Hypersonic Vehicle Reentry Research Articles

Low electron density channel revealed in the plasma layer of hypersonic vehicle under a novel magnetic control

The “communication blackout” occurs during the reentry of hypersonic vehicles, that is, the electromagnetic wave cannot pass through the plasma sheath due to high electron density formed around the vehicle, which has drawn much attention but has not yet been solved. In this paper, a novel magnetic control approach is proposed, in which a periodic magnetic field is applied near the head of the aircraft. Based on the magnetohydrodynamic simulation, a low electron density channel across the plasma sheath of vehicle under the magnetic control is revealed for the first time, which probably make Ka-band electromagnetic wave pass through. We also find that the reason for the low electron density channel is the variation of the vortex structure in the plasma flow near the wall, by the electromagnetic force exerted on the flow. Furthermore, the optimal magnetic field frequency for generating the low electron density channel is obtained. These findings will be of significant benefit to the solutions for the communication blackout problems.

EM Waves Propagation Characteristics Based on Modified Dielectric Constant Model in Nonuniform Weakly Ionized Dusty Plasma

The influence of weakly ionized dusty plasma on electromagnetic (EM) wave propagation was investigated to understand blackouts in communications during the reentry of hypersonic vehicles. Adopting the Bhatnagar–Gross–Krook (BGK) collision model and charging theory, the total complex dielectric constant of weakly ionized dusty plasma is derived considering solely: 1) a nonzero minimum velocity of the electron; 2) a contribution of the second term of the collision cross-section; and finally, 3) both 1) and 2) considered. Using the propagation matrix method, we analyzed the dielectric constant and propagation properties from our modified models and those of the traditional model for weakly ionized plasma with and without dust. The results show that, regarding EM waves, the dust-free weakly ionized plasma has a larger coefficient of reflection than weakly ionized dusty plasma. Simultaneous considering nonzero velocity and contribution of the second term of the collision cross-section significantly changed the dielectric constant and propagation properties, indicating the nonnegligible role of these two factors. Furthermore, the influence of dust size and concentration on the propagation properties of the EM wave was discussed with considering the two factors. The simulated results show that the coefficient of absorption increases and the coefficient of transmission decreases with increase in size and concentration of dust particles.

Numerical investigation of transpiration and ablation cooling

To predict the integral performance of transpiration and ablation cooling during the reentry of hypersonic vehicles, an unsteady numerical model based on the assumption of thermal equilibrium is presented. The non-thermal equilibrium model and the thermal equilibrium model are coupled by the effective thermal properties of the porous matrix and the coolant. The calculation using the thermal equilibrium model shows the influence of the variation of the effective thermal properties on the numerical results by a comparison between constant and variable thermal properties. The comparison indicates that near the melting temperature of the porous matrix, the position of the moving boundary due to ablation is sensitive to the temperature, therefore, the variation of the thermal properties are considered in this paper. The process of ablation and transpiration cooling is simulated under different numerical conditions. The simulations demonstrate that the injection rate of coolant mass flow and initial temperature of cooling are important parameters for the control of the ablation process.