Experimental Characterization of an Isothermal Swirler Flowfield

A method for characterizing the flowfield associated with an ensemble of production swirl cups before their implementation into an aircraft engine is presented. LDV is used to acquire mean, rrns, and skewness velocity profiles downstream of the swirlers' venturi. The skewness of the streamwise velocity data is used to locate the fluid boundary between the primary and secondary corotating streams. The data reduction technique utilizes the modality transformation of the streamwise velocity histograms as the LDV probe volume is translated from the low-speed secondary stream to the high-speed primary stream. By locating this boundary, primary and secondary flowfield metrics such as swirl number and primary-secondary mass flow split compliment the conventional effective area measurements. To corroborate the LDV measurements, digital particle image velocimetry images are used to qualify the size and position of the recirculation zone created at the venturi exit as well as highlight the unsteady nature of the feature. Instantaneous side- and end-view digital particle image velocimetry images provide evidence of coherent radial movement, that is, wagging of the recirculation zone and the presence of large-scale vortices in the secondary stream.