NUMERICAL INVESTIGATIONS OF A SWIRL-STABILIZED PREMIXED FLAME AT ULTRA-WET CONDITIONS

摘要

The present study focuses on the numerical investigation of a generic swirl-stabilized burner operated with methane at ultra-wet conditions. The burner is fed with a preheated homogeneous mixture formed by steam and air. As a set of operating conditions atmospheric pressure, inlet temperature of 673 K, equivalence ratio of 0.85 and a steam content of 30% is applied. Large eddy simulations have been performed to investigate the flow features. In a first step the non-reacting flow field was investigated with water as working medium. Comparison with Particle Image Velocimetry (PIV) and Laser-Doppler Velocimetry (LDV) measurements conducted in a water tunnel facility showed that an excellent agreement within the experimental uncertainty is obtained for the flow field. A dominant frequency in the turbulent energy spectrum was identified, which corresponds to the motion associated with a precessing vortex core (PVC). In order to investigate the reactive flow in a second step, a customized solver for handling low Mach number reacting flows based on an implicit LES approach was developed. As reaction mechanism a reduced 4 steps / 7 species global scheme was used. To compare the simulations qualitatively with a wet flame, OH chemiluminescence pictures serve as a reference. The simulations showed a more compact flame compared to the OH pictures. Nevertheless, the prolongation and position of the flame were found to be reasonable. The reduced mechanism captures the main effects, such as the reduction of the peak and mean temperatures. Furthermore, the presence of a PVC in the reacting flow could be determined and was not suppressed by heat-release.