An Experimental Study of Transition to Turbulence in Vertical Mixed Convection Flows

[+] Author and Article Information
R. Krishnamurthy

Department of Mechanical Engineering, The Catholic University of America, Washington, DC 20064

B. Gebhart

Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, PA 19104

J. Heat Transfer 111(1), 121-130 (Feb 01, 1989) (10 pages) doi:10.1115/1.3250631 History: Received October 30, 1987; Online October 20, 2009


Results are reported from an experimental study of a mixed convection flow, that is, combined forced and natural convection, undergoing transition to turbulence, adjacent to a vertical, uniform-heat-flux surface. Small and aiding forced convection effects were studied. The measurements, in air, were made at pressure levels ranging from 4.4 bars to 8 bars, at flux levels q ″ in the range 14–1300 W/m2 . The imposed free-stream velocities U ∞ were around 5 cm/s. One objective was to determine any quantitative parameters that would predict the bounds of the transition region. Another was to measure disturbance growth characteristics during transition. Results show that, at a given U ∞ , the beginning of transition is not correlated by the local Grashof number Grx * alone. An additional dependence on both the downstream location and pressure level was found. Thermal and velocity transitions were found to begin when the mixed convection parameter εM reached a value of 0.18. Transition was found to be complete when the nondimensional convected energy in the boundary region, βq ″ x /5k , reached a value of 7.10. These experimental results confirm the prediction of linear stability analysis, that aiding mixed convection stabilizes the flow, compared to pure natural convection flow. The data also support a physical explanation of these mechanisms.

Copyright © 1989 by ASME
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