Design of Hypervelocity Flow Generator (HFG) and Its Diagnostics

Abstract

Ground facility for hypersonic research is a key element for successful development of aerodynamically proven hypervelocity vehicles. Design concept and diagnostics of hypervelocity flow generator (HFG) were made as a test platform for hypersonic/hypervelocity spacecraft models at NASA Langley Research Center. The HFG is a hypersonic flow field generator using optically heated gas which was blown into an 80-m 3 large vacuum chamber. The vacuum chamber is kept at a stable vacuum pressure with a combination of three large vacuum pumps, while the HFG is in the test mode. The HFG provides relatively a small test section with approximately a 20 cm window. This facility was designed to generate 2.45 km/sec of flow speed, and possibly to generate a continuous flow with the nozzle and vacuum system. The window at test section provides a direct observation of shock wave around a model in order to measure temperature, pressure, and density profile within the shock layer. One of the key test goals under this project was to understand why the emission spectra from the standing shockwave plasma predicted by Lora-Loran codes are significantly different from the measured emission spectra from the Flight Investigation Reentry Environment (FIRE II) Flight. The correct estimate of thermal loading on the leading edge of hypersonic vehicles greatly improves the aerodynamic design, the material selection for vehicle, and the cooling requirement and can be obtained by the precise modeling of emission spectra from shockwave plasma. However, the estimation of thermal loading is not an easy task due to complex non-equilibrium radiative process within high temperature shock layers that still falls into a category of cold plasma. Direct flight experiments are the most desirable, but not a cost-effective approach. Analysis by computational fluid dynamics (CFD) offers many test flexibilities. However, the CFD codes must be fully tested and validated with experimental data before the codes are effectively used for practical design. The large discrepancies between experiments and codes are appeared in hypersonic/hypervelocity flow regime at high altitude of 60-90 km. This HFG facility offers some important parameters for CFD code validation, such as collision cross-sections, relaxation times, reaction rate coefficients and transportation coefficients. The HFG test facility is based on the ejection flow of high temperature gas heated over to 3500 °K through a nozzle. The tungsten gas chamber of HFG is heated up to a desired temperature by a 60-kW optical power beam source. This system consists of an optical power source, a thermal chamber, an expansion nozzle, a test section, and an 80 m 3 vacuum tanks. Total 60 kW optical input power is obtained from the 150 kW Vortek arc lamp system. This optical beam is focused to heat the gas chamber within which a flow media is heated. The maximum achievable temperature of the flow medium reached approximately 3500K or even higher but is limited by the melting point of the chamber material used. The exhaus...