The Influence of Nucleation on Cavitation Inception in Tip-Leakage Flows

<p>Cavitation in tip leakage flow for a stationary hydrofoil analogy is investigated experimentally in a cavitation tunnel. Details of the hydrofoil design process, including the development of rigorous mathematical tools for definition of hydrofoil section geometries and fairing of the tip to suppress flow separation in the gap, are discussed. The experiments were performed for different tip clearances (τ = gap height/maximum profile thickness) and hydrofoil incidences (α), but for a fixed chord based Reynolds number of 3 × 106. The influence of nucleation on cavitation inception is evaluated by performing tests with a natural nuclei population and an abundantly seeded population of large nuclei. Cavitation was characterized using high-speed imaging and acoustic measurements. The hydrofoil design was shown suitable for studying tip leakage flow cavitation, addressing the issues reported in the previous work. Following an initial survey of developed cavitation topology for a range τ and α values, α = 6◦ was selected for more detailed study of cavitation inception. From the acoustic measurements a critical gap height, with the worst performance in terms of cavitation inception, was established at τ = 0.8 for natural nuclei flow. For the abundantly seeded flow cavitation was present for the highest cavitation number achievable in the experimental facility across the complete range of τ values and inception could not have been characterized. Acoustic measurements reveal cavitation to be generally intermittent for natural nuclei flow, becoming continuous as seeding is introduced. While a continuous cavity in the seeded flow resulted with a higher baseline acoustic signature, cavity collapse observed during merging of subsequent events in the natural nuclei flow was observed to be a feature generating the highest instantaneous peaks in the acoustic pressure.</p>