Abstract: A new type of bowed blade based on spline function is proposed and its analytic expression of the stacking line is simultaneously derived by introducing two parameters, i.e., bowness and bowed angle. By this new bowed blade technique, four types of bowed blade, i.e. W type, middle inflexion type, C type and natural spline type can be generated according to different boundary conditions and bownesses. Its application is attempted to micro axial fans with detail numerical investigations on its aerodynamic performance. Results indicate that the bowed blade of W type may deteriorate the flow inside the impeller and go against the improvement of the impeller performance; bowed blade of C type, especially as its particular form natural spline type may effectively restrain the flow separation in the vicinity of the blade top and enlarge the stable operating range for the impeller under small flow rate conditions but its aerodynamic performance is not as good as the corresponding straight blade under large-medium flow rate conditions; bowed blade of middle inflexion type may not only enlarge the stable operating range under small flow rate conditions but also keep its aerodynamic performance almost as good as the corresponding straight blade under large-medium flow rate conditions. So bowed blade of middle inflexion has great practical value.

Key words: Aerodynamic performance, Bowed blade, Micro axial fan, Spline function, critical load , numerical calculation , Bolt , localized slip, loosening