The Drag Reduction Research Based On Improving Flow Field Characteristic Of Ship Bow And Stern

Following the appearance of new material and new process, the research on ship's technology of energy conservation and drag reduction obtains rapid development. For most ships, the viscous resistance shares the largest part of the total drag. With large-scale, specialized and integrated for international ocean ships, the big block coefficient ships are well received and more and more scholars put their attentions on research of viscous resistance reduction.The drag reduction technology of leading edge holes dates from blunt body ambient flow. Through opening a hole in the higher-pressure region of bow and leading water to the afterbody, the technology can realize viscous resistance reduction. The application foundation:1) opening hole decreases the pressure difference and reduces the form resistance.2) opening hole changes flow field distribution in ship bow and stern, delays the transition from laminar flow to turbulence flow and reduces the friction resistance.This paper relies on the State Natural Sciences Foundation of "Experimental investigation on the drag reduction by leading edge holes and micro bubbles" (NO.10972167),adopts the numerical calculation method to analyze the influence of drag reduction by opening hole in the higher-pressure region of bow .The research purpose is to obtain the holes parameter under the condition of having effective drag reduction, and provide the reference for the technology's application on the model and full-scale ship.The object of study is a low-speed and two-tailed ship with no bulbous bow, and the modeling adopts the experiment scale(λ,=8.3).The paper discusses the influence of different turbulence model, different grid type and different discretization scheme on the numerical results in the prototype numerical calculation and gets the reasonable rule of model parameter set which is suitable to the actual value.Then, the paper discusses the influence of flow field characteristics under different opening form, opening size and outflow location,.obtains the rule of drag reduction at opening hole condition, analyzes the distribution of micro bubbles and flow field on the hull surface ,gets the change of total drag and the rule of drag reduction. In order to simplify the question, we suppose the ship is floating and no drift, neglect the influence of free surface, and concern about the viscous resistance only.The following shows the conclution of model numerical culculation:1) The computation using SSTk-ωturbulence model can obtain precision results. When the discretization of momentum and turbulent kinetic energy uses the second-order upwind scheme, and the dissipation rate adopts the first-order upwind scheme, the stability of numerical culculation result is better.2) The obvious higher-pressure region in the ship bow provides the basis for the drag reduction research by opening hole. The streamlines in screw shaft place have obvious separation which is easy to produce eddy, increases the resistance and provides the basis for the form resistance reduction research.3) Under the same flow area and the same outlet location, the added value of total drag coefficient from low to high shows:model with round hole (midship) flowing, model with round hole (side) flowing and model with square hole. Under the same flow area and the same opening hole form, the increase of total drag coefficient from low to high shows:outflow location at (1#-2#) division, at (3#-4#) division and at transom stern position.4) Under the same inlet area and the same outlet location, when outflow area is bigger than inlet area,the added value of total drag coefficient will increase following the outflow area increase. On the contrary, the added value of total drag coefficient will decrease with the outflow area decrease when outflow area is smaller than inlet area. After the outflow area relegate a balance point, the total drag coefficient will increase.5) Compared with the prototype computation, the opening hole flow has a distinct improvement on the wake field in stern, and the wake flow distribution is uniform, increasing thevalue of average wake, being good at ship's propulsive efficiency.6) Under the combined action of opening hole and micro bubble, the model can realize the effective drag reduction, and the propulsive efficiency has obvious enhancement.