Cascade flow theory is based on cascade flow theory. When the turbine speed is low, the flow through the stator blade flow path is small, the axial velocity component of the flow is small, and the corresponding circumferential velocity component is large, and the flow path between the blades is formed. Flow, and at this time, the flow angle of attack on the stator vanes is large, resulting in thicker boundary layer thickness on the side of blade suction, reduced effective flow area of ​​the blade, increased flow velocity in the main flow zone, and uneven velocity distribution. Show. With the increase of the rotating speed of the turbine, the flow rate increases, the axial velocity component increases, the circumferential velocity component decreases, the flow between the vanes disappears, and the flow velocity gradient in the mainstream decreases. Therefore, the flow image obtained in the experiment reflects the true flow in the flow path of the stator blade. In the vicinity of the trailing edge of the suction side of the blade, due to the complicated boundary layer flow, the magnitude and direction of the flow velocity are greatly changed. When the turbine rotation speed is low, there is often a separation flow in the region, and the velocity distribution is more complicated, and the light source conditions The limitation is that the particle size of the tracer particles used in the experiment is large, and the particle concentration cannot be high, so the number of particles entering the boundary layer is small, and the available particle velocity vector is naturally less, making it difficult to accurately display the flow.

The influence of the study area was determined by the use of the bulk illumination method due to the limitation of the equipment, so that the measurement area was actually a space area, but since the mirror was placed in the hollow shaft with a 45° angle to the shaft, the recorded two-dimensional image was basically It reflects the two-dimensional flow conditions of the flow path of the blade in the circumferential plane. However, due to the use of body lighting, the distribution of particles in the image represents the spatial location, so that there will be overlap in the particles, which will make part of the particle information lost and reduce the particle correspondence rate. In this experiment, the particle concentration is not high. Therefore, the overlap phenomenon is not serious.

Errors generated by different media In the process of transforming the two-dimensional flow velocity and the image velocity, it is assumed that the particle imaging point, the imaging center, and the particle point are in three lines, so that the particle point corresponding to the imaging point is p, as shown. However, because the refractive index of the wall surface of the research object is different from that of the fluid medium, the actual particle point corresponding to the imaging point is p′, which results in the position error of R. As can be seen from the figure, the different refractive index shadows of different media are farther away from the wall surface, and R is larger; the thicker the wall surface is, the larger R is; the farther the particle is from the optical axis, the larger R is, so in order to reduce this error, Consider these factors comprehensively, such as reducing the wall thickness, selecting the appropriate size of the study area, and so on.

Conclusion In this paper, the flow of the flow field in the internal blade flow path of the torque converter (T/C) in the stepless speed regulation device of a car is measured by using two-dimensional PIV technology. The measurement results show that when the ratio of the speed of the pump to the turbine is small, T/C The internal flow performance is poor; as the speed ratio increases, the performance improves. Qualitative analysis of the theory of cascade flow shows that the results of measurement using the two-dimensional PIV technique are reliable. And by analyzing the background noise, body lighting method and the error caused by different refractive indices of different media, a method to reduce these errors is proposed, which ensures the measurement accuracy.

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