# Self-Noise modelling and acoustic scaling of an axial fan configured with rotating controlled diffusion blade

## TL;DR

This study adapts a semi-empirical acoustic model to predict self-noise of an axial fan with controlled diffusion blades, validating it with experimental data and analyzing the effects of operating conditions on noise levels.

## Contribution

The paper introduces a semi-empirical acoustic model tailored for axial fans with RCDB blades, validated against experimental data, and explores the frequency-dependent acoustic scaling behavior.

## Key findings

- Rozenberg's model predicted fan noise more accurately than Goody's.
- The model showed reasonable agreement with experimental measurements.
- Acoustic scaling varies significantly with frequency and operating conditions.

## Abstract

A semi-empirical acoustic model for self-noise was adapted to predict the sound radiated from an axial fan featuring rotating controlled diffusion blades (RCDB). Experimental data for wake velocity, mass flow rate across the fan, and fan rotational speed were obtained. These experimental data along with typical characteristics of turbulent boundary layers were used to predict the noise of the axial fan. Hot-wire wake measurements were made in the near region downstream of the fan plane. The fan noise was measured upstream of the fan. The experimentally obtained self-noise was then compared to the predictions made by the semi-empirical acoustic model. Goody's and Rozenberg's models for surface pressure spectra were used in the semi-empirical acoustic model. Rozenberg's model offered a more accurate prediction in the final fan noise spectra. The predictions were in reasonable agreement with experimental data, and the model was found to be a useful tool to reasonably estimate acoustic emissions of a fan with limited information about the velocity field in the fan wake. Different operating conditions and blade configurations were examined. For a given dimensionless operating condition, the self-noise was obtained for different rotational speeds, and the effect of the fan speed on the propagated noise was evaluated. The acoustic scaling function was experimentally obtained as a function of normalized frequency and dimensionless operating condition and it was found to be quite frequency dependent despite it is often assumed as a constant value.