RESONANT ENHANCEMENT OF NATURAL-CONVECTION HEAT-TRANSFER IN A SQUARE ENCLOSURE

A numerical investigation is made of natural convection of an incompre ssible fluid in a square cavity having a constant-temperature cold sid ewall and an opposite hot sidewall with sinusoidally-varying temperatu re. Comprehensive numerical solutions to the Navier-Stokes equations a re acquired for a fixed Rayleigh number and a Prandtl number, Ra = 10( 7) and Pr = 0.7. The amplitude and frequency of the hot wall temperatu re oscillation are varied. The lime-mean heat transfer in the interior as well as the amplifications of fluctuations of instantaneous heat t ransfer are analyzed. The results disclose that a large-amplitude wall temperature oscillation causes an augmentation of the time-mean heat transfer rate. The maximum gain of the time-mean Nusselt number in the interior occurs at the resonance frequency, at which maximal fluctuat ions of the Nusselt number are found. The mechanism for resonant enhan cement of the time-mean heat transfer is described. (C) 1998 Elsevier Science Ltd. All rights reserved.