| Part of the ship resistance is viscous resistance, which divided into form drag and friction resistance. Many ways to reduce the ship resistance ,with different advantages and disadvantages, long-term concerned by both engineers and academics. This paper relies on the National Natural Science Foundation of "Experimental investigation on the drag reduction by leading edge holes and micro bubbles" (Approval No.10972167), for a medium or low speed ship, using numerical calculation method to study the influence of the drainage opening and export's location, shape, geometry on the flow field around the craft and drag reduction effect, seek the key parameters for effective drag reduction and drag reduction mechanism.This paper targets at one two-tailed full-formed craft with bulbous bow, considering the craft floating positively ,no yaw, neglecting the influence of Free-surface, discussing resistance and flow field characteristics of the craft by numerical calculation. In order to compared with the experimental results conveniently and save computer memory, modeling one side of the hull in the longitudinal section with 1:15.5 scale, calculating the four models respectively: original ship model, stepped ship model, stepped ship model with leading edge holes and non-stepped ship model with leading edge holes. Discussion of the grid type, discrete scheme, turbulence model and other factors on the impact of the numerical results; analyzing the influence around the craft's flow field, pressure distribution, wall shear stress distribution and viscous resistance characteristics by the leading edge holes and stepped bottom under a series of geometric parameters, then obtained the geometric parameters and drag reduction effect of the leading edge holes. The following conclusions:①The result computed by SST k-ωturbulence model sounds more reasonable.②Reasonable choice of the suitable location and geometry parameters for drainage opening and export, besides smoothing the drainage channel or not, have a significant impact on the drag reduction effect. In the calculation, set the drainage opening at the high pressure location on the bow, and place the export at the bottom which stepped from the 14th station, choose 0.0375% of ship draft(T) as the stepped height, adopt smoothly drainage channel, then the total resistance coefficient reduction ratio reaches 2.268%.③Draining form bow to stern on the non-stepped craft, choosing the export position and geometry reasonably, the form drag coefficient decreases drastically.④By changing the position of drainage, outflow, stepped place and the corresponding geometric parameters, the results show that the significant changes of pressure distribution on the bow and stern is the key criterion for its drag reduction.In this paper, only compared the completed a number of examples' results with the result of original craft model data, and the examples were calculated under the simplified premise that the ship is floating positively, no yaw, neglecting the influence of Free-surface. Considering the results of leading edge holes examples should be compared with experimental results, and further studies to determine the key parameters of the effective drag reduction. Limited by the computer configuration, the accuracy of computational results needs to be improved.
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