Vorticity transport within twin jets in crossflow

The present experimental work is concerned with “twin jets in crossflow” (TJICF) concentrating upon the vorticity distribution and turbulent vorticity transport associated with the dominant vortical structure of the TJICF. The configuration of the TJICF consists of a pair of identical jet nozzles and jet-flow conditions at the nozzle exits. The twin jets are issuing normally into a crossflow. The mean-flow velocity vector and associated turbulence statistics of the TJICF are determined using the standard crossed hot-wire anemometry technique. In the present contribution two geometrically symmetric TJICF arrangements, namely tandem and side-by-side arrangements (both with a nozzle centre-to-centre separation of 5 D), are examined, focusing upon the dominant vortical structure rather similar to that of the well-known contrarotating vortex pair of the single JICF. The formation and decay of this dominant vortical structure is closely associated with the turbulent vorticity transport. The two TJICF arrangements under consideration have their own specific vorticity transport features which are, firstly, visualized and interpreted in terms of turbulent vorticity fluxes. Secondly, the vorticity transport analysis shows the vortex-strength decay (i.e. circulation decay) as described by the corresponding integral decay-rate formula. The similarities and differences between the vorticity (distribution and transport) features associated with the two different TJICF arrangements, tandem and side-by-side, and the single-jet case are examined and discussed. The TJICF flow phenomenon represents an interaction of two single JICF and the gross qualitative features of the vortex formation process of the resulting (mean-flow) dominant vortical structure are described.