Arturo Orozco Santillan

A demonstration of rotating sound waves in free space and the transfer of their angular momentum to matter

We describe an apparatus for generating rotating sound waves in free space by superimposing two orthogonal standing modes with a quarter wave phase lag. The creation of a standing wave from the superposition of two counter-rotating waves is also possible with the same apparatus. The experiment permits direct measurement of both the amplitude and phase structure of the sound waves. A demonstration of angular momentum transfer from rotating acoustic waves to matter in free field is also described.

Time-domain simulations of the acoustic streaming produced by a propagating wave radiated by a circular piston

Results of numerical simulations of the sound field produced by a circular piston in a rigid baffled are presented. The aim was to calculate the acoustic streaming and the flow of mass generated by the sound field. For this purpose, the classical finite-difference time-domain method was implemented, and the complete equations of conservation of mass and conservation of momentum were used together with the state equation for and adiabatic process in and ideal gas. Thermal effects were neglected to simplify the problem. The obtained numerical results illustrate the applicability of the method. The simulations show that a net flow of mass is produced along the axis of the piston, which correspond to the jet-like wind effect in a beam of sound.

Numerical study of the acoustic streaming and mean excess pressure produced in a small gap between a vibrating surface and a thin boundary

In this paper, a circular plane piston located horizontally and immersed in water is considered, and a rigid pipe is assumed to be placed vertically with its lower end very closed to the vibrating surface. The general objective of the work has been to investigate the acoustic streaming produced in the gap between the piston and the lower end of the pipe, and to study the associated spatial distribution of the mean excess pressure in the fluid and the flow of mass. For this purpose, the classical finite-difference time-domain method has been implemented, and the complete equations of conservation of mass and conservation of momentum were used together with the state equation to a second order approximation for an adiabatic process. Thermal effects were neglected to simplify the problem. The obtained numerical results illustrate the applicability of the method. The simulations show that a net flow of mass is produced in the gap between the piston and the end of the tube. The results illustrate the dependence of the flow on the size of the gap, the thickness of the wall of the pipe, and its inner radius.

Analysis of oscillational instabilities in acoustic levitation using the finitedifference time-domain method

The aim of the work described in this paper has been to investigate the use of the finite-difference time-domain method to describe the interactions between a moving object and a sound field. The main objective was to simulate oscillational instabilities that appear in single-axis acoustic levitation devices and to describe their evolution in time to further understand the physical mechanism involved. The study shows that the method gives accurate results for steady state conditions, and that it is a promising tool for simulations with a moving object.

Experimental investigation on the jet-like acoustic streaming in front of an oscillating circular piston

Results of an experimental investigation on the sound field produced by a circular piston and the flow of air generated by the radiated acoustic wave are presented. The aim has been to create a strong jet-like wind by means of a beam of sound radiated by a powerful ultrasonic source, and to measure the speed of the airflow. The experimental data are compared with results of numerical simulations obtained by means of the finite-difference time-domain method. Two Langevin type transducers were used as the sound sources; one had a radiating surface with a diameter of 1.5 cm and the diameter of the other was 5 cm. The experimental results show that the speed of the airflow is more intense along the axis of the circular source, and that this flow extends along a larger distance for a source with a bigger diameter. The experimental data agree qualitatively well with the numerical simulations, but the obtained measurements were approximately twenty times larger than the values expected from the numerical simulations.