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 modeling of cavitationphenomena, from a 2D turbulent shear flow to rocket engine turbopomp inducers. This 2D mixinglayer flow provided us with a well documented test case to be used for comparisons betweenbehavior with and without cavitation. Similarities and differences enabled us to characterize theeffects of cavitation on flow dynamics. The experimental facility enabled us to set up a mixinglayer configuration with different cavitation levels. The development of a velocity gradient wasobserved inside a liquid water flow using PIV–LIF (particle image velocimetry–laser inducedfluorescence). Kelvin-Helmholtz instabilities developed at the interface and vaporizations andimplosions of cavitating structures inside the vortices were observed. The mixing area grewlinearly, showing a constant growth rate, for the range of cavitation levels studied. The spatialdevelopment of the mixing area seemed hardly to be affected by cavitation. Particularly, theself-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 areagenerated additional velocity fluctuations due to the strong density changes. Moreover, whencavitation developed, the Kelvin-Helmholtz vortex shape was modified, inducing a stronganisotropy (vortex distortion as ellipsoidal form) due to the vapor phase. The main results of thisstudy clearly showed that the turbulence-cavitation relationship inside a mixing layer was notsimply a change of compressibility properties of the fluid in the turbulent field, but a mutualinteraction between large and small scales of the flow due to the presence of a two-phase flow.