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In earlier experimental studies of the authors a previously unknown mechanism leading to flame flashback—combustion induced vortex breakdown (CIVB)—was discovered in premixed swirl burners. It exhibits the sudden formation of a recirculation bubble in vortical flows, which propagates upstream into the mixing zone after the equivalence ratio has exceeded a critical value. This bubble then stabilizes the chemical reaction and causes overheat with subsequent damage to the combustion system. Although it was shown earlier that the sudden change of the macroscopic character of the vortex flow leading to flashback can be qualitatively computed with three-dimensional as well as axisymmetric two-dimensional URANS-codes, the proper prediction of the flashback limits could not be achieved with this approach. For the first time, the paper shows quantitative predictions using a modified code with a combustion model, which covers the interaction of chemistry with vortex dynamics properly. Since the root cause for the macroscopic breakdown of the flow could not be explained on the basis of experiments or CFD results in the past, the vorticity transport equation is employed in the paper for the analysis of the source terms of the azimuthal component using the data delivered by the URANS-model. The analysis reveals that CIVB is initiated by the baroclinic torque in the flame and it is shown that CIVB is essentially a two-dimensional effect. As the most critical zone, the upstream part of the bubble was identified. The location and distribution of the heat release in this zone governs whether or not a flow field is prone to CIVB.

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Within the framework of the development of a preliminary aero engine compressor casing design methodology, prompt tip clearance assessments between casing and rotor blades are aspired. Based on the Finite Element Method and proceeding from the 3D model of a generic axial compressor casing, the intention is to first investigate and quantify the effect of various 3D features on radial displacement during steady state engine operation. Bleed air ports and bolted joints are the 3D features this work is devoted to address. Parameter studies varying the circumferential quantity and dimension of the stated 3D features are conducted for purposeful validity. Constructive on these deliverables and the desire for reduced preprocessing and computational time consumption, the transition from 3D to 2D axisymmetric Finite Element modeling by implementing diverse model simplifications is focused. Considering the numerical effort towards prompt clearance assessments, reducing the nodal quantity of the computational grid through transition from 3D to 2D is an expedient issue that has to be resumed in future work, since it turned out that the circumferential and longitudinal track generated by the 3D features covered can be approximately neglected.