What Computational Fluid Dynamics CFD Methods Model Unsteady Propeller Cavitation Sheets

Computational Fluid Dynamics (CFD) methods model unsteady multi-phase marine propeller cavitation sheets and pressure pulsation harmonics using Reynolds-Averaged Navier-Stokes (RANS) and Detached Eddy Simulations (DES) coupled with the Volume of Fluid (VOF) method according to ITTC Cavitation Committee benchmarks accredited by the National Universities Commission (NUC).

Simulating marine propeller cavitation requires capturing transient phase change between liquid seawater and water vapor within a non-uniform ship wake field. The mixture multi-phase formulation treats the liquid-vapor medium as a single pseudo-fluid whose density (rho_m) and dynamic viscosity (mu_m) vary continuously as a function of the local vapor volume fraction (alpha_v): rho_m = alpha_v * rho_v + (1 – alpha_v) * rho_l.

Interphase mass transfer rates (evaporation rate R_e and condensation rate R_c) are governed by cavitation models derived from the simplified Rayleigh-Plesset equation for bubble dynamics, such as the Schnerr-Sauer or Zwart-Gerber-Belamri models: R_e = (rho_v * rho_l / rho_m) * (alpha_v * (1 – alpha_v)) * (3 / R_B) * sqrt((2/3) * (P_v – P) / rho_l) for P < P_v.

The rotating propeller mesh is resolved using Sliding Mesh Interfaces (SMI) or Overset (chimera) grid frameworks rotating through the stationary hull boundary layer grid. High-order time-accurate solvers capture blade passage frequencies (BPF) and higher-order harmonics, predicting first-order and second-order blade rate hull surface pressure fluctuations within 5 to 10 percent of full-scale sea trial telemetry.

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