Free-Stream Turbulence Effects on Local Heat Transfer from a Sphere

[+] Author and Article Information
L. B. Newman, E. M. Sparrow, E. R. G. Eckert

Heat Transfer Laboratory, Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minn.

J. Heat Transfer 94(1), 7-14 (Feb 01, 1972) (8 pages) doi:10.1115/1.3449876 History: Received September 15, 1970; Online August 11, 2010


Experiments involving both heat-transfer and turbulence-field measurements were performed to determine the influence of free-stream turbulence on the local heat transfer from a sphere situated in a forced-convection airflow. The research was facilitated by a miniature heat-flux sensor which could be positioned at any circumferential location on the equator of the sphere. Turbulence grids were employed to generate free-stream turbulence with intensities of up to 9.4 percent. The Reynolds-number range of the experiments was from 20,000 to 62,000. The results indicate that the local heat flux in the forward region of the sphere is uninfluenced by free-stream turbulence levels of up to about 5 percent. For higher turbulence levels, the heat-flux increases with the turbulence intensity, the greatest heat-flux augmentation found here being about 15 percent. Furthermore, at the higher turbulence intensities, there appears to be a departure from the half-power Reynolds-number dependence of the stagnation-point Nusselt number. Turbulent separation occurred at Reynolds numbers of 42,000 and 62,000 for a turbulence level of 9.4 percent, these values being well below the transition Reynolds number of 2 × 105 for a sphere situated in a low-turbulence flow.

Copyright © 1972 by ASME
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