A turbulent premixed plane jet flame is analyzed by large-eddy simulations. The analysis shows that the flame front wrinkling is strongly influenced by the shear layer effect when the gas expansion effects are small leading to larger flame front amplitudes at the flame base than at high gas expansion ratios. However, the hydrodynamic instability effect induces a continuously increasing flame front amplitude which yields an enhanced flame pocket generation at the flame tip. Both phenomena influence the magnitude of the turbulent burning area and burning area rate response through the flame front deflections which are determined by the contribution coefficient. This coefficient represents the mutual interaction between the flame and the flow. At low gas expansion ratios, the total heat release rate spectra of the turbulent flame are wider in terms of dominant modes at Strouhal numbers which are linked to the mean flame height oscillations. Thus, at low gas expansion ratios, the vortex-flame interaction is less damped by the flame in the sense that vortices can perturb the flame front stronger. The total heat release rate trend of St−2.2 previously found for a round jet flame is also determined for the current slot jet at realistic gas expansion ratios indicating a general tendency to transfer energy from large to small flame structures. At high gas expansion ratios, an increasing Markstein length leads to an energy transfer between neighboring dominant modes in the low frequency range 1 < St < 10 and the burning area rate response becomes more important for the total heat release rate spectra of the turbulent slot flames which agrees with recent findings for a laminar premixed plane flame.
In this paper an advanced thermal lumped parameter model for a switched reluctance electric motor (SRM) is constructed, based on a 2D thermal finite element simulation of a radial cross section of the motor. When applying and combining advanced cooling methods such as direct coil cooling, end winding cooling (radial stretched) and spray cooling on an SRM, the conventional lumped parameter models can no longer be used due to the 3D and complex temperature gradients in the motor. In standard LP models, mostly one simple cooling method is implemented by which the thermal gradients are also quite simple (1D or 2D). When combining different cooling methods, the gradients become highly 3D and these LPM are no longer valid. To improve the accuracy of this problem, a fully 3D thermal finite element simulation could be performed, but this would unnecessarily increase effort, complexity and computational time. To avoid this an advanced lumped parameter model is constructed in this paper, such that the high thermal gradients are modeled in more detail. The results from one 2D finite element simulation of a radial cross section of half of a stator tooth are reduced to a simpler lumped parameter model with more nodes in the most crucial parts, i.e., where the highest thermal gradients are expected. The 2D thermal model is then expanded to a 3D lumped parameter model, including the gradients in axial direction. Using this model, various cooling configurations and geometry parameters can be varied easily such that the design of an SRM with advanced cooling can be optimized efficiently.
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