Stagnation heat flux estimation in spherically blunt axisymmetric hypersonic models

Hypersonic flows have high heat transfer rates, and their management is essential to avoid detrimental effects. Since accurate prediction and measurement of heat flux in hypersonic test facilities are complicated, heat flux at the stagnation point is mostly estimated using Fay and Riddell formulation with Newtonian tangential velocity gradient approximation. Although it is relatively accurate and reliable, some errors creep in due to incompetent modelling of the tangential velocity gradient. This article studies the applicability of Olivier's tangential velocity gradient formulation for a sphere in the estimation of stagnation heat flux for spherically blunt axisymmetric hypersonic models. Oliver's estimation accurately models the tangential velocity gradient of spherically blunt axisymmetric hypersonic models as the heat flux estimates deviated only by approx. 2%-4% from the measured heat flux. A simplified model for tangential velocity gradient using Shock Standoff Distance and density ratio is also derived and tested for accuracy.