Using RANS CFD to determine self-propulsion
As CFD techniques and computer power are developing, the significance of complex CFD simulations as support to traditional towing tank tests, is increasing rapidly.
Especially in the phase of hull form development and optimisation of hull lines and appendages, the numerical self-propulsion simulation plays an important role. To be able to capture the impact of the propeller on the flow field around the rudder, the aft body and the general flow fields, allows for a more accurate prediction of the power demand.
We are currently working on implementing a simple Body-Force propeller model in StarCCM+ to include better simulation of ships during self-propulsion. Body forces are computed by a quasi-steady blade element theory method. This adds more complexity to the flow field and capture more of the rudder-propeller-hull interaction than simpler actuator disk models.
The propeller model computes thrust and torque of the propeller, depending on lift, drag, the hydrodynamic pitch angle, the radial distance to the centre of the propeller and Prandtl’s tip correction factor. The propeller velocity field when working behind the hull shows qualitatively good results when compared to other measurements.
Experimental open water data is used to fine tune the numerical propeller model. The computed self-propulsion results are in quite good agreement with the measured self-propulsion test results from our towing tank.