Velocity and NO-Lifetime Measurements in an Unseeded Hypersonic Air Flow

Abstract

A laser-induced fluorescence (LIF)-based nitric-oxide flow-tagging technique was applied to measure both velocity and NO lifetime in a hypersonic shock tunnel from two experimental test runs. The results were supported by an analytical profile proposed in this paper that provides a way to correct velocity measurements under unknown systematic error sources. This procedure provided velocities with discrepancies lower than 3% for a total of five measurements, and lower than 2% when compared with that obtained from a linear fit. Additionally, the comparison between the proposed and experimental profiles allowed us to obtain the fluorescence NO lifetime from only one image.

Single-Laser Krypton Tagging Velocimetry Investigation of Supersonic Air and N2 Boundary-Layer Flows over a Hollow Cylinder in a Shock Tube

“…Its advantage over PIV techniques in high-speed facilities is that it is not limited by timing issues associated with tracer injection [12] or reduced particle response at Knudsen and Reynolds numbers [4] characteristic of high-speed wind tunnels. Methods of tagging velocimetry include the VENOM [13][14][15][16][17], APART [18][19][20], RELIEF [21][22][23][24][25], FLEET [26,27], STARFLEET [28], PLEET [29], NO [30][31][32][33][34], argon [35], iodine [36,37], sodium [38], acetone [39][40][41], NH [42], and the hydroxyl group techniques [43][44][45][46], among others [47][48][49][50][51][52].…”

“…Hydroxyl tagging velocimetry (HTV) was used to make measurements behind the bow shock wave that formed on a model in a shock tube [68]. Additionally, NO has been used as a tagging tracer to measure the freestream flow [34] and flow over test articles in reflected-shock tunnels [31].…”

Single image molecular tagging velocimetry

“…To validate the obtained results, the velocity measurements are compared with velocimetry results from [16] in figure 9, where both results show agreement. In that study, NO flow tagging was performed under the same shock-tunnel conditions, and velocity was calculated from two and five delayed images.…”

“…The constant S 0 absorbs the optical efficiency, spectroscopic, flow and laser parameters. From simplifications in the calculation of the instantaneous profile, the above integration was calculated by [16] and the resulting profile, as shown in equation ( 1), was used by the authors to fit experimental distributions and to evaluate the velocity from biased displacement measurements. The simplifications were as follows: (1) the laser beam has a spatial Gaussian shape centered at x = x 0 and full width at half maximum (FWHM) given by √ 2ln2(2σ); (2) the fluorescence lifetime is much larger than the laser pulse duration and the laser, therefore, acts instantaneously in the tagging step; (3) the instantaneous tagged-flow intensity shape reproduces the laser beam intensity distribution.…”

Freestream velocity-profile measurement in a large-scale, high-enthalpy reflected-shock tunnel

“…( 2003 ) used NO as a tracer to measure shear flows in the T2 and T3 reflected-shock tunnels; those measurements used a mixture of approximately 97–99% N2 and 1–3% O2 in the driven section to “produce an amount of NO sufficient to produce good fluorescence but that would minimize the amount of the gases (O2, O, and NO) that are efficient quenchers.” de S. Matos et al. ( 2018 ) made velocity measurements in unseeded hypersonic air flows in a reflected-shock tunnel at an enthalpy of approximately 6 MJ/kg; that work presents a strategy where a reference image was taken before the test, which is not possible in some impulse facilities due to vibration.…”