal turbulent heat flux with the positive sign of mean velocity and temperature gradients. In the case of strong occurrence of CDP, the local Richardson number always exceeds the critical Richardson number, but the turbulence is maintained. Also, the anisotropy tensor and invariant map are indicated in this paper. It is found that the state of turbulent stress rapidly arrives in the axisymmetric in the case of occurrence of CDP. The turbulent heat flux tensor is also shown in order to indicate the variation of thermal field, in which the streamwise turbulent heat flux tensor maintains high value even in the case of strong occurrence of CDP. The relation between the vortex structure and the fluctuation of Reynolds shear stress is shown, where the negative value of fluctuation of Reynolds shear stress frequently appears around the vortex structure in the case of occurrence of CDP.