Blade solidity

Blade solidity is an important design parameter for the axial flow impeller and is defined as the ratio of blade chord length to spacing.

Where In case of an axial flow impeller, the mean radius is defined in terms of hub (

If an impeller has only a few blades (i.e a large pitch), it will result in less lift force and in a similar manner for more blades (i.e. very low pitch), there will be high drag force.

Lift and drag coefficient for an airfoil is inter related to blade solidity as shown: where: In an airfoil, the mean line curvature is designed to change the flow direction, the vane thickness is for strength and the streamlined shape is to delay the onset of boundary layer separation.

To illustrate the dependence, an expression for axial flow pump and fan is shown: where: Cordier diagram can be used to determine specific speed and impeller tip diameter