Numerical Investigation of Plasma Flows Inside Segmented Constrictor Type Arc-Heater

Abstract

Arc-jet wind tunnels produce the flow conditions as an entry vehicle entering the atmosphere of a planet. They are widely used in experimental investigations of heat shield materials and thermal protection systems (TPSs). For a detailed analysis of experimental data, it is very important to know the conditions of the plasma flow that reaches a specimen of heat shield material or the TPS; e.g., the total pressure, total temperature and turbulence intensity of the plasma flow. However, it is hard to measure the properties of plasma flow because of its high temperature. In particular, it is almost impossible to measure the turbulence intensity inside an arc heater. On the other hand, if accurate physical models are adopted, computational fluid dynamics (CFD) can provide very useful information on plasma flow, and play an important role on the analysis of experimental data. Several types of arc heaters have been developed according to the required range of total pressure and total enthalpy; these include the Huels type, constricted type, segmented constrictor type, inductively-coupled plasma (ICP), MPD (magnetoplasmadynamic) and so on. Among them, the segmented type and the Huels-type arc heaters have been widely used in aerospace applications since they can provide a large amount of plasma flow at a high total pressure condition. Compared to other types of arc heaters, the Huels arc heater produces a severe arc fluctuation phenomenon in time and space whereas a segmented arc heater produces stable arc flow throughout a long constrictor. At present, CFD analysis is more useful for the analysis of segmented type arc heaters since it is not easy to calculate a Huels-type arc heater accurately, even though state-of-the-art CFD technologies have been applied. There have been several numerical investigations of the flow inside segmented arc heaters; these studies mainly focused on the improvement of physical models including radiation and the turbulence model. In the 1970s, Nicolet et al. (1975), based on the work of Watson and Pegot (1967), developed the ARCFLO numerical code. The ARCFLO code adopted a two-band radiation model and an algebraic turbulence model. However, since ARCFLO uses the space marching technique, it requires knowledge of downstream conditions in advance. Thus, the applicability of the ARCFLO code was quite restrictive in the actual design of arc heaters. Therefore, Kim et al. (2000) developed a time-marching code, ARCFLO2, to overcome this shortcoming. ARCFLO2 retained the two-band radiation model and the algebraic turbulence model. Sakai and Olejniczak (2001, 2003) improved the numerical models of ARCFLO and ARCFLO2 by adopting a new three-