The Control of Junction Flows.
Final rept. Oct 93-May 97,
LEHIGH UNIV BETHLEHEM PA DEPT OF MECHANICAL ENGINEERING AND MECHANICS
Pagination or Media Count:
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.
- Fluid Mechanics