Measurement Techniques: Viscosity and Surface Drag in Quasi-Two-Dimensional Flows

The effects of kinematic viscosity and linear drag are both significant in many quasi-two-dimensional (Q2D) flows in nature and the laboratory. These effects, however, are difficult to measure and to distinguish from one another. We demonstrate precise, independent measurement of both kinematic viscosity and linear drag using decay rates of vortices of varying scales in a Q2D experiment involving soap films in a circular Couette cell. As expected, we have found both the kinematic viscosity and the linear drag to depend inversely on film thickness. The approach can be generalized to apply to other configurations and experiments.