Simulating entry into polyatomic atmospheres

To better understand the physical and chemical impacts on spacecraft surfaces during (re-)entry into atmospheres like those of Mars and Saturn’s moon Titan that contain polyatomic molecules, researchers at the Institute of Space Systems, University of Stuttgart extended PICLas, a particle simulation suite and coupled solver with Particle-in-Cell (PIC) and Direct Simulation Monte Carlo (DSMC) modules, to the treatment of polyatomic molecule interactions. The researchers report these latest findings in Physics of Fluids.

The DSMC method is particularly known for its accuracy in modeling rarefied gas flows and accounting for microscopic details, like individual particle velocity and energy in severe flow environments. Moreover, the Total Collision Energy (TCE) model within the DSMC method holds the capacity to simulate chemical processes for variable hard sphere molecules. To measure the method’s simulation accuracy, the researchers compared their PICLas simulation calculations for various measurements, which included mean reaction rates, chemical composition, and collisional energy redistribution, and compared those calculations to analytical Arrhenius solutions for polyatomic reactions. Lastly, the researchers simulated the real-life trajectory point of the Huygens probe into Titan’s atmosphere to produce a feasible simulation of a polyatomic gas flow field around the probe.

Lead author Paul Nizenkov says the team’s method will help engineers to confidently “design a spacecraft’s heatshield and back cover” that would increase “the available mass load needed to transport instruments that will facilitate scientific discoveries at the destination point.”

Nizenkov anticipates that his team’s next step will include a focus on polyatomic gas flow and radiative energy transport behind the spacecraft to enhance prediction of aerothermal and radiative loads.

Source: “Modeling of chemical reactions between polyatomic molecules for atmospheric entry simulations with direct simulation Monte Carlo,” by P. Nizenkov, M. Pfeiffer, A. Mirza, and S. Fasoulas, Physics of Fluids (2017). The article can be accessed at https://doi.org/10.1063/1.4995468 .