Frequency response of the flow in a radial swirler

We report the results of an experimental study on flow with a precessing vortex core in an isothermal radial swirler burner model. It was shown for the first time that in radial swirler flow, the Strouhal number (the dimensionless precession frequency of the vortex core) is inversely related to the swirl number in the range 0.5 < S < 0.8. A minimum occurs in the precessing vortex core frequency due to the reduced velocity of the helical vortex structure in the axial flow direction and the axial stretching of the helical vortex structure. This finding emphasizes the importance of accounting for the helical geometry of the precessing vortex when predicting the frequency response of burner installations.