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Paul M. Danehy

Publications and source records attributed to Paul M. Danehy.

30 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Review of planar laser-induced fluorescence measurements in the NASA Langley 31-Inch Mach 10 Air Tunnel

In 2003 a mobile planar laser-induced fluorescence (PLIF) system was constructed at NASA Langley Research Center to visualize and quantify high speed flow fields containing fluorescent species such as nitric oxide (NO). Thereafter, a series of test entries utilizing NO PLIF were conducted in the NASA Langley Research Center’s 31 Inch Mach 10 air wind tunnel, which is a hypersonic blowdown wind tunnel located in Hampton, Virginia. This paper briefly reviews laser-based measurements previously performed in hypersonic blowdown wind tunnel facilities and then details NO PLIF measurement campaigns performed at this facility in the 20 years to date. Measurements were performed to develop 2D and 3D visualization capabilities and quantitatively measure velocity and temperature. Applications described herein include historical models (e.g., Apollo, X-33 and X-43), flight vehicles under development at the time (e.g., Mars Science Lab (MSL), Orion, and LOFTID), as well as fundamental research (e.g., flat plates with and without discrete roughness).

PLIF↗
NASA NTRSDate not supplied

Velocity Measurements in the Wake of the Swept Wing Flow Test Model at the National Transonic Facility

Femtosecond laser electronic excitation tagging (FLEET) was applied to obtain flowfield velocity data for the Swept Wing Flow Test (SWiFT) at the NASA Langley Research Center National Transonic Facility (NTF). Despite numerous challenges associated with performing flow velocimetry measurements within a large-scale cryogenic wind tunnel facility, the experimental campaign was conducted under various conditions, including dry air at 320 K, cool nitrogen at 240 K, and Mach numbers of 0.2 and 0.8. FLEET velocimetry measurements were performed in the downstream wake of the SWiFT model, providing a quantitative dataset. This dataset includes one-dimensional velocity profiles and two-dimensional velocity maps acquired at different angles of attack and Reynolds numbers. The two-dimensional single component velocity maps indicate relatively uniform flow across the 120-mm wide wake flow survey suggesting that the main flow features can be represented by single-position linear velocity profiles. The measured instantaneous velocity profiles at variable angles of attack are compared to model lift coefficient information obtained at Mach 0.2. At high Reynolds numbers, a sudden velocity decrease was observed in the FLEET measurements at the same time as stall in lift coefficient was observed. At a low Reynolds number, both the velocity profiles and the lift coefficient show a smoother transition, without a sudden stall. Furthermore, the two-dimensional, one component velocity map reveals a velocity deficit region at Mach 0.8 at various angles of attack. Both single shot and mean velocity measurements were acquired allowing assessment of flowfield fluctuations and measurement precisions. The uncertainties are within 4 m/s in mean measurements based on repeatability data and about 5 m/s in instantaneous single-shot measurements. Measurements are reported with ~4.8 mm spatial resolution with 32-pixel averaging used to reduce measurement errors.

femtosecond↗
NASA NTRSDate not supplied

Flow Visualization for Plume-Surface Interaction at Martian-Relevant Lander Environments

This paper describes a jet impingement experiment performed in a large-scale vacuum chamber at Martian-relevant ambient pressure conditions, with the motivation of studying plume-surface interaction (PSI) caused by the exhaust plume of a lander interacting with the planetary surface. Flow visualization of an inert supersonic jet was performed using planar laser-induced fluorescence (PLIF), which is a molecular-based, two-dimensional measurement technique. Representative instantaneous and time-averaged visualizations of the impinging jet at two different nozzle flow conditions corresponding to the underexpanded and overexpanded jet regimes are presented for up to six different dimensionless altitudes h/De. The time-averaged measured spatial distribution of impingement pressures at these conditions is also reported. The PLIF visualizations appear to be critical towards explaining unexpected behavior in the impingement pressure, such as a higher impingement pressure for the underexpanded condition at h/De = 10, compared to a lower altitude of h/De = 8. This behavior can be attributed to differences in the stagnation shock structure observed in the PLIF images. The PLIF images also reveal significant flow separation at the nozzle exit for the overexpanded jet conditions. Further analysis of the test data as well as combined flow visualization and surface diagnostics for future ground tests will help inform engineering designs for landings on the Martian surface while mitigating PSI risks.

PLIF↗
NASA NTRSDate not supplied

PLIF for Space Technology and Exploration Applications

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.

PLIF↗
NASA NTRSDate not supplied

Velocity Measurements in the Wake of the Swept Wing Flow Test (SWIFT) Model at the National Transonic Facility

Femtosecond laser electronic excitation tagging (FLEET) was applied to obtain flowfield velocity data for the Swept Wing Flow Test (SWiFT) at the NASA Langley Research Center National Transonic Facility (NTF). Despite numerous challenges associated with performing flow velocimetry measurements within a large-scale cryogenic wind tunnel facility, the experimental campaign was conducted under various conditions, including dry air at 320 K, cool nitrogen at 240 K, and Mach numbers of 0.2 and 0.8. FLEET velocimetry measurements were performed in the downstream wake of the SWiFT model, providing a quantitative dataset. This dataset includes one-dimensional velocity profiles and two-dimensional velocity maps acquired at different angles of attack and Reynolds numbers. The two-dimensional single component velocity maps indicate relatively uniform flow across the 120-mm wide wake flow survey suggesting that the main flow features can be represented by single-position linear velocity profiles. The measured instantaneous velocity profiles at variable angles of attack are compared to model lift coefficient information obtained at Mach 0.2. At high Reynolds numbers, a sudden velocity decrease was observed in the FLEET measurements at the same time as stall in lift coefficient was observed. At a low Reynolds number, both the velocity profiles and the lift coefficient show a smoother transition, without a sudden stall. Furthermore, the two-dimensional, one component velocity map reveals a velocity deficit region at Mach 0.8 at various angles of attack. Both single shot and mean velocity measurements were acquired allowing assessment of flowfield fluctuations and measurement precisions. The uncertainties are within 4 m/s in mean measurements based on repeatability data and about 5 m/s in instantaneous single-shot measurements. Measurements are reported with ~4.8 mm spatial resolution with 32-pixel averaging used to reduce measurement errors.

Transonic↗
NASA NTRSDate not supplied

Wall-Jet Evolution During Plume-Surface Interaction Using PLIF Imaging

Planar laser-induced fluorescence (PLIF) flow visualization was used to examine the spatial evolution for the wall-jet formed by an impinging supersonic jet in a large-scale vacuum environment. This canonical configuration is representative of the plume-surface interaction induced by a rocket exhaust plume impinging on the planetary surface at lunar-relevant and Martian-relevant environments. PLIF flow visualization of the very low-density environment (as low as ~0.006% of standard atmospheric density) was performed using seeded nitric oxide in a nitrogen flow at three test conditions. Two conditions are representative of the lunar environment, and one is representative of the Martian environment. The combined images from two simultaneous PLIF views were used to construct a 2D slice of the flowfield spanning approximately 150 mm in height (determined by the laser sheet) and 500 mm in width (determined by the camera views). The three test conditions showed different behavior for the wall-jet, largely due to the different levels of lifting above the surface and the appearance of a physical process similar to a Kelvin–Helmholtz instability for the Martian-relevant case, which appeared to create a dramatic expansion of the wall-jet height with increased radial distance.

PSI↗