Effect of flow and polymer properties on near wall mean and fluctuating velocity profiles

Polymer additives are known to reduce the local skin friction drag within a turbulent boundary layer (TBL) with a corresponding modification of the near wall velocity profile. The classical view of the modification is that the log region slope is unchanged though the intercept constant increases in proportion to the drag reduction level until the maximum drag reduction (MDR) asymptote is achieved. However, recent experimental and numerical studies have demonstrated that the slope does vary at high drag reduction levels. These deviations from the classical view must be due to flow properties and/or polymer properties. The current study uses a homogeneous concentration of polymer solution within a developing TBL to enable precise control of the polymer properties. The near-wall modified TBL velocity profiles were acquired with particle image velocimetry with the flow (Reynolds number) and polymer (Weissenberg number) properties well characterized. Mean and fluctuating velocity profiles will be presented and analyzed to assess their sensitivity to these parameters. Note that the impact of polymer degradation on molecular weight will be quantified and accounted for when estimating polymer properties.