Cold Flow Measurements of Supersonic Low Aspect Ratio Jet-Surface Interactions

In streamlined airplane configurations, additional noise sources can be created from interactions between the jet flow and surfaces on an aircraft’s body. During takeoff and landing procedures the ground is close enough to already cause jet-surface interference. To assess this interaction, the presence of a flat plate impinging on a supersonic jet of a low aspect ratio (2:1) rectangular nozzle of equivalent exit diameter, De = 20.65 mm, is studied from the minor and major axis orientation. The impact of the plate, 30De in length to resemble an aircraft carrier deck, is studied at supersonic nozzle pressure ratios (NPRs) of 2.5–4.5 for a low jet temperature ratio of TR = 1.1. Streamwise particle image velocimetry (PIV) data was taken to extract average velocity and turbulence kinetic energy (TKE) of the flow. Plate offset (h) distances of h/De = 0, 1, 2, and 3 from the nozzle lip are studied to assess trends related to shock cell spacing, potential core length, and shear layer development relative to a free jet configuration. The surface offset from the nozzle is shown to vary flow properties and even increase screech tones particularly at h/De = 1 and 3, while the in between distance of h/De = 2 is shown to reduce them. These off-design conditions causing screech are of particular interest in this study.