Blunt-body Reentry Research Articles

Development of a Nonequilibrium Finite-Rate Ablation Model for Radiating Earth Reentry Flows

Thermal protection system design for atmospheric reentry vehicles remains a challenging and complex problem. Recent advances in computational modeling of air–carbon interactions consider competing finite-rate reactions on a limited number of available surface sites. One of the most advanced kinetic models is due to Zhluktov and Abe. However, the Zhluktov and Abe model only describes the oxidation and sublimation of carbon and has no nitridation mechanism. The following study develops several modifications to the Zhluktov and Abe air–carbon model that account for all three reaction mechanisms with the goal of improving cyanogen shock-layer radiation predictions to recent experimental results. First, the study examines two possible paths for carbon nitridation and then assesses the augmented surface reaction model in a representative blunt-body reentry flow. Second, a sensitivity analysis is performed to determine which surface reactions have the most impact on altering cyanogen radiance predictions. It was found that modifications to the oxidation mechanisms significantly improved the comparisons and the nitridation mechanism had a minor effect. Specifically, it was determined that carbon monoxide must be the principal oxidation product at high surface temperatures instead of carbon dioxide, as the Zhluktov and Abe model had originally predicted. More detailed measurements of both the carbon oxidation and nitridation reactions at higher surface temperatures are required to further validate and improve the rate parameters derived in this study.

The First Mission of Iranian Spacecraft: Heat Shield Design

In the present paper, the Iranian spacecraft is considered, and is studied from an aero thermo dynamic viewpoint to design the proper thermal protection system, for its first mission: the suborbital flight. The design procedure is based on the decoupling of the aerodynamic heating phenomena and the solid phase heating process. Due to the sub-orbital mission of this spacecraft as a first flight, an elastomeric material is used as an unconventional heat shield to protect the blunt body reentry vehicle. The full Navier-Stokes equations are used for heat-flux estimation during flight, and the one-dimensional equations for an ablative materials are used to design the thermal protection system, according to the structural criteria.

Aerothermodynamics of generic re-entry vehicle with a series of aerospikes at nose

Re-entry of a blunt nosed vehicle is one of the most intriguing problems in any space programme. Especially in light of various space tourism possibilities, there are many works concerning re-entry of commercial blunt nosed space vehicles. In this paper, a generic blunt body re-entry model represented by a hemisphere-cylinder, fitted axisymmetrically with an aerodisk aerospike at the nose is investigated numerically with commercially available control volume based axisymmetric flow solver. The scaled down re-entry model has a base diameter of 40mm and an overall length of 100mm. A 6mm diameter aerospike fitted axisymmetrically at the nose has a hemispherical cap from which another aerospike of 4mm diameter protrudes which again has a hemispherical cap. Two dimensional compressible, axisymmetric Navier Stokes Equations are solved for a turbulent hypersonic flow of a 5 species, chemically reacting air in thermal equilibrium with free stream conditions of Mach no., static pressure and temperature of 10.1, 16,066Pa and 216.65K, respectively. The results are compared with that of re-entry model without any aerospike. Among the cases investigated, the spiked blunt body having two aerospikes in series with lengths l1 and l2 equal to 30 and 20 respectively and overall length-to-diameter ratio of 1.5 showed a favourable reduction in the peak reattachment heat flux along with high reduction in aerodynamic drag and thus stands as a prospective case for blunt body nose configuration for hypersonic flight.

Flowfield Uncertainty Analysis for Hypersonic Computational Fluid Dynamics Simulations

Uncertainty quantification in the hypersonic flow regime offers valuable information to determine physical models in need of improvement and to assist in design of vehicles and flight experiments. Here we present results of uncertainty quantification analysis based on polynomial chaos method to determine flowfield and surface heat flux uncertainty under typical blunt-body reentry conditions. The NASA Langley Aerothermodynamic Upwind Relaxation Algorithm code [Cheatwood, F., and Gnoffo, P., Manual for the Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA), NASA TM 4674, 1996.], was used for axisymmetric computational fluid dynamics calculations of chemically-reacting, hypersonic flow over FIRE 2 configuration. A third-order polynomial chaos method using the Gauss―Hermite quadrature was applied for determining probability density functions and moments of output quantities. Input parameters such as freestream density, velocity, and temperature were varied, and the propagation of their corresponding uncertainties on output properties of interest through the flowfield were studied. The flowfield regions where the uncertainties are amplified due to nonlinear effects have been determined. An order of magnitude increase in surface heat flux uncertainties was observed for an input freestream velocity uncertainty of ±30 m/s, or 0.29%. This parameter thus has the greatest sensitivity to variations, and conversely the freestream temperature has the least sensitivity. The utility of analyzing higher moments, such as skewness, in addition to mean and deviation of the uncertain output parameters has also been demonstrated.

Attitude Stability of Blunt-Body Capsules in Hypersonic Rarefied Regime

To assess the attitude stability of blunt-body reentry capsules in the hypersonic rarefied flight regime, a systematic numerical procedure has been developed and applied practically to the asteroid sample return capsule. The low-density flows around the capsule are solved by the direct simulation Monte Carlo (DSMC) method in the three-dimensional geometry to determine the low-density aerodynamic coefficients. The overall aerodynamic coefficients are defined by an empirical bridging formula from the results of the DSMC analysis and the continuum coefficients obtained by the modified Newtonian method. By the use of these overall coefficients, the six-degree-of-freedom dynamics of the capsule is analyzed along the reentry trajectory. It is shown that the static instability about the pitching axis occurs in the low-density environments when the center of gravity is located in the rear part of the capsule. However, the pitching motion is found to be stabilized safely by initiation of the spin around the capsule axis at appropriate frequencies.

Comparison of Theoretical and Flight-Measured Ionization in a Blunt Body Re-Entry Flowfield

Plasma diagnostic data from onboard Langmuir probes, reflectometers, antenna VSWR and beacon and telemetry attenuation for blunt body reentry flow field