Chemistry Modelling for Planetary Space Craft

 

Hypersonic space craft which typically operate in rarefied gas environments are subject to extremes of velocity and altitude, so it is important that the aerodynamic and thermal loads on the vehicle are properly characterised if the feasibility of the vehicle design is to be accurately assessed. The vehicle may also encounter gas-side chemical reactions that can have a significant influence on aerodynamic performance and vehicle surface heat flux. Numerical models which fail to incorporate such reacting flows miss out on an essential part of the flow physics surrounding the vehicle.

An open source implementation of chemistry modelling for the direct simulation Monte Carlo (DSMC) method has been developed by researchers in the James Weir Fluids Laboratory (www.strath.ac.uk/mae/jwfl) and the Centre for Future Air-Space Transportation Technologies (www.strath.ac.uk/fastt). A recent approach known as the quantum kinetic (Q-K) method has been adopted to describe chemical reactions in a 5-species air model using DSMC procedures based on microscopic gas information. The Q-K technique has been implemented within the framework of the dsmcFoam code, a derivative of the open source CFD code OpenFOAM. Results for vibrational relaxation, dissociation and exchange reaction rates for a single cell, adiabatic bath demonstrate the successful implementation of the Q-K model when compared with analytical solutions for both inert and reacting conditions. Finally, a comparison is made between the Q-K and total collision energy (TCE) chemistry approaches for a hypersonic test case.

 

Figure 1 shows the comparison of NO production for hypersonic air flow over a 2D cylinder. The conditions correspond to an altitude of 86 km in the Earth’s atmosphere and a Mach number of 24.85. The results demonstrate the successful implementation of the Q-K chemistry approach in comparison with the established DSMC code MONACO which uses an alternative chemistry technique called the total collision energy (TCE) model.

For further details please contact Dr Tom Scanlon,  Senior Lecturer at the Department of Mechanical and Aerospace Engineering at the University of Strathclyde (tom.scanlon [at] strath [dot] ac [dot] uk).

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