Numerical simulation of a double helix vortex structure in a tangential chamber

Abstract

The paper investigates the flow structure in a tangential vortex chamber based on numerical simulation of unsteady turbulent flow by the LES method. The swirl flow in a cylindrical chamber was organized using 12 nozzles, supplying the flow tangentially. Three regimes were considered with different design swirl number S = 5.78, 8.67, and 17.34, which was varied by closing one or two nozzle rows. The unsteady computation shows the formation of a rotating double helix vortex structure in the regimes with S equal to 8.67 and 17.34, which is also verified by experimental observations. Several recirculation zones were formed in the tangential chamber near its axis, as well as along the wall at the lower part, and on the axis near the top lid. A dominant frequency was observed in the pressure pulsation spectrum, which increased with increasing swirl parameter, and for the S = 8.67 regime, it was approximately twice the rotational frequency of the double helix structure. In the course of rotation of the double helix structure, the vorticity redistributed between its branches from an approximately symmetric pattern and up to approaching a single-vortex structure at certain points in time.