The last two decades have brought two important developments for aeroth-
modynamics. One is that airbreathing hypersonic flight became the topic
of technology programmes and extended system studies. The other is the
emergence and maturing of the discrete numerical methods of aerodyn-
ics/aerothermodynamics complementary to the ground-simulation
facilities, with the parallel enormous growth of computer power.
Airbreathing hypersonic flight vehicles are, in contrast to aeroassisted
re-entry vehicles, drag sensitive. They have, further, highly integrated
lift and propulsion systems. This means that viscous eflFects, like
boundary-layer development, laminar-turbulent transition, to a certain
degree also strong interaction phenomena, are much more important for
such vehicles than for re-entry vehicles. This holds also for the
thermal state of the surface and thermal surface effects, concerning
viscous and thermo-chemical phenomena (more important for re-entry
vehicles) at and near the wall. The discrete numerical methods of
aerodynamics/aerothermodynamics permit now - what was twenty years ago
not imaginable - the simulation of high speed flows past real flight
vehicle configurations with thermo-chemical and viscous effects, the
description of the latter being still handicapped by in- sufficient
flow-physics models. The benefits of numerical simulation for flight
vehicle design are enormous: much improved aerodynamic shape definition
and optimization, provision of accurate and reliable aerodynamic data,
and highly accurate determination of thermal and mechanical loads. Truly
mul- disciplinary design and optimization methods regarding the layout
of thermal protection systems, all kinds of aero-servoelasticity
problems of the airframe, et cetera, begin now to emerge.
