Open and ducted propeller virtual mass and damping coefficients by URANS-method in straight and oblique flow

The virtual mass and damping coefficients of an open and ducted propeller are determined using URANS computations. Time-accurate simulations are carried out for an open propeller forced to harmonic motion in two separate directions, translational x₁- and rotational x₄- directions. The analysis produces the diagonal coefficients of the virtual mass m₁₁, m₄₄ together with the diagonal damping terms c₁₁, c₄₄. The cross-terms m₁₄, m₄₁ and c₁₄, c₄₁ are also evaluated. A range of advance numbers is considered in the simulations. Several excitation frequencies and amplitudes are applied in order to determine the impact of viscosity on the vibrational coefficients. Oblique flow cases are also considered and the related virtual mass and damping coefficients are analyzed. The computed cases are compared to potential flow simulations and to published semi-empirical results. The average magnitudes of the coefficients correspond quite reasonably to those computed by the CFD method. However, the viscous effects are found to have a certain impact on some coefficients.