A study of internal energy relaxation in shocks using molecular dynamics based models

Area of Science:

• Chemical Physics
• Aerospace Engineering
• Computational Chemistry

Background:

• Hypersonic flows involve complex molecular interactions and energy transfer processes.
• Accurate simulation of nitrogen (N2) relaxation is crucial for understanding high-temperature gas dynamics.
• Existing models may not fully capture the behavior of N2 under extreme conditions.

Purpose of the Study:

• To simulate vibrational and rotational relaxation rates for N2 + N and N2 + N2 systems under hypersonic flow conditions.
• To calculate cross sections for V-T energy transfer, collisions, and dissociation.
• To evaluate the impact of new potential energy surfaces on Direct Simulation Monte Carlo (DSMC) models.

Main Methods:

• Utilized molecular dynamics (MD) simulations with recent potential energy surfaces (PESs).
• Employed MD-quasi-classical trajectory (QCT) methods to compute energy transfer and collision cross sections.
• Integrated MD/QCT results into DSMC simulations for hypersonic flow over a blunt body.

Main Results:

• Rotational relaxation number increases with translational temperature and decreases as rotational temperature approaches translational temperature.
• Vibrational relaxation number decreases with translational temperature and approaches the rotational relaxation number at high temperatures.
• N2 + N2 system generally exhibits larger relaxation numbers compared to N2 + N.
• DSMC simulations incorporating new data show decreased translational temperature and rotational temperature near vibrational temperature.

Conclusions:

• New potential energy surfaces provide valuable insights into N2 relaxation dynamics at high temperatures.
• Current physical models in DSMC may require revision based on these advanced simulation results.
• Accurate PESs are essential for improving the fidelity of hypersonic flow simulations.