Aeroacoustics of aircraft cavities

Abstract

The purpose of this study is to determine the aeroacoustic and fluid-dynamic nature of the flow field in and around a generic aircraft cavity in order to characterise the physical mechanism of noise and vibration generated by the flow. This paper discusses the experimental investigation of a narrow, shallow, rectangular cavity in both wind and water tunnel facilities. The experimental investigation primarily focuses on boundary layer characteristics, surface pressure distributions and surface flow visualisation. Qualitative and quantitative results are discussed. This paper reports results for cavities of length:depth:width ratios of 6:1:2. The principal findings are in agreement with an "open" type flow as stated in the literature, however the flow within the cavity is highly three-dimensional in contrast with the suggestions of Stallings & Wilcox (1987). Significant three-dimensionality is also evident downstream of the cavity, close to the training edge. Further findings suggest the shear layer impinges below the edge of the rear wall in the mean, leading to a net inflow of free-stream fluid into the cavity at the centre line, which is balanced by an outflow adjacent to the side walls. Finally, a number of vortices are present at the rear wall, including a corner vortex at the base of the rear wall, and a vortex associated with flow separation on the trailing board adjacent to the rear wall edge.