Hirofumi Onitsuka

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

Acoustic Property Simulation for Building Components

This chapter shows practical examples of numerical simulation results for acoustical characteristics of building elements, such as the sound absorption, sound-scattering, and sound insulation performance. Additionally, radiation characteristics of speaker systems are also treated. In each section, methodologies and numerical modeling schemes of the simulation, and the calculated results for practical cases are illustrated. The results are validated through comparison with the measurement results, and the applicability of the numerical methods is discussed.