GENERALIZED REFERENCE ENTHALPY FORMULATIONS AND SIMULATION OF VISCOUSEFFECTS IN HYPERSONIC FLOW

A generalized reference enthalpy formulation for the skin friction, he at transfer and radiation-equilibrium temperature distributions over a erodynamic surfaces in attached hypersonic/hyperenthalpic flow is prop osed. The formulation. which has been extensively employed in various forms by numerous investigators in the perfect gas regime, has also be en recently demonstrated to provide adequate estimates of the heat tra nsfer distribution in thermochemically active high enthalpy flow condi tions when coupled to thermochemically active Euler solutions. It is n ow used to reveal the relevant similitude parameters for viscous effec ts in hypersonic flow, and the importance of the temperature distribut ion across the boundary layer and of the temperature-viscosity relatio n. It is shown that, although reproduction of the flight total flow en thalpy as well as surface temperature is the obvious solution for full viscous simulation in (perfect gas) hypersonic flow, the hot surface testing requirement and, in a number of practical applications, also t he hot flow requirement mag be relaxed with reasonably small error tha t can be of the same order as the measurement accuracy in present-day hypersonic testing. This similitude error; however, may increase signi ficantly in cases exhibiting strong viscous/inviscid interaction or wh en the laminar-turbulent transition process becomes important. In this respect, alternative full simulation solutions, which are less demand ing in terms of reproduction of the high levels of flight freestream a nd surface temperature or even Reynolds number, are discussed.