Turbulent Flow of Polymer Solutions in a Square Duct Roughened with Transverse Ribs*

In this research, a direct numerical simulation of the turbulent flow of a polymer solution is performed in a ribbed square duct of different blockage ratios, with the FENE-P model used to simulate the presence of polymers. The effects of parameters defining the viscoelastic behavior of the polymer flow such as the Weissenberg number are investigated for both cases with and without riblets. The numerical results are compared with those of a smooth duct polymer flow as well as with those of a Newtonian ribbed duct flow. The results indicated that the turbulence field is influenced by the rib elements, the four duct sidewalls and also the polymer additives. It was observed that, in the Newtonian ribbed duct flow, when increasing the blockage ratio, due to the strong shear layer formed immediately above the rib crest, strong turbulent secondary flow motions are formed in that region, which facilitates the transport of Turbulent Kinetic Energy (TKE) in the cross-stream directions. In the polymer ribbed duct flow, the aforementioned strong secondary flow is altered, so that the locations of the maximum vorticity move away from the wall, towards the centerline, and also the circulation is improved in each of the 8 sectors of the duct.