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Show -4- In addition to confirming geometric hypotheses, the results of this test study also served to validate the numerical simulation of non-reactive flows. 3.2 Numerical simulation 3.2.1 Introduction Burner B81-1 was simulated using the Phoenics computing code in 20 or 3D according to whether the staged combustion were represented or not. Curvilinear meshing was used, owing to the relatively complicated geometry of the burner. The 3D meshing comprises some 60,000 mesh representing 1/12 of the burner (six holes are used for the staging of combustion air). Figure 4 shows a diagram of 20 meshing. 3.2.2 Description of the models used The Phoenics [1] computing code is a 3D code for compressible fluid mechanics. The system of equations based on partial derivatives, which is used to model these flows, is derived from the expression of laws relating to the conservation of mass and momentum [2]. The system is closed by the k-E two-equations turbulence model [3]. Numerical simulation reveals the same recirculation zones as in visualization tests. Nevertheless, the location of the main recirculation in the quarl is not correctly predicted. As a result, the axial velocity in the burner is overestimated. This phenomenon can be observed for simulations with or without staged combustion even though the distribution of primary and secondary air flows is correctly calculated. The k-E turbulence model does not appear to be appropriate for this type of flow. However, more suitable models are not yet available on the market. The k-E model will therefore continue to be used for the rest of the study. It must be remembered, moreover, that reactive flows and non-reactive flows do not have the same recirculation zones in theory. 4. Simulation of reactive flows 4.1 Test measurements 4. 1. 1 Introduction Detailed flame analysis studies were performed on the burner. The objective was to constitute the data base of results necessary to validate the numerical simulation of reactive flows. Moreover, an analysis of results also improves our knowledge of flows and of burner combustion. . .. 1 .. |
