An experimental study of supersonic microjets

Scroggs, S. D.; Settles, Gary S.

doi:10.1007/bf00189042

Cited by 65 publications

(47 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For under-expanded jets of relatively low Reynolds number, as well as for micro jets, smaller cell spacing values than those derived by Equation (5) have been reported in the literature [23][24][25]. Thicker boundary layers due to low Reynolds numbers and associated viscous effects were suggested as possible causes for this discrepancy.…”

Section: Core Shock Cellsmentioning

confidence: 74%

See 1 more Smart Citation

Gas dynamics and flow characteristics of highly turbulent under-expanded hydrogen and methane jets under various nozzle pressure ratios and ambient pressures

Hamzehloo

Aleiferis

2016

International Journal of Hydrogen Energy

View full text Add to dashboard Cite

The current study used large eddy simulations to investigate the sonic and mixing characteristics of turbulent under-expanded hydrogen and methane jets with various nozzle pressure ratios issued into various ambient pressures including elevated conditions relevant to applications in direct injection gaseous-fuelled internal combustion engines. Due to the relatively low density of most gaseous fuels such as hydrogen and methane, DI requires high injection pressures to achieve suitable mass flow rates for fast in-cylinder fuel delivery and rapid fuel-air mixing. Such pressures typically form an under-expanded fuel jet past the nozzle exit. Test cases of hydrogen injection with nozzle pressure ratio (NPR) of 10 issued into quiescent air with pressure P ∞ ≈1, 5 and 10 bar were simulated. Direct comparison between hydrogen and methane jets with NPR=8.5 and P ∞ ≈1 was also made. The effect of ambient pressure on features of transient development of the nearnozzle shock structure and tip vortices (vortex ring) was investigated. It was observed that at constant NPR, higher ambient pressure resulted in slightly faster formation of the Mach reflection and shorter Mach disk settlement time. Different mechanisms were observed between hydrogen and methane with regards to transient formation of their initial tip vortex rings. It was found that the initial transient tip vortices of hydrogen jets may also contribute to the flow instabilities at the boundary of the intercepting shock and, unlike for methane, promote fuel-air mixing before the Mach reflection. It was also shown that the nearnozzle shock structure was only affected by NPR regardless of the ambient pressure. Furthermore, no flow recirculation zone was found just downstream of the Mach disk, a finding comparable to all previous experimental investigations. Also, it was observed that a locally richer mixture was created for jets with higher NPR or with higher ambient pressure at constant NPR. Based on the results of the current study, correlations were proposed for the shock cell spacing and jet tip penetration of highly under-expanded jets issued from millimetre-size circular nozzles.

show abstract

Section: Core Shock Cellsmentioning

confidence: 74%

“…As discussed earlier, correlations proposed in the literature based on Equation (3) may not be extended as a general formulation for all types of under-expanded jets [23][24][25]. Therefore, Equation (10) should be considered only for highly under-expanded jets under comparable NPR and nozzle scale to those used in the present study.…”

Section: Shock Cell Spacingmentioning

confidence: 98%

Gas dynamics and flow characteristics of highly turbulent under-expanded hydrogen and methane jets under various nozzle pressure ratios and ambient pressures

Hamzehloo

Aleiferis

2016

International Journal of Hydrogen Energy

View full text Add to dashboard Cite

show abstract

“…Light refracted away from the cut-off will pass unobstructed, but light refracted into it will be blocked. For many applications, a razor blade will serve very well as a cut-off, though graded cut-off filters may be used at high magnification, to reduce diffraction [11]. With a straight edge as cut-off, visualization of refraction in different directions is accomplished by rotation of the sample around the optical axis of the setup.…”

Section: Schlieren Imagingmentioning

confidence: 99%

Schlieren imaging of microthruster exhausts for qualitative and quantitative analysis

Lekholm

Palmer

Thornell

2012

Meas. Sci. Technol.

View full text Add to dashboard Cite

Abstract. Schlieren imaging is a method used to visualize differences in refractive index within a medium. It is a powerful and straightforward tool for sensitive and high-resolution visualization of, e.g., gas flows.Here, heated cold gas microthrusters were studied with this technique. The thrusters are manufactured using microelectromechanical systems technology, and measure 22×22×0.85 mm. The nozzles are approximately 20 µm wide at the throat, and 350 µm wide at the exit. Through these studies, verification of the functionality of the thrusters, and direct visualization and of the thruster exhausts was possible. At atmospheric pressure, slipping of the exhaust was observed, due to severe overexpansion of the nozzle. In vacuum (3 kPa), the exhaust was imaged while feed pressure was varied from 100 to 450 kPa. The nozzle was overexpanded, and the flow was seen to be supersonic. The shock cell period was linearly dependent on feed pressure, ranging from 320 to 610 µm. With activated heaters, the shock cell separation increased. The effect of the heaters was more prominent at low feed pressure, and an increase in specific impulse of 20% was calculated. It was also shown that schlieren imaging can be used to detect leaks, making it a valuable, safe, and noninvasive aid in quality control of the thrusters.

show abstract

“…For optically transparent fluids mixing in optically transparent microstructures, microscale schlieren technique 3,[9][10][11][12][13][14] provides an attractive alternative to analyze mixing inhomogeneity. In the past, microscale schlieren technique has been mostly used to visualize compressible flow [9][10][11][12][13]15 or phase gradient 16 .…”

Section: Introductionmentioning

confidence: 99%

“…In the past, microscale schlieren technique has been mostly used to visualize compressible flow [9][10][11][12][13]15 or phase gradient 16 . Microscale schlieren technique benefits from both a simple optical layout and high sensitivity and enables not only the non-invasive investigation of specific flow feature that causes optical disturbance but is well suited for use in assessing mixing.…”

Section: Introductionmentioning

confidence: 99%

Analyzing Mixing Inhomogeneity in a Microfluidic Device by Microscale Schlieren Technique

Sun

Hsiao

2015

JoVE

View full text Add to dashboard Cite

In this paper, we introduce the use of microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. The microscale schlieren system is constructed from a Hoffman modulation contrast microscope, which provides easy access to the rear focal plane of the objective lens, by removing the slit plate and replacing the modulator with a knife-edge. The working principle of microscale schlieren technique relies on detecting light deflection caused by variation of refractive index [1][2][3] . The deflected light either escapes or is obstructed by the knife-edge to produce a bright or a dark band, respectively. If the refractive index of the mixture varies linearly with its composition, the local change in light intensity in the image plane is proportional to the concentration gradient normal to the optical axis. The micro-schlieren image gives a twodimensional projection of the disturbed light produced by three-dimensional inhomogeneity.To accomplish quantitative analysis, we describe a calibration procedure that mixes two fluids in a T-microchannel. We carry out a numerical simulation to obtain the concentration gradient in the T-microchannel that correlates closely with the corresponding micro-schlieren image. By comparison, a relationship between the grayscale readouts of the micro-schlieren image and the concentration gradients presented in a microfluidic device is established. Using this relationship, we are able to analyze the mixing inhomogeneity from associate micro-schlieren image and demonstrate the capability of microscale schlieren technique with measurements in a microfluidic oscillator 4 . For optically transparent fluids, microscale schlieren technique is an attractive diagnostic tool to provide instantaneous full-field information that retains the three-dimensional features of the mixing process. Video LinkThe video component of this article can be found at

show abstract

An experimental study of supersonic microjets

Cited by 65 publications

References 9 publications

Gas dynamics and flow characteristics of highly turbulent under-expanded hydrogen and methane jets under various nozzle pressure ratios and ambient pressures

Gas dynamics and flow characteristics of highly turbulent under-expanded hydrogen and methane jets under various nozzle pressure ratios and ambient pressures

Schlieren imaging of microthruster exhausts for qualitative and quantitative analysis

Analyzing Mixing Inhomogeneity in a Microfluidic Device by Microscale Schlieren Technique

Contact Info

Product

Resources

About