Study on the secondary flow in T-shaped pipe with different outlet surfaces

The flow within different cross sections of T-shaped pipes is analyzed using experimental measurements using particle image velocimetry technology and simulation modeling at different fluid velocities and outlet diameters. The study shows that the flow within the pipes predominantly exhibits multiple vortex patterns, with the evolution of the vortex patterns at different cross sections showing similar patterns and some degree of periodicity. It is also found that as the pipe diameter increases, the flow pattern in the main pipeline is relatively stable, although vortices form on the underside of the outlet pipe walls. Conversely, if the pipe diameter is smaller, vortices will not form within the outlet pipe, and the vortex patterns within the blind pipe will be unstable. In particular, as the velocity increases and the diameter of the outlet pipe decreases, the period of the vortex oscillation shortens. The research establishes a numerical equation relating the dominant frequency of vortex oscillations to the velocity and outlet pipe diameter, further demonstrating the mathematical relationship between the three in the outlet pipe.