On the dynamic subgrid scale modeling and mechanism of tip vortex cavitating flows

The urgent need to reduce underwater radiated noise (URN) from marine propellers necessitates the use of tip vortex cavitation (TVC) mitigation strategies. Developing such methods requires an understanding of the TVC mechanism and its contribution to URN. Using our 3D variational finite element solver, we investigate TVC phenomenon in flow over an elliptical NACA662-415 hydrofoil at Re = 8.95 × 10⁵, via dynamic subgrid scale modeling and homogeneous mixture theory. In the first step, we address the lack of grid resolution guidelines by introducing a new length scale based on the radial pressure gradient (∂p/∂r), which is crucial to capture in these simulations. This length scale is related to the priori known flow properties using the Rankine vortex model, lifting line theory and boundary layer thickness, and is employed to establish mesh requirements for simulating TVC accounting for the vortex strength through the vortex Reynolds number (Re_Γ = Γ/ν). In the next step, simulations are conducted for various working conditions to investigate TVC modes and their contribution to the generated noise. We aim to find methods to prevent modes with higher levels of noise and attenuate their adverse effects. The oscillations of cavity radius are studied to understand the underlying physics of cavity oscillation modes. We analyze pressure fluctuations at different locations within the tunnel to identify the signature noise generated by various cavity oscillation modes under different working conditions.