In order to study the effect of the diffusion angle on the turbulence in the venturi tube, in this work, the stereo-particle image velocimetry is used to measure the transient velocity of the diffusion part of venturi tube, which diffusion angle is 10°, 12.5°, 15°and 20°, respectively, and the time-averaged velocity is obtained. Based on the transient velocity of the diffusion part of the venturi tube, the distribution of turbulent kinetic energy in the diffusion section is obtained by statistical analysis of the instantaneous velocity field. It is shown that the average velocity in the diffusion section of the venturi tubes of different structures presented an axisymmetric single peak distribution in the direction of the section diameter, and the turbulent kinetic energy presented an axisymmetric double peak distribution in the section diameter. Flow separation can be observed in all experimental condition. With the increasing of the diffusion angle, the largest turbulent kinetic energy increases, but the radial width of the main flow zone does not change, and the radial width of the separation flow zone increases, but the effect on the proportion of the separation flow zone is small, and the high turbulent kinetic energy zone widens. With the increasing of Reynolds number, the peak value of turbulent kinetic energy increases, which is mainly caused by the axial Reynolds stress, and the proportion of separated flow area decreased slightly, but the distribution of main flow area and separated flow area changes little. This study provides an experimental basis for studying the flow field of the venturi tube with high Reynolds number at different angles.
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