实验空化混合层的速度场分析

The purpose of this experimental study was to analyze a two-dimensional cavitating shear layer.
The global aim of this work was to improve understanding and mode领 of cavitation
phenomena, from a 2D turbulent shear flow to rocket engine turbopomp inducers. This 2D mixing
layer flow provided us with a well documented test case to be used for comparisons between
behavior with and without cavitation. Similarities and differences enabled us to characterize the
effects of cavitation on flow dynamics. The experimental facility enabled us to set up a mixing
layer configuration with different cavitation levels. The development of a velocity gradient was
observed inside a liquid water flow using PIVLIF (particle image velocimetrylaser induced
fluorescence). Kelvin-Helmholtz instabilities developed at the interface and vaporizations and
implosions of cavitating structures inside the vortices were observed. The mixing area grew
linearly, showing a constant growth rate, for the range of cavitation levels studied. The spatial
development of the mixing area seemed hardly to be affected by cavitation. Particularly, the
self-similar behavior of the mean flow was preserved despite the presence of the vapor phase.
Successive vaporizations and condensations of the fluid particles inside the turbulent area
generated additional velocity fluctuations due to the strong density changes. Moreover, when
cavitation developed, the Kelvin-Helmholtz vortex shape was modified, inducing a strong
anisotropy (vortex distortion as ellipsoidal form) due to the vapor phase. The main results of this
study clearly showed that the turbulence-cavitation relationship inside a mixing layer was not
simply a change of compressibility properties of the fluid in the turbulent field, but a mutual
interaction between large and small scales of the flow due to the presence of a two-phase flow. 德国LaVision PIV/PLIF粒子成像测速场仪