Numerische spektrale Modellierung der Interaktion zwischen Gasen und Wärmestrahlung zum Einsatz in CFD-Verfahren

  • Numerical Spectral Modelling of Interaction between Gases and Thermal Radiation for Application in CFD Solvers

Habermehl, Martin; Kneer, Reinhold (Thesis advisor); Janicka, Johannes (Thesis advisor)

Aachen (2016, 2017)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2016

Abstract

The interaction of radiative interactive gases and thermal radiation is an essential heat transfer mechanism which has to be considered in numerical simulations of flow and heat transfer processes in furnaces and high temperature process equipment.This work presents the development of a non-gray wide band model specifically adopted for the use in CFD calculations. The model aims at the band-wise provision of a spectrally averaged absorption coefficient serving as input for a non-correlated solution method for the radiative transfer equation. Such a solution method can be calculated using the same compuatational grid as CFD calculations.The physical effects of interaction between gases and thermal radiation are explained prior to the actual model development work in order to clarify the integrations over the radiative spectrum, the solid angle and along the radiative path as well as the implied resulting challenges regarding the modeling. Numerical methods for the calculation of the radiative transport are explained as well.Subsequently, a model for the calculation of a spectrally averaged absorption coefficient for a wide band approach is developed based on the Exponential Wide Band Model. The smooth averaging of the absorption coefficient is performed using analytically constructed antiderivatives. This model is compared to more detailed reference models using simple test cases for radiative interactive gas species (\ce{H2O}, \ce{CO2}) as well as typical flue gas compositions with homogeneous and non-homogeneous conditions and different spatial resolutions of the radiative path.In comparison to its predecessor, the presented model shows a significantly reduced grid dependency of the results and a smaller deviation of the results in comparison to the detailed reference models. However, the results also show that the use of the EWBM in a wide band model with fixed band widths is somewhat problematic regarding precision - especially considering wall heat fluxes. Thus, possible alternative calculation methods are outlined in the outlook.