Speaker
Description
Introduction
During atmospheric entry flights, a substantial amount of radiative heat transfer occurs around surface of spacecraft and this affects the success of designed mission. The radiative heat transfer roughly depends on the fourth power of governing temperature which implies the accurate representation of it is one of the crucial components to design a thermal protection system (TPS).
Depending on purposes, radiation analysis requires a wide range of fidelity in its numerical approach. For example, to identify stagnation point heating during an atmospheric entry flight, the radiative transfer equation (RTE) can be integrated using quasi-one-dimensional approximations, such as the tangent-slab and the spherical-cap methods, without significant loss of accuracy. However, to identify the radiative heat flux incident to the afterbody of a spacecraft by including the radiative cooling effect, a flow-radiation coupled approach to multi-dimensional spatial grid topology is inevitable. This aspect requires the development of a numerical framework that can manage the radiative heat transfer problem accurately and efficiently with variable levels of numerical fidelity.
To this end, this work aims to develop such an improved numerical toolbox for the high-temperature radiation analyses, currently targeting applications to hypersonic aerothermodynamics study. This abstract summarizes the modeling framework with selected results of applications.
Overview of Radiation Modeling Framework
In this work, a numerical toolbox MURP (MUlti-fidelity Radiation Package) has been developed to encapsulate various kinds of radiation analysis strategies required for high-temperature aerothermodynamics and astrophysical studies. It provides a flexible, efficient, and accurate numerical framework and this has been achieved by integrating the following three key components.
a. Radiative Transport
The MURP supports integration of the radiative transfer equation (RTE) in one-, two-, and three-dimensional spatial grid topology that includes absorbing, emitting, and scattering non-gray medium. For one-dimensional cases, either SHOCK-TUBE or HEATING modes can be used. The former provides a spatially-resolved intensity profile that can be compared against shock-tube measured data. The latter can be used to compute wall-directed radiative heat flux based on the tangent-slab or spherical-cap methods to integrate the RTE.
In multi-dimensional grid cases, the MURP supports two-dimensional, which includes axisymmetric, and three-dimensional RTE solvers. In these cases, the RTE is integrated by applying a finite-volume method (FVM) for both spatial and angular discretizations. The parallel I/O and distribution of the spatial mesh along the multiple processors are performed using a DMPlex object within the open-source library PETSc.
b. Spectral Property
A line-by-line (LBL) radiation module is employed to simulate detailed non-Boltzmann spectral properties at a given thermodynamic condition. This model includes bound-bound, bound-free, and free-free transitions from atomic, diatomic, and triatomic species. The non-Boltzmann electronic populations of upper and lower states of radiating species are computed based on the concept of non-Boltzmann correction factor. The radiation spectra emitted from species that can exist in the atmospheric compositions of Earth, Mars, Titan, Jupiter, and other kinds of ablative gaseous species from meteorite can be simulated to estimate spectral properties.
Several kinds of reduced-order modeling strategies have been implemented in the MURP to reduce computational costs required for radiative heat transfer simulations. In this study, we demonstrate the multi-band opacity binning (MBOB) approach, which guarantees accuracy and efficiency for analyses of the diatomic molecular band systems.
c. Coupling
Coupling with other numerical codes, for example, the one between flow and radiation fields, is achieved through a volumetric coupling strategy. An open-source library preCICE is used to take care of the description of the coupler environment along with data exchange. A flow field solver HEGEL (High fidElity tool for maGnEto-gas-dynamics simuLations) developed at the University of Illinois is employed to obtain temperature and species number density distributions including thermochemical nonequilibrium effects. The MURP then determines the amount of radiative cooling by solving the RTE and feeds it back to the energy source term of HEGEL until the temperature field is frozen. The present study demonstrates a flow-radiation coupling for Titan atmospheric entry flight conditions.
Applications to Hypersonic Non-Boltzmann Radiation Analysis
In the present study, electronic non-Boltzmann radiative heat transfer has been analyzed for Titan atmospheric entry flight conditions. First, we have studied features of electronic non-Boltzmann radiation by simulating the test campaigns measrued from NASA Ames EAST facility. The EAST shot 61-19 is considered benchmark data. The condition of shock is 0.1 Torr and 6.1 km/s with composition of 98% of $\text{N}_2$ and 2% of $\text{CH}_4$. From the present analysis, it has been found that not only the CN Violet and Red bands but also contributions from N and $\text{N}_2$ from the vacuum ultraviolet range are significantly affected by the radiative heat flux.
Second, a Titan atmospheric entry flight trajectory(t=211 s) of Dragonfly is simulated in a flow-radiation coupled manner. This second part of the analysis is ongoing work and improvement of physical model's accuracy has been achieved by modifying chemical-kinetic parameters for the Titan mixture. Through sensitivity analyses, the most influential reaction processes are determined and calibrated against shock tube measurements. Then they are employed to investigate hypersonic flow and radiation fields around the Dragonfly entry capsule. The radiative cooling effect from Deep VUV to infrared is considered via efficient spectral data management by the MURP that identifies individual contributions from several different spectral ranges.
Concluding Remarks
In the present study, a multi-fidelity modeling framework for high-temperature gas radiation has been developed and applied to hypersonic atmospheric entry conditions. For accurate and efficient analyses of radiative heat transfer, spectral, radiative transport, and reduced-order modeling framework have been integrated into a single numerical code, MURP. Applications to hypersonic aerothermodynamics study for the Titan composition have been performed to demonstrate the capability of the MURP. This investigation first revealed the additional influential radiators in the high-energy spectral region in addition to the well-known strong radiator in the ultraviolet. Then the massive flow-radiation coupling analysis has been carried out and will be refined through future investigation to thoroughly identify the mechanism of radiative heat transfer in the Titan atmospheric entry conditions.
Acknowledgement
This work has been supported under a NASA Space Technology Research Institute Award (ACCESS, grant number 80NSSC21K1117).
Summary
During atmospheric entry flights, a substantial amount of radiative heat transfer occurs around the surface of the spacecraft and this affects to the success of designed mission. Depending on purposes, radiation analysis requires wide range of fidelity in its numerical approach. This work aims to develop an improved numerical toolbox for the high-temperature radiation analyses, MURP (MUlti-fidelity Radiation Package), currently targeting applications to hypersonic aerothermodynamics study. The MURP encapsulates various kinds of radiation analysis strategies required for high-temperature aerothermodynamics and astrophysical studies. It provides a flexible, efficient, and accurate numerical framework and this has been achieved by integrating the three key components; (1) radiative transport from one- to three-dimension, (2) spectral modules from LBL to order-reduction approaches, and (3) coupling approach with other numerical codes. This abstract summarizes the modeling framework with selected results of applications to the hypersonic Titan atmospheric entry conditions.
