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A common fan model to use in automotive under hood simulations is the Multiple Reference Frame (MRF) model and within the industry, for this specific application, this model is well known to under predict performance. In this paper we have examined the possibilities of correcting this deficiency with a simple “speed correction”. This is done by testing and simulating a production fan in the Volvo Fan Test Rig for two operating speeds, 1200 rpm and 2400 rpm. Pressure rise, fan power and static efficiency are presented as functions of volumetric flow rate. The simulations verify that using the MRF model the common behavior of under predicting pressure rise and performance of the fan occur. In addition, this work shows that; although the MRF is not predicting fan performance correctly it constitutes a reliable fan modeling strategy.

The most common fan model to use in commercial CFD software today is the Multiple Reference Frame (MRF) model. This is at least valid for automotive under hood applications. Within the industry, for this typical application, this model is commonly known to under predict performance. This under prediction has been documented by the authors' of this paper in SAE paper 2009-01-0178 and VTMS paper 2009-01-3067. Furthermore has this been documented by S.Moreau from Valeo in “Numerical and Experimental Investigation of Rotor-Stator Interaction in Automotive Engine Cooling Fan Systems”, ETC, 7th European Conference on Turbomachinery, 2007. In preceding papers a specific methodology of use has been documented and it has been shown that the MRF model under predicts performance for the airflow in a cooling system commonly with 14% in volumetric flow rate. This is for a system dominated by inertial effects.