Ship motions in seaway can result in the partial or full emergence of the propeller. In these situations the propeller ventilates, which causes strong variations in thrust and torque. The latter can contribute to enhanced damage risks and life-cycle costs. The primary objective of the joint industrial/academic project is to gain knowledge about the dynamic loads during (partial) emergence. The exploitation of the results should ensure optimum reliability of new designs and enable operational guidance on existing systems.
The comprehensive project involves full-scale investigations, model-scale tests as well as numerical investigations in order to establish a fine grasp of the involved phenomena (e.g. scaling, seaway, submergence effects). TUHH focuses on the development of improved prediction methods for forces and moments acting on the propeller blades and on the shaft. The approach involves different numerical methods, which have to be improved in order to accurately capture the related effects.
Figure 1: Viscous flow simulation of a ventilating propeller operating in the vicinity of the undisturbed free-surface.
For calculating the unsteady flow around the propeller, different numerical methods will be used and developed in order to obtain a better understanding of the physical effects. The final aim is to establish an efficient viscous/inviscid-coupling procedure for ventilating propellers behind a ship. All methods are validated against measurements performed by the project partners. Moreover, scaling effects will be investigated in order to support the extrapolation of model-test results to full scale.
The respective coupling consists of three software parts
- for the viscous calculations of the floating vessel, the in-house code FreSCo and the commercial solver CFX will be used,
- the inviscid in-house propeller simulation code (panMare-Hydro) is used for the simulations of the ventilating propeller flow,
- a coupling algorithm between the inviscid and the viscous solver will be established, which combines the advantages of both methods. Accordingly, an actuator-disc model is used within the viscous solver. The body forces for the propeller model are calculated using the inviscid solver while the input for the inviscid solver (velocity distribution in front of the propeller and the position of the free surface) is provided by the viscous solver.
Figure 2: Result example of the inviscid solver IST-Hydro
Norsk Marinteknisk Forskningsinstitutt (MARINTEK)
Norges teknisk-naturvitenskapelige universitet (NTNU)
Rolls-Royce Marine AS
Germanischer Lloyd AG
Farstad Shipping ASA
Figure 3: Result examples of the viscous solvers CFX (left) and FreSCo (right)