A Fluid and Aero-Acoustic Investigation of Bay Door Effects on Cavity Flows

Abstract

Recent interest in cavity flow dynamics is derived from the intense fluid-acoustic coupling induced structural damages in weapon bays, landing gear compartments, and ducts and cavities of aero-engines. Next-generation Fighter Aircraft require bays for reduced radar cross-section, mission survivability, and low drag configuration. Even at steady flights, flow inside cavities is highly unsteady and inherently transient. When flow approaches the cavity leading edge, it separates and forms a shear layer that is prone to instabilities like Kelvin Helmholtz instability. Vibrations induced by such flows in the form of near-field acoustics can damage the structure and residing stores – a major design concern. A few studies in the literature focus on subsonic cavity flows (Mach 0.6), and there are no studies on comparative analysis of the effect of bay doors as the length-to-depth (L/D) ratio varies. This study is an effort to fill this gap. It starts with successfully validating cavity acoustics on two open-cavity configurations with L/D of 5 (deeper bay) and 10 (shallow bay) using uRANS. A design modification is also tested by ramping the trailing wall. Bay doors held at different angles are then introduced to both open cavities. Finally, in an effort to further refine results, a relatively younger version of detached eddy simulation (DES), namely stress-blended eddy simulation (SBES), is investigated. It was found that cavities show remarkable differences in acoustic levels by altering L/D. Both cavities show different profiles of pressure distribution and acoustic loads. The feature of pressure variation within these bays is usually responsible for the trajectory alteration of stores being dropped. Similarly, acoustic loads also vary drastically due to ramping trailing walls. The deeper bay (L/D of 5) showed improvement, whereas the shallow bay behaved peculiarly as loads decreased in rear-cavity but increased in fore-cavity. The addition of bay doors also resulted in quiet different results as the shallow bay became calmer in general, but the deep bay showed alleviation of loads at some angles. Drag due to doors, however, increased for both configurations. Using such bays is an essential design consideration for UCAVs and drones. Since traditional experimentations are done to obtain features affiliated with cavity-type structures, this study is an effort to investigate high-fidelity techniques that can be relayed for a better understanding of complex fluid phenomena.