Radiatively Driven Hypersonic Wind Tltnnel

This paper outlines a new approach to the design of hypersonic wind tunnels. This new approach is motivated by fundamental limitations of conventional isentropic expansions that arise from the very high temperatures required to achieve the necessary enthalpy for hypersonic flow. These high temperatures lead to excessive throat degradation and contaminated air in the test section. The consequence is that the run times of conventional facilities must be short, and tests are conducted in "air " of unknown composition containing exceedingly high concentrations of radical and superequilibrium species such as NO as well as ablated plenum and throat material. The radiatively driven wind-tunnel approach takes advantage of the real gas properties of air to achieve high enthalpy at low temperature in the plenum, thus minimizing throat degradation and suppressing the formation of unwanted species in the plenum. Additional energy is radiatively added downstream of the throat in the expansion section to achieve the desired test conditions. The temperature of the air is kept low throughout the expansion, so that the formation of superequilibrium species and radicals is kept to a minimum. Radiative sources that couple to air include high-power lasers and microwave devices. A one-dimensional model including optical coupling is developed using, as an example, an HF laser coupled to the naturally occurring CCh in air