An experimental investigation of supersonic swirling jets

The addition of swirl to scramjet fuel jets has been proposed as a method of enhancing fuel mixing, but little of a fundamental nature is known about supersonic swirling flows. This is a study of mixing in supersonic swirling air jets created by tangential injection and acceleration through a convergent-divergent nozzle into stagnant air. Several cases with different vortex circulations were investigated using pitot, cone and total-temperature probes, and Rayleigh scattering from a laser light sheet. The results show that tangential injection is an efficient method for generating swirling jets; that the swirling jets mix much more rapidly with the ambient air than comparable straight jets; and that when overexpanded, considerable turbulence and increased mixing is created as a result of vortex breakdown.