Rarefaction criterion and non-Fourier heat transfer in hypersonic rarefied flows

As a hypersonic flow transits from continuous to more and more rarefied, both the bow shock wave and the boundary layer over a leading edge will gradually become thickening, touching, and interlacing with each other, characterizing the evolution of the flow field structure. Correspondingly, an increasing nonlinear non-Fourier feature emerges from the aeroheating instead of the linear Fourier’s law. An intuitive theoretical model is proposed, and it is found that the ratio of the non-Fourier’s part to Fourier’s part of the heat flux term is a universal flow parameter to predict and describe both the physical phenomena above-mentioned. This model leads to a physically meaningful criterion to classify hypersonic rarefied flow regimes. New conclusions obtained are validated by present direct simulation Monte Carlo results.