Characteristics of Streaming caused by Local Heating in Standing Sound Waves

[Abstract] The mechanism of the streaming caused by local heating in standing sound waves is investigated through experiments and numerical simulations. The prediction of combustion oscillation occurrence requires knowledge on the interference of acoustic oscillation and combustion. The research on the phenomenon had discovered a new thermal convection. When a heat source, such as a burning droplet of fuel, is placed in a standing sound wave, the burnt gas around the heat source is blown towards the nearest node. To clarify the characteristics of this streaming, both numerical simulations and experiments using a hot wire as a substitute of the burning droplet have been done. For the numerical simulations, the Finite Difference Time Domain method (FDTD) and the Acoustic Radiation Force (ARF) model were used. The ARF model incorporates a simplified acoustic radiation force as an external force in the Navier-Stokes equation. The heat source was located at three positions, which are a velocity node, a velocity anti-node, and the middle of the node and the anti-node. From the results, the streaming parallel to the direction of the acoustic vibration is found to be well explained by the acoustic radiation force. From the FDTD results especially at the anti-node, the streaming perpendicular to the vibration direction was found, that requires consideration of two-dimensional radiation force. From analyzing the FDTD results, a correlation term of the velocity oscillation and a pressure gradient term are found to dominate the two-dimensional radiation force.