Aerodynamic Characterisation of a Bidimensional Subsonic Bevelled Nozzle

Abstract

The paper presents part of the experimental activities carried out within the framework of the NATO AVT-415 programme aimed at characterising the flow behaviour of a bidimensional rectangular bevel nozzle. 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 involves investigating the flow behaviour inside a bevelled nozzle characterised by an internal S-shape and 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 using 44 pressure taps; inlet Mach distribution was investigated using two static and total-pressure probe rakes; and the flow evolution downstream of the nozzle exit was depicted by multiplane PIV measurements up to 15 nozzle slot widths. Tests were conducted at a Reynolds number based on the slot width (h) and exit centreline velocity of Reh = 3.22 * 105, and a mass flow rate of Q=1.55 kg/s (for AR =13.3). Vertical and horizontal measurement planes were investigated to consider the three-dimensionality of the highly 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. The turbulent jet presents an asymmetric behaviour with an axial velocity decay varying along the spanwise position and different spreading rates for the upper and lower shear layers.