Self‐Sustained Pressure Oscillations in Two‐Dimensional Cavity

The pressure oscillations within a two-dimensional, rectangular cavity have been explored. The flow was subsonic and the chord-to-depth ratio of the cavity ranged between 0.25 and 1.25. The experimental setup, comprised a plexiglass channel-cavity model, was inserted within the test section of a wind tunnel. The moveable walls of the cavity were adjusted for various cavity geometries. A pressure transducer was flush mounted along the upstream wall of the cavity and was used to monitor, with the help of an oscilloscope, the pressure fluctuations within the cavity. Within a Strouhal number range of 0.4 - 2.4, periodic pressure fluctuations as high as 50% of the free-stream dynamic pressure were observed. The modulation of the external flow is influenced by the cavity which acts as a simple harmonic oscillator with a certain natural frequency. As the velocity of the external flow is increased gradually, the frequency of the pressure fluctuations experiences step changes, shifting to higher or lower frequency levels. Of the two parameters describing the cavity geometry and their effects on pressure oscillations, the cavity length appears to influence the frequency, and the cavity depth effects the amplitude. The maximum amplitude of the pressure oscillations within the cavity were observed to occur under mode 2 and for a cavity geometry corresponding to a chord-to-depth ratio of about 0.5.