Early turbulence in von Karman swirling flow of polymer solutions

We present quantitative experimental results on the transition to early turbulence in von Karman swirling flow of water- and water-sugar-based polymer solutions compared to the transition to turbulence in their Newtonian solvents by measurements of solely global quantities as torque $\Gamma(t)$ and pressure p(t) with large statistics as a function of Re. For the first time the transition values of $Re_c^{\textit{turb}}$ to fully developed turbulence and turbulent drag reduction regime $Re_c^{\textit{TDR}}$ are obtained as functions of elasticity El by using the solvents with different viscosities and polymer concentrations ϕ. Two scaling regions for fundamental turbulent characteristics are identified and they correspond to the turbulent and TDR regimes. Both $Re_c^{\textit{turb}}$ and $Re_c^{\textit{TDR}}$ are found via the dependence of the friction coefficient Cf and Cp, defined through scaled average torque $\bar{\Gamma}$ and rms pressure fluctuations $p_{\textit{rms}}$ , respectively, on Re for different El and ϕ and via the limits of the two scaling regions