Numerical analysis of turbulent swirling decay pipe flow

Turbulent swirling decay pipe flow has been investigated numerically in a vertical straight fixed pipe. The swirling flow is created by means of a rotating honeycomb which produces the solid body rotation at the inlet of the fixed pipe. Since there are no experimental data at the inlet of the fixed pipe; different axi-symmetric approaches may be considered to model the honeycomb effects at the downstream flow. Considering the appropriate approach and using the resulting flow field properties from the exit of the modeled swirl generator which are applied as the inlet boundary condition for the fixed pipe, several high Reynolds turbulence models are used to predict this type of the swirling flow. For wall treatments, both the standard wall function and the two-layer zone model are used. The comparison between the numerical and the existing experimental results shows that the RSM with two-layer zone model is generally more powerful than the others. Results show that the two-equation models with different near wall approaches are fairly well to predict the swirling flow in solid body rotation regions, but they fail to predict the pressure distribution along the pipe wall. Regarding the swirl intensity decay rate, irrespective of the inlet swirl type, the obtained decay rates from computations are in good agreement with the existing experimental results.