Numerical investigations on swirl intensity decay rate for turbulent swirling flow in a fixed pipe

Due to the importance of predicting the SIDR1 associated with engineering problems such as combustion chambers, draft tube of the Francis and Kaplan turbines, heat exchanger tubes, separators and so forth, in this research the trend of SIDR and its affecting factors, through a turbulent swirl decay pipe flow have been investigated. The swirling flow is created by means of a rotating honeycomb which produces solid body rotation at the inlet of a fixed pipe. First of all, turbulent swirling decay flow has been numerically surveyed using different flow conditions at the pipe inlet. The numerical results have been validated and compared with the existing experimental data and mathematical relations, showing satisfactory coincide. The obtained results show that, the SIDR depends mainly on the Reynolds number of the passing flow. On this basis, correlations have been proposed in order to improve the predictions of swirl intensity decay rate at upstream regions as well as those with high swirl intensity. In addition, conducted analyses demonstrates (analyses have been made to demonstrate) that the previous developed correlations for predicting swirl intensity decay rate, agree with those provided in this study only for regions far enough from downstream having the low swirl intensity. This implies that the swirl intensity decay rate should be a function of the type of swirl generator at the pipe inlet.

► Turbulent swirling decay flow has been numerically surveyed using different flow conditions at the pipe inlet.
► The Swirl intensity decay rate depends mainly on the Reynolds number of the passing flow.
► Correlations have been proposed in order to improve the predictions of swirl intensity decay.
► Swirl intensity decay rate are a function of the type of swirl generator at the pipe inlet.