Rarefied Multiphase Flow

Solid-propellant rocket motors are widely used in space applications due to their reliability and durability. One example is the kick motor, designed to circularize or transfer satellite orbits at the final stages of a rocket launch. 

These motors emit exhaust gas in the form of cylindrical plumes. However, in space, some propellants may flow backward due to the near vacuum condition, which can cause damage to the rocket. Therefore, analyzing solid-propellant rocket plumes is critical. 

The degree of rarefaction makes it difficult to replicate solid-propellant rocket plumes experimentally on Earth. Also, at this rarefaction, the number of collisions between particles is inadequate for the flow regime to establish Maxwell distribution, making the Navier-Stokes equation and Computational Fluid Dynamics (CFD) ineffective in analyzing this type of flow regime. Hence, a particle-based numerical analysis is required. 

Solid-propellant rocket motor plume is unique in that it contains about 38% of aluminum oxide (Al2O3). Therefore, considering these solid particles and their interactions with neighboring particles will give a more accurate result. A simultaneous flow of two or more phases is called the multiphase flow. Because solid particles are generally larger than most gas particles, the increased collision cross-section and collision frequency are subjects of interest to many engineers trying to recreate the flow using particle-based simulation such as Direct Simulation Monte Carlo (DSMC).

Landing probes on other celestial bodies is quite a challenging task. For instance, when landing on the moon, the presence of lunar regolith particles makes it difficult to predict what might happen during the landing. These particles can interact with the plume generated by the spacecraft, potentially causing damage to the lunar lander. This situation involves a complex multiphase flow where solid regolith particles coexist with gaseous plume particles. Using a rarefied multiphase flow solver scheme is crucial for making accurate predictions.

Multiphase flow isn't limited to engineering scenarios; it also occurs in natural settings. Take, for example, Enceladus, one of Saturn's moons, known for its icy surface and the active jets it emits, reaching altitudes of 20-40 kilometers. The specific composition of these jets is still unknown. Simulating the Enceladus jets can help scientists better understand their composition, as these plumes are believed to be multiphase in nature.