The Manoeuvring Committee - Final Report and Recommendations to the 23rd ITTC.

Rudder, Propeller and Hull Interaction by RANS

The calculation of the effective wake within the CFD context is usually made by combining a potential-flow method for modeling the propeller forces with a RANS equation solver for simulating the viscous flow around the hull and possible appendages. The different assumptions and/or simplifications made in the potential flow model relative to the viscous flow solver may result in significant errors in the prediction of the effective wake particularly for high loadings. This is especially troublesome for ships with full forms where large differences are expected between the nominal and effective wake, and for special propulsion applications such as contra-rotating units. Such errors are responsible within the hydrodynamic design problem for an unadjusted prediction of the propeller pitch, and within the hydrodynamic analysis problem for a deficient prediction of self-propulsion point. This paper presents an approach based on correction factors which converts propeller-induced velocities approximately estimated via potential flow theory into viscous induced velocities on the basis of a viscous flow RANS analysis. The correction factors are calculated for one reference advance number and work accurately in a neighboring region where the propeller loading may change about ±50 %. This procedure allows controlling one of the errors present in the calculation of effective wakes, namely the error derived from coupling a potential-flow method for the representation of the propeller with a RANS solver. Consequently, it permits calculating the effective wake more precisely. The approach is illustrated for a simple case in which the potential flow model representing the propeller is an actuator disk.

On the enhancement of coupling potential flow models to RANS solvers for the prediction of propeller effective wakes

Within EU Project SUPERPROP, fishing vessels have been studied. Usually their propulsion units consist of ducted propellers in order to provide large thrust in trawling. Rudders may significantly influence the performance of ducted propellers especially if they are located at short distance from the duct. This paper summarizes some of the CFD calculations performed as the starting point for the development of a new propeller design for a reference fishing boat. The basic design performance particulars were obtained from the analysis of the existing conventional ducted propeller installed in the ship. The flow around the original propeller geometry and around one of the alternative designs is simulated using RANS code FINFLO. As a part of the project the rudder blockage effect has been investigated using a quasi-steady approach.

Simulation of the Incompressible Viscous Flow around Ducted Propellers with Rudders Using a RANSE Solver

Gemi Formu, Dümen Ve Pervane Etkileşiminin Sayısal İncelenmesi

A linear method which calculates the steady forces of the propeller-rudder system working in a uniform flow is presented. A propeller with an infinite number of blades is used and modelled by a bound vortex sheet, a hub vortex filament and a series of free vortex sheets with an assumption that the free vortex sheets are undisturbed by the rudder. A lifting-line analysis method is incorporated to estimate the propeller performance characteristics. The rudder is represented by vortex and source/sink filaments on its mean plane. A vortex lattice method is used to estimate the rudder performance characteristics. Comparisons of the steady forces with experiments show a reasonable agreement. A rudder located in the accelerating flow just behind a propeller experiences a pressure drag. It is shown that this drag is an internal force which is counterbalanced by an increased propeller thrust. Due to the propeller induced tangential velocities in the slipstream a rudder thrust is created and the work done by the rudder thrust is a measure of the energy recovered by the rudder. The rudder in the test cases can recover up to 40% of the rotational energy and can increase the open water efficiency by up to 1.7%.

G Dyne

Papers

Study of propeller-rudder interaction based on a linear method