Influence of Roughness on Flow Characteristics and Resistance in Cone-Straight Nozzle

Rough walls are widely used in aerospace and submarines and can reduce the flow resistance by 8%–10%. In this paper, the rough walls are introduced into the jet nozzle to explore the effect of the rough walls on the flow characteristics in the cone-straight nozzle and the drag reduction effect. The effect of different roughness and roughness structures on the flow near the wall is analyzed by the numerical simulation method. The results show that reasonable roughness can increase the jet velocity and delay the jet velocity decay after the exit; different roughness ranges correspond to different flow rates, within this range, the effect of speed increase and drag reduction is the best; the riblet structure achieves the effect of drag reduction by changing the flow state at the near wall, and the eddy current flow in the riblet makes the flow resistance at the near wall change from sliding friction to rolling friction. The skin friction resistance in the influence range of the riblet is reduced; the flow in the riblet gives the originally static wall fluid an initial velocity so that the shear velocity in the shear layer near the wall is smaller, and the viscosity in the entire boundary layer is reduced. Hysteresis: riblet spacing affects the degree of flow resistance reduction, and the isosceles triangle geometry with 0 riblet spacing is considered in the design of riblet drag reduction. The purpose is to provide theoretical support for the introduction of rough structure into the jet nozzle to further reduce the flow resistance of the nozzle.