High speed tangential flow over open cavities (e.g. aircraft weapon bays) can invoke large pressure oscillations within the cavity. These large oscillations can damage the cavity structure as well as items placed within the cavity. The purpose of this experimental study was to determine the effectiveness of suppressing pressure oscillations by manipulating the shear layer over a two-dimensional cavity with a length-to-depth ratio of two. Two methods, a frequency controllable control surface (fence) and pulsating secondary airflow at the cavity leading edge, were used to manipulate the shear layer. The suppression effectiveness of the fence utilized in both passive and active modes (zero to 120 Hz) was evaluated at six airflow Mach numbers (0.62, 0.76, 0.90, 1.07, 1.28, 1.53). The effectiveness of pulsating secondary airflow was evaluated at one airflow Mach number (1.28) and two flow injection angles (parallel and 45 degrees to the flow) at frequencies ranging from zero to 80 Hz. The effect of steady flow injection was also evaluated at mass flow rates per unit width ranging from 0.323 to 1.27 (lbm/sec/ft). Pressure recordings from within the cavity were made for each test. The effectiveness of a pulsating fence in suppressing the peak mode pressure oscillations proved to be less than that achievable with the fence static. The pulsed secondary flow injection technique was most effective when pulsed at a 45 degree angle to the external flow. Theses.

The resonant excitation of a cavity by an equilibrium turbulent grazing flow was investigated. The objectives of the research were first, to understand the dynamic processes related to the shear tones generated by vortex shedding from the upstream edge, and then to determine practical techniques for controlling the excitation and reducing the resonance. Detailed measurements of the cavity pressure and the velocity field in the opening were performed. Spectral data on cavity pressure fluctuations were analyzed over a range of speeds to determine the behavior of both the shear tones and cavity tones during non-resonant and resonant conditions. The cross-spectral properties between the velocity components and cavity pressure were also obtained. The data support the finding that the resonant and nonresonant conditions are distinguished by the behavior of the convection velocity and by the distribution of energy production in the flow field. Techniques for controlling cavity resonance were also investigated. The measurements and data analyses techniques discussed above were also performed for three practical devices. These include a technique, developed by the author, whereby fluid is diverted into the cavity from the boundary layer. The diversion technique is the most effective in reducing cavity resonance.

The resonant excitation of a cavity by an equilibrium turbulent grazing flow was investigated. The objectives of the research were first, to understand the dynamic processes related to the shear tones generated by vortex shedding from the upstream edge, and then to determine practical techniques for controlling the excitation and reducing the resonance. Detailed measurements of the cavity pressure and the velocity field in the opening were performed. Spectral data on cavity pressure fluctuations were analyzed over a range of speeds to determine the behavior of both the shear tones and cavity tones during non-resonant and resonant conditions. The cross-spectral properties between the velocity components and cavity pressure were also obtained. The data support the finding that the resonant and nonresonant conditions are distinguished by the behavior of the convection velocity and by the distribution of energy production in the flow field. Techniques for controlling cavity resonance were also investigated. The measurements and data analyses techniques discussed above were also performed for three practical devices. These include a technique, developed by the author, whereby fluid is diverted into the cavity from the boundary layer. The diversion technique is the most effective in reducing cavity resonance.

An experimental study was undertaken to investigate the use of a water table to define the parameters that influence the pressure oscillations resulting from air flow over open cavities. Tests were also conducted to investigate means to eliminate or reduce these oscillations. (Author).