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DSMC-Neutrals Case Study - Hypersonic Rarefied Flow Simulation

Wave Front ＞ CAE Solution ＞ DSMC-Neutlrals ＞ Hypersonic Rarefied Flow Simulation [日本語] / [English]

DSMC-Neutrals is a 3D rarefied gas analysis software package that utilizes the Direct Simulation Monte Carlo (DSMC) method. By employing an unstructured mesh, it enables simulations of complex geometries. It also supports chemical reaction calculations, making it suitable not only for simulating rarefied gas flows within vacuum chambers but also for modeling thin-film deposition in semiconductor manufacturing processes such as Chemical Vapor Deposition (CVD). If reading this article has made you even slightly interested in rarefied gas analysis or gas flow simulation, please feel free to contact us at any time to request materials or for further information.

Hypersonic Rarefied Flow Simulation

The following shows a simulation of hypersonic rarified flow analysis. The flow velocity is 7.5 km/s, which is 20 times the speed of sound. The chemical reaction calculations take into account the dissociation, recombination, and atomic exchange reactions of nitrogen and oxygen. It can be seen that most of the oxygen has dissociated due to the extremely high temperature on the object’s surface. DSMC-Neutrals is capable of reproducing hypersonic gas flows that cannot be calculated using standard fluid dynamics analysis software. Furthermore, the results from DSMC-Neutrals closely match those reported by Dogra et al. [1].



Computational Domain and Boundary Conditions

▲ Computational Domain and Boundary Conditions



Model Geometry and Mesh

▲ Model Geometry and Mesh



Collision Model


  • Elastic Collision
      Variable Hard Sphere (VHS) model using null-collision method


  • Inelastic Collision

    • Rotation
      Calculated using the elimination method based on the Larsen-Bolgnakke distribution function.
      Degrees of freedom for N2 and O2 ： $2$
      Relaxation value $Zr$ ： $5$

    • Vibration
      Calculated using the exclusion method based on the quantized Larsen-Bolgnakke distribution function.
      The relaxation value $Z_v$ is calculated using the following equation: \begin{align*} Z_v = ( C_1 / T^w ) e^{C_2 T^{-1/3}} \end{align*} Here, the constants $C_1$ and $C_2$ are species-dependent constants.


Chemical Reaction Model

Total Collision Energy (TCE) model calculating collision probabilities based on total collision energy and the constants of the Arrhenius equation


    • Chemical equation
      N2 + M <---> N + N + M
      O2 + M <---> O + O + M
      NO + M <---> N + O + M
      M is the third body particle.

  • Exchange
    • Chemical equation
      NO + O <---> N + O2
      N2 + O <---> N + NO


Results

The results obtained using DSMC-Neutrals are shown below. Although the mesh and detailed configuration parameters used may differ from those in the reference, the results from DSMC-Neutrals reproduce the results presented there.



2D total particle density distribution normalized by a molecular density of 6.98 × 10^19 molecules per cubic meter

▲ Particle density distribution



2D average temperature distribution normalized by 188K

▲ Average Temperature Distribution



Stagnation line上の並進、回転、振動温度 Stagnation line上のモル分率

Results. (Left) Translation, rotation, and vibration temperatures on the stagnation line. (Right) Molar fractions on the stagnation line.



Adiabatic Compression

▲ Adiabatic Compression by Hypersonic Rarefied Flow in Atmospheric Entry of Sphere Object



Reference

    [1] Dogra V. K., Wilmoth R. G., and Moss J. N., AIAA Journal, Vol. 30, No.7, 1789-1794 (1992), https://arc.aiaa.org/doi/10.2514/3.10729


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