Ankit Bansal

Advanced Radiation Calculations of Hypersonic Reentry Flows Using Efficient Databasing Schemes

Efficient schemes for databasing emission and absorption coefficients are developed to model radiation from hypersonic nonequilibrium flows. For bound-bound transitions, spectral information including the line-center wavelength and emission and absorption coefficients is stored for typical air plasma species. Since the flow is nonequilibrium, a rate equation approach including both collisional and radiatively induced transitions is used to calculate the electronic state populations, assuming quasi steady state. The general Voigt line-shape function is assumed for modeling the line-broadening. The accuracy and efficiency of the databasing scheme was examined by comparing results of the databasing scheme with those of NEQAIR for the Stardust flowfield. An accuracy of approximately 1 % was achieved with an efficiency about three times faster than the NEQAIR code.

Multigroup Correlated-k Distribution Method for Nonequilibrium Atomic Radiation

the shock layer were overcome by splitting the full spectrum into a number of nonoverlapping part spectra. Results for one-dimensional nonhomogeneous gas slabs are presented, comparing line-by-line benchmarks with the fullspectrum correlated-k model, showing very good accuracy with a maximum error of 2–3% for the stagnation-line flowfield of the Stardust vehicle and more severe nonhomogeneous two-cell problems.

Narrow-Band k-Distribution Database for Atomic Radiation in Hypersonic Nonequilibrium Flows

Full-spectrum k-distribution (FSK) and multi-group FSK approaches make it possible to evaluate radiative fluxes at a fraction of the cost needed for line-by-line calculations. However, the required k-distributions need to be assembled from accurate absorption coefficient data for each flow condition, which is computationally expensive. An accurate and compact narrow-band k-distribution database has been developed for the most important species encountered in hypersonic nonequilibrium flow. The database allows users to calculate desired full-spectrum k-distributions through look-up and interpolation. Strategies for k-distribution data generation are outlined. The accuracy of the database is tested by comparing narrow-band mean absorption coefficients and narrow-band emissivities with those obtained from line-by-line calculations. Application of the database to construct full-spectrum k-distributions accurately and efficiently is discussed, and results from a number of heat transfer calculations and cpu-time studies are presented.Copyright

Perfusion kinetics in human brain tumor with DCE-MRI derived model and CFD analysis

Cancer is one of the leading causes of death all over the world. Among the strategies that are used for cancer treatment, the effectiveness of chemotherapy is often hindered by factors such as irregular and non-uniform uptake of drugs inside tumor. Thus, accurate prediction of drug transport and deposition inside tumor is crucial for increasing the effectiveness of chemotherapeutic treatment. In this study, a computational model of human brain tumor is developed that incorporates dynamic contrast enhanced-magnetic resonance imaging (DCE-MRI) data into a voxelized porous media model. The model takes into account realistic transport and perfusion kinetics parameters together with realistic heterogeneous tumor vasculature and accurate arterial input function (AIF), which makes it patient specific. The computational results for interstitial fluid pressure (IFP), interstitial fluid velocity (IFV) and tracer concentration show good agreement with the experimental results. The computational model can be extended further for predicting the deposition of chemotherapeutic drugs in tumor environment as well as selection of the best chemotherapeutic drug for a specific patient.

Multiscale Part-Spectrum k-Distribution Database for Atomic Radiation in Hypersonic Nonequilibrium Flows

An accurate and compact part-spectrum k-distribution database has been developed for the two most important radiating species N and O encountered in hypersonic nonequilibrium flows. The database allows users to calculate the desired full-spectrum k-distributions through look-up and interpolation, providing an efficient means to perform radiative transfer calculations. A detailed methodology of the k-distribution data generation is presented. An optimized Gauss quadrature scheme is implemented for reducing the size of the database. The accuracy of the database is determined by comparing partspectrum emissivities with those obtained from line-by-line calculations. The application of the database to construct full-spectrum k-distributions at arbitrary gas states is discussed. Heat transfer results for the stagnation line of the Stardust vehicle are discussed and CPU-time studies are presented, demonstrating the accuracy and efficiency of the k-distribution database. [DOI: 10.1115/1.4004528]

Spatial Approach of Artificial Neural Network for Solar Radiation Forecasting: Modeling Issues

Design of neural networks architecture has been done on setting up the number of neurons, delays, and activation functions. The expected model was initiated and tested with Indian solar horizontal irradiation (GHI) metrological data. The results are assessed using the effect of different statistical errors. The effort is made to verify simulation capability of ANN architecture accurately, on hourly radiation data. ANN model is a well-organized technique to estimate the radiation using different meteorological database. In this paper, we have used nine spatial neighbour locations and 10 years of data for assessment of neural network. Hence, overall 90 different inputs are compared, on customized ANN model. Results show the flexibility with respect to spatial orientation of model inputs.

k-Distributions for Gas Mixtures in Hypersonic Nonequilibrium Flows

A k-distribution model is presented for gas mixtures in thermodynamic nonequilibrium, containing strongly radiating atomic species N and O together with molecular species of N2, N+2 , NO and O2. In the VUV range of the spectrum there is strong absorption of atomic radiation by bands of N2. For this spectral range, a multiscale model is presented, where RTEs are solved separately for each emitting species and overlap with other species is treated in an approximate way. Methodology for splitting the gas mixture into scales and evaluation of the overlap parameter between different scales is presented. Accuracy of the new model is demonstrated by solving the radiative transfer equation along the stagnation line flow field of the Crew Exploration Vehicle (CEV).

Correlated-k Distribution Method for Atomic Radiation in Hypersonic Nonequilibrium flows

Radiation from the shock layer during atmospheric entry plays a significant role in the design of modern space vehicles, particularly in the design of the thermal protection system. This makes it necessary to predict the e ects of radiation accurately and, at the same time, e ciently for the optimum design of new generation space vehicles. Line-by-line calculations are the most accurate method to solve the radiative transfer equation (RTE); however, they are not practical because of their large computational cost. In this work a correlatedk distribution method has been developed for the most important atomic species (N and O, as well as their ions), which provides great accuracy with high numerical e ciency for the evaluation of radiative transfer in a hot plasma. Challenges posed by typical nonequilibrium gas conditions in the plasma were overcome by splitting the full spectrum into a number of nonoverlapping part-spectra. Results for one-dimensional inhomogeneous gas slabs are presented and compared with line-by-line benchmarks and the full-spectrum correlated-k (FSCK) model, showing very good accuracy in typical nonequilibrium gas conditions as are found in atmospheric reentry of space vehicles.

Spectral Modeling of Radiative Heat Transfer in Carbonaceous Atmospheres Using New k-Distribution Models

Multi-scale correlated-k distribution models are presented for the red and violet bands of CN for applications relevant to entry into the atmospheres of Titan, Mars,Venus and flows over an ablating heat shield. In the multi-scale model spectral lines are separated into di fferent scales to improve correlation among absorption coefficients. The methodology for scaling absorption coe fficients into such groups is presented. A new emission-weighted full-spectrumk-distribution model is proposed as an improvement over the more popular Planck function-weighted full-spectrum k-distribution model. In the new model, the emission coe fficient replaces the Planck-function as weight in the reordering sche me. Accuracies of the two models are compared by solving severe two-cell problems. To exploit the full poten tial of the k-distribution method databasing schemes for k-distributions are discussed and cpu-time studies are presnted. The accuracy of the new model and the database is demonstrated by solving the radiative transfer equation along the stagnation line flow field of the Huygens spacecraft.

Variance Reduction Techniques For Monte Carlo Solutions of Radiative Transfer in Hypersonic Flows: Hybrid P 1 -Monte Carlo

A hybrid P1-Monte Carlo method is developed for hypersonic plasma radiation simulations. A scheme is presented to divide the spectrum into optically thick and optically thin regions. The optically thick regions are solved using the P1 method, which is well suited for such problems, and the optically intermediate to thin portions are treated with the photon Monte Carlo method, which is accurate for the entire spectrum, but requires more computational effort for extreme optical thickness. Sample results showing the accuracy and efficiency of the hybrid method are presented for a sample CEV stagnation line.