Knowledge of the motion of propellants in the fuel tanks of spacecraft is essential to understanding various aspects of their operation and performance. Propellant motion impacts such propulsion functions as expulsion of liquid, venting of gases, and pressurization. In some cases the forces produced by the propellant motion must also be known. This is particularly true when the liquid mass is a significant portion of the total spacecraft mass.
Visualizing Non-Inertial Reference Frame Motion
Fuel tank sloshing constitutes slosh dynamics of the fuel, where the dynamics of the fuel can interact with the container to alter the system dynamics. Typically, the fuel has a free surface. FLOW-3D is an excellent software for simulating fuel sloshing dynamics because of the accurate free surface tracking using TruVOF. Additionally, FLOW-3D’s Non-Inertial Reference Frame (NIRF) module allows easy and computationally efficient setup for visualization of the fuel and the moving container (fuel tank) from a stationary frame of reference.
To highlight FLOW-3D’s NIRF module capabilities, a sample simulation showing the fuel sloshing in the space shuttle is set up. The space shuttle accelerates upwards for initial 25 seconds and then de-accelerates by the same amount for the next 25 seconds. After that, using angular acceleration, the shuttle rotates by 90 degrees and then continues to accelerate linearly again. It is interesting to see the complex free surface fluid motion during this complicated space shuttle maneuver. The RNG turbulence model is used to estimate the turbulent kinetic energy of the fluid.
The left pane of the animation shows NIRF visualization created in FlowSight, while the right viewport shows the non-NIRF visualization, again created using FlowSight. NIRF visualization helps to understand the motion of the fluid and the tank from a stationary frame of reference, hence highlighting the overall dynamics of the system in a more relatable way.