Scalar transport in a swirling transverse jet

The scalar transport in a swirling jet in a crossflow has been investigated in water tunnel experiments. The jet to freestream velocity ratio was varied from 4.9 to 11.1, and the jet swirl numbers ranged from 0 to 0.17. The jet exit Reynolds number was kept at 1.3 × 10⁴ during the experiments. Planar laser-induced fluorescence was utilized to measure planar cross sections of the mean concentration field of the jet up to 68 jet diameters downstream of the exit. The jet penetration depth, half-value radius, and maximum concentration were determined from these concentration fields. For jets without swirl, measured cross-sectional mean concentration distributions have symmetric double-lobed kidney shapes that are consistent with the counter-rotating vortex pair that is known to exist in the far field of the jet. The addition of swirl causes the far-field distributions to become nonsymmetric, with one of the lobes increasing in size and the other decreasing, resulting in a comma shape. Swirl is also observed to decrease jet penetration but not to significantly affect the decay of maximum mean concentration for the range of swirl numbers investigated.