Sloshing reduction in microgravity: Thermocapillary-based control and passive baffles

Abstract

In this work, we numerically analyze different thermocapillary-based strategies for active control of sloshing in microgravity. The fluid system considered is an open rectangular container holding a L×H=30 × 15 mm2 volume of liquid. A classical controller is implemented to reduce the natural sloshing motion of the system, which is characterized by its decay time τd. The controller produces an output signal ΔT that is applied anti-symmetrically at the lateral walls of the container, driving thermocapillary flow. Its performance is characterized via the functional P=(1−λ) τ̂+λ κ̂, which allows for a trade-off between the damping of unwanted sloshing modes and the cost of implementing the control, with normalized decay time τ̂ and cost κ̂, and modulated by λ∈[0, 1]. We optimize P for discrete values of λ and determine the optimal performance envelope. The results show that thermocapillary controllers are generally able to reduce τd by a 50% factor, with reasonable cost and controller output. A novel strategy combining thermocapillary controllers and passive baffles is further proposed and assessed. On their own, passive baffles can reduce the natural decay time of sloshing by an 80% factor at zero cost. In addition, they significantly alleviate the thermal requirements associated with the control, while providing additional improvements in τd. Finally, the aforementioned strategies are tested against a reboosting maneuver of the International Space Station, showing their potential for sloshing reduction in microgravity.