Numerical Simulation Of Radiative Transfer Research Articles

Effects of multiple scattering and atmospheric aerosol on the polarization of the twilight sky

The paper presents a review of a number of wide-angle polarization CCD-measurements of the twilight sky in V and R color bands with effective wavelengths 550 and 700nm. The basic factors affecting (usually decreasing) the polarization of the twilight sky are the atmospheric aerosol scattering and multiple scattering. These effects were distinguished from each other, and a method of multiple-scattering separation is discussed. The results are compared with the data of numerical simulation of radiative transfer in the atmosphere for different aerosol models. The whole twilight period is divided into different stages with different mechanisms forming the twilight-sky polarization properties.

Detailed numerical simulation of radiative transfer in a nonluminous turbulent jet diffusion flame

Radiative transfer in a turbulent jet diffusion flame has been calculated using the discrete ordinates and the ray tracing. The radiative properties of the medium were computed using the correlated k-distribution method and the statistical narrow-band model. The interaction between turbulence and radiation was examined and ways to account for this interaction were compared. Calculations using a stochastic semicausal model were carried out to accurately simulate that interaction, and to provide reference solutions for evaluating the precision of simpler approaches. The models were applied to decoupled radiative transfer calculations in a flame, using experimental fields for temperature and species' concentrations as an input. The correlated k-distribution method, along with the full turbulence/radiation interaction, gave results in very good agreement with the statistical narrow band along with the stochastic model, but the total measured radiative heat loss was underestimated by ∼11.5%. This is likely to be mainly due to the need to extrapolate the data downstream of the last measured radial profile. Enhancement of the radiative heat loss due to turbulent fluctuations was almost 50% in this flame; this exceeds a previous estimate based on a simpler model for the radiative properties of a gas.

Numerical simulation of radiative heat transfer from non-gray gases in three-dimensional enclosures

The discrete ordinates and the discrete transfer methods are applied to the numerical simulation of radiative heat transfer from non-gray gases in three-dimensional enclosures. Several gas radiative property models are used, namely the correlated k-distribution (CK), the spectral line-based weighted-sum-of-gray-gases (SLW) and the weighted-sum-of-gray-gases (WSGG) methods. The results are compared with recently published accurate calculations based on the statistical narrow band model. The WSGG model is computationally efficient, but often yields relatively large errors. It should be used only if moderate accuracy is sufficient. The SLW model is the best alternative regarding the compromise between accuracy and numerical efficiency. However, an optimization of the coefficients of the model is essential to reduce the computational requirements, especially in the case of gas mixtures. The CK model is the most accurate of the methods evaluated here, but too time consuming for engineering applications, although recent developments may partly overcome this shortcoming.

Estimation of the absorption and backscattering coefficients from inߚwater radiometric measurements

Numerical simulations of radiative transfer within the ocean surface mixed layer have been used to derive a set of simple equations for estimating the absorption, a, and backscattering, bb, coefficients in the blue‐green spectral region from measurements of downwelling irradiance, Ed, upwelling irradiance, Eu, and upwelling nadir radiance, Lu. Two relationships are used in this derivation: (i) irradiance reflectance, R = Eu/Ed, is approximately proportional to bb/a and inversely proportional to the average cosine of the underwater light field, µ; and (ii) radiance reflectance, RL = Lu/Ed, is proportional to bb/a but changes little with µ. Accordingly, µ is first estimated from Lu/Eu and then the absorption coefficient is obtained from Gershun's equation. Having determined a, bb is estimated from the relation between RL and bb/a. We also show how the estimation of µ, a, and bb is improved with additional data of the beam attenuation coefficient, c. The retrieval of a and bb from Ed, Eu, and Lu has been tested using field data collected in the Southern California Bight. The a values predicted by the model show good agreement with absorption determinations from the ac‐9 instrument and on‐board spectrophotometric method, and the modeled bb agrees well with the backscattering determinations from the Hydroscat‐6 instrument. The algorithm has been derived for a broad range of the ocean inherent optical properties that do not necessarily covary with one another like in chlorophyll‐based bio‐optical models. However, the model should be used with caution if significant departure from the average Petzold particle scattering phase function is expected, for example in waters with high load of mineral particles.

Effect of Narrow Band Nonuniformity on Unsteady Heat Up of Water vapor under Radiation-Conduction Combined Heat Transfer.

Effect of narrow band nonuniformity on unsteady heat up process of water vapor under radiation-conduction combined heat transfer is examined by comparing the result of numerical simulations with and without incorporation of narrow band nonuniformity. The authors propose a rational and comprehensive computational approach for incorporating the narrow band nonuniformity into numerical simulations of radiative heat transfer when the considered field is nonisothermal. Results of examination exhibited that the contribution of radiative heat transfer to the heat up rate of water vapor may be almost twice overestimated, if the narrow band nonuniformity effect is neglected. Separate analyses of radiative energy attributed to wall emission and gas emission clarified that the absorption of wall emission is overestimated and, on the contrary, the absorption of radiation energy emitted by water vapor itself is underestimated if the narrow band nonuniformity is neglected. The reason why such over- or under-estimation is induced is understood by examining the influence of line overlap parameter on the transmittance averaged within a narrow band. Smaller value of line overlap parameter {gamma}/d means more violent narrow band nonuniformity. The broken lines show the narrow band transmittance for flat incident power spectrum, and the solid lines show that for themore » radiative emission from the absorbing gas itself. It is also clarified that the disregard of the narrow band nonuniformity give rise to serious error in the estimation of absorption rate of wall and gas emission even in the case where the disregard of narrow band nonuniformity bring little change to the temperature distribution. The results illustrated in this paper suggest that the narrow band nonuniformity should not be neglected.« less

A numerical simulation of radiative heat transfer coupled with Czochralski flow in cusp magnetic field

The characteristics of flow and oxygen concentration are numerically studied in Czochralski 8 silicon crystal growing process considering radiative heat transfer. The analysis of net radiative heat flux on all relevant surfaces shows growing crystal affects the heater power. Furthermore, the variation of the radiative heat flux along the crystal surface in the growing direction is confirmed and should be a cause of thermal stress and defect of the crystal. The calculated distributions of temperature and, heat flux along the wall boundaries including melt/crystal interface, free surface and crucible wall indicate that the frequently used assumption of the thermal boundary conditions of insulated crucible bottom and constant temperature at crucible side wall is not suitable to meet the real physical boundary conditions. It is necessary, therefore, to calculate radiative heat transfer simultaneously with the melt flow in order to simulate the real CZ crystal growth. If only natural convection is considered, the oxygen concentration on the melt/crystal interface decreases and becomes uniform by the application of a cusp magnetic filed. The heater power needed also increases with increasing the magnetic field. For the case of counter rotation of the crystal and crucible, the magnetic field suppresses azimutal flow produced by the crucible rotation, which results in the higher oxygen concentration near the interface.

Diagnostics of dust content in spiral galaxies: Numerical simulations of radiative transfer

view Abstract Citations (120) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Diagnostics of Dust Content in Spiral Galaxies: Numerical Simulations of Radiative Transfer Byun, Y. I. ; Freeman, K. C. ; Kylafis, N. D. Abstract In order to find the best observable diagnostics for the amount of internal extinction within spiral galaxies, we have constructed realistic models for disk galaxies with immersed dust layers. The radiative transfer including both scattering and absorption has been computed for a range of model galaxies in various orientations. Standard galaxy surface photometry techniques were then applied to the numerical data to illustrate how different observables such as total magnitude, color and luminosity distribution behave under given conditions of dust distribution. This work reveals a set of superior diagnostics for the dust in the disk. These include not only the integrated parameters, but also the apparent disk structural parameters, the amplitude of the asymmetry between the near and far sides of the galaxy as divided by the apparent major axis and their dependence on the orientation of the galaxy with respect to the observer. Combining the above diagnostics with our impressions of real galaxies, we arrive at the qualitative conclusion that galaxy disks are generally optically thin. Quantitative conclusions will appear in subsequent work. Publication: The Astrophysical Journal Pub Date: September 1994 DOI: 10.1086/174553 Bibcode: 1994ApJ...432..114B Keywords: Astronomical Models; Astronomical Photometry; Computerized Simulation; Cosmic Dust; Interstellar Extinction; Interstellar Matter; Mathematical Models; Radiative Transfer; Spiral Galaxies; Brightness; Light Scattering; Radiation Absorption; Stellar Color; Stellar Luminosity; Stellar Magnitude; Astrophysics; GALAXIES: PHOTOMETRY; GALAXIES: SPIRAL; ISM: DUST; EXTINCTION; METHODS: NUMERICAL; RADIATIVE TRANSFER full text sources ADS | data products SIMBAD (1)

Numerical simulation of radiative heat transfer to high-pressure turbine-cooled nozzle vanes of aeroengines.

Combined radiative and convective heat transfer is analyzed numerically in the combustion chamber of aeroengines by using the Monte Carlo method to obtain the profiles of heatflux onto the surfaces of high-pressure turbine-cooled nozzle vanes and cooled rotor blade group. The following results are obtained from the parametric studies : (1)radiative heat flux onto the nozzle vanes is over l0% of the convective flux for the nozzle-inlet temperature of 1700 K, (2)the radiative heat flux onto the rotor blade group is about half of that onto the leading edge of the nozzle vanes and (3)the radiative heat flux onto the nozzle vanes is affected by the absorption coefficient of the flame zone rather than by the nozzle-inlet temperature.