Effect of Reduced Suction Side Volume on Cross-Flow Fan Performance

D3 - Fan Performance (i)

Cross-flow fans are widely used in industrial and domestic applications in which the radial space availability for fan installation is limited. Unlike other type of fans, the cross-flow fan internal flow field is characterised by an eccentric vortex resulting from blades circulation, which forces the flow to be worked out two times by the rotor blades. A vortex stabiliser wall is needed to fix the position of the vortex core and avoid its revolution along a circular path centred on the impeller axis. The fan casing is completed by a rear wall, which guides the flow through the impeller, and by two side walls perpendicular to the impeller axis.
In most of the high-performance cross-flow fans appeared in the literature the position of the vortex stabiliser wall and the shape of the rear casing yield an approximately ninety degrees air flow deflection between inlet and outlet sides. However, applications in ventilation/air conditioning, aircraft propulsion and automotive systems may require different layouts due to physical constraints which limit the radial width of the fan and reduce its suction side volume, and there are very few studies in the literature which deal with similar restrictions.
In the present work, the effect of the suction side volume limitation along the radial direction on the performance of a small cross-flow impeller is experimentally investigated. A baseline fan configuration is chosen among several configurations featuring different rear wall shapes and vortex wall positions because of its best trade-off between efficiency, maximum flow rate, pressure rise and stability of the performance curve. Two sets of tests were performed by modifying this baseline configuration. In the first set, the effect of the inlet wall size was investigated. Then, the suction side was constrained by using a flat plate parallel to the outlet flow direction to achieve an in-line flow layout. The flat plate was gradually moved to reduce the available volume at the suction side. Fan performance was measured for each position of the flat plate to evaluate the performance reduction with respect to the baseline configuration. Results may support fan design choices when the application imposes limited operating volumes.