On the Effect of Forced-Oscillation Amplitude upon the Flow in a Cubic Cavity Heated Below

Abstract

The authors numerically investigate the forced-oscillation-frequency responses on flow and thermal characteristics of the thermal convection in a cubic cavity heated from below in the gravitational field, concerning global quantities such as spatially-averaged kinetic energy and so on. The authors assume incompressible fluid with a Prandtl number Pr = 7.1 (water) and a Rayleigh number Ra = 1.0×104. The direction of a forced sinusoidal oscillation is parallel to that of the terrestrial gravity. The authors focus their special attention on the amplitude effects of the forced oscillation upon kinetic energy, the optimum frequency for response and flow structure. The obtained results are as follows. Even at large acceleration amplitudes, the optimum frequency exists. At the optimum frequency, periodicity is exact, while the wave form is far from sinusoidal at a non-dimensional acceleration amplitude η ≥ 1. A boundary exists at η = 1.5, where both the increasing rate of a spatially-averaged kinetic energy and the flow structure change abruptly, and where the optimum frequency attains the minimum. This abrupt change in the flow structure can be explained by an indicial response.

Keywords

• natural convection
• heat transfer
• oscillatory flow
• forced vibration
• mixing