Large-eddy simulation of flow characteristics near the wall of cone-straight nozzle

Nozzles are widely used in the petroleum industry, including cleaning, auxiliary rock breaking, perforation, and other functions. As the most commonly used nozzle type, the cone-shaped nozzle has been widely studied, the flow properties nearwall play an essential role in flow resistance and need to be revealed. In this paper, the large eddy simulation model numerically were used to simulate the flow field in the nozzle. The velocity field distribution, velocity gradient, wall pressure, wall shear stress, skin friction coefficient in the nozzle were analyzed. The following results were concluded: the velocity distribution of the fluid changes from a parabola to an M shape during the acceleration process in the contraction section, and Peaks appear near the wall; boundary layer transitions and vortices appear near at the beginning of the converging section; boundary layer transitions and separations occur near at the end of the converging section and the beginning of straight pipe sections, where the velocity gradient, wall shear force, and skin friction coefficient all have peak values; the flow near the wall of the straight pipe section is vortex-laminar alternately; the wall shear force, velocity gradient, and skin friction coefficient of the straight pipe section show periodic fluctuations, which alternate with the flow state near the wall. Most of the nozzle flow resistance is generated in the nozzle straight pipe section, and the appearance of the vortex reduces the skin friction coefficient. When the nozzle drag reduction is performed, the contour of the transition from the nozzle contraction section to the straight pipe section can be optimized, and the straight pipe section should also be considered when passive drag reduction design is carried out inside. By describing the flow characteristics near the inner wall of the nozzle, the location and reason of the frictional resistance of the internal flow characteristics of the nozzle were analyzed, which aimed to provide theoretical support for further optimizing the nozzle structure and reducing the nozzle flow resistance.