Impact of rectangular, half-elliptical, trapezoidal, and triangular tabs on the mixing behavior of circular sonic jets

This study investigates the mixing characteristics of sonic jets with and without control mechanisms. Specifically, passive controls in the form of tabs placed at the exit of a convergent nozzle are examined both computationally and experimentally. The research focuses on the jet decay characteristics and flow development of a plain nozzle compared to nozzles equipped with square, half-elliptical, triangular, and trapezoidal tabs. The realizable k-ε turbulence model is employed, as it effectively captures the structures of sonic jets in both correctly expanded and underexpanded states. The tabs were found to cause significant distortions in the jet structure, leading to increased mass entrainment and lateral spread of the jet. Notably, half-elliptical tabs were the most effective across all expansion levels compared to square, trapezoidal, and triangular tabs. Half-elliptical tabs had a maximum reduction of 69.2 % in sonic core length for underexpanded jets at a nozzle pressure ratio (NPR) of 4. Additionally, reductions in core lengths were 55.5 % for correctly expanded jets at NPR 2 and 66.6 % for underexpanded jets at NPR 3.