An Efficient Computational Method for Thermal Radiation in Participating Media

Computational Thermal Radiation;QL Method;Radiative Heat Transfer;Finite Volume Method;CFD;Participating Media;Mechanical Engineering

Hassanzadeh, Pedram

University of Waterloo

关键词: Computational Thermal Radiation;    QL Method;    Radiative Heat Transfer;    Finite Volume Method;    CFD;    Participating Media;    Mechanical Engineering;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/3135/1/Pedram%20Hassanzadeh.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

Thermal radiation is of significant importance in a broad range of engineeringapplications including high-temperature and large-scale systems. Although thegoverning equations of thermal radiation have been known for many years, thecomplexities inherent in the phenomenon, such as the multidimensionality andintegro-differential nature of these equations, have made it difficult to obtain anaccurate, efficient, and robust computational method. Developing the finite volumeradiation method in the 1990s was a significant progress but not a panaceafor computational radiation. The major drawback of this method, which is commonamong all methods that solve for directional intensities, is its slow convergencerate in many situations which increases the solution cost dramatically. These situationsinclude large optical thicknesses, strongly reflecting boundaries, and anyother factor that causes strong directional coupling like complex geometries.Several acceleration schemes have been developed in the heat transfer and neutrontransport communities to expedite the convergence and reduce the solutioncost, but none of them led to a general and reliable method. Among these availableschemes, the two most promising ones, the multiplicative scheme and coupledordinates method, suffer from failing on fine grids and being very complicated forcomplex scattering phase functions, respectively.In this research, a new computational method, called the QL method, has beenintroduced. The main idea of this method is using the phase weight concept torelate the directional and average intensities and re-arranging the Radiative TransferEquation to find a new expression for the radiant heat flux. This results in anelliptic-type equation for the average intensity at each control volume which conservesthe radiant energy in all directions in the control volume. This formulationgives the QL method a great advantage to solve for the average intensity whileincluding the directional effects. Since the directional effects are included and theradiant energy is conserved in each control volume, this method is expected to beaccurate and have a good convergence rate in all conditions. The phase weightdistribution required by the QL method can be provided by a method like the finitevolume method or discrete ordinates method.The QL method is applied to several 1D and 2D test cases including isotropicand anisotropic scattering, black and partially reflecting boundaries, and emitting absorbingproblems; and its accuracy, convergence rate, and solution cost are studied.The method has been found to be very stable and efficient, regardless of gridsize and optical thickness. This method establishes very accurate predictions on thetested coarse grids and its results approach the exact solution with grid refinement.