Acoustic coupling-coherent structures - An experimental and theoretical approach on a base configuration

The experimental apparatus and early results are presented from a study of acoustic coupling and structural coherence in a test chamber with a convergent-divergent nozzle into which was placed a prismatic body. The studies are of interest in the development of ramjets, whose propulsive functioning can be greatly affected by coherent acoustic structures propagating from downstream of the exhaust. The chamber nozzles permit examining flows from Mach 1.5-3.5, and downstream expansion permits flows from Mach 0.05-0.15. Microphones inserted into the flow at points along the chamber gather acoustic spectra and amplitude data. Acoustic structures shed from the blunt body were modeled with the Lighthill equation and the volumic mass displaced was calculated with the Green functions. The structures shed from the body in the tests were demonstrably similar to those shed from similar structures in the real world, thereby raising confidence that the test channel will provide valid data.