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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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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Effects of surface perturbations on the asymmetric vortex flow over a slender body

An experimental investigation of the effects of surface perturbations on the asymmetric flow past a slender body has been conducted for laminar flow conditions. Beads with diameters ranging from 3/32 to 12/32 in. were attached near the apex of a cone/cylinder model having a base diameter of 3.5 in. and a cone semiapex angle of 9 deg at an angle of attack of 40 deg in an attempt to alter the sense of the asymmetric vortex flow pattern. Circumferential position as well as longitudinal location were varied to determine the most effective bead position. Whether or not the beads were effective in controlling the magnitude and direction of the vortex asymmetries was determined by 3 circumferential rows of pressure taps and by a helium-bubble flow visualization technique. The most effective circumferential position was found to be approximately 140 deg from the windward ray. While holding this circumferential position constant, the effect of bead size at three stations further along the body was also investigated. It was found that the size of the bead necessary to reverse the asymmetry increased more rapidly than the growth in cylinder radius. In general, these results indicate that discrete geometric imperfections on a body's surface can force asymmetry in a given direction if they are sufficiently large relative to the local radius.

Moskovitz, Cary A.↗
NASA NTRS1990

Experimental investigation of a new device to control the asymmetric flowfield on forebodies at large angles of attack

An exploratory experimental investigation of a new device to control the asymmetric flowfield on forebodies at large angles of attack has been conducted. The device is a rotatable forebody tip, which varies in cross section from circular at its base to elliptic at its tip. The device itself extends over a small portion of the aircraft or missile forebody. The device provides two important improvements. First, it replaced the normally random behavior of the nose side force as a function of nose tip orientation with a predictable and generally sinusoidal distribution and, second, the device showed promise for use as part of a vehicle control system, to be deflected in a prescribed manner to provide additional directional control for the vehicle. The device was tested on a cone/cylinder model having a 10 deg semiapex angle and on a 3.0 caliber tangent ogive model, each with a base diameter of 3.5 in, for angles of attack from 30 to 60 deg. Data were taken from 3 circumferential rows of pressure taps on each model at a Reynolds number of 84,000 based on cylinder diameter and by a helium-bubble flow visualization technique at a Reynolds number of 24,000.

Moskovitz, Cary A.↗
NASA NTRS1990

A survey of techniques for refrigeration, reliquefaction, and production of slush for hydrogen

Several techniques were surveyed for the refrigeration, reliquefaction and production of slush from hydrogen. The techniques included auger; bubbling helium gas; Simon desorption; the Petlier effect; Joule-Kelvin expansion using Stirling, Brayton, and Viulleumirer approaches; rotary reciprocating; a dilution refrigerator; adiabatic demagnetization of a paramagnetic salt; and adiabatic magnetization of a superconductor.

Overcash, Dan R.↗
NASA NTRS1991

Effect of a simulated ice accretion on the aerodynamics of a swept wing

The effect of a simulated glaze ice accretion on the aerodynamic performance of a three-dimensional swept wing is studied experimentally. A semispan wing of effective aspect ratio four was mounted from the sidewall of the UIUC subsonic wind tunnel. The model uses a NACA 0012 airfoil section on a rectangular planform with interchangeable tip and root sections to allow for 0- and 30-degree sweep. A sidewall suction system is used to minmize the tunnel boundary-layer interaction with the model. Surface pressure data from five spanwise stations are compared to earlier data from a similar tunnel. A three-component sidewall balance has been designed, built and used to measure lift, drag and pitching moment on the clean and iced model. The data compare well to the integrated pressure data and to theory on the clean model. In addition, helium-bubble flow visualization has been performed on the iced model and reveals extensive spanwise flow in the separation bubble aft of the upper surface horn. This compares well to the computational results of other researchers. Sidewall suction was found to have no effect on the aerodynamics of the swept wing.

Bragg, M. B.↗
NASA NTRS1992

Stability test and analysis of the Space Shuttle Primary Reaction Control Subsystem thruster

The results are reported of a test program conducted on the Space Shuttle Primary Reaction Control Subsystem thruster in order to investigate the effects of trapped helium bubbles and saturated propellants on stability, determine if thruster-to-thruster stability variations are significant, and determine stability under STS-representative conditions. It is concluded that the thruster design is highly reliable in flight and that burn-through has not occurred. Significantly unstable thrusters are screened out, and wire wrap is found to protect against chamber burn-throughs and to provide a fail-safe thruster for this situation.

Applewhite, John↗
NASA NTRS1992

Flow visualizations of perpendicular blade vortex interactions

Helium bubble flow visualizations have been performed to study perpendicular interaction of a turbulent trailing vortex and a rectangular wing in the Virginia Tech Stability Tunnel. Many combinations of vortex strength, vortex-blade separation (Z(sub s)) and blade angle of attack were studied. Photographs of representative cases are presented. A range of phenomena were observed. For Z(sub s) greater than a few percent chord the vortex is deflected as it passes the blade under the influence of the local streamline curvature and its image in the blade. Initially the interaction appears to have no influence on the core. Downstream, however, the vortex core begins to diffuse and grow, presumably as a consequence of its interaction with the blade wake. The magnitude of these effects increases with reduction in Z(sub s). For Z(sub s) near zero the form of the interaction changes and becomes dependent on the vortex strength. For lower strengths the vortex appears to split into two filaments on the leading edge of the blade, one passing on the pressure and one passing on the suction side. At higher strengths the vortex bursts in the vicinity of the leading edge. In either case the core of its remnants then rapidly diffuse with distance downstream. Increase in Reynolds number did not qualitatively affect the flow apart from decreasing the amplitude of the small low-frequency wandering motions of the vortex. Changes in wing tip geometry and boundary layer trip had very little effect.

Rife, Michael C.↗
NASA NTRS1996

Turbulent Inflow Measurements

In the present research, tilt rotor aeroacoustics have been studied experimentally and computationally. Experimental measurements were made on a 1/12.5 scale model. A dimensional analysis showed that the model was a good aeroacoustic approximation to the full-scale aircraft, and scale factors were derived to extrapolate the model measurements to the full-scale XV-15. The experimental measurements included helium bubble flow visualization, silk tuft flow visualization, 2-component hot wire anemometry, 7-hole pressure probe measurements, vorticity measurements, and outdoor far field acoustic measurements. The hot wire measurements were used to estimate the turbulence statistics of the flow field into the rotors, such as length scales, velocity scales, dissipation, and turbulence intermittency. To date, these flow measurements are the only ones in existence for a hovering tilt rotor. Several different configurations of the model were tested: (1) standard configurations (single isolated rotor, two rotors without the aircraft, standard tilt rotor configuration); (2) flow control devices (the 'plate', the 'diagonal fences'); (3) basic configuration changes (increasing the rotor/rotor spacing, reducing the rotor plane/wing clearance, operating the rotors out of phase). Also, an approximation to Sikorsky's Variable Diameter Tilt Rotor (VDTR) configuration was tested, and some flow measurements were made on a semi-span configuration of the model. Acoustic predictions were made using LOWSON.M, a Mathematica code. This hover prediction code, from HOVER.FOR, used blade element theory for the aerodynamics, and Prandtl's Vortex theory to model the wake, along with empirical formulas for the effects of Reynolds number, Mach number, and stall. Aerodynamic models were developed from 7-hole pressure probe measurements of the mean velocity into the model rotors. LOWSON.M modeled a rotor blade as a single force and source/sink combination separated in the chordwise direction, at an effective blade radius. Spanwise, Mach-weighted integrals were used to find the equivalent forces and equivalent source strengths.

George, Albert R.↗
NASA NTRS1996

Tilt Rotor Aircraft Aeroacoustics

A fleet of civil tilt rotor transports offers a means of reducing airport congestion and point-to-point travel time. The speed, range, and fuel economy of these aircraft, along with their efficient use of vertiport area, make them good candidates for short-to-medium range civil transport. However, to be successfully integrated into the civilian community, the tilt rotor must be perceived as a quiet, safe, and economical mode of transportation that does not harm the environment. In particular, noise impact has been identified as a possible barrier to the civil tilt rotor. Along with rotor conversion-mode flight, and blade-vortex interaction noise during descent, hover mode is a noise problem for tilt rotor operations. In the present research, tilt rotor hover aeroacoustics have been studied analytically, experimentally, and computationally. Various papers on the subject were published as noted in the list of publications. More recently, experimental measurements were made on a 1/12.5 scale model of the XV-15 in hover and analyses of this data and extrapolations to full scale were also carried out. A dimensional analysis showed that the model was a good aeroacoustic approximation to the full-scale aircraft, and scale factors were derived to extrapolate the model measurements to the full-scale XV-15. The experimental measurements included helium bubble flow visualization, silk tuft flow visualization, 2-component hot wire anemometry, 7-hole pressure probe measurements, vorticity measurements, and outdoor far field acoustic measurements. The hot wire measurements were used to estimate the turbulence statistics of the flow field into the rotors, such as length scales, velocity scales, dissipation, and turbulence intermittency. Several different configurations of the model were tested: (1) standard configurations (single isolated rotor, two rotors without the aircraft, standard tilt rotor configuration); (2) flow control devices (the 'plate', the 'diagonal fences'); (3) basic configuration changes (increasing the rotor/rotor spacing, reducing the rotor plane/wing clearance. operating the rotors out of phase). Also, an approximation to Sikorsky's Variable Diameter Tilt Rotor (VDTR) configuration was tested, and some flow measurements were made on a semi-span configuration of the model. Acoustic predictions were made using LOWSON.M, a Mathematica code Mean aerodynamic models were developed based on hover performance predictions from HOVER.FOR. This hover prediction code used blade element theory for the aerodynamics, and Prandtl's Vortex theory to model the wake, along with empirical formulas for the effects of Reynolds number, Mach number, and stall. Aerodynamic models were developed from 7-hole pressure probe measurements of the mean velocity into the model rotors.

George, Albert R.↗
NASA NTRS1999

Sensitized Liquid Hydrazine Detonation Studies

Vapor-phase hydrazine (N2H4) is known to be very sensitive to detonation while liquid hydrazine is very insensitive to detonation, theoretically requiring extremely high pressures to induce initiation. A review of literature on solid and liquid explosives shows that when pure explosive substances are infiltrated with gas cavities, voids, and/or different phase contaminants, the energy or shock pressure necessary to induce detonation can decrease by an order of magnitude. Tests were conducted with liquid hydrazine in a modified card-gap configuration. Sensitization was attempted by bubbling helium gas through and/or suspending ceramic microspheres in the liquid. The hydrazine was subjected to the shock pressure from a 2 lb (0.9 kg) Composition C-4 explosive charge. The hydrazine was contained in a 4 in. (10.2 cm) diameter stainless steel cylinder with a 122 in(sup 3) (2 L) volume and sealed with a polyethylene cap. Blast pressures from the events were recorded by 63 high speed pressure transducers located on three radial legs extending from 4 to 115 ft (1.2 to 35.1 in) from ground zero. Comparison of the neat hydrazine and water baseline tests with the "sensitized" hydrazine tests indicates the liquid hydrazine did not detonate under these conditions.

Rathgeber, K. A.↗
DOE OSTI2024

Transport of Highly Volatile Gases Related to Noble Gases and Tritium in the MSRE

This study aims to comprehend mass transfer in the closed-loop circulation of highly volatile gases, including noble gases and tritium. We explore the impact of steady-state xenon-135 and tritium on the MSRE and reveal their isotopic distributions using online noble gas stripping of fuel salts. The MSRE was engineered to extract fission product gases from fuel salts and efficiently eliminate inert gases with the help of helium bubbles within a circulating fuel pump. These reactors introduce significant theoretical challenges in estimating interfacial area and mass transfer coefficients, crucial for modeling mass transfer processes. An essential component of our analysis is the mass transfer coefficient. These coefficients are important for understanding how radionuclides move during various phase transitions within a nuclear reactor. Xenon-135 and tritium are found in both liquid and gas phases within the reactor system. In the liquid phase, they dissolve in molten salts, while in the gas phase, they manifest as bubbles. These elements have significant adverse effects on reactor operation due to their strong neutron absorption properties, influencing both safety and performance. The Mole code, which predicts the behavior of chemical species under steady-state conditions, facilitates multiphysics coupling with Griffin to update species distributions and address inherent MSR safety.

Lee, Kyoung↗
NASA NTRS1968

Reducing bubbles in glass coatings improves electrical breakdown strength

Helium reduces bubbles in glass coatings of accelerator grids for ion thrustors. Fusing the coating in a helium atmosphere creates helium bubbles in the glass. In an argon atmosphere, entrapped helium diffuses out of the glass and the bubbles collapse. The resultant coating has a substantially enhanced electrical breakdown strength.

Banks, B.↗
DOE OSTI2020

Corrigendum and Addendum: Helium flux effects on bubble growth and surface morphology in plasma-facing tungsten from large-scale molecular dynamics simulations (2019 Nucl. Fusion 59 066035)

Two of the simulations discussed in a prior article (Hammond et al 2019 Nucl. Fusion 59 066035) were affected by a simulation glitch. We repeated the affected calculations and discuss them here. Here, the overall conclusions are essentially unchanged, though the details are different. In particular, observations that we referred to as ‘concerted bursting’ were caused primarily by non-physical heating and cooling applied by the thermostat after most atoms’ velocities were deleted (for reasons that are not known for certain). The phenomenon of one bubble bursting and causing another nearby bubble to burst does exist, though its effects are much less spectacular in the absence of non-physical driving forces. The observation of an interconnected network of sub-surface cavities formed by burst bubbles is real, and the observation of holes on the surface 1–2 nm in diameter is also confirmed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Microstructural Effects of High Dose Helium Implantation in ErD 2

Metal hydrides can store hydrogen isotopes with high volumetric density. In metal tritides, tritium beta decay can result in accumulation of helium within the solid, in some cases exceeding 10 at.% helium after only 4 years of aging. Helium is insoluble in most materials, but often does not readily escape, and instead coalesces to form nanoscale bubbles when helium concentrations are near 1 at.%. Blistering or spallation often occurs at higher concentrations. Radioactive particles shed during this process present a potential safety hazard. This study investigates the effects of high helium concentrations on erbium deuteride (ErD 2 ), a non-radioactive surrogate material for erbium tritide (ErT 2 ). To simulate tritium decay in the surrogate, high doses of 120 keV helium ions were implanted into ErD 2 films at room temperature. Scanning and transmission electron microscopy indicated spherical helium bubble formation at a critical concentration of 1.5 at.% and bubble linkage leading to nanoscale crack formation at a concentration of 7.5 at.%. Additionally, crack propagation occurred through the nanocrack region, resulting in spallation extending from the implantation peak to the surface. Electron energy loss spectroscopy was utilized to confirm the presence of high-pressure helium in the nanocracks, suggesting that helium gas plays a predominant role in deformation. This work improves the overall understanding of helium behavior in ErD 2 by using modern characterization techniques to determine: the critical helium concentration required for bubble formation, the material failure mechanism at high concentration, and the nanoscale mechanisms responsible for material failure in helium implanted ErD 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2021

Experimental observations of shock-wave-induced bubble collapse and hot-spot formation in nitromethane liquid explosive

We studied the collapse of individual helium gas bubbles in the homogeneous explosive nitromethane (NM) to investigate effects of hot-spot formation on the detonation process. A bubble was injected into a NM sample, and a shock wave from an explosive detonator compressed the bubble, creating a localized hot spot. We measured shock and detonation wave speeds with optical velocimetry, and we used a high-speed camera to image the shock propagation and the pre- and post-bubble collapse processes. An infrared camera image showed the residual radiance temperature distribution after the bubble collapse, and an optical fiber pyrometer measured the time-resolved thermal radiance. We measured the optical spectra of light emitted from detonating NM without a bubble and from a collapsing bubble in shocked, undetonated NM. We estimated temperatures of the detonation fronts and of the hot spots formed by bubble collapse. To study the incipient detonation process, we performed all bubble collapse experiments at pressures below the threshold for creating a sustained detonation. Where the bubble collapsed, we observed an opaque, thermally emissive region believed to be chemical reaction products. Chemical reactions in NM can be produced with lower shock pressures (~1 GPa) when a helium bubble is present than without a bubble (~10 GPa). We used hydrodynamic modeling to predict shock wave propagation, extent of chemical reaction, and subsequent temperature rise from the collapsing bubble. Simulations using a temperature-dependent Arrhenius burn model gave much better results than reactive burn models that depend only on pressure and density.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Helium effects and bubbles formation in irradiated Ti 3 SiC 2

Ti 3 SiC 2 is a potential structural material for nuclear reactor applications. However, He irradiation effects in this material are not well understood, especially at high temperatures. Here, we compare the effects of He irradiation in Ti 3 SiC 2 at room temperature (RT) and at 750 °C. Irradiation at 750 °C was found to lead to extremely elongated He bubbles that are concentrated in the nano-laminate layers of Ti 3 SiC 2 , whereas the overall crystal structure of the material remained intact. In contrast, at RT, the layered structure was significantly damaged and highly disordered after irradiation. Our study reveals that at elevated temperatures, the unique structure of Ti 3 SiC 2 can accommodate large amounts of He atoms in the nano-laminate layer, without compromising the structural stability of the material. The structure and the mechanical tests results show that the irradiation induced swelling and hardening at 750 °C are much smaller than those at RT. Overall, these results indicate that Ti 3 SiC 2 has an excellent resistance to accumulation of radiation-induced He impurities and that it has a considerable tolerance to irradiation-induced degradation of mechanical properties at high temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Origin of increased helium density inside bubbles in Ni (1–$x$) Fe $x$ alloys

Due to virtually no solubility, He atoms implanted or created inside materials tend to form bubbles, which are known to damage material properties through embrittlement. Higher He density in nano-sized bub- bles was observed both experimentally and computationally in Ni (1–$x$) Fe $x$ -alloy samples compared to Ni. The bubbles in the Ni (1–$x$) Fe $x$ -alloys were observed to be faceted, whereas in elemental Ni they were more spherical. Molecular dynamics simulations showed that stacking fault structures formed around bubbles at maximum He density. Higher Fe concentrations stabilize stacking fault structures, suppress evolution of dislocation network around bubbles and suppress complete dislocation emission, leading to higher He density.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Collapse of helium-filled voids in extreme deformation: Dislocation mechanisms

The mechanisms responsible for the collapse of helium-filled bubbles during the passage of shock waves in monocrystalline copper are revealed. Both internal pressure (caused by pre-existing helium atoms) and bubble size are varied in molecular dynamics simulations to understand the atomistic scale deformation as they are subjected to shock compression at pressures of 48, 123, and 170 GPa, corresponding to particle velocities of 1.0, 2.0, and 2.5 km/s. Both empty and helium filled bubbles serve as dislocation sources, generating intense, localized plastic regions. There are distinct differences in the collapse of empty voids compared to He-filled bubbles, the former requiring less stress and generating a greater density of dislocations for a given shock strength. Additionally, a generalized model for dislocation emission is proposed, where the inclusion of shear stress generated by the helium bubble increases the critical stress to generate dislocations at the defect surface, demonstrating the change in plastic deformation.

36 MATERIALS SCIENCE↗