A modified schlieren technique for micro flow visualization

Huang, Chih-Yung; Gregory, James W.; Sullivan, John P.

doi:10.1088/0957-0233/18/5/n04

Cited by 19 publications

(13 citation statements)

References 6 publications

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“…The reference image will be used for normalization with the traditional schlieren image, and the process can eliminate the noise from the back ground and the non-uniform illumination, and improve the contrast. To investigate the flow field in the micronozzle, the images collected with modified schlieren technique are used to help analysis the PSP data (Huang et al, 2007b). …”

Section: Modified Schlieren Techniquementioning

confidence: 99%

Flow visualization and pressure measurement in micronozzles

Huang

Gregory

Sullivan

2007

J Vis

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Micro devices have been widely used in aerospace engineering for years. Engineers are interested in applications of micro devices such as microjets, micro actuators, and micronozzles. The small size nozzles can be used for attitude adjustment and propulsion of micro-satellites or mini-spacecraft. In this paper, convergent-divergent micronozzles have been investigated at supersonic speed with various total pressures and Reynolds numbers. The throat of the micronozzle is 250 micron wide and the nozzle is designed as de Laval type. For the measurements, the Reynolds number at the throat varies from 1200 to 11000 and total pressure varies from 6 psia to 55 psia. Experimental results are obtained with pressure-sensitive paint for pressure measurement and schlieren imaging for flow visualization. Flow visualization is a challenge for conventional techniques due to the small length scales and small depth of the density gradient. A modified schlieren technique is used to increase the sensitivity by taking the ratio of wind-on and wind-off images. Pressure-sensitive paint is also used to obtain global pressure measurement of the flow field and to compare with the schlieren results.

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Section: Modified Schlieren Techniquementioning

confidence: 99%

Flow visualization and pressure measurement in micronozzles

Huang

Gregory

Sullivan

2007

J Vis

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“…A micro-jet exhausting into vacuum, rather than ambient conditions, has also been investigated using the schlieren technique [40]. A 2D Laval nozzle with a 250 µm throat was used and a jet extending over several millimetres was imaged.…”

Section: Previous Work On Mems Nozzles and Micro-jets And Miniature Smentioning

confidence: 99%

Supersonic jet interactions with a micro-engineered skimmer

Wright¹,

Syms²

2018

J. Micromech. Microeng.

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A micro-engineered, skimmer-based vacuum interface has been demonstrated and used to investigate gas dynamics on a sub-millimeter length scale. The interface is fabricated as a stacked assembly of silicon dies, based on an anisotropically etched inlet orifice and a pyramidal skimmer cone formed in electroplated nickel. Expansion of gas into vacuum, interaction of a supersonic jet with the skimmer and transmission of a collimated beam into a second vacuum stage have all been imaged with a schlieren microscope. Using a glasswalled vacuum chamber, flow patterns upstream and fully downstream of the skimmer have been imaged together for the first time. At low first-stage pressures, the 150-200 µm tall skimmers cannot fully penetrate the shock arising from interaction of the jet with the back wall. However, as the pressure is increased, a multiple shock cell structure evolves, the jet narrows and transmission rises sharply. Eventually, a collimated beam is transmitted to the second stage. When the skimmer aperture is smaller than the source aperture, a series of distinct peaks is evident in a plot of transmission against first-stage pressure. Imaging shows that at each successive peak, the number of shock cells increases by one and the skimmer inlet is coincident with a node.

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“…Wereley et al (2007) used the same technology to visualize the fluid flow through a macroscale thruster. Huang et al (2007) modified the Schlieren photography technique to visualize supersonic flow through a micro-nozzle and measured the magnitude of the resulting shock wave.…”

Section: Introductionmentioning

confidence: 99%

Studying on water nanojet ejection and the wetting phenomena on the nozzle surface

Lin

2012

Microfluid Nanofluid

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In this research, molecular dynamics simulations of water nanojet ejection out of nozzle holes with various sizes under various pressing forces are performed. The water molecules are ejected out the nozzle by a back plate on which a constant force is applied. The results of MD simulations of water ejection show that after one ejection, about 1.3-2.5% of total molecules accumulate on the nozzle plate surface. These molecules affect the ejection of water jet thereafter. The cause of the accumulation of wetting water is investigated by analyzing the trajectories of these molecules. It is found that in the firing chamber near the nozzle plate wall, the arrangement of water molecules is aligned by the surface topology of the metal wall. Water molecules are packed into filamentous structure and these lines stack up at equal distances to each other. Water molecules drift along these lines, the trajectories of these molecules are sinuous, the velocity directions of them are random; molecules drift along the parallel lines until they reach a region of low pressure beneath the nozzle opening. These molecules eject out through the edge of the nozzle, they fall back on to the nozzle surface and eventually deposit on the nozzle surface due to low ejection velocity.

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A modified schlieren technique for micro flow visualization

Cited by 19 publications

References 6 publications

Flow visualization and pressure measurement in micronozzles

Flow visualization and pressure measurement in micronozzles

Supersonic jet interactions with a micro-engineered skimmer

Studying on water nanojet ejection and the wetting phenomena on the nozzle surface

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