Water jet technology has been widely used for many years. It is an effective and clean approach for breaking, cutting or cleaning materials. Nozzle is the crucial component for implementing the water jet technology in practice. The structural parameters of nozzle directly determine its hydraulic performance. In the meantime, the nozzle's hydraulic performance directly determines the operational efficiency of water jet technology. The straight cone nozzle and the conical nozzle are two kinds of typical direct jet nozzles, which have been widely used in the practice. Comprehensively using the orthogonal experimental design, CFD numerical simulation, theoretical calculation, experiments of testing the water jets' impact forces and breaking the artificial sandstones, the optimal structural parameters of straight cone nozzle can be obtained. Moreover, the impact force of water jet produced by the straight cone nozzle increases with its outlet diameter increasing significantly. In addition, the cylindrical outlet section of straight cone nozzle is good for improving its hydraulic performance, resulting that its hydraulic performance is better than the conical nozzle.

High-pressure water jet technology is a clean and effective approach to break, cut or clean solid materials. The nozzle's hydraulic performance determines the efficiency and quality of the high-pressure water jet technology implementation. The fluid resistance reduction technology of bionic non-smooth surface is applied to the structural design of the straight cone nozzle successfully. The circular groove is selected as the bionic unit. The selection results in the investigation and development of a bionic straight cone nozzle with the optimum hydraulic performance. Moreover, the separated nozzle machining method is successfully implemented. A comprehensive approach that implements the orthogonal experiment, high-pressure water jets' impact forces testing and range analysis results in the optimization of the bionic straight cone nozzle's structure. The optimal structural parameters of the nozzle as follows: the outlet diameter is 4 mm, length-to-diameter ratio is 2.5, contraction angle is 60°, the circular groove width is 3 mm, the circular groove depth is 2 mm and the circular groove number is 2. In addition, the circular grooves are uniformly arranged on the surface of the straight cone nozzle's internal chamber resulting in reduction of the fluid resistance effectively. Under the same experimental conditions, the impact forces of high-pressure water jets produced by the bionic straight cone nozzles are greater in comparison with the impact forces of high-pressure water jets produced by the ordinary straight cone nozzles. The average rate of fluid resistance reduction of bionic straight cone nozzles is up to 2.33%. Furthermore, the results of CFD numerical simulation show that the circular grooves at the contraction and the outlet sections can also reduce the high-pressure water flow resistance effectively. In the meantime, the opposite rotating vortexes in the circular grooves are the main reason for the reduction in fluid resistance of the bionic straight cone nozzle.

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