Heat transfer in nonequilibrium flows with homogeneous and heterogeneous recombination reactions

The aeroheating performance of hypersonic vehicles is usually significantly influenced by the chemical reaction processes. For the new-generation hypersonic cruise vehicles, the boundary-layer flow is shown to be in chemical nonequilibrium due to rarefied gas effects. As a result, there will be a competition between the homogeneous recombination of atoms in the near-wall flowfield and the heterogeneous recombination on the catalytic wall surface, which, leading to a coupling of the heat diffusion and conduction, is beyond the application scope of the classical theories developed originally for the traditional blunt reentry vehicles. In this paper, the theoretical modeling and the direct simulation Monte Carlo method are employed to study the corresponding rarefied nonequilibrium flow and heat transfer phenomena near the sharp leading edges. A generalized model is proposed to evaluate the deviation of the actual aeroheating performance from the classical description. Based on this model, an integrated nonequilibrium criterion and a simple but effective bridging function are introduced to predict the stagnation-point heat transfer under the competitive effects between the homogeneous and heterogeneous recombination of atoms. The analytical formula is validated by the numerical results under various flow conditions. Copyright © 2018 by the American Institute of Aeronautics and Astronautics, Inc.