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 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.

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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.

The evaluation of temporal and spatial fluctuations of energy using compressible fluid analysis is proposed as an effective method to clarify the fundamental mechanism of the self-sustained oscilla-tions in a actual recorder. The main factors of the self-sustained oscillations are investigated in more detail by evaluating not only the steady state of the sound where the flow field and the sound field are completely coupled, but also the characteristics at the attack transient of the sound before the coupling is established. By analyzing the large energy fluctuations that occur just below the edge of the labium in the attack transient, it was shown that this phenomenon may be one of the main causes of the self-sustained oscillations. And the characteristics of the energy fluctuations and sound power generation during the steady state of the sound are discussed. It was also focused on the energy variations in another region that is near the exit of the windway.