Response of coaxial air-assisted liquid jets in an acoustic field: atomization and droplets clustering

A. Ficuciello (1) , J. Blaisot (1) , F. Baillot (1) , C. Richard (2) , M. Theron (3)

1 CORIA - Complexe de recherche interprofessionnel en aérothermochimie
2 LMRS - Laboratoire de Mathématiques Raphaël Salem
3 CNES - Centre National d’Études Spatiales [Paris]

High-frequency combustion instabilities have been proven to be extremely harmful to liquid rocket engine operation , even leading to the destruction of the combustion chamber. The coupling between acoustic field and combustion heat release rate in the combustion chamber is considered as the driving phenomenon. Experiments have shown that intense acoustic field can deeply affect atomization process thereby causing a non-uniform heat release distribution which can couple with the resonant mode shapes of the combustion chamber and consequently trigger or sustain combustion instability. The effects of acoustic acting on atomization of coaxial air-assisted liquid jets have been investigated experimentally and results are presented in this paper. The experimental setup is composed of three coaxial injectors installed on the roof of a semi-open resonant cavity provided with 4 compression drivers. An acoustic field corresponding to the 2 nd transverse mode of the cavity is forced into that at a frequency of 1 kHz. Acoustic levels up to 174 dB are produced. High speed visualizations are performed in order to observe the response of the jet to the acoustic perturbations. In the case of low Weber numbers (We < 30) the jet can be considered as cylindrical and depending on the position of the injector with respect to the acoustic axis different responses can be observed. If the injector is placed in correspondence of the velocity antinode the jet is flattened into a liquid sheet perpendicular to the acoustic axis, if the injector is located in correspondence of an intensity antinode the jet is deviated toward the velocity antinode. Combined response can be observed at intermediate positions. For higher Weber numbers the jet is no more cylindrical and a spray is formed, characterized by with a certain spray angle. Such a spray is can still be affected by the acoustics but it is not always possible to get evidence of this from observation of raw images. To quantify these effects, image analyses have been carried-out to determine how spatial distributions of droplets are affected by acoustics. Results are presented for Weber numbers ranging from 30 to 1500, with and without acoustic. Clustering of droplets is shown as well as improvement of atomization process.

Mots clés: Atomization; acoustics; combustion instability; liquid rocket engine

Domaines: Acoustique [physics.class-ph]; Mécanique des fluides [physics.class-ph]

A. Ficuciello, J. Blaisot, F. Baillot, C. Richard, M. Theron. Response of coaxial air-assisted liquid jets in an acoustic field: atomization and droplets clustering. ICLASS 2015, Aug 2015, Tainan, Taiwan. ⟨hal-02370084⟩