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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 NTRS1973

Droplet breakup in accelerating gas flows. Part 2: Secondary atomization

An experimental investigation to determine the effects of an accelerating gas flow on the atomization characteristics of liquid sprays was conducted. The sprays were produced by impinging two liquid jets. The liquid was molten wax and the gas was nitrogen. The use of molten wax allowed for a quantitative measure of the resulting dropsize distribution. The results of this study, indicate that a significant amount of droplet breakup will occur as a result of the action of the gas on the liquid droplets. Empirical correlations are presented in terms of parameters that were found to affect the mass median dropsize most significantly, the orifice diameter, the liquid injection velocity, and the maximum gas velocity. An empirical correlation for the normalized dropsize distribution is also presented. These correlations are in a form that may be incorporated readily into existing combustion model computer codes for the purpose of calculating rocket engine combustion performance.

Zajac, L. J.↗
NASA NTRS1973

An auroral breakup mechanism

A purely growing electrostatic drift instability driven by the electron temperature gradient at the inner edge of the plasma sheet can grow for large enough values of the temperature gradient. The parallel electric field associated with the instability is localized near the magnetic equator. The growth of the drift instability leads to enhanced whistler noise and increased electron pitch angle diffusion. If the current limit is exceeded in the ionosphere while the parallel electric field of the drift instability exists along the field line, rapid electron precipitation (the auroral breakup) can result.

Maggs, J. E.↗
NASA NTRS1974

Low-altitude acceleration of auroral electrons during breakup observed by a mother-daughter rocket

By the use of a mother-daughter rocket combination and ground-based observations with television, time and space variations are resolved in particle measurements in breakup aurora. The spectral variations measured during a temporal variation in the aurora can be explained by a nearly uniform acceleration of all the electrons such as would be caused by an electric potential drop along the magnetic field lines. Many other explanations can be eliminated.

Johnstone, A. D.↗
NASA NTRS1981

Acceleration wave breakup of liquid jets with airstreams

Characteristic mean drop diameters were determined for downstream and upstream injection into nonswirling and swirling airflows. The effects of the aerodynamic and liquid surface forces on the mean drop size were obtained with a scanning radiometer. Water jet breakup was studied primarily in the acceleration wave regime with values of WeRe 10 to the 6th power and the following empirical expression was obtained: D(o)/D(m) =C (WeRe) to the 0.4, power where D(o) and D(m) are the orifice and mean drop diameters, respectively. We and Re are the Weber and Reynolds numbers defined as repectively, We = rho(a)D(o)V(r)/sigma and Re = D(o)V(r)/nu, where V(r) and rho(a) are airstream relative velocity and density, respectively, and sigma and nu are surface tension and kinematic viscosity of the liquid, respectively. The proportionally constant C was evaluated as follows: for downstream injection, C = 0.023 with nonswirling airflow, and C = 0.027 with swirling airflow. For upstream injection, the empirical expression D(o)/D(m) = 0.0045 (WeRe) to the 0.5 power was obtained with nonswirling airflow. Experimental conditions included a water flow rate of 68 liter per hour and an airflow rate per unit area range of 4.6 to 25.2 gm/sq cm sec at 293 K and atmospheric pressure.

Ingebo, R. D.↗
NASA NTRS1980

Drag reduction - Jet breakup correlation with kerosene-based additives

The drag-reduction effectiveness of a number of high-polymer additives dissolved in aircraft fuel has been measured in a turbulent-flow rheometer. These solutions were further subjected to high elongational stress and breakup forces in a jet discharging in air. The jet was photographed using a high-resolution camera with special lighting. The object of the work was to study the possible spray-suppression ability of high-polymer additives to aircraft fuel and to correlate this with the drag-reducing properties of the additives. It was found, in fact, that the rheometer results indicate the most effective spray-suppressing additives. Using as a measure the minimum polymer concentration to give a maximum friction-reducing effect, the order of effectiveness of eight different polymer additives as spray-suppressing agents was predicted. These results may find application in the development of antimisting additives for aircraft fuel which may increase fire safety in case of crash or accident.

Hoyt, J. W.↗
NASA NTRS1980

Large-eddy breakup scheme for turbulent viscous drag reduction

A concept for reducing turbulent skin friction drag by altering/controlling the large coherent eddy structures within the turbulent boundary layer is proposed. Results of an ongoing experimental and numerical investigation to develop large-eddy breakup devices (LEBU devices) are presented and indicate that the average skin friction drag downstream of the LEBU devices is reduced by up to 24% compared to 'undisturbed' flat plate levels; device drag requires further reduction before net drag reductions can be realized. Future work is discussed and will focus on reducing device drag by taking advantage of the unsteady 'freestream' ahead of the LEBU devices.

Hefner, J. N.↗
NASA NTRS1982

Hydrodynamic and aerodynamic breakup of liquid sheets

The effect of hydrodynamic, aerodynamic and liquid surface forces on the mean drop diameter of water sprays that are produced by the breakup of nonswirling and swirling water sheets in quiescent air and in airflows similar to those encountered in gas turbine combustors is investigated. The mean drop diameter is used to characterize fuel sprays and it is a very important factor in determining the performance and exhaust emissions of gas turbine combustors.

Ingebo, R.↗
NASA NTRS1982

Electrohydrodynamic (EHD) stimulation of jet breakup

Electrohydrodynamic (EHD) excitation of liquid jets offers an alternative to piezoelectric excitation without the complex frequency response caused by piezoelectric and mechanical resonances. In an EHD exciter, an electrode near the nozzle applies an alternating Coulomb force to the jet surface, generating a disturbance which grows until a drop breaks off downstream. This interaction is modelled quite well by a linear, long wave model of the jet together with a cylindrical electric field. The breakup length, measured on a 33 micrometer jet, agrees quite well with that predicted by the theory, and increases with the square of the applied voltage, as expected. In addition, the frequency response is very smooth, with pronounced nulls occurring only at frequencies related to the time which the jet spends inside the exciter.

Crowley, J. M.↗
NASA NTRS1984

Full scale experiments into the use of large eddy breakup devices for drag reduction on aircraft

An experimental investigation in flight was performed to explore the feasibility of using LEBU (Large-Eddy-Breakup) devices to reduce the drag of aircraft. Two geometrical shapes of ribbons were used, and the development of local skin friction was monitored downstream. The aircraft was a swept-wing attack aircraft, and the flights covered the entire subsonic regime from M=0.92 down to stall conditions; flight altitudes were 1, 4.5, 7 and 10 km to explore various combinations of angle of attack, Mach - and Reynolds numbers. Some information was obtained concerning the turbulence characteristics downstream, and a discussion of the downstream amplification due to the drag at the device is also presented.

Bertelrud, A.↗