Search

Radio frequency blackout indicates the communication interruption between signal monitoring sites and re-entry vehicles; it is a serious threat to the safety of astronauts and the space exploration missions. In this study, a surface catalytic model coupled with a thermochemical non-equilibrium computational fluid dynamic model is developed to study the catalytic wall effect on the plasma sheath of a hypersonic re-entry vehicle. The mechanism of the surface catalytic effect on the plasma sheath of a re-entry capsule is revealed by a comparative study. The flow-field characteristics simulated under conditions of the full-catalytic and non-catalytic walls are compared and discussed for the hypersonic atmospheric re-entry capsule at different altitudes. The chemical and physical mechanisms behind the surface catalytic effect of the re-entry capsule are analyzed. The experimental data of Radio Attenuation Measurement-C-II are used to validate the numerical model established in the present study. It is found that the numerical results simulated with the fully catalytic wall are more consistent with the experimental data. Near the capsule wall, the mole fractions of the species N, O, N+, and O+ decrease as the catalytic recombination coefficient increases. Because of the surface catalytic effect, the communication black is mitigated due to the reduction of the electron number density in the wake zone of the capsule. [ABSTRACT FROM AUTHOR]

A multi-physics thermochemical non-equilibrium model is established to study the flow characteristics of the plasma sheath around an atmospheric reentry demonstrator. This model includes the tight coupling of Navier–Stokes equations, 54 chemical reactions of air, and a four-temperature model. The processes of dissociation, ionization, and the internal energy exchanges of air components were successfully simulated during aerodynamic heating of the reentry vehicle. The distributions of plasma sheath temperature, the molar fraction of air species, stagnation pressure, surface pressure, and electron number density around the reentry vehicle were obtained at different flight altitudes. Additionally, to validate the numerical model developed in this study, the flow characteristics of the Radio Attenuation Measurement-C-II (RAM-C-II) vehicle are also simulated and then compared with corresponding experimental data. They show good consistency in general. It is found that when the vehicle is at a high flight altitude, there is a strong thermochemical non-equilibrium phenomenon around the vehicle. However, the plasma sheath tends to be in local thermal equilibrium at a low flight altitude. The distance from the shock layer to the stagnation point decreases with a decrease in reentry altitude from 90 to 65 km but increases with a decrease from 65 to 40 km. The electron number density in the shock layer is maximum. The distribution of the electron number density in the wake region differs significantly at different flight altitudes. [ABSTRACT FROM AUTHOR]

In order to investigate the relationship between the flow-field parameters outside the vehicle and the altitude, this paper takes the Atmospheric Reentry Demonstrator (ARD) with an angle of attack of â€"20° as the research object and adopts a two-temperature model coupled with the shear-stress transport k â€" ω turbulence model to focus on the variation of flow-field parameters including flow-field pressure, Mach number and temperature with the reentry altitude. It is found that the flow-field high-pressure region and low-Mach region both appear in the shock layer near the head of the ARD, while the maximum pressure of the surface appears on the windward side of the ARD’s head with a toroidal distribution, and the numerical magnitude is inversely proportional to the radius of the torus. With fluid through the shoulder of the ARD flow expansion plays a dominant role, the airflow velocity increases, the Mach number of the windward side of the rear cone increases and the flow-field pressure and surface pressure rapidly decrease. When the fluid passes through the shock layer, the translationalâ€"rotation temperature will increase before the vibrationâ€"electron temperature, there is a thermal non-equilibrium effect and the two temperatures will rapidly decrease again when approaching the surface of the ARD due to the existence of temperature gradient. At the same time, both the windward side of the shoulder and the back cover of the ARD suffer from a large thermal load and require thermal protection. [ABSTRACT FROM AUTHOR]

Correlation diagnosis in multivariate process quality management is an important and challenging issue. In this paper, a new diagnostic method based on quality component grouping is proposed. Firstly, three theorems describing the properties of the covariance matrix of multivariate process quality are established based on the statistical viewpoint of product quality, to prove the correlation decomposition theorem, which decomposes the correlation of all the quality components into a series of correlations of components pairs, and then by using the factor analysis method, all quality components are grouped in order to maximize the correlations in the same groups and minimize the ones between different groups. Finally, on the basis of correlations between different groups are ignored, T2 control charts of component pairs in the same groups are established to form the diagnostic model. Theoretical analysis and practice prove that for the multivariate process quality whose the correlations between different components vary considerably, the grouping technique enables the size of the correlation diagnostic model to be drastically reduced, thus allowing the proposed method can be used as a generalized theoretical model for the correlation diagnosis. [ABSTRACT FROM AUTHOR]

In the present study, a multiphysics mathematical model for reproducing the flow field characteristics of an inflatable aeroshell was developed to study the aerodynamic properties of the flow around a membrane reentry vehicle. Firstly, the configuration and flight sequence of a membrane reentry vehicle used in the experiment were introduced. Secondly, mathematical equations of multiphysics fields, such as the Navier–Stokes equations, the heat conduction equation, and the membrane deformation equation, were introduced and numerically solved. The variation characteristics of the flow properties during the aerodynamic heating of a membrane vehicle were studied and discussed in detail under the conditions of different flight altitudes. The results showed that for the membrane vehicle, the high-temperature flow field at the front of its capsule was in a state of thermal non-equilibrium with the decrease of flight altitude and its membrane deformation degree was proportional to the pressure. The translational temperature and electron number density of the plasma flow around the aeroshell remained at a relatively low level for the membrane vehicle so that the blackout phenomenon scarcely occurred during its atmospheric reentry. [ABSTRACT FROM AUTHOR]