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MIXED CONVECTION ADJACENT TO A VERTICAL FORWARD-FACING STEP

H. I. Abu-Mulaweh
Mechanical Engineering Department, Purdue University at Fort Wayne, Fort Wayne, IN 46805, USA

Bassem F. Armaly
Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, USA

T. S. Chen
Department of Mechanical and Aerospace Engineering and Engineering Mechanics University of Missouri-Rolla, Rolla, MO 65401, USA

B. Hong
Department of Mechanical and Aerospace Engineering and Engineering Mechanics University of Missouri-Rolla, Rolla, MO 65401

Abstract

Measurements and predictions of buoyancy-assisting laminar mixed convection air flow over a vertical, two-dimensional forward-facing step are reported. The surface upstream of the step simulated an adiabatic surface, while both the step and the surface downstream from the step were heated to a uniform temperature that is higher than the approaching air temperature. The ranges of approaching air velocity, temperature difference between the heated wall and the free stream, and step height used in this study were 0.25 m/s ≤ uo ≤ 0.60 m/s, 0°C ≤ ΔT ≤ 37°C, and 0.79 cm ≤ s ≤ 1.75 cm, respectively. The results reveal that the buoyancy-assisting force due to wall heating, affects significantly the velocity and temperature distributions and the reattachment length. It was found that the downstream reattachment length increases as the approaching air velocity and/or the step height increase in the forced convection case, and it decreases as the level of wall heating increases in the mixed convection case. The length of the upstream recirculation region is not affected by the heating of the downstream wall but it increases as the approaching air velocity and the step height increase. The local Nusselt number is found to increase as the wall heating and the approaching air velocity increase. Correlation equation is developed to predict the reattachment length, and the measured results agree well with numerical predictions.

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