Multi-point Focused Laser Differential Interferometry for Noise Measurements in High-Speed Tunnels

This paper presents an experimental study of the effect of wall cooling on the boundary-layer structures of a sharp-nosed, 5° half-angle cone in Mach 6 flow. An experimental methodology was developed that allowed quantitative measurements of second-mode disturbance growth over a range of wall-temperature ratios from [Formula: see text] without modifying the freestream disturbance environment. The cooling system comprised probe cooling, liquid nitrogen injection, and thermal insulation. The model temperature was monitored before each run, with thermocouples mounted at the base and nosetip piece agreeing within 3.3 K. Calibrated schlieren provided global and time-resolved measurements of the boundary-layer features at a freestream unit Reynolds number of [Formula: see text]. An increase in wall-cooling level was associated with a shrinking of the boundary layer and a lowering of wavepacket structure angle at the wall. Despite some outlying results, an overall trend of increasing disturbance frequency with decreasing surface temperature was observed; additionally, cooling increased the spectral amplitude and growth rate of second-mode disturbances, pushing the point of saturation upstream.

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Megahertz-Rate Imaging of Hypersonic Boundary-Layer Instabilities in a Mach 10 Shock Tunnel

Jiang¹,

Hsu²,

Slipchenko³

et al. 2023

AIAA Journal

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The transition of the boundary-layer state from laminar to turbulent on a 7° sharp cone in Mach 10 flow is measured using several high-speed optical diagnostics capable of time-resolved measurements of the second-mode instability with high spatial resolution. Specifically, megahertz-rate nitric oxide planar laser-induced fluorescence (NO PLIF) imaging is done at 1 MHz to provide a non-path-integrated visualization of second-mode associated structures in the transitioning boundary layer. A recent variation of focused laser differential interferometry (FLDI), namely, linear array FLDI (LA-FLDI), is also applied for multipoint measurements of frequency content in the transitioning boundary layer. From each data set, the frequency of the most unstable second-mode instability is obtained along with the phase velocity of the second-mode waves. Measurements show good agreement relative to each other and also with surface pressure sensors and high-speed schlieren imaging. Furthermore, the 1 MHz NO PLIF imaging demonstrated here shows great potential for visualization of transitional and turbulent boundary layers when path-integrated diagnostics cannot be used.

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Multi-point Focused Laser Differential Interferometry for Noise Measurements in High-Speed Tunnels

Cited by 5 publications

References 32 publications

Interpreting single-point and two-point focused laser differential interferometry in a turbulent jet

Interpreting single-point and two-point focused laser differential interferometry in a turbulent jet

Hypersonic Boundary-Layer Disturbances on a Cooled, Slender Cone at Mach 6

Megahertz-Rate Imaging of Hypersonic Boundary-Layer Instabilities in a Mach 10 Shock Tunnel

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