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TURBULENT STRUCTURE OF COMBINED-CONVECTION BOUNDARY LAYER ALONG A VERTICAL HEATED PLATE

Yasuo Hattori
Fluid Dynamics Sector, Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba, 270-1194, Japan

Toshihiro Tsuji
Department of Mechanical Engineering, Nagoya Institute of Technology Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan

Yasutaka Nagano
Nagoya Industrial Science Research Institute; Department of Mechanical Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan

Nobukazu Tanaka
Fluid Dynamics Sector, Central Research Institute of Electric Power Industry 1646 Abiko, Abiko-shi, Chiba 270-1194, Japan

Resumo

The turbulent structure of a combined-convection boundary layer along a vertical isothermally-heated plate in air aided by a uniform freestream has been experimentally investigated with a particle image velocimetry. High-speed and large-scale fluid motions, which strongly generate turbulent energy, are frequently observed in the natural-convection boundary layer. On the contrary, in the combined-convection boundary layer, fluctuating velocities become small with a decrease in the scale of fluid motions as freestream velocity increases. Fluctuating velocity vectors clearly indicate that the freestream imposed at the edge of the boundary layer restrains large-scale fluid motions in the outer region. In addition, any quasi-coherent structures as observed in ordinary boundary layers do not exist in the near-wall region of the combined-convection boundary layer, which shows a significant difference of the turbulent energy production through deformation of the mean motion by Reynolds shear stress between combined and forced convection.