Christopher S. Combs

NO PLIF Visualizations of the Orion Capsule in LENS-I

Planar laser-induced fluorescence (PLIF) of nitric oxide (NO) was used to visualize the interaction of reaction-control-system (RCS) jet flows in the wake of a hypersonic capsule reentry vehicle. The tests were performed at the Calspan University at Buffalo Research Center’s (CUBRC) LENS-I reflected shock tunnel facility. This was the first application of PLIF to study RCS jets in a large-scale pulsed hypersonic facility. The LENS-I facility allowed RCS jet flows to be studied while varying the flow enthalpy, Reynolds number, angle of attack and jet configuration. The interaction of pitch and roll jets with the flowfield was investigated. Additionally, thin film sensors were used to monitor heat transfer on the surface of the model to detect any localized heating resulting from the firing of the RCS jets. Tests were conducted with the model held at angles of attack of 18° and 22°. The nominal Mach number in all tests was 8, while Reynolds number based on model diameter ranged from 2.2x10 6 – 1.5x10 7 . Images were processed using the Virtual Diagnostics Interface (ViDI) system developed at NASA Langley Research Center to provide a three-dimensional display of the experimental data.

Naphthalene laser-induced fluorescence measurements at low temperature and pressure.

Few studies on naphthalene vapor fluorescence have been conducted at low temperature and pressure conditions. The current study focuses on conducting measurements of naphthalene quenching and absorption cross section in a temperature- and pressure-regulated test cell with 266 nm laser excitation. The test-cell measurements were of the naphthalene-fluorescence lifetime and integrated fluorescence signal over the temperature range of 100 to 525 K and pressure range of 1 to 40 kPa in air. These data enabled the calculation of naphthalene-fluorescence quantum yield and absorption cross section over the range of temperatures and pressures tested, which were then fit to simple functional forms for future use in the calibration of naphthalene laser-induced fluorescence (LIF) measurements. Furthermore, the variation of naphthalene-fluorescence signal with respect to temperature was investigated for four different excitation wavelengths, demonstrating that a two-line naphthalene LIF thermometry technique may be feasible.

Heat-Shield Ablation Visualized Using Naphthalene Planar Laser-Induced Fluorescence

A combined experimental and computational study is conducted of heat-shield ablation from a scaled model of NASA’s Orion Multi-Purpose Crew Vehicle in a Mach 5 wind tunnel. The ablating heat shield...

Simultaneous Measurements of Scalar and Velocity in a Mach 5 Turbulent Boundary Layer using Naphthalene PLIF and PIV

Scalar transport in a Mach 5 boundary layer is investigated using planar laser-induced fluorescence (PLIF) of a low-temperature sublimating ablator (naphthalene). Naphthalene vapor is introduced into the flow by ablation of a solid naphthalene plug located upstream of the imaging field of view and mounted flush with the wind tunnel floor. The naphthalene PLIF technique is used quantitatively, and is employed simultaneously with PIV to acquire two-dimensional fields of naphthalene mole fraction and velocity. The naphthalene mole fraction was measured with an uncertainty of ± 20%. The turbulent scalar structures between 0 < y/δ < 0.2 had a naphthalene mole fraction on the order of 1.5 × 10-4, which is approximately 6% of the saturation mole fraction in the boundary layer. The naphthalene vapor structures were primarily confined within y/δ < 0.4 and these large-scale naphthalene vapor structures appeared to coincide with regions of relatively low streamwise velocity. However, a correlation between naphthalene mole fraction and wall-normal velocity was not obvious from a visual inspection of the simultaneous image sets. Profiles of velocity and naphthalene mole fraction were both shown to exhibit logarithmic behavior from 100 < y+ < 300 when plotted in wall units, in agreement with several previous works. Root-mean-square profiles of the naphthalene mole fraction and velocity in the boundary layer were also acquired and the two profiles appeared similar, with the peak r.m.s. values occurring at the wall, then exhibiting a steady decay away from the wall. Lastly, by calculating the covariance of with respect to and , it was demonstrated that regions of high scalar coincided with negative fluctuations in streamwise velocity and positive fluctuations in wallnormal velocity away from the wall, indicating that an ejection mechanism is transporting low-momentum, high-scalar-concentration fluid away from the wall.