Experimental Investigation of Cavity Mode Frequencies on an External Aircraft Store

This work describes part of an experimental investigation about cavity mode frequencies on a chaff/flare dispenser pod within the pod integration on an aircraft. Magazines in the pod with empty chaff/flare cartridges demonstrate the condition after chaff/flare dispense. The empty cartridges with their deep cavities generate cavity tones due to grazing flow over their orifices during flight. Additionally, higher tone modes are excited due to the varying flow over the cavities. The tone frequencies show correlation to theoretical estimations of cavity response in depth related direction such as standing waves in a rectangular volume or as Helmholtz frequency. The variation of aircraft angles during flight maneuvers has influence of the mode excitation such as angle of attack, angle of sideslip, and bank angle. The combination of these aircraft angles shows the most significant excitation. Due to the varying flow direction over the empty cartridges, the cartridge cavities are excited separately. Thus, the single tone splits up into multiple tones showing multiple frequency peaks. Because this effect does not show any influence on the tone amplitude, an interaction of multiple cavity tones could not be detected.