Control of Junction Flows

摘要

An experimental study of the effects of spatially-limited (i.e. localized)surface suction on unsteady laminar and turbulent junction flows was performed using hydrogen bubble flow visualization and Particle Image Velocimetry (PIV). Results indicate that suction on the laminar system can effectively modify the flow topology and periodicity. Detailed analysis of laminar PIV results indicates that it is the impinging boundary layer instability which is the mechanism for vortex generation frequency in the unsteady laminar case. Application of external perturbations to the impinging boundary layer can be used to initiate 'lock-on' of the vortex formation frequency to the forcing frequency over a narrow range of frequencies. PIV results of turbulent junction flow indicate that surface suction effectively weakens both the instantaneous turbulent vortex and the associated surface interactions on the symmetry plane, can eliminate the average turbulent necklace vortex on the symmetry plane, and weakens the average downstream strength of the vortex. It was also determined that suction effectively reduces the Reynolds-stress levels in both the symmetry plane and cross-stream planes, as well as reducing the unsteady behavior of the turbulent vortex legs.