1. The width and spacing of the leading edge jets were varied in an attempt to optimize the performance. The various jets tested are shown in Figure 5. The variation in jet spacing can be more clearly seen in 5-b. All of the jets shown in the figure consist of two openings, but during the testing the largest jet openings were modified to become a four jet configuration. As the spacing between the two jets was increased the length of the jets were decreased resulting in a reduction of mass flow. It was speculated that there would be an optimum configuration for acoustic reduction. However, only a small effect (2-3 dB) in acoustic suppression was observed for the various width and spacing configurations. The most dramatic geometry effect is shown in Figure 20 where the spectrum for the largest two-jet configuration is compared to the spectrum for the single jet. The span-wise shape of the nozzle can have a major affect on the suppression effectiveness of the active flow control actuator. Assuming both configurations are choked and since the mass flow is constant, the momentum isthe same forboth nozzle designs.The segmented design is seen to be much more effective in controlling the instabilities than the full span nozzle. The segmented nozzle alters the spanwise coherence of the energy entering the shear flow whereas the full width nozzle maintains spanwise coherence. By segmenting the nozzle the generation of stream-wise vorticity is also enhanced. Stream-wise vorticity is one of the mechanisms which makes passive suppressors effective in controlling cavity acoustics. The two-jet configuration clearly results in much lower levels for boththetones and the broadband levels.
2. Acoustic environment in large enclosures with a small opening exposed to flow
3. Response of the cavity shear layer oscillations to external forcing
4. The forced mixing layer between parallel streams