Abstract:
Flow around ship hull considering rudder-propeller interaction has always been a subject of great concern both for naval architects and shipyards in order to ensure that a ship can operate efficiently and economically at a desired speed. Although extensive researches concerning the flow around bare ship hull have been carried out in the past decades, the hull-propeller-rudder interaction is very much important for accurate prediction of flow specially at stern region of ship. In this research, the flow around ship hull is numerically simulated considering the hull-propeller-rudder interaction. The effect of rudder positions on propeller efficiency is also determined for different longitudinal distances from propeller.
Firstly, the flow around the bare ship hull is computed using ‘Zonal Approach’. In this approach, ‘potential flow solver’ is used in the region outside the boundary layer and wake whereas ‘boundary layer solver’ is used in thin boundary layer region near the forward half of the hull. On the other hand, viscous flow solver is used in the stern/wake region. Three dimensional Rankine source panel method with non-linear free-surface boundary condition is used to capture free-surface potential flow around ship hull. The results of potential flow solver are provided as an input to boundary layer solver to predict transition and boundary layer parameters on the forward half of the ship. In the stern region where the viscous effects are predominant, RANS (Reynolds-Averaged Navier-Stokes) solver is used to analyze the flow incorporating k-ω SST turbulence model. Propeller open water characteristics are determined utilizing an open source code OpenProp based on Lifting Line theory. The computed open water characteristics are given as input for determining self propulsion characteristics.
To analyze the flow physics and validate computed results, two cases of simulations are carried out with KRISO Container Ship (KCS) and Japan Bulk Carrier (JBC). Free-surface wave pattern, wave elevation and wave making resistance coeffieicent are obtained from potential flow solution. Frictional resistance coefficients are obtained from boundary layer and viscous flow solver respectively. A Verification and Validation (V&V) study for resistance coefficients has also been carried out using ITTC recommended procedure.
To determine open water and self propulsion characteristics, KP 505 and DTMB 4119 propellers are used for KCS and JBC hull respectively. The computed results of propeller open water characteristics show good agreement with the available experiemental results. Semi balanced horn type rudder is used for both hulls to compare self propulsion characteristics at varying rudder positions.
Finally, the flow around ship hull considering rudder-propeller interaction has been computed using RANS solver coupled with Lifting Line theory. All the above mentioned simulations are implemented using commercial Computational Fluid Dynamics (CFD) software ‘Shipflow’ developed by Chalmers University of Technology. It is revealed that CFD can be successfully applied to determine the preliminary resistance and power in maritime industry.
