Blockage Effects on the Pressure Fields of 3D-Printed Small-Scale Jet Nozzles

Abstract

This paper presents a preliminary investigation into the pressure fields of jets exhausting from partially blocked nozzles. Measurements are performed for a series of asymmetric, small-scale, single stream nozzles mimicking the bypass flow from an engine-pylon-wing configuration. The hydrodynamic and acoustic pressure fields of the pylon nozzles are compared to data from an axisymmetric, annular jet baseline nozzle. For the good aerodynamic pylon designs, the isolated jet mixing noise source is slightly modified at azimuthal angles near the blockage. The blockage effects on the installed jet-wing interaction noise source are also small, even when corrections for thrust are applied. In-flight data suggest that a significant increase in the pressure levels exist at relatively high flight-to-jet-velocity ratios for the blocked configurations. For the poorly aerodynamically designed blockages, flow separation occurs close to the nozzle exit. This flow separation induces an augmentation of the jet noise sources. The near-field pressure data shows that the main effects of the pylon are, firstly, an increase in the strength of the hydrodynamic pressure field perpendicular to the pylon surface due to vortex shedding and, secondly, a fast recovery of symmetry downstream of the pylon trailing edge.