Akira Miki

Direct numerical simulation of fluid–acoustic interactions in a recorder with tone holes

To clarify fluid-acoustic interactions in an actual recorder with opened and closed tone holes, flow and acoustic fields were directly numerically simulated on the basis of the compressible Navier-Stokes equations. To validate the simulation accuracy, the flow field around the windway and sound pressure above the window were measured. The predicted acoustic fields clarify changes of the positions of pressure nodes and anti-nodes in accordance with the state of the tone holes and the Mach number of the jet velocity. The fundamental mechanism of the self-sustained oscillations in a three-dimensional actual recorder is visualized by the predicted acoustic and flow fields. This result is also consistent with the relationship between the jet behaviors and pressure fluctuations based on the jet-drive model. Moreover, the effects of the fine vortices in the jet, which appear at the high Mach number of jet velocity of 0.099, on the sound are discussed. The time difference between the generation of the disturbances and the most intense deflection of the jet is identified and compared with the time delay of acoustic reflection around the window.

Direct aeroacoustic simulations and measurements of flow and acoustic fields around a recorder with tone holes

Direct aeroacoustic simulations and experiments were performed regarding the flow and acoustic fields around a recorder, which is one of air-reed instruments. The present simulations reproduced the jet oscillations and acoustic radiation around the recorder with tone holes. The effects of conditions of the tone holes and the jet velocity on the flow and acoustic fields are discussed.

DIRECT AEROACOUSTIC SIMULATION RELATED WITH MODE CHANGE IN A RECORDER

In musical instruments, the mode change of radiating sound is related with their quality. To clarify the flow and acoustic fields related with this mode change, we performed direct aeroacoustic simulations of flow and acoustic fields around two actual recorders with different shapes of windway. The computations are based on the compressible Navier-Stokes equations to predict the fluid-acoustic interactions. It is shown that the relationship between the mean velocity at the windway exit and the mode of the radiating sound for the two models is in good agreement with the measured results. The velocity of the mode change depends on the shape and configurations of the windway and edge. Based on the predicted flow fields, the asymmetry of the jet oscillations between in the upward and downward directions is observed in the recorder model for the earlier mode change. H. Yokoyama, R. Hamasuna., A. Miki, H. Onitsuka and A. Iida

Dynamic sound image creation by un‐directional sound beam reproduction toward an interior surface with a DSP controlled line array speaker for Surround Sound Composition

Surround Sound Composition in an indoor space is frequently provided with spatial sounds, giving both a sound localization and surround sound effect. Systems have been installed in public spaces such as a museum and retail shops. However, technical improvements are required to provide a small sweet spot and to address architectural designs for speaker installation, because multiple speakers are required for surround sound effect. Recently, we have been applying DSP beam‐forming technology with a line‐array speaker to create a 3D sound image by scanning a focused sound beam onto an interior surface. The DSP array speaker is capable of providing static and dynamic control in beam steering and sound focusing. Therefore, dynamic spatial sound effect on the interior surface is possible, wherein un‐directional sound reproduction is analogous to un‐directional lighting. We present three case studies; 1) Virtual 3D Surround Sound in multi‐media improvisation, 2) 3D Spatial Sound Synthesis in sound installation an...