Wall shear stress mapping in the rotating cage geometry and evaluation of drag reduction efficiency using an electrochemical method

The local wall shear stress (WSS) mapping in the rotating cage (RC) has been obtained from measuring the diffusion current due to the electrochemical reduction of methyl viologen used as tracer system for both Newtonian and non-Newtonian solutions. The latter were achieved with oleyltrimethyl ammonium, a cationic surfactant, and sodium salicylate as counter-ion, forming thread-like micelles which induce drag reduction conditions.The maximum WSS values were detected in the middle of the coupon in agreement with observation of corroded coupons in erosion–corrosion tests. Maximum values of 65% for drag reduction were measured at the same locations.