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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Turbulent density fluctuations in a subsonic and transonic free jet using crossed-beam schlieren techniques

Scalar density fluctuations were measured nonintrusively in the shear layer of a 5.08-cm (2-in.) cold air jet using a crossed-beam schlieren method. Two statistics, covariance and three-dimensional spectrum function, were estimated for an exit Mach number range of 0.3 to 0.97. The density fluctuation intensity, integral scale, and eddy convection speed were calculated and compared to available data where possible. Spectra were found to change significantly in shape becoming less peaked between 3 and 9 jet diameters downstream from the orifice, but they consistently exhibited a -5/3 power law decay at 3, 6, and 9 diameters for frequencies above the peak.

Martin, R. A.↗
NASA NTRS1984

Laser Diode Schlieren Photography

Laser diodes preferable to conventional lasers or incandescent lamps for Schlieren flow analysis because they are smaller, more rugged, less costly and have lower power requirements.

Franke, J. M.↗
NASA NTRS1986

Laser Schlieren Crystal-Growth Imager

Crystal observed as it grows from melt with aid of laser schlieren imaging. Observation method allows entire perimeter of growing crystal to be inspected. Isolated crystal facets examined, convection flows and temperature and concentration gradients revealed. Method does not require contact with, or proximity to, crystal.

Owen, R. B.↗
NASA NTRS1990

Laser Schlieren System Detects Sounds Of Leaks

Hostile environments monitored safely and noninvasively. Modified laser schlieren system acts as microphone to detect sounds of leaks remotely. Sensitive to acoustical frequencies above audible range and especially suited for monitoring leaks of high-pressure steam from boilers or chemical vapors from processing equipment. Does not require placement of delicate equipment in harsh environment monitored, and no contact needed with boiler or other unit being monitored. Detects sound waves via variation of index of refraction of air at acoustical frequencies. Used to monitor sound frequencies beyond range of human hearing.

Shakkottai, Parthasarathy P.↗
NASA NTRS1990

Schlieren System For Flow Studies In Round Glass Pipes

In schlieren system for studying flow of gas in transparent pipe of circular cross section, cylindrical lenses placed on opposite sides of pipe compensate for refraction caused by wall of pipe. Enables direct visualization of such phenomena as laminar or turbulent flow, shock waves, vortexes, and flow separations in systems having inherently cylindrical geometry; potentially unreliable extrapolations from results in flat-sided test cells no longer necessary.

Costen, Robert C.↗
NASA NTRS1990

Schlieren studies of compressibility effects on dynamic stall of airfoils in transient pitching motion

Compressibility effects on the flowfield of an airfoil executing rapid transient pitching motion from 0 - 60 degrees over a wide range of Mach numbers and pitching rates were studied using a stroboscopic schlieren flow visualization technique. The studies have led to the first direct experimental documentation of multiple shocks on the airfoil upper surface flow for certain conditions. Also, at low Mach numbers, additional coherent vortical structures were found to be present along with the dynamic stall vortex, whereas at higher Mach numbers, the flow was dominated by a single vortex. The delineating Mach number for significant compressibility effects was 0.3 and the dynamic stall process was accelerated by increasing the Mach number above that value. Increasing the pitch rate monotonically delayed stall to angles of attack as large as 27 degrees.

Chandrasekhara, M. S.↗
NASA NTRS1992

Schlieren Photographic Studies Of Dynamic Stall

Report describes stroboscopic Schlieren photographic observations of flows around airfoil oscillating sinusoidally about fixed angle of attack. Conducted in wind tunnel on (NACA) 0012 airfoil oscillating with amplitude of 10 degrees about mean angle of attack of 10 degrees. Photographs taken along span of airfoil. Mach numbers and frequencies chosen to encompass conditions on retreating blades of helicopter rotors in forward flight.

Carr, L.↗
NASA NTRS1992

Interferograms, Schlieren, and Shadowgraphs Constructed from Real- and Ideal-Gas, Two- and Three-Dimensional Computed Flowfields

The construction of interferograms, schlieren, and shadowgraphs from computed flowfield solutions permits one-to-one comparisons of computed and experimental results. A method for constructing these images from both ideal- and real-gas, two- and three-dimensional computed flowfields is described. The computational grids can be structured or unstructured, and multiple grids are an option. Constructed images are shown for several types of computed flows including nozzle, wake, and reacting flows; comparisons to experimental images are also shown. In addition, the sensitivity of these images to errors in the flowfield solution is demonstrated, and the constructed images can be used to identify problem areas in the computations.

Yates, Leslie A.↗
NASA NTRS1993

A piston-actuated shock-tube, with laser-Schlieren diagnostics

The essential construction features of a piston actuated shock tube are described, and its advantages relative to the conventional use of diaphragm ruptures for shock initiation are listed. Typical operational parameters are presented to illustrate the levels of reproducibility achieved. Tests with He and N2 drivers into about 99 percent Ar covered shock speeds from 1.539 +/- 0.002-0.8143 +/- 0.002 mm/microsec, corresponding to 2390-847 K incident shock temperatures. Application of this tube for recording postshock front density gradients of the endoergic dissociation of ethane and the exoergic condensation of iron atoms via the laser-Schlieren technique is described.

Hurst, S. M.↗
NASA NTRS1993

Interferograms, schlieren, and shadowgraphs constructed from real- and ideal-gas, two- and three-dimensional computed flowfields

The construction of interferograms, schlieren, and shadowgraphs from computed flowfield solutions permits one-to-one comparisons of computed and experimental results. A method of constructing these images from both ideal- and real-gas, two and three-dimensional computed flowfields is described. The computational grids can be structured or unstructured, and multiple grids are an option. Constructed images are shown for several types of computed flows including nozzle, wake, and reacting flows; comparisons to experimental images are also shown. In addition, th sensitivity of these images to errors in the flowfield solution is demonstrated, and the constructed images can be used to identify problem areas in the computations.

Yates, Leslie A.↗
NASA NTRS1994

Visualization of the multiple supersonic jet oscillations by swept focused strobed schlieren technique

The natural flapping mode oscillations of a multiple rectangular supersonic jet is visualized by the newly developed strobed focusing schlieren technique. Four parallel underexpanded, converging rectangular jets, exhausting into ambient air at a fully expanded Mach number of 1.61 are visualized in this study. This technique clearly shows the oscillations at the natural screech frequency and offers tremendous flexibility in the study of these flow fields.

Raman, Ganesh↗
NASA NTRS1995

Quantitative rainbow schlieren deflectometry

In the rainbow schlieren apparatus, a continuously graded rainbow filter is placed in the back focal plane of the decollimating lens. Refractive-index gradients in the test section thus appear as gradations in hue rather than irradiance. A simple system is described wherein a conventional color CCD array and video digitizer are used to quantify accurately the color attributes of the resulting image, and hence the associated ray deflections. The present system provides a sensitivity comparable with that of conventional interferometry, while being simpler to implement and less sensitive to mechanical misalignment.

Greenberg, Paul S.↗
NASA NTRS1996

Compact Color Schlieren Optical System

Compact, rugged optical system developed for use in rainbow schlieren deflectometry. Features unobscured telescope with focal-length/aperture-width ratio of 30. Made of carefully selected but relatively inexpensive parts. All of lenses stock items. By-product of design is optical system with loose tolerances on interlens spacing. One of resulting advantages, insensitivity to errors in fabrication of optomechanical mounts. Another advantage is ability to compensate for some of unit-to-unit variations inherent in stock lenses.

Buchele, Donald R.↗
NASA NTRS1996

Retroreflection Focusing Schlieren System

A retroreflective type focusing schlieren system which permits the light source to be positioned on the optic side of the system is introduced. The system includes an extended light source, as opposed to a point source, located adjacent to a beam splitter which projects light through the flow field onto a reflecting grating in the form of a grid which generates sheets of light that are directed back through the flow field and the beam splitter onto a primary lens behind which is located a cut-off grid having a grid pattern which corresponds to the grid pattern of the reflecting grating. The cut-off grid is adjustably positioned behind the primary lens and an image plane for imaging the turbulence is adjustably located behind the cut-off grid.

Heineck, James T.↗
NASA NTRS1999

Application Focused Schlieren to Nozzle Ejector Flowfields

The motivation of the testing was to reduce noise generated by eddy Mach wave emission via enhanced mixing in the jet plume. This was to be accomplished through the use of an ejector shroud, which would bring in cooler ambient fluid to mix with the hotter jet flow. In addition, the contour of the mixer, with its chutes and lobes, would accentuate the merging of the outer and inner flows. The objective of the focused schlieren work was to characterize the mixing performance inside of the ejector. Using flow visualization allowed this to be accomplished in a non-intrusive manner.

Mitchell, L. Kerry↗
NASA NTRS2005

High-Speed Rainbow Schlieren Visualization of an Oscillating Helium Jet Undergoing Gravitational Change

Rainbow schlieren deflectometry combined with high-speed digital imaging was used to study buoyancy effects on flow structure of a helium jet discharged vertically into air. The experimental data were taken using the 2.2-sec drop tower facility at the NASA John H. Glenn Research Center in Cleveland, Ohio. The test conditions pertained to jet Reynolds number of 490 and jet Richardson number of 0.11, for which buoyancy is often considered unimportant. Experimental results show global oscillations at a frequency of 27 Hz in Earth gravity. In microgravity, the jet oscillations vanished and the jet width increased. Results provide a direct physical evidence of the importance of buoyancy on the flow structure of low-density gas jets at a Richardson number considered too small to account for gravity.

Leptuch, Peter A.↗
NASA NTRS2000

Ultrasonic Waves in Water Visualized With Schlieren Imaging

The Acoustic Liquid Manipulation project at the NASA Glenn Research Center at Lewis Field is working with high-intensity ultrasound waves to produce acoustic radiation pressure and acoustic streaming. These effects can be used to propel liquid flows to manipulate floating objects and liquid surfaces. Interest in acoustic liquid manipulation has been shown in acoustically enhanced circuit board electroplating, microelectromechanical systems (MEMS), and microgravity space experiments. The current areas of work on this project include phased-array ultrasonic beam steering, acoustic intensity measurements, and schlieren imaging of the ultrasonic waves.

Juergens, Jeffrey R.↗