Wind Tunnel Testing of a Nacelle Bypass Concept for a Quiet Supersonic Aircraft
Yong Han Yeong, Ingrid M. Chiles, Michael B. Bragg, Gregory S. Elliott and Eric Loth
University of Illinois, Urbana, Illinois, 61801
and
Timothy R. Connors
Gulfstream Aerospace Corporation, Savannah GA 31402
ABSTRACT
Sonic boom attenuation is a considerable design challenge to enable civilian aircraft to
operate at supersonic flight conditions. One technology proposed by Gulfstream Aerospace
for the production of low-noise supersonic aircraft is the high-flow nacelle bypass concept in
which an outer nacelle surface is used to encircle the asymmetric external engine
protuberances of a traditional turbine engine. Although this bypass flow may reduce the
overall sonic boom signature of the vehicle, the engine mechanics and mounting create a
highly complex 3-D flow in the annular bypass region. To better understand the 3-D flow
features, an approximately 1/6th engine model has been tested complete with fairings to
transition the flow smoothly around the protuberances. The model was installed in a newly
constructed 11.1 inch diameter axisymmetric tunnel at the University of Illinois to simulate
the bypass flow path. Pressure measurements were taken over a range of circumferential
angles and radial positions and are used to create planar maps of total and dynamic pressure
upstream and downstream of the bypass model. Wind tunnel testing was performed on the
empty axisymmetric wind tunnel followed by model configurations of increasing complexity
until a full test configuration of the engine model with all the gearbox fairings and crane
beam mounts was achieved. Results show significant pressure losses behind the gearbox
fairing with a large flow recirculation zone, which was also characterized by surface flow
visualizations. Due to the blockage created by the gearbox fairing mounted at the underside
of the model, results also show increased flow velocity in the upper section of the bypass
duct. These results are currently being utilized to confirm computational results of the flow
field and to aid in the design of the next generation of fairings and crane beam supports.