Newsletter 2023.10 Index
Theme : "AJK FED 2023"
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Unsteady Characteristic of Tip Leakage Vortex Cavitation in the Occurrence of Cavitation Instability in Inducer
 Koki TAMURA Tohoku University，  Yuto NAKURA Tohoku University，  Satoshi KAWASAKI Japan Aerospace Exploration Agency，  Yuka IGA Tohoku University |
Abstract
Cavitation is a phase change phenomenon from liquid to gas that occurs in the low-pressure region of high-speed fluid machinery. In liquid rocket inducer, the tip leakage vortex cavitation (T.L.V.C.) is the primary occurrence, and unsteady oscillation of T.L.V.C. causes pump unstable, called cavitation instability. This instability frequently encountered during the development of the turbopump. Therefore, it is crucial to elucidate the unsteady characteristics of T.L.V.C. as a cause of cavitation instability. The present study focuses on T.L.V.C. arising in the inducer, with particular emphasis on cavity length. Additionally, the fundamental characteristics of T.L.V.C. arising in NACA0009 hydrofoil with tip clearance is also examined to consider the characteristics of T.L.V.C. in the inducer.
The tested inducer and hydrofoil are depicted in Fig. 1 and 2. Cavitation was visualized to determine the cavity length and frequency of cavity oscillation in both experiments, and the Strouhal number based on cavity length (
) was calculated.
In the inducer experiment, it was found that the characteristic of 
of T.L.V.C. in the occurrence of cavitation surge (C.S.) differ from that of T.L.V.C. in super-synchronous rotating cavitation (super-S R.C.). The result of 
in super-S R.C. at the beginning to the middle is consistence with that of T.L.V.C. arising in the hydrofoil. However, the characteristic of 
of T.LV.C. at the end of super-S R.C. showed a different trend than before. Assuming that the characteristic of 
of T.L.V.C. arising in the hydrofoil represents the natural oscillation characteristic of T.L.V.C., the T.L.V.C. at the beginning to the middle of super-S R.C. oscillate naturally. Subsequently super-S R.C. ended when the T.L.V.C. become less prone to oscillation and starts transitioning to different mode of oscillation. In contrast, the T.L.V.C. in the occurrence of C.S., which has different characteristic of 
from T.L.V.C. arising in hydrofoil, oscillates unnaturally.
Key words
Rotating Cavitation, Cavitation Surge, Tip Leakage Vortex Cavitation, Inducer, NACA0009
Figures
Fig. 1 Tested inducer (THK inducer).
Fig. 2 Tested hydrofoil (NACA0009).