CFD STUDY OF THE LEAKAGE FLOW IN LOW-SPEED AXIAL-FAN WITH ROTATING SHROUD

Authors

Mohammad Amir Neshat  - university of Genova, Italy
Edward Canepa - university of Genova, Italy
Andrea Cattanei - university of Genova, Italy

Abstract

The axial fans employed in automotive cooling systems are commonly provided with a rotating shroud which improves the volumetric efficiency and strengthens the whole assembly. The tip clearance between the rotating shroud and the stationary casing has a great impact on the development of a leakage flow which is released from the gap and is re-ingested by the fan. As a matter of fact, such a leakage flow is highly turbulent and may be characterized by large scale periodical structures hence affecting largely the operating conditions of the blade portion which is interested by the re-ingestion process. Different gap geometries, which may be resulting from design strategies or from fan deformation may induce highly different leakage flow patterns. The present work reports a detailed CFD analysis on the same geometry which has been experimentally studied in previous work. A coupled CFD – FEM approach has been adopted to evaluate the deformed fan shape in two operating conditions, and the so-obtained geometries have been studied through the employ of a URANS approach. The results have been validated through the available experimental data. The simulated leakage flow has demonstrated to be highly sensitive to slight modifications of the gap geometry due to the fan deformation, leading to completely different recirculation bubbles. As a consequence, the mixing process between the incoming undisturbed flow and the recirculating one is also affected, leading to the generation of largely different turbulent structures which are able to affect the unsteady pressure field of the blades. The blade loading variations have been statistically evaluated and the results indicated that a more compact recirculation bubble, i.e. a more direct re-ingestion of the leakage flow is able to affect largely the blade tip pressure field. For completeness and as a reference case a geometry without gap has been also considered.