Experimental observations on Weissenberg number-controlled developing turbulent boundary layers

Drag reduction within a turbulent boundary layer was achieved with dilute polymers that were controlled such that the Weissenberg number (Wi) was uniform in the flow. Two conditions were selected for comparison: (i) different Wi at similar drag reduction (DR) levels and (ii) different DR at comparable Wi. While the mean velocity had a secondary Wi dependence, the fluctuating statistics had a strong Wi dependence. Similarly, proper orthogonal decomposition showed the polymers deplete energy for the small scales. These trends underscore the importance of Wi when seeking a universal scaling of polymer-modified flows