Types of lean combustion of premixed gas fuel in a radial burner

This paper presents the results of an experimental study of the characteristics of a swirling flow with the formation of vortex structures in a radial burner under isothermal and reacting conditions for various flow swirling parameters. For isothermal conditions, the distributions of average and fluctuating velocity fields, including those tied to the phase of a precessing vortex, are obtained, the pressure fluctuations induced by the precessing vortex are analyzed, and the contribution of the precessing vortex structure to the overall level of turbulence is determined. The studies are carried out using modern contactless experimental methods of flow diagnostics, such as optical imaging and particle image velocimetry (PIV). An acoustic field generated by the vortex core precession (VCP) is recorded using four measuring microphones with pressure taps. The contribution of the VCP to the overall level of turbulence is revealed using the method of proper orthogonal decomposition (POD), also applied to analyze the velocity distributions obtained by the PIV method. The experiments show that, in the isothermal case, the VCP that occurs after the twist parameter overcomes a value $S=0.6$ is a single-helix vortex structure, whose contribution to the overall level of kinetic turbulence energy is up to $27\%$. For reacting conditions, the flame is visualized at different flow swirls and the frequency characteristics of the VCP occurring in the flow at $S\ge0.6$ are measured. It is shown that the dependence of the dimensionless frequency of the VCP as a function of the flow swrl $S$ has the same nonmonotonic character both in the case of combustion and in the isothermal case.