Abstract

Hard Disk Drive (HDD) system enclosures in a data center require effective cooling systems to avoid HDD overheating. These systems often rely on air cooling because of their cost efficiency and maintainability. Air cooling systems typically consist of an array of axial fans which push or pull the air through the system. These fans emit high level tonal noise particularly at high tip-speed ratios (TSR). High-capacity HDDs, on the other hand, are sensitive to high acoustic noise, which consequently increases the risk of read/write error and deteriorates drive performance. Therefore, cooling fan noise adversely affects the function of the HDD enclosure systems and emphasizes the need to understand the noise sources and develop methods to mitigate HDD noise exposure. This study focuses on understanding the aerodynamic properties and related aeroacoustic behavior of a contra-rotating fan representative of the types used in a modern data center cooling system. A numerical investigation was conducted using high fidelity Large Eddy Simulation (LES) and the Ffowcs Williams and Hawkings (FW-H) acoustic analogy, as well as using experimentally measured acoustic data as a validation. Initial simulation results showed a good agreement with the experimental data and led to a better understanding of noise directivity.