Study Of Drag Reduction Capability Of The Dimple Bionic Non-smooth Surface

Based on the essential bionic research method and combined with engineering, a simple non-smooth shape, dimple, is obtained by abstracting non-smooth surface information of the animal surfaces. The model is created to calculate the drag reduction effect of the dimple non-smooth surface in several velocities and to analyze the cause of drag reduction.Because of the high expense and the difficulty to do experiments and in order to shorten the time of research, the method of numerical simulation is used instead of the wind tunnel experiment ways to simulate the flow of some surfaces, explore the theory of drag reduction and the influence of dimple size on drag reduction effect, which would provide academic support to design more effective dimple shapes.Four dimple bionic non-smooth surfaces are designed and simulated and each of the four models are simulated in seven different velocities. After figuring out the model and the size of dimples, use tetrahedron unstructured grid to dispose the model to fill the mesh requires. As for the mathematical model, standard k-εturbulent model and low Re k-εmodel are applied. In order to get the exact result, the second order upwind format is used to discrete the mathematical model. Based on the results of simulation, the flow of boundary layer on both non-smooth surface and smooth surface are presented to discuss the drag reduction quality of dimple shape structure and to study the theory of drag reduction deeply.Through a lot of calculation, the qualitative and quantitative conclusions are as follows:(1) Compared with smooth surface, the dimple non-smooth surface has a little higher pressure resistance but has a much lower viscous friction resistance, which leads to a reduction on total resistance. (2) When the diameter of the dimple is twice larger as the height, the non-smooth surfaces which have dimple structures with a diameter of 0.8mm have a much better performance on drag reduction than those which have dimple structures with a diameter of 1.0mm. (3) Under the premises that the diameter of all the dimples is 0.8mm, it proves that the height seems to have little influence on the resistance reduction effect. Each of the models simulated has a good drag reduction effect. (4) The flow inside the boundary layer is studied. It is found that the dimples on the unsmooth surface are able to change the thickness and some other aspects of the boundary layer, which leads to a drag reduction on dimple unsmooth surface. (5) The path lines and velocity vectors inside the dimples are depicted. It is found that as there is solid-fluid boundary between the coming fluid and smooth surface, unsmooth structure makes flows slow down inside the dimples. When air flows through dimple unsmooth surfaces, higher speed flows contact with some lower speed flows that exist in unsmooth structures, which would be able to change the flows inside the boundary of unsmooth surfaces, reduce the friction resistance and lead to a drag reduction.