RESEARCH CENTER

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FLUID DYNAMICS

Single-Phase and Boiling Flow in Microchannels with High Heat Flux

Author(s): Elmer Galvis(© 2012)

A cooling system for high heat flux applications is examined using microchannel evaporators with water as the working uid and boiling as the heat transfer mechanism. Experimental studies are performed using single channel microevaporators allowing for better control of the flow mechanics unlike other investigations where multiple, parallel, flow channels can result in a non-uniform distribution of the working fluid. High-speed flow visualizations are performed in conjunction with heat transfer and pressure drop measurements to support the quantitative experimental data.

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High speed imaging of micro-sized droplet jetted on surface with wettability pattern

Author(s): Lim, C.Y. and Lam, Y.C. (© 2014)

Experimental results based on high speed imaging of micro-sized droplet jetted on a hydrophobic surface with hydrophilic lines are presented. The effects of the hydrophilic line and the initial impact offset distance from the line on the droplet spreading behaviour are studied. Two distinct processes have been identified, namely the centering and conforming processes. During the centering process, the droplets which impinge at a certain offset distance from the center of the hydrophilic lines migrate towards the center
of the line. A droplet with a larger offset distance experiences a slower centering process.

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Ultrafast imaging method to measure surface tension and viscosity of inkjet‑printed droplets in flight

Author(s): Hendrink J.J. Staat, Arjan van der Bos, Marc van den Berg, Hans Reinten, Herman Wijshoff, Michel Verluis and Detlef Lohse(© 2017)

In modern drop-on-demand inkjet printing, the
jetted droplets contain a mixture of solvents, pigments and surfactants. In order to accurately control the droplet formation process, its in-flight dynamics, and deposition characteristics upon impact at the underlying substrate, it is key to quantify the instantaneous liquid properties of the droplets during the entire inkjet-printing process.

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MATERIALS TESTING

Experimental studies on the deformation and rupture of thin metal plates subject to underwater shock wave loading

Author(s): Pengwan Chena, Han Liu, Shaolong Zhang, Haibo Liu, Ang Chen, and Baoqiao Guo       (© 2015)

In this paper, the dynamic deformation and rupture of thin metal plates subject to underwater shock wave loading are studied by using high-speed 3D digital image correlation (3D-DIC). An equivalent device consist of a gas gun and a water anvil tube was used to supplying an exponentially decaying pressure in lieu of explosive detonation which acted on the panel specimen. The thin metal plate is clamped on the end of the shock tube by a flange.The deformation and rupture process of the metal plates subject to underwater shock waves are recorded by two high-speed cameras.

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Experimental Study of the Effectiveness of Sacrificial Cladding Using Polymeric Foams as Crushable Core with a Simply Supported Steel Beam

Author(s): H. Ousji, B. Belkassem,1M. A. Louar, B. Reymen, L. Pyl, and J. Vantomme (© 2016)

The present paper focuses on the study of the effectiveness of the sacrificial cladding using polymeric foam as crushable core to reduce the delivered blast energy using a simplified structure. The latter consists of a simply supported steel beam under a localized blast load.The tested sacrificial cladding has a cross-sectional area of 80 × 80mm2. The effect of the front plate mass and the crushable core properties (plateau stress and thickness) is studied.

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Synchrotron-based radioscopy employing spatio-temporal micro-resolution for studying fast phenomena in liquid metal foams

Author(s): A. Rack, F. Garc´ıa-Moreno, T. Baumbach and J. Banhartd © 2007

Investigations of pore coalescence and individual cell wall collapse in an expanding liquid metal foam by means of X-ray radioscopy with spatio-temporal micro-resolution are reported. By using white synchrotron radiation for imaging, the rupture of a film and the subsequent merger of two neighboring bubbles could be recorded with a time sampling rate of 40 000 frames/s (25 μs exposure time) and a spatial sampling rate of 20 μm.

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DEFENSE

Dynamic Fracture in Carbon-fibre Composites: Effect of Steel and Ice Projectiles

Author(s): Laurence A. Cloes, Anish Roy, Leonid Voronov, Sergey Semyonov, Mikhail Nikham, Vadin V. Silberschmidt (© 2016)

This study the resultant ballistic dynamic response observed in a 2x2 twill weave T300 carbon fibre/epoxy composite flat-plate specimen is examined, using a combination of non-invasive analysis techniques. The study investigates deformation, damage and fracture following the impacts with both solid (steel) and fragmenting (ice) projectiles travelling with velocities of 70-90 m/s and 300-500 m/s, respectively. Digital image correlation was employed to obtain displacement data for the rear surfaces of the specimens in each experiment, and used to assess the effect of impact velocity and projectile material on the specimen’s response.

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Comparison of JP-8 Sprays from a Hydraulically Actuated Electronically Controlled Unit Injector and a Common Rail Injector

Author(s): Matthew Kurman, Michael Tess, Luis Bravo, Chol-Bum Kweon, and Craig Hershey (© 2015)

JP-8 sprays from a hydraulically actuated electronically controlled unit injector (HEUI) and a common rail injector (CRIN) were investigated to compare the effects of the fuel delivery system on the spray behavior of the fuel. The fuel pressurization method between injectors is fundamentally different. The HEUI system utilizes engine oil to pressurize the fuel, whereas, the CRIN system pressurizes the fuel directly. To explore the different injection methods, rate of injection (ROI) experiments were initially conducted to measure shot-to-shot fuel quantity and rate of injection of both injector types.

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The Analysis Of The Vibratory Movement Of The Gun Barrel And Its Influence On The Firing Accuracy

Author(s): Alin-Constantin Sava, Ioan-Liviu Piticari, Diana-Georgeta Nistoran and Christian-Emil Moldoveanu (© 2015)

It is known that the forces and shocks that occur during the firing process of a firearm induce vibrations to the barrel of the weapon and to the weapon as a whole. There are flexural, longitudinal, radial and torsional vibrations. The most important ones are considered to be the flexural or bending vibrations, especially the ones recorded in the muzzle section. This paper presents a method of recording the flexural vibrations of the barrel in the muzzle section of a 5,56mm automatic rifle and the influence of muzzle devices, using modern equipment (high speed cameras) and dedicated software.

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AEROSPACE

Experimental study of spray characteristics and functionality of small pressure-swill atomizers

Author(s): Bc. Milan Malý1, Lada Janáková, Jan Jedelský and Miroslav Jícha (© 2016)

An experimental investigation of characteristics of spray generated by a pressure-swirl atomizer (spill-return type) was performed using shadowgraphy and Phase-Doppler Anemometry (PDA). Several different geometries of the spill-return orifice were tested in terms of a spray stability and quality on a cold test bench. PDA measurement yields a drop-size distribution and velocity data while the shadowgraphy unveils a break-up process in detail. Performed measurements reveal significant differences in spray characteristics aswell as differences in spray stability. The results suggest that the air core, formed inside the swirl chamber, passes through the spill orifice, which causes instability of the inner flow.

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Development of Background-Oriented Schlieren for NASA Langley Research Center Ground Test Facilities

Author(s): Brett F. Bathel, Stephen Borg, Stephen Jones, Austin Overmeyer, Eric Walker, and William Goad (© 2016)

This paper provides an overview of recent wind tunnel tests performed at the NASA Langley Research Center where the Background-Oriented Schlieren (BOS) technique was used to provide information pertaining to flowfield density disturbances. The facilities in which the BOS technique was applied included the National Transonic Facility (NTF), Transonic Dynamics Tunnel (TDT), 31-Inch Mach 10 Air Tunnel, 15-Inch Mach 6 High-Temperature Air Tunnel, Rotor Test Cell at the 14×22 Subsonic Tunnel, and a 13-Inch Low-Speed Tunnel.

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Mode Transitions in Hall Effect Thrusters                                                                       

Author(s): Sekerak, M. J., Longmier, B. W., Gallimore, A. D., Brown, D. L., Hofer, R. R.,
Polk, J. E. (© 2013)

Mode transitions have been commonly observed in Hall Effect Thruster (HET) operation where a small change in a thruster operating parameter such as
discharge voltage, magnetic field or mass flow rate causes the thruster discharge current mean and oscillation amplitude to increase significantly. Mode transitions in a 6-kW class HET called the H6 were induced by varying the magnetic field intensity while holding all other operating parameters constant and measurements were acquired with ion saturation probes and ultra-fast imaging.

 

Application of FLEET Velocimetry in the NASA Langley 0.3-meter Transonic Cryogenic Tunnel

Author(s): Ross A. Burns, Paul M. Danehy, Benjamin R. Halls and Naibo Jiang (©)

Femtosecond laser electronic excitation and tagging (FLEET) velocimetry is demonstrated in a large-scale transonic cryogenic wind tunnel. Test conditions include total pressures, total temperatures, and Mach numbers ranging from 15 to 58 psia, 200 to 295 K, and 0.2 to 0.75, respectively. Freestream velocity measurements exhibit accuracies within 1 percent and precisions better than 1 m/s.

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American Institute of Aeronautics and Astronautics Precision of FLEET Velocimetry using High-Speed CMOS Camera Systems

Author(s): Christopher J. Peters, Paul M. Danehy, Brett F. Bathel, Niabo Jiang, Nathan D. Calvert and Richard B. Miles (©)

Femtosecond laser electronic excitation tagging (FLEET) is an optical measurement technique that permits quantitative velocimetry of unseeded air or nitrogen using a single laser and a single camera. In this paper, we seek to determine the fundamental precision of the FLEET technique using high-speed complementary metal-oxide semiconductor (CMOS) cameras. Also, we compare the performance of several different high-speed CMOS camera systems for acquiring FLEET velocimetry data in air and nitrogen free-jet flows.

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A High-Speed X-Ray Detector System for Noninvasive Fluid Flow Measurements

Author(s): Timothy B. Morgan, Benjamin R. Halls, Terrence R. Meyer, Theodore J. Heindel (© 2013)

This paper provides an overview of recent wind tunnel tests performed at the NASA Langley Research Center where the Background-Oriented Schlieren (BOS) technique was used to provide information pertaining to flowfield density disturbances. The facilities in which the BOS technique was applied included the National Transonic Facility (NTF), Transonic Dynamics Tunnel (TDT), 31-Inch Mach 10 Air Tunnel, 15-Inch Mach 6 High-Temperature Air Tunnel, Rotor Test Cell at the 14×22 Subsonic Tunnel, and a 13-Inch Low-Speed Tunnel.

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