Numerical Analysis of Turbulent Flow of Non-Newtonian Fluids in Curved Pipes.

Abstract

A numerical analysis has been performed for developing turbulent flow of non-Newtonian fluid in curved pipe, Numerical results are shown in two cases of power-law fluids, i.e. power index 0.76 and 0.9, at Reynolds number 19000. The ratio of bend mean radius of curvature to radius is 10 and straight duct of 40 and 100 diameters are attached to the inlet and outlet of the bend, respectively. In numerical analysis, an algebraic Reynolds stress model was adopted in order to predict precisely the anisotropic turbulent flow and boundary-fitted coordinate system was introduced as the method of coordinate transformation. The numerical results are compared with the experimental data measured by laser-Doppler anemometer. Mean velocity and fluctuating velocity in axial direction are examined into detail to clarify the validity of the turbulent model and present numerical method. As a result of this research, it is found that the present method could predict well the streamwise mean-velocity in both cases of power-law fluids. As for the comparison of fluctuating velocity, characteristic features are reproduced except for the outer region of pipes. The present method predicts its value in outer regin smaller than that of the experiment, while the present method realized the phenomenon of decaying mean fluctuating velocity with decreasing power index. The results of comparison with the experimental data suggest that algebraic turbulent model is applicable to the non-Nowtonian fluid although agreement between both results is certainly not perfect in all detail.