Axial fans often show adverse flow conditions at the fan hub and at the tip of the blades. Modification of conventional axial fan blades is presented. Hollow blades were manufactured from the hub to the trailing edge at the tip of the blades. Hollow blades enabled the formation of self-induced internal flow through internal passages. The internal flow enters the internal radial flow passages of the hollow blades through the openings near the fan hub and exits through the tip trailing edge slots. Study of the influence of internal flow on the flow field of axial fan and modifications of axial fan aerodynamic characteristics is presented. The characteristics of the axial fan with the internal flow were compared to characteristics of a geometrically equivalent fan without internal flow. The results show integral measurements of performance testing using standardized test rig, and the measurements of local characteristics. The measurements of local characteristics were performed with a hot-wire anemometry, five-hole probe and computer-aided visualization. We attained reduction of adverse flow conditions near the blade tip trailing edge, boundary-layer reduction on the blade suction side and reduction of flow separation. Introduction of the self-induced blowing led to the preservation of external flow direction, defined by blade geometry and enabled maximal local energy conversion. The integral characteristic reached higher degree of efficiency.

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