Investigation of the effects of air injection on the unsteady sheet/cloud cavity behaviors

Asian Working Group- IAHR's Symposium on Hydraulic Machinery and Systems

Wang, C.C.^1 ; Wang, G.Y.^1 ; Huang, B.^1

School of Mechanical Engineering, Beijing Institute of Technology, Beijing, China^1

关键词: Air injection;    Cavitation number;    Divergent channel;    Power spectral densities (PSD);    Reynold number;    Sheet breakups;    Spectral content;    Transient cavities;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/163/1/012005/pdf
DOI  :  10.1088/1755-1315/163/1/012005

来源: IOP

【 摘 要 】

The objective of this paper is to investigate the effect of air injection on unsteady sheet/cloud cavity behaviors. Experiments are conducted in the divergent section with a ventilation slit downstream the throat of a convergent-divergent channel, using high-speed camera to visualize the transient cavity behaviors. Results are presented for the sheet/cloud cavitation characterized by the periodic large-scale cavity cloud being shed at a cavitation number of σ=0.8 and the Reynold number of Re=0.97×106, for three normalized air injection volume flow rates, namely CI =0, 1.135×10-3 and 2.270×10-3. The results show that air injection can significantly influence the unsteady sheet/cloud cavity behaviors. With the increase of the air injection rate, the length of the attached cavity sheet and the size of the shedding cavity cloud increase. During the attached cavity sheet breakup and being shed process, the distance between the new partial cavity sheet and the shedding cavity cloud increase. The power spectral density (PSD) of the cavity area (Scav /Sthroat ) indicates that, with the increase of the air injection rate, the cavitation cycle decreases and the spectral content attenuates, especially the low spectral between 0-20 Hz which is supposed to be induced by unsteady sheet/cloud cavitation.