A Practical Approach for Design of Marine Propellers with Systematic Propeller Series
Original scientific paper Although there have been important developments in marine propellers since their first use in 1850, the main concept has been conserved. Parallel to the developments in the computer technologies in the past 50 years, methods based on the circulation theory are often used for the design and analysis of propellers. Due to the ability to predict the propulsion performance with just a few design parameters, the use of systematic propeller series based on open water model experiments is still widespread. The design with standard propeller series is usually made with diagrams developed from model experiments. Reading errors during the use of these diagrams are inevitable. In the presented study a practical approach is developed for preventing reading errors and time loss during the design with standard propeller series. A practical approach based on empirical formulas for the design and performance prediction for four-bladed Wageningen B propeller series is presented, and design applications for three propellers with different loading conditions are realized. The results obtained from the presented method are compared with those of open water diagram data and a good agreement between the results is observed.
New developments and propeller design
The use of newly available tools in propeller design is discussed. It is stated that new tools are too much used to imitate experimental results. The paper takes a step back and investigates new approaches to ship propeller design in which new tools are better integrated or calibrated.
Unsteady Wake Alignment for Propellers in Nonaxisymmetric Flows
A low-order boundary element method is applied to predict the trailing wake geometries shedding from hydrofoil and marine propellers in steady and unsteady flows, as well as the vortex motions of the classical lifting line problem with elliptic loading distribution. In order to prevent the numerical instability near the vortex roll-up region, a tip vortex with finite core size is introduced at the end of the vortex line (or at the tip of the wake sheet in the case of a three-dimensional problem), and the induced velocities are evaluated at the displaced control points instead of the actual control points on the vortex (or wake) panels. Green's integral equation with boundary conditions is formulated based on the perturbation potential and solved for the potentials on the lifting bodies and the tip vortex surface. The three-component velocities on the tip vortex surface are computed by numerically differentiating the solution potentials, and the induced velocities on the wake surface are directly determined from the integral equation derived from analytical differentiation of Green's integral equation. The new geometries of the vortex line or the trailing wake as well as the location of the tip vortex core center are then determined by aligning them to the flow so that the force-free condition is satisfied on the wake. The method is applied for the two-dimensional and three-dimensional problems, and validated with experiments and other numerical methods in terms of tip vortex trajectory and blade forces.