Numerical and experimental study of flow structure and heat release distribution in a stratified swirl flame with high-speed PIV and OH* measurements

Stratified swirled flame is widely used in gas turbines and aero engines to achieve low emissions. However, the limitation of implementing laser diagnostic in real combustors acquires more accurate measurements of field information in the flame, especially the unsteady heat release, which relates to a lot of important phenomena, such as combustion instability and blow-off. The present study employs large eddy simulation (LES) combined with a detailed OH* chemiluminescence reaction mechanism to validate the chemiluminescent image of OH* in a stratified swirled flame at the atmosphere condition. 10 kHz particle image velocimetry images and OH* filtered images are recorded during the experiment. The heat release and flow structure of the stratified swirled flame at two different fuel stratification ratios show distinguished flame shapes. In general, the velocity results of LES have good agreement with the measurement. The numerical OH* and heat release comparison reveals a strong dependence on the local strain rate and turbulence level of OH* emissions. It is also noticed that the wrong flame shapes may be deduced from the Abel inversed OH* image since the signals are weak in the outer recirculation zone. This indicates that the strain rate in different regions of stratified swirl flame has a significant impact on OH* signal distribution. The results provide insight into the ability of chemiluminescent emissions, such as OH*, to indicate heat release in more complex industrial flames.