Flow momentum behind a conventional nozzle is modulated by four different bluff-body cones - non-rifled, 1-rifled, 2-rifled and 3- rifled cones. This novel rifled-cone swirl generator (RCSG) includes the blockage disc and rifled bluff-body cones. The rifled bluff-body cone transforms the axial momentum (or the axial velocity) into the angular momentum (or the tangential velocity). The swirling flow is enhanced by increasing the tangential velocity of central jet. In this investigation, the carbon-dioxide ($CO_2$) is utilized as the index gas to determine the mixing index of RCSGs. Namely, the mixing index between the central $CO_2$-jet and the annular air-jet is increased using the RCSGs. The cold-flow patterns behind the rifled bluff-body cones are visualized using the smoke-wire scheme. The cold-flow patterns are categorized as - jet-flow, single-bubble and dual-bubble modes. The jet-flow mode occurs at low ua. Additionally, the jet-flow and single-bubble modes are further classified as - Type-I and type-II sub-modes. The particle-image velocimetry (PIV) measures the cold-flow velocity vectors. The mixing levels of $CO_2$ in the cold-flow modes are detected using a gas concentration analyzer.