| Marine propulsors operate in an inherently unsteady flowfield. To design a propulsor that meets the conditions imposed by hydrodynamic and hydroacoustic requirements, knowledge of component interactions and unsteady flow patterns throughout the propulsor is essential. At the present time, the effect of the unsteady flow on the performance of the propulsor is not thoroughly understood. The goal of this work is to use computational fluid dynamics (CFD) coupled with measurements and analytic methods to provide some insight into the physics associated with unsteady propulsor flows.; The unsteady, incompressible Reynolds-Averaged Navier Stokes (RANS) code developed at Mississippi State University has been extended for use in analyzing the unsteady flow interaction between blade rows in relative motion. The approach used to model the dynamic interface between the blade rows is the localized grid distortion technique of Janus. The spatial and temporal discretizations result in third order spatial accuracy and second order (implicit) temporal accuracy.; To validate the dynamic grid capabilities, computed results for the unsteady flow around a two-dimensional hydrofoil undergoing a high, reduced-frequency gust loading are compared with measured data. The unsteady gusts are generated by a pair of oscillating foils (flappers) upstream of the hydrofoil. A dynamic grid is used around the oscillating foils. The results from a parametric study indicate that 500 time steps per flapper period with three subiterations at each time step are sufficient to capture the time-accurate behavior of both the inviscid and viscous flow fields.; The algorithm is then used to compute the unsteady flow through a three-dimensional, high Reynolds number pump consisting of 13 stator blades and 7 rotor blades. A detailed analysis of the primary, secondary and unsteady flow effects is presented along with an investigation of the effects of sub-iterations on the time-accuracy on the solution. The unsteady interaction between the blade rows is apparent in both the stator and rotor blade rows. The computations verify that the potential flow interaction leads to unsteady pressures on the stators and the wake interaction leads to unsteady loadings on the rotor. |
