Experimental study of restrictor noise in ventilation duct systems

Abstract

Single-hole restrictors are widely used in the aircraft air distribution system (ADS). The noise generated due to the flow passing over the restrictor is a main interior noise source of the cabin. Prediction of the restrictor noise generation is important for a quite ADS design.

This work experimentally and analytically studies the noise generation mechanisms of the single-hole restrictor. An experimental rig to investigate the restrictor self-noise and interaction noise generated by the turbulent wake produced by in-duct elements installed in the duct and impinging on the restrictor has been developed and constructed. Aeroacoustic measurements of the restrictor self-noise have been made both inside and in the far field of the duct. Two models have been developed to understand the restrictor noise generation mechanisms and predict the sound power level (PWL). One model is based on the surface pressure cross spectrum to compute the effective axial dipole distribution. The other is an extension of previous work and based on the static pressure drop across the restrictor. The restrictor dimension is shown to have a large effects on the restrictor noise generation.

For the interaction noise generation, the important parameters including mean flow speed, restrictor dimension, turbulence level and characteristic length, that determine the sound power radiation spectrum are studied. A semi-empirical model has been developed to predict the sound power spectrum due to interaction noise. The link between the interaction noise generation and the restrictor surface pressure has been investigated.

In addition to the investigation of the restrictor noise generation, this work conducted a short study into the use of surface roughness on the upstream side of the restrictor to reduce the noise generation whilst maintaining the pressure drop across it. It is shown that the noise generation can be reduced above the first cut-on frequency of the duct by increasing the upstream surface roughness.

More information

Identifiers

Catalogue record

Export record