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FLOW STRUCTURES AND HEAT TRANSFER ENHANCEMENT ON ASYMMETRIC DIMPLES

Johann Turnow
Chair of Modeling and Simulation, Department of Mechanical Engineering and Marine Technology, University of Rostock, Albert-Einstein-Str. 2, 18055 Rostock, Germany

Nikolai Kornev
Chair of Modeling and Simulation, Department of Mechanical Engineering and Marine Technology, University of Rostock, Albert-Einstein-Str. 2, 18055 Rostock, Germany

Egon P. Hassel
Institute for Technical Thermodynamics Faculty of Mechanical Engineering and Marine Technology University of Rostock Albert-Einstein-Str. 2, D-18059 Rostock, Germany

Résumé

Numerical and experimental investigations of fully turbulent flow over an asymmetric dimple with a geometric ratio of dimple depth to diameter of t/D = 0.26 in a narrow channel have been performed to identify vortex structures and its influence on heat transfer enhancement at Reynolds number ReD = 40000 based on the dimple print diameter. The inclination angle of the asymmetric cavity is varied from 0° to 90° towards the main flow direction. Every 15° step the velocity profiles and pressure distribution obtained from LES are compared to parallel conducted experiments in a closed water test channel. Unsteady effects and vortex structures are analyzed and have been opposed to results for a symmetric dimple. Further, the effect of vortex structures on local heat transfer rates are determined and are quantified in reference to the values for a smooth surface. Integral results show best thermo-hydraulic performance for dimples aligned 45° to the flow direction.