Effect of the sliding friction on heat transfer in high-speed rarefied gas flow simulations in CFD

Different nature of the heat transfer computation between the CFD and DSMC methods in rarefied gas flow simulations leads to the difference of their heat transfer results. This paper will revisit a formulation of heat transfer in CFD that includes the sliding friction part for a planar surface. The sliding friction was first introduced by Maslen, and used to be omitted in calculating the CFD heat transfer. This formulation will be extended to compute the heat transfer over the curved surfaces such as NACA0012 micro-airfoil and the sharp 25–55-deg. biconic. Two these configurations 1) NACA0012 micro-airfoil (M = 2) with various Kn = 0.026, 0.1 and 0.26 with the angles-of-attack from 0-deg. to 20-deg., and a sharp 25–55-deg. biconic (M = 15.6) are simulated by the CFD method, which solves the Navier-Stokes equations within the OpenFOAM framework. Moreover, the flat plat cases with various wall temperatures (Tw = 77 K and 294 K) are also undertaken to investigate the significance of the sliding friction on the heat transfer. The CFD simulation results of the heat transfer involving the sliding friction give good agreements with the DSMC data, especially the NACA0012 micro-airfoil cases with high Knudsen numbers Kn = 0.1 and 0.26.