Comptes Rendus
Combustion, flow and spray dynamics for aerospace propulsion
Study of a liquid–gas mixing layer: Shear instability and size of produced drops
Comptes Rendus. Mécanique, Volume 341 (2013) no. 1-2, pp. 26-34.

We study experimentally the atomization of a thick liquid film by a parallel gas flow, in order to understand the conditions of destabilization of the liquid film and the conditions of drop creation. We study in particular the regimes at low M (ratio of gas/liquid dynamic pressures), to test the scaling law proposed and validated in previous studies at large M (M=16).

The spatial inviscid stability analysis of the system is carried out with a new velocity profile taking into account the wake of the splitter plate (zero speed at the level of the splitter plate): the influence of liquid velocity on the shear instability frequency turns out to be significantly stronger for this type of velocity profile than for continuous profile.

An asymptotic study of the dispersion relation leads to a new scaling law giving the wavenumber of the shear instability as a function of gas velocity Ug, with a corrective term in M. Frequency measurements carried out by a spectral method show a good agreement with this corrected law.

We investigate by way of optical probe measurements the size distribution of produced drops downstream. The difficulty of these measurements live in the decrease of the number density flux of drops at low M. Results obtained for the mean chord are consistent with previous studies. Diameter distributions are obtained from chord distributions with a numerical conversion procedure.

Nous étudions expérimentalement lʼatomisation dʼune nappe liquide par un courant parallèle gaz, afin de comprendre les conditions de déstabilisation de la nappe liquide et les conditions de formation de gouttes. Nous étudions en particulier les régimes de faible M (rapport de pression dynamique gaz/liquide), afin de tester les lois dʼéchelle mises en évidence lors dʼétudes précédentes et validées sur un régime à grand M (M=16).

Lʼanalyse de stabilité inviscide du système est menée avec un nouveau profil de vitesse prenant en compte le sillage de la plaque séparatrice (vitesse nulle au niveau de la plaque de séparation) : lʼinfluence de la vitesse de phase liquide sur la fréquence de lʼinstabilité de cisaillement est significativement plus forte pour ce type de profil de vitesse que pour les profils classiques. Une étude asymptotique de la relation de dispersion permet de trouver une nouvelle loi dʼéchelle reliant le nombre dʼonde du mode le plus instable à la vitesse gaz Ug, avec un correctif en M. Les mesures de fréquence réalisées par une méthode spectrale montrent un bon accord avec cette loi dʼéchelle corrigée.

Connaissant les mécanismes en amont nous nous intéressons également aux distributions de taille de gouttes en aval, mesurées par sonde optique. La diminution du flux numérique de goutte et le changement des plages de vitesse des fluides à faible M rendent les mesures plus complexes. Les résultats sur les cordes moyennes mesurées sont cohérents avec les études précédentes.

Published online:
DOI: 10.1016/j.crme.2012.10.009
Keywords: Combustion, Liquid–gas mixing layer, Stability analysis, Droplet
Mot clés : Combustion, Couche de mélange liquide gaz, Analyse de stabilité, Distributions de taille de gouttes

Sylvain Marty 1; Jean-Philippe Matas 1; Alain Cartellier 1

1 Laboratoire des écoulements géophysiques et industriels (LEGI), CNRS – Université de Grenoble, BP53 38041, Grenoble cedex 9, France
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Sylvain Marty; Jean-Philippe Matas; Alain Cartellier. Study of a liquid–gas mixing layer: Shear instability and size of produced drops. Comptes Rendus. Mécanique, Volume 341 (2013) no. 1-2, pp. 26-34. doi : 10.1016/j.crme.2012.10.009. https://comptes-rendus.academie-sciences.fr/mecanique/articles/10.1016/j.crme.2012.10.009/

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