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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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78 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Comparative study between experimental measurements and model predictions of bubble rise velocity in molten LiCl-KCl

This research investigated the shape and rise velocities of gas bubbles (helium, nitrogen, argon, and krypton) in molten LiCl-KCl at 500 °C using a specialized optical visualization apparatus. The apparatus features a custom quartz rectangular prism cell housed in a furnace, enabling the application of the shadowgraph measurement technique. Bubbles with diameters between 0.45 and 3.2 mm were produced via a capillary, and their equivalent diameters and rise velocities were analyzed using high-resolution imaging and centroid tracking algorithms. Important non-dimensional parameters were calculated to characterize behavior. Bubbles with 0.03 < Eo < 1.32, 17 < Re < 718, and Mo order of 10 -11 were generated in the molten LiCl-KCl, revealing that bubbles with diameters less than 1.46 mm remain spherical, whereas those with larger diameters are ellipsoidal. The transition and oscillation onset for bubble shape occurred at larger diameters than those previously observed in air–water systems. Comparative analysis of the gas-molten salt data against existing air–water bubble rise velocity correlations highlighted inaccuracies in predictions, particularly across the different bubble regimes. An existing correlation was calibrated to the molten salt data to improve the bubble velocity predictions. In conclusion, this study contributes essential experimental data for the design and safety evaluation of molten salt reactors and offers insights for the optimization of sparge systems for fission product removal.

Bubble rise velocity↗
NASA NTRS2002

Caustics and Caustic-Interference in Measurements of Contact Angle and Flow Visualization Through Laser Shadowgraphy

As one of the basic elements of the shadowgraphy optical system, the image of the far field from the droplet implicates plentiful information on the droplet profile. An analysis of caustics by wave theory shows that a droplet with a cylindrically symmetric Gaussian-hill-type profile produces a circular directional caustic in far field, which arises from the singularities (inflection line on the surface). The sessile liquid droplets, which profiles are restricted by surface tension, usually have a 'protruding foot' where the surface inflects. Simple geometrical optics indicates that the circular caustic stemming from the surface inflection at the protruding-foot takes the shape of the outmost ring on the image of the far field. It is the diameter of the outmost ring that is used as one of the key parameters in the measurements of contact angle through the laser shadowgraphic method. Different surface characteristics of the droplets produce different type of caustics, and therefore, the shape of the caustics can be used to determine the surface property of the sessile droplets. The present paper describes the measurement method of contact angIe using the circular caustics and the estimation of the protruding-foot height through the caustic interference.

Chao, David F.↗
NASA NTRS1986

Improvement in the quality of flow visualization in the Langley 0.3-meter transonic cryogenic tunnel

Optical diagnostic techniques have not been as successful in the 0.3-Meter Transonic Cryogenic Tunnel as in conventional wind tunnels. This paper describes a simple shadowgraph experiment which allowed evacuation of the optical paths outside the test section. The results show that refractive index variations induced by temperature gradients outside the test section account for most of the image degradation. Earlier reports had erroneously attributed this degradation to inhomogeneities in the test section. Evacuation of the paths leading to and from the test section significantly improves the quality of flow visualization.

Snow, W. L.↗
NASA NTRS2017

Upgrades and Modifications of the NASA Ames HFFAF Ballistic Range

The NASA Ames Hypervelocity Free Flight Aerodynamics Facility ballistic range is described. The various configurations of the shadowgraph stations are presented. This includes the original stations with film and configurations with two different types of digital cameras. Resolution tests for the 3 shadowgraph station configurations are described. The advantages of the digital cameras are discussed, including the immediate availability of the shadowgraphs. The final shadowgraph station configuration is a mix of 26 Nikon cameras and 6 PI-MAX2 cameras. Two types of trigger light sheet stations are described visible and IR. The two gunpowders used for the NASA Ames 6.251.50 light gas guns are presented. These are the Hercules HC-33-FS powder (no longer available) and the St. Marks Powder WC 886 powder. The results from eight proof shots for the two powders are presented. Both muzzle velocities and piston velocities are 5 9 lower for the new St. Marks WC 886 powder than for the old Hercules HC-33-FS powder (no longer available). The experimental and CFD (computational) piston and muzzle velocities are in good agreement. Shadowgraph-reading software that employs template-matching pattern recognition to locate the ballistic-range model is described. Templates are generated from a 3D solid model of the ballistic-range model. The accuracy of the approach is assessed using a set of computer-generated test images.

Ballistic Range↗
NASA NTRS2017

Upgrades and Modifications of the NASA Ames HFFAF Ballistic Range

The NASA Ames Hypervelocity Free Flight Aerodynamics Facility ballistic range is described. The various configurations of the shadowgraph stations are presented. This includes the original stations with film and configurations with two different types of digital cameras. Resolution tests for the 3 shadowgraph station configurations are described. The advantages of the digital cameras are discussed, including the immediate availability of the shadowgraphs. The final shadowgraph station configuration is a mix of 26 Nikon cameras and 6 PI-MAX2 cameras. Two types of trigger light sheet stations are described visible and IR. The two gunpowders used for the NASA Ames 6.251.50 light gas guns are presented. These are the Hercules HC-33-FS powder (no longer available) and the St. Marks Powder WC 886 powder. The results from eight proof shots for the two powders are presented. Both muzzle velocities and piston velocities are 5 9 lower for the new St. Marks WC 886 powder than for the old Hercules HC-33-FS powder (no longer available). The experimental and CFD (computational) piston and muzzle velocities are in good agreement. Shadowgraph-reading software that employs template-matching pattern recognition to locate the ballistic-range model is described. Templates are generated from a 3D solid model of the ballistic-range model. The accuracy of the approach is assessed using a set of computer-generated test images.

Ballistic Range↗
NASA NTRS2020

Development of Unsteady Pressure-Sensitive Paint Application on NASA Space Launch System

The key measurement to acquire for understanding unsteady flow is surface pressure. Unsteady Pressure-Sensitive Paint (uPSP) is an emerging optical technique used in wind tunnel testing to measure fluctuating surface pressures. Recently, tests were conducted on NASA’s Space Launch System in NASA Ames Research Center’s Unitary Plan Wind Tunnel to determine the aeroacoustics environment and assist in developing the buffet forcing functions. Unsteady PSP data was collected during this test campaign. Steady state PSP data, infrared thermography, shadowgraph, accelerometer data, and dynamic pressure transducer data were also collected. In all 50 TB of data were collected during the three days of testing. During these three days of testing, a repeating transonic and supersonic alpha sweep condition was acquired. This paper presents these two wind tunnel conditions and examines how the temperature influences the PSP data. In the first large demonstration of uPSP in 2015 on an NESC-, AETC-sponsored wind tunnel test, lifetime PSP results highlighted the influence the model temperature had on the PSP data. A best practice of heat soaking the model before acquiring calibration images was followed during the test campaign presented in this paper. An infrared thermography camera and thermocouples were installed in the model to collect more details of the model surface temperature. Data processing schemes for uPSP are still in development but will be briefly presented here as well.

Roozeboom, Nettie H.↗