A thin metal foam structure was used as an inflow diffuser for small scale axial fans in order to improve inflow conditions. When the inflow condition of an axial cooling fan in a tightly packed electronic device is disturbed by closely located components, the aerodynamic and acoustic performance of the axial fan is degraded. Large static pressure differences between the tip and hub regions on the inlet side causes significant efficiency drops due to deviations from ideal fluid flow around the fan blades. The proposed metal foam acts as a pressure diffuser at the inlet, and helps to prevent surging due to unstable aerodynamic behavior. Since the foam diffuser also acts as an aerodynamic resistance element, the flow rate is decreased at lower pressure loading conditions. But the benefit is a stable operation over a wider pressure load range. Acoustically, the diffuser helps to reduce BPF tones but tends to increase higher harmonics and broadband noise while keeping the overall level approximately the same. A hybrid CAA method was used to simulate the tonal noise components generated by the flow through the diffuser structure as well as the operating fan. In the work described in this paper, the inflow of a 120 mm axial fan was disturbed by a 130 mm diameter disk, and an inflow diffuser was introduced in order to recover the degraded fan performance. The effect of the inflow diffuser was experimentally investigated and a numerical model was built to look into the effect of the diffuser on fan operation. An aeroacoustic noise model was also included in the CFD model to compare the effect of the inflow diffuser on noise generation.


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    Title :

    Inflow treatment for small scale axial fans under unfavorable inflow conditions


    Contributors:


    Publication date :

    2009


    Size :

    9 Seiten, 14 Bilder, 3 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English