Acoustic-driven self-rotating cylinders.

This paper introduces the concept of ultrasound acoustic self-rotating cylinders, in which the source of self-rotation is due to the acoustic field radiation into the ambient fluidic environment. For a monochromatic radiating cylindrical body, we derive analytical expressions for the acoustic radiation torque and force and show that for particular designs of imposed normal velocity patterns over the cylinder's surface, the wave-solid-fluid interactions lead to the exertion of non-zero torque on the body while maintaining zero net motion. The mathematical modeling of the self-excitation of the body is simplified as a distribution of normal velocities across the cylinder's boundary with specified amplitude, frequency, and phases. We then propose several simple and versatile scenarios of velocity distribution and introduce several cases of desirable distributions as design strategies for self-rotating cylinders, which are validated numerically. Assuming a low Reynolds number condition, the frequency-dependent rotation velocity is estimated as a function of design parameters, and the feasible operating conditions are obtained.