Flow Characterisation of Highly Integrated High-Aspect-Ratio Rectangular Nozzle

The paper presents part of the experimental activities carried out within the framework of the NATO AVT-415 activities aimed at characterising the flow behaviour of a bidimensional bevel rectangular nozzle. The optimisation of Unmanned Air Vehicles (UAVs), for both military and civil applications, necessitates conducting advanced computational studies that rigorously analyse aerodynamic and aeroacoustic behaviours, particularly in proximity to the exhaust region of the propulsion system. This investigation focuses on a wing-blended vehicle with a fully integrated propulsion system. The primary objectives are to enhance aerodynamic performance while concurrently minimising radar cross-section, thermal detection and acoustic emissions. The activity foresees investigating the flow behaviour inside a bevel nozzle characterised by an internal S-shape, an internal section variation from elliptical at the nozzle entrance to rectangular at the exit, for three different mass flow rates. Pressure distribution along the nozzle symmetry plane was investigated by 44 pressure taps, inlet Mach distribution was investigated by two static and total pressure probe rakes and the flow evolution downstream the exit nozzle was depicted by multiplane PIV measurement up to 15 nozzle heights. Vertical and horizontal measurement planes were investigated to consider the three-dimensionality of the wing-bleed vehicle and the integrated nozzle. The paper deals with flow behaviour and pressure distribution inside and outside the nozzle. The velocity fields are discussed in terms of flow velocity and flow fluctuations, taking into consideration the highly three-dimensional nature of the flow velocity.