S Jafargholinejad - University of Tehran
K Sadeghy - University of Tehran

In the present work, we examined the drag reduction efficiency of two different coatings, i.e., 1) RTV (Room Temperature Vulcanized) Silicon rubber, and 2) PTFE (Poly-tetra fluoro ethylene), using a Rotating Disk Apparatus (RDA). The drag reduction performance of these coatings will be judged by their effect on the resisting torque in the RDA device. The device was fabricated with high accuracy using CNC machine. During the test, the disk was rotated at constant speed using the rotor system. With this rotor system, the rotational speed of the disk could be controlled from 0 up to a maximum of 2000 rpm. In addition, the rotor system was equipped with a torque sensor having a capacity of 200 N.cm and an accuracy of 0.1 N.cm. Tests were performed using water as the fluid surrounding the disk. The device could display the torque applied on the disk by the action of the shear stress at any given rpm. Based on the experimental data obtained in this work, at high enough Reynolds numbers, a drag reduction percentage of 11% and 18% can be achieved with RTV Silicon and PTFE, respectively. It is concluded that in the range of the Reynolds number used in this work PTFE is more efficient than RTV in reducing drag of blunt bodies in external flows.

drag reduction, polymeric coatings, rotatingdisk, skin friction drag