Cracks may occur at the connection of the impacting T-junction and the position of the clapboard at regular intervals in intake pipelines of 24 m transonic wind tunnel. In order to understand the causes of cracks and provide a basis for improving design

CFD (computational fluid dynamics) was used to compare the existing tee and optimization schemes in wind tunnel. The governing equations are three-dimensional viscous incompressible Navier-Stokes equations. The results showed that the flow in the tee was the most common type without clapboard. There were three separation zones in the branch pipe. The first separation zone was horseshoe vortex

followed by the second separation zone. A pair of reverse rotating eddies

Dean eddies

and a third separation zone were formed on the top wall of the tee. The flow field was basically symmetrical along the y=0 mm and z=0 mm planes. When there was a clapboard

the left and right structures of the flow field were asymmetrical and the upper and lower structures were also asymmetrical. A small range of standing vortices were formed at the corner between the clapboard and the outer wall

and unstable spiral separation vortices were formed in the branch pipe

resulting in air flow oscillation and causing cracks in the pipe wall at the tee connection and the clapboard. According to the above flow pattern

pipeline optimization scheme and flow control device were designed. Separation zones could be effectively reduced or eliminated. Removal of the clapboard was the simplest and easiest way to solve the problem of cracks in the pipe.