High-Bandwidth Optical Measurements of the Second-Mode Instability in a Mach 6 Quiet Tunnel

Effects of Shock-Tube Cleanliness on Hypersonic Boundary Layer Transition at High Enthalpy

“…2b, recorded after the T5 cleaning procedure was implemented, exhibit a narrowband response at distinct frequencies associated with the second mode. This is qualitatively similar to the spectrograms of a slender-body hypersonic boundarylayer instability obtained in a low-disturbance facility by Hofferth et al [5].…”

“…Hypersonic wind tunnels exist where there are low disturbance levels, such as those at Purdue University [2][3][4] and Texas A&M University [5,6]. Currently, the parameter space available to lowdisturbance hypersonic wind tunnels does not permit the study of the interaction of boundary-layer instability and thermochemistry, which is important for accurately modeling realistic reentry flows; this is because low-disturbance hypersonic tunnels have a low-ordered kinetic energy, or total enthalpy, in the freestream relative to relevant chemical or vibrational energy levels.…”

Transition in Hypersonic Boundary Layers: Role of Dilatational Waves

“…Instead of hot-wire, Fujii [10] and Zhang et al [13] observed second-mode waves on a cone model using PCB fast-response pressure sensors. Hofferth et al [36] measured second-mode instabilities on a Mach 6 flared-cone model using a unique focused Schlieren method. They observed interactions between the second-mode fundamental and its harmonics in the nonlinear growth stage.…”

Visualization of Hypersonic Boundary-Layer Transition on a Slender Cone (Invited)

“…The flow investigated in all of these instances was turbulent. The first measurements of instability waves in a laminar boundary layer using schlieren deflectometry were performed by [23]; more recently, extensive second-mode measurements were made on a flared cone in a quiet tunnel [24]. In both of these investigations, the facility was long duration and a focusing schlieren setup was employed.…”

“…Understanding of boundary-layer transition is thus a critical Related optical techniques have been implemented recently by other researchers: VanDercreek et al [23] and Hofferth et al [24] employed focused schlieren deflectometry for second-mode measurement in longduration hypersonic tunnels; and notably, Parziale et al [25,26,27] obtained quantitative density disturbance measurements, including instability amplification rates, in the T5 hypervelocity shock tunnel at Caltech using focused laser differential interferometry (FLDI). One typical drawback of such optical techniques (even in focusing form), namely that they integrate along the line-of-sight, is of limited relevance to the measurement of second-mode disturbances, since they are primarily two-dimensional [4], i.e., the wave fronts form normal to the flow direction.…”