Fractal Simulation For Turbulent Chemical Reaction

The fractal model of turbulent chemical reaction (FM) is developed based on the phenomenological concept of vortex cascade and on fractal theory. In order to realize the simulation, user-level development of software-ANSYS CFX is conducted. Using the user FORTRAN subroutines, FM model is compiled into software-ANSYS CFX 10.0. First, transport phenomena of fluid flow and turbulent combustion process for a big space underground channel is simulated and is discussed. Based on this, the fractal model of turbulent chemical reaction (FM) is tested qualitatively by simulating combustion in a Can Combustor. Finally, in order to validate FM model, comparisons and analysis are carried for fire scenarios of Steckler. Comparisons are also made with the numerical simulations from other combustion models including the eddy dissipation model (EDC) and the eddy break-up model (EBU) for the same fire experiments. The main research works and results are summarized as follows:(1) Based on the phenomenological concept of vortex cascade and on fractal theory, fractal model of turbulent chemical reaction (FM) is developed which can describe the characteristics of fractal scales of turbulent chemical reaction.(2) By using Visual Fortran compiler, FM model is compiled into ANSYS CFX10.0. User-level subroutine Cfx5mkext is developed and incorporated into CFX link. The numerical simulation is carried out using FM model on the platform of ANSYS CFX.(3) In the study of smoke transport for underground channel, a three dimensional dynamic field simulation including smoke flow, the heat transfer of conduction, convection and radiation is accomplished, in which two equations k—εturbulent model with buoyancy modification is used and Rosseland radiation model is applied to take radiation into consideration. The fire is set as a heat source with smoke components. The transport process of fluid flow, heat and smoke transfer and the throttle effect, floatation effect resulted from the change of air density are discussed in detail. The study of this work will provide theoretic base for further study.(4) In the combustion simulation of Can Combustor, two equations k—εturbulent model with buoyancy modification and Rosseland radiation model, FM model are applied. Meanwhile, EBU and FM models are compared and FM model is tested qualitatively. The results of numerical simulations show the structure of fractal vortexes by FM simulation.(5) The combustion simulation of the Steckler's room fire is carried out with the fractal model of turbulent combustion chemical reaction (FM) and the eddy-break-up model (EBU). The results from references are compared with the results of FM.(6) The numerical simulation results shows FM and EDC simulation agree better with experimental data and FM can describe the interaction between turbulence and chemical reaction. FM is proved to be a promising mathematical model for turbulent chemical reaction.(7) Future work should be focused on the structure of fractal and vortexes. PIV and PLIF method will be applied to obtain the characteristics of multiscale and vortexes structure, which will provide the bases for the further application and observation for turbulent chemical reaction processes.