Search NASA⌕ Search

SEARCH · Search NASA

Results for “Breakup”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Airfoil large-eddy breakup devices for turbulent drag reduction

Large-eddy breakup devices were tested in a turbulent boundary layer at a momentum thickness Reynolds number of 7400. The drag reducing characteristics of thin, tapered plates, NACA 0009, and NACA 4409 airfoil shapes were determined and compared with lower Reynolds number data obtained with thin elements. The results indicate that at the higher Reynolds numbers of the present tests the thin, tapered plates in a tandem arrangement produced large downstream skin-friction reductions (maximum 0/40 percent/), and gave net drag reductions at least as large as for lower Reynolds numbers. Tandem NACA 0009 airfoils, which were approximately 10 times thicker than the thin plates, gave similar results with a maximum downstream skin-friction reduction of 0(30 percent) and a net drag reduction of 7 percent. The device drag for this shape was determined to be near laminar skin friction. The NACA 4409 airfoils suffered large regions of separated flow and produced no net drag reduction.

Anders, J. B.↗
NASA NTRS1986

Turbulent Reynolds analogy factors of stacked large-eddy breakup devices

Direct measurements are made of turbulent Reynolds analogy factors, referenced to a flat plate, for turbulent boundary layer flows altered by stacked arrays of large eddy breakup devices (LEBUs). These are of interest as drag reducers when inserted into a boundary layer transverse to the flow. The data thus obtained furnish evidence that heat transfer, skin friction drag, and LEBU performance factors in low Reynolds number flows are sensitive to flow history. Attention is given to the apparatus and measurement procedures used.

Lindemann, A. M.↗
NASA NTRS1986

Large eddy breakup devices as low Reynolds number airfoils

Turbulent drag reduction downstream of large-eddy breakup (LEBU) devices is analyzed from the viewpoint of low-Reynolds number airfoil aerodynamics. It is argued that the variability of results between different research labs is primarily due to low Reynolds number 'phenomena' associated with unsteady separation/transition of the LEBU device boundary layer. LEBU drag reduction is shown to be an extremely sensitive function of device microgeometry at the low Reynolds numbers of all current investigations, and by analogy with conventional low-Reynolds number airfoil testing, the conclusion is drawn that the full potential for LEBU drag reduction must be explored at chord Reynolds numbers of 300,000 and above.

Anders, John B.↗
NASA NTRS1986

Airfoil large eddy breakup devices for turbulent drag reduction

It was determined from the present LaRC experiments that tandem, airfoil-shaped large eddy breakup (LEBU) devices can reduce local skin friction as much as 30 percent with a recovery region extending more than 100 boundary layer thicknesses downstream. These airfoils experience near laminar skin friction device drag and produce net drag reductions of up to 7 percent. In contrast to the thin plates used in previous experiments, these airfoils are more than 1000 time stiffer and hence have the potential to withstand the real flight environment (dynamic pressure 36 times larger than in low-speed wing tunnels). In addition, the higher Reynolds numbers of the present tests indicate drag reduction performance is at least as good (or better) as at lower Reynolds numbers.

Anders, J. B.↗
NASA NTRS1988

A hybrid computational approach to multiple-body viscous flow problems - Application to large-eddy breakup in a boundary layer

By combining stream-function and integral-velocity formulations, the hybrid computational procedure is rendered applicable to unsteady, two-dimensional flows about multiple bodies; the bodies in the flow are replaced by distributions of bound vorticity over their surfaces. By expressing the rotational velocity field generated by the free vorticity in terms of the stream function, stream function boundary conditions are required only on the periphery of the computational domain. The procedure is employed in the simulation of coherent eddy breakup by a single flat plate that is embedded in a viscous boundary layer, exhibiting significant unsteady flow features through the graphical presentation of vorticity contours.

Kinney, R. B.↗
NASA NTRS1990

Scattered-light scanner measurements of cryogenic liquid-jet breakup

The effect of highly turbulent Mach 1 gas flow and high thermal gradients on drop size measurements was investigated with a scattered light scanner. The instrument, developed at NASA-Lewis, was used to measure characteristic drop diameters or cyrogenic liquid sprays. By correcting for gas turbulence and thermal gradient affects, it was possible to obtain good reproducible data with the scattered light scanner. Tests were conducted primarily in the aerodynamic-stripping regime of liquid atomization and it was found that the loss of small droplets due to vaporization and dispersion had a marketed effect on drop size measurements. The nitrogen gas flow rate exponent of 1.33 is the same as that predicted by atomization theory for liquid jet breakup in high velocity gas flow. However, when the sprays were sampled farther downstream of the atomizer, at axial distances of 2.5 and 4.5 cm, the exponent for W sub n decreased 1.2 and 0.9, respectively. This was attributed to the loss of small droplets due to vaporization when values of downstream axial distances exceeded 1.3 cm.

Ingebo, Robert D.↗
NASA NTRS1989

Shear stabilization of the capillary breakup of a cylindrical interface

A cylindrical interface containing a viscous liquid set into axial motion is subject to a capillary and to a surface-wave instability. Clues from previous studies suggest that, even though both mechanisms separately are destabilizing, under certain circumstances their mutual interaction can lead to a stable interface; shear can stabilize capillary breakup. Here, an axial flow through an annular cross section bounded on the inside by a rigid rod and on the outside by a deformable interface is considered. The competition between the two mechanisms is studied through the temporal growth of infinitesimal axisymmetric and nonaxisymmetric disturbances. This examination of temporal stability shows that, indeed, for geometries corresponding to thin annular layers both instabilities can be completely suppressed (disturbances of all wavelengths decay).

Russo, Mathew J.↗
NASA NTRS1990

Satellite formation in capillary jet breakup

Computations of finite-amplitude, spatially periodic wave growth on a cylindrical jet have been carried out using a boundary integral method. The initial wave growth is in agreement with Rayleigh's linear theory. When followed to completion these waves pinch off large drops separated by smaller satellite drops (spherules) that decrease in size with decreasing wavelength. The computed sizes of both drops and satellites agree with experiment. It is found that satellites will form for all unstable wave numbers. The small satellites that are computed at wave numbers near the critical wave number were not predicted by near-linear analysis but are observed in experimental photographs of jet breakup. Computation of the collapse of elongated satellites shows short waves propagating on their surfaces.

Mansour, Nagi N.↗
NASA NTRS1991

Thermocapillary stabilization of the capillary breakup of an annular film of liquid

It is known that the breakup by surface tension of a cylindrical interface containing a viscous liquid can be damped by axial motion of the underlying liquid and that for an annular film the capillary instability can be completely suppressed (disturbances of all wavelengths decay) by certain axial velocity profiles. Here, using a linear stability analysis, it is shown that complete stabilization can also occur for thermocapillary-driven axial motions. However, the influence of thermocapillary instabilities typically shrinks the window in parameter space where stabilization is found, relative to the isothermal case. The influence of Reynolds, surface tension, Prandtl, and Biot parameters on limits of stabilization is calculated using continuation techniques. It is observed that windows of stabilization first open with topological changes of the neutral curves in parameter space.

Dijkstra, Henk A.↗
NASA NTRS1991

Breakup of meteoroids in the Venusian atmosphere and its effects on crater formation

Early results of the Magellan mission to Venus show that almost all of the observed impact craters appear to be unaffected by erosion, burial, and tectonic deformation. Therefore it is reasonable to assume that the observed paucity of small craters in the cumulative size-frequency distribution (SFD) relative to the simple power laws observed on airless planets is most likely due to atmospheric effects on the incoming meteoroids. A model was developed earlier for travel and breakup of a meteoroid in an atmosphere, but this model was never used to estimate a SFD. An attempt is made to match the cumulative SFD and the number and size distribution of multiple-floored craters and crater fields using this model.

Herrick, R. R.↗
NASA NTRS1992

Space debris characterization in support of a satellite breakup model

The Space Kinetic Impact and Debris Branch began an ambitious program to construct a fully analytical model of the breakup of a satellite under hypervelocity impact. In order to provide empirical data with which to substantiate the model, debris from hypervelocity experiments conducted in a controlled laboratory environment were characterized to provide information of its mass, velocity, and ballistic coefficient distributions. Data on the debris were collected in one master data file, and a simple FORTRAN program allows users to describe the debris from any subset of these experiments that may be of interest to them. A statistical analysis was performed, allowing users to determine the precision of the velocity measurements for the data. Attempts are being made to include and correlate other laboratory data, as well as those data obtained from the explosion or collision of spacecraft in low earth orbit.

Fortson, Bryan H.↗
NASA NTRS1992

Effect of gas mass flux on cryogenic liquid jet breakup

A scattered-light scanning instrument developed at NASA Lewis Research Center was used to measure the characteristic drop size of clouds of liquid nitrogen droplets. The instrument was calibrated with suspensions of monosized polystyrene spheres. In this investigation of the mechanism of liquid nitrogen jet disintegration in a high-velocity gas flow, the Sauter mean diameter, D32, was found to vary inversely with the nitrogen gas mass flux raised to the power 1.33. Values of D32 varied from 5 to 25 microns and the mass flux exponent of 1.33 agrees well with theory for liquid jet breakup in high-velocity gas flows. The loss of very small droplets due to the high vaporization rate of liquid nitrogen was avoided by sampling the spray very close to the atomizer, i.e., 1.3 cm downstream of the nozzle orifice. The presence of high velocity and thermal gradients in the gas phase also made sampling of the particles difficult. As a result, it was necessary to correct the measurements for background noise produced by both highly turbulent gas flows and thermally induced density gradients in the gas phase.

Ingebo, R. D.↗
NASA NTRS1992

The breakup of a meteorite parent body and the delivery of meteorites to earth

Whether many of the 10,000 meteorites collected in the Antarctic are unlike those falling elsewhere is contentious. The Antarctic H chondrites, one of the major classes of stony meteorites, include a number of individuals with higher induced thermoluminescence peak temperatures than observed among non-Antarctic H chondrites. The proportion of such individuals decreases with the mean terrestrial age of the meteorites at the various ice fields. These H chondrites have cosmic-ray exposure ages of about 8 million years, experienced little cosmic-ray shielding, and suffered rapid postmetamorphic cooling. Breakup of the H chondrite parent body, 8 million years ago, may have produced two types of material with different size distributions and thermal histories. The smaller objects reached earth more rapidly through more rapid orbital evolution.

Benoit, Paul H.↗
NASA NTRS1989

Holographic diagnostics of breakup phenomena of impinging jets for liquid rocket motor applications

The use of pulsed laser holography in analyzing the atomization of impinging jets is evaluated using a holographic camera system capable of recording a 3D image of the atomization process in 3 x 10 exp -8 seconds. The holocamera and the experimental configuration and procedure are described in detail. Two nozzles were fabricated to produce 1-mm diameter liquid water jets that impinged at 60 and 90 deg. Holograms were obtained for each nozzle at liquid velocities of 20 and 40 m/s. Analysis of the holograms revealed the evolution of the jets from the plane of emergence through the region of droplet formation. Features of interest included the growth of disturbances prior to the breakup region and the effect of these disturbances on the formation of ligaments and liquid globules. Preliminary analyses show that waves of atomized liquid formed after impingement are closely correlated to waves measured on the jets, leading to the possibility of controlling the atomization process at the nozzle.

Hess, C. F.↗
NASA NTRS1992

Inferences Concerning the Magnetospheric Source Region for Auroral Breakup

It is argued that the magnetospheric source region for auroral arc breakup and substorm initiation is along boundary plasma sheet (BPS) magnetic field lines. This source region lies beyond a distinct central plasma sheet (CPS) region and sufficiently far from the Earth that energetic ion motion violates the guiding center approximation (i.e., is chaotic). The source region is not constrained to any particular range of distances from the Earth, and substorm initiation may be possible over a wide range of distances from near synchronous orbit to the distant tail. It is also argued that the layer of low-energy electrons and velocity dispersed ion beams observed at low altitudes on Aureol 3 is not a different region from the region of auroral arcs. Both comprise the BPS. The two regions occasionally appear distinct at low altitudes because of the effects of arc field-aligned potential drops on precipitating particles.

Lyons, L. R.↗
NASA NTRS1993

Impacts, tillites, and the breakup of Gondwanaland

Mathematical analysis demonstrates that substantial impact crater deposits should have been produced during the last 2 Gy of Earth's history. Textures of impact deposits are shown to resemble textures of tillites and diamictites of Precambrian and younger ages. The calculated thickness distribution for impact crater deposits produced during 2 Gy is similar to that of tillites and diamictites of 2 Ga or younger. We suggest, therefore, that some tillites/diamictites could be of impact origin. Extensive tillite/diamictite deposits predated continental flood basalts on the interior of Gondwanaland. Significantly, other investigators have already associated impact cratering with flood basalt volcanism and continental rifting. Thus, it is proposed that the breakup of Gondwanaland could have been initiated by crustal fracturing from impacts.

Oberbeck, Verne R.↗
NASA NTRS1993

Analytical description of the breakup of liquid jets in air

A viscous or inviscid cylindrical jet with surface tension in a vacuum tends to pinch due to the mechanism of capillary instability. Similarity solutions are constructed which describe this phenomenon as a critical time is encountered, for two physically distinct cases: inviscid jets governed by the Euler equations and highly viscous jets governed by the Stokes equations. In both cases the only assumption imposed is that at the time of pinching the jet shape has a radial length scale which is smaller than the axial length scale. For the inviscid case, we show that our solution corresponds exactly to one member of the one-parameter family of solutions obtained from slender jet theories and the shape of the jet is locally concave at breakup. For highly viscous jets our theory predicts local shapes which are monotonic increasing or decreasing indicating the formation of a mother drop connected to the jet by a thin fluid tube. This qualitative behavior is in complete agreement with both direct numerical simulations and experimental observations.

Papageorgiou, Demetrios T.↗
NASA NTRS1994

A model to predict the conditions for liquid drop breakup and the resultant mean fragment size

The potential significance of drop fragmentation in sprays and other propulsion-related multiphase flows has been noted in the literature. This has motivated recent experimental and theoretical works to: better understand the fundamentals of physics of drop breakup processes, and develop models of drop fragmentation suitable for use in multiphase flow codes. The works summarized below aim to contribute to both sides of this two-pronged attack.

Wert, K. L.↗