Images of Air Bubbles Included in a Cylindrical Liquid Jet : First Steps for Improving the Caracterisation of the cavitation phenomenon

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Granulométrie et Morphologie des Sprays par Imagerie

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Investigation of air-assisted sprays submitted to high frequency transverse acoustic fields: Droplet clustering

WOS:000404636900052International audienceAn experimental investigation of the effects of a high amplitude transverse acoustic field on coaxial jets is presented in this paper. Water and air are used as working fluids at ambient pressure. The coaxial injectors are placed on the top of a semi-open resonant cavity where the acoustic pressure fluctuations of the standing wave can reach a maximum peak-to-peak amplitude of 12 kPa at the forcing frequency of 1 kHz. Several test conditions are considered in order to quantify the influence of injection conditions, acoustic field amplitude, and injector position with respect to the standing wave acoustic field. A high speed back-light visualization technique is used to characterize the jet response. Image processing is used to obtain valuable information about the jet behavior. It is shown that the acoustic field drastically affects the atomization process for all atomization regimes. The position of the injector in the acoustic field determines the jet response, and a droplet-clustering phenomenon is highlighted in multi-point injection conditions and quantified by determining discrete droplet location distributions. A theoretical model based on nonlinear acoustics related to the spatial distribution of the radiation pressure exerted on an object explains the behavior observed. Published by AIP Publishing

Behaviour of an air-assisted jet submitted to a transverse high-frequency acoustic field

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Experimental investigation of supercritical injection

International audienceOver a certain value of temperature and pressure, known as the critical point, pure fluids enter the supercritical domain where the separation between the liquid and the gas states becomes much less apparent. The clear discontinuity observed when crossing the saturation curve is then replaced by a continuous evolution from liquidlike to gas-like states. Such a behavior can be found in combustion applications such as rocket engines or gas turbines (including turbojets) [1] and their improvements require a better understanding and control of the mixture of fuel and oxidizer. As very few experimental data on the behavior of injection and mixing under supercritical conditions are available in the literature, the modeling of the flame under such conditions lacks data and the validation of the simulations becomes very limited [2]. The objective of this work is to fill this gap by providing experimental quantitative data on a jet of ethane in a high-pressure chamber, filled with nitrogen at rest from atmospheric up to 6 MPa [2]. For example, Fig. 1 shows a jet of ethane (300 K) into nitrogen (333 K) at 4.5 MPa, i.e. below the critical point of ethane, 4.87 MPa. Various injection regimes are studied by shadowgraphy imaging varying the temperature, the pressure as well as the fuel mass flow rate. Then, through adequate post-processing, the spreading angle of the jet is computed, and its evolution analyzed. Finally, a thorough study of the velocity evolution for a supercritical jet is achieved for a broad range of inlet conditions (50 cases) using the Image Correlation Velocimetry (ICV) technique [3]