Significance of Nonequilibrium Surface Interactions in Stardust Return Capsule Ablation Modeling

Abstract

The gas-surface modeling of high-density materials exposed to high-pressure atmospheric reentry conditions was extended to include low-density materials interacting with low-pressure atmospheric conditions. The fully implicit ablation thermal response code and multicomponent ablation thermochemistry program were extended to include nonequilibrium surface conditions for the Stardust return capsule. The Stardust return capsule reentered Earth's atmosphere experiencing low pressure and had a low-density heat shield material. The material response of the Stardust return capsule was previously only modeled with surface equilibrium. Validation against Stardust reentry flight data showed that the equilibrium assumption led to an overprediction of recession and that the inclusion of nonequilibrium reduced the overprediction of this parameter. Incorporating the Park finite rate model nonequilibrium surface conditions led to a reduction in the calculated value of recession at the stagnation point from 1.12 to 0.72 cm in a nominal simulation of the Stardust return capsule. The nonequilibrium recession was closer to the measured recession of 0.65 cm. Incorporating nonequilibrium conditions also decreased the calculated total heat load from 28 to 19 kJ=cm 2 . The improved material response method is applicable to a range of reentries, including future missions such as the Orion crew exploration vehicle. NomenclatureB = preexponential factor, s 1 B 0 = dimensionless mass blowing rate, _ m= e u e C M C H = Stanton number for heat transfer C i = mass fraction for species i C M = Stanton number for mass transfer c p = specific heat, J=kg-K D i = diffusion coefficient for species i, m 2 =s E = activation temperature, K F = view factor H r = recovery enthalpy, J=kg h = enthalpy, J=kg h = partial heat of charring, J=kg k = Boltzmann constant, J=K M = molecular weight, kg=mole m = mass, kg _ m = mass flux, kg=m 2 s p = pressure, N=m 2 q c = conductive heat flux, W=m 2 q rad = radiative heat flux, W=m 2 T = temperature, K u = velocity, m=s v w = mass injection velocity, m=s x = moving coordinate system, y s, m Y = element mass fraction y = stationary coordinate, m = surface absorption = efficiency of gas-surface interaction = volume faction of resin " = surface emissivity = blowing reduction parameter = density, kg=m 3 = Stefan-Boltzmann constant, W=m 2 K 4 = decomposition reaction order Subscripts c = char d = density component e = boundary-layer edge g = pyrolysis gas i = surface species k = element or gaseous base species s = surface v = original w = wall

Coupled Radiation-Gasdynamic Model for Stardust Earth Entry Simulation

“…Nevertheless, the present result is comparable to the numerical value of 24,000 K by Oylnick et al [2]. The vibrational relaxation phenomenon associated with the collision process is also correctly duplicated by the computational simulations by comparison with results in literature [2][3][4][5]. The results show that the vibrational temperatures equilibrate with translational mode toward the stagnation point by the isothermal condition of all excited chemical species.…”

“…Nevertheless, all reduced-dimension computational approximations at an angle of attack condition are degraded by omitting the three-dimensional relief effect in the shock layer. Figure 9 displays the distributions of species concentration in mass fractions at the trajectory stages; t 42, 48, and 54 s. The surface of the Stardust space vehicle is assumed to be fully catalytic like most reentry simulations [2][3][4][5]. The computed species concentration profiles agree extremely well with the results of Park [16].…”

“…Aerothermodynamic computational analyses of the Stardust capsule have been carried out by several investigations in the past years [2][3][4][5][6][7]. The present investigation continues these efforts for improving the interdisciplinary computational capability with increased physical fidelity by duplicating the flight-test condition at an angle of attack.…”

“…Solving thermal radiation heat transfer problems associated with reentry space vehicles requires the coupling of aerodynamics, chemical kinetics, and quantum physics [4,5]. In practical applications, a classification of the problems into Martian/orbital Earth entry and Earth superorbital entry can further focus the required scientific disciplines.…”

Effect of Nonlocal Vacuum Ultraviolet Radiation on a Hypersonic Nonequilibrium Flow

“…Ai; j = Einstein coefficient for spontaneous emission from state i to state j, s 1 Ai; c = Einstein coefficient for photoionization from state i to continuum state, s 1 Bi; j = Einstein coefficient for stimulated emission and absorption, cm 3 m=J-s c = speed of light, 2:9979 10 10 cm s 1 d = distance of a traveling photon, cm D surf = distance from vehicle surface, m e = electron charge, 4:8030 10 10 statcoul E i = electronic term energy for atomic level i, J E emis = total emission energy, W=m 3 G = incoming radiative intensity integrated over all directions, w=cm 2 -m g = degeneracy, dimensionless h = Planck's constant, 6:6262 10 34 Js I = radiative intensity, w=cm 2 -m-sr i, j = index of electronic state, dimensionless K e i; j = excitation rate coefficient of collisional transition from state i to state j by electron impact, cm 3 s 1 Ki; c = excitation rate coefficient of collisional transition from state i to continuum state, cm 3 s 1 K n; 1 = freestream Knudsen number, dimensionless k = Boltzmann's constant, 1:3806 10 23 such as the Stardust sample return capsule (SRC) [1][2][3][4][5][6] or Crew Exploration Vehicle [7] experience thermochemical nonequilibrium flow conditions where molecules and atoms are strongly dissociated and weakly ionized. These complex chemical phenomena occurring behind the shock wave lead to high-temperature ionized flows that generate a severe heating load on the thermal protection system (TPS).…”