Evaluation of the local effective eddy viscosity of complex fluids in Taylor-Couette flow

We propose a novel method to evaluate the influence of local momentum transport by eddies for drag reduction studies using complex fluids. To demonstrate the method, this method was applied to the complex fluids such as surfactant aqueous solution. This method quantifies the contribution of interactions between turbulent eddies and additives as the eddy viscosity in a Taylor-Couette geometry. The eddy viscosity is calculated as spatial profile by substituting the velocity profile information captured with ultrasonic velocity profiler into the Reynolds Averaged Navier-Stokes (RANS) equation. The azimuthal and radial velocity fields are measured as a function of radial position and time by vertically traversing the two ultrasonic transducers. Then, the velocity field data at each height are averaged to input them to the RANS equation. In the RANS equation, the terms related to the Reynolds shear stress are modeled by the concept of eddy viscosity. This method also obtains the correlation between the local mean shear rate and the eddy viscosity. This correlation explains the modification of local turbulent diffusion influenced by the shear-rate-dependent viscosity in non-Newtonian fluids. The modification of the momentum transport can be evaluated even when the constitutive equation is unknown. In the presentation, we will explain the validation of the method using the Newtonian fluid and the application example using complex fluids.