Experimental Research On Drag Reduction Performance Of The Skin Made Of Floating Raft Arrays

Marine organisms have evolved a unique body structure to adapt to the harsh living environment in the ocean.The skin structure of dolphins which shows excellent drag reduction performance among them can be used in the research of drag reduction of underwater vehicles.The skin made of micro floating raft arrays studied in this paper is a new type of skin structure based on dolphin skin.A small curvature rotor experimental device with a data acquisition system is designed according to the principle of rotor resistance measurement in order to verify the drag reduction performance of the skin.This paper mainly carries out the following work:Firstly,the internal flow field of the rotor experimental device is analyzed.Fluent is used to analyze the influence of different radius ratio of rotor and outer cylinder on internal flow field.The analysis results show that the flow field can be approximately regarded as an infinitely wide pool within the range of the test speed when the radius ratio is 0.4.Based on the VOF model of fluent,the simulation analysis of free surface with or without the fan blade is carried out.The simulation results show that the fan blade can suppress the rise of the free surface near the outer cylinder wall,ensuring that the flow field state of the experimental device meets the experimental requirements.Secondly,the overall structure design of the experimental device is completed.The structure of each part of the experimental device is established and the static analysis and modal analysis are carried out by using ANSYS Workbench.The simulation results show that the strength of the experimental device meets the requirements and the rotor will not resonate within the test speed range.At the same time,a data acquisition system supporting the experimental device is designed.The upper computer program is made by Labviews to realize the control and monitoring of the motor and the collection of the rotor resistance torque.Then,the skin made of micro floating raft arrays is prepared.Matlab is used to solve the flow stability equation under the action of the skin structure.The influence of different structural parameters of the skin on the stability of the flow field is obtained,which provides a theoretical basis for the actual structural size design of the skin.The modular structure for 3D printing is designed,and the printing parameters are selected according to the printing accuracy.At the same time,the installation process design of each component of the skin is completed.Finally,the drag reduction performance of the skin is tested and analyzed.The experimental platform is used to measure the resistance moment of the rotor with and without skin.The drag reduction rate of the skin is calculated to draw the drag reduction characteristic curve of the skin with the change of speed.The experimental results show that the skin in air has the drag reduction effect when the rotor speed is 100rpm-340 rpm and the average drag reduction rate is 10.66%,while the skin in water has the drag reduction effect when the rotor speed is 20rpm-80 rpm and the average drag reduction rate is 3%.The parametric model of the resistance moment of the rotor with the change of speed is constructed.The empirical formula suitable based on experimental data for this experiment is summarized,which provides a reference for the follow-up experiments.The mechanism of skin drag reduction is analyzed based on the theory of fluid-structure coupling.The results show that the skin can absorb the turbulent kinetic energy of the rotor surface.