Nonequilibrium shock layer in large-scale arc-heated wind tunnel

Abstract

An arc-heated wind tunnel is one of the most important facilities to reproduce the high-temperature environment during atmospheric entry for plasma studies and spacecraft development. However, the properties of the plasma flow cannot be determined easily, because of the complex physical phenomena, such as arc discharge and supersonic expansion, occurring inside the tunnel. The shock-layer structure should be clarified to evaluate the aerodynamic characteristics, communication conditions, and thermal- protection performance in a high-temperature environment. In this study, shock-layer spectroscopic measurements of a plasma flow in a 1 MW-class arc-heated wind tunnel were performed. The γ-band system spectra of nitric oxide (NO) molecules in the ultraviolet region were measured, and the rotational temperature was determined via spectral fitting through comparison with numerical spectra. The rotational temperature of the NO molecules in the shock layer was 6,620±350 K, whereas that in the free jet was much lower at 770±60 K. This difference is attributed to the increase in translational temperature by flow stagnation across the shock wave, followed by the increase in rotational temperature owing to energy relaxation. A computational science approach revealed the detailed structure of the flow through comparisons with the spectroscopic measurement data. The wind tunnel flow became hypersonic with high temperature and low pressure due to the expansion and acceleration at the nozzle and test chamber. Although the temperature increased across the shock wave, the chemical reaction progressed slowly owing to the low-pressure environment. The rotational temperature in the shock layer increased with the translational temperature; this agrees with the trend of the measurement results. The arc-heated flow was found to be in strong thermo- chemical nonequilibrium in the shock layer. Through this study, a detailed structure of arc-heated flow was revealed and its methodology was also proposed.

Experimental study on the life and performance of an improved DC arc plasma torch

“…The DC arc plasma torch, which can generate hightemperature thermal plasma with high energy density (∼10 6 -10 7 J m −3 ) and high heat flux density (∼10 7 -10 9 W m −2 ) [1][2][3], is widely used in many industrial applications, such as materials processing [4][5][6], waste treatment [7][8][9], energy * Authors to whom any correspondence should be addressed. conversion [10][11][12], aerospace [13][14][15][16] and so on. As a high temperature heat source as well as a chemically reactive particles source, the critical problem limiting the DC arc plasma torch applications is the electrode erosion caused by the extremely high current density and heat flux [17][18][19], which can not only reduce the service life of the device but also contaminate the plasma environment by the erosion products, further limiting the performance of arc plasma torch.…”