Drag Reduction Characteristics of the Self-excited Oscillation Pulse Jet Based on Shear Vortex Motion1

The fluid motion specialty has an important influence on the resistance at the near wall surface. The frictional resistance of the wall surface is linearly represented by the velocity gradient and the shear stress. The evolution of the shear eddy current and the distribution of eddy current in the self-excited oscillation chamber are analyzed. The numerical analysis method of large eddy simulation is used to find out instantaneous and average flow speeds of an axial section and normal plane in the outflow pipe, the shear stress of the near wall surface under different upstream and downstream pipe diameter ratios, and velocity gradient of normal plane under different aspect ratios in the outflow pipe. The results show that the self-excited oscillation pulse jet flow is strongly specialty of three-dimensional affected by the reverse boost vortex, forming a "wave-like" flow and circumferential deflection, and the flow velocity and flow pattern decreases with the change of position in a pulse-like manner; when th