Schlieren photography of water flow

Fiedler, H. E.; Nottmeyer, Kay; Wegener, Peter P.; Raghu, S.

doi:10.1007/bf00280452

Cited by 50 publications

(7 citation statements)

References 8 publications

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“…Introduction of a controlled vorticity distribution into the boundary layer of the flow partition by the surface heaters is accompanied by small localized density gradients in the adjacent fluid. The corresponding refractivc index gradients are exploited for flow visualization by means of a sensitive double-pass Schlieren system (Fiedler et al 1985). This technique allows the effect of forcing t o be studied non-intrusively in planes parallel and normal to the flow span.…”

Section: Flow Visualizationmentioning

confidence: 99%

Evolution of stream wise vortices and generation of small-scale motion in a plane mixing layer

Nygaard

Glezer

1991

J. Fluid Mech.

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The evolution of streamwise vortices in a plane mixing layer and their role in the generation of small-scale three-dimensional motion are studied in a closed-return water facility. Spanwise-periodic streamwise vortices are excited by a time-harmonic wavetrain with span wise-periodic amplitude variations synthesized by a mosaic of 32 surface film heaters flush-mounted on the flow partition. For a given excitation frequency, virtually any span wise wavelength synthesizable by the heating mosaic can be excited and can lead to the formation of streamwise vortices before the rollup of the primary vortices is completed. The onset of streamwise vortices is accompanied by significant distortion in the transverse distribution of the streamwise velocity component. The presence of inflexion points, absent in corresponding velocity distributions of the unforced flow, suggests the formation of locally unstable regions of large shear in which broadband perturbations already present in the base flow undergo rapid amplification, followed by breakdown to small-scale motion. Furthermore, as a result of spanwise-non-uniform excitation the cores of the primary vortices are significantly altered. The three-dimensional features of the streamwise vortices and their interaction with the base flow are inferred from surfaces of r.m.s. velocity fluctuations and an approximation to cross-stream vorticity using three-dimensional single component velocity data. The striking enhancement of small-scale motion and the spatial modification of its distribution, both induced by the streamwise vortices, can be related to the onset of the mixing transition.

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Section: Flow Visualizationmentioning

confidence: 99%

Evolution of stream wise vortices and generation of small-scale motion in a plane mixing layer

Nygaard

Glezer

1991

J. Fluid Mech.

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“…In order to generate the conditions required for Schlieren photography in water, Fiedler et al [27] recommended to create gradients in the temperature of the fluid by heating its surface. They found that a temperature difference over the tank depth as minimum as 0.15 °C was enough.…”

Section: Methodsmentioning

confidence: 99%

Study of drag and orientation of regular particles using stereo vision, Schlieren photography and digital image processing

Carranza

Zhang

2017

Powder Technology

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A new experimental, image-based methodology suitable to track the changes in orientation of non-spherical particles and their influence on the drag coefficient as they settle in fluids is presented. Given the fact that non-spherical solids naturally develop variations in their angular orientation during the fall, none-intrusiveness of the technique of analysis is of paramount importance in order to preserve the particle/fluid interaction undisturbed. Three-dimensional quantitative data about the motion parameters is obtained through single-camera stereo vision whilst qualitative visualizations of the adjacent fluid patterns are achieved with Schlieren photography. The methodology was validated by comparing the magnitudes of the drag coefficient of a set of spherical particles at terminal velocity conditions against those estimated from drag correlations published in the literature. A noteworthy similarity was attained. During the fall of non-spherical solids, once the particle Reynolds number approximated 163 for disks, and 240 for cylinders, or exceeded those values, secondary motions composed by regular oscillations and tumbling were present. They altered the angular orientation of the particles with respect to the main motion direction and caused complete turbulent patterns in the surrounding flow, therefore affecting the instantaneous projected area, drag force, and coefficient of resistance. The impact of the changes in angular orientation onto the drag coefficient was shown graphically as a means for reinforcing existing numerical approaches, however, an explicit relation between both variables could not be observed.

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“…Schlieren photography is another wavefront imaging technology for macro wavefront disturbances which is used to capture flows of fluids of varying densities [20][21][22]. It is widely used in aeronautical engineering to photograph the flow of air around an object.…”

Section: Schlieren Photographymentioning

confidence: 99%

Optical Wavefront Detection: A Beginner Tutorial

Zheng¹,

Ibrahim²,

Ng³

et al. 2021

Digital Encyclopedia of Applied Physics

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This article is designed to help readers understand some typical wavefront detection techniques and gain a preliminary understanding of wavefront detection. In this tutorial, the wavefront definition used in wavefront technology is given and we divide wavefront detection technologies into qualitative and quantitative categories. In each category, we discuss some typical systems and provide simulation results. This tutorial comes with Matlab simulation codes that readers can use to simulate mentioned wavefront detection technologies on their computers. We hope that this tutorial provides readers with all the tools needed to understand and simulate the different wavefront technologies and modify them based on their needs and interest.

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Schlieren photography of water flow

Cited by 50 publications

References 8 publications

Evolution of stream wise vortices and generation of small-scale motion in a plane mixing layer

Evolution of stream wise vortices and generation of small-scale motion in a plane mixing layer

Study of drag and orientation of regular particles using stereo vision, Schlieren photography and digital image processing

Optical Wavefront Detection: A Beginner Tutorial

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