Time-dependent convection under reduced gravity

The transient development of thermal convection in a rectangulr container is theoretically and experimentally investigated for the case of a time-dependent body force. The time law according to which convective streaming develops when an instantaneous acceleration in the form of a step function acts on a thermally layered fluid is examined. Explicit, two-dimensional differential equations are used to calculate the time-dependent convection, and the numerical results are compared with analytical solutions based on linear theory. The transient development of the flow field is quantitatively studied using differential interferometry. The characteristic development times for the thermal convection are presented as a function of the Rayleigh and Prandtl numbers and of the angle between the temperature gradient and the direction of acceleration. The results are used to evaluate the extent to which time-dependent g disturbances in a space laboratory can induce noticeable convection flows.