Swirl number and nozzle confinement effects in a flat-vane axial swirler

Abstract This paper presents the results of a parametric experimental study of free swirling flow at the exit of a flat-vane axial swirler. A total of 16 data sets were acquired by combining four swirler vane angles (22°, 29°, 50.5°, and 58.3°) and four exit nozzles of different diameters (30, 40, 52, and 76 mm). Sophisticated pressure probes consisting of precise microphones and a two-component LDV system were used to investigate the effect of these geometrical parameters on swirling flow regimes characterized by the swirl number. Particular attention was paid to the precessing vortex core (PVC) phenomenon observed at the exit of the swirler nozzle. It has been shown that by varying the vane angle and the diameter of the exit nozzle, it is possible to independently control the swirl number value and the occurrence of a PVC. A distinct correlation has been found between the PVC-induced pressure pulsations detected by acoustic probes and the tangential velocity fluctuations measured by LDV. The use of microphones provides a quick way to measure the frequency response of swirl flow in a wide range of geometries and flow configurations. The PVC effect does not occur at low subcritical values of the integral swirl number (S