The paper presents the numerical modelling of the effects of surface roughness on heat transfer of high Mach number flow to a blunt body. Computational fluid dynamics (CFD) is pursued using our in-house Clithium2 code for axisymmetric flow of M = 6 impinging on a flat-faced circular cylinder. Laminar and ideal gas conditions are assumed due to the short flow time and low stagnation temperature (<2000 K). Good to excellent agreement is achieved with known results of stagnation flow over flat smooth surface. The heat flux is indirectly calculated using CFD results of boundary layer edge condition due to the layer’s thin thermal thickness. A peak at the cylinder’s face centre is found, where roughness initially causes a decline in the heat flux but an increase at 1000 micron or above. The stand-off distance of the bow shock wave behaved inversely to the heat flux. Real gas effects and the breakdown of the continuum assumption are also discussed for further analysis.