Validation of an advanced fan model with multiple reference frame approach

Electronic enclosures commonly use fans, including axial fans, impellers and centrifugal blowers, when cooling by forced convection is required. Computational fluid dynamics (CFD) models of electronic enclosures have traditionally employed abstract fan models. These abstract fan models possess highly simplified fan geometries and numerical flow characteristics. The fan geometry is usually a rectangular or circular planar face with or without an inner concentric no-flow region representing the hub. The flow characteristics are typically summarized by a vendor supplied “pressure head-flow rate” (P-Q) curve, which, along with the continuity equation, is applied between the inlet and exhaust faces of the fan. It is generally expected that these fan curves are obtained through careful experimentation on laboratory apparatus conforming to test codes published by societies such as ASME and AMCA. The usefulness of this approach depends upon the acceptable error margin of the thermal-flow design as well as the specific cooling situation or application. In recent times, this acceptable error margin has been decreasing steadily, leading to a quest for alternate, more accurate and more robust fan modeling techniques. The Multiple Reference Frame (MRF) fan modeling technique is one such approach. Although this fan modeling technique has already been in use elsewhere, it is relatively new in electronics cooling. Insufficient validation has sometimes been suggested as one of the reasons for the lack of widespread usage of the MRF fan model. This paper aims to provide a validation of the MRF fan model through suitable comparisons between the MRF and the abstract fan models. Comparisons are made in terms of the fan (P-Q) curve, and the non-axial flow vector components. The vendor fan curve is used as the basis for comparison. The CFD model of an AMCA approved wind tunnel is utilized in this study. The comparison of flow characteristics shows that the MRF fan model approach is more representative of the fan prototype than that of the abstract fan model.