Numerical analysis of the interaction between fluid flow and acoustic field at the mouth-opening of a flue instrument

Abstract

The fluid-sound interaction is the key to understanding the sounding mechanism of flue instruments. The formula introduced by Howe allows us to estimate the energy transfer between acoustic field and hydrodynamic field. For calculation of Howe's formula, it is necessary to divide acoustic field from fluid flow. Recently, several authors developed approximate methods to evaluate Howe's formula and applied to experiments of cavity noise and flue instruments. In this talk, we introduce a numerical method to calculate Howe's formula, which is similar to those introduced by the above authors. Our model is a small flue-organ like instrument with an end stop. We use compressible Large-eddy simulation (LES), which is able to reproduce the fluid flow and acoustic field, simultaneously. First, the pipe is driven by the jet and the fluid flow and acoustic oscillation excited in the pipe are reproduced by LES. Next, an acoustic field generated without the jet-injection but with driving at the far end is reproduced by LES. To excite the acoustic field, we can use several methods, pressure driving, particle velocity driving or oscillating wall driving (like a loudspeaker). Combining those results enables us to calculate Howe's formula and to estimate the fluid-sound interactions.