A METHOD OF DESIGNING A LOW NOISE PROPELLER FAN

摘要

Propeller fans are commonly equipped in outdoor units of air-conditioners to provide effective cooling in a dried heat exchanger. A new design technique was developed to satisfy requirements of aerodynamic and aeroacoustic performance, which employs the intersection method of two cylinders for mean camber line. Three proto-types of propeller fan including Palm-Shaped, Highly-Swept (PSHS) fan (proto III) were designed not only to provide low lift forces for dipole sound, but also to reduce the organized tip vortices interacting with the fan guide causing narrow-banded rotating instabilities.The performance and noise characteristics were measured using ANSI test plenum for air-moving devices (AMDs) as a test apparatus. Detailed measurements were made of the three-dimensional turbulent flow fields behind rotating fan blades to see the change of flow structures with respect to operating range. The PSHS fan were proved to provide more uniform flows in an outdoor unit of air-conditioner with at least 2 dB reduction of noise than the quietest commercial fan(T-model) and other proto-type fans compared, which reflects less contamination by tip vortices, with low lift forces.The noise measurements reveal that the most appropriate means to estimate the noise levels for propeller fans should not be the method of acoustical similarity law but rather a different method employing lift forces and dominant length scales of turbulent structures.