Reducing aeroacoustics caused by cooling air flow with segmented foam baffles in an information handling system

#The present disclosure relates in general to air cooling in an information handling system (IHS), and more particularly to internally suppressing noise in an IHS due to air cooling.

#As the value and use of information continue to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems (IHSs). An IHS generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes, thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, IHSs may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in IHSs allow for IHSs to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, IHSs may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.

#New generations of enterprise IHSs have higher computing density and thus have a corresponding increase in cooling requirements. To meet the higher cooling requirements, to cool heat-generating functional components, such as central processing units (CPUs), Peripheral Component Interconnect (PCI) cards, etc., higher airflow is needed, and thus air movers at much higher speeds than for conventional cooling. Current server fan technology has reached such extreme fan speeds as to induce HDD throughput failure from acoustics and vibration transmitted to the HDDs, which is generally referred to as aeroacoustics. Aeroacoustics is a branch of acoustics that studies noise generation via either turbulent fluid motion or aerodynamic forces interacting with surfaces. In some conventional applications, sufficient mitigation of aeroacoustic disturbance to throughput by the HDDs has been provided by increasing the distance between fans and HDDs or adding acoustic foams. This solution is no longer effective in some instances for the high-frequency disturbances coming from today's high-performance fans. The amount of distance required for an affected HDD to be in the reverberant field and no longer in direct noise impact of the fans cannot be allocated within the chassis without substantially reducing room for functional components. In addition to the increases in vibration and acoustics predicted for future air movers, the problem is further exacerbated, as HDD sensitivity to vibration and acoustics is also projected to increase with storage capacity and transfer speeds.

#The description of the illustrative embodiments can be read in conjunction with the accompanying figures. It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements. Embodiments incorporating teachings of the present disclosure are shown and described with respect to the figures presented herein, in which:

#FIG. 1 is block diagram representation illustrating an example information handling system (IHS) having an air-cooled enclosure with internal acoustic attenuation, according to one or more embodiments;

#FIG. 2 is an isometric diagram of an example IHS having segmented foam blocks between air duct baffles for acoustic noise attenuation, according to one or more embodiments;

#According to aspects of the present innovation, a method, a memory subsystem, and an information handling system (IHS) each provide incorporating baffles within an air duct that create a vertically alternating air flow pattern, such as a triangular or square wave air flow pattern, to attenuate noise between air movers and functional components. In addition to providing baffles and absorbing foam strategically placed along the longitudinal path of the air duct, the present disclosure recognizes that a horizontal space between first and second baffles enable certain frequencies of aeroacoustic noise from the air movers to resonate within the air duct. The resonance in turn propagates to the functional components. The resonance of aeroacoustic noise disrupts performance of the functional components when the air movers are operating at an upper range of fan speed. For some sensitive hard drives and some high-performance fans, performance has been observed to degrade as low as 80% or more of full fan speed. For example, each HDD and fan combination have a fan speed past which HDD throughput degradation exceeds a company's goal, e.g., a recent test with 60 mm/25000-rpm fans resulted in HDDs performing at 20% of maximum throughput. Air movers of other types, operating speeds or dimensions, such as 40 mm fan modules, may have other frequencies of aeroacoustic disturbances. Alternatively, a frequency band that is not the most dominate aeroacoustic disturbance frequency for an air mover may resonate for the particular dimensions of an air duct, requiring mitigation. In addition to longitudinally positioned noise mitigation structures, the present innovation provides further attenuation of acoustic resonant frequencies across the air duct between pairs of baffles. In particular, segmented foam blocks that are entirely, or substantially free standing are positioned at antinode transverse points defined by one or more of the acoustic resonant frequencies.

#In physics and engineering, for a dynamical system according to wave theory, a mode is a standing wave state of excitation, in which all the components of the system will be affected sinusoidally under a specified fixed frequency. A mode of vibration is characterized by a modal frequency and a mode shape. It is numbered according to the number of half waves in the vibration. For example, if a vibrating beam with both ends pinned displayed a mode shape of half of a sine wave (one peak on the vibrating beam) it would be vibrating in mode 1. If it had a full sine wave (one peak and one trough) it would be vibrating in mode 2.

#An antinode position can correspond to one of a pressure antinode and a velocity antinode. Without having to block air flow substantially across the horizontal dimension of the air duct, the segmented foam blocks absorb acoustic energy at particularly active points in horizontally resonate noise from the air movers. Thus, the segmented foam blocks mitigate the effects of operating air movers at high speeds, which in turn mitigates reduction in reliability and performance of the air-cooled functional components. Specifically, being placed at the antinode position of the resonate frequencies increases the absorption. Although the segmented foam blocks divide the vertically alternating air flow into longitudinally parallel air flows, the segmented foam blocks do not significantly constrain the amount of cooling air passing through the air duct to the functional components.