CFD analysis of thermal fluid dynamic parameters inside an organ pipe: influence of air temperature variations

Abstract

Organ pipes represent a fluid-dynamic challenge since the time of Bernoulli and Reynolds. A complete and reliable description of the fluid behaviour at the basement of the resonator named the “mouth” of the pipe is still absent. In the context of the design of an air-heating system for the attenuation of the inconsistencies between sounding frequencies of organ pipes, computing efforts were carried out focusing on the fluid-dynamic behaviour of the air at the mouth of the pipe at different temperature conditions. Describing the air dynamic and the heat transfer at the mouth level of the pipe, it would be possible to predict the heating conditions within the pipe resonator, which was the main subject of the project. Multiple points on the pipe organ air blowing scheme were considered for simulation results extraction. Temperature, pressure, and audio measurements were performed and no significant influence of the temperature on those parameters was raised from measurements, rising questions about the effective behaviour of the blowed air at the mouth of the pipe. Simulations were performed to predict both the fluid dynamic and the heat transfer. A finite volume approach in Fluent environment was chosen. The SST k-omega model was considered in reliability vs computation time balance. 3D simulations were performed based on a CAD reconstructed model of a real pipe. The results of the simulations confirmed experimental data, and they may prove the absence of a significant mass exchange between the in and outside of the mouth of the pipe. The oscillation of the air membrane at the mouth of the pipe may be cleared from instabilities and turbulence regime phenomena, as usually described in the literature.