Numerical and Experimental Analysis of the Airflow Inside an A250 Diffuser Tube

The diffuser tube of the Allison 250 gas turbine has been investigated in this paper. It consists of a diverging conical section that transitions into a constant diameter S-shaped tube, and connects the exit of the compressor to the inlet of the combustion chamber. The shear stress transport model (SST) in ANSYS-CFX has been used for the numerical prediction of the flow and an experimental rig was built in order to collect data in four directions and at three stations along the diffuser tube. The calculated results perfectly matched the experimental data. The development of the stream-wise velocity profile, the velocity contours at different stream-wise stations, and the friction and pressure coefficients were calculated and discussed. A secondary flow in the plane of the cross-section has thus been evidenced, and resulted in a shift towards the outer wall of the first bend of the region of the flow where the velocity is greatest. It has also been shown that the friction coefficient decreased as the Reynolds number was increased, while the opposite trend was observed for the pressure coefficients. The effect of the inlet turbulence intensity on the main flow features was generally small.