Paul M Danehy

• Kennedy Space Center

A tunable diode laser absorption spectroscopy sensor and a high-speed camera measuring narrow-band emission are deployed at the NASA Langley Hypersonic Materials Environmental Test System, a hypervelocity arc-heated tunnel. Both sensors target electronically-excited atomic oxygen. The sensors are used in conjunction to measure bulk translational te...

Pulse-burst, cross-correlation Doppler global velocimetry was used to perform kHz-rate velocity measurements in the NASA Langley 4-Foot Supersonic Unitary Plan Wind Tunnel. Planar, one component (2D-1C) velocity measurements were made at rates up to 6 kHz in a canonical, oblique shockwave flowfield, generated by a full-span splitter plate in a Mach...

Molecular Rayleigh scattering (RS) is sensitive to the pressure, temperature, velocity, and number density of the gaseous flow. Filtered Rayleigh scattering (FRS) utilizes a narrowband molecular filter to remove stray scattering and deconvolve the effect of flow conditions on the signal intensity. As single-frequency, intensity-based FRS techniques...

Planar laser-induced fluorescence (PLIF) was applied for the first time in the 20-ft vacuum chamber at the Marshall Space Flight Center to visualize the plume-surface interaction (PSI) of a nitrogen jet seeded with nitric oxide (NO). A Mach 5.3 nozzle was used to simulate the exhaust of a landing spacecraft for two different jet stagnation pressure...

Streamwise vortices present in the freestream of the NASA Langley 4-Foot Supersonic Unitary Plan Wind Tunnel have been observed experimentally for the first time. A high-energy, burst-mode laser system was used to conduct time-resolved planar laser Mie scattering in the freestream of this facility. The freestream of the facility was observed over M...

The successful demonstration of long-lived nitric oxide (NO) fluorescence for molecular tagging velocimetry (MTV) measurements is described in this Letter. Using 1 + 1 resonance-enhanced multiphoton ionization (REMPI) of NO at a wavelength near 226 nm, targeting the overlapping Q1(7) and Q21(7) lines of the A–X (0, 0) electronic system, the lifetim...

An injection-seeded, burst-mode optical parametric oscillator (OPO) operating at a repetition rate of 100 kHz is used to demonstrate the multiline molecular tagging velocimetry of an underexpanded jet using nitric oxide fluorescence. The very narrow linewidth of the OPO system, along with the relatively high pulse energies of the burst-mode system,...

This work investigates the feasibility and performance of an ultra-narrowband and a rapidly wavelength-tunable burst-mode filtered Rayleigh scattering (FRS) system for single- or multi-parameter measurements of density, pressure, temperature, and velocity in high-speed flows.

Highlights from recent PLIF test campaigns at large-scale NASA facilities and lab-scale developments are summarized. The measurements presented here have the potential to aid researchers in validating complex simulations and inform designs for spaceflight vehicles.

Long-lived NO fluorescence with a lifetime of several microseconds is demonstrated for MTV using an efficient 1+1 resonant-enhanced-multiphoton-ionization (REMPI) process. This measurement technology is particularly applicable to high-speed flows under a wide pressure range.

In the filtered Rayleigh scattering (FRS) technique, Doppler or homogeneously broadened light from weak molecular scattering is separated from orders-of-magnitude stronger elastic scattering from surfaces, windows, particles, and/or droplets using a narrowband filter. In this work, high-speed detection of such weak molecular scattering is enabled b...

The current work demonstrates the efficacy of a simple and fast model for nitric oxide (NO) laser-induced fluorescence (LIF). The model is validated with experimental LIF spectra computed from captured images of fluorescence from a gas cell filled with a known amount of NO. These data are obtained for several segments of the NO fluorescence spectru...

We demonstrate a hybrid time–frequency spectroscopic method for simultaneous temperature/pressure measurements in nonreacting compressible flows with known gas composition. Hybrid femtosecond–picosecond, pure-rotational coherent anti-Stokes Raman scattering (CARS), with two independent, time-delayed probe pulses, is deployed for single-laser-shot m...

View Video Presentation: https://doi.org/10.2514/6.2022-3562.vid When landing on the moon, understanding the interaction of the engine exhaust plume with the lunar surface is critical for the success of the descent and landing flight phases. Two evaluation tools currently used are computational simulations and ground test measurements. Computationa...

Long-lasting emission from femtosecond excitation of nitrogen-based flows shows promise as a useful mechanism for a molecular tagging velocimetry instrument. The technique, known as femtosecond laser electronic excitation tagging (FLEET), was invented at Princeton a decade ago and has quickly been adopted and used in a variety of high-speed ground...

In the current work, the "Venturi seeder" method for nozzle plumes is improved and studied to determine suitability for particle image velocimetry. This seeding method involves independently pressurizing the primary flow path and a separate seed liquid reservoir, connecting them at the throat of a Venturi contraction upstream of the nozzle. The pre...

View Video Presentation: https://doi.org/10.2514/6.2022-0900.vid The flowfield around a Co-Optimization Blunt-body Reentry Analysis Mid-lift/drag-ratio Rigid Vehicle (CobraMRV) vehicle is investigated with a combination of high-speed planar laser Mie scattering (PLMS) and pulse-burst cross-correlation Doppler global velocimetry (PB-CC-DGV). Tests w...

View Video Presentation: https://doi.org/10.2514/6.2022-1523.vid Two-color Planar Laser-Induced Fluorescence (TC-PLIF) thermometry techniques that employ two laser systems and two cameras face challenges when implemented in practical combustion facilities because of experimental complexity and multiple laser and camera requirements, particularly fo...

View Video Presentation: https://doi.org/10.2514/6.2022-0897.vid Planar laser-induced fluorescence (PLIF) of the nitric oxide (NO) molecule has been widely used in wind tunnel facilities for flow visualization, velocity, and temperature measurements. The experimental PLIF measurements are often compared with synthetic PLIF images using computationa...

View Video Presentation: https://doi.org/10.2514/6.2022-1693.vid Plume-surface interactions between a rocket plume and the lunar surface will be studied in-situ during two of NASA’s upcoming Commercial Lunar Payload Services Program missions. The payload, Stereo Cameras for Lunar Plume-Surface Studies (SCALPSS), will employ a multiple-camera photog...

View Video Presentation: https://doi.org/10.2514/6.2021-2964.vid As part of studying the ability of Computational Fluid Dynamics (CFD) to accurately model important flow physics in the high-supersonic Mach number range, control-surface effectiveness on an entry vehicle for Mars exploration was examined. As with several other important flow regimes...

Nonintrusive three-component (3C) velocity measurements of free jet flows were conducted by stereoscopic picosecond laser electronic excitation tagging (S-PLEET) at 100 kHz. The fundamental frequency of the burst-mode laser at 1064 nm was focused to generate the PLEET signal in a free jet flow. A stereoscopic imaging system was used to capture the...

10-kHz hydroxyl radical (OH) two-color planar laser-induced fluorescence (TC-PLIF) thermometry was demonstrated with a single burst-mode optical parametric oscillator (OPO) and a single camera. A fast, dual-wavelength switched seed laser enabled a high-energy, high-repetition-rate burst-mode laser to generate two 10-kHz pulse trains at wavelengths...

Femtosecond laser electronic excitation tagging (FLEET) velocimetry was applied in the National Transonic Facility and assessed for its use in providing quantitative velocity measurements in a large-scale cryogenic wind tunnel. Comparisons of freestream results with theory and existing tunnel measurements indicate that FLEET velocity measurements a...

The injection of liquid nitrogen droplets to cool the gas temperature in cryogenic wind tunnels is discussed as a method of natural seeding for velocimetry-focused, particle-based, laser diagnostics. Historical observations and issues with seeding are presented for both ground-test facilities of interest in this work at NASA Langley: the 0.3-m Tran...

Pulse-burst cross-correlation Doppler global velocimetry is performed in the NASA Langley Unitary Plan Wind Tunnel. The technique is used to make planar velocity measurements across an oblique shockwave, which is generated by a large splitter plate set at a -2° angle of attack in a Mach 2.4 flow. Assessment of the velocimetry indicates agreement wi...

NASA tests new launch and reentry vehicle configurations in wind tunnels, where flow visualizations and quantitative flowfield measurements are often desired. Some of these vehicles have rocket motors for propulsion, retro-propulsion, or reaction control. High-pressure air is used to supply these rocket motor plumes. However, it is difficult to mak...

During the rocket-powered landing of a vehicle on a planetary body, the interaction between the rocket plume and the surface material beneath the vehicle plays a significant role in the descent dynamics and the safety of powered descent. However, in situ data taken to investigate plume-surface interaction has been limited. The upcoming flight and l...

Femtosecond laser electronic excitation tagging velocimetry is experimentally characterized in pure nitrogen at pressures (0.228–101 kPa) and temperatures (72–298 K) relevant to high-speed ground testing. Evaluated metrics of performance include signal intensity/lifetime and velocity accuracy/precision. A fast-framing camera lens-coupled to a bandp...

An image-based flow velocimetry technique coupling pulse-burst laser technology and the cross-correlation Doppler global velocimetry (CC-DGV) technique is presented as a faster variant of the CC-DGV method. By scanning the laser frequency during the burst, the total scan time per velocity measurement can be reduced from 2–4 minutes (Cadel and Lowe,...

Selective two-photon absorptive resonance femtosecond laser electronic excitation tagging (STARFLEET) velocimetry is characterized for the first time at high-pressure, low-temperature conditions. Studies were carried out in the NASA Langley Research Center’s 0.3 meter transonic, cryogenic wind tunnel, with flow conditions spanning the entire operat...

Nitric oxide planar laser-induced fluorescence was performed to measure the wall-normal distribution of static temperature through a hypersonic boundary layer. A 10-degree half-angle wedge model was oriented at a 5-degree angle of attack in the NASA Langley 31-in Mach 10 facility, resulting in a 5-degree flow turning angle and an edge Mach number o...

Simultaneous multi-point multi-parameter flow measurement using Interferometric Rayleigh scattering (IRS) at 100-kHz repetition rate is demonstrated. Using a burst-mode laser and an un-intensified high-speed camera, interferograms are obtained that contain spatial, temporal and scattered light frequency information. The method of analysis of these...

NASA’s Space Launch System (SLS) and Orion Crew Module have been studied in wind tunnels using the planar laser-induced fluorescence (PLIF) technique for flow visualization and quantitative thermometry and in flight using high-resolution imagery and quantitative infrared surface heating measurements This paper reviews both types of measurements.

10-kHz tomographic Rayleigh scattering (RS) imaging was demonstrated in non-reacting flows employing a high- energy burst-mode laser system. Image sequences of flow mixture fraction were directly derived from high-speed 4-dimensional (4D) RS images.

Two-dimensional, Rayleigh-scattering-based temperature measurements utilizing a turbulent jet flame were performed in this study at 100-kHz frequency. This tenfold increase in measurement speed—compared to the 10-kHz frequency considered previously—facilitated identification and tracking of several highly dynamic flow features. Findings of this stu...

Selective two-photon absorptive resonance femtosecond laser electronic excitation tagging (STARFLEET) velocimetry is demonstrated for the first time in a NASA Langley Research Center wind tunnel with high-repetition-rate and single-shot imaging. Experiments performed in the 0.3 m transonic cryogenic tunnel allowed for testing at 300 K in gaseous ni...

Two-dimensional (2D) Rayleigh scattering (RS) imaging at an ultrahigh repetition rate of 100 kHz is demonstrated in non-reacting flows employing a high-energy burst-mode laser system. Image sequences of flow mixture fraction were directly derived from high-speed RS images. Additionally, a 2D instantaneous flow velocity field at 100 kHz was obtained...

Femtosecond laser tagging is demonstrated for the first time in R134a (1,1,1,2-tetrafluoroethane) gas and in mixtures of R134a with small quantities of air. A systematic study of this tagging method is explored through the adjustment of gas pressure, mixture ratio, and laser properties. It is found that the signal strength and lifetime are greatest...

The High Temperature Test Facility (HTTF) is a quarter-scale integral-effect facility designed to study pressurized and depressurized conduction cooldowns (PCC and DCC, respectively) in high temperature, gas-cooled reactors (HTGR). This study focuses on DCC and aims to characterize the gas exchange between the reactor core and the reactor cavity to...

Molecular tagging velocimetry (MTV) is a nonintrusive velocimetry technique based on laser spectroscopy. It is particularly effective in challenging gas flow conditions encountered in thermal hydraulics where particle-based methods such as particle image (or tracking) velocimetry do not perform well. The main principles for designing and operating...

Picosecond laser electronic excitation tagging (PLEET) is implemented in a large-scale wind tunnel for the first time. High-speed, unseeded velocimetry is performed in the NASA Langley 0.3 m transonic cryogenic tunnel; repetition rates up to 25 kHz are tested. Velocity measurements are assessed for accuracy and precision. Measurement errors vary in...

Femtosecond laser electronic excitation tagging (FLEET) velocimetry is characterized for the first time at high-pressure, low-temperature conditions. FLEET signal intensity and signal lifetime data are examined for their thermodynamic dependences; temperatures range from 89 K to 275 K while pressures are varied from 85 kPa to 400 kPa. The FLEET sig...

High-repetition-rate interferometric-Rayleigh-scattering (IRS) velocimetry is demonstrated for non-intrusive, high-speed flow-velocity measurements. High temporal resolution is obtained with a quasi-continuous burst-mode laser that is capable of operating at 10–100 kHz, providing 10-ms bursts with pulse widths of 5–1000 ns and pulse energy > 100 mJ...

Transmission of intense ultrashort laser pulses through hollow-core fibers (HCFs) is investigated for molecular-tagging velocimetry. A low-vacuumed HCF beam-delivery system is developed to transmit high-peak-power pulses. Vacuum pressure effects on transmission efficiency and nonlinear effects at the fiber output are studied for 100 ps and 100 fs l...

Spallation is a phenomenon in which solid particles are ejected off the surface of an ablative material in a high-enthalpy, high-shear flow field. The main contributor to this phenomenon in carbon-based heat shields is the mechanical erosion of carbon fibers weakened by oxidation decomposition. The dynamics of this phenomenon, which are poorly char...

A molecular tagging velocity (MTV) technique is developed to non-intrusively measure velocity in an integral effect test (IET) facility simulating a high-temperature helium-cooled nuclear reactor in accident scenarios. In these scenarios, the velocities are expected to be low, on the order of 1 m/s or less, which forces special requirements on the...

Femtosecond laser electronic excitation tagging velocimetry was used to study the flowfield around a symmetric, transonic airfoil in the NASA Langley Research Center's 0.3 m transonic cryogenic tunnel facility. A nominal Mach number of 0.85 was investigated with a total pressure of 125 kPa and a total temperature of 280 K. Two components of velocit...

Hypersonic airbreathing engines rely on scramjet combustion processes, which involve high-speed, compressible, and highly turbulent reacting flows. The combustion environment and the turbulent flames at the heart of these engines are difficult to simulate and study in the laboratory under well-controlled conditions. Typically, wind-tunnel testing i...

Hydroxyl tagging velocimetry (HTV) is characterized for the first time at extended pressures (1 and 3 atm) and temperatures (295 K to 673 K) in an attempt to improve measurement precision for low speed flows. While previous investigations have focused on ambient and flame temperatures (1400 K), the present study investigates between these two extre...

Tracer-free mixture-fraction measurements were demonstrated in a jet using femtosecond-laser electronic-excitation tagging. Measurements were conducted across a turbulent jet at several downstream locations both in a pure-nitrogen jet exiting into an air–nitrogen mixture and in a jet containing an air–nitrogen mixture exiting into pure nitrogen. Th...

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 is made of naphthalene, which sublimates at room temperature and below, and thus is suitable for ablation studies in low-enthalpy supersonic wind tunnel...