Numerical simulations of swirling pipe flows- decay of swirl and occurrence of vortex structures

The present work aims at better understanding of the physics underlying swirling flows in pipes by means of numerical simulations. Direct numerical simulations have been carried out by using two different inlet swirl conditions. In one case, rotating honeycomb is used as the means to generate swirl whereas in the other case a solid body rotation is provided at the inlet. The inlet swirl intensity is varied in order to scan the underlying physics. Reynolds number 1730 is selected so that the flow remains in laminar regime. The results are compared with those obtained from the experiments using a similar experimental set-up. It is shown that the increase in the inlet swirl intensity leads to a faster decay of swirl downstream of the pipe. Similarly certain specific vortex structures are observed in the radial velocity contours. These structures are thought to be analogous with those found in the Taylor-Couette flow between a stationary outer cylinder and inner rotating cone. The reported investigations reveal dependence of swirl decay on the inlet swirl intensity and occurrence of vortex structures.