Swirl-Nozzle Interaction Experiments: Influence of Injection-Reservoir Pressure and Injection Time

Quantitative measurements of sound due to swirl-nozzle interaction are presented for the first time. In the experiment a swirl structure was generated by means of tangential injection into a steady swirl-free flow upstream from a choked convergent-divergent nozzle. Ingestion of swirl by the choked nozzle caused a mass-flow rate change, which resulted in a downstream measured acoustic response. The amplitude of this acoustic response was found to be proportional to the square of the tangential mass-flow rate used to generate swirl. This was, assuming that the upstream generated swirl intensity is proportional to the tangential injection mass-flow rate, predicted by a previously published quasi-steady model for the swirl-nozzle interaction sound source (Hirschberg, L., Hulshoff, S. J., and Bake, F., “Sound Production due to Swirl-Nozzle Interaction: Model-Based Analysis of Experiments,” AIAA Journal, Published online on Nov. 11th 2020, doi: 10.2514/1.J059669.). The tangential-injection time was varied, and found to not influence the amplitude of the acoustic response. This indicates that quasi-steady modelling remains applicable, even for smallest achievable upstream swirl structure with an axial length of ca. three upstream diameters.