Coherent structures in an impinging jet with swirl and combustion

The present paper reports on an experimental study of flow structure and coherent structures in impinging jets with strong swirl and combustion of lean propane/air mixture by a combined application of OH, HCHO PLIF and PIV. The equivalence ratio of the mixture was 0.7, the Reynolds number of the jet was 5000. Thru to the use of modern panoramic optical methods PIV, OH and HCHO PLIF (these methods are based on anemometry on particle images and registration of plane laser-induced fluorescence of formaldehyde, respectively), the velocity distributions and the position of the flame front in the axial section of the flow were measured. For the flame, a significant increase in the fluorescence intensity of formaldehyde and other organic compounds were detected upon excitation at a wavelength of 355 nm in the near-wall region at a distance of three calibers from the nozzle to the surface. To reveal coherent structures, the experimental data were processed by proper orthogonal decomposition (POD). It is expected that this effect is caused by the cooling of the combustion products due to heat exchange with a surface, lowering the temperature inside the recirculation zone and reducing the completeness of fuel combustion.