Experimental investigation of noise sources in cross-flow fans

Abstract

Cross-flow fans are unusual types of blowers which operate in a fundamentally different way from axial or centrifugal fans. The flow enters and leaves the impeller in a direction vertical to its axis and passes the blade row twice, first radially inward and then radially outward. Hence, cross-flow fans are basically two-stage fans. Aerodynamic and acoustic modeling of cross-flow fans is extremely difficult because of the complexity of the flow field in the rotating impeller channels with a reversal of the flow direction during each revolution and large regions of severe flow separations. To obtain experimental input data for modeling efforts, experiments were performed with a scaled up model fan. The fan was installed in an open-inlet/ducted outlet test rig. Measurements were made of the unsteady pressures on the impeller blades and on the fan casing, in particular the vortex wall. The flow fields inside the impeller and at its outer periphery were studied by using hot wire anemometry and a three-hole probe. The effect of different casing geometries was examined. A simple model for broadband noise radiation involving surface dipole sources as suggested in an early paper by Sharland [JSV 1, 302–322 (1964)] predicts the spectrum measured in an anechoically terminated outlet duct reasonably well for Now with Behr GmbH & Co., Mauserstrasse 3, 70469 Stuttgart, Germany