Effect of swirl on the turbulent behaviour of a dump combustor flow

This article reports an experimental investigation of non-reacting flow in a low aspect ratio dump combustor with a tapered exit. The length of this combustor was less than the separated flow reattachment length. The turbulent intensity variation inside the combustor without swirl was found to be axi-symmetric. The turbulent intensity increases in the shear layer between the potential core and the recirculation eddy. The intensity in the core region increases as one moves along the centre-line in the axial direction. The turbulence behaviour significantly changed with the use of a swirler at the inlet of the combustor. The average turbulent intensity increased inside the combustor and the differences in the magnitude of the intensity along the axial and radial directions were less compared to the non-swirling flow. For a high swirl number ((SN) = 1.48), the intensity in the core region was higher compared to other regions inside the combustor. The intensity variation inside the combustor was more uniform than in the case of the low swirl number flow. The r.m.s. velocity studies also suggest more turbulence generation due to swirl. The presence of the swirler increased the turbulence kinetic energy and dissipation rate in the central vortex core region. The power spectral density distribution shows the alteration of the frequency content of the power spectrum, which can be attributed to the forced recirculation due to swirl. The effect of a high swirl number and Re on the frequency peak shows similar behaviour. Therefore, turbulence inside the combustor increased due to the swirler; hence, better mixing of the fuel and air and efficient and stable combustion is expected to be achieved.