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Wind tunnel experiments on the flow over rectangular cavities at subsonic and transonic speeds
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1964
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AeroacousticsEngineeringFluid MechanicsCavity FlowWave MotionNonlinear AcousticBoundary LayerUnsteady FlowVibrationsWind Tunnel ExperimentationRectangular CavitiesNoiseResonance PhenomenaWind Tunnel ExperimentsSound PropagationPeriodic ComponentsPhysicsTransonic SpeedsWave PropagationFlow PhysicAerospace EngineeringAerodynamicsAcoustic Resonance
The periodic pressure component is attributed to acoustic resonance within the cavity, similar to edge‑tone excitation. The study measured time‑averaged and unsteady pressures on the roof and behind rectangular cavities mounted on the roof of a 2 ft × 1 ft transonic tunnel. Random pressure fluctuations dominate in shallow cavities (L/D > 4) and are strongest near the rear wall, while periodic fluctuations dominate in deeper cavities (L/D < 4), forming standing‑wave patterns that can be mitigated by a small front spoiler.
Measurements have been made of the time average and unsteady pressures acting on the roof and behind a series of rectangular cavities set in the roof of the 2 ft x 1tr ft transonic tunnel. It was found that the unsteady pressures contain both random and periodic components. The random component predominates in the shallower cavities (length/depth ratio> 4) and is most intense near the rear wall. The periodioc component predominates in the deeper cavities (length/depth ratio < 4) and may form standing wave patterns. It is suggested that the periodic component is due to an acoustic resonance within the cavity excited by a phenomenon similar to th at causing edge-tones. It may be suppressed by fixing a small spoiler at the front of the cavity.