J. J. , J. Hoepffner-acknowledge-gilles-agbaglah, and D. Fuster, Pierre-Yves Lagrée, and Pascal Ray of the Institut D'Alembert for useful discussions on using Gerris We also thank Antoine Delon's kind assistance during our visit to LEGI. This project has been supported by the ANR VAA (ANR-2010-BLAN-0903) program, the ANR DYNAA (ANR-2005-BLAN-0213) program, and the FIRST (Fuel Injector Research for Sustainable Transport)

H. Lefebvre, Atomization and Sprays (Taylor and Francis, 1989.
DOI : 10.1201/9781315120911

P. Bayvel and Z. Orzechowski, Liquid Atomization, 1993.

. Eggers, Nonlinear dynamics and breakup of free-surface flows, Reviews of Modern Physics, vol.69, issue.3, pp.865-929, 1997.
DOI : 10.1103/RevModPhys.69.865

P. Lin and R. D. Reitz, DROP AND SPRAY FORMATION FROM A LIQUID JET, Annual Review of Fluid Mechanics, vol.30, issue.1, pp.85-105, 1998.
DOI : 10.1146/annurev.fluid.30.1.85

C. Lasheras and E. J. Hopfinger, Liquid Jet Instability and Atomization in a Coaxial Gas Stream, Annual Review of Fluid Mechanics, vol.32, issue.1, pp.275-308, 2000.
DOI : 10.1146/annurev.fluid.32.1.275

E. Eggers and . Villermaux, Physics of liquid jets, Reports on Progress in Physics, vol.71, issue.3, p.36601, 2008.
DOI : 10.1088/0034-4885/71/3/036601
URL : https://hal.archives-ouvertes.fr/hal-00098347

D. Duke, J. Honnery, and . Soria, Experimental investigation of nonlinear instabilities in annular liquid sheets, Journal of Fluid Mechanics, vol.5, pp.594-604, 2012.
DOI : 10.1017/S0022112010001217

L. Rayleigh, On the Stability, or Instability, of certain Fluid Motions, Proceedings of the London Mathematical Society, vol.1, issue.1, pp.57-72, 1879.
DOI : 10.1112/plms/s1-11.1.57

. Villermaux, Auto-oscillation et mélange dans lesécoulementsles´lesécoulements recirculants, 1993.

E. Raynal, J. C. Villermaux, E. J. Lasheras, and . Hopfinger, Primary instability in liquid gas shear layers, Proceedings of the 11th Symposium on Turbulent Shear Flows, INP-CNRS-UJF, pp.27-28, 1997.

. Villermaux, On the role of viscosity in shear instabilities, Physics of Fluids, vol.10, issue.2, pp.368-373, 1998.
DOI : 10.1063/1.869529

. Raynal, Instabilitée te n t r a ? ?nementà?nement`?nementà l'interface d'une couche de mélange liquide-gaz, 1997.

B. Rayana, A. Cartellier, and E. J. Hopfinger, Assisted atomization of a liquid layer: Investigation of the parameters affecting the mean drop size prediction, Proceedings of the International Conference on Liquid Atomization and Spray Systems (ICLASS), 2006.
URL : https://hal.archives-ouvertes.fr/hal-00224338

B. Rayana, ContributionàlContribution`Contributionàl'´ etude des instabilités interfaciales liquide-gaz en atomisation assistée et tailles de gouttes, 2007.

J. Matas, S. Marty, and A. Cartellier, Experimental and analytical study of the shear instability of a gas-liquid mixing layer, Physics of Fluids, vol.23, issue.9, p.94112, 2011.
DOI : 10.1063/1.3642640
URL : https://hal.archives-ouvertes.fr/hal-00644002

M. Otto, T. Rossi, and . Boeck, Viscous instability of a sheared liquid-gas interface: Dependence on fluid properties and basic velocity profile, Physics of Fluids, vol.25, issue.3, p.32103, 2013.
DOI : 10.1063/1.4792311
URL : https://hal.archives-ouvertes.fr/hal-01447120

J. Fuster, S. Matas, S. Marty, J. Popinet, A. Hoepffner et al., Primary atomization regimes in two planar coflowing fluid sheets, J. Fluid Mech

M. Huerre and . Rossi, Hydrodynamic instabilities in open shear flows Hydrodynamics and Nonlinear Instabilities, pp.81-386, 1998.
DOI : 10.1017/cbo9780511524608.004

E. Marmottant and . Villermaux, On spray formation, Journal of Fluid Mechanics, vol.498, pp.73-111, 2004.
DOI : 10.1017/S0022112003006529
URL : https://hal.archives-ouvertes.fr/hal-00014875

. Hong, Atomization et mélange dans les jets coaxiaux liquide-gaz, 2003.

S. Yecko and . Zaleski, Transient growth in two-phase mixing layers, Journal of Fluid Mechanics, vol.528, pp.43-52, 2005.
DOI : 10.1017/S0022112005003307

J. Boeck, E. Li, P. López-pagés, S. Yecko, and . Zaleski, Ligament formation in sheared liquid???gas layers, Theoretical and Computational Fluid Dynamics, vol.14, issue.6, pp.59-76, 2007.
DOI : 10.1007/s00162-006-0022-1

-. Ng, R. Sankarakrishnan, and K. A. Sallam, Bag breakup of nonturbulent liquid jets in crossflow, International Journal of Multiphase Flow, vol.34, issue.3, pp.241-259, 2008.
DOI : 10.1016/j.ijmultiphaseflow.2007.07.005

E. Scharfman and A. H. Techet, Bag instabilities, Physics of Fluids, vol.24, issue.9, p.91112, 2012.
DOI : 10.1063/1.4748933

. Jeffreys, On the Formation of Water Waves by Wind, Proc. R. Soc, pp.189-206, 1925.
DOI : 10.1098/rspa.1925.0015

. Jeffreys, On the Formation of Water Waves by Wind, Proc. R. Soc, pp.241-247, 1926.
DOI : 10.1098/rspa.1925.0015

H. Peregrine, Breaking Waves on Beaches, Annual Review of Fluid Mechanics, vol.15, issue.1, pp.149-178, 1983.
DOI : 10.1146/annurev.fl.15.010183.001053

L. Banner and W. K. Melville, On the separation of air flow over water waves, Journal of Fluid Mechanics, vol.47, issue.04, pp.825-842, 1976.
DOI : 10.1063/1.1692549

L. Banner, The influence of wave breaking on the surface pressure distribution in wind???wave interactions, Journal of Fluid Mechanics, vol.88, issue.-1, pp.463-495, 1990.
DOI : 10.1007/BF02113819

H. Reul, J. P. Branger, and . Giovanageli, Air flow separation over unsteady breaking waves, Physics of Fluids, vol.11, issue.7, pp.1959-1961, 1999.
DOI : 10.1063/1.870058
URL : https://hal.archives-ouvertes.fr/hal-00106741

K. Melville, F. Veron, and C. J. White, The velocity field under breaking waves: coherent structures and turbulence, Journal of Fluid Mechanics, vol.454, pp.203-233, 2002.
DOI : 10.1017/S0022112001007078

A. C. Alexakis, L. J. Calder, R. Dursi, J. W. Rosner, B. Truran et al., On the nonlinear evolution of wind-driven gravity waves, Physics of Fluids, vol.16, issue.9, pp.3256-3268, 2004.
DOI : 10.1063/1.1771695

H. Reul, J. P. Branger, and . Giovanageli, Air Flow Structure Over Short-gravity Breaking Water Waves, Boundary-Layer Meteorology, vol.21, issue.5, pp.477-505, 2008.
DOI : 10.1007/s10546-007-9240-3
URL : https://hal.archives-ouvertes.fr/hal-00193129

P. Sullivan and J. C. Mcwilliams, Dynamics of Winds and Currents Coupled to Surface Waves, Annual Review of Fluid Mechanics, vol.42, issue.1, pp.19-42, 2010.
DOI : 10.1146/annurev-fluid-121108-145541

J. P. Touboul, C. Giovanangeli, E. Kharif, and . Pelinovsky, Freak waves under the action of wind: experiments and simulations, European Journal of Mechanics - B/Fluids, vol.25, issue.5, pp.662-676, 2006.
DOI : 10.1016/j.euromechflu.2006.02.006
URL : https://hal.archives-ouvertes.fr/hal-00703734

J. P. Kharif, J. Giovanangeli, L. Touboul, E. Grare, and . Pelinovsky, Influence of wind on extreme wave events: experimental and numerical approaches, Journal of Fluid Mechanics, vol.173, pp.209-247, 2008.
DOI : 10.1016/j.euromechflu.2006.02.006
URL : https://hal.archives-ouvertes.fr/hal-00159430

C. Pilch and . Erdman, Use of breakup time data and velocity history data to predict the maximum size of stable fragments for acceleration-induced breakup of a liquid drop, International Journal of Multiphase Flow, vol.13, issue.6, pp.741-757, 1987.
DOI : 10.1016/0301-9322(87)90063-2

. Villermaux, Fragmentation, Annual Review of Fluid Mechanics, vol.39, issue.1, pp.419-446, 2007.
DOI : 10.1146/annurev.fluid.39.050905.110214
URL : https://hal.archives-ouvertes.fr/hal-00435635

B. Villermaux and . Bossa, Single-drop fragmentation determines size distribution of raindrops, Nature Physics, vol.15, issue.9, pp.697-702, 2009.
DOI : 10.1175/1520-0469(1969)026<0545:OOSDOH>2.0.CO;2
URL : https://hal.archives-ouvertes.fr/hal-00426817

. Popinet, Gerris: a tree-based adaptive solver for the incompressible Euler equations in complex geometries, Journal of Computational Physics, vol.190, issue.2, pp.572-600, 2003.
DOI : 10.1016/S0021-9991(03)00298-5
URL : https://hal.archives-ouvertes.fr/hal-01445436

. Popinet, An accurate adaptive solver for surface-tension-driven interfacial flows, Journal of Computational Physics, vol.228, issue.16, pp.5838-5866, 2009.
DOI : 10.1016/j.jcp.2009.04.042
URL : https://hal.archives-ouvertes.fr/hal-01445445

S. Scardovelli and . Zaleski, DIRECT NUMERICAL SIMULATION OF FREE-SURFACE AND INTERFACIAL FLOW, Annual Review of Fluid Mechanics, vol.31, issue.1, pp.567-603, 1999.
DOI : 10.1146/annurev.fluid.31.1.567

R. Tryggvason, S. Scardovelli, and . Zaleski, Direct Numerical Simulations of Gas-liquid Multiphase Flows, 2011.

R. Hoepffner, S. Blumenthal, and . Zaleski, Self-Similar Wave Produced by Local Perturbation of the Kelvin-Helmholtz Shear-Layer Instability, Physical Review Letters, vol.106, issue.10, p.104502, 2011.
DOI : 10.1103/PhysRevLett.106.104502

J. Orazzo and . Hoepffner, The evolution of a localized nonlinear wave of the Kelvin???Helmholtz instability with gravity, Physics of Fluids, vol.24, issue.11, p.112106, 2012.
DOI : 10.1063/1.4767512

K. Batchelor, An Introduction to Fluid Dynamics, 2000.
DOI : 10.1017/CBO9780511800955

E. Dimotakis, Two-dimensional shear-layer entrainment, AIAA Journal, vol.24, issue.11, pp.885-889, 1986.
DOI : 10.2514/3.9525