Fractal and turbulence characteristics of aerodynamic fields of swirl burners

Abstract

Turbulence intensities at the exit of a centrally fuel rich (CFR) burner were measured employing a probe with hot-film sensors. In addition, using glycol as a smog tracer, optical images of the highlighted primary airflow were taken with a CCD camera and contrast-enhanced by computer. Profiles of the interface between primary and secondary air were obtained from which fractal dimensions (FDs) of the primary air boundary were estimated. Results indicate that FDs of this air boundary are in the range of 1.10–1.30 depending on burner conditions. As the FD and mean turbulence intensities of the primary air boundary have uniform distributions, they can be used to analyze coal combustion and NOx formation characteristics of the burner. When either decreasing the outer secondary air vane angle or increasing either the inner secondary air vane angle or total mass flow rate of the secondary air, the burner swirl number increases which subsequently shows up as an increase in the FD and mean turbulence intensities of the primary air boundary. Increasing the ratio of the mass flow rate of inner to outer secondary air decreases the burner swirl number, but increases the FD and mean turbulence intensities of primary air boundary.