Material Thermal Response Code Research Articles

Evaluation of Sublimation Kinetics for Phenolic Impregnated Carbon Ablator

Recession analyses of stagnation tests conducted in NASA Ames Research Center arcjet facilities with surface heat fluxes high enough for carbon char to sublimate are performed and compared with data. The axisymmetric recession computations are based on both the finite-rate gas–surface interaction model and the standard chemical equilibrium surface ablation model. The finite-rate gas–surface interaction model is studied using three different sets of sublimation coefficients, which are obtained through direct measurements. The standard chemical equilibrium ablation model is established through the tables. The ablating material used in these arcjet tests is phenolic impregnated carbon ablator. The prediction of axisymmetric surface recession is achieved by implicitly coupling a material thermal response code and a flow code. The material thermal response code used in this study is the Two-Dimensional Implicit Thermal-Response and Ablation program, which predicts charring material thermal response and shape change. The flow code solves the reacting Navier–Stokes equations using the data parallel line relaxation method. The recession predictions for three selected arcjet conditions with various base radii are presented. The effect of sticking coefficient for carbon sublimation on recession prediction is investigated, and the prediction discrepancy between finite-rate and chemical equilibrium models is examined and discussed in detail.

Coupled simulation for reentry ablative behavior of hypersonic vehicles

Numerical analyses of hypersonic vehicles ablative behaviors focus on the accurate models of the thermochemical reaction flow field. The assumptions of chemical equilibrium and non-catalytic wall cannot meet the ablative behavior prediction requirements for high Mach number flights with multiphase materials. In this paper, the numerical analysis of hypersonic vehicle reentry involves the nonequilibrium thermochemical flow field and thermodynamic structure with moving boundary. Two surface models, finite rate catalysis model and Park finite rate surface interaction model were applied into the flow field simulation. And the reentry ablative behaviors of two hypersonic vehicles were simulated by the partitioning methods using the computational fluid dynamics code Fluent and the material thermal and structural response code Abaqus with user defined codes. And the two codes were loosely coupled in time to exchange the data. The structural temperature, surface shape change at the wall under different reentry altitudes and various angles of attack were obtained. The validity and reliability of frame work set up were validated with previous work.

Thermal Ablation Simulations of Quartz Materials

A thermal ablation model for glassy materials is proposed. The model includes mass losses from evaporation and condensation as well as from the moving molten layer driven by surface shear force and pressure gradient. This ablation model can be applied in simulations of meteoroid or glassy thermal protection systems for spacecraft. Time-dependent axisymmetric computations are performed by coupling the fluid dynamics code, Data-Parallel Line Relaxation program, with the material thermal response and ablation code, Two-Dimensional Implicit Thermal Ablation simulation program, to predict surface mass lost rate and shape change. For model validation, surface recession and shape change of a quartz sphere–cone arc-jet model are computed, and the predictions are consistent with arc-jet data obtained at NASA Ames Research Center. Parametric studies are also performed to understand the effect of uncertainties of surface heat flux, surface emissivity, and viscosity of molten layer on the recession prediction.

Radiation Modeling for Reentry of Hayabusa Sample Return Capsule

Predicted shock-layer emission signatures during the reentry of the Japanese Hayabusa capsule are presented and compared with flight measurements conducted during an airborne observation mission in NASA’s DC-8 Airborne Laboratory. For selected altitudes at 11 points along the flight trajectory of the capsule, lines of sight were extracted from flowfield solutions computed using the high-fidelity computational fluid dynamics code Dplr. These lines of sight were used as inputs for the line-by-line radiation code Neqair, and emission spectra of the air plasma were computed in the wavelength range from 300 to 1600 nm, a range that covers all of the different experiments onboard the DC-8. In addition, the computed flowfield solutions were postprocessed with the material thermal response code Fiat, and the resulting surface temperatures of the heat shield were used to generate thermal emission spectra based on Planck radiation. Both spectra were summed and integrated over the flowfield. The resulting emission at each trajectory point was propagated to the DC-8 position and transformed into incident irradiance to be finally compared with experimental data.

Evaluation of Finite-Rate Gas/Surface Interaction Models for Carbon-Based Ablator

Two sets of finite-rate gas/surface interaction model between air and the carbon surface are studied. The first set is an engineering model with one-way chemical reactions, and the second set is a more detailed model with two-way chemical reactions. Each of these two proposed models intends to cover the carbon surface ablation conditions including the low-temperature rate-controlled oxidation, the midtemperature diffusion-controlled oxidation, and the high-temperature sublimation. The prediction of carbon surface recession is achieved by coupling a material thermal response code and a Navier–Stokes flow code. The material thermal response code used in this study is the Two-Dimensional Implicit Thermal-Response and Ablation Program, which predicts charring material thermal response and shape change on hypersonic space vehicles. The flow code solves the reacting full Navier–Stokes equations using the data parallel line relaxation method. Recession analyses of stagnation tests conducted in NASA Ames Research Center arc-jet facilities with heat fluxes ranging from 45 to are performed and compared with data for model validation. The ablating material used in these arc-jet tests is phenolic impregnated carbon ablator. Computational predictions of surface recession and shape change are in good agreement with measurement for arc-jet conditions.

Implicit Coupling Approach for Simulation of Charring Carbon Ablators

This study demonstrates that coupling of a material thermal response code and a flow solver with nonequilibrium gas–surface interaction for simulation of charring carbon ablators can be performed using an implicit approach. The material thermal response code used in this study is the three-dimensional version of fully implicit ablation and thermal response program, which predicts charring material thermal response and shape change on hypersonic space vehicles. The flow code solves the reacting Navier–Stokes equations using data-parallel line relaxation method. Coupling between the material response and flow codes is performed by solving the surface mass balance in the flow solver and the surface energy balance in the material response code. Thus, the material surface recession is predicted in the flow code, and the surface temperature and pyrolysis gas injection rate are computed in the material response code. It is demonstrated that the time-lagged explicit approach is sufficient for simulations at low surface heating conditions, in which the surface ablation rate is not a strong function of the surface temperature. At elevated surface heating conditions, the implicit approach has to be taken because the carbon ablation rate becomes a stiff function of the surface temperature, and thus the explicit approach appears to be inappropriate, resulting in severe numerical oscillations of predicted surface temperature. Implicit coupling for simulation of arc-jet models is performed, and the predictions are compared with measured data. Implicit coupling for trajectory-based simulation of Stardust forebody heat shield is also conducted. The predicted stagnation point total recession is compared with that predicted using the chemical equilibrium surface assumption.

Effect of Nonequilibrium Surface Thermochemistry in Simulation of Carbon-Based Ablators

This study demonstrates that coupling of a material thermal-response code and a flow solver using a nonequilibrium gas/surface-interaction model provides time-accurate solutions for the multidimensional ablation of carbon-based charring ablators. The material thermal-response code used in this study is the two-dimensional implicit thermal response and ablation program, which predicts the charring-material thermal response and shape change on hypersonic space vehicles. Its governing equations include total energy balance, pyrolysis-gas mass conservation, and a three-component decomposition model. The flow code solves the reacting Navier–Stokes equations using the data-parallel-line-relaxation method. Loose coupling between the material-response and flow codes is performed by solving the surface mass balance in the flow code and the surface energy balance in the material-response code. Thus, the material surface recession is predicted by finite rate gas/surface-interaction boundary conditions implemented in the flow code, and the surface temperature and the pyrolysis-gas injection rate are computed in the material-response code. Two sets of nonequilibrium gas/surface-interaction chemistry between air and the carbon surface are studied. Coupled fluid-material-response analyses of stagnation tests conducted at the NASA Ames Research Center arcjet facilities are considered. The ablating material used in these arcjet tests was phenolic impregnated carbon ablator. Computational predictions of in-depth material thermal response and surface recession are in excellent agreement with the data for conditions in which carbon recession rate is limited by species diffusion.

Multiphysics Coupled Fluid/Thermal/Structural Simulation for Hypersonic Reentry Vehicles

The main goal of the work described in this paper was to set up a procedure for modeling a thermal protection system for a hypersonic reentry vehicle by extending earlier work done by the authors. A multiphysics framework has been setup for the simulation of hypersonic reentry vehicles using commercial codes FLUENT and LS-DYNA with user-defined programming. The computational fluid dynamics code (FLUENT) and the material thermal and structural response code (LS-DYNA) are loosely coupled to achieve the solution. The surface recession resulting from ablation in the reentry vehicle is simulated by implementing a mesh movement algorithm in LS-DYNA. The vehicle considered in the calculation is an axisymmetric vehicle flying at zero degree angle of attack. DOI: 10.1061/(ASCE)AS.1943- 5525.0000113. © 2012 American Society of Civil Engineers. CE Database subject headings: Simulation; Fluid-structure interactions; Vehicles; Thermal factors. Author keywords: Reentry simulation; Multiphysics simulation; Fluid/structure/thermal interaction of reentry vehicle.

Radiation Modeling For the Reentry of the Stardust Sample Return Capsule

Predicted shock-layer emission signatures during the reentry of the Japanese Hayabusa capsule are presented and compared with flight measurements conducted during an airborne observation mission in NASA's DC-8 Airborne Laboratory. For selected altitudes at 11 points along the flight trajectory of the capsule, lines of sight were extracted from flow field solutions computed using the in-house high-fidelity CFD code, DPLR. These lines of sight were used as inputs for the line-by-line radiation code NEQAIR, and emission spectra of the air plasma were computed in the wavelength range from 300 nm to 1600 nm, a range which covers all of the different experiments onboard the DC-8. In addition, the computed flow field solutions were post-processed with the material thermal response code FIAT, and the resulting surface temperatures of the heat shield were used to generate thermal emission spectra based on Planck radiation. Both spectra were summed and integrated over the flow field. The resulting emission at each trajectory point was propagated to the DC-8 position and transformed into incident irradiance to be finally compared with experimental data.

One-Dimensional Ablation Using a Full Newton's Method and Finite Control Volume Procedure

The development and verification of a one-dimensional constant density material thermal response code with ablation is presented. The implicit time integrator, control volume finite element spatial discretization, and Newton's method (with an analytical Jacobian) for the entire system of residual equations have been implemented and verified for variable material properties, Q* ablation, and thermochemical ablation problems. Timing studies were performed, and when accuracy is considered, the method developed in this study exhibits significant time savings over the property lagging approach. In addition, maximizing the Newton solver's convergence rate by including sensitivities to the surface recession rate reduces the overall computational time when compared to excluding recession rate sensitivities.

Predictions of Ablating Hypersonic Vehicles Using an Iterative Coupled Fluid/Thermal Approach

A new iterative approach for the prediction of the ablation of hypersonic vehicles is presented. The solution technique is achieved by an iterative coupling of a computational e uid dynamics code and a material thermal response code through mass and energy balances at a common interface. The iterative approach proved necessary due to severe numerical instabilities that resulted when an explicit technique was employed involving a loose coupling approach between the two codes. The results presented are for an axisymmetric carbon ‐carbon nosetip on a reentry vehicle e ying a ballistic trajectory. Details of the computational technique and the computed e owe eld and materialthermalresponsearepresented.Comparisonsweremadewith thewidelyusedABRES ShapeChange Code (ASCC), and favorable results were obtained.