Numerical Modelling of Anisotropic Heat Recirculation in Microcombustors

The primary motivation for this study is provided by the need for numerical simulations of anisotropic walls of microcombustors which are hypothesised to have a stabilising effect on flame temperatures in microcombustion. A literature review on the topics of wall conduction effects and heat recirculation on flame stability, anisotropic thermal conduction and heat conduction numerical methods are conducted. It is concluded that a finite volume method is most suitable for the desired purpose due to existing code infrastructure in The University of Queensland’s own gas dynamics solver Eilmer, for which the capability upgrade is being designed and implemented. An implicit Euler method is selected and the method outlined and implemented using Newton’s method. The implementation is verified using observed order of error (OOE). Suitable values for solver tolerances are found specific to the problem tested but also considered indicative of a reasonable range for default values. Homogeneous thermal anisotropy in the form of orthotropy is verified (using OOE via method of manufactured solutions (MMS)) and validated (using an experimental case from Hornbaker [17]). A demonstration of thermal orthotropy on a simplified microcombustor is presented, confirming that significant redirection of heat can be achieved for the purposes of improving flow preheating and reducing external heat losses. Suggestions for future work are provided; in particular, highlighting the need for completion of inhomogeneous anisotropy implementation, full thermal anisotropy (as opposed to orthotropic anisotropy) and temporal lagging.