Sound production of vortex-nozzle interactions

The factors which affect the sound production of a vortex as it passes thro ugh a nozzle are investigated at both low and high Mach numbers using time- accurate inviscid-flow computations. Vortex circulation, initial position, and mean-flow Mach number are shown to be the primary factors which influen ce the amplitude and phase of the sound produced. Nozzle geometry and distr ibution of vorticity are also shown to play significant roles in determinin g the detailed form of the signal. Additionally, it is shown that solution bifurcations are possible at sufficiently large values of vortex circulatio n. Comparisons are made between sound signals computed directly using a num erical method for the Euler equations and predictions obtained using a comp ressible vortex-sound analogy coupled with a compact-source assumption for the computation of vorticity dynamics. The results confirm that the latter approach is accurate for a range of problems with low mean-flow Mach number s. At higher Mach numbers, however, the non-compactness of the source becom es apparent, resulting in significant changes to the character of the signa l which cannot be predicted using the analogy-based approach. Implications for the construction of simplified models of vortex sound in solid-rocket n ozzles are discussed.