Approximations for nonequilibrium hypervelocity aerodynamics

The exponential term in the expression for the forward reaction rate in a nonequilibrium dissociating gas has been exploited to produce three simplified, approximate concepts that assist in understanding the effects of nonequilibrium in hypervelocity flows. The concepts are as follows: a constant-temperature approximation, the thermodynaniic decoupling of the temperature, and pressure-gradient reaction quenching. These concepts are seen to allow satisfactory prediction of shock standoff on a sphere, the growth of shock detachment on a wedge, the variation of shock standoff on a delta wing, and the shock-layer density profile downstream of a curved shock. The mechanism underlying the constant-temperature approximation also makes it possible to develop a second-order theory of nearly constant-pressure flows, which is used to predict the nonequilibrium center-of-pressure shift on wedges and delta wings

Species measurements in a hypersonic, hydrogen-air, combustion wake

A continuously sampling, time-of-flight mass spectrometer has been used to measure relative species concentrations in a two-dimensional, hydrogen-air combustion wake at mainstream Mach numbers exceeding 5. The experiments, in a free piston shock tunnel, yielded distributions of hydrogen, oxygen, nitrogen, water, and nitric oxide at stagnation enthalpies ranging from 5.6 MJ kg to 12.2 MJ kg and at a distance of approximately 100 times the thickness of the initial hydrogen jet. The amount of hydrogen mixed in stoichiometric proportions was approximately independent of the stagnation enthalpy, despite the fact that the proportion of hydrogen in the wake was increased with stagnation enthalpy. Roughly 50% of the mixed hydrogen underwent combustion at the highest enthalpy. The proportion of hydrogen reacting to water could be approximately predicted using reaction rates based on mainstream temperatures

The effect on an acoustic wave as it traverses an unsteady expansion

The shift in fundamental frequency that occurs in acoustic waves is obtained for waves traversing an unsteady expansion. It is shown analytically that downstream of the unsteady expansion all frequencies approach one of an infinite number of discrete frequencies independent of the frequency upstream of the unsteady expansion. This theoretical analysis is used to accurately predict the period of noise observed in an expansion tube when operated at low enthalpies

Scramjet testing in the T4 impulse facility

Scramjet testing in the free piston driven shock tunnel T4 has been undertaken for the past 10 years with a range of experiments spanning diagnostic pressure measurements hi simple combustors to force measurements on complete and integrated scramjet models. Although scramjet models have been shown in the T4 facility to developing sufficient thrust to offset their drag using both hydrogen and hydrogen/silane mixtures, these engines were not highly efficient. In response to this, the majority of the recent scramjet experimentation at the T4 facility has been directed towards improving this efficiency. This paper discusses the success and failures of this line of experiments and highlights some of the concepts which have been found to be important hi the development of these engines