Nozzle Modifications for High-Reynolds-Number Quiet Flow in the Boeing/AFOSR Mach-6 Quiet Tunnel

摘要

The Boeing/AFOSR Mach-6 Quiet Tunnel was designed to have laminar nozzle-wall boundary layers and therefore low noise levels for stagnation pressures up to 150 psia. From its initial operation in 2001 until March 2005, the tunnel only exhibited low noise levels up to 8 psia. A surrogate aluminum nozzle was fabricated to replace 30 in. of the original electroformed nickel and steel nozzle, starting at the throat region. Improving the surrogate nozzle's polish and other modifications improved its maximum quiet pressure from 20 psia to as high as 130 psia, though not reliably. Quiet flow is regularly achieved for 60-90 psia. A flaw in the electroformed nozzle bleed lip inner contour was identified as the probable cause of early transition on the electroform. The bleed-lip contour was remachined and the flaw was eliminated. As of August 2006, the electroformed nozzle exhibited performance similar to the surrogate. Measurements in the downstream half of the nozzle found no quiet pressure dependence on axial location, suggesting that bypass transition near the bleed lip is still responsible for the limited performance.