Control of cloud cavitation through microbubbles

The dynamics of cloud cavitation about a 3D hydrofoil are investigated experimentally in a cavitation tunnel with deplete, sparse and abundant freestream nuclei populations. The rectangular-planform, NACA 0015 hydrofoil was tested at a Reynolds number of 1.4 × 10⁶, an incidence of 6^◦ and a cavitation number of 0.55. High-speed photography of cavitation shedding phenomena was acquired simultaneously with unsteady force measurement to enable identification of cavity shedding modes corresponding with force spectral peaks. Nuclei populations were varied through the injection of polydisperse microbubbles. Both the deplete and abundant cases were characterised by large-scale cloud cavitation. For a sparsely seeded flow, however, coherent fluctuations are significantly reduced due to random nuclei activation and cavity breakup resulting in minimum relative unsteady lift.