Development of Hypersonic Quiet Tunnels

Abstract

Conventional hypersonic wind tunnels and shock tunnels sufier from high levels of freestream ∞uctuations which are typically one to two orders of magnitude above ∞ight levels. These freestream ∞uctuations are generally dominated by acoustic noise radiated from the turbulent boundary layers on the nozzle walls. Although the efiects of the noise are often small, and so can be neglected, this noise often has a dramatic efiect on laminar-turbulent transition on models, and it can have an signiflcant efiect on other phenomena as well. Quiet-∞ow hypersonic tunnels with low noise levels comparable to ∞ight have therefore been sought for more than 50 years. The development of these tunnels is reviewed. The largest efiort was carried out at NASA Langley from the late 1960’s through the middle 1990’s, and resulted in successful quiet tunnels at Mach 3.5 and 6, although the Mach 6 tunnel was later decommissioned. The effort was then carried forward at Purdue University from 1990 through the present, leading to the nowsuccessful Boeing/AFOSR Mach-6 Quiet Tunnel.