Experimental Study of Parameters Affecting Friction Reduction in Solid-Liquid Interfaces using Ultrasonic Vibrations

The utilization of ultrasonic waves is a method to reduce frictional drag. Available hypotheses state that ultrasonic vibrations reduce frictional drag by creating cavitation, forming a fluid vapor layer surrounding the surface, and reducing its contact surface. This paper examines the hypothesis by performing experimental tests to eliminate the cavitation effect via increasing the pressure and investigates other factors affecting the frictional drag reduction. Experimental tests showed that by applying ultrasonic vibrations, frictional drag is reduced by an average of about 9%. Besides, by eliminating the cavitation effect, the frictional drag reduction is nearly 6%. It reveals that about 3% of frictional drag reduction was related to cavitation. The shear stress relation shows that the effect of variation of shear surface and distance in the presence of ultrasonic vibrations are negligible, and therefore the only factor that affects the drag force reduction is viscosity. It can be hypothesized that ultrasonic vibrations reduce viscosity by mechanisms such as increasing both local temperature and the distance between molecules. The tests showed that the viscosity was reduced by 6% by using ultrasonic waves.