The Effect of Shear Thinning Behaviour on Turbulent Pipe Flow

Direct numerical simulation of the weakly turbulent flow of non-Newtonian fluids is undertaken for two different generalised Newtonian rheology models using a spectral element--Fourier method. Results for a power law (shearthinning) rheology agree well with experimentally determined logarithmic layer correlations and with other previously published experimental work. As the flow index becomes smaller for the same Reynolds number, the flow deviates further from the Newtonian profile and the results suggest that transition is delayed. Predicted friction factors fall above those in the literature, but below the Newtonian values indicating that shear thinning behaviour alone can result in drag reduction. Results for a Herschel-Bulkley model (yield stress + shear-thinning) are compared to corresponding experimental measurements and found to be in good agreement. Use of this DNS technique shows great promise in understanding transition and turbulence in non-Newtonian fluids.