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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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264 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Response of a Bifurcated Shock Train to Combustion Drive Force Dynamics

A bifurcated normal shock train in a Mach 2.2 constant area, rectangular duct is investigated in the combustion driven Air Force Research Lab RC-18 Sub-scale Direct Connect Supersonic Combustion Facility. High-speed shadowgraph images are captured simultaneously with high-speed wall static pressure measurements along the isolator and combustor walls. The establishment of the shock train following ignition is studied to better understand the flow pathways and fluid dynamical mechanisms that link combustor dynamics to the motions and stability of the isolator shock train. To that end, cross-spectral and wavelet analysis is leveraged to determine the spectral and temporal characteristics of upstream traveling disturbances on the isolator-combustor system in RC-18.

Shock Train↗
NASA NTRSDate not supplied

Seeding Method for Velocimetry and Visualization of Supersonic Retropropulsion Nozzle Plumes

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 pressure differential at the throat causes the liquid to enter the nozzle channel where it is atomized into particles by strong shearing forces. This new seeding system was characterized by conducting a series of diagnostics using different exit nozzle pressure ratios and seed reservoir pressures. Shadowgraph imaging confirmed the nozzle plumes to be underexpanded jets. A particle sizing device determined that generated DEHS oil particles had median aerodynamic diameters of 0.67, 0.69, and 0.73 μm for seed liquid reservoir pressure supplies of 0.67, 0.60, and 0.93 MPa and primary flow path pressures of 0.67, 0.76, and 0.93 MPa measured downstream of the Venturi throat, respectively. These diameters were within the threshold for acceptable response time in typical gas flows (≤ 1 μm). PIV experiments were conducted on the nozzle plume for all presented cases; mean axial and transverse velocities appeared as expected for the underexpanded jet structure, including the Mach disk and re-acceleration regions. Additional sizing analysis based on the particle response times across the normal shock again showed particle diameters to be well less than 1 μm for all cases. The results suggest that this method is an inexpensive and relatively simple solution to the problem of seeding nozzle plumes. The method will be used in testing of supersonic retropropulsion models in the Unitary Plan Wind Tunnel at The NASA Langley Research Center in 2022.

particle image velocimetry↗
NASA NTRSDate not supplied

Reference-Free, Projection Background-Oriented Schlieren

A projection background-oriented schlieren (P-BOS) system is developed and demonstrated. Instead of a background that has a speckle pattern printed, painted, or otherwise deposited onto its surface, and can thus not be altered, the pattern here is projected onto the background. This allows for changes to the speckle pattern without replacement of the background material, which can be time-consuming and expensive. Reference images are acquired simultaneously with flow images. A pre-test transformation between the reference and flow images allows for on-the-fly changes to the speckle pattern during a test without requiring a stoppage of the flow, allowing for optimization of the BOS signal. Using a programmable LCD screen as the speckled optic allows for remote control of the speckle pattern. Because the background is not speckled, the system can be easily transformed to acquired shadowgraph images by removing the speckled optic and closing the aperture of the light source, which is useful for achieving measurements with higher spatial resolution. The system can be nearly as compact as a conventional BOS system, and can be assembled with polarized optics to reduce or eliminate window reflections and glare, making this system particularly well-suited for wind tunnel testing.

Joshua M Weisberger↗
NASA NTRS2022

Flow Visualization to Complement Modern Wing Tunnel Testing

In recent times, wind tunnel testing at the NASA Ames Unitary Plan Wind Tunnel (UPWT) seeks to validate computational fluid dynamics (CFD) tools. To that end, we find that now more than ever, flow visualization is a powerful capability that provides context to the experimental results bringing real-time insight to the researcher. It enables us to answer questions like: “Why does this drag polar look different?” or “What is the source of this tone in the microphone data?”. Flow visualization can verify that assumptions made in the CFD model are correct, addressing questions like: “Are our trip dots the correct size and location?” or “Does the position of this shock match our prediction?”. Techniques such as infrared flow visualization and schlieren / shadowgraph are powerful capabilities that when taken together can provide results as to the nature of the fluid structure interaction at a test condition in a format that pairs well with computational results. When properly integrated these measurements can be taken with no impact on the productivity of the test program, supplementing traditional measurements and often discovering something unforeseen, helping the researcher to answer those slippery aerodynamic questions and ultimately build confidence in the accuracy of a model.

wind tunnel↗
NASA NTRSDate not supplied

Updated Numerical Analysis Benchmarks for Meteoroid Relevant Materials

Proposal for update of numerical analysis benchmark for meteoroid relevant materials. - Two recently performed shots are proposed to be numerical analysis benchmarks for numerical simulations of impacts of high-density meteoroids (Al 2 O 3 surrogate) and low-density meteoroids (Nylon surrogate). - A pair of general Whipple shields have been studied: - Bumper and rear walls are the same material and thickness between shields - Separation is 4.5 cm for Al 2 O 3 and 1.5 cm for Nylon - Information gathered includes high speed (1 MHz) shadowgraphs of debris cloud, bumper hole size and rear wall hole area.

Orbital Debris↗
DOE OSTI2015

Astrophysical blast wave data

The data described in this document consist of image files of shadowgraphs of astrophysically relevant laser driven blast waves. Supporting files include Mathematica notebooks containing design calculations, tabulated experimental data and notes, and relevant publications from the open research literature. The data was obtained on the Z-Beamlet laser from July to September 2014. Selected images and calculations will be published as part of a PhD dissertation and in associated publications in the open research literature, with Sandia credited as appropriate. The authors are not aware of any restrictions that could affect the release of the data.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Ultralow-dose, feedback imaging with laser-Compton X-ray and laser-Compton gamma ray sources

Ultralow-dose, x-ray or gamma-ray imaging is based on fast, electronic control of the output of a laser-Compton x-ray or gamma-ray source (LCXS or LCGS). X-ray or gamma-ray shadowgraphs are constructed one (or a few) pixel(s) at a time by monitoring the LCXS or LCGS beam energy required at each pixel of the object to achieve a threshold level of detectability at the detector. An example provides that once the threshold for detection is reached, an electronic or optical signal is sent to the LCXS/LCGS that enables a fast optical switch that diverts, either in space or time the laser pulses used to create Compton photons. In this way, one prevents the object from being exposed to any further Compton x-rays or gamma-rays until either the laser-Compton beam or the object are moved so that a new pixel location may be illumination.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Enhanced flow boiling heat transfer on chromium coated zircaloy-4 using cold spray technique for accident tolerant fuel (ATF) materials

Flow boiling heat transfer tests were conducted to evaluate the Critical Heat Flux (CHF) and Heat Transfer Coefficient (HTC) of conventional and accident tolerant fuel (ATF) cladding materials, i.e., bare Zircaloy-4 (Zr4), and Zircaloy-4 coated with Chromium using physical vapor deposition (PVD) (Zr4-Cr-PVD) and cold spray process (Zr4-Cr-CS), respectively. The tests were performed on a single heater rod with a uniform heat flux profile, at the atmospheric pressure, inlet temperature (24 °C) and mass flow rate (750 kg/m 2 s). HTC’s were increased by 5.2% and 3.3% on Zr4-Cr-CS compared to bare Zr4 and Zr4-Cr-PVD. Improved HTCwas attributed to the increased void fraction and high roughness (Ra = 532 nm) of the Zr4-Cr-CS. In detail, the micro-cavities, which act as bubble seeds, were entirely distributed on the Zr4-Cr-CS, and these micro-cavities generated smaller and faster bubbles, thus the void fraction increased by 10.9% compared to bare Zr4. HTC is improved by these smaller and faster bubbles which can remove heat from the heater rod surface more efficiently. To identify the exact location of CHF, the surface temperature profile was measured using advanced fiber-optic sensors which have high temporal/spatial resolution (distance between point to point: ~2.5 mm, frequency ~100 Hz). CHF occurred at 80–95% along the heated length and showed an 11.6% reduction on Zr4-Cr-CS compared to bare Zr4. We hypothesize the CHF reduction was caused by the lower wettability of the Zr4-Cr-CS which reduces the liquid supply to the surface, and vigorous bubble accumulation owing to high void fraction near the outlet, which results in early formation of the vapor film. During the post-CHF quenching phase, the rougher Zr4-Cr-CS showed larger cooling rates compared to the bare Zr4 and Zr4-Cr-PVD, preventing of oxidation by chromium layer. In conclusion, we demonstrate that the high roughness on the Zr4-Cr-CS increased the number of micro-cavities on the surface, resulting in 5.2% increase in HTC and improvement in the quenching heat transfer performance whereas CHF was 11.6% reduced compared to bare Zr4. Overall statistically there is little effect in the coating with regards to CHF and slight improvement in HTC.

42 ENGINEERING↗
NASA NTRS2013

Preparation for Scaling Studies of Ice-Crystal Icing at the NRC Research Altitude Test Facility

This paper describes experiments conducted at the National Research Council (NRC) of Canadas Research Altitiude Test Facility between March 26 and April 11, 2012. The tests, conducted collaboratively between NASA and NRC, focus on three key aspects in preparation for later scaling work to be conducted with a NACA 0012 airfoil model in the NRC Cascade rig: (1) cloud characterization, (2) scaling model development, and (3) ice-shape profile measurements. Regarding cloud characterization, the experiments focus on particle spectra measurements using two shadowgraphy methods, cloud uniformity via particle scattering from a laser sheet, and characterization of the SEA Multi-Element probe. Overviews of each aspect as well as detailed information on the diagnostic method are presented. Select results from the measurements and interpretation are presented which will help guide future work.

Ice formation↗