Nonequilibrium Radiation Research Articles

Numerical modeling of non-equilibrium neutrino radiation field by solving quantum kinetic equation

Numerical modeling of neutrino quantum kinetics is a new frontier in the study of core-collapse supernova (CCSN) and binary neutron star merger (BNSM). The noticeable feature in the quantum kinetics is neutrino flavor conversion driven by neutrino self-interactions. Although there remain many unresolved issues in their non-linear properties of flavor conversions, rapid progress has been made in the last few years. In this article, we introduce the current status for the study of collective neutrino oscillations, which are representative characteristics in self-induced flavor conversions, and then we show our recent results: global quantum kinetic simulations in CCSN and BNSM environments.

The voxelized photon Monte Carlo method for hypersonic radiation modeling

A novel method of solving for radiative energy transfer at hypersonic speeds, the voxelized photon Monte Carlo (voxPMC) method, is presented. The voxPMC method is implemented in the Discrete Adaptive Radiative Transport (DART) code and results are given for radiative heat transfer of Mach 9.6 flow over a cylinder. Simulation parameters for this method were tuned to determine requirements for accurate solutions, using benchmark results from NASA’s Nonequilibrium Radiative Transport and Spectra Program (NEQAIR). It was found that of the tuning parameters, the mesh resolution and number of simulated photon packets had the largest effect on the resulting solution accuracy. It was found that 108 photon packets, or 5 photon packets per smallest mesh cell dimension, produced accurate results. Voxel resolution refinement and optical boundary conditions were also tested and 2 voxels per smallest mesh cell dimension and an optical symmetry boundary condition produced results that aligned with those given by NEQAIR. Future work will determine if recommendations for these parameters hold for a wider range of applications. Loose coupling between flowfield results and radiation analysis resulted in radiative cooling, which smeared the shock gradients and led to a slight increase in convective heating at the stagnation point.

Numerical simulation of an iron meteoroid entering into Earth’s atmosphere using DSMC and a radiation solver with comparison to ground testing data

Observation missions of meteoroids entering the Earth’s atmosphere are conducted regularly. Meanwhile a method to replicate the flight in a ground test facilities has been established. However, numerical simulations with subsequent comparison of the spectroscopic data, on the other hand, are not yet widely used in this field. This is mainly due to the complex flow environment, which includes not only non-equilibrium radiation, but also the outgassing of species from the meteoroid that do not enter the shock since they have only the thermal velocity of the wall without macroscopic flow and therefore cannot heat up as much as the other species. This paper presents a numerical approach to replicate experimental measurements. The Direct Simulation Monte Carlo (DSMC) method is used and bi-directionally coupled with a radiation solver to simulate the atmospheric entry in 80km of an iron meteorite with a diameter of 38mm. The paper provides information and references on the numerical models used, the challenges encountered, and the simulation results. The study shows that the simulation models are well-suited to handle the non-equilibrium effects of meteorite entry and show good agreement with the experimental measurements.

Global existence for a class of non-equilibrium reaction–diffusion systems with flux limitation

For a class of general reaction–diffusion systems with flux limitation in one dimension, when homogeneous Neumann boundary conditions are considered, we will prove global upper and lower boundness estimates for the positive classical solutions and boundness for their first-order spatial derivatives. In particular, the non-equilibrium radiation flux-limited diffusion coupled with material heat conduction model is included as a special case of the general reaction–diffusion systems. The key point of our method is to at first prove that the second-order spatial derivative of the solution of the second diffusion equation can be linearly controlled by the first-order spatial derivative of the solution of the flux-limited diffusion equation. Then, with this control, we can apply the Bernstein method to the flux-limited diffusion equation, while a stratifying time technique is introduced to get a complete first order spatial derivative estimate. With these global prior estimates, the global existence and uniqueness of positive classical solutions for the general flux-limited diffusion systems are proved.

Analysis of Shock Deceleration Effects in the NASA Electric Arc Shock Tube

Complex processes related to nonequilibrium thermochemistry and radiation are a fundamental aspect of atmospheric entry flowfields. Shock tubes provide a means of generating test gas conditions analogous to those found on the stagnation line of flight shock layers, which allows extraction of thermochemical rates and radiative intensities. Currently, the NASA Electric Arc Shock Tube (EAST) is the best source of such data. Although simple in principle, nuances of these experimental facilities can affect the observed results. Notably, electron densities and radiance levels in excess of equilibrium predictions have been observed at EAST for many years. The deceleration of the shock as it passes along the tube has been posited as a source of these discrepancies. In this work, a recently developed numerical methodology (LASTA) is applied to these results from the literature. Using the experimental shock speed profile as an input, trends in postshock electron density are computed. Radiance throughout the shock layer is also predicted by coupling the simulation to the NASA NEQAIR code. It is shown that the predictions of LASTA provide a good match to the magnitudes and trends of the experimental differences, confirming shock speed deceleration as their cause.

Application of Quasistationary eRC-Models for Calculating Nonequilibrium Radiation of Shock Waves at Velocities of Approximately 10 km/s

Application of Quasistationary eRC-Models for Calculating Nonequilibrium Radiation of Shock Waves at Velocities of Approximately 10 km/s

Use of Thermal Radiation for Remote Identification of Liquids in Closed Dielectric Containers

Remote determination of substances, including liquids, is an urgent problem, the solution of which requires fundamentally new approaches to both methods and measurement techniques. This is due to the fact that standard liquid analysis methods are mainly spectroscopic methods in various frequency ranges from neutron diffractometry to acoustic spectroscopy, which are very difficult or even impossible to apply in remote sensing. Conventional radar methods are usually unacceptable due to the impossibility of covert removal of information using active location and obtaining data on the composition of the irradiated object based on it. Therefore, at present, methods and techniques of passive location are being used more and more, but in order to solve quite specific problems of remote identification of substances, they must be significantly modernized.
 This article discusses a technique and a modernized measuring complex for remote study of liquid electrolytes and non-electrolytes using measurements and subsequent analysis of fluctuations in the temperature difference of the intermediate liquid medium (distilled water) in which the container with the liquid under study is located. To date, there is no clear understanding of how thermally stimulated radiation depends on the composition of a macroscopic body, and also on whether thermal radiation is in equilibrium or non-equilibrium. The investigated object, at a given temperature, emits electromagnetic waves associated with the thermal motion of the molecules and atoms of its constituents. That’s, why thermal radiation is random (fluctuation) process, which means that the average value of the electromagnetic field is equal to zero, but other averaged features, such as quadraticity in the field, may differ from zero. The quadratic characteristics of a thermal electromagnetic field determine its energy, which has a finite value other than zero, which can be measured by an appropriate sensor and characterizes the field source — a macroscopic body heated to a certain temperature. The paper presents the results of studies of mixtures of electrolytes and non-electrolytes of various concentrations. An example of non-equilibrium thermal radiation is given. It is shown that it is possible to distinguish between the studied liquids and methods of combining the components of solutions of given concentrations to obtain the given properties of the entire solution.

Using a collision-radiation model with extended excitation rates to calculate the OH spectrum in the ultraviolet band

To improve the calculation accuracy of the ultraviolet (UV) nonequilibrium radiation spectrum in the plume and shock layer, an extended transition process collision-radiation model of hydroxyl (OH) is proposed. The transition processes for the vibrational level of the OH(A) state in the exchange reaction are extended, including both the fundamental band (Δν=1) and the universal band (Δν=2). Eight air components (N2, O2, H2, H2O, CO2, CO, H and O) are used instead of two components (N2 and O2) in the quenching and exchange reactions to make the extended model applicable to both a plume and shock layer. The accuracy of the extended model is verified by comparing the calculated number density for the OH(A) state of an Atlas III plume and the calculated spectral radiance of a BSUV-2 shock layer against experimental data. By comparing with the Atlas plume and error analysis, the results show that the calculated results of the extended C-R model are in better agreement with the experimental data than that of the original model. The accuracy of the developed spectral-line prediction model is higher than that the existing model, which is very important for research on target early warning, detection and recognition.

Analysis of nonequilibrium atomic and molecular nitrogen radiation in pure N2 shockwaves

This paper presents an analysis of data previously reported from a test series in the Electric Arc Shock Tube Facility for incident shocks composed of pure nitrogen. The present work focuses on the lowest velocity measured in the test (approximately 7 km/s) where both molecular and atomic radiation are significant. Analysis of the spectral data with the NEQAIR radiative transport code obtains post-shock trends in temperature and number densities of the states of N2 and atomic N. The results suggest that chemical, and possibly thermal, equilibrium has not been obtained within the distance/time measured (about 5 cm/80 µs). In the nonequilibrium region of the shock, differences between rotational temperatures of different species are observed, as well as differences between rotational and vibrational temperatures. Population of rotational states above the dissociation limit is observed to occur over a distance of several cm. Finally, these data suggest that predissociation strongly affects the C3Πu state of N2, leading to a lower measured radiation than predicted. An effective average pre-dissociation rate is shown to produce reasonable agreement under quasi-steady state approximation.

A Positivity-Preserving Finite Volume Scheme for Nonequilibrium Radiation Diffusion Equations on Distorted Meshes.

In this paper, we propose a new positivity-preserving finite volume scheme with fixed stencils for the nonequilibrium radiation diffusion equations on distorted meshes. This scheme is used to simulate the equations on meshes with both the cell-centered and cell-vertex unknowns. The cell-centered unknowns are the primary unknowns, and the element vertex unknowns are taken as the auxiliary unknowns, which can be calculated by interpolation algorithm. With the nonlinear two-point flux approximation, the interpolation algorithm is not required to be positivity-preserving. Besides, the scheme has a fixed stencil and is locally conservative. The Anderson acceleration is used for the Picard method to solve the nonlinear systems efficiently. Several numerical results are also given to illustrate the efficiency and strong positivity-preserving quality of the scheme.

Application of Quasi-Stationary eRC Models for the Calculation of Non-Equilibrium Radiation of Shock Waves at Velocity about 10 km/s

Application of Quasi-Stationary eRC Models for the Calculation of Non-Equilibrium Radiation of Shock Waves at Velocity about 10 km/s

A machine learning approach to the prediction of transport and thermodynamic processes in multiphysics systems - heat transfer in a hybrid nanofluid flow in porous media

Comprehensive analyses of transport phenomena and thermodynamics of complex multiphysics systems are laborious and computationally intensive. Yet, such analyses are often required during the design of thermal and process equipment. As a remedy, this paper puts forward a novel approach to the prediction of transport behaviours of multiphysics systems, offering significant reductions in the computational time and cost. This is based on machine learning techniques that utilize the data generated by computational fluid dynamics for training purposes. The physical system under investigation includes a stagnation-point flow of a hybrid nanofluid (Cu−Al2O3/Water) over a blunt object embedded in porous media. The problem further involves mixed convection, entropy generation, local thermal non-equilibrium and non-linear thermal radiation within the porous medium. The SVR (Support Machine Vector) model is employed to approximate velocity, temperature, Nusselt number and shear-stress as well as entropy generation and Bejan number functions. Further, PSO meta-heuristic algorithm is applied to propose correlations for Nusselt number and shear stress. The effects of Nusselt number, temperature fields and shear stress on the surface of the blunt-body as well as thermal and frictional entropy generation are analysed over a wide range of parameters. Further, it is shown that the generated correlations allow a quantitative evaluation of the contribution of a large number of variables to Nusselt number and shear stress. This makes the combined computational and artificial intelligence (AI) approach most suitable for design purposes.

A model for thermal protection ablative material with local thermal non-equilibrium and thermal radiation mechanisms

Novel resin-based ablative materials are manufactured for the Thermal Protection System (TPS) of hypersonic aircraft in recent years to adapt more extreme aerothermodynamic environment. The establishment of theoretical model and simulation method for accurately predicting material's responses can guide design of TPS and significantly reduce Research and Development (R&D) cycle and cost. In order to solve the problem of inaccurate material response calculated by the heritage models, which is caused by the new mechanisms involved in new materials. On the basis of heritage physical and chemical mechanisms for resin-based ablative materials, this study further introduces the mechanisms of the local thermal non-equilibrium and thermal radiation, and a developed thermal-fluid-ablation coupled theoretical model is established. The coupled model is numerically solved by writing computer codes. After completing the verification of the model and simulation codes, the influences of the new mechanisms on the performance of ablative material are analyzed. The results show that the effect of local thermal non-equilibrium and thermal radiation cannot be ignored for current ablative materials, in which the key factors are the pore size and porosity.

Argon radiation behind of shock wave front

In this article, the results of an experimental study of non-equilibrium radiation of pure argon are presented. These results were obtained at the Institute of Mechanics of Lomonosow Moscow State University Shock Tube experimental complex. The main attention is focused to the study of the initial phase of radiation take place before the sharp increase electron concentration. The electron number density was determined with using of Stark broadening of Hα hydrogen line method. The panoramic spectra and individual radiation line evolution are presented. It is noted that radiation evolution at the initial stage depends strongly from radiation wavelength.

On the Velocity Drift between Ions in the Solar Atmosphere

Abstract The solar atmosphere is composed of many species, which are populated at different ionization and excitation levels. The upper chromosphere, transition region, and corona are nearly collisionless. Consequently, slippage between, for instance, ions and neutral particles, or interactions between separate species, may play important roles. We have developed a 3D MFMS numerical code (Ebysus) to investigate such effects. Ebysus is capable of treating species (e.g., hydrogen, helium, etc.) and fluids (neutrals, excited and ionized elements) separately, including nonequilibrium ionization, momentum exchange, radiation, thermal conduction, and other complex processes in the solar atmosphere. Treating different species as different fluids leads to drifts between different ions and an electric field that couples these motions. The coupling for two ionized fluids can lead to an anti-phase rotational motion between them. Different ionized species and momentum exchange can dissipate this velocity drift, i.e., convert wave kinetic energy into thermal energy. High-frequency Alfvén waves driven by, e.g., reconnection thought to occur in the solar atmosphere, can drive such multi-ion velocity drifts.

Simulating the Benešov bolide flowfield and spectrum at altitudes of 47 and 57 km

This paper develops a computational fluid dynamics capability for simulating the radiative emission from a meteor shock-layer and wake to an external observer. The developed capability includes the impact of radiation and ablation on the meteor flowfield, where coupled radiation accounts for the impact of radiation on the flowfield energy equations and coupled ablation accounts for the injection of ablation species from the meteoroid surface into the flow. This capability includes updated flowfield chemistry and nonequilibrium radiation models, which are compiled from the literature. To provide a level of validation for this capability, the Benešov spectral measurements are considered. Although the meteoroid was likely fragmented at the 47 and 57 km altitudes considered, and the measurement uncertainty is roughly ±50%, these measurements represent the best available spectral measurements for a relatively large (meter-class) bolide. To determine the equivalent meteoroid diameter for the Benešov simulations, the continuum component of the spectrum in the 570 to 610 nm range is considered. This wavelength range is dominated by air emission from the high pressure and temperature shock-layer in front of the meteoroid, which is simulated with a relatively small uncertainty (compared to the wake emission) and is sensitive to the equivalent meteoroid diameter. Because of these characteristics, the simulated meteoroid diameter is adjusted until the continuum component in this wavelength range matches the measurements. This results in equivalent diameters ranging from 0.62 to 0.9 m. The range of equivalent diameters is due to the various meteoroid geometries considered, where increasing the bluntness decreases the required diameter. Applying these diameters to simulations at 47 and 57 km results in simulated spectra that compare within 30% of the measured values, considering the wavelength integrated values between 400 and 650 nm. This agreement is well within the estimated measurement uncertainty of ±50%. All major spectral features are captured by the simulations. A comparison with the measured wake-only spectrum suggests that emission from wake locations over 150 m from the meteoroid are the primary source of the small disagreement seen between the measurements and simulations. Overall, the relatively good agreement between the simulations and measurements provides a level of validation for the developed model that has not been previously available.

Simulations of Infrared Radiation Measurements in Shock and Expansion Tubes

This Paper presents the simulations of and CO infrared radiation behind shock waves and in expansion flows. This work is motivated by the little amount of characterizations of infrared radiation in these expansion flows and thermodynamic regimes, whereas carbon dioxide infrared radiation is deemed to contribute significantly to the afterbody heating withstood by a Martian spacecraft. Japan Aerospace Exploration Agency (JAXA) shock-tube facilities were operated at conditions generating flow velocities ranging from 2.8 to . Absolute infrared spectra of and CO were obtained under equilibrium and nonequilibrium conditions and used to assess the performances of the spectral solvers. Specifically, this Paper introduces the recent enhancements brought to JAXA in-house codes to compute nonequilibrium infrared radiation. Schemes to split the level energy into its pure vibrational, rotational, and vibration–rotation coupling and interactions contributions are proposed and implemented. The implementation was evaluated with comparison with literature data and recent measurements. Infrared radiation behind shock waves and under expansion regimes was analyzed with a newly developed model to infer the vibrational and rotational temperatures and determine the degree of thermal nonequilibrium. The latter outlines the highly complicated vibrational energy distribution of carbon dioxide during expansion and the subsequent radiation, as well as the possible shortcomings of the multitemperature models. Therefore, these studies of carbon dioxide nonequilibrium radiation during expansion pose new challenges to the community and will enable the upgrade and validation of the multitemperature and state-to-state models currently in use.

Rebuilding experimental nonequilibrium radiation in shock-heated Martian-like mixture flows using electronic state-to-state approach

An electronic state-to-state approach is developed to reproduce numerically the radiative processes in the experiments on the Electric Arc Shock Tube facility at NASA Ames Research Center. The experiments measured the spectral radiance of C2 Swan band and CO 4th Positive band behind the strong shock wave in a Martian-like mixture. The present state-to-state approach solves the electronic states of strong radiators by integrating the collisional-radiative model into the master equations in the frame of Euler equations. Particularly, the electron impact dissociation of CO is included, and the rate coefficients are proposed for the electronic state-specific heavy-particle impact excitation and dissociation of C2. The nonequilibrium radiation behind the shock is calculated by the line-by-line method, and it is then convoluted using the calibrated smearing function in order to compare with the experiments. The state-specific simulation results is found to agree well with both spectral and spatial measurement data. The simulated electronic state populations of CO and C2 deviate from Boltzmann distributions significantly, which could explain the failure of previous two-temperature quasi-steady-state based simulations.

Experimental study of high temperature oxidation of dimethyl ether, n-butanol and methane

An experimental study of the kinetics of oxidation of dimethyl ether, n-butanol, and methane was carried out using emission and atomic resonance absorption spectroscopy. All experiments were performed in a shock tube behind reflected shock wave in a wide temperature range from 1890 to 3250 K at a pressure of 2.4 ± 0.4 bar. In all investigated conditions, the peaks of nonequilibrium UV radiation of electronically excited carbon monoxide CO(a3Πr) were observed. Besides, the resonant absorption profiles of atomic oxygen in the ground electronic state O(3P) converted to O-atom concentration profiles were for the first time measured at this temperature range. For simulating the CO(a3Πr) radiation experimental profiles a kinetic mechanism of its formation and consumption was developed. This mechanism was implemented into existing comprehensive detailed kinetic models (such as Ranzi et al. (2014), Vasu and Sarathy (2013), NUIG Mech 56.54 (2013), GRI-Mech 3.0 (1999) and Alviso et al. (2018)), which were then tested on the obtained experimental profiles of atomic oxygen and electronically excited carbon monoxide. It was shown that the proposed CO(a3Πr) sub-mechanism nearly correct describes the ongoing reaction processes, however, complete compliance was not achieved. To elucidate reactions responsible for the differences observed, a sensitivity analysis was performed. As a result, the most important elementary reactions were determined.

Measurement of Radiative Nonequilibrium for Air Shocks Between 7 and

This paper describes a characterization of thermochemical nonequilibrium radiance for shock speeds between 7 and in the NASA Ames Electric Arc Shock Tube. Data are spectrally resolved from 190 to 1450 nm and spatially resolved behind the shock front on the order of 10 cm. The data are analyzed in terms of a spectral nonequilibrium metric, defined as the average radiance within of the peak radiance and presented in a format that may be used to test predictive nonequilibrium radiation tools. The data collected in two shock tubes of differing diameter (10 and 60 cm) at the same nominal shock condition agree within 30%. The spectra are compared with simulations using the DPLR/NEQAIR software tools using a combination of different modeling options (reaction rates, energy mode accounting, and electron impact excitation rates). The results show mixed agreement, with no one modeling option being a clear preference. This suggests that the data may be used to help to identify improvements to methodologies for modeling nonequilibrium air radiation.