Multi-scale analysis of a viscoelastic liquid jet

WOS:000403628200001International audienceA multi-scale analyzing tool is now available to investigate the temporal evolution of two phase flows such as liquid systems experiencing an atomization process. Thanks to its multi-scale and global nature, it allows identifying all dynamics simultaneously involved in the process with no restriction of the liquid system shape. In the present work this multi-scale tool is applied on 2D visualizations of free falling jets of a low-viscosity viscoelastic solution. The jets are produced from a cylindrical discharge orifice and the liquid is a very dilute polymer solution containing 5 ppm of Poly(ethylene oxide). High spatial resolution images of the free falling jets are performed as a function of the velocity and at several distances from the discharge orifice. For every operating condition, the liquid jet remains cylindrical first, then shows the development of a sinusoidal perturbation and finally adopts a beads-on-a-string pattern before breakup occurs. The multi-scale analysis is performed on a high number of images and at several spatial positions in order to return statistical and temporal information, respectively. The results of this analysis show that during the sinusoidal perturbation stage, the large-scale region follows an exponential increase as predicted by the linear stability theory and during the beads-on-a-string stage, the small-scale region follows an exponential decrease similar to an elasto-capillary regime from which the relaxation time of the polymer solution can be extracted. This work positions the multi-scale approach as a promising and complementary tool to the currently used techniques in order to probe complex liquid rheology, especially in the case of mobile viscoelastic solutions

Scientific drilling projects in ancient lakes: integrating geological and biological histories

Sedimentary sequences in ancient or long-lived lakes can reach several thousands of meters in thickness and often provide an unrivalled perspective of the lake's regional climatic, environmental, and biological history. Over the last few years, deep drilling projects in ancient lakes became increasingly multi- and interdisciplinary, as, among others, seismological, sedimentological, biogeochemical, climatic, environmental, paleontological, and evolutionary information can be obtained from sediment cores. However, these multi- and interdisciplinary projects pose several challenges. The scientists involved typically approach problems from different scientific perspectives and backgrounds, and setting up the program requires clear communication and the alignment of interests. One of the most challenging tasks, besides the actual drilling operation, is to link diverse datasets with varying resolution, data quality, and age uncertainties to answer interdisciplinary questions synthetically and coherently. These problems are especially relevant when secondary data, i.e., datasets obtained independently of the drilling operation, are incorporated in analyses. Nonetheless, the inclusion of secondary information, such as isotopic data from fossils found in outcrops or genetic data from extant species, may help to achieve synthetic answers. Recent technological and methodological advances in paleolimnology are likely to increase the possibilities of integrating secondary information, e.g., through molecular dating of molecular phylogenies. Some of the new approaches have started to revolutionize scientific drilling in ancient lakes, but at the same time, they also add a new layer of complexity to the generation and analysis of sediment core data. The enhanced opportunities presented by new scientific approaches to study the paleolimnological history of these lakes, therefore, come at the expense of higher logistic, communication, and analytical efforts. Here we review types of data that can be obtained in ancient lake drilling projects and the analytical approaches that can be applied to empirically and statistically link diverse datasets for creating an integrative perspective on geological and biological data. In doing so, we highlight strengths and potential weaknesses of new methods and analyses, and provide recommendations for future interdisciplinary deep drilling projects

Cavitation and primary atomization in real injectors at low injection pressure condition

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Empirical Protocol to Correct Laser-Diffraction Measurements from Multiple-Scattering Effects

The present work addresses the problem of multiple-scattering effects on Laser-Diffraction spray drop-size distribution measurements. The Laser-Diffraction Technique (LDT) is a rather straightforward diagnostic often used in industries and universities to characterize liquid sprays. Recent LDT equipments have been especially conceived for highly transient and dense sprays such as those encountered in car injection applications (direct gasoline injection or diesel injection). In particular, they are equipped with an optional algorithm to correct the effects of multiple-scattering that occurs when the spray density is great. However, experimental investigations of the literature reported that this algorithm was not able to treat all situations. An explanation for this could be found in the assumptions of the model that are often not satisfied by real sprays. For several years, an alternative to this approach has been explored: it consists in establishing an empirical correction protocol. In a recent approach, this empirical correction protocol received a mathematical description. The work in the present contribution generalizes this mathematical model and demonstrates that it is able to describe the influence of multiplescattering for other working conditions. The sprays investigated here are produced by a three-jet gasoline direct injection device. We found that the mathematical model was adaptable to this case. Therefore, the present empirical correction protocol appears to be easily applicable and should be recommended at least to test a theoretical model or at most to replace it

Injector Internal Geometry and Sub-Atmospheric Back Pressure Influence on Low Weber Number Liquid Flow

International audienceThe experimental work presented in this paper investigates the influence of the injector internal geometry on the primary atomization process in sub-atmospheric back pressure condition. A series of four injectors is studied. High-rate shadowgraph films of the liquid flow issuing from the nozzle are performed (66 667 fr/s). In order to have exploitable images, the injection pressure is maintained low (less than 1 MPa). On each image, the interface length per unit liquid surface area, e 2 (0), is measured. The examination of this parameter and of the images reveals that under atmospheric pressure, the primary atomization process is rather independent of the injectors. However, as the ambient pressure decreases, the injectors show different behaviour and the atomization process becomes intermittent. This behaviour is attributed to the apparition of cavitation in the injector. The characteristics of this intermittency are evaluated. Among other results, we observed that atomization process produced by cavitating flows are more sensitive to the injector internal geometry, the intermittency is due to the production of vortex cavitation, and, contrary to what is usually reported in the literature, cavitation does not enhance atomization in the present case. These results, as well as others, are presented and discussed in this paper

Addressing the numerical and experimental study of supercritical fluid flows.

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Cavitation in a Scaled-up 2D-Transparent Nozzle: Experimental Rig Realization & Preliminary Results

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Addressing the numerical and experimental study of supercritical fluid flows.

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Experimental investigation of Ethane and Propane injection under sub- and super-critical conditions

International audienceStudying a fluid flow under high-pressure conditions through reliable experiments is still nowadays a challenge.When the chamber pressure exceeds the critical pressure of working fluids the supercritical state of matter is reached and the distinction between gas and liquid becomes blurred. For such special conditions, experimental data are scarce and need to be consolidated. Indeed, the modification of the local refractive index induced by den- sity gradient needs to be analyzed with appropriate image-based technique.In the present study, the REFINE test bench (Real-gas Effect on Fluid Injection: a Numerical and Experimental study) has been designed at CORIA Lab to study the non-reactive injection of Ethane and Propane into Nitrogen under sub- and supercritical conditions. The ambient gas pressure can be raised up to 6 MPa and warmed up to 573 K to scan sub- and trans-critical injections. The chamber is equipped with two perpendicular optical axes allowing simultaneously different optical diagnostics. Experimental data are collected from shadowgraph and dif- fused backlight illumination techniques. Quantitative measurements of jet spre ding angle and breakup length arecompared to results coming from literature exhibiting multiple flows topologies

Multi-Scale Analysis of the Atomization of the Liquid Sheets issuing from a Compound Nozzle.

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