Abstract

This work points out a stability bifurcation which appears at low mass flow rates when simulating the flow inside of a compressor rotor alone, using the Body Force Modeling (BFM) approach with the Hall–Thollet formulation. This phenomenon is observed for a small propulsive axial fan, with and without model calibration. It does not have any consequence, since it happens far beyond the surge limit of the fan stage and involves “virtual” operating points which cannot be captured with blade simulations. However, this bifurcation also exists with centrifugal impellers, for which a flow recirculation usually takes place at low mass flow rates, enabling extension of the stable operating range. Thus, this represents a serious limitation of this method. This numerical behavior has not yet been documented in the BFM literature. Given the complexity of this subject and the number of parameters, the intention is not to carry out an exhaustive study here. But since the Hall–Thollet formulation is now quite commonly used in turbomachinery CFD, the objective of this work is to briefly report and describe the dichotomy in the solutions obtained.

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