Title:	DES for simulating flow and tonal noise in centrifugal fans
DNr:	SNIC 2020/5-458
Project Type:	SNIC Medium Compute
Principal Investigator:	Alf-Erik Almstedt <affe@chalmers.se>
Affiliation:	Chalmers tekniska högskola
Duration:	2020-10-01 – 2021-10-01
Classification:	20306
Keywords:

Abstract

Heating, ventilating, and air conditioning systems (HVAC) are today an important part of many people’s life. They provide a sufficient amount of airflow with the correct temperature, quality, and humidity. The negative side is the noise it produces. Modern HVAC systems are driven by low-speed isolated centrifugal fans which produce the dominant tonal noises. There are no obstacles that the blades pass in this type of fan. However, the dominant tonal noise produced by the fan is at the blade passing frequency (BPF). This fan has a gap between the rotating shroud and the stationary inlet duct. Previous studies have shown that the flow through the gap causes turbulence that develops along the shroud wall and interacts with the blades at their leading edge. The interaction renders uneven surface pressure distributions among the blades as well as significant peak differences. The location of the tonal noise sources for BPF agrees with the locations of these interactions and surface pressure peaks. In this study, the size of the gap and its effect on the tonal noise is investigated. Three different gap sizes are investigated, one smaller and one larger than the reference gap. The approach is to use the hybrid computational aeroacoustics (CAA) method, that couples the improved delayed detached eddy simulation (IDDES) method with the Ffowcs Williams and Hawkings (FW-H) acoustic analogy. Our simulations show that the surface pressure distributions among the blades and pressure peaks changes when the gap size changes. The surface pressure distribution becomes more evenly distributed when the gap size is increased. Also, the amplitude for the wall-pressure fluctuations decreases when the gap size is increased. The predicted amplitude for the tonal frequencies, BPF0 and BPF1, decreases for the larger gap size and increases for the smaller gap size. The fan performance is also affected by the gap size. The static pressure rise increases for the small gap size and decreases for the larger gap size.