Time-dependent convection

The possibility of buoyancy driven convection flows in a space laboratory submitted to time dependent g disturbances with maximal amplitudes up to 0.1g are investigated. A finite difference method is used to simulate the transient development of thermal convection in rectangular enclosures. The influence of step function, single pulse, pulse sequence, sinus function and a typical acceleration profile of a crew motion are studied. The temporal development of the flow field is calculated for different Rayleigh numbers, Prandtl numbers and frequencies. The transient behavior of the convection flow significantly depends on whether temperature gradient and direction of acceleration are parallel (cellular convection or perpendicular (free convection) to each other. This is confirmed by analytical solutions of unsteady convection. By means of similarity laws the results are transferred to the conditions of microgravity in a space laboratory. Investigation of planned space experiments shows that disturbances by convection flows are only possible in extreme cases, especially if g pulses of high amplitude occur.