Fluid Oscillations of a Swirl Coaxial Injector Under High-Frequency Self-Pulsation

This study examines data from experiments conducted on a liquid-centered swirl coaxial injector under self-pulsation. The element was operated over ranges of water [20-73g/s] and air [1.6-11.6g/s] flow. Inner post recess was varied from 0 to 2mm. Strong self-pulsations in the range of 1000-4000Hz were observed with and without inner post recess. An analytical survey of potential fluid-dynamic/resonant oscillators is carried out, which includes consideration of swirl post pressure eigenmodes and liquid film hydrodynamics. Measured self-pulsation frequencies are found to correspond well to a family of computed injector responses attributed to liquid surface wave patterns within the swirl injector vortex chamber. This result provides support for the conclusion that the principal fluid oscillator in defining the frequency of self-pulsation for the test article and conditions investigated here is natural surface wave motion within the injector, and it guides the broader notion that self-pulsation is a state that can develop when internal swirl injector hydrodynamics become sensitive to downstream forcing and feedback.