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

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 LxH=30 x 15 mm(2) volume of liquid. A classical controller is implemented to reduce the natural sloshing motion of the system, which is characterized by its decay time tau d . The controller produces an output signal Delta T that is applied anti-symmetrically at the lateral walls of the container, driving thermocapillary flow. Its performance is characterized via the functional P=(1-lambda) tau+lambda kappa which allows for a trade-off between the damping of unwanted sloshing modes and the cost of implementing the control, with normalized decay time tau and cost kappa, and modulated by lambda is an element of[0, 1]. We optimize P for discrete values of lambda and determine the optimal performance envelope. The results show that thermocapillary controllers are generally able to reduce tau dby 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 tau d. Finally, the aforementioned strategies are tested against a reboosting maneuver of the International Space Station, showing their potential for sloshing reduction in microgravity.