EXPERIMENTAL INVESTIGATION OF ROSSITER MODES FOR AN OPEN BOX CAVITY WITH ADJUSTABLE DEPTH

摘要

Resonance in aerospace is a phenomenon that engineers have been trying to predict and avoid for a long time. Acoustic resonance is only a part in this field. When it was previously studied, it was mostly in connection with long slender gaps at the fuselage of aircrafts. Lately it has become a focus in the development of highly efficient aero engines. Bleed systems in the compressor part of engines are needed but not easy to place aerodynamically. Additionally, these bleed systems have complex geometries. These geometries coupled with the operational range of modern aircraft from low to high subsonic Mach numbers can create unwanted acoustic resonances. This paper is part of project study of these resonances. Here the bleed geometry is simplified to an open box cavity that is studied experimentally in order to measure its acoustic behavior in low to high subsonic flow. The experimental data is compared to theoretical prediction models to create a baseline for future studies. The results show a good agreement between Rossiter prediction and experiments for a shallow cavity of L/D=4. Deeper cavities with a length to depth ratio of one and 0.5 represent more organ pipe resonance phenomena. This is especially governed by the geometry of the cavity itself and the height of the test section. All cavities experience a shift in modes depending on the operating point. This mode shift pattern is similar for deeper cavities. However, the operating range can be divided into four sections in which a mode shift occurs for all cavities.