Fluid and aero-acoustic analysis of internal bays: Geometric length-to-depth effects

National University of Sciences and Technology, Islamabad, Pakistan

^* Corresponding author: adnan@sines.nust.edu.pk

Abstract

Weapon bays are essential for any bomber, Next Generation Fighter Aircraft, and unmanned combat air vehicles (UCAVs). As flow approaches the leading edge of such cavity, it separates and forms a shear layer. The structure of bays and residing stores thus become prone to intense acoustic and aerodynamic loading– a major design concern. Cavity flow shows significant dependence on its shape. This makes flow actuation possible by only changing the geometric variable of length-to-depth (L/D) ratio. This study compares two bays with an L/D ratio of 5 (deep) and 10 (shallow) in terms of acoustics and affiliated aerodynamic drag. A transient RANS formulation obtained overall sound pressure levels (OASPL) on bay ceilings. An integral-based method was also used to predict far-field noise propagation due to flow fields of both cavities. It is argued that at Mach 0.6, the character of bays changes remarkably when its L/D is altered. Deeper bays show a smoother pressure profile and significantly less drag while operating in shear mode. Shallow bays, on the other hand, show bluff body type drag with uneven pressure distribution, having the potential of causing downwash on residing stores. At the same time, acoustic loads on the ceiling and acoustic signatures in the far-field are comparable for both cavities.