Fluid Mechanics and Acoustics Laboratory - UMR 5509

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Home > Research Support > Scientific instrumentation > Techniques > Visualization techniques

Visualization techniques

Tracer use

  • on a surface

The tufts approach is probably the simplest way to visualize the flow on a surface.

Caractérisation du bruit de décrochage dynamique en soufflerie (film LMFA)

The oil film technique is used to visualize the flow topology on a wall. The following parietal visualization shows the huge detachment of a turbulent limit layer on a plane plate.

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Bulle de décollement turbulente (photo ETS)
  • in the flow

The tomography allows to observe a flow by visualizing sections of it. To do so, we illuminate a section of this flow with a laser sheet seeded beforehand with thin particles. The particles inside this thin section diffuse the laser light in accordancec with the Lorenz-Mie laws. The lit particles image is recorded with a camera.

Smoke injection in a wind-tunnel

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Enroulement tourbillonnaire dans une cavité (photo LMFA)
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Tourbillons en aval d’une aile delta (photo VKI)
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Visualisation de l’évolution d’un panache de pollution (photo LMFA)

Air bubbles in a hydrodynamic tunnel

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Visualisation par bulles autour d’une maquette d’avion (photo ONERA)

Colored tracers in a hydrodynamic tunnel

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Emissions colorées au bord d’attaque d’une aile delta (photo ONERA)

Optic methods

The optic methods are based on the change of the refractive index of a gas when its density changes. A variable density flow can then be seen as a refractive index field. The measurement of the index leads to the density.

  • [fr]Ombroscopie (Shadowgraph)[en]Shadowgraph

The shadowgraph technique is the simplest way to observe density inhomogeneities. It is a non-intrusive flow visualization technique which consists in placing the disturbed fluid to study between a quasi-point light source and a sensor receiving the light.

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Montage optique Ombroscopie

It highlights the 2nd order refractive index derivative, which is proportional to density variations, so to temperature or to pressure variations.

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Visualisation d’une cellule de choc par ombroscopie (photo LMFA)
  • Schlieren

The schlieren technique is set up with a light source, two lenses or mirrors and a cutter. It is a technique close to the shadowgraph one but the light not deflected by the flow index gradient is suppressed by a cutter.

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Montage optique Strioscopie

It highlights the 1st order refractive index derivative, which is related to density variations, so to temperature or to pressure variations. The schlieren technique offers a high dynamics of the gray levels of the photo. The vertical or horizontal position of the cutter also allows to choose the direction of the variations to observe.

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Image strioscopique instantanée et moyenne d’un jet (photo LMFA)
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Visualisation par strioscopie d’un écoulements compressibles libres (film LMFA)
  • Interferometry

Mach-Zehnder interferometer