Sensitivity to tab disturbance of the mean flow structure of nonswirling jet and swirling jet in crossflow

Sensitivity to tab disturbance of the mean flow structure of nonswirling jet in crossflow (JICF) and swirling jet in crossflow (SJICF) is investigated. For the swirling jet, the nonzero tangential velocity, nonzero circulation jet configuration is employed. The configuration allows for the development of the skewed mixing layer at each lateral edge of the jet not to be obscured and modulated by the jet cross-stream boundary layer and the associated vorticity of the opposite sign to that of the imposed swirl. In the investigation, a heated jet is used and the temperature distributions in the cross planes downstream of the jets are surveyed upto x/rd=1, where r is the effective velocity ratio and d is the diameter of the jet exit. A single stationary tab is alternately placed at eight different azimuthal positions along the periphery of the jet exit. For both JICF and SJICF, the results show that the mean flow structure is most sensitive to tab disturbance in the region centered on the pressure-windward to the windward position and is less sensitive in the leeward region. Specifically, for JICF the sensitive region covers approximately from lateral to windward; for SJICF, from pressure to suction-windward when moving in the same rotational sense as the swirl. The tab disturbance in these sensitive regions has pronounced and effectively lasting effect on the flow structure; the transformed structure persists downstream to the last measurement station. These results indicate that the generation mechanism of the flow structure in both jets is sensitive to tab disturbance in these regions. They also suggest it to be closely related to the development of the skewed mixing layer along the surrounding crossflow direction and around the jet exit column. (C) 2005 American Institute of Physics.