Hypersonic boundary layer stability experiments in a quiet wind tunnel with bluntness effects.

摘要

Hypersonic boundary layer measurements over both a straight and flared cone were conducted in a quiet wind tunnel. Four interchangeable nose-tips, including a sharp-tip, were tested for the flared cone geometry, and a sharp-tip was tested for the straight cone geometry. All tests were conducted at a freestream unit Reynolds number of {dollar}2.82times10sp6{dollar}/ft in a Mach 6 flow. This Reynolds number provided laminar-to-transitional flow over the cone models in a low-disturbance environment. Point measurements with a single hot-wire using a novel constant voltage anemometry system were used to measure the boundary layer disturbances. Surface temperature and schlieren measurements were also conducted to characterize the laminar-to-transitional state of the boundary layer and to verify the existence of instability modes.; Flared cone results suggest that second mode disturbances were the most unstable and scaled with the boundary layer thickness. The second mode integrated growth rates compare well with linear stability theory in the linear stability regime. The second mode is responsible for transition onset despite the existence of a second mode sub-harmonic. The sub-harmonic disturbance wavelength scales with the boundary layer thickness by about a factor of 2 greater than the second mode scaling. Furthermore, the existence of higher harmonics of the fundamental suggests that non-linear disturbances are not associated with "high" free stream disturbance levels. Nose-tip radii greater than 2.7% of the base radius completely stabilized the second mode. For the straight cone, both first and second mode disturbances are observed. The integrated growth rates, of both first and second modes, compare reasonably well with linear stability theory.