Jean-Pierre Prenel

Visualisation des ondes de choc dans un ejecteur supersonique

Abstract Shock waves generated in a supersonic ejector are visualized by light scattering by use of a laser beam directed into a region where jet expansion gives rise to a high density of tiny droplets.

An optical analysis of an induced flow ejector using light polarization properties

This paper presents an optical analysis of an induced flow ejector by means of plane laser sheets. The visualization method, which is developed here, takes advantage of the polarization properties of the light scattered by the fine droplets produced by condensation within the flow. This optical analysis shows that the droplets scatter near the Rayleigh scattering regime, thereby proving that their mean radius does not exceed 0.05 μm. Furthermore, the injection of depolarizing tracers into the induced stream makes it is possible to distinguish visually between the supersonic primary jet and the subsonic induced stream, and to obtain information about the mixing of the two streams.

Interface measurement technique for liquid film flowing inside small grooves by laser induced fluorescence

Abstract During the recent past, an optical investigation method of liquid films flowing within grooves of small dimensions, was developed by our research team. This non-intrusive method, based on the visualization of a transverse flow section, uses the laser induced fluorescence and image processing techniques in order to characterize the geometry of the liquid–gas interface. This article proposes to describe the principle and the practical application of this method and to present its possibilities through a certain number of applications carried out within our laboratory on isothermal flows and two-phase flows running in small grooves.

Theoretical and experimental intensity analysis of laser light sheets for flow visualization

Abstract The use of thermoelectric microsensors to control energy profiles of laser sheets is proposed. The correlation between calculated and measured light distributions is presented for two types of laser sheets used in flow visualization techniques; choice criteria are deduced.

Micropositioning and intensity analysis of laser beam waists by means of thermoelectric sensors

Abstract The use of thermoelectric microsensors to control the position, focusing and energy profile of laser beam waists is proposed. Two different types of sensors are tested: rectilinear junctions and reticles, the junction diameter being about 12 μm.

Performance limits of microthermocouples as opto-thermal sensors

Abstract Recently the authors showed practical applications of thermoelectric sensors for optics and laser characterization. Now the use of thinner probes is proposed and the consequences on its possible application field. The diameter of these thermocouples is about 5 μm, and allow experimental investigations in a brief measurement time and the visualization - for compatible dimensions - of optical phenomena as thin as interferometric fringes.

Analyse tomographique d'écoulements tridimensionnels par nappes laser en translation

Abstract In a recent article, we have presented a general method for three-dimensional flow visualizations using the sweep of a laser pencil. Its principal restriction is the stroboscopic effect which is induced by the interaction between the tracer movements and the laser beam motion; this prohibits especially the flow studies in some ranges of velocity. In this paper, we propose a complementary method using a static laser sheet whose movement of translation is synchronized with the photographic recording. This electro-optical device allows the tomographic analysis of the stream with a short operating time.

Wavelength tunable particle velocimetry for flow measurements

The use of polychromatic sequential light pulses in particle streaking and tracking velocimetry is proposed. The main advantage of this technique is the easy determination of the velocity direction, even in recycling flows. The method has been validated on a hydrodynamic flow, in the wake of a conventional cylindrical model.

Visualisations tridimensionnelles d'écoulements non axisymétriques par balayage programmé d'un faisceau laser

Abstract Previous articles described new methods of tomographic flow visualizations by means of plane laser light sheets. This paper shows new improvements of these methods using 2D sweeps of a laser pencil which generate 3D dynamical light sheets. Two examples are presented: very slow flows (heat convection) and fast flows (supersonic velocities).

Analyse quantitative par moyens optiques des instabilities d'ecoulement en regime supersonique

Abstract Previous articles described a method of tomographic visualizations of turbulent mixing zones, stationary structures and instabilities in supersonic flows. This paper shows new improvements of this method which thus becomes quantitative and able to give the nature of such instabilities (unstationary flow) and the parameters of the shock waves oscillations.