Investigation of noise generation inventilation systems

Abstract: The ventilation systems are becoming more compact so as to save buildings space. In return, the velocity, in ventilation units, is increased and the air flows are also more turbulent. The hotwire investigation aims to correlate this increase of turbulence with the increase of the noise level. The investigation was done for industrials purposes and is based on empirical researches completed with theoretical knowledge. For the investigation, the hotwire sensor is chosen for its ability to detect small velocity fluctuations at high frequency. Two different prototypes are designed in order to highlight the influence of the turbulence level in the sound generation, especially at ventilation outlets. A procedure is also introduced, in which the hotwire is used for the turbulence measures and a reverberation room for the sound measurement. General conclusions are finally identified and explain the influence of the turbulence in the sound generation mechanisms. The influence of the prototypes geometries, on both the sound and the turbulence, is analyzed and the master thesis describes how the air flow velocity in ducts and the static pressure could modify both the turbulence and the sound levels. The stated conclusions imply that the designers of new ventilation systems should take into account the turbulence generated by their experimental product if they want to conserve good sound properties.