Free-stream density perturbations in a reflected-shock tunnel

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

“…To reduce the effects of particulates of BLT on slender cones [20][21][22][23][24][25][26][27], we devised a new cleaning and fill procedure for the shock tunnel, which is the subject of this Note. Possible sources of particles include piston buffer material, piston brakes, test gas impurities, and the Mylar secondary diaphragm.…”

“…Possible sources of particles include piston buffer material, piston brakes, test gas impurities, and the Mylar secondary diaphragm. In particular, Parziale et al [25] noted that experiments performed immediately after an experiment where the piston buffers shattered had less predictable noise profiles. With stringent cleaning of the shock tube, it was possible to mitigate particulate contamination and repeatedly obtain transition at specified locations through a careful selection of reservoir conditions.…”

“…One reason for a higher transition N factor for the current data may be the mismatch between freestream noise spectrum and boundary-layer unstable frequencies for second-mode disturbances, whereas the relatively large scatter may result from particulate-induced bypass transition affecting some experiments. Parziale et al [25] found that noise in the T5 freestream was relatively low frequency compared with the most unstable boundary-layer frequencies. This hypothesis was implicitly supported by the recent analysis of Gronvall et al [28], who found a transition onset value of N ≈ 8 for the experiments of Tanno et al [12], which were also performed in a reflected-shock tunnel, although at lower enthalpy than the present study, and for a limited range of conditions, with unspecified cleaning procedures.…”

Analysis of focused laser differential interferometry

“…The technique was limited in its usefulness at that time because of limitations on photodetectors and data acquisition systems as well as the availability of suitable lasers. Parziale revitalized the technique in 2013 [6][7][8] to measure instabilities in a hypervelocity boundary layer on a slender body in the T5 hypervelocity tunnel at Caltech and to make measurements of the free stream environment in T5 [9]. This paper will develop some general results for the FLDI but will concentrate on the application of measuring second-mode (Mack) waves in hypersonic boundary layers [10].…”

Observations of hypervelocity boundary-layer instability

“…The reflection of the shock at the end of the shock tube generates the high-enthalpy reservoir used to supply a converging-diverging nozzle; quasi-steady flow in the nozzle creates the hypervelocity flow over the cone model located near the nozzle exit. The noise level in the free stream flow is characterized using single-point FLDI density fluctuation measurements in the free stream, as discussed in Parziale et al (2014). The typical RMS fluctuation intensity is less than 0.5 % for disturbance wavelengths between 0.7 and 10 mm, the range relevant to direct excitation of second-mode instabilities in our study.…”