Heat Transfer In Hypersonic Flows
The aircraft around us are either subsonic i.e Mach number less than 1 or supersonic i.e Mach number greater than 1, with most of them being subsonic.The main design goals of such aircraft are minimizing weight and maximizing stability. However, in the case of hypersonic aircraft, another very important design consideration is aerodynamic heating. The flight is considered to be hypersonic if the flight velocity is greater than Mach-5. There isn’t any sudden change when Mach number reaches five but generally this number is considered as the threshold. Extensive research had been done for more than half a century on aerodynamic heating. Two approximate methods to estimate the heat transfer are discussed here. Eckert's reference temperature method for estimation of heat flux for flow over a flat plate and Fay-Riddell’s relation for estimation of stagnation point heat flux. Although solutions by computational fluid dynamics (CFD) would give the most precise prediction, CFD is still costly in terms of its long computing-time. So simple approximate methods are needed for a practical engineering analysis because of their short computing-time. These methods are applied for estimation of heat flux on a wave rider, which is a hypersonic vehicle in which attached or nearly attached shock wave is used to improve aerodynamic efficiency. To calculate heat flux over the surface of a wedge shaped waverider, Eckert’s reference temperature method is used and to calculate heat flux on a blunt body, Fay-riddell’s relation is used. The heat flux values are computed at various Mach numbers and plots are made to understand the variation of these values.
Keywords: Aerodynamic heating, Eckert, Fay-Riddell, Heat Flux, Temperature